Design of a Wastewater Treatment Plant

DESIGN OF SECONDARY BIOLOGICAL TREATMENT PLANT

Abstract

TO PROVIDE A DESIGN APPRAISAL FOR INCLUSION OF A SECONDARY TREATMENT PLANT THAT IS CURRENTLY EQUIPED WIH A PRIMARY TREATMENT PLANT

TABLE OF CONTENTS

1. INTRODUCTION

2.INTRODUCTION TO BIOLOGICAL NUTRIENT REMOVAL (BNR)

3. DESIGN DATA & PARAMETERS ASSUMED

3.1 DESIGN FLOW Q

3.2 PROCESSING TEMPERATURE

3.3 INFLUENT TKN

3.4 READILY BIODEGRADABLE CHEMICAL OXYGEN DEMAND

4. DESIGN PROCEDURE

5. BIOWIN MODELLING

6. CONCLUSION

7. REFFERENCES

APPENDEX

Wastewater Treatment Plant Design

1.INTRODUCTION

The Coastal Wastewater treatment plant currently has a Primary Treatment Plant only. A design appraisal has been requested for a secondary treatment plant. This report is to design a draft based on the influent characteristics of the waste water and designed for the give effluent characteristics.

The accumulation of nutrients in the waste water especially nitrogen and phosphorous leads to decrease in water quality. To control and treat the waste water various treatment methods have been tested. After careful consideration of various influent parameters like BOD, COD, Ammonia-N, TSS, Total Nitrogen and Total Phosphorous etc., the “Anerobic-anoxic-aerobic (A²O)” process was employed due to its ease of working and diverse advantages.

2.Intoduction to Biological Nutrient Removal Process (BNR)

Biological Nutrient Removal Process was developed in the 1960s, it has been used since then due to is various advantages over other Chemical Process. BNR is a modification of Activated Sludge Treatment Process that incorporates an Anoxic and/or anerobic zones to enables removal of nitrogen and phosphorous from the wastewater.

“Anerobic-anoxic-aerobic” is a type of BNR which has a 3 stage Phoredox Anerobic-Anoxic-Oxic (A²O) system. The stages in this system are Anerobic system, anoxic system, and aerobic system. Each system treats a certain type of effluent. The treatment of phosphorous takes place in the anerobic stage whereas BOD gets treated in the aerobic stage by the process of nitrification. Denitrification process removes the nitrate in the anoxic stage. (Metcalf & Eddy, 2003). Any process has certain limitation, so does A²O process. Some of the limitations of the process are, i) decrease in the reduction of the removal of the Phosphorous due to recycling of RAS along with nitrate in the anerobic stage. ii) decrease in removal of Nitrogen due to internal recycling ratio (Metcalf & Eddy, 2003). iii) reduction in activity of PAOs.

Fig shows the proposed A²O process secondary treatment plant

3. Design data and Parameters assumed.

The designing of the Secondary wastewater Treatment Plant is based on the provided design data, Kinetic data and few important assumptions made. Some of the Kinetic data is incorrect so corrections had to be made to bring them in the recommended range as given in the Metcalf & Eddy, (2003).

3.1 Design Flow Q

To obtain the daily flow rate ‘Q’ for the give proposed capacity of 210,000 Equivalent Population (EP), an average daily consumption of 340 L/ep (Riverina Water County Council, NSW) was taken for calculation along with an 80% recovery factor. A peaking factor of 1.93 was taken (Harmon Coefficient). So, the flow rate, Q= 340 x .8 x 1.93 x 210,000 = 110,241.6 m³/day.

3.2 Processing Temperature

Average processing temperature of 20⁰ was set for easy calculation therefore there was no need for corrections for Kinetic coefficients.

3.3 Influent TKN

The TKN value is taken in the form of NH4-N

3.3 Readily Biodegradable Chemical Oxygen Demand (rbCOD)

A major design parameter rbCOD was not given, therefore the value of rbCOD is assumed from Metcalf & Eddy, 2003. 15% – 25% of bCOD was taken at the end. To consider for the rbCOD consumed in anerobic stage, 25% was assigned for removal of Phosphorous removal and 10% was assigned for denitrification.

