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Download software engineering project and more Study Guides, Projects, Research Software Engineering in PDF only on Docsity! Vertical hydroponic production of leafy vegetables with human-excreta-derived- materials (HEDMs) from decentralised sanitation technologies by Sisekelo S Sihlongonyane (213504731) Dissertation submitted in partial fulfilment of the requirements for the degree of Master of Science in Agriculture in the Discipline of Crop Science School of Agricultural Earth and Environmental Sciences College of Agriculture, Engineering and Science University of KwaZulu-Natal Pietermaritzburg Campus South Africa December 2020 i PREFACE The research contained in this dissertation was completed by the candidate while based in the Discipline of Crop Science, School of Agricultural, Earth and Environmental Sciences of the College of Agriculture, Engineering and Science, University of KwaZulu-Natal, Pietermaritzburg Campus, South Africa. The research was financially supported by the University of South Florida through the Pollution Research Group at the University of KwaZulu-Natal, Howard Campus, in South Africa. The contents of this work have not been submitted in any form to another university and, except where the work of others is acknowledged in the text, the results reported are due to investigations by the candidate. _ ________________ Signed: Prof LS Magwaza Date: _____________________ Signed: Dr AO Odindo Date: _________________________ Signed: Prof DH Yeh Date: _________________________ Signed: Prof CA Buckley Date: 2020-11-30 10/06/2021 10/06/2021 iv ABSTRACT Hydroponic production of leafy vegetables with human-excreta-derived-materials (HEDMs) extracted by decentralised sanitation technologies is projected to reduce food shortages while improving sanitation services in peri-urban communities, particularly in informal settlements. This study investigated the potential use of HEDMs generated by decentralised sanitation technologies for hydroponic production of leafy crops. HEDMs generated by decentralised sanitation technologies, namely: Anaerobic Baffled Reactor (ABR) and Nutrients, Water and Energy Generator (NEWgenerator) were used as treatments. A vertical hydroponic system called ZipGrow Farm Wall was assembled to conduct horticultural trials at Newlands Mashu Research site in Durban, South Africa. The vertical hydroponic system had eight vertical growing towers. Four vertical growing towers were fertigated with commercial hydroponic fertiliser mix (CHFM) as a control and the other four fertigated with HEDM as a treatment. A literature review was undertaken on open field and hydroponic production of crops with HEDMs. Previous and current studies indicated that nutrients derived from human-excreta have the potential to support the growth of plants even though low yields are obtained in some instance, and faecal pathogen contamination in crops occurs due to fertigation with infected nutrients. Only drip irrigation systems were reported to limit the transfer of faecal pathogens from nutrient source to plants. The first research study investigated the potential use of anaerobic baffled reactor (ABR) effluent on growth and yield of Swiss chard in a vertical hydroponic system. The results revealed that Swiss chard grown with CHFM performed better than those in ABR effluent and gave a significantly (p<0.05) higher plant height and fresh yield. Fresh leaf mass of Swiss chard was reduced in ABR effluent by 78 % when compared to CHFM. Sodium toxicity, ammonium toxicity, aphids and flea beetles reduced the growth and yield of Swiss chard grown with ABR effluent. Amaranthus in planted wetlands of ABR system hosted aphids and flea beetles who moved to defoliate matured Swiss chard leaves grown with ABR effluent as they thought it is a similar crop. In contrast, Swiss chard fertigated with CHFM suffered minimum effects of pest outbreak due to absence of faecal smell and nutrient stress. The second research study investigated the potential of diluted NEWgenerator permeate + hydroponic fertiliser (DNP + HF) on growth, and yield of hydroponically grown non-heading Chinese cabbage. The results revealed there was no significant difference in all determined growth parameters except for fresh yield (p>0.05) between plants fertigated by CHFM and v DNP + HF. Fresh leaf mass of non-heading Chinese cabbage leaves was reduced in DNP + HF by 26 % when compared to CHFM. Significant yield decline in non-heading Chinese cabbage grown with DNP + HF was a result of nutrient conditions affecting the uptake and accumulation of nutrients in leaf tissues. Plant analysis revealed that uptake of macronutrients and micronutrient significantly varied in leaf tissues of non-heading Chinese cabbage between fertigation with CHFM and DNP + HF. Leaf tissues of non-heading Chinese cabbage showed higher levels of N, P, Mg, Mn, Na, Cu, Fe and Al while lower levels of K, Ca and Zn were observed when compared to plants grown with CHFM treatment. The deficiency and toxicity of nutrients in leaf tissues led to interference in photosystem activity of non-heading Chinese cabbage grown with DNP + HF which resulted on decline in final yield. On a positive note, harvested leaves were without faecal coliforms. These findings show that fertigation with ABR effluent and DNP + HF has the potential to support the growth of leafy vegetables in a hydroponic system. However, there is a need for further research to look at other aspects with negatively affected the final yield of crops. vi ACKNOWLEDGEMENTS I extend sincere gratitude to the following individuals: ❖ My supervisors; Prof L.S. Magwaza, Dr A.O Odindo, Prof CA Buckley and Prof D.H Yeh for their invaluable contribution while undertaking this research project. ❖ The Pollution Research Group and its research partner, the University of South Florida who financially supported all research expenses. ❖ Students supervised by Prof D.H Yeh from the University of South Florida who provided technical expertise in assembling and running the vertical hydroponic system. ❖ Workshop team from the Pollution Research Group who assisted in assembling the vertical hydroponic system. ❖ Newlands Mashu research site technicians for their immense contribution while conducting a research project. ❖ Mr Lindelani Xaba, the prototype engineer of NEWgenerator who worked tirelessly towards making sure the system produces permeate needed for crop trials. ❖ Researchers, administration and laboratory staff at the Pollution Research Group. ❖ Talbot laboratories for their assistance in chemical analysis. ❖ Plant and soil laboratory at CEDERA (Department of Agriculture and Rural Development) in Pietermaritzburg, KwaZulu-Natal, South Africa for plant tissue analysis. ❖ The eThekwini municipality for permitting us and providing their facilities to conduct the research project. ❖ Fellow research students in PRG and UKZN PMB-Agric campus for sharing information on how to improve my research work. ❖ Prof Isa Bertling, Dr Sabelo Shezi and Dr Shirley Phoku-Magwaza for their academic support. ❖ Friends; Sikelela Buthelezi, Sanele Kubheka, Dr Pumelele Zakwe, and Lindiwe Khoza for emotional support. ❖ Jaca family in Durban for warm reception while staying with them. ❖ The following hardware shops for fantastic support in the selection of irrigation equipment; Natal plastics, Builder's warehouse and Controlled irrigation. ❖ To God and my ancestors for always being there when faced with personal obstacles and tribulations. ix 2.3 Challenges facing the global sanitation ................................................................. 27 2.4 Recovering nutrients from human-excreta ............................................................ 28 2.5 Wastewater sources in informal settlements ......................................................... 30 2.5.1 Community ablution blocks....................................................................... 30 2.6 Problems faced in running centralised wastewater treatment systems .................. 30 2.7 Introduction of decentralised wastewater treatment systems ................................ 31 2.7.1 Nutrient recovery in wastewater with Algae ............................................. 31 2.7.2 Nutrient recovery in wastewater with an anaerobic baffled reactor (ABR) system ............................................................................................ 31 2.7.3 Nutrient recovery in wastewater with an anaerobic membrane bioreactor (AnMBR) ................................................................................. 32 2.8 Reuse of wastewater in crop production ............................................................... 32 2.9 Crop production with wastewater.......................................................................... 33 2.10 Effects on soils due to irrigation with wastewater ................................................ 34 2.11 Hydroponic production of crops using wastewater ............................................... 35 2.12 Effects of using wastewater on plants ................................................................... 36 2.12.1 Physiological response .............................................................................. 36 2.12.2 Morphological response ............................................................................ 37 2.12.3 Yield .......................................................................................................... 37 2.12.4 Contamination with human pathogens ...................................................... 37 2.12.5 Heavy metal contamination and toxicity ................................................... 38 2.13 Food and Agriculture Organisation (FAO) and World Health Organisation (WHO) standards for the consumption of crops irrigated with treated wastewater ............................................................................................................. 38 x 2.14 Conclusion and future aspects ............................................................................... 38 2.15 References ............................................................................................................. 39 CHAPTER 3 : Evaluating the feasibility of ABR effluent as a nutrient source for Swiss chard (Beta vulgaris subsp. cicla) production in a vertical hydroponic system ............ 49 3.1 Introduction ........................................................................................................... 50 3.2 Materials and Methods .......................................................................................... 51 3.2.1 Site location ............................................................................................... 51 3.2.2 Hydroponic system .................................................................................... 52 3.2.3 Experimental set-up in the vertical hydroponic system ............................ 52 3.2.4 Preparation of nutrient feeds...................................................................... 53 3.2.5 Municipality tap water ............................................................................... 53 3.2.6 Flow-rate of drippers ................................................................................. 54 3.2.7 Planting date, planting method and operation of vertical hydroponic system ........................................................................................................ 54 3.2.8 Data collection and harvesting date ........................................................... 54 3.2.9 Data analysis .............................................................................................. 55 3.3 Results ................................................................................................................... 55 3.4 Nutrient analysis .................................................................................................... 55 3.4.1 Effect of nutrient sources on growth and biomass production in hydroponically grown Swiss chard ........................................................... 57 3.4.2 Biomass lost to pests and diseases ............................................................. 59 3.4.3 Fresh yield ................................................................................................. 59 3.5 Discussion ............................................................................................................. 59 3.6 Conclusions and future aspects ............................................................................. 