WASTEWATER TREATMENT PROCESS DESIGN CALCULATOR | NO 2

Activated sludge process – Blower sizing

(Blower sizing for BOD removal only excluding nitrification demand)

Objectives:

  • Calculate size of blower for aeration – BOD removal and nitrification

  • Calculate blower discharge head required

  • Convert blower size to field condition suction side conditions

 

Theoretical basis:

 

Design Philosophy (Courtesy: reprint from CPHEEO manual on wastewater engineering 2013)

 

Oxygen required in the activated sludge process for the oxidation of as part of the influent organix matter and for the endogenous respiration of the micro organism in the system. The total oxygen requirement of the process may be formulated as follows



where,

 

f : Ratio of BOD to ultimate BOD

1.42 : Oxygen demand of biomass, g/g

X : Biological sludge produced per day.

X = Q × Yobs × (So-S)

Yobs = Y/(1+Kdx0c)

Where Y is 0.5 and Kd is 0.06

 

The formula does not allow for nitrification but allows only for carbonaceous BOQ removal. The extra theoretical oxygen requirement for nitrification is 4.56 kg Oxygen per kg Ammonical Nitrogen. The Ammonical nitrogen oxidized to nitrate. The recommended dissolved oxygen concentration in aeration tank is in the range of 2mg/l, below that there is inhibition in biological activity, moreover in case of MBBR systems, the bulk dissolved oxygen requirement to provide for ideal flux in the biofilm might even go upto 3-4 mg/l if <1 mg/l ammonical nitrogen is required in the effluent

 

Calculator

 

(Note – all Yellow are user defined value, all white are fixed values, all green are calculated value, all orange is calculated not to be shown)

Instructions

Enter values highlighted in the Yellow

Green highlights are the results

In case of any invalid result of non-functioning of the calculator, please write to us at urvpatel@swaenviro.com. We will try and help you with your sizing and calculation

 

INPUT

Parameter Value Unit Remarks
Flowrate MLD
42.92 cum/hr
Enter Wastewater characteristics
Chemical Oxygen Demand, COD mg/l Typically in sewage 250-450 mg/l
Effluent COD desired  
Biochemical Oxygen Demand, BOD   Typically in sewage 100-250 mg/l
Total Suspended Solids, TSS Typically in sewage 250-350 mg/l
Voltalite Suspecded Solids, VSS   Typically in sewage 200-250 mg/l
gram COD per gram of VSS Typically in sewage 0.125
nbVSS mg/l Typically in sewage 10% of VSS
Total Kjehaldhal Nitrogen, TKN mg/l Typically in sewage 40-50 mg/l ; (Note for special case like TKN > 100 mg/l, contact our design engineering team for more accurate process deisgn)
Ammonical Nitorgen, NH4-N mg/l Typically in sewage 40-50 mg/l (Note for special case like NH4-N > 100 mg/l, contact our design engineering team for more accurate process deisgn)
Total Phosphorous, TP mg/l Typically in sewage 7.1 mg/l
Design parameter
Select SRT days Changed based on the nutrient removal req; For BOD removal use 3-5 days & For BOD + Nitrification use 8-10 days
Select X,TSS mg/l Change based on process ASP, Extended aeration, MBBR
Depth of aeration tank m As per design
Temperature (Min) deg C As per site condition extreme
Temperature (Max) deg C As per site condition extreme
Treated Sewage Quality Summary
Biochemical Oxygen Demand, BOD mg/l  
Chemical Oxygen Demand, COD  
Total Suspended Solids, TSS  
Total Nitorgen, TN   Organic Nitrogen + Ammonical Nitrogem + Nitrates
Total Phophorous, TP    
Ammonical Nitorgen, NH4-N    
Aeration tank size – BOD removal only
P_X,Bio,VSS     Biomass Production
Heterotrophic Biomass Solids 91.69 kg/day  
Non Biodegradable VSS in influent 14.056 kg/day  
Solids generation biological, P_X,Bio,VSS 105.7 kg/day  
Solids generation VSS, P_X,VSS 131.5 kg/day  
Solids generation TSS,P_X,TSS 201.7 kg/day Sludge production on 100% dry basis
Net sludge generation assuming 1% solids consistency 20.17 cum/day @1% solids w/w
Net sludge generation assuming 30% solids consistency after dewatering 672.2 kg/day  
Mass of VSS in aeration tank 920.5 kg  
Mass of TSS in aeration tank 1411.5 kg  
Volume of aeration tank 471 cum  
Detention time (HRT) 11.0 hours Based on Plant average flowrate + Recirculated
F/M (Food to Microorganisms ratio) 0.23 g BOD/g VSS * d 0.15-0.25 as per CPHEEO MLVSS=0.8 MLSS
Side water depth of aeration basin m
Aeration requirement
Oxygen demand 274.30 kg/day  
Oxygen credit from Denitrification kg/day Only applicable if denitrifiction is provided in form of anoxic tank (For calculation of anoxic tank size refer Metclaf & Eddy)
Oxygen demand 6.72 kg/hr Considering denitrification
Calculating SOTR     Standard Oxygen Trasnfer Rate
Temperature of wastewater deg-C Based on Maximum wastewater temperate in the influent parameter section
Actual Oxygen Trasfer Rate required, AOTR 6.72 kg/hr  
C, 20 deg cel mg/l From saturation table
C, t deg cel mg/l From saturation table and maximum temp of wastewater and salinity
C, tank 2 mg/l Required minimum 2 mg/l
Alpha   Typical value : 0.65
Beta   Typical value : 0.95
F   Typical value : 0.9
Mid depth correction factor   0.25-0.4
Depth of diffusers 4.3    
Temp correction 0.70    
Elevation of site m As per site elevation from sea level
Std barometric pressure 0.989    
Saturated DO due to pressure from water column 10.60    
Standard Oxygen Trasnfer Efficiency 27.86 kg/hr  
Trasfer efficiency 0.32 fraction 7.5% per meter of water depth as per vendor
Weight of Oxygen per cum of air kg O2/cum-air  
Efficiency    
Normal Temperature 20    
Temperature of Air 45    
Air Flowrate required in terms of NTP 355.5 Ncum/hr Normalized @20 deg C
Total head loss in aeration
Total head loss in piping mm Typical 100 mm
Total head loss in in Elbow, Valves, Tee & Meteres mm Typical 100 mm
Total head loss in blower assembly 100.0 mm Typical 100 mm
Head loss in fine bubble diffuser mm Typical 200 mm
Submergence head 3800.0 mm 200 mm diffuser height
Head loss due to clogging 215.0 mm 5 % of a+b+c+d
Total head loss across the pneumatic system 4515.0 mm Desired blower pressure head required
Provide 4515.0 mm WC  
SELECT BLOWER WITH
Air Flowrate required 355.5 Ncum/hr Discharge side capacity @ NTP
Head 4.52 m Submergence + Head loss in air piping
Inlet temp 318.15 K Maximum assumed 45 C (for peak estimate)
Air flow @ Max Inlet temprature 265.64 cum/hr @ Max air temperature i.e. 45 C
Air flow @ 35 Inlet temprature 257.58 cum/hr @ Max air temperature i.e. 35 C
Density of air at 45 C 1.09 kg/cum @ 45 C temp & 30 % Humidity
Weight of air flowrate 0.08 kg/s @ Max air temperature i.e. 49 C
Universal gas constant 8.31 J/mole.K
Inlet temperature 318.15 K 45 dec C
Aboslute inlet pressure 0.98 atm
Absolute outlet pressure 1.43 atm
n 0.283
Molecular weight of dry air 28.97
Efficiency 0.70
Power requirement 4.2 kW
Power requirement 5.6 hp
Motor required as per Mfg. datasheet 15.0 kW Check with vendor
Summary of result
Volume of aeration tank 351 cum  
Sludge Generation 21.08 cum/day  
F/M ratio 0.30 g BOD/g VSS * d  
Hydraulic retention time 8.4 hours  
Blower capacity 355.5 Ncum/hr  
Blower head 0.45 kg/cm2  