Table containing the design data and the assumed parameters

INFLUENT PARAMETERS			EFFLUENT PARAMETERS
Parameter	Unit	Value	Parameter	Unit	Value
Alkalinity	mg as CaCO₃/L	269	BOD	mg/L	21
COD	mg/L	201	TSS	mg/L	4
pH	–	7.78	Ammonia-N	mg/L	1
TSS	mg/L	98	Total N	mg/L	27
VSS	mg/L	80	Total P	mg/L	6
Ammonia-N	mg/L	34.7
Total N	mg/L	48.2
Total P	mg/L	7.63

PARAMETER	UNITS	VALUE	REMARKS
Kinetic Data
Y	g MLVSS/g BOD removed	0.60	Given data
K₁	kg BOD utilized/kg VSS.day	10	Given data
K_d	day^-1	0.1	Given data
K_s	mgBODµ/L	20	Given data
Kinetic Constant for Nitrifying Bacteria
µNmax	d-1 at 20°C	0.7	Given data
K_N	mg NH4 + as N /L	0.7	Given data
Y_N	Kg VSS/ Kg NH4+ as N nitrified	0.12	Given data
Assumptions
MLSS	mg/L	2400	Given data
Water consumption/per capita	L/ep. Day	340	(Riverina Water County Council, NSW)
Recovery factor	Percentage	80
Peaking factor (Harmon coefficient)		1.93
rbCOD/bCOD	—	0.25	(Metcalf & Eddy)
rbCOD/bCOD	—	1.6	(Metcalf & Eddy)
FS (TKN peak /TKN average)	—	1.5	(Metcalf & Eddy)
DO	mg/L	2	(Metcalf & Eddy)
BOD/COD Ratio		0.5
Average process temperature	⁰C	20
K_o	g/m3	0.5	(Metcalf & Eddy)
K_dn	g VSS/g VSS.d	0.08	(Metcalf & Eddy)
F_d	—	0.15	(Metcalf & Eddy)
Nox/TKN	—	0.78	(Metcalf & Eddy)
VSS/TSS	—	0.8	(Metcalf & Eddy)
Px,bio = Px,vss
rbCOD/NO3-N	g/g	6.6	(Metcalf & Eddy)
rbCOD/P	g/g	8	(Metcalf & Eddy)
Detention time in the anoxic tank	H	1	(Metcalf & Eddy)

4. Design Procedure

The various design data was changed to need for calculation purpose. Some of the kinetic constants were assumed. The assumed constants and other design data are mentioned in the above Table. Some of the missing data were also assumed for calculations. All these data and constants were obtained for “Metcalf & Eddy,2003”.

The design process was carried out in 3 stages. The first stage was the design for BOD and Nitrification. The second stage was for removal of Phosphorous. The third stage was designed for Denitrification process. An Activated Sludge process, single sludge bio-N removal process and an Anoxic/Aerobic process design was considered. (Metcalf & Eddy,2003).

BOD & Nitrification

The BOD and Nitrification removal process by Activated Sludge process was carried out by the following steps.

1. The DO concentration was assumed to 2 mg/L to calculate growth rate aimed at Nitrification µ_nby means of Eq.1. The nitrification factor of 1.5 was taken. Design SRT was computed using Eq.3 (Metcalf & Eddy,2003).

2. Using the Eq.4 the max Specific growth rate µ_m was calculated. Based on the Kinetic constants Y & K1, the effluent substrate (S) was calculated by means of Eq.5

3. P_x,_bio(Biomass Production) was calculated by means of Eq.9 grounded on the ideals of A, B and C using Eqs. 6, 7, 8. The NO_x was assumed to be approximately equal to 0.8 TKN (Metcalf & Eddy,2003). But the real value was calculated using the Eq. 10. The obtained value was found to be similar to that of the assumed value.

