WASTEWATER TREATMENT PROCESS DESIGN CALCULATOR | NO 1

Biological process design (Biokinetics approach) for
Modified activated sludge process – Extended aeration for BOD removal only

Objectives:

  • Calculate size of aeration tank

  • Calculate sludge production

  • Calculate F/M ratio

  • Calculate aeration blower size

 

Theoretical basis:

 

Design Philosophy

The design is based on the substrate utilization rate following microbial kinetics (Michaelis – Menten Enzyme Substrate reaction). The approach used in the design was as follows:

 

  • Selection of target SRT
  • Solving the solids generation based on the above SRT, minimum wastewater temperature & at a fixed MLSS concentration
  • The volume of the aeration reactor is calculated after estimation of solids generation at a fixed MLSS
  • After the volume of aeration reactor is determined, Oxygen requirement is calculated based on the standard equation considering the tender specifications
  • For sizing denitrification reactor, and for arriving at most optimal reactor sizing equations governing denitrification kinetics are used
  • After sixing the denitrification reactor the anaerobic tank is sized by choosing a fixed reactor volume from 0.5-1 hr HRT
  • Solid separation is then design based on the maximum of SOR, SOR at peak flow, SLR and SLR of peak flow and also considering all other specifications as per tender requirements

 

All design specification used were as per tender document and CPHEEO. In case, if neither CPHEEO nor tender stipulated a specification, standard texts like Metcalf & Eddy, Syed R. Qasim, WEF MOP were used as reference.

 

Design parameters

Biokinetic parameter at 20 C
Description Parameters Units COD oxidation NH4 oxidation NO2 oxidation
Maximum Specific Growth rate µ_max g bsCOD/g VSS.d 6.00 0.9 1
Half Velocity Constant K_s /K_nh4/K_no2 mg/L 8 0.5 0.2
Synthesis yield Y mg VSS/mg substrate 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

 

Temperature correction coefficients for biokinetic 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

 

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

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

INPUT

 