62 xi 3.7 Acknowledgements ............................................................................................... 63 3.8 References ............................................................................................................. 63 CHAPTER 4 : Evaluating the feasibility of NEWgenerator permeate as a nutrient source for non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis (Halnelt)) production in a vertical hydroponic system .................................................. 67 Abstract .......................................................................................................................... 67 4.1 Introduction ........................................................................................................... 68 CHAPTER 5 : GENERAL DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER RESEARCH ....................................................................................... 92 5.1 General discussion ................................................................................................. 92 5.2 CONCLUSIONS, RECOMMENDATIONS AND FUTURE RESEARCH STUDIES............................................................................................................... 95 5.3 References ............................................................................................................. 96 APPENDICES ....................................................................................................................... 97 xiv Table 4.6: Effect of nutrient sources on plant growth and yield of hydroponically grown non-heading Chinese cabbage. The two nutrient sources used were, commercial hydroponic fertiliser mix (CHFM) and diluted NEWgenerator permeate + hydroponic fertiliser (DNP + HF). ..................................................... 79 Table 4.7: Mineral content in plant tissues of non-heading Chinese cabbage expressed as g/kg. .................................................................................................................. 81 15 CHAPTER 1 : INTRODUCTION 1.1 The rationale for the research Poverty and unemployment are one of the main push factors for people to migrate from rural to urban areas to seek job opportunities and a better life (Smit, 1998). Job seekers and those who earn paltry wages construct temporary housing structures in unauthorised vacant land closer to cities. These temporary housing structures have mushroomed and grown to form multiple informal settlements in South African cities (Huchzermeyer, 2006). Informal settlements accommodate about 10 to 20 % of the national population. The number of people living in informal settlements is growing at a higher rate than the construction of new houses aimed to improve their living conditions (Abbott, 2002). Informal settlements are often overcrowded, lack basic amenities, and in some instances, they are characterised by filthiness (Huchzermeyer, 2006). Most informal settlements are located in marginalised places, such as dumpsites and marshlands, with certain areas lacking necessary sanitation facilities (Wekesa et al., 2011). The provision of onsite sanitation facilities by local municipalities namely; urine diversion dry toilets, ventilated improved pit toilets, and community ablution blocks have improved the level of hygiene in informal settlements (Still et al., 2012). The usage of some onsite sanitation facilities such as pit latrines and urine diversion dry toilets exposes children to a danger of falling into pits (Mkhize et al., 2017). For example, in South Africa, there have been occasions whereby pupils drown into old pit toilets at schools (Nhamo et al., 2019). Nevertheless, there were no reported cases of drowning in ablution blocks constructed in communities and schools. Community ablution blocks are much safer than other onsite sanitation facilities and have flushing pedestals for transportation of faecal matter to sewer lines connected to centralised wastewater treatment systems (Buckley, 2012; Strande and Brdjanovic, 2014). The expansion of peri-urban households and community ablution blocks connected to municipality sewer lines has increased the volume of domestic wastewater needed for treatment at centralised wastewater treatment systems. This has led to an increase in pressure on existing centralised wastewater treatment systems which are already faced with challenges 16 of adequately sustaining the operation of wastewater treatment. Henceforth, the establishment of decentralised wastewater treatment systems to ease pressure on centralised wastewater treatment systems (Amoah et al., 2018a). In addition, decentralised wastewater treatment systems are projected to provide wastewater treatment in areas not connected to centralised wastewater treatment systems, especially those at the periphery of municipal boundaries (Massoud et al., 2009). Nutrient recovery with decentralised wastewater treatment systems is seen as a beneficial way of improving sanitation services in peri-urban areas of developing countries (Gutterer et al., 2009a). Domestic wastewater, either treated or raw contain macronutrients and micronutrients with low concentrations of heavy metals (Pb and Cd), while sodium and chlorine contents are relatively high (Jordán et al., 2008; Yang et al., 2015). A study conducted by Mihelcic et al. (2011) reported that phosphorus present in urine and faeces could account for 22 % of phosphorus needed for global supply. Newly developed decentralised wastewater treatment systems have shown their ability to recover nutrients from domestic wastewater for crop production (Mehta et al., 2015; Otterpohl et al., 2002). In Durban, South Africa, a decentralised wastewater treatment system called an anaerobic baffled reactor (ABR) was installed for the treatment of domestic wastewater. The anaerobic baffled reactor was designed to treat domestic wastewater from 83 peri-urban households connected to a municipality sewer line (Foxon et al., 2004; Gutterer et al., 2009a; Nasr et al., 2009). In a study conducted using Swiss chard, fertigation with nutrient-rich ABR effluent had a liming effect on acid soils and increased crop growth (Musazura et al., 2015). The contamination of crops with faecal pathogens has been one of the reasons there is reluctance in the usage of human-excreta derived nutrients. An anaerobic membrane bioreactor sanitation technology has been developed to extract pathogen-free nutrients on sanitation facilities of densely populated areas such as informal settlements (Bair et al., 2015). This technology is referred to as NEWgenerator (nutrients, energy, and water generator), designed to solve sanitation problems for about 2.6 billion people worldwide when mass-produced. The system occupies 6.25 m2 of space when installed onsite (Peterson, 2017). The NEWgenerator recycles nutrients, electricity, and potable water from domestic wastewater produced by sanitation facilities (Cook, 2016). 19 superior quality, high yield and allow for rapid harvest (Hussain et al., 2014). The success of previous hydroponic horticultural trials with nutrient-rich ABR effluent (Magwaza et al., 2020a; Magwaza et al., 2020c) and NEWgenerator permeate support advances in further research studies to improve productivity with human-excreta-derived-materials. 1.4 Aim This study aims to generate knowledge on the use of human-excreta-derived-materials generated by off-the-grid decentralised sanitation technologies for the production of safe, nutritious, and quality horticulture produce using a vertical hydroponic system. 1.5 Objectives The specific objectives of this study were to: 1. Determine the nutrient composition of commercial hydroponic fertiliser mix and human-excreta-derived-material used as nutrient sources for Swiss chard and non- heading Chinese cabbage growing in a vertical hydroponic system. 2. Compare the effect of commercial hydroponic fertiliser mix and human-excreta- derived-material as nutrient sources on growth and yield of Swiss chard and non- heading Chinese cabbage leafy vegetables in a vertical hydroponic system. 3. Assess the presence of microbial loads in harvested leaves grown with human- excreta-derived-material as nutrient sources in a vertical hydroponic system. 1.6 Outline of the dissertation structure Literature review and experimental chapters will be written as research papers. The structure is a laid out as follows; CHAPTER 1: provides the background and significance of the research. The chapter highlights the problems faced with faecal sludge management practices in informal settlements and nutrient recovery from human-excreta in sanitation facilities with decentralised sanitation technologies for agricultural use. 20 CHAPTER 2: reviews in-depth the depletion of mineral rocks to process chemical fertilisers, nutrient recovery from human-excreta, and application of recovered nutrients in agriculture. This section also covers the implications of using wastewater for open field crop production, hydroponic crop production, health effects on workers, and contamination of crops. CHAPTER 3: is an experimental chapter reporting on evaluating the feasibility of ABR effluent as a nutrient source for Swiss chard (Beta vulgaris subsp. cicla) in a vertical hydroponic system. CHAPTER 4: is also an experimental chapter reporting on evaluating the feasibility of NEWgenerator permeate as a nutrient source for non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis (Halnelt)) in a vertical hydroponic system. CHAPTER 5: is the general discussion linking two experimental chapters and concludes the dissertation. The chapters offer insight on challenges experienced, future possibilities, recommendations, and final comments. 1.7 References Abbott, J. (2002). An analysis of informal settlement upgrading and critique of existing methodological approaches. Habitat International 26, 303-315. Akponikpè, P. I., Wima, K., Yacouba, H., and Mermoud, A. (2011). Reuse of domestic wastewater treated in macrophyte ponds to irrigate tomato and eggplant in semi-arid West-Africa: Benefits and risks. Agricultural Water Management 98, 834-840. Amoah, I. D., Reddy, P., Seidu, R., and Stenström, T. A. (2018). Removal of helminth eggs by centralized and decentralized wastewater treatment plants in South Africa and Lesotho: health implications for direct and indirect exposure to the effluents. Environmental Science and Pollution Research 25, 12883-12895. Bair, R. A., Ozcan, O. O., Calabria, J. L., Dick, G. H., and Yeh, D. H. (2015). Feasibility of anaerobic membrane bioreactors (AnMBR) for onsite sanitation and resource recovery (nutrients, energy and water) in urban slums. Water Science and Technology 72, 1543-1551. Buckley, C. (2012). Good Science Makes Good Policy. E-Thekwini Water and Sanitation Innovations, 5-6. 21 Butler, J., Loveridge, R., Bone, D. J. W. s., and technology (1989). Crop production and sewage treatment using gravel bed hydroponic irrigation. 21, 1669-1672. Calabria, J. L., Lens, P. N., and Yeh, D. H. (2019). Zeolite ion exchange to facilitate anaerobic membrane bioreactor wastewater nitrogen recovery and reuse for lettuce fertigation in vertical hydroponic systems. 36, 690-698. Cook, G. (2016). New generator Could Potential Provide 2,6 Billion People with Safe Sanitation. USF Engineering Magazine- Envion-Spring, 20-21. Esray, S. A. (2001). Towards a recycling society: ecological sanitation-closing the loop to food security. Water Science and Technology 43, 177-187. Foxon, K., Pillay, S., Lalbahadur, T., Rodda, N., Holder, F., and Buckley, C. (2004). The anaerobic baffled reactor (ABR): an appropriate technology for on-site sanitation. Water SA 30, 44-50. Gagnon, V., Maltais-Landry, G., Puigagut, J., Chazarenc, F., and Brisson, J. (2010). Treatment of hydroponics wastewater using constructed wetlands in winter conditions. Water, Air, & Soil Pollution 212, 483-490. Gutterer, B., Sasse, L., Panzerbieter, T., and Reckerzügel, T. (2009). Decentralised wastewater treatment systems (DEWATS) and sanitation in developing countries. A practical guide, Publishing House: Borda Bremen-Germany, 20-22. Huchzermeyer, M. (2006). "Informal settlements: A perpetual challenge?," Juta and Company Ltd. Hussain, A., Iqbal, K., Aziem, S., Mahato, P., and Negi, A. (2014). A review on the science of growing crops without soil (soilless culture)-a novel alternative for growing crops. International Journal of Agriculture and Crop Sciences 7, 833. Jordán, M., Pina, S., García-Orenes, F., Almendro-Candel, M., and García-Sánchez, E. (2008). Environmental risk evaluation of the use of mine spoils and treated sewage sludge in the ecological restoration of limestone quarries. Environmental geology 55, 453-462. Magwaza, S. T., Magwaza, L. S., Odindo, A. O., Mashilo, J., Mditshwa, A., and Buckley, C. (2020a). Evaluating the feasibility of human excreta-derived material for the production of hydroponically grown tomato plants-Part I: Photosynthetic efficiency, leaf gas exchange and tissue mineral content. Agricultural Water Management 234, 106114. 