4. The mass of VSS and TSS was calculated using Eqs. 12 and 13. The concentration of VSS was taken to be same as P_x,_bioas there was no info about the _nbVSS. The concentration of TSS was calculated using Eq.11 presuming that VSS = 80% TSS (Metcalf & Eddy,2003).

5. The volume of the aeration tank was figured by Eq.14 for the given MLSS. Four number of basins were assumed with a depth of 6.5m and a width ratio of 1.5 : 1(Metcalf & Eddy,2003).

Phosphorous Removal

The removal of Phosphorous takes place in the anerobic stage in the A²O Process. The following are the procedures of the removal:

1. The determination of the _rbCOD available for the removal of Phosphorous, Eq.25 was used. The nitrate mass balance was performed at the influent using Eq.22 bearing in mind no NO3 concentration in the influent. Taking _rbCOD/nitrate = 6.6, _bCOD/BOD= 1.6 and _rbCOD/_bCOD = 0.25 equivalent _rbCOD was computed (Metcalf & Eddy,2003).

2. The P removed by Biological Phosphorous Removal was computed by Eq.26 taking 8g of _rbCOD/g Phosphorous is removed BPR (Metcalf & Eddy,2003).

3. The concentration of Phosphorous removed was calculated by Eq.29 taking that the concentration of Bio P removed and the concentration of P used for biomass growth.

Denitrification

The anoxic stage is responsible for the denitrification. A recycle stream from aerobic zone with oxygen form nitrification being removed is considered. The design process carried out is as follows;

1. The biomass concentration was calculated by Eq.32, the volume of nitrite nursed into the anoxic tank is computed by Eq.33, Eq.34 and Eq.35. The volume of anoxic zone is computed by Eq.36 for a suitable detention time.

2. The amount of nitrate reduced was calculated by Eq.38. when the nitrate fed is not equal to the nitrate reduced, detention times must be varied. Specific Denitrification Rate as a function of MLSS with observed were computed, the SDNR was got using Eq.39.

3. The oxygen credit and the net oxygen needed was calculated using Eq.40 and Eq.41. The air flow rate was computed using Eq.42 and Eq.43. The equation 43 was used to convert mass flow rate to volumetric flow rate.

4. The required alkalinity was as conc of CaCO₃ was computed by Eq.46 and Eq.47. It is an important factor as some of the reactions have the propensity to change the pH which impacts the system performance.

Design of Secondary Clarifier

Secondary clarifier was needed to settle and remove the suspended solids that include the nutrients. The design is a 3-step process, defining the return sludge recycle ratio, determine the clarifier size and loading volume of solid. The area of clarifier was determined using Eq.54 as a purpose of design flowrate and supposed hydraulic application rate. The diameter of the basin was designed based on the number clarifiers. The loading volume of solids was computed based on the Eq.58. The number of clarifiers varies based on the loading rate of solids.

5.BioWin Modeling:

BioWin is simulator used in designing of a wastewater treatment process, that bonds together the biological, chemical and the process models. BioWin is used all over the world to design, advancement and enhance wastewater treatment plants of all types. The core of BioWin is an exclusive biological model which is accompanied with other process models (e.g. water chemistry models for calculation of pH, mass transfer models for oxygen modelling and other gas-liquid interactions).

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The Biowin modeling was used to validate the theoretical values obtained. It was found that the theoretical values satisfied curtained parameters but did not satisfy other parameter. The model was edited to obtain the required effluent parameters. Parameter like Ammonia and COD obtained by the theoretical calculations were not in the required effluent range. Hence the model was reconfigured, like the theoretical volume of the aeration tank was very less and thus Ammonia couldn’t be reduced to the required effluent range. Therefore, the volume of the Aeration tank was increased by trial and error method to achieve the effluent standards.

The kinetic constants were entered. Mixers were used to mix the influent before it was inlet into the aeration tank. Splitters with a constant of 0.6 were used to recycle the RAS back to the Aeration tank from the Clarifiers. The treated biowaste was collected as sludge and was disposed. All the given Influent parameters were reduced successfully in the Biowin model.

