Evaluation of Blower and Diffuser Requirement in the Aeration System

Evaluation of Blower and Diffuser Requirement in the Aeration System

Sanjay Kumar

Department of Mechanical Engineering IEC College of Engineering & technology Greater Noida, India

Ijlal Ahmad Rizvi

Assistant Professor, Department of Mechanical Engineering IEC College of Engineering & technology

Greater Noida, India

Abstract: – Most of energy that is used for running the waste water treatment goes to biological treatment unit. 70-75 percent of energy used by the waste water treatment plant is spend to run the blower to deliver the air for aeration of waste water. The energy needed by the blower depends upon the efficiency of the aeration system. The more will be the efficiency of the aeration system, lessor energy will be required by the aeration system. So it is very crucial to design the whole aeration system i.e. from blower to diffuser including piping. This research paper focuses on the need of blower and the number of diffuser required because these two are the most important part of the aeration system.

Keywords: Waste water treatment plant, Aeration system, Blower size calculations, Number of diffuser, AOTE, Oxygen requirement, SOTE, TDS Activated sludge.

INTRODUCTION

Waste water generated by the people living in metropolitan cities as well as in small cities has been a major problem and increasing industrialization aggravates this problem. So it is very necessary to handle this waste water very delicately to make our earth green and clean.

Now a days to eradicate waste water problem the developed nations are using and developing are going forward to use the waste water treatment plants. Commissioning cost of the plant is not a problem but the running cost of the plant is great cause of concern for the industries as well as for the government also.

So for a researcher is worth focusing on minimize the cost of running of the plant. Mostly the cost of running spend in the aeration system for biological treatment of the waste water. The location of the plant plays a significant role in minimizing the cost of operation of the aeration system. So we can say that the designing of aeration system is very important [4].

It is very necessary to be familiar about the few terms to understand about the most important terms:

SOLIDS IN WATER

Solids in the water are of the two types which can be classified according to their size and shape, chemical properties and size distribution. Theses solids can also be classified as organic, inorganic and immiscible liquids. The biological degradation of solids results in objectionable by products. So solids removal from water is of great importance.

TURBIDITY

The turbidity of water is the measure of ability of light passing through it. Its ability measured against a turbidity index. The water having turbidity index five allows no passage of light, while index one shows little or no turbidity.

COLOR

The pure water is colorless but foreign substances can often tint water. These foreign substances are vegetation, soils, municipal and industrial waste and aquatic organisms. Water color is measured by standard color solution or colored glass disc.

TASTE AND ODOR

Minerals, metals, salt from soil and end products of biological reaction decides the taste and odor of water. The taste and odor has little impact on safety. Potassium permanganate, chlorine and other oxidants are used to remove taste and odor by oxidation

TEMPERATURE

The temperature of water is very important for aquatic life because temperature of water affects the solubility of oxygen in the water. The temperature of waste water is also very significant for industrial purposes because the cold water needs more chemicals for efficient coagulation and flocculation.

TOTAL DISSOLVED SOLIDS

Dissolve solids can be present in the form of organic, inorganic matter in water. The dissolve solids occurs in water by the contact with substances in soil, on surfaces and in the atmosphere. Decayed vegetation, organic chemicals and gases are the major sources of organic dissolve solids. These sources causes the physiological effects and color, taste and odor problems. The dissolve solids can be separated from water by filtration, evaporation, electro dialysis, reverse osmosis and ion exchange.

ALKALINITY

Alkalinity is the measure of waters ability that how much it can neutralize the acids. In other words we can say that it is the buffering capacity of water. Bicarbonate, carbonate and hydroxyl ions are responsible for the alkalinity of the water. Carbon dioxide from the different sources is also responsible for alkalinity of the water. High alkaline water can be bitter in taste but has no serious effect on human health.

HARDNESS

Minerals of calcium and magnesium present in the water are responsible for hardness, so hardness indicates the concentration of these minerals in water. Deposits is the major problem in hot water due to these minerals in pipeline. Hard water also have many advantages i.e. it helps tooth and bone growth.

FLUORIDES

Little fluoride ions in potable water is good for dental health. Fluoride ions in large quantity can be toxic for human. The surface water has fluoride ions in appreciable quantity.

METAL

Metals in water may harm the human health even in little quantity. It can be divided into two categories i.e. toxic and non-toxic. These metals be present in natural water due to dissolution from natural deposits and discharges of industrial wastes.

ORGANICS

Color, taste and odor is affected by the organic matter present in water. Halogenated compound be formed in the water undergoing chlorine disinfection due to the presence of organic matter. Organic matter present in water affects the solubility of oxygen that interferes the water treatment process. Presence of organic matter is the most important cause of the BOD increase.