24 CHAPTER 2 : Crop production with human-excreta-derived-materials in urban and peri-urban areas: A review Abstract Global food security remains threatened by the rising costs of chemical fertilisers and persistent drought affecting the supply of fresh water for irrigation of crops. Irrigation of crops with wastewater has been seen as an alternative way for nutrient supply to plants. Peri- urban farmers in some developing countries irrigate their crops with wastewater to supply nutrients in dry months due to a shortage of rainfall. Wastewater contains water and nutrients needed in crop production. Crops grown with wastewater were reported to record high yields while certain crop species recorded low yields. Furthermore, crops raised with wastewater were found to be contaminated with human pathogens and heavy metals. Farmers and workers were reported to develop skin and nail problems afterwards due to constant contact with wastewater. Soils were reported to accumulate high concentrations of sodium and heavy metals due to continuous irrigation with wastewater. As a result, farmers are now encouraged to use hydroponic systems for crop production to limit environmental pollution caused by irrigation with wastewater. Low-cost off-the grid-sanitation technologies have been developed to be installed for onsite treatment and processing of human-excreta into nutrient- rich wastewater for irrigation of crops. This review aims to provide deep insight into the progress made in reusing human-excreta derived nutrients for crop production as a way of reducing food shortages and presenting it as an alternative nutrient source for the near future. Keywords: Sanitation technologies, human-excreta, nutrient recovery, human-excreta- derived-materials, agriculture, hydroponic systems 25 2.1 Introduction The United Nations estimates the global population to reach 8.6 billion in 2030 and 9.8 billion in 2050 (Acedański and Włodarczyk, 2018). In addition, food insecurity and malnutrition continue to affect poverty-stricken communities, especially in developing countries (Godfray et al., 2010). For instance, Sub-Saharan Africa experiences high poverty levels in villages or communities due to low crop yields (Chianu et al., 2012). Improvement in quantity and quality of crop yields is mostly sustained by fertilisation with chemical fertilisers. Chemical fertilisers are known for their high nutrient content and immediate availability of mineral elements in solution (Chen, 2006; Savci, 2012). Unfortunately, application of high amounts of chemical fertilisers was reported to cause soil deterioration and loss of nutrients in agricultural fields (Wang et al., 2018). The nitrogen in chemical fertilisers was reported to promote the incidence of sap-feeding insects due to its contribution to protein production and insect development (Garratt et al., 2011). Small-scale and large-scale crop production remains heavily reliant on the fertilisation of plants with chemical fertilisers towards obtaining high yields (Van Averbeke and Yoganathan, 2003). As a result, there is an increase in the rate of mining and depletion of mineral rocks used for the production of chemical fertilisers. Thus, the focus has turned into finding alternative sources of nutrients for crop production in the event of shortages in the supply of chemical fertilisers. The usage of organic fertilisers derived from animal-waste and urban-waste has been foreseen as one of the sustainable and reliable nutrient sources (Case et al., 2017). Application of composted litter and waste allows farmers to recycle nutrients back into the soil and improve soil fertility (Ouédraogo et al., 2001). The usage of sewer sludge compost in grapevines positively contributed to soil management practices such as a reduction in chemical control of weeds and replacing chemical fertilisers without experiencing loss on vigour and yield (Pinamonti, 1998). Trading of faecal sludge fertiliser was popular in the mid-19 century where it was transported from urbanised towns to farming areas due to urban sprawl. This led to improved sanitation in urban areas (Semiyaga et al., 2015). The approach was abandoned in the 20th century due to; availability of cheaper and safer mineral fertilisers, the presence of nematodes in faecal fertiliser, faecal-oral disease, 26 logistics in the transportation of faecal based fertiliser and reduction in excreta available due to sewered sanitation (Semiyaga et al., 2015). In the 21st century, there has been an increase in the volume of biosolids generated from the treatment of domestic wastewater in urban areas. Landfills of most municipalities in developing and developed countries are reportedly reaching full capacity due to rising capacity of bio-solids (Cofie et al., 2006). Bio-solids generated from drying beds of centralised wastewater treatments contain nutrients (Tiwari et al., 2017). Thus, recycling nutrients from domestic wastewater allows for the reduction of municipal bio-solids and provides farmers with needed nutrients for crop production (Cofie et al., 2006). Untreated faecal sludge has been used for agriculture in Tamale, Ghana, as a disposal method (Cofie et al., 2005). Small-holder farmers in peri-urban areas of developing countries have adopted the practice of using wastewater as a nutrient treatment and water supply to support their crops in dry months (Drechsel et al., 2006). Reusing treated wastewater for crop irrigation has been recommended for areas facing water shortages (Pereira et al., 2002). The reuse of treated wastewater in hydroponic systems showed efficiency in producing commercially valuable plants (Adrover et al., 2013; Oyama et al., 2005). Hydroponic systems are reportedly used for secondary treatment of municipal wastewater and crop production (Boyden and Rababah, 1996; Zheng et al., 2015). The chemical composition of treated wastewater from non-industrial sources which had at least received secondary treatment was reported not to cause adverse effects on plant growth and public health (Adrover et al., 2013). This review aims to cover depletion of mineral rocks and nutrient recovery from human- excreta sources and reuse of human-excreta derived materials in crop production as an alternative source of nutrients. 2.2 Depletion of potassium and phosphorus rocks The depletion of mineral rocks used to produce phosphorus and potassium fertilisers remains a major concern to farmers and a threat to global food security. Most farmers rely on chemical fertilisers to meet the nutrient requirements for their crops. For instance, Wang et al. (2018) reported that China used more chemical fertilisers on high-value horticultural crops. Unfortunately, potassium and phosphorus rock mining takes place in a few countries for 29 synthetic nitrogen fertiliser. Hydrolysed urine is processed through nitrification and distillation to obtain a concentrated urine-based liquid fertiliser (Harder et al., 2019; Heinonen-Tanski and van Wijk-Sijbesma, 2005). 2.4.2 Macronutrient solutions (Urea – N) Urea – N is processed from hydrolysed urine under a technique of sorption and desorption from activated carbon then passed through nanofiltration membrane separation. Nanofiltration membrane removes pathogens and organic pollutants. This fertiliser can be used as a feedstock for the production of synthetic fertilisers such as methylene urea (Harder et al., 2019; Pronk et al., 2006). 2.4.3 Macronutrient solutions (Ammonia-N) A solution rich in ammonium - N is produced by nanofiltration membrane of hydrolysed urine. Urine and treated effluent are air stripped to produce ammonia – N. In addition, sewage sludge undergoes thermal drying and absorption in an acid trap to produce fertilisers such as ammonium sulphate, ammonium borate, and ammonium chloride, ammonium, and ammonium phosphate. Each fertiliser product is solely dependent on the acid trap used during the absorption process. These products are free from pathogens, organic pollutants, and heavy metals. Ammonium nitrate is also a feedstock in the production of synthetic fertilisers (Harder et al., 2019; Horttanainen et al., 2017). 2.4.4 Macronutrient solutions (NK or NPK) Urine undergoes sorption followed by desorption to recovery NH4 + and K+ separated from Na+. Hydrothermal processes on wet faecal matter transfer N, P, and K to a liquid residue. In contrast, other nutrients such as calcium, magnesium, zinc, aluminium, and iron are transferred into solid waste (Casadellà et al., 2016; Harder et al., 2019; Lu et al., 2017). 2.4.5 Macronutrient solutions (P) Solutions rich in phosphorus are extracted from organics or inorganics of sewage. The product obtained is a phosphoric acid that can range from diluted to very pure and concentrated (Egle et al., 2015). The phosphoric acid also serves as a feedstock in the production of synthetic fertilisers. Sorption and desorption of treated effluent can also 30 produce a solution rich in phosphorus, which can be a useful fertiliser, especially in the formation of struvite (Harder et al., 2019; O'Neal and Boyer, 2013; Schaum et al., 2007). 2.5 Wastewater sources in informal settlements 2.5.1 Community ablution blocks There has been a demand for provision and rendering of better sanitation facilities to curb the transfer of pathogens from hosts to humans (Tumwine et al., 2002). Community ablution blocks are sanitation facilities replacing pit toilets in informal settlements designed to provide urban sanitation services. They are made of a modified shipping container to have showers, toilets and laundry sinks. South African municipalities use them to render better communal and sanitation facilities in informal settlements. Sanitation needs for males and females are separately catered for with different facilities (Crous et al., 2013b). Community ablution blocks are designed to serve between 50 and 75 households within a radius of 200 m (Roma and Buckley, 2011). They are connected to municipality sewer lines for transportation of human-excreta to centralised wastewater treatment systems. Municipalities employ caretakers to ensure sustainable utilization of the ablution blocks. At night, the facilities are closed to prevent theft and vandalism. The proximity and size of community ablution blocks still fail to fully cater for sanitation needs to all residents compared to those in urban areas (Roma et al., 2010a). 2.6 Problems faced in running centralised wastewater treatment systems Centralised treatment systems continue to generate municipal biosolids derived from domestic wastewater which are causing an environmental hazard and economic burden (Nahman et al., 2012). The nutrient removal technique practised by centralised wastewater treatment systems (air stripping and chemical precipitation) continues to be a costly process for most municipalities resulting on insufficiently treated effluent due to cutting down of costs in treating wastewater (Odjadjare et al., 2010; Santos and Pires, 2018). Existing centralised wastewater treatment systems are faced with delays in expansion due to; budget restrictions, inadequate funding from the private and public sector (Paraskevas et al., 2002). 31 2.7 Introduction of decentralised wastewater treatment systems Small and isolated villages or settlements with low population densities were identified to be suitable in being served by decentralised wastewater treatment systems that are simpler and cost-effective (Butler and MacCormick, 1996; Paraskevas et al., 2002). However, lack of research, poor planning, and development activities in developing countries lead to the selection of inappropriate technologies to suit local conditions. In addition, financial and human resource affordability, and social or cultural acceptability have hindered efforts towards the provision of decentralised wastewater treatment systems (Massoud et al., 2009). However, various decentralised wastewater treatment systems have been launched and being towards nutrient recovery from domestic wastewater in peri-urban areas (Foxon et al., 2004). 