Changes made in the design for attaining the given range was very sensitive. Change in dimensions in the Aeration tank or the clarifiers had subtle changes in the output.

6.Conclusion

To achieve the given effluent values for the influent values an Anerobic-Anoxic-Aerobic process was adopted for the design purpose. The 3-stage process consisted of BOD removal, Nitrification, Phosphorous removal & Denitrification in addition to design of clarifiers for settling and removal of biological suspended solids. Due to insufficient data given for designing several kinetic data and certain values were assumed as per requirement.(Metcalf & Eddy 2003). A few changes were made to the obtained values from the theoretical calculations to achieve the required effluent parameters.

The anticipated effluent values were achieved based on the proposed design. The Treatment plant can be implemented based on the proposed design and will have a high success rate in removal of the influent parameters.

APPENDEX-A

ASSUMPTIONS
PARAMETERS	UNIT	VALUE	REMARKS
Depth of basin	m	6.5	(Metcalf & Eddy)
Width to depth ratio		1.5 : 1	(Metcalf & Eddy)
CS,20	mg/L	9.08	(Metcalf & Eddy)
Α	—	0.65	(Metcalf & Eddy)
Β	—	0.95	(Metcalf & Eddy)
F	—	0.9	(Metcalf & Eddy)
CS,TH=CS,TH=CS,20			(Metcalf & Eddy)
Fine bubble ceramic diffusers with an aeration clean water O2 transfer efficiency	—	35%	(Metcalf & Eddy)
Required alkalinity to transform ammonium to nitrate	g CaCO3/g NH4-N	7.14
Residual alkalinity concentration to maintain pH in range 6.8-7	g/m3	80	(Metcalf & Eddy)
Influent alkalinity	g/m3 as CaCO3	140	(Metcalf & Eddy)
Return sludge mass concentration	g/m3	8
Design MLSS XTSS concentration	g/m3	3
Hydraulic application rate	m3/m2.d	22	(Metcalf & Eddy)
Number of clarifiers		3
Phosphorus content of heterotrophic	g P/g	0.015	(Metcalf & Eddy)
Alkalinity as CaCO3 produced per NO3-N Oxidized	g/g	3.57	(Metcalf & Eddy)

APPENDEX-B

SUMMARAY OF RESULTS

PARAMETERS	UNIT	VALUE	REMARKS
BOD REMOVAL AND NITRIFICATION
Average wastewater flow	m3/d	110,241.6	1ep =340 L/day
Average BOD load	kg/d	100.5
Average TKN load	kg/d	18
Aerobic SRT	d	3.198	>7, (Metcalf & Eddy)
Aeration tanks		4	4 tanks (Metcalf & Eddy)
Aeration tank volume, each	m3	4600
Aeration Tank Length	M	31	approx. 150m per tank, (Metcalf &eddy)
Aeration Tank Width	M	15	W:D ratio 1.5, (Metcalf & Eddy)
Aeration Tank Depth	m	10	Assumed
Hydraulic retention time	h	6.5
MLSS	g/m3	2400
MLVSS	g/m3	1582.642
F/M	g/g.d	0.593	0.04-1, (Metcalf & Eddy)
BOD loading	kg BOD/m3.d	0.939	0.04-1, (Metcalf & Eddy)
Observed yield	kg TSS/kg bCOD	0.810
	kg VSS/kg BOD	1.296
Oxygen required	kg/h	1393.62
Air flowrate at average wastewater flow	m3/min	396.50
RAS ratio	—	0.6
Clarifier hydraulic application rate	m3/m2.d	22	16-24, (Metcalf & Eddy Table 8.7)
Clarifiers	Nos	3
	Diameter ,m	46
Alkalinity addition as Na(HCO3)	kg/d	27410.47
BIOLOGICAL PHOSPHOROUS REMOVAL
P used for biomass growth	g/m3	1.22
P removed	mg/L	5.7387
P content of waste sludge	%	7.146
DENITRIFICATION
Effluent NO3-N	g/m3	6
Internal recycle ratio		6.266
RAS recycle ratio		0.6
Anoxic volume	m3	6429.98
Overall SDNR	g NO3-N/g MLSS.d	0.140
Detention time	h	1.2
Alkalinity required	kg/d as CaCO3	16316.08
EFFLUENT QUALITY PARAMETERS
Effluent BOD	mg/L	19.02	Target value achieved
Effluent NH4-N	mg/L	0.17	Target value achieved
Effluent N	mg/L	15.37	Target value achieved
Effluent P	mg/L	3.92	Target value achieved
Effluent TSS	mg/L	0	Target value achieved