TABLE-1 AERATION TANK DESIGN DATA (BIOKINETIC COEFFICIENT)

Reference: CPHEEO & Metcalf & Eddy Edition-4, Section 8-3, Table-8.11, Page-705

Biokinetic parameter at 20 C

Description

Parameters

Units

COD oxidation

NH4 oxidation

NO2 oxidation

Maxiumum Specific Growth rate

µ_max

g bsCOD/g VSS.d

6.00

0.9

1

µ_max = k * Y

Half Velocity Constant

K_s /K_nh4 /K_no2

mg/L

8

0.5

0.2

Synthesis yield

Y

mg VSS/mg sustrate

0.45

0.15

0.05

Specific Endogenous Decay Rate

b

g VSS/g VSS.d

0.12

0.17

0.17

Fraction of Biomass that remain as cell debris

f_d

unitless

0.15

0.15

0.15

Half Velocity Constant for Oxygen

K_o2

mg/L

0.2

0.5

0.9

Temperature correction coeffcients for biokinetci parameters

Theta value

Units

COD oxidation

NH4 oxidation

NO2 oxidation

µ_max

unitless

1.07

1.072

1.063

b

unitless

1.04

1.029

1.029

K_s /K_nh4 /K_no2

unitless

1

1

1

Temperature dependability of biokinetics coefficient

Temperature

25

deg C

Biokinetic parameter at T deg C

Description

Parameters

Units

COD oxidation

NH4 oxidation

NO2 oxidation

8.42

1.274

1.36

8

0.5

0.2

0.45

0.15

0.05

0.146

0.196

0.196

0.15

0.15

0.15

0.2

0.5

0.9

6

30

15

0.6

0.45

0.1

4

3

2

1

0.8

0.5

Maxiumum Specific Growth rate

µ_max

g bsCOD/g VSS.d

6.87

1.034

1.13

Half Velocity Constant

K_s /K_nh4 /K_no2

mg/L

8

0.5

0.2

Synthesis yield

Y

mg VSS/mg sustrate

0.45

0.15

0.05

Specific Endogenous Decay Rate

b

g VSS/g VSS.d

0.130

0.180

0.180

Fraction of Biomass that remain as cell debris

f_d

unitless

0.15

0.15

0.15

Half Velocity Constant for Oxygen

K_o2

mg/L

0.2

0.5

0.9

Biokinetic parameter at 20 C (Range of values)

Description

Parameters

Units

Range

Typical

maximum specific sustrate utilization rate

k

g bsCOD/g VSS.d

4-12

6

half velocity constant

Ks

mg/L BOD

20-60

30

mg/L bsCOD

5-30

15

sysntesis yield coeficient

Y

mg VSS/mg BOD

0.4-0.8

0.6

mg VSS/mg COD

0.4-0.6

0.45

decay coeficient

b

g VSS/g VSS.d

0.06-0.15

0.1

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