2.7.1 Nutrient recovery in wastewater with Algae Algae is grown in domestic wastewater that has received primary treatment. The microalgae- based technology is considered a low-cost renewable, sustainable, and environment-friendly wastewater treatment process. It can grow in various living conditions and extreme conditions with high salinity, for example, Dunaliella salina (Wu et al., 2014). Microalgae are known to be efficient in removing nitrogen, phosphorus, and toxic metals from wastewater under controlled environments, which can be used for the production of biochemical, biofuels, and biofertilisers when produced with concentrated urine (Tuantet et al., 2014). 2.7.2 Nutrient recovery in wastewater with an anaerobic baffled reactor (ABR) system An off-the-grid sanitation technology called anaerobic baffled reactor (ABR) was developed and constructed to operate without energy input for the biological treatment of domestic wastewater from middle-class households in peri-urban areas. Domestic wastewater passes through a series of anaerobic membrane baffled reactors and filters with microorganisms degrading faecal matter to recover a nutrient-rich treated wastewater (Gutterer et al., 2009a). The nutrient-rich treated wastewater collected after anaerobic filters were reported to support crop production (Nasr et al., 2009; Salukazana et al., 2005). The nutrient-rich wastewater had a liming effect on acid soils and increased Swiss chard growth (Musazura et al., 2015). 34 2.10 Effects on soils due to irrigation with wastewater Irrigation with untreated wastewater increases soil organic matter, nitrogen and concentration of major ions (Tam, 1998). However, excessive provision of nutrients in the soil may have adverse effects, especially phosphorus (PO4 3-) and nitrate, which can be leached into the surface and groundwater, causing eutrophication (Knobeloch et al., 2000; Wu, 1999). Magesan et al. (2000a) reported that an increase in wastewater C: N ratio increases soil microbial biomass, carbohydrate, nematode population while decreasing nitrate leaching with hydraulic conductivity raised to 80 %. Magesan et al. (2000b) further revealed that the organic and inorganic nutrients in treated effluent that had a high carbon to nitrogen ratio stimulated the soil microorganisms, subsequently decreased the hydraulic activity in the irrigated soil. Wastewater contains organic and inorganic nutrients, with dissolved organic carbon (DOC) being the most common natural nutrient. Organic carbon often influences the bioavailability of nutrients in the water and stimulates the activity of soil microorganisms (Ramirez-Fuentes et al., 2002). The major disadvantage of using wastewater for irrigation is the accumulation of immobile heavy soils (Abedi-Koupai et al., 2006). Sodium and other forms of salinity are the most persistent in treated wastewater which are often most challenging to remove in wastewater (Toze, 2006). Irrigation of crops with wastewater affects the chemical and physical properties of the soil. Wastewater irrigation increases Mg2+ and K+ losses in calcareous soils (Jalali et al., 2008). Soils irrigated with wastewater had a significant decrease in soil pH and an increase in salinity, organic matter content, and cation exchange capacity (Kiziloglu et al., 2008). Antolín et al. (2010) reported that wastewater had a liming effect on acidic soils. Bame et al. (2014), revealed that irrigation with wastewater had residual effects after harvesting on soil for phosphorus and magnesium. In addition, Latare et al. (2014) reported that high application of wastewater caused residual effects and led to a build-up of N, K, S, and Zn contents in the soil after the harvest of wheat. 35 2.11 Hydroponic production of crops using wastewater Hydroponic systems limit soils being damaged by salts when applied for the treatment of wastewater and crop production (Haddad and Mizyed, 2011). In some countries, hydroponic systems are used for secondary and tertiary treatment of domestic wastewater (Vaillant et al., 2003). For instance, constructed wetlands in decentralised wastewater treatment systems provide the final treatment of wastewater through nutrient removal by plants (Gutterer et al., 2009b). The wastewater retention time in planted constructed wetlands allows for efficient nutrient removal by plants (Gutterer et al., 2009b). Plants grown in constructed wetlands are selected mainly based on their ability to acclimatise in local weather conditions quickly, and they require less management to enable efficient treatment of wastewater. In decentralised wastewater systems, reeds are planted on constructed wetlands as they immediately adapt to local climates and grow well in partially treated wastewater loaded with nutrients (Gutterer et al., 2009a). Constructed wetlands resemble open hydroponic systems, but they are designed to discharge nutrient-depleted effluent after final treatment (Gutterer et al., 2009a). In addition, constructed wetlands were found to constitute an efficient and safe alternative to treat and then reuse greenhouse wastewater after showing a 99.99 % removal efficiency of plant pathogens (Pythium ultimum and Fusarium oxysporum) (Gruyer et al., 2013). The success of reeds and grasses in nutrient removal of wastewater on constructed wetlands prompted researchers to consider growing useful crops in hydroponics systems. Various hydroponic systems namely; wick system (Haddad and Mizyed, 2011), water culture (Oron, 1994), drip (recovery) (Haddad and Mizyed, 2011), flood and drain (Haddad and Mizyed, 2011), nutrient film technique (Vaillant et al., 2003) and aeroponics (Jurga and Kuźma, 2018) have been used for growing edible crops with wastewater. Hydroponic systems are now considered as one of the options for decentralised wastewater treatment systems for domestic wastewater and effluent reuse in rural areas, for example, in Palestine. In addition, hydroponic systems have shown to successfully provide tertiary treatment of domestic wastewater while growing edible crops (Haddad and Mizyed, 2011). Crop production with wastewater in hydroponic systems has only been restricted to closed hydroponic systems in order to limit environmental pollution (Truong and Hart, 2001). 36 In closed hydroponic systems, wastewater is retained in nutrient reservoirs and continuously recirculated in plants with pumps (Jurga and Kuźma, 2018). Haddad and Mizyed (2011) evaluated various hydroponic systems as decentralised wastewater treatment system and reuse for the production of vegetable crops, cut flowers, citrus and olive trees, and herbs. Unfortunately, a hydroponic system was found not suitable for the production of green beans with wastewater (Haddad and Mizyed, 2011). The application of a vertical recirculating hydroponic system for lettuce production with nitrogen recovered from wastewater produced by an anaerobic membrane bioreactor called NEWgenerator resulted in an 11 % and 19 % increase in fresh and dry mass respectively when compared to the control (Calabria et al., 2019b). The stage of crop development and harvesting frequency affects the treatment of wastewater in a hydroponic system (Zheng et al., 2015). Hydroponics perfectly fit to be used as decentralised wastewater treatment and reuse systems as they are cheaper to construct and much easier to operate (Haddad and Mizyed, 2011). 2.12 Effects of using wastewater on plants 2.12.1 Physiological response Macro-elements and micro-elements concentrations increases in leaves of plants fertigated with wastewater (Abedi-Koupai et al., 2006). Wastewater application on palak (Beta vulgaris var. Allagreen H-1) plants led to a decrease in the rate of photosynthesis, stomatal conductance, and chlorophyll content. In contrast, it increases lipid peroxidation, peroxidase activity, and protein together with proline contents (Singh and Agrawal, 2007). Photosynthesis improved on alfalfa plants under drought conditions due to wastewater application (Antolín et al., 2010). Fertigation of three vegetable species (Colocasia esculentum, Brassica nigra and Raphanus sativus) with wastewater led to decrease in total chlorophyll and total amino acids levels in plants, and an increase in amounts of soluble sugars, full protein, ascorbic acid, phenol with B. nigra the only exception (Gupta et al., 2010). Lower doses of wastewater had a stimulating effect on stomatal conductance in Szarvasi-1 grass (Rév et al., 2017). Odindo et al. 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Resources, Conservation and Recycling 104, 109-119. 49 CHAPTER 3 : Evaluating the feasibility of ABR effluent as a nutrient source for Swiss chard (Beta vulgaris subsp. cicla) production in a vertical hydroponic system Abstract Treated domestic wastewater contains nutrients such as nitrogen and phosphorus needed for crop production. For example, effluent from Anaerobic Baffled Reactor (ABR) can be used in hydroponic systems for crop production, particularly in peri-urban areas of developing countries. This study investigated the potential use of ABR effluent on the growth and yield of Swiss chard (Beta vulgaris subsp. cicla) in a vertical hydroponic system at Newlands Mashu Research Site, Durban, KwaZulu-Natal, South Africa. Swiss chard seedlings were transplanted in a vertical hydroponic system with eight vertical growing towers. The study was set-up in a completely randomised design with four replicates for each treatment giving a total of eight experimental units. Four vertical growing towers were fertigated with commercial hydroponic fertiliser mix (CHFM) as a control and the other four with ABR effluent as a treatment. After transplanting, plant height, number of leaves with disorders, biomass lost and fresh mass of leaves were measured. Swiss chard grown with CHFM performed better than those in ABR effluent and gave a significantly (p<0.05) higher plant height and fresh mass of leaves. The number of leaves with disorders was lower in CHFM treatment than in ABR effluent. Swiss chard fertigated with ABR effluent recorded the highest biomass lost to defoliation by pests. Nitrogen, zinc, and boron content were found to be the limiting elements in ABR effluent to maintain high productivity of Swiss chard. High sodium content (153 mg/L) in ABR effluent had a negative effect on growth of Swiss chard. Thus, the fresh mass of Swiss chard leaves was significantly reduced in ABR effluent by 78 % when compared to fertigation with CHFM. This study demonstrated that ABR effluent has the potential to support the growth of Swiss chard in a vertical hydroponic system but its chemical composition requires supplementation with a chemical fertiliser to maintain high productivity of plants. Adaptation of seedlings to nutrient conditions of ABR effluent before transplanting and replenishing nutrients weekly should be considered as part of further investigation when using ABR effluent as a nutrient source without supplementation with a fertiliser. Keywords: Swiss chard, ABR effluent, commercial hydroponic fertilisers, hydroponics 50 3.1 Introduction Treated domestic wastewater which is a mixture of grey water and black water produced by centralised wastewater systems is used for irrigation of crops in semi-arid rural and peri- urban areas of developing countries (Asano, 1998; Case et al., 2017). Irrigation of crops with treated domestic wastewater is practised to supply nutrients to plants (Obuobie et al., 2006). In, Accra, a majority of peri-urban farmers recorded high yields when using domestic wastewater to irrigate their crops (Drechsel and Keraita, 2014). However, the irrigation of vegetable crops with domestic wastewater is not yet fully embraced by farmers and consumers due to the health risks and perceptions associated with its usage (Saldías et al., 2016). Farmers and workers in Nam Dinh, Vietnam were reported to develop skin problems due to constant contact with treated domestic wastewater during irrigation (Trang et al., 2007). Vegetable crops grown with domestic wastewater in Malamulele, Limpopo, South Africa were found to contain faecal microbes, and farmers sold their produce in markets for their livelihoods (Gumbo et al., 2010). Decentralised wastewater systems are now being constructed in rural and peri-urban areas for generation of pathogen-free treated domestic wastewater for irrigation of crops in farms and family gardens (Capodaglio, 2017). In Durban, South Africa, a decentralised wastewater treatment system called an Anaerobic Baffled Reactor was implemented for treating wastewater from peri-urban households, and it recovers nutrient-rich effluent as part of the treatment process (Gutterer et al., 2009a; Musazura, 2014). This system provides biological treatment of raw domestic wastewater through a series of anaerobic baffled reactors (ABR), anaerobic filters and two constructed wetlands. After the anaerobic filters, nutrient-rich