APPENDEX – C

NOMENCLATURE

Q: influent wastewater flowrate (m³/d)	*Ko:* oxygen inhibition coefficient, g/m³	µ_m: Maximum specific growth rate (d)
*BOD:* Biological oxygen demand (mg/L)	DO: Dissolved oxygen, mg/L	*Fd:* cell debris fraction (unitless)
*TSS:* Total suspended solids (mg/L)	µ*_Nmax*: Maximum specific growth rate of nitrifying bacteria, g new cells/g cells . d	*MLSS:* mixed-liquor suspended solids, mg/L
*TKN:* influent TKN concentration (mg/L)	µ_m: Maximum specific growth rate, (d)	P_X,bio: Biomass production (kg VSS/d)
*Ne:* effluent NH4-N concentration, mg/L	*µn:* Specific growth rate for nitrification (d^-1)	P_X,VSS: Solid production as VSS (kg/d)
*Total P*: Total phosphorus (mg/L)	µ: Specific growth rate (d-1)	P_X,TSS: Solid production as TSS (kg/d)
*NH4-N:* Ammonia as Nitrogen (mg/L)	*SRT:* Solid retention time (d)	*Fraction VSS:* fraction of VSS over TSS, unitless
Y: Heterotrophic yield coefficient (kg VSS produced/Kg BOD	*FS:* Safety Factor	X_VSS * V: Mass of VSS (kg)
K1: Maximum specific substrate utilization rate (Kg BOD/Kg VSS.d)	*So:* Influent substrate concentration (mg/L)	X_TSS * V: Mass of TSS (kg)
*Kd:* Microbial decay coefficient (d-1)	S: Effluent substrate concentration (mg/L)	V: Total volume of aeration tanks (m3)
*Ks:* Saturation coefficient (mg/L)	A: heterotrophic biomass, kg/day	Ƭ: Detention time (h)
Y_N: Nitrifier yield coefficient (Kg VSS produced/Kg NH4+ – N nitrified)	B: cell debris, kg/d	*Lorg*: Volumetric BOD (kg/m3.d)
K_dn: Endogenous decay coefficient for nitrifying organisms (g VSS/g VSS∙d)	C: nitrifying bacteria biomass, kg/day	Y_obs,TSS: Observed yield base on TSS (g TSS/gBOD)
K_N: Half-velocity constant, substrate concentration at one-half the maximum specific substrate utilization rate (g/m³)	D: Nonbiodegradable VSS in influent, kg/day	Y_obs,VSS: Observed yield base on VSS (g VSS/gBOD)
*rbCOD:* Readily biodegradable chemical oxygen demand (mg/L)	*TSSo:* influent wastewater TSS concentration (mg/L)	*NOx influent*: Concentration of NH4-N in the influent flow that is nitrified (mg/L)
N: nitrogen concentration, g/m³	*VSSo:* influent wastewater VSS concentration (mg/L)	β: Salinity-surface tension correction factor (unitless)
X_b : active biomass concentration (mg/L)	*F/M*_b: BOD F/M ratio based on activated biomass concentration (gBOD/g biomass .d)	F: fouling factor (unitless)
k_d: endogenous decay coeff. (1/day)	*NOr:* nitrate removed (g/d)	C_S,T,H: Oxygen saturation concentration in clean water at temperature t and altitude h (mg/L)
NO_{x effluent}: nitrogen oxides in the effluent (mg/L)	*SDNR (MLSS):* specific denitrification rate referred based on MLSS (g NO3-N/g MLVSS. d)	C_S,20: Dissolved oxygen saturation concentration in clean water at 20C and 1 atm or 760 mmHg (mg/L)
*IR :* internal recycle ratio (unitless)	R₁: Oxygen credit (kg/h)	C_L : operating oxygen concentration
Q_anoxic : flow rate to anoxic tank (m³ /d)	R_o: Net oxygen required (kg/h)	E: diffusers oxygen transfer efficiency
*NOx feed:* NO₃– N fed to the anoxic tank (kg/d)	*AOTR:* actual oxygen transfer rate under field conditions(kg O₂/h)	*Alk* *_{produced-denitrification}*: alkalinity produced in denitrification (g/m³)
*Vnox:* volume anoxic tank (m³)	*SOTR:* Standard Oxygen Transfer Rate in Tap Water at20°C and zero dissolved oxygen (kg O₂/h)	*NOx RAS:* nitrogen oxides in the effluent in the return activated sludge (mg/L)
*SDNR:* Specific denitrification rate (g NO3-N /g MLVSS.d)	α: Oxygen transfer correction factor for waste (unitless)	D: diameter (m)
*Qr:* RAS flowrate (m3/d)	R: return activated sludge (RAS) recycle ratio (unitless)	A: total area of clarifier (m²)
*Xr:* Return sludge mass concentration (g/m3)	X: Mixed-liquor suspended solids (mg/L)