PH

PH is the measure of hydrogen ion concentration in water. In other words it can be said that it is the measure of acidity or alkalinity of water. The biological and chemical reaction are affected by the PH. Water with higher PH level has more chlorine contact time for disinfection.

CHLORIDES

Chlorides be there in groundwater naturally. Higher concentration of chloride does not have any effect to human health but it causes salty taste.

DESIGN PROCEDURE OF AERATION SYSTEM

Fig. Different stages of water treatment plant [4]

1. Information required for designing of plant [5]

   NOTE: Based on an assumption of no biological degradation in the secondary clarifier, the BOD5 in the waste activated sludge and recycle activated sludge are taken to be equal to that in the effluent stream.

   The symbols used in the flow diagram at the left and the equations below are as follows:

   NOTE: Based on an assumption of no biological degradation in the secondary clarifier, the BOD5 in the waste activated sludge and recycle activated sludge are taken to be equal to that in the effluent stream.

   The symbols used in the flow diagram at the left and the equations below are as follows:

   Q is volumetric flow rate in m3day S is BOD5 concentration in g/m3

   X is total suspended solids concentration in g/m3 The subscript o refers to the primary effluent stream.

   The subscript e refers to the secondary effluent stream. The subscript w refers to the waste act. Sludge stream. The subscript r refers to the recycle act. Sludge stream.

   V is the volume of the aeration tank in m3.

   X is the mixed liquor suspended solids concentration in he aeration tank in g/m3.

   Waste water properties supplied to the plant

   Waste water flow rate, Qo in (m3/d) Primary Effluent BOD5, So in (g/m3) Aeration Tank MLSS, X in (g/m3) Percentage volatile MLSS, in % Vol

   Waste/recycle activated sludge properties Sludge SS concentration Xw in (g/m3) Secondary Effluent TSS, Xe in (g/m3)

2. Aeration tank sizing calculations

   SIZING BASED ON VOLUMETRIC LOADING

   Volumetric Loading: VL in g/kg) (given)

   Design Aeration Tank Volume = Qo* So /(VL*1000) Values of other Design Parameters

   Aeration Tank Hydraulic Retention Time = 24*V/Qo hr Aeration Tank F:M Ratio = (Qo *So)/(% Vol.*X* V) kg BOD5/day/kg MLVSS

   Sizing based on hydraulic retention time [6] Hydraulic Loading: HRT = 24*V/Qo hr (given) Aeration Tank Volume = Qo*HRT/24

   Values of other Design Parameters

   Aeration Tank Volumetric Loading = (Qo *So)/(V*1000) kg BOD5/day/m3

   Aeration Tank F:M Ratio = (Qo *So)/(%Vol*X*V) kg BOD5/day/kg MLVSS

   Sizing based on F:M ratio

   F:M Ratio: F:M in kg BOD5/day/kg MLVSS (given) Aeration Tank Volume = (Qo* So)/(%Vol*X* F:M Ratio) Values of other Design Parameters

   Aeration Tank Volumetric Loading = (Qo* So)/(V*1000) kg BOD5/day/m3

   Aeration Tank Hydraulic Retention Time = V*24/ Qo* hr

3. Aeration tank operation calculations

   Standard pressure and temperature for Sm3/m calculation (per ASME & CAGI) – changeable by user
   Standard Pressure, PS	1.014 bar	Standard Temperature, TS	20 oC

   Standard pressure and temperature for Sm3/m calculation (per ASME & CAGI) – changeable by user
   Standard Pressure, PS	1.014 bar	Standard Temperature, TS	20 oC

   ESSENTIAL DATA REQUIRED

   Constants and conversion factors used in the calculations
   Temp. coeff for kd	1.024		Saturation D.O. in water at 20oC & 1 atm, Css	9.17	g/m3
   Ideal Gas Law Constant, R	8.3145	kN- m/kgmole-K	Molecular weight of air	28.97
   Specific Weight of water, H2O	9.807	kN/m3	Molecular weight of oxygen	32
   Conversion g Factor, Cf1	1000	g/kg	Atmospheric Press. at sea level, Pstd	1.014	bar
   o Conversion n Factor, Cf2	60	min/hr or sec/min	Oxygen mole fraction in air	0.209
   CbCOD e (BODult) equivalent of VSS:	1.42	kg COD/kg VSS	Conversion Factor, Cf3	24	hr/day
   O2 equivalent e of NH3-N:	4.57	kg O2/kg NH3-N	Conversion Factor, Cf4	100	kPa/bar