effluent undergoes nutrient removal in constructed wetlands (Capodaglio, 2017; Gutterer et al., 2009a). Previous studies revealed that irrigation with nutrient-rich ABR effluent supported the growth of plants from seedling stage to maturity (Musazura, 2014; Nasr et al., 2009). Swiss chard irrigated with nutrient-rich ABR effluent showed a significantly higher dry mass, fresh mass and leaf area index compared to those irrigated with tap water in pot trials inside a polyethylene tunnel (Musazura, 2014). Magwaza et al. (2020) reported that hydroponically 51 grown tomato plants irrigated with nutrient-rich ABR effluent had the highest harvest index compared to plants irrigated with commercial hydroponic fertiliser mix. Irrigation with wastewater in hydroponics is regarded as an effective and beneficial way of wastewater reuse (Magwaza et al., 2020b). In addition, hydroponic production of crops with wastewater is seen as a way to meet the demands for the production of high-quality crops while reducing losses of water and nutrients (Haddad and Mizyed, 2011). However, farmers and consumers remain concerned about the accumulation of toxic concentration of micronutrients and pharmaceuticals in edible parts of crops hydroponically grown with domestic wastewater (Herklotz et al., 2010; Madikizela et al., 2018; Sharma et al., 2006). The presence of toxic concentrations of micronutrients and pharmaceuticals in domestic wastewater was reported to cause harmful effects on growth of plants which often leads to reduced yields (Amy-Sagers et al., 2017; Kong et al., 2007). Swiss chard was successfully produced with nutrient-rich ABR effluent in an open field at Newlands Mashu Research site (Musazura, 2014). However, there is little information on vertical hydroponic production of Swiss chard with nutrient-rich ABR effluent. Therefore, this study investigated the potential use of ABR effluent on the growth and yield of Swiss chard (Beta vulgaris subsp. cicla) in a vertical hydroponic system inside a polyethylene tunnel at Newlands Mashu research site. 3.2 Materials and Methods 3.2.1 Site location The research site is located at 71 John Dory Road, Newlands-Mashu, Durban, KwaZulu- Natal, South Africa (29o 46' 25.648' S; 30o 58' 28.329' E). This site was built by the BORDA Bremen Overseas Research and Development Association (BORDA) and its global partners for the introduction of a decentralised wastewater treatment system focusing on providing sanitation amenities to disadvantaged communities (Gutterer et al., 2009b). Currently, the site provides biological treatment of raw domestic wastewater from 84 low-to-middle income households connected to a sewer system (Musazura, 2014). Raw domestic wastewater undergoes treatment by anaerobic microorganisms breaking down faecal matter in the settling chamber before flowing by gravity flow to three parallel 54 3.2.6 Flow-rate of drippers The flow-rate was fixed at 3.6 L/h in all drippers with microjet valves in order to maintain uniformity in fertigation of plants in vertical growing towers. The flow-rate was adapted from who used it for fertigation of lettuce with diluted synthetic NEWgenerator permeate in a vertical hydroponic system. 3.2.7 Planting date, planting method and operation of vertical hydroponic system Swiss chard (Beta vulgaris subsp. cicla) seedlings that were four weeks old were bought from Tropical nursery, Durban, South Africa. Swiss chard seedlings were planted in the vertical hydroponic system on 15 August 2018. The seedlings were transplanted in the morning (09h00 to 10h00) by placing onto a white strip in a slanting position 15 mm apart inside the supporting medium of the vertical growing towers. The supporting medium was folded and inserted inside the vertical growing tower after transplanting. Each fold had five transplants, and the vertical growing towers were designed to carry two folds. Therefore, ten seedlings were transplanted in each vertical growing tower, and there were 40 plants per treatment which made up a total of 80 Swiss chard transplants cultivated into the vertical hydroponic system. Power was then turned on after cultivation to begin irrigation of plants by submersible pumps continuously recirculating nutrients around in roots. Nutrient sources were replenished every two weeks of recirculation until end of eight week study period. 3.2.8 Data collection and harvesting date Data was collected after a week upon transplanting and every week until harvesting phase for plant height, the number of leaves with disorders (misshaped leaves) and the total biomass lost in each treatment to determine the effect of nutrient sources on Swiss chard grown in a vertical hydroponic system. Above ground biomass losses in plants was accounted for pruned leaves which had died (green leaves turning brown) due to effects of leaves shading each other caused by delayed harvesting. In addition, leaves which died due after infection with Swiss chard pests and diseases were also recorded as part of above ground biomass loss in plants. Biomass lost per plant was determined through weighing dead matter of Swiss chard on an analytical balance (RADWAG, PS 4500.RS, Poland). Swiss chard leaves were harvested once only on 15 October 2018 at the end of the study period. The study lasted for eight weeks. Fresh leaf mass per plant was determined through weighing fresh matter of 55 Swiss chard (leaf fresh mass) on an analytical balance (RADWAG, PS 4500.RS, Poland) after harvesting. 3.2.9 Data analysis The collected data for growth parameters were subjected to statistical analysis using GenStat version 17th Edition (VSN International, Hemel Hempstead, UK). Analysis of variance (ANOVA) was performed for evaluating the effects of nutrient solutions on crop development. Treatment means separated using Fisher's Least Significant Difference (LSD) test at 5 % level of significance. 3.3 Results 3.4 Nutrient analysis Nutrient analysis results indicated that the municipality tap water used for preparation of CHFM had a neutral water pH (7.6). The pH of CHFM was slightly acidic (6.4) and ABR effluent was neutral (7.0). Nitrogen in a fresh solution of CHFM was mostly available in nitrate form while ABR effluent had ammonium as the predominant form of nitrogen. The electrical conductivity in a fresh solution of CHFM was higher than of ABR effluent. CHFM had a higher concentration of Nitrogen (N), Potassium (K), Magnesium (Mg), Calcium (Ca), Iron (Fe), Manganese (Mn), Zinc (Zn) and Boron (B) than ABR effluent. Only concentrations of copper (Cu), molybdenum (Mo) and sodium (Na) were lower in CHFM than in ABR effluent (Table 3.2). 56 Table 3.2: Chemical composition of municipality tap water and nutrient sources used for crop production. Parameters UNITS Municipality tap water CHFM ABR effluent DO mg/L - 8.7 2.1 EC mS/m 17.6 102 95.3 pH - 7.6 6.4 7 NH4-N/NO3-N - - 18:82 100:0 NH4-N mg/L <0.10 10.7 77.4 NO3-N mg/L 0.6 48 0.3 Nitrogen mg/L 1.3 121 80 Phosphorus mg/L 0.01 22 17.1 Potassium mg/L 3.51 108 22 Magnesium mg/L 2.2 23 9.3 Calcium mg/L 6.8 78 21 Sulphur mg/L 0.73 39 27 Iron mg/L 0.11 0.45 0.13 Manganese mg/L bdl 0.12 0.02 Zinc mg/L 0.84 0.09 bdl Boron mg/L 0.06 0.18 bdl Copper mg/L 0.06 bdl 0.02 Molybdenum mg/L bdl bdl 0.55 Sodium mg/L 3.53 16.5 153 Cadmium mg/L 0.01 bdl bdl Chromium mg/L bdl bdl bdl Nickel mg/L 0.16 bdl bdl Lead mg/L bdl bdl bdl CHFM, Commercial hydroponic fertiliser mix; ABR effluent, treated wastewater from an Anaerobic Baffled Reactor system; DO, dissolved oxygen; EC, electrical conductivity; NH4- N, ammonium nitrogen; NO3-N, nitrate nitrogen; bdl, below detection level; dash, units not available; Detection limit: Zinc, 0.02 mg/L; Boron, 0.02 mg/L; Copper, 0.02 mg/L; Molybdenum, 0.11 mg/L; Cadmium, 0.02 mg/L; Chromium, 0.02 mg/L; Nickel, 0.02 mg/L; Lead, 0.02 mg/L. 59 3.4.2 Biomass lost to pests and diseases Figure 3.1: Appearance of Swiss chard leaves showing symptoms of; spinach leaf miner (A), aphids (B), powdery mildew (C) and flea beetles (D) infection three weeks after transplanting. 3.4.3 Fresh yield The fresh mass of leaves per plant harvested at the end of the study showed that Swiss chard grown with CHFM produced a significantly higher fresh yield than plants treated with ABR effluent (Table 3.4). 3.5 Discussion This study investigated the potential use of ABR effluent on the growth and yield of Swiss chard (Beta vulgaris subsp. cicla) in a vertical hydroponic system at Newlands Mashu Research Site, Durban, KwaZulu-Natal, South Africa. Nutrient-rich ABR effluent has been reported as a good source of nitrogen and phosphorus for growth of plants (Foxon et al., 2004; Nasr et al., 2009). Treated wastewater such as ABR effluent which has received at least secondary treatment is without heavy metals and does not affect plant growth (Adrover et al., 2013). Musazura (2014) reported that growth parameters and yield of Swiss chard showed no significant difference between irrigation with tap water + fertilisers and ABR effluent on an open field. However, in this study, Swiss chard grown with CHFM performed better than those in ABR effluent and gave a significantly (p<0.05) higher plant height and fresh mash of leaves (Table 3.3). A B C D 60 The stunted growth in Swiss chard grown with ABR effluent was related to its reduced nutrient supply lower than CHFM and the low dissolved oxygen content which contributed in a reduction in nutrient uptake (Schröder and Lieth, 2002). The dissolved oxygen in ABR effluent was 1.3 mg/L compared to 8.7 mg/L present in prepared nutrient solution of CHFM (Table 3.2). Brechner et al. (1996) reported that leafy vegetables required at least 4 mg/L of dissolved oxygen to grow satisfactorily in hydroponics. Deficiency of dissolved oxygen affects root formation and plant growth (Schröder and Lieth, 2002; Suyantohadi et al., 2010). The effects of dissolved oxygen deficiency were observed in poor root development in Swiss chard grown with ABR effluent. There was an absence of roots hairs in Swiss chard grown with ABR effluent whilst roots hairs developed in plants of CHFM treatment (Appendix 12). Sodium content in ABR effluent also affected the growth of Swiss chard, as it was approximately five times the concentration found in CHFM (Table 3.2). Swiss chard which belongs to the beet family requires sodium as a beneficial nutrient source when it is less than 36.8 mg/L (Kronzucker et al., 2013). Toxicity of sodium in wastewater is reported to adversely affect plant growth as it increases exchangeable sodium ions on the exchange complex at the expense of Ca2+, Mg2+ and K+ (Jalali et al., 2008). In addition, higher amounts of Na+ inactivates and affect metabolic processes in plants (Sudhir and Murthy, 2004). The K and Ca content was low in ABR effluent which had adverse effects on mitigating the damage of Na+ in plant tissues of Swiss chard (Adrover et al., 2013; Tester and Davenport, 2003). Nitrogen supply had a major effect on the growth of Swiss chard fertigated by ABR effluent as it was mainly available as ammonium (Nasr et al., 2009). Feeding leafy vegetables such as Swiss chard with nutrient solutions rich in ammonium was reported to cause ammonium toxicity resulting in stunted growth, foliar chlorosis and stunted roots (Santamaria et al., 1999). A proper combination of ammonium and nitrates was recommended for good growth of vegetable crops (Liu et al., 2017; Song et al., 2017). The ammonium to nitrate ratio in a nitrogen fertiliser plays a considerable role in the growth of vegetable crops in hydroponic systems. A ratio of 25:75 is mostly suggested and considered suitable for high productivity of leafy vegetables (Song et al., 2017). The ammonium to nitrate ratio was 18:82 in CHFM with nitrates as the dominant form of nitrogen. In contrast, ABR effluent had a ratio of 100:0 with ammonium the dominating form 61 of nitrogen. Hydroponic solutions were reported to enhance good growth of leafy vegetables when nitrates are the dominating form of nitrogen (Song et al., 2017). Ammonium has a stimulating effect on plant growth and development when it is not a significant source of nitrogen (Savvas et al., 2006). Swiss chard grown with ABR effluent suffered negative effects of ammonium being a dominating form of nitrogen in a nutrient solution which resulted in reduced growth and crop productivity (Savvas et al., 2006; Song et al., 2017). Furthermore, the availability of nitrogen in nutrient sources favoured Swiss chard grown with CHFM than ABR effluent. CHFM had a nitrogen content of 121 mg/L compared to ABR effluent which had 80 mg/L. Leafy vegetables such as Swiss chard require at least 100 mg/L of nitrogen