APPENDEX – D

FORMUAL USED

EQUATION

FORMULA

EQUATION

FORMULA

BOD REMOVAL AND NITRIFICATION

m = K

₁ * Y =10 *0.6 = 6 Effluent Substrate Conc (BOD Effluent)

S = \frac{K_{s} (1 + k_{d} . SRT)}{SRT (μ_{m} - k_{d}) - 1}

$S = \frac{20 (1 + 0.1 * 3.198)}{3.198 (6 - 0.1) - 1}$

S=1.47726 mg/L

Biomass Production

A (heterotopic Biomass)

$A = \frac{QY (S_{o} - S (\frac{1 kg}{10^{3} g})}{1 + (k_{d}) SRT}$

$= \frac{11024106 * 0.6 (100.5 - 1.4772}{1 + (0.1) 3.198}$

=4962.760 Kg/d

B (Cell Debris)

$B = \frac{(f_{d}) (k_{d}) QY (S_{O} - S) SRT (\frac{1 kg}{10^{3} g})}{1 + (k_{d}) SRT}$

$B = \frac{(0.15) (0.1) 110241.6 * 06 (100.15 - 1.4772) 3.198}{1 + (0.1) 198}$

=396.772 Kg/d

C (Nitrifying Bacteria Biomass)

$C = \frac{QY ({NO}_{x}) (\frac{1 kg}{10^{3} g})}{1 + (k_{dn}) SRT}$

$C = \frac{110241.6 * 0.12 (47.1994)}{1 + (0.1) 3.198}$

=477.10325 Kg/d

$P_{X, bio} = A + B + C$

$P_{X, bio} = 4962.760 + 396.772 + 477.10325$

=5836.6352 Kg VSS/d

Oxidation of Ammonia to Nitrate

${NO}_{x} = TKN - N_{e} - 0.12 ∙ P_{X, bio} / Q$

${NO}_{x} = 48.2 - 1 - 0.12 ∙ 5836.6352 / 110241.6$

=47.1994 g/m³

Concentration of VSS and TSS

$P_{X, TSS} = \frac{A}{0.85} + \frac{B}{0.85} + \frac{C}{0.85} + D + Q ∙ ({TSS}_{o} - {VSS}_{o})$

$P_{X, TSS} = \frac{4962.760}{0.85} + \frac{396.772}{0.85} + \frac{477.1832}{0.85} + 0 + 110241.6 ∙ (98 - 80 / 1000)$