Parameter Value Unit Remarks
Flowrate MLD
41.67
Recirculated flow % Typical 3% | Range from 2-5% | May be higher based on wastewater
Recirculated flowrate 1.25 cum/s
Average flowrate 0.01 cum/s
Enter Wastewater characteristics
Chemical Oxygen Demand, COD Typically in sewage 250-450 mg/l
Effluent COD desired 100
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 Kjheldhal 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
Temperature (Min) deg C As per site condition extreme
Temperature (Max) deg C As per site condition extreme
Aeration tank water depth m
Treated Sewage Quality Summary
Biochemical Oxygen Demand, BOD
Chemical Oxygen Demand, COD mg/l
Total Suspended Solids, TSS mg/l
Total Nitorgen, TN mg/l Organic Nitrogen + Ammonical Nitrogem + Nitrates
Total Phophorous, TP mg/l
Ammonical Nitorgen, NH4-N mg/l
PART A- Tank sizing or HRT , Sludge generation & F/M ratio
Outlet BOD theoritical 0.284 mg/l Theoritical based on steady state condition and mass balance as per the SRT
µmax, 20 deg C, g/g-d
Kn, mg/L
µmax theta
Kn, theta
bn, g/g-d
bn theta
Temperature, deg C
µmax, g/g-d 1.27
Kn 0.50
bn 0.20
DO Choosing worst case scenario
Ko
Assumed effluent N, mg/L Choosing lower than required effluent limit
µ, g/g-d for CSTR 1 stage 0.44
1 stg CSTR required SRT, days 2.27 days
SRT provided 7.00 days
Initial Guess for Nox 32.00 mg/l Change value here by iteration till the calculations shows “CONVERGE” Start with intial guess of 80% of NH4-N
P_X,Bio,VSS Biomass Production
Heterotrophic Biomass Solids 88.96 kg/day First iteration
Non Biodegradable VSS in influent 13.637 kg/day
Nitrifier Biomass solids 2.02 kg/day
Nox (Based on P_x, Bio) 17.4500 (If negative then add the same amount in positive +10 mg/l in TKN input)
P_X,Bio,VSS Second iteration
Heterotrophic Biomass Solids 88.96 kg/day
Non Biodegradable VSS in influent 13.637 kg/day
Nitrifier Biomass solids 1.10 kg/day
Nox (Based on P_x, Bio) 17.5600 mg/l
P_X,Bio,VSS Third iteration
Heterotrophic Biomass Solids 88.96 kg/day
Non Biodegradable VSS in influent 13.64 kg/day
Nitrifier Biomass solids 1.11 kg/day
Nox (Based on P_x, Bio) 17.5600 mg/l
CONVERGED
Solids generation biological, P_X,Bio,VSS 104.6 kg/day
Solids generation VSS, P_X,VSS 129.6 kg/day
Solids generation TSS,P_X,TSS 198.1 kg/day Sludge production on 100% dry basis
Net sludge geenration assuming 0.8% solids consistency 24.76 cum/day @0.8% solids w/w OR 8000 mg/l TSS in Waste acitvated sludge wasted fro clarifier bottom
Net sludge geenration assuming 30% solids consistency after dewatering 660.3 kg/day Wet sludge with 70% w/w moisture content
Mass of VSS in aeration tank 907.3 kg
Mass of TSS in aeration tank 1386.6 kg 787.991549737191
Volume of aeration tank 462 cum RESULT
Detention time (HRT) 10.8 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
Denitrification Design
Active biomass 1016.8 mg/l Ref: Metcalf & Eddy Edition-4, Chapter-7, Section-7.6, Page 592, Equation-7.42
IR ratio
Recycle ratio operating normal Normal assumed
Recycle capcity provided Times Q
Effluent Nitrates (Assumed) mg/l
IR (Iternal Recycle ratio) required -0.2
IR capacity provided Times Q Installed capacity
Nox Feed to Anoxic tank
Nitrate concentration entering via IR & R flow 10 mg/l
Total flowrate into anoxic tank 756.00 cum/d (IR + R)*Q
Nox Feed to Anoxic tank 7560 g/d
Anoxic tank volume
First iteration h
Volume of anoxic tank 107.2916667 cum
F/M_b ratio 2.29 g/g-d
rbCOD/bCOD %
Specific Denitrification Rate (SDNR) @ 20 C g/g-d Using Curve generated from ASM1 model simulations; Ref from Metcalf & Eddy Edition-4, Section-8.5, Page-754-755, Figure-8.23; Considering F/Mb ratio calculated above & rbCOD as 30% (assumed as per literature review)
SDNR temp corrections 0.3 g/g-d
SDNR temp corrections 0.3 g/g-d
SDNR IR corrections Based on Metcalf & Eddy Edition-4, Section-8.5, Page-756, Equation-8.45 & 8.46
If IR = 2 0.29 g/g-d
If IR =3-4 0.27 g/g-d
SDNR selected 0.27 g/g-d
Amount of NO3-N reduced 29555 g/d
Amount feed/Amount reduced 0.26
Excess capacity 74.4 % Lower detention time can be used
New HRT 1.86 hr Reducing the size of Anoxix tank by the excess capacity
New HRT used for re-evaluation hr SDNR will be higher for smaller HRT ; As per the tender document 1.5 hr
Volume of Anoxic tank 64.38 cum
F/M_b 1.97 g/g-d
New SDNR values based on the methodology mentioned before g/g-d
SDNR temp corrections 0.4 g/g-d
SDNR IR corrections Based on Metcalf & Eddy Edition-4, Section-8.5, Page-756, Equation-8.45 & 8.46
If IR = 2 0.39 g/g-d
If IR =3-4 0.38 g/g-d
SDNR selected 0.38 g/g-d
Amount of NO3-N reduced 24000.3 Based on new HRT
Excess capacity ratio 3.17
Excess capacity 217.46 %
OK
Effluent Nitrates (Assumed) 5 mg/l
Oxygen credit (from denitrification) 35.607 kg/d IMPORTANT NOTE: Applicable denidrification is provided in the form of anoxic tank, otherwise zero. For current use case the effluent nitrate level assumed as <5 mg/l | (For calculation of anoxic tank size refer Metclaf & Eddy)
PART B- Blower sizing
Oxygen demand 263.54 kg/day
Oxygen credit from Denitrification 30.27 kg/day 85% of the denitrification oxygen credit used
Oxygen demand 9.72 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 9.72 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 40.28 kg/hr
Trasfer efficiency 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 514.0 Ncum/hr Normalized @20 deg C
Total head loss in aeration
Total head loss in piping 100.0 mm Typical 100 mm
Total head loss in in Elbow, Valves, Tee & Meteres 50.0 mm Typical 100 mm
Total head loss in blower assembly 100.0 mm Typical 100 mm
Head loss in fine bubble diffuser 200.0 mm Typical 200 mm
Submergence head 3800.0 mm 200 mm diffuser height
Head loss due to clogging 212.5 mm 5 % of a+b+c+d
Total head loss across the pneumatic system 4462.5 mm Desired blower pressure head required
Provide 4.5 mm WC
SELECT BLOWER WITH
Air Flowrate required 514.0 Ncum/hr Discharge side capacity @ NTP
Head 4.47 m Submergence + Head loss in air piping
Inlet temp 318.15 K Maximum assumed 45 C (for peak estimate)
Air flow @ Max Inlet temprature 424.41 cum/hr @ Max air temperature i.e. 45 C
Air flow @ 35 Inlet temprature 411.53 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 0.13 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 atm
Absolute outlet pressure 1.43 atm
n
Molecular weight of dry air
Efficiency
Power requirement 6.7 kW
Power requirement 9.0 hp
Motor required as per Mfg. datasheet 15.0 kW Check with vendor
Summary of result
Volume of aeration tank 462 cum
Hydraulic retention time 11 hr
Sludge Generation 24.76 cum/day
F/M ratio 0.23 g BOD/g VSS * d
Hydraulic retention time 10.8 hours
Blower capacity 514.0 Ncum/hr
Blower head 0.45 kg/cm2

Download Result