1. DESIGN OF CONVENTIONAL ASP AERATION
DETAIL VALUE UNITS Formulae
Plant Design Flow 10 MLD As per Tender
Number of Tanks 1 Unit Tender Requirement
Elevation Of Site above MSL 30 m As per Tender
Operating Temperature in Deg 30 Celcius From CPHEEO Manual
Influent BOD 250 mg/l Specified - as per Tender
Effluent BOD 20 mg/l Specified - as per Tender
BOD to be removed in Aeration Tank, 'x' 230 mg/l Influent BOD-Effluent BOD
MLSS 3000 mg/l From Table 5.9,Pg.5-64 in CPHEEO manual
F/M 0.35 /day From Table 5.9,Pg.5-64 in CPHEEO manual
F (BOD load/day) 2300 kg/day F=BOD x Design Flow
M (Biomass) 6571.43 Kg From F/M Ratio
AERATION TANK
Aeration Tank Volume calculated from F/M 2190.48 m3 Volume=Q*x +(F/M * MLSS)
Mean Cell Residence Time,θc 3 days SRT as a function of aeration basin temperature for 90-95% BOD removal (From Fig
5.38,Pg.5-64 in CPHEEO Manual)
Constant Y 0.5 Maximum Yield Coefficient (As per CPHEEO Pg.5-62)
Constant Kd 0.06 Endogenous decay constant (As per CPHEEO Pg.5-62)
Aeration Tank Volume calculated from MCRT 1218.2 m3 V=Y*Q*1000*BOD/(MLSS*0.8*(1/(θc+Kd)))
HRT 5 Hrs From Table 5.9,Pg.5-64 in CPHEEO manual
Aeration Tank Volume calculated from HRT 2083.33 m3 V=Q*1000/24*θc
Providing volume of aeration tank 2190.48 m3
Actual HRT 5.257152 Hrs
Liquid Depth 5.5 m Manual Practice as per CPHEEO
Free Board 0.5 m Pg.5-67, CPHEEO Manual
Surface area of Aeration Tank 398.27 m2 Volume Obtained From HRT / Depth
Length:Width Ratio 2 : 1 Assumed as per CPHEEO Manual Page.5-67
Width 14.1 m Assumed as per CPHEEO Manual Page.5-67
Length 28.3 m L=Area/Width
BOD removed in aeration tank 2300 kg/day BOD*Q
Kg Oxygen/Kg of BOD Removed 0.9 From Table 5.9,Pg.5-64 in CPHEEO manual
Oxygen AOTR 2070 Kg/day BOD removed x (Amount of Oxygen used per Kg of BOD Removed)
Residual D.O. in Aeration Tank 2 mg/l Standard operating condition for Aeration Tanks
OXYGEN REQUIREMENT
If Surface Aerators are Used
Alpha Value,α 0.65 Pg.429, Metcalf Eddy, Wastewater Treatment & Reuse
Beta Value,β 0.95 Pg.429, Metcalf Eddy, Wastewater Treatment & Reuse
D.O at Operating Temperature 7.43 mg/l 14.42+(0.003×Operating Temperature in Deg^2)−(0.323×Operating Temperature in Deg)
D.O at Operating Elevation 7.41 mg/l 1−(Elevation Of Site above MSL÷152)×0.017)×D.O at Operating Temperature
Fouling Factor,F 0.95 Pg.429, Metcalf Eddy for Wastewater Treatment
Pressure at Elevation 30m 101.00774 KN/m2 Pb=P x exp^[-gM(Zb-Za)/RT]
757.62 mm of mercury 1KPa = 7.50062 mm of mercury
Pressure at Liquid Depth 5.5 m of Water
53.955 KPa 1 m of water= 9.81 KPa
404.7 mm of mercury 1KPa = 7.50062 mm of mercury
Dissolved Oxygen,Ot 19 % Pg.430, Metcalf Eddy for Wastewater Treatment
Oxygen Saturation Conc.,Cs,T,H 7.49 mg/l Metcalf & Eddy, Pg.1747, Table D-2
CŠ,T,H 9.13 mg/l CŠ,T,H=Cs,T,H x1/2 x [(Pd/Patm,h)+Ot/21)]
(Pd = Pressure at the Depth of Air Release = Patm,H + Peffective Aeration Depth)
CL 2 mg/l Oxygen Conc. at Operating Temperature in Tank
Cs,20 9.08 mg/l Metcalf & Eddy, Pg.1747, Table D-2
SOTR 3598.04 Kg/day SOTR=AOTR / [ βCs,T,H -CL ]((1.024)^(T−20))(α)(F)
Cs,20
Oxygen Tension 5.04 mg/l (D.O at Operating Elevation × β)−Residual D.O. in Tank
Oxygen Gradient 0.55 mg/l Oxygen Tension/9.17
Temperature Difference 10 Celcius Operating Temp.-20
Temperature Coefficient 1.03 Fixed Value
Temperature Correction Factor 1.34 Temp. coefficient ^Temp. Difference
Conversion Factor to standard conditions 0.47905 Correction Factor x α x O2 gradient
Oxygen needed under standard conditions 4321.05 kg/day AOTR/Conversion Factor
Factor of Safety 1.1 Fixed Value
Oxygen Needed after Factor of Safety 4753.155 kg/day Oxygen under standard conditions x Factor of safety
Oxygen Transfer Capacity of Aerator 1.8 Kg/day 1.2 to 2.4 in clause 5.8.1.7.5.3,CPHEEO Manual
Kw of Aerator needed 110.03 Kw Oxygen Needed after Factor of Safety/24/1.8
1

2. If Diffused Aeration is Used
Factor for Temperature power 3 0.027 Temp.^3/ 10^6
Factor for Temperature power 2 0.0013 Temp.^2/10^5/7.4
Factor for Temperature power 1 0.09 0.003*Temp.