to enhance good growth (Hopper et al., 1997). Therefore, Swiss chard grown with CHFM had better growth due to adequate supply of nitrogen, zinc and boron as compared to those of ABR effluent. Reduced supply of boron and zinc results in stunted growth, malformations of leaves and yield reduction in leafy vegetables (Eaton, 1940; Hajiboland and Amirazad, 2010). Toxicity of molybdenum in ABR effluent affected the growth of Swiss chard too. The growth of young pea plants was inhibited by the toxicity of molybdenum (Kevresan et al., 2001). Molybdenum and ammonium toxicity inhibits the activity of nitrate reductase needed for the assimilation of nitrates in green plants resulting in disorders (Kaiser et al., 2005; Kevresan et al., 2001). Swiss chard grown with ABR effluent had a higher number of leaves with disorders (misshaped leaves) which was an indication of nutrient stress and a pest problem (Table 3.4). The outbreak of Swiss chard pests (aphids and flea beetles) contributed to stunted growth and distortion of leaves. Initially, there was effective chemical control of pests with an agricultural disinfectant called sporekill (Appendix 10), However, it was not an insecticide even though pests were successfully controlled in Swiss chard fertigated by CHFM. On the other hand, the shortcomings of sporekill was observed in its failure to control persistent pest infection in Swiss chard fertigated with ABR effluent, which can be attributed to various factors. Thus, Swiss chard pests later developed resistance to chemical control on plants mainly fertigated with ABR effluent. Matured Swiss chard leaves were defoliated by aphids and flea beetles which are common pests affecting leafy vegetables (Mou, 2005). The outbreak of 64 Gumbo, J. R., Malaka, E. M., Odiyo, J. O., and Nare, L. (2010). The health implications of wastewater reuse in vegetable irrigation: a case study from Malamulele, South Africa. International journal of environmental health research 20, 201-211. Gutterer, B., Sasse, L., Panzerbieter, T., and Reckerzügel, T. (2009). Decentralised wastewater treatment systems (DEWATS) and sanitation in developing countries. A practical guide, Publishing House: Borda Bremen-Germany, 20-22. Hajiboland, R., and Amirazad, F. (2010). 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J., Coskun, D., Schulze, L. M., Wong, J. R., Britto, D. T. J. P., and soil (2013). Sodium as nutrient and toxicant. 369, 1-23. Liu, G., Du, Q., and Li, J. (2017). Interactive effects of nitrate-ammonium ratios and temperatures on growth, photosynthesis, and nitrogen metabolism of tomato seedlings. Scientia Horticulturae 214, 41-50. Magwaza, S. T., Magwaza, L. S., Odindo, A. O., and Mditshwa, A. (2020a). Hydroponic technology as decentralised system for domestic wastewater treatment and vegetable production in urban agriculture: A review. Science of the Total Environment 698, 134154. Magwaza, S. T., Magwaza, L. S., Odindo, A. O., Mditshwa, A., and Buckley, C. (2020b). Evaluating the feasibility of human excreta-derived material for the production of hydroponically grown tomato plants-Part II: Growth and yield. Agricultural Water Management 234, 106115. 65 Mou, B. (2005). Screening and Breeding for Leafminer Resistance in Spinach. HortScience 40, 1114D-1115. Musazura, W. (2014). Effect of ABR Effluent Irrigation on Swiss Chard (Beta Vulgaris Subsp. cicla) Growth and Nutrient Leaching, University of KwaZulu Natal, Crop Science Research Space for Master's Degrees. Nasr, F. A., Doma, H. S., and Nassar, H. F. (2009). Treatment of domestic wastewater using an anaerobic baffled reactor followed by a duckweed pond for agricultural purposes. The Environmentalist 29, 270-279. Santamaria, P., Elia, A., Serio, F., Gonnella, M., and Parente, A. (1999). Comparison between nitrate and ammonium nutrition in fennel, celery, and Swiss chard. Journal of Plant Nutrition 22, 1091-1106. Savvas, D., Passam, H., Olympios, C., Nasi, E., Moustaka, E., Mantzos, N., and Barouchas, P. (2006). Effects of ammonium nitrogen on lettuce grown on pumice in a closed hydroponic system. HortScience 41, 1667-1673. Schröder, F.-G., and Lieth, J. H. (2002). Irrigation control in hydroponics. pp. 263-298. Embryo Publications: Athens, Greece. Semiyaga, S., Okure, M. A., Niwagaba, C. B., Katukiza, A. Y., and Kansiime, F. (2015). Decentralized options for faecal sludge management in urban slum areas of Sub- Saharan Africa: A review of technologies, practices and end-uses. Resources, Conservation and Recycling 104, 109-119. Song, S., Yi, L., Zhu, Y., Liu, H., Un, G. S., and Chen, R. (2017). Effects of ammonium and nitrate ratios on plant growth, nitrate concentration and nutrient uptake in flowering Chinese cabbage. Bangladesh Journal of Botany 46, 1259-1267. Sudhir, P., and Murthy, S. (2004). Effects of salt stress on basic processes of photosynthesis. Photosynthetica 42, 481-486. Suyantohadi, A., Kyoren, T., Hariadi, M., Purnomo, M., and Morimoto, T. (2010). Effect of high consentrated dissolved oxygen on the plant growth in a deep hydroponic culture under a low temperature. IFAC Proceedings Volumes (IFAC-PapersOnline) 3. Tester, M., and Davenport, R. (2003). Na+ tolerance and Na+ transport in higher plants. Annals of botany 91, 503-527. Trang, D. T., Van Der Hoek, W., Tuan, N. D., Cam, P. D., Viet, V. H., Luu, D. D., Konradsen, F., and Dalsgaard, A. (2007). Skin disease among farmers using 66 wastewater in rice cultivation in Nam Dinh, Vietnam. Tropical Medicine and International Health 12, 51-58. 69 detection level in treated wastewater. Barley requires more than 100 mg/L of nitrogen in nutrient solutions for normal growth of plants (Hopper et al., 1997). Hydroponically grown tomato plants with anaerobic baffled reactor (ABR) effluent supplemented by commercial hydroponic fertilisers showed better growth, biomass gains and higher mineral accumulation in shoots than those grown with commercial hydroponic fertilisers (Magwaza et al., 2020c). In some instances, hydroponic systems are also used for secondary treatment of wastewater through the production of crops (Haddad and Mizyed, 2011). Spinach grown for 21 days with diluted urine in a hydroponic system showed comparable growth to those raised with a commercial nutrient solution. The waste solution discarded at the end of the experiment met Singapore discharge standards to watercourses. The discharge standards met were; chemical oxygen demand (<30 mg/L), total soluble solids (<10 mg/L), nitrates (< 4.5 mg/Land total phosphorus (<0.76 mg/L) (Yang et al., 2015). Previous studies have shown that fertigation of vegetable crops with wastewater have both positive and negative effects on plants. Some crops were reported to produce good yields, for example, Swiss chard (Musazura, 2014). In contrast, other crops were found to experience a decline in yield; for example, Black mustard (Gupta et al., 2010). The physiological response of crops produced using wastewater differs amongst species due to their differences in their genetic make-up. Thus, further research is required in understanding the implications of growing local leafy vegetables with nutrients derived from domestic wastewater in a closed hydroponic system. Amaranth and non-heading Chinese cabbage were successfully grown in a closed hydroponic system with commercial hydroponic fertilisers (Maboko and Du Plooy, 2019). Calabria et al. (2019a) reported that lettuce grown for 14 days with diluted synthetic NEWgenerator permeate in a vertical hydroponic system showed a higher average fresh mass than the control. This study investigated the potential use of diluted NEWgenerator permeate + hydroponic fertiliser (DNP + HF) on the growth of Chinese cabbage (Brassica rapa L. subsp. chinensis (Halnelt)) in a vertical hydroponic system. 70 4.2 Materials and Methods 4.2.1 Research sites 4.2.1.1 Nutrient extraction research site This research site is located in Thandanani informal settlement (29.7835o S, 31.0206o E), Durban, KwaZulu-Natal, South Africa. An off-the-grid decentralised wastewater treatment system (refer to appendix 3) was installed to treat human excreta from toilets of a male community ablution block which is used daily by people living in the informal settlement. The sanitation technology is an anaerobic ultrafiltration membrane bioreactor system referred to as NEWgeneratorTM (the University of South Florida, Tampa, USA) with the ability to process domestic wastewater into nutrient-rich wastewater, potable water and biogas (Bair et al., 2015). 4.2.1.2 Agricultural research site The research site is located at 71 John Dory Road, Newlands-Mashu, Durban, KwaZulu- Natal, South Africa (29o 46' 25.648' S; 30o 58' 28.329' E). This site was built by the BORDA Bremen Overseas Research and Development Association (BORDA) and its global partners for the introduction of a decentralised wastewater treatment system focusing on providing sanitation amenities to disadvantage communities (Gutterer et al., 2009b). Currently, the site provides biological treatment of raw domestic wastewater from 84 low-to-middle income households connected to a sewer system (Musazura, 2014). Raw domestic wastewater undergoes treatment by anaerobic microorganisms breaking down faecal matter in the settling chamber before flowing by gravity flow to three parallel anaerobic baffled reactor trains which have compartments. Train 1 and train 2 consist of seven compartments, while train 3 has four compartments. The first three compartments in train 3 are double in size while the last compartment is equal to the size of the other trains. After anaerobic baffled reactor trains, there are anaerobic filters to filter floating particles in partially treated effluent before further treatment in planted wetlands (Magwaza et al., 2020). 71 4.2.2 Hydroponic system A vertical hydroponic system called a ZipGrow Farm WallTM (ZipGrow Inc., Ontario, Canada) was assembled inside the polyethylene tunnel (refer to appendix 6). The vertical hydroponic system was internally modified to have two units merged in one system. Each unit had its drip line, four vertical growing towers and a nutrient reservoir with a submersible pump (pump head = 4.0 m and flow-rate = 6 200 L/h) for transportation of nutrients in a continuous recirculation method. Each vertical growing tower had two folding supporting growing media to hold plants. The supporting inorganic medium was made of fibrous, thermos-polypropylene with a white strip inside to channel the flow of nutrients from drippers to the plant roots (Calabria et al., 2019a). The system has two troughs (top and bottom) for holding vertical growing towers. The top trough has a drip line to supply nutrients into vertical growing towers, and the bottom trough collects nutrient solutions drained from vertical growing towers to return into reservoirs. The vertical hydroponic had the following dimensions; 2.0 m (width) × 2.6 m (height); area required was 5.3 m2. Vertical growing towers are spaced by 0.0038 m (3.8 cm) apart. 4.2.3 Experimental set-up in the vertical hydroponic system The vertical hydroponic system had eight vertical growing towers. Four vertical growing towers were fertigated with commercial hydroponic fertiliser mix (CHFM), and the other four vertical growing towers were fertigated with diluted NEWgenerator (nutrients, water and energy generator) permeate + hydroponic fertiliser (DNP + HF). The study was set-up in a completely randomised design with four replicates for each treatment giving a total of eight experimental units. Table 4.1: Layout of experimental design. CHFM DNP + HF VGT 1 VGT 5 VGT 3 VGT 2 VGT 6 VGT 4 VGT 7 VGT 8 VGT, Vertical growing tower. 74 USA) were installed and used to measure the micro-climate around the vertical hydroponic system inside the polythene tunnel. The average growing conditions (night/day) were: temperature (33.1/15.6; o C), relative humidity (77.6/77.1; %), active photosynthetic radiation (29.8/18.6; µmol/m2s1), solar radiation (31.3/0.6; W/m2) and dew point temperature (28.7/11.6; o C). Non-heading Chinese cabbage leaves were harvested once only on 03 July 2019 at the end of the study period. The fresh leaf mass and fresh root per plant was determined through weighing on an analytical balance (RADWAG, PS 4500.RS, Poland) after harvesting. 4.2.9 Plant tissue analysis Samples of freshly harvested leaves were taken from each treatment for blending with deionised water. The blended solutions were taken for faecal coliform analysis at Talbot Laboratories, Pietermaritzburg, KwaZulu-Natal, South Africa. The remaining fresh leaves and roots (washed off potting soil) were dried in an oven at 60 o C for 48 hours. The dried plant material (leaves and roots) of each treatment was replicated three times for macronutrients and micronutrients analysis at the Soil and Plant Laboratory, CEDERA (Department of Agriculture and Rural Development), Pietermaritzburg, KwaZulu-Natal, South Africa. 