   Constants and conversion factors used in the calculations
   Temp. coeff for kd	1.024		Saturation D.O. in water at 20oC & 1 atm, Css	9.17	g/m3
   Ideal Gas Law Constant, R	8.3145	kN- m/kgmole-K	Molecular weight of air	28.97
   Specific Weight of water, H2O	9.807	kN/m3	Molecular weight of oxygen	32
   Conversion g Factor, Cf1	1000	g/kg	Atmospheric Press. at sea level, Pstd	1.014	bar
   o Conversion n Factor, Cf2	60	min/hr or sec/min	Oxygen mole fraction in air	0.209
   CbCOD e (BODult) equivalent of VSS:	1.42	kg COD/kg VSS	Conversion Factor, Cf3	24	hr/day
   O2 equivalent e of NH3-N:	4.57	kg O2/kg NH3-N	Conversion Factor, Cf4	100	kPa/bar

   Aeration Tank Volume, V in m3 (given)

   Target Sludge Retention Time in SRT days (given)

   Activated sludge operational parameters calculation

   Recycle Act. Sludge Rate, Qr = Qo-X/(Xw-X) m3/d

   Waste Act. Sludge Rate, Qw = (V*X/SRT-Qo*Xe)/Xw m3/d Aer. Tank F:M Ratio, F:M = (Qo*So)/(%VOL*X*V) k BOD/day/kg MLVSS

   Note: In Calculating Qw, the effluent flow rate, Qe is taken t be equal to the influent flow rate, Qo, based on the assumptio that liquid streams separated from the waste activated sludg are sent back into the wastewater stream.

4. Oxygen requirements/blower sizing calculations

   Note: To aid in setting the design WW flow rate for thes calculations, it is recommended that the maximum, minimum and average WW flow rates be identified and that the oxygen requirement rates be calculated for each.

   ESSENTIAL DATA REQUIRED

   Permitted Secondary effluent BOD, BODe in g/m3 Permitted Secondary effluent TSS, TSSe in g/m3

   % volatile solids in effluent TSS in % Vol Sludge Retention Time, SRT in days

   Synthesis Yield Coefficient, Y in kg VSS/kg BOD5 Endogenous Decay Coefficient (at 20oC), kd20 in kg VSS/d/kg VSS

   Std. O2 transfer Efficiency, SOTE in % (from diffuser mfr or vendor)

   Press.drop across diffuser, Pdiff in bar (from diffuser mfr or vendor)

   Depth of Diffuser, ddiff in m (from installation or plans) Design ambient air Temperature, Ta in o C

   Influent TKN, TKNo in g/m3

   Effluent NH4-N Concentration, Ne in g/m3

   Design Barometric Press., Patm in bar (ambient pressure at site)

   Design wastewater Temperature Tw in o C Ratio of BOD5/BODu, f in ratio

   Blower efficiency, h in %

   Ratio of oxygen transfer rate in wastewater to that in clean water, a in ratio

   Ratio of D.O. saturation in wastewater to that in clean water at same T & P, B in ratio

   D.O. saturation concentration for clean water at waste water temp. & 1 atm, Cs in g/m3

   D.O conc. to be maintained for WW treatment operation, CL in g/m3

   Diffuser fouling factor, F = 0.8

   Pressure drop at blower inlet, Pin = in bar (due to filter, silencer, etc.)

   Oxygen requirement/blower specifications (BOD Removal Only)

   AIR REQUIREMENT/BLOWER DESIGN CALCULATIONS

   Effluent Soluble BOD, Se = BODe-(f*cbCOD*%VOL*TSSe) g/m3

   Endog. Decay Coeff. (at 20oC), kd20 = kd20*( ^(Tw-20) kg VSS/d/kg VSS

   Observed Yield (with recycle), Yobs =Y/(1+ kd20*SRT) kg VSS/kg BOD5

   Required O2 flow rate = Qo/Cf1)*(So-Se)((1/f-cbCOD*

   Yobs)/Cf3) kg/hr

   Act. O2 transfer Efficiency, AOTE*

   =SOTE**F*(((B*(PD/Pstd)*C5)-CL)/C55)* ^(Tw-20) % Pressure at Mid Depth, PD = Patm+( H2O*(ddiff/2)/Cf4 bar Standard Air Density, air = Mole. Wt .of air*(Ps*100)/(R(Ts+273.15)) kg/m3 (from Ideal Gas Law)

   Design Air Flow Rate, SCMM = (Req.O2 flow rate/AOTE)*Mol. Wt. of air/(O2 mole frction in air*Mol. Wt. of O2* air* Cf2) mstd3/min

