Aerated Stabilization Basins (ASBs) Design and Operation, Study notes of Chemistry

Download Aerated Stabilization Basins (ASBs) Design and Operation and more Study notes Chemistry in PDF only on Docsity! 1 Aerated Stabilization Basin (ASB) Design 2 Be able to work through Examples 8-14 & 8-15 5 ASB “Field Trip” Courtesy of Google Earth 6 Escanaba, MI ASB Palatka, FL ASB [eet mersSesy Ae) lon tts Eel a PL ai cey er varcarlley ter) 2006 Navieq Cemex GSS Mu MINT MDM koe oer) 10 ASB Design/Operating Considerations – Influent BOD & TSS loads, temperature, flow – Required effluent BOD, TSS concentrations/loads – Nutrient requirements for bacterial growth – Available land area, configuration, lagoon depth – Flow/mixing: complete, plug, “dead” (unmixed) zones, flow curtains – Ambient temperature, seasonal temperature changes – Oxygen requirements/equipment/power requirements – Mixing requirements/equipment/power requirements – Solids handling – Odors, algae growth, foam 11 Types of Treatment Lagoons • Of primary interest: Aerobic flow-through partially mixed lagoons (ASBs) • Others mentioned in M&E – Facultative partially mixed lagoon (no mechanical aeration) – Aerobic lagoon with solids recycle (really a type of activated sludge treatment) 12 ASB Design Equations Reflect The Same Basic Concerns As The Equations For Activated Sludge • Soluble substrate concentration, S • Biomass concentration, X • Microorganism growth rate, Px • Oxygen requirement, RO2V ASB Process Analysis, cont’d (Leow previous slide :) ey = QS. -@S + Vln) =O (aby stele) Fst Order Removal => lsu = Stee “kS feenshire to M-M) “ ee k= fist order rat const -y, QS. -QS- VkS=O sinilac 4 Bop el vt ~ Con observ: mn en eT SH ELS =O Jeb, but mast be S65 St TkS puasured under cerefia condutions 22 = (+ tk expected in the Field, Ss. le co COU ETA l Nole: ALL scbstrab ubihgitcon expressions ore of Hy form 2: TEE So Where E = sort ex presslom olited to the oubsteode 15 LC Moo eK PLESS (OA = ~fsu/S 16 Lagoons in Series • Why? Flow is closer to “plug flow” regime, reduced tendency for short-circuiting, heat conservation. • The first order approximation simplifies multi-lagoon designs… …as long as the formula is right… ASBs in Series Q,5..Xe, TX,,5, [AS X CYS, - T, My, Ss [253% d ) 2 “ fast ordec lanutics simplifies molti- basin dos con : = Se te) «(sat)+ (3) a ~ 12 order ASB = 7 + th)” Ln Series whose T= HRT of one of n denticnd vopamdronds >F ASsus k TEMAS Comstint 17 —tempecatuce effects 7? 20 BOD Removal ( )728. 1 1 00 − + == Eq kC C S S τ So= Co = influent BOD conc., g/m3 S = C = effluent BOD conc. from lagoon n, g/m3 k = 1st order BOD removal rate constant, d-1 tau = SRT = HRT = V/Q, d …the first-order BOD removal alternative approach: This equation is for an ideal, single aerated lagoon. Could use the activated sludge design equations, including Michaelis-Menton for substrate utilization, but we will consider… M&E gives k values in the range of 0.5-1.5 d-1 for total BOD removal (rates for soluble BOD removal would be higher). Determine k for a given wastewater using pilot study: 21 Published Equations Can Be Wrong ( ) ( )aEq C n 1074. ]/nQkV [1 C total 0 n − + = ( ) ( )bEq C n 1074. ]k/n [1 C 0n − + = τ Co = influent BOD conc., g/m3 Cn = effluent BOD conc. from lagoon n, g/m3 k = 1st order BOD removal rate constant, d-1 BOD Removal tau = SRT = HRT = Vtotal/Q, d n = number of equally sized lagoons 22 Published Equations Can Be Wrong, cont’d ( ) ( )aEq C n 1074. ]kV/nQ [1 C 0n −+ = ( ) ( )bEq C n 1074. ]/nk [1 C 0n − + = τ 25 Basin Temperature ( )748. Q A T iaw − + + = Eq f QTAfT We’ve seen ASBs in a number of climates, Maine, Washington, Florida… Temperature effects biological reaction rates, and ice can form on the surface. Ti = influent waste temp, oC Tw = lagoon (& outlet) temp oC Ta = ambient air temp oC f = proportionality factor (aeration, wind, humidity), 0.5 for eastern U.S. A = surface area, m2 Q = flow rate, m3/d k2/k1 = θ(T2-T1) k2 = k1 θ(T2-T1) Adjusting reaction rates for temperature: Foaming effect: 26 Solids Produced From Conversion of Soluble Organic Waste ( )ifiedmod437. k 1 )( X d 0 − + − = Eq SSY τ ( ) ( )1 o d Y S SSRT X k SRTτ  − =    +    Equation 7-43 Modify this equation for a flow through, completely mixed system, no solids recycle system… X = susp. solids from growth, g/m3; Y = biomass yield coef, g cells/g substrate; kd = endogenous decay rate, d-1; tau = V/Q Solids Concentration: 27 Solids Produced…cont’d ( ) ( )SRTk1 SSQY P d o X + − = Eq. 7-52a ( )ifiedmod437. k 1 )( X d 0 − + − = Eq SSY τ Therefore, Px = QX (from previous slide) Solids mass generated per day: Algebra Applied to Eq. 5-55... 5-69 aoe soTR (Poe) (rou) AF Cs,20 o ce « dor surface aeraten>, F= ( (10 defer foslins), C aT,H* = Cory wher’) = = clan ole Oz eabrcadionn ak WC and = Chan iter Oz “ee got acatiion | (te feng T+ aktetale t Carron ge equot ic : C. 20-T SoTR = nome (C22 9,2 Pe) 1,02 ) P Cor 7 Ce rail 4 gastiwelir chance istics Now con odvst Hr actual Or coq ui tements docs: ter . » 31 Mixing Requirement – What About Keeping Solids In Suspension? Factors to Consider: -Type and design of aeration system -Concentration and nature of suspended solids -Lagoon temperature -Lagoon size, geometry (aspect ratio) -Curtain placement -Portion of lagoon set aside for solids settling M&E give a “threshold” value of 1.5 to 1.75 kW/1000 m3 (7.5 to 8.75 hp/Mgal). -More is required to keep all solids in suspension. -NCASI study indicated 14-15 hp/Mgal. -Old Crown Zellerbach recommendation (given in M&E): spacing of surface aerators should not exceed 75 m. 32 Solids Separation • Considerations for Settling Basin Design – Adequate detention time for solids settling • M&E: HRT => 1 day • Need to accommodate volume loss from accumulated solids – Volume needed to store accumulated sludge – Algae growth (M&E says keep HRT< 2 days, or filter/strainer to remove. None of these are practical in many circumstances.) – Odors, typically H2S (M&E says use water depths of 1-2 m to control. This may be partially effective.) – Need for lining (groundwater protection)