4.2.10 Data analysis The collected data for growth parameters and elements accumulated in plant tissues were subjected to statistical analysis using GenStat version 17th Edition (VSN International, Hemel Hempstead, UK). Analysis of variance (ANOVA) was used to determine the effect of nutrient solutions on crop development and nutrients accumulated in plant tissues. Treatment means were separated using Fisher's Least Significant Difference (LSD) test at 5 % level of significance. 4.3 Results 4.3.1 Nutrient analysis Dilution of high strength NEWgenerator permeate in order to supplement deficient micronutrients (Manganese (Mn) and zinc (Zn)) resulted in decline macronutrients (Nitrogen (N), Phosphorus (P), Potassium (K) and Calcium (Ca)) in DNP + HF (Table 4.2 and Table 75 4.3). However, K, Mg, Ca, and S contents in high strength NEWgenerator permeate were lower than the concentration of these nutrients in CHFM before dilution (Table 4.2). Mg and S contents increased in DNP + HF when compared to the concentration of these nutrients in NEWgenerator permeate due to supplementation with chemical fertiliser (Table 4.2 and Table 4.3). However, Mg and S content in DNP + HF remained low when compared to the concentration of these nutrients in CHFM (Table 4.3). DNP + HF had a very low dissolved oxygen content compared to CHFM. Ammonium was the predominant form of N in DNP + HF while in CHFM, most of N was in nitrate form. DNP + HF had a lower N, K, Ca, S, Fe, Mn, Zn, and B content than CHFM. In contrast, Mg, P and Na content were higher in DNP + HF than in CHFM. Magnesium, boron, copper, and sodium contents increased in waste solution of CHFM while the waste solution of DNP + HF recorded an increase in nitrates, phosphorus, magnesium, manganese, zinc, boron, copper and sodium (Table 4.3). The pH was alkaline in DNP + HF and neutral in CHFM (Table 4.4). After five days of transplanting, the pH dropped to fluctuate to highly acidic conditions in DNP + HF while it fluctuated in slightly acidic conditions in CHFM (Table 4.4). 76 Table 4.2: Chemical composition of municipality tap water and NEWgenerator permeate before dilution. Elements (mg/L) Units Municipality tap water NEWgenerator permeate Faecal coliforms CFU/mL 0 0 DO mg/L - 4.1 EC mS/m 17.6 228 pH - 7.6 7.1 NH4-N mg/L <0.10 210 NO3-N mg/L 0.6 0 Nitrogen mg/L 1.3 282.3 Phosphorus mg/L 0.01 67 Potassium mg/L 3.51 70 Magnesium mg/L 2.2 10.4 Calcium mg/L 6.8 38 Sulphur mg/L 0.73 12 Iron mg/L 0.11 0.16 Manganese mg/L bdl bdl Zinc mg/L 0.84 bdl Boron mg/L 0.06 0.07 Copper mg/L 0.06 0.08 Molybdenum mg/L bdl bdl Aluminium mg/L 3.53 bdl Sodium mg/L 0.01 87 Cadmium mg/L bdl bdl Chromium mg/L 0.16 bdl Nickel mg/L bdl bdl Lead mg/L bdl bdl CHFM, Commercial hydroponic fertiliser mix; NEWgenerator permeate, treated wastewater from NEWgenerator system; DO, dissolved oxygen; EC, electrical conductivity; NH4-N, ammonium nitrogen; NO3-N, nitrate nitrogen; bdl, below detection level; dash, units not available; Detection limit: Manganese, 0.02 mg/L; Zinc, 0.02 mg/L; Aluminium, 0.02 mg/L; Molybdenum, 0.11 mg/L; Cadmium, 0.02 mg/L; Chromium, 0.02 mg/L; Nickel, 0.02 mg/L; Lead, 0.02 mg/L. 79 Table 4.5: Analysis of variance showing mean squares and significant test of plant growth and yield of hydroponically grown non-heading Chinese cabbage treated with different nutrient sources (CHFM and DNP +HF). Source of variation DF Number of leaves/plant FLM DLM Root length Nutrient source 1 0.00ns 35.66* 0.134* 1.051ns Residual 6 4.130 5.69 0.0170 Total 7 CHFM, commercial hydroponic fertiliser mix; DNP + HF, diluted NEWgenerator permeate + hydroponic fertiliser; FLM, fresh leaf mass; DLM, dry leaf mass; * Significant at p<0.05; NS, non-significant; DF, degrees of freedom. Table 4.6: Effect of nutrient sources on plant growth and yield of hydroponically grown non-heading Chinese cabbage. The two nutrient sources used were, commercial hydroponic fertiliser mix (CHFM) and diluted NEWgenerator permeate + hydroponic fertiliser (DNP + HF). Nutrient source Number of leaves/plant FLM(g/plant) DLM(g/plant) Root length(cm/plant) CHFM 9.0 16.34 1.47 6.5 DNP + HF 9.0 12.12 1.21 5.8 P-value 1.00 <0.01 <0.05 0.23 LSD 1.181 2.283 0.226 1.315 CHFM, commercial hydroponic fertiliser mix; DNP + HF, diluted NEWgenerator permeate + hydroponic fertiliser. FLM, fresh shoot mass; SDM, dry leaf mass; LSD 0.05. 80 4.3.2 Mineral content in leaves and roots Mineral content in leaves was statistically significantly different (p<0.05) between nutrient sources. Only Na content in leaves and N in roots showed no significant difference between nutrient sources. Leaves of non-heading Chinese cabbage grown with CHFM had higher K, Ca and Zn content and a lower N, P, Mg, Na, Mn, Fe and Cu content than those of non- heading Chinese cabbage grown with DNP + HF. Similar results were found in roots except for N and Na content (Table 4.7). 81 Table 4.7: Mineral content in plant tissues of non-heading Chinese cabbage expressed as g/kg. N P K Ca Mg Na Zn Mn Fe Cu Al Nutrient sources (Leaves) CHFM 56.8 8.4 93.1 25 7.3 5.2 0.18 0.074 0.15 0.029 0.12 DNP + HF 59.6 9.5 68.3 17.8 8.3 5.3 0.13 0.101 0.24 0.030 0.16 P-value < 0.05 <0.001 <0.001 <0.001 <0.001 0.43 <0.001 <0.001 <0.001 <0.001 <0.01 LSD 1.80 0.195 0.979 0.321 0.207 0.333 0.0028 0.00016 0.0055 0.00028 0.0055 Nutrient sources (roots) CHFM 22.5 5.8 14.8 15 8.5 2.1 0.17 0.14 4.1 0.24 2.5 DNP + HF 22.3 6.2 10.9 11.1 9.7 1.6 0.12 0.16 5.8 0.32 3.0 P-value 0.79 <0.001 <0.001 <0.001 <0.001 0.11 <0.001 <0.001 <0.001 <0.001 <0.001 LSD 1.95 0.096 0.207 0.293 0.185 0.63 0.0044 0.0044 0.133 0.0049 0.064 CHFM, Commercial hydroponic fertiliser mix; DNP + HF, diluted NEWgenerator permeate + hydroponic fertiliser; LSD 0.05. 84 conditions due to precipitation with P, Al and Mn (Trejo-Téllez and Gómez-Merino, 2012). Waste solutions of DNP + HF had a higher Ca content, which was released by the absorption of P into plant tissues (Table 4.2). Ca precipitated with phosphates at pH 8.4 in a fresh solution of DNP + HF, thus having a lower content than the waste solution (Penn and Camberato, 2019; Trejo-Téllez and Gómez-Merino, 2012). High P content in leaves of DNP + HF treatment can be associated to a lower N: P ratio and higher supply of P in hydroponic solution which can lead to toxic effects in plant tissues (Güsewell, 2004). The critical level of P concentration between sufficient and toxicity was suggested to be 8.0 g/kg (0.8 %) in plants. Phosphorus toxicity was observed in plants when tissues have their content level between the range of 9.0 to 18 g/kg (Jones Jr and Analysis, 1998). Therefore, leaf tissues of plants fertigated with DNP + HF had accumulated toxic level of P (9.5 g/kg) as it was within the range of toxicity. The excess phosphorus concentration in leaf tissues of non-heading Chinese cabbage grown with DNP + HF resulted in zinc deficiency. Phosphorus toxicity induces zinc deficiency which results in a reduction in yields of crops (Gianquinto et al., 2000). The surplus concentration of P in the root zone was reported to cause reduced plant growth and uptake of Zn (Gianquinto et al., 2000; Hochmuth et al., 2004). The waste solution of DNP + HF recorded an increase in Zn concentration which was liberated by the uptake of P as it was precipitated at alkaline pH in the fresh solution and indicated a reduced uptake of the element compared to plants treated with CHFM (Table 4.3). In addition, the availability of Zn to plants was limited in very strong acidic conditions as P content increased in waste solution resulting in precipitation of Zn (Table 4.3). Zinc deficiency is also caused by iron toxicity which occurred in plants treated with DNP + HF (Hägnesten, 2006). Zinc deficiency was found to cause stunted growth in cabbage plants due to a drastic decrease in leaf surface area and the number of leaves (Hajiboland and Amirazad, 2010). Furthermore, zinc deficiency may induce boron toxicity which often leads to a reduction in yield (Cartwright et al., 1984; Singh et al., 1990). The magnesium content in shoots and roots of non-heading Chinese cabbage treated with DNP + HF was significantly higher than of CHFM treatment. Fresh solution of DNP + HF had a higher magnesium content than in CHFM (Table 4.3). Plants require magnesium 85 content in plant tissues to range between 2.5 to 3.5 g/kg (0.25 to 0.35 %) in dry matter content (Jones Jr and Analysis, 1998; Przybysz et al., 2016). In our study magnesium content in dry matter of non-heading Chinese cabbage was beyond the optimum range needed by plants. Significantly higher dry matter content in plants grown with DNP + HF treatment resulted in magnesium toxicity effects. Magnesium toxicity has a depressive effect on the uptake of K and Ca, which were found deficient in plant tissues (Fageria, 2001). K and Ca are responsible for translocation of nutrients, activation of enzymes, and their deficiency results in reduced yields (Fageria, 2001; Hara and Sonoda, 1981). The waste solution of DNP + HF recorded an increase in Mg content (Table 4.3). Absorption of nutrients by plants in a closed hydroponic system was found to result in an increase in Ca and Mg content (Trejo-Téllez and Gómez-Merino, 2012). Iron toxicity is mostly commonly associated with highly acidic soil or hydroponic nutrient environments. This was observed in the study as the pH of DNP + HF fluctuated within highly acidic range during the second week of fertigation resulting in plant tissues accumulating toxic concentrations of iron (Table 4.7). Iron content was 0.1 mg/L in fresh solution of DNP + HF, less than the required range (0.5 – 3.0 mg/L) for growth of plants. However, when iron is in low concentration in the medium (nutrient solution) it can accumulate in high concentrations in leaf tissues (Twyman, 1951). Iron toxicity in leaf tissues was created by manganese toxicity in shoots of plants (El‐Jaoual and Cox, 1998). At low levels of iron, manganese was reported to accumulate in higher concentrations in leaf tissues (Twyman, 1951). Manganese toxicity in plants grown with DPN + HF resulted in leaf tissues having a higher copper content. However, manganese was reported to reduce copper toxicity in plants (El‐Jaoual and Cox, 1998). Toxic concentrations of copper affect a plant's capacity to absorb and translocate other nutrients (Fageria, 2001). In addition, high amounts of copper inhibit plant growth, induces chlorophyll degradation and interferes with photosystem activity resulting in depressive effects on yield (Rouphael et al., 2008; Xiong and Wang, 2005). Aluminium content in leaves and roots of plants treated with DNP + HF was significantly higher than of CHFM treatment. Aluminium toxicity causes a low rate of water and nutrient uptake, which results in shorter roots, decrease in leaf growth and biomass accumulation 86 (Amist et al., 2017; Panda et al., 2009). The aluminium content increased in the waste solution of DNP + HF as it formed precipitates with phosphorus under very acidic conditions (Penn and Camberato, 2019). Roots had significantly higher aluminium content than shoots (Table 4.5). As a result, there was reduced uptake of K and Ca into plant tissues due to aluminium toxicity in roots (Rengel, 1992). The K and Ca deficiency failed to mitigate the effects of Na damage in plant tissues as there was reduced uptake of their concentration (Kader and Lindberg, 2010; Liu and Zhu, 1998; Tester and Davenport, 2003). Roots and shoots of DNP + HF treatment had relatively higher sodium content and lower levels of K and Ca than of CHFM. Thus the concentration of Na resulted in reduced growth due to the toxicity of Na+ (Tester and Davenport, 2003). Heavy metals contents of nutrient sources were all below critical levels to induce toxicity in non-heading Chinese cabbage. Faecal coliforms were absent in harvested leaves as DNP + HF was without faecal coliforms too. However, researchers have edged consumers to properly cook or disinfect edible parts of vegetable crops raised with treated wastewater before eating (Akponikpè et al., 2011). 