Design Calculator | No 1

ESTIMATION OF SLUDGE GENERATION–IN BIOLOGICAL TREATMENT PROCESS

(Biokinetics based design approach)

Calculate biological sludge production in activated sludge process

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 SRT based on actual physical plant characteristics and change till the aeration tank size match with the actual site condition

  • Solving the solids generation based on the above SRT, minimum wastewater temperature & at a fixed MLSS concentration

All design specification used were as per 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.

(For detailed process design calculation as the references please refer the Process Design Calculations file submitted with the bid)

Sludge generation based on bio-kinetic model

Firstly, make select SRT and make initial guess for NOx and solve the below equation:

where,

Px,bio = Rate of biomass generation (kg/day)
Q= Influent flow rate
So= Influent bCOD
S= Effluent bCOD desired
SRT= Sludge Retention Time selected
Y= Biomass Yield (Maximum Bacterial Growth Rate / Maximum Substrate Utilization Rate)
fd= fraction of biomass undergoing endogenous decay
kd= Endogenous decay coefficient
NOx= TKN oxidized

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 sales@dynamicequipments.co.in. We will try and help you with your sizing and calculation

INPUT

Parameter Value Unit Remarks
41.67 2.08
Flowrate MLD
Recirculated flow % Typical 3% | Range from 2-5% | May be higher based on wastewater
Average flowrate
0.01
cum/s
Enter Wastewater characteristics
Chemical Oxygen Demand, COD mg/l Typically in sewage 250-450 mg/l
Biochemical Oxygen Demand, BOD mg/l Typically in sewage 100-250 mg/l
Total Suspended Solids, TSS mg/l Typically in sewage 250-350 mg/l
Voltalite Suspecded Solids, VSS mg/l Typically in sewage 200-250 mg/l
gram COD per gram of VSS mg/l 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
Enter 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 3-6 meter typically
Treated Sewage Quality Summary
Biochemical Oxygen Demand, BOD mg/l
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
Design Calculations
Aeration tank size - BOD removal + Nitrification in Single Stage
Outlet BOD theoritical
0.284
mg/l Theoritical based on steady state condition and mass balance as per the SRT
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 (For simplicity non iterative approach is provided herewith, in a regular spreadsheet, it is advised to program for an iterative approach so that the solutions converge)
P_X,Bio,VSS Consists of 3 parts --- Heterotrophic biomass + Non biodegradable VSS in inlfuent + Nitrifier biomass
Heterotrophic Biomass Solids
177.98
kg/day
Non Biodegradable VSS in influent
27.284
kg/da
Nitrifier Biomass solids
2.02
kg/day
Nox (Based on P_x, Bio)
5.1300
If negative then add the same amount in positive +10 mg/l in TKN input
Solids generation biological, P_X,Bio,VSS
207.3
kg/day
Solids generation VSS, P_X,VSS
232.3
kg/day
Solids generation TSS,P_X,TSS
318.9
kg/day Sludge production on 100% dry solids basis
Net sludge geenration assuming 0.8% solids consistency
31.89
cum/day @1% 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
1062.9
kg/day Wet sludge with 70% w/w moisture content
Mass of VSS in aeration tank
1626.0
kg
Mass of TSS in aeration tank
2232.1
kg
Volume of aeration tank
744
cum
Detention time (HRT)
17.0
hours Based on Plant average flowrate + Recirculated
F/M (Food to Microorganisms ratio)
0.28
g BOD/g VSS * d 0.15-0.25 as per CPHEEO MLVSS=0.8 MLSS
Effluent Nitrates (Assumed)
5
mg/l
Oxygen credit (from denitrification)
0.3718
kg/d IMPORTANT NOTE: Applicable denitrification 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)
Summary of result
Volume of aeration tank
744
cum
Hydraulic retention time
17
hr
F/M ratio
0.28
g BOD/g VSS * d
Hydraulic retention time
17.0
hours
Sludge Generation
31.89
cum/day @ 1% solids w/w

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