Density of air at operating temperature 1.2207 Kg/m3 1.285+Factor for Temp. power 3-Factor for Temp. power 2-Factor for Temp. power 1
Content of Oxygen in Air 0.23 Fixed Value
Oxygen needed for residual DO 12 Kg/day Q/Residual D.O.
Oxygen needed per day 2082 Kg/day AOTR + Oxygen needed for Residual DO
Air needed 7415.56 m3/day Oxygen needed per day÷Density of air at operating temperature÷Content of Oxygen in
Air
Transfer Efficiency of diffuser system 0.05 /m Fixed Value
Transfer Efficiency at design depth 0.275 Liquid Depth x Transfer Efficiency
Diffuser Fouling Factor per Year 0.04 /year Source CPHEEO Manual,Appendix
Diffuser life cycle 3 years Source CPHEEO Manual,Appendix
Diffuser Fouling Factor for its life cycle 1.12 (1+Diffuser Fouling Factor per Year)^Diffuser life cycle
Provide factor of safety 1.1 Fixed Value
Air needed for oxygenation 33221.71 m3/day Air needed×Diffuser Fouling Factor for its life cycle×Factor of safety÷Transfer Efficiency
at design depth
Air needed for oxygenation 1384.24 m3/hr Air needed for Oxygenation / 24
Air Mixing criteria 16 m3/min/1000m3
of tank
As in clause 5.8.1.7.5.6 ,CPHEEO Manual
Air needed to be mixed as per manual 2000 m3/hr Aeration Tank Volume calculated from HRT×Air Mixing Criteria×60÷1000
Air needed to be mixed as per manual 2.7 m3/hr 1.8 to 2.7 as per US EPA, 625/8-85/0100, p 38
Surface area of Aeration Tank 378.79 sqm Aeration Tank Volume calculated from HRT÷Liquid Depth
Maximum air needed for mixing 2000 m3/hr Taking Maximum of the Two derived value
Air needed as higher of oxygenation and Mixing 2000 m3/hr Taking Maximum of the Two derived value
Air needed as under standard conditions 4174.93 m3/hr Air needed for Mixing / Conversion Factor
Friction and other losses 0.2 From Experience
Liquid depth as water column for air pressure 6.6 Depth + (1/Losses)
Kw of needed compressor at 1400rpm 105.37 KW 0.746×((0.03×Air needed as under standard conditions)+16)
Sludge Flows
Yobs=Y/(1+Kd*θC) 0.42 Yobs=Y/(1+Kd*θC)
Excess Sludge mass wasted Kg/day 966 kg/day Yobs x BOD x Q
Kgd of excess sludge/Kg of BOD removed 4321.05 AOTR / Conversion Factor
Conc. factor for MLSS in return/excess sludge 3.3 From Experience
Return/Excess sludge MLSS concentration 9900 mg/l MLSS x Conc. Factor
Cells in aeration 6249.99 Kg MLSS x Volume from HRT/ 1000
Cells wasting from system 4321.05 Kg/day AOTR / Conversion Factor
Volume of excess sludge 436.47 m3/day Cells wasting from system×1000000÷Return/Excess sludge MLSS concentration÷1000
Resulting theta C 1.45 days Cells in Aeration / Cells Wasted
Least Theta C in design 1.45 days Cells in Aeration / Cells Wasted
Volume of excess sludge for least Theta C 436.47 m3/day Volume of excess sludge×Resulting theta C÷Least Theta C in design
Excess sludge pump set duty 436.47 m3/day Maximum of arrived Sludge Values
Recirculation ratio 0.5 0.25 to 0.8 as per Table 5.8
Return sludge pump set duty as MLD 5 MLD Q x Recirculation Ratio
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