=8850.97 Kg/d

Mass of VSS and TSS

$(X_{VSS}) ∙ (V) = (P_{X, VSS}) ∙ SRT$

$(X_{VSS}) ∙ (V) = (5836.6352) ∙ 3.198$

=18665.55 Kg

$(X_{TSS}) ∙ (V) = (P_{X, TSS}) ∙ SRT$

$(X_{TSS}) ∙ (V) = (8850.97) ∙ 3.198$

=28305.402 Kg

Design of Aeration Tank

$V = \frac{(X_{VSS}) ∙ (V)}{MLSS}$

$V = \frac{28305.402}{2400}$

=11793.91 m³

Assumed no of Tanks = 4

Volume of basin = V/4

=11793.91 / 4

=2948.44 m³

Assumed Depth = 6.5

Width to depth ratio = 1.5 : 1

Width = 6.5*1.5 = 9.5

=10 m

Length of the tank = Volume of tank /width * depth

=2948.44/ 10*6.5

=46 m

Detention time

$τ = \frac{V}{Q}$

$τ = \frac{29900}{110241.6}$

=6.5 h

Fraction of VSS

$Fraction VSS = \frac{(X_{VSS}) ∙ (V)}{(X_{TSS}) ∙ (V)}$

$Fraction VSS = \frac{18665.55}{28305.402}$

=0.659

MLVSS

MLVSS=Fraction VSS*MLSS

=0.659*2400

=1582.642 g/m³

Volumetric BOD

$L_{org} = \frac{Q * S_{O}}{V}$

$L_{org} = \frac{110241.6 * 100.5}{11793.91}$

=0.939 Kg/m³.d

Observed Yield based on VSS

$Y_{obs, TSS} = \frac{P_{X, TSS}}{Q ∙ (S_{O} - S)}$

$Y_{obs, TSS} = \frac{8850.97}{110241.6 ∙ (100.5 - 1.4774)}$

=0.810 gTSS/g bCOD

$Y_{obs, VSS} = Y_{obs, TSS} * \frac{VSS}{TSS}$

$Y_{obs, VSS} = 0.63 * 0.816$

=0.5142 g VSS/gBOD

Oxygen Demand

R_o=Q (So – S) – 1.42P_x,bio + 4.33 Q (NO₃)

=110241.6(100.5-1.499) – 1.42*5836.63 + 4.33*110241.6*47.1994

=1393.62 Kg/h

Mass of Alk needed as CaCO3 for nitrification

Alk used for nitrification = 7.14g CaCO3 g NH₄– N*NO_x g/m³

=7.14*47.1994

=337 g/m³ used as CaCO3

Alk to be added = Alkalinity – pH -Influent Alk + Alk used

=80 – 269 +337

=148

Alk to be added = 110241.6*148/1000

=16315.756 Kg/d as CaCO₃

Na(HCO₃) needed =Alkalinity needed as CaCO_{3 *}Equivalent amt of Na(HCO₃) / Equivalent weight of CaCO₃

=(163150456 +80)/ 50

=27410.47 Kg/d Na(HCO₃)

Phosphorous Removal

P removal design requirement

NO₃ = 27 mg/L

NO₃-N in RAS

NO₃-N in RAS = NO₃-N = Total N -NH₄-N

=27-1

=26 mg/L

Nitrate mass balance at influent in the reactor

NO₃-Nreact = NO₃ RAS * Q / Q + Q_r

=(26*110241.6*0.6) / (110241.6 + (110241.6 * 0.6))

=9.75 mg/L

rbCOD available for P removal

rbCOD equivalent = NO_{3 react} * 6.6

=9.75*6.6

=64.35 mg/L

rbCOD available for P removal

rbCOD available for P removal =rbCOD influent – rbCOD equivalent

but rbCOD influent = 0.25(1.6*BOD)

=0.25(1.6*100.5)

=36.15 mg/L

Phosphorous removed by BPR mechanism

Bio P removal = rbCOD available for P removal / (ratio of rbCOD/BOD)

=36.15 / 8

=4.518 mg/L

P used for heterotrophic biomass synthesis in addition to phosphorous storage due to BOD