4.5 Conclusion and future aspects This study demonstrated that diluted NEWgenerator permeate + hydroponic fertiliser can support the growth of non-heading Chinese cabbage in a vertical hydroponic system. Plants grown with diluted NEWgenerator permeate + hydroponic fertiliser showed comparable growth (number of leaves and root length) to those of commercial hydroponic fertiliser mix. The smaller biomass produced by DNP + HF was associated to its reduced nutrient supply lower than of CHFM and very low water pH (fluctuating within 4.0 and 5.0) during the second week of fertigation which reduced the availability of some elements in solution. Further research is required whereby commercial hydroponic fertiliser mix and diluted NEWgenerator permeate have the same concentration of nutrients before fertigation and the pH of nutrient sources is maintained within the range needed by plants for absorption of nutrients. 89 Güsewell, S. (2004). N: P ratios in terrestrial plants: variation and functional significance. New phytologist 164, 243-266. Haddad, M., and Mizyed, N. (2011). Evaluation of various hydroponic techniques as decentralised wastewater treatment and reuse systems. International journal of environmental studies 68, 461-476. Hägnesten, H. (2006). Zinc deficiency and iron toxicity in rice soils of office du Niger, Mali. Hajiboland, R., and Amirazad, F. (2010). Growth, photosynthesis and antioxidant defense system in Zn-deficient red cabbage plants. Plant, Soil and Environment 56, 209-217. Hara, T., and Sonoda, Y. (1981). The role of macronutrients in cabbage-head formation: II. Contribution to cabbage-head formation of calcium, magnesium or sulfur supplied at different growth stages. Soil Science and Plant Nutrition 27, 45-54. Hochmuth, G., Maynard, D., Vavrina, C., Hanlon, E., and Simonne, E. (2004). Plant tissue analysis and interpretation for vegetable crops in Florida. Hopper, D. A., Stutte, G. W., McCormack, A., Barta, D. J., Heins, R. D., Erwin, J. E., and Tibbitts, T. W. (1997). Crop growth requirements. Plant growth chamber handbook. North Central Regional Research Publication, 217-225. Kader, M. A., and Lindberg, S. (2010). Cytosolic calcium and pH signaling in plants under salinity stress. Plant signaling & behavior 5, 233-238. Liu, J., and Zhu, J.-K. (1998). A calcium sensor homolog required for plant salt tolerance. Science 280, 1943-1945. Maboko, M. M., and Du Plooy, C. P. (2019). Yield response of hydroponically grown mustard spinach and non-heading Chinese cabbage to frequency of leaf harvest and flower removal. International journal of vegetable science 25, 185-195. Magwaza, S. T., Magwaza, L. S., Odindo, A. O., Mditshwa, A., and Buckley, C. (2020). Evaluating the feasibility of human excreta-derived material for the production of hydroponically grown tomato plants-Part II: Growth and yield. Agricultural Water Management 234, 106115. Maneejantra, N., Tsukagoshi, S., Lu, N., Supoaibulwatana, K., Takagaki, M., and Yamori, W. (2016). A quantitative analysis of nutrient requirements for hydroponics Spinach (Spinacia oleracea L.) production under artificial light in a plant factory. Journal of Fertilizers & Pesticides 7, 170-174. 90 Massoud, M. A., Tarhini, A., and Nasr, J. A. (2009). Decentralized approaches to wastewater treatment and management: applicability in developing countries. Journal of environmental management 90, 652-659. Mehta, C. M., Khunjar, W. O., Nguyen, V., Tait, S., and Batstone, D. J. (2015). Technologies to recover nutrients from waste streams: a critical review. Critical Reviews in Environmental Science and Technology 45, 385-427. Meketa, T. (2017). Invention generates power, cleans water using untapped source. Energy and Green technology. Musazura, W. (2014). Effect of ABR Effluent Irrigation on Swiss Chard (Beta Vulgaris Subsp. cicla) Growth and Nutrient Leaching, University of KwaZulu Natal, Crop Science Research Space for Master's Degrees. Panda, S. K., Baluška, F., and Matsumoto, H. (2009). Aluminum stress signaling in plants. Plant signaling & behavior 4, 592-597. Penn, C. J., and Camberato, J. J. (2019). A critical review on soil chemical processes that control how soil pH affects phosphorus availability to plants. Agriculture 9, 120. Rengel, Z. (1992). Role of calcium in aluminium toxicity. New Phytologist 121, 499-513. Rév, A., Tóth, B., Solti, Á., Sipos, G., and Fodor, F. (2017). Responses of Szarvasi-1 energy grass to sewage sludge treatments in hydroponics. Plant Physiology and Biochemistry 118, 627-633. Roma, E., Buckley, C., Jefferson, B., and Jeffrey, P. (2010). Assessing users’ experience of shared sanitation facilities: A case study of community ablution blocks in Durban, South Africa. Water SA 36, 6. Rouphael, Y., Cardarelli, M., Rea, E., and Colla, G. (2008). Grafting of cucumber as a means to minimize copper toxicity. Environmental and Experimental Botany 63, 49-58. Singh, J., Dahiya, D., and Narwal, R. (1990). Boron uptake and toxicity in wheat in relation to zinc supply. Fertilizer research 24, 105-110. Song, S., Yi, L., Zhu, Y., Liu, H., Un, G. S., and Chen, R. (2017). Effects of ammonium and nitrate ratios on plant growth, nitrate concentration and nutrient uptake in flowering Chinese cabbage. Bangladesh Journal of Botany 46, 1259-1267. Tester, M., and Davenport, R. (2003). Na+ tolerance and Na+ transport in higher plants. Annals of botany 91, 503-527. 91 Trejo-Téllez, L. I., and Gómez-Merino, F. C. (2012). Nutrient solutions for hydroponic systems. Hydroponics-a standard methodology for plant biological researches, 1-22. Xiong, Z. T., and Wang, H. (2005). Copper toxicity and bioaccumulation in Chinese cabbage (Brassica pekinensis Rupr.). Environmental Toxicology: An International Journal 20, 188-194. Yang, L., Giannis, A., Chang, V. W.-C., Liu, B., Zhang, J., and Wang, J.-Y. (2015). Application of hydroponic systems for the treatment of source-separated human urine. Ecological engineering 81, 182-191. 94 had a high microbial load compared to plants irrigated with commercial hydroponic fertiliser mix. Only leafy vegetables to be consumed after cooking such as Swiss chard can be grown with ABR effluent. Cooking was reported to destroy faecal pathogens left in leafy vegetables after disinfecting them (Hillers et al., 2003). The second research study conducted in chapter 4 which investigated the potential use of diluted NEWgenerator permeate + hydroponic fertiliser (DNP + HF) on the growth and yield of non-heading Chinese cabbage (Brassica rapa L. subsp. chinensis (Halnelt)) in a vertical hydroponic system. The results revealed that non-heading Chinese cabbage grown with CHFM and DNP + HF showed no significant difference for growth parameters (number of shoots per plant and length of roots), but significantly varied in shoot fresh mass and shoot dry mass. The smaller biomass produced by DNP + HF was associated to its reduced nutrient supply lower than of CHFM and very low water pH of nutrient source (4.0 – 5.0) during the second week of fertigation which reduced the availability of some elements in solution. The dominance of ammonium as a nitrogen source in DNP + HF resulted in an increase in acidity levels as hydrogen ions were released during nutrient uptake causing a decrease in pH of nutrient source (Table 4.4). Maboko and Du Plooy (2019) maintained the pH of CHFM within range of 5.8 to 6.1 in order to enhance good growth of non-heading Chinese cabbage in a hydroponic system. In our study non-heading Chinese cabbage grown with CHFM produced a significantly higher yield as pH value fluctuated within 5.3 – 6.3 during fertigation. On the other hand, the pH value of DNP + HF fluctuated within 4.0 – 5.0 during fertigation, which affected biomass production. Plant tissue analysis conducted in non-heading Chinese cabbage revealed that the pH value of DNP + HF had a significant impact on uptake of macronutrients and micronutrients. The reduction in yield was associated with leaf tissues having Zn deficiency, Ca deficiency, K deficiency, P toxicity, Mn toxicity, Cu toxicity and Fe toxicity when compared to shoots of CHFM treatment. On a positive note, non-heading Chinese cabbage of DNP + HF treatment was without faecal coliforms which reduced the risk of developing human infectious pathogens associated with the consumption of crops grown with nutrients derived from human-excreta. 95 5.2 CONCLUSIONS, RECOMMENDATIONS AND FUTURE RESEARCH STUDIES Commercial hydroponic fertiliser mix had a higher nutrient supply than human-excreta derived materials (ABR effluent and DNP + HF) used as treatments. Swiss chard grown with CHFM had a significant higher plant height and yield than of ABR effluent in a vertical hydroponic system. Non-heading Chinese cabbage grown with CHFM and DNP + HF showed no significant difference for growth parameters (number of shoots per plant and length of roots), but significantly varied in shoot fresh mass and shoot dry mass. This is because the uptake of macronutrients and micronutrients in non-heading Chinese cabbage significantly varied between fertigation with CHFM and DNP +HF. The pH of nutrient sources dropped during fertigation of plants which affected nutrient uptake and biomass production. There was a significant effect in biomass production with DNP + HF due to the pH value fluctuating below the range of 5.5 – 6.5 required for production of non-heading Chinese cabbage. CHFM produced a significantly higher biomass as the pH value fluctuated within the range normally needed by non-heading Chinese cabbage for absorption of nutrients in adequate amounts. ABR effluent and DNP + HF showed their potential to support the growth of Swiss chard and non-heading Chinese cabbage respectively, although there was significant decline in final yield. It was observed that their limitations in biomass production were mainly associated with their chemical composition (high sodium content, very low dissolved oxygen content and high ammonium content) which required plants to be adapted to their nutrient conditions before transplanting. In addition, ABR effluent and DNP + HF required different nutrient management practices from the one normally used when feeding plants with a commercial hydroponic fertiliser mix as nutrient source. When using ABR effluent as a nutrient source it is advisable to replenish it weekly instead of every fortnight in order to maintain adequate supply of nutrients. When using DNP + HF as a nutrient source, it advisable to daily monitor and maintain the pH value to be within the range need by selected crop. Tap water must be considered to maintain the pH of human-excreta derived materials (ABR effluent and DNP + HF) as it would be replacing water lost in nutrient sources through evaporation and evapotranspiration. Addition of tap water to 96 maintain pH would also reduce acidity levels in nutrient sources caused by increase in hydrogen ions released by high ammonium content during nutrient uptake. Future studies must consider adapting seedlings of leafy vegetable to nutrient conditions of ABR effluent and diluted NEWgenerator permeate before transplanting into hydroponic system. Leafy vegetable weeds growing in the planted wetland of the ABR system have to be removed as they are a host and breeding site of pests. NEWgenerator permeate must be diluted to have the same concentration of nutrients to those of commercial hydroponic fertiliser mix before fertigation of plants in order to determine if the differences in nutrients played a significant role in reduction of yield in our study. 5.3 References Adrover, M., Moyà, G., and Vadell, J. (2013). Use of hydroponics culture to assess nutrient supply by treated wastewater. Journal of environmental management 127, 162-165. Foxon, K., Pillay, S., Lalbahadur, T., Rodda, N., Holder, F., and Buckley, C. (2004). The anaerobic baffled reactor (ABR): an appropriate technology for on-site sanitation. Water SA 30, 44-50. Hillers, V. N., Medeiros, L., Kendall, P., Chen, G., and DiMASCOLA, S. (2003). Consumer food-handling behaviors associated with prevention of 13 foodborne illnesses. Journal of Food Protection 66, 1893-1899. Hopper, D. A., Stutte, G. W., McCormack, A., Barta, D. J., Heins, R. D., Erwin, J. E., and Tibbitts, T. W. (1997). Crop growth requirements. Plant growth chamber handbook. North Central Regional Research Publication, 217-225. Maboko, M. M., and Du Plooy, C. P. (2019). Yield response of hydroponically grown mustard spinach and non-heading Chinese cabbage to frequency of leaf harvest and flower removal. International journal of vegetable science 25, 185-195. Magwaza, S. T., Magwaza, L. S., Odindo, A. O., Mditshwa, A., and Buckley, C. (2020). Evaluating the feasibility of human excreta-derived material for the production of hydroponically grown tomato plants-Part II: Growth and yield. Agricultural Water Management 234, 106115. Musazura, W. (2014). Effect of ABR Effluent Irrigation on Swiss Chard (Beta Vulgaris Subsp. cicla) Growth and Nutrient Leaching, Citeseer.