   Design Air Flow Rate, ACMM = SCMM*(Pstd/PB2)*(Ta+273.15)/(Ts+273.15) m3/min (at delivery point)

   Blower outlet pressure, PB2 = Patm+Pdiff +(H2O* ddiff / Cf4) bar

   constants
   Standard O2 solubility (DO.std)	9.08	mg/L, DO solubility in clean water at 20 °C and at 1 ATMambient atmospheric pressure
   Process temperature correction factor, (theta)	1.024	unit less
   Atmospheric temperature lapse coefficient (B.atm)	0.0065	K/m, used with normal atmospheric pressure computation
   Universal gas constant (R.univ)	0.082057	(m3-ATM)/(k mol-K)
   Mass-based gas constant for air (R.M)	286.9	J/(kg-K), used with normal atmospheric pressure computation
   Standard meteorlogical temperature (T.met)	288	K, used with normal atmospheric pressure computation
   Gravitational acceleration (g)	9.806	m/s2, used with normal atmospheric pressure computation
   Standard process temperature (T.std)	20	°C, base T for process computation and for use of standard cubic meter
   Standard atmospheric pressure (P.std)	1	ATM (much more convenient than kPa), normal ambient pressure at sea level
   Specific weight of water (SW.w)	9.789	kN/m3, taken at 20 °C and considered constant with process temperature
   Standard atmospheric O2 content (Y.O2.std)	0.209	(molO2/molair)
   Molecular mass of O2 (MW.O2)	32	kg/kmol
   Molar specific volume of ideal gas at STP (SV.stp)	24.0427	m3/kmol; SV.air =ROUND(R.univ*(T.std+273)/P.std, 4)
   Conversion from ATM to kPa (kpa.atm)	101.325	kPa/ATM
   The a.DO – d.DO coefficients fit a third-order polynomial to the data presented at right from the USGS database
   a.DO	-0.00007021

   constants
   Standard O2 solubility (DO.std)	9.08	mg/L, DO solubility in clean water at 20 °C and at 1 ATM ambient atmospheric pressure
   Process temperature correction factor, (theta)	1.024	unit less
   Atmospheric temperature lapse coefficient (B.atm)	0.0065	K/m, used with normal atmospheric pressure computation
   Universal gas constant (R.univ)	0.082057	(m3-ATM)/(k mol-K)
   Mass-based gas constant for air (R.M)	286.9	J/(kg-K), used with normal atmospheric pressure computation
   Standard meteorlogical temperature (T.met)	288	K, used with normal atmospheric pressure computation
   Gravitational acceleration (g)	9.806	m/s2, used with normal atmospheric pressure computation
   Standard process temperature (T.std)	20	°C, base T for process computation and for use of standard cubic meter
   Standard atmospheric pressure (P.std)	1	ATM (much more convenient than kPa), normal ambient pressure at sea level
   Specific weight of water (SW.w)	9.789	kN/m3, taken at 20 °C and considered constant with process temperature
   Standard atmospheric O2 content (Y.O2.std)	0.209	(molO2/molair)
   Molecular mass of O2 (MW.O2)	32	kg/kmol
   Molar specific volume of ideal gas at STP (SV.stp)	24.0427	m3/kmol; SV.air =ROUND(R.univ*(T.std+273)/P.std, 4)
   Conversion from ATM to kPa (kpa.atm)	101.325	kPa/ATM
   The a.DO – d.DO coefficients fit a third-order polynomial to the data presented at right from the USGS database
   a.DO	-0.00007021

5. Computation of actual oxygen transfer efficiency and diffuser requirements – diffuser aeration systems [5] Constants (from literature and computed) used in AOTE computations.

Input data required for site-specific conditions

Computed parameter values for site-specific conditions

The saturation value of DO at a specified T.des is given by: DO.sat.T = a.DO*T.des3 + b.DO*T.des2 + c.DO*T.des + d.DO DO.sat.T = a.DO*T.des3 + b.DO*T.des2 + c.DO*T.des + d.DO mg/L

P.H = P.std*(1-B.atm*H.site/T.std)^(g/R.M+B.atm) atm P.mid = P.H+(SW.w*D.sub/2)/P.std.kPa atm

P.disch = P.H+SW.w*D.sub/P.std.kPa atm DO.sat.T.H=DO.sat.T*P.H/P.std mg/L

Calculation for the number of diffuser required

Calculation of actual (Field) oxygen transfer efficiency (AOTE) requires manufacturers value of standard oxygen transfer efficiency (SOTE). By using AOTE the number of diffusers necessary at the design maximum case is computed. For these computations manufacturers data correlating with gas flow per diffusers are necessary for the computation of AOTE and number of diffusers required.