P_x,bio= A + B

= 4962.760 + 477.10325

=5439.86 Kg/d

P used for biomass growth = pH content of heterotrophic biomass * P_x,bio

=0.015 * 5439.8

=1.22 mg/L

P removed = Bio p removed + P_used for biomass

=4.158 + 1.22

=5.7387 mg/L

P content of waste sludge

Total P in sludge = p removed * Q / 1000

=(5.7387 * 110241.6) / 1000

=632.54 Kg/d

P % = ( Total P in sludge/ P_x,TSS) * 100

=(632.54 * 100) / 8850.97

= 7.146 %

Denitrification

Active biomass calculation

$X_{b} = [\frac{Q ∙ SRT}{V}] [\frac{Y ∙ (S_{o} - S}{1 + (k_{d}) SRT}]$

$X_{b} = [\frac{110241.6 ∙ 3.198}{11793}] [\frac{0.6 ∙ (100.5 - 1.4997}{1 + (0.1) 3.198}]$

=1345.78 mg/L

Internal recycle ratio

$IR = \frac{{NO}_{X}}{{No}_{x} effluent} - 1 - R$

$IR = \frac{47.1994}{6} - 1 - 0.6$

=6.266

Amount of NO₃-N to the anoxic tank

Flowrate to anoxic tank = IR * Q + R * Q

=6.266*110241.6 + 110241.6 * 0.6

=756980.93 m³/d

NO_x=feed = Q_anoxic * NO_xeffluent

(756980.93 * 6) / 1000

=4541.88 Kg/d

Volume of anoxic tank

V_nox = τ * Q

=0.05 * 110241.6

=6429.98 m³

SDNR

SDNR = 0.42

Amount of NO₃-N that can be reduced

NO_r= V_nox* SDNR * MLVSS

=6429.98 * 0.42 * 1582.642

=7094.68 kg/d

Capacity ratio

Capacity ratio = NO_x/ NO_{x feed}

=7097.68 / 4541.88

=1.56

>T =1.4 therefore acceptable

Airflow rate

$SOTR = AOTR [\frac{C_{s, 20}}{α ∙ F ∙ (β ∙ C_{S, T, H} - C_{L}}]$

$SOTR = 766.66 [\frac{9.08}{0.65 ∙ 0.9 ∙ (0.95 ∙ 908 - 2}]$

=1795.8 Kg/L

$Air Flow Rate = \frac{SORT}{E * 0.27 * 60}$

$Air Flow Rate = \frac{1795.8}{0.3 * 0.27 * 60}$

=369.50 m³/min

Alk to be added = alkalinity – pH – influent Alk + Alk used – Alk produced – denitrification

=80 – 269 -337.003

=148.003 g/m³

Mass of alkalinity needed

Mass of alk needed = Alk to be added * Q /1000

=(148.003 * 110241.6) / 1000

=16316.098 Kg/d CaCO₃

Anoxic zone mixing energy

Anoxic zone mixing energy = V * Mixing energy

=6429.98 *10 / 1000

=64.29 KW

Secondary clarifier Design

Return sludge recycle ratio

RAS recycle ratio = Q_r / Q

=(110241.6 * 0.6) /110241.6

=0.6

Size of clarifier

Area = Q / hydraulic application rate

=110241.6 / 22

=5010.98 m³

Area per clarifier = Area / No of clarifier

=5010.98 / 3

=1670 m³

$D = \sqrt{\frac{4 * Area}{π}}$

$D = \sqrt{\frac{4 * 1670}{π}}$

=46.12

=46 m

$A = (\frac{π}{4}) * D^{2} * 3$

$A = (\frac{π}{4}) * 46^{2} * 3$

=4983 m³

Solid loading

$Solid Loading = \frac{(1 + R) Q (MLSS)}{A}$

$Solid Loading = \frac{(1 + 0.6) 110241.6 * 2400)}{4983 * 24}$

=3.53 kg MLSS / m²h

APPENDEX -F

BIOWIN MODEL

7.References

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