The following graph and eqution is obtained by using excel with the help of manufacturers data of sote and gas flow rate for a particular diffuser.

The number of diffusers necessary to deliver air at the maximum OUR is determined by simultaneously solving following set of equation yielding Yo2.avg, Csat.avg and AOTE.

sote vs gas flow rate

The images of excel sheet is provided as below.

I. Computations for the maximum oxygen demand case – sets the number of diffusers

I. Computations for the maximum oxygen demand case – sets the number of diffusers

45

y = 21.71×3 + 60.298×2 – 50.855x + 47.725

44 R² = 0.9994

43

sote

sote

42

41

40

39

38

37

0 0.1 0.2 0.3 0.4

gas flow rate

Yo2.avg =Yo2.std* (1+(1-AOTE/100)/(1- Yo2.std* AOTE/100)) Csat.avg =Csat.T.H*(PD/2Yo2.avg/(PH* Yo2.std)) AOTE=SOTE*((Csat.avg-CMLSS)/ Csat.avg))*(Tdes-Tstd) **F

The corresponding oxygen application rate is determined using the following equation.

OAR=AOTE*100/AOTE

The total air delivery rate is computed from the following equation.

Qstd.air=OAR*Vair.spec/(MWo2* Yo2.std)

The number of diffusers necessary is computed from the following relation.

Ndiff= Qstd.air/qdiff

Once the number of diffusers is known for non maximum OUR the air deliver per diffuser is computed by simultaneous solution of the following two equation with the three from the above.

qdiff=AOTR*Runiv*(Tstd+273)/((AOTE/100)* Ndiff* MWo2* Yo2.std*Pstd)

SOTE=asote*qdiff+ bsote*qdiff2+ csote*qdiff3+ dsote

(The values of coefficients of this equation will be equal to the coefficients of the equation obtained from the graph by using excel tool.)

We can solve the simultaneous system of equation by using the excel solver tool by using established relation between sote and gas flow rate and can compute the number of diffusers for maximum oxygen demand case and required gas delivery for non max oxygen delivery case.

CONCLUSION

The goal of this research paper is to understand the necessity and design of the aeration system. In this research paper we have learned about parameters affecting the operation and design procedure of aeration system. So we can summarize that this research paper dealt with aeration tank sizing, aeration tank operations, activated sludge operational parameters, oxygen requirements, blower sizing, air requirement, computation of actual oxygen transfer efficiency and number of diffuser required.

Published by :

International Journal of Engineering Research & Technology

Published by :

International Journal of Engineering Research & Technology

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 8 Issue 06, June-2019

International Journal of Engineering Research & Technology (IJERT)

ISSN: 2278-0181

Vol. 8 Issue 06, June-2019

REFERENCES

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Design of Municipal Wastewater Treatment Plants, WEF MOP No. 8, 5th Ed., Sec. 14.1.3 Activated Sludge Environment, McGraw- Hill Education

Standard Handbook of Environmental Engineering, 2nd Ed, Sec

6.5.1 Activated Sludge, McGraw-Hill Education

Oliver Marunlu, Elena Elisabeta Manea. Research on the Aeration Systems Efficiency of a Lab-Scale Wastewater Treatment Plant, International Journal of Environmental and Ecological Engineering, Vol:9, No:9, 2015

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Fundamentals of Biological Wastewater Treatment Biological Wastewater Treatment by Arun Mittal.

https://www.wikipedia.org/ https://www.google.com/ http://water.usgs.gov

Shriram, Manogaran, "Economic life cycle assessment of aeration blowers used in waste water treatment systems" (2013)

Design of Municipal Wastewater Treatment Plants, WEF MOP No. 8, 5th Ed., Sec. 14.1.3 Activated Sludge Environment, McGraw- Hill Education

Standard Handbook of Environmental Engineering, 2nd Ed, Sec

6.5.1 Activated Sludge, McGraw-Hill Education

Oliver Marunlu, Elena Elisabeta Manea. Research on the Aeration Systems Efficiency of a Lab-Scale Wastewater Treatment Plant, International Journal of Environmental and Ecological Engineering, Vol:9, No:9, 2015

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IJERTV8IS060582

IJERTV8IS060582

www.ijert.org

(This work is licensed under a Creative Commons Attribution 4.0 International License.)

www.ijert.org

(This work is licensed under a Creative Commons Attribution 4.0 International License.)

II. Computations for a non-max oxygen demand case – computes required gas delivery