BIOLOGICAL TREATMENT SYSTEM FOR
VEHICLE SERVICE STATIONS

Ramya Wijesekara
Research Engineer
WEPA, Cinnamon Grand Hotel, Colombo
Industrial Technology Institute

VER 6

Wastewater / Effluent Sources

Body washing

Under carriage cleaning

Main Pollutants
Mud

Oil & GreaseSoap / Detergent



Kerosine

Major Pollution ParameterspH

Oil & Grease

BOD – Biochemical Oxygen Demand

COD - Chemical Oxygen Demand

TSS

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QUALITY -TYPICAL FIGURESpH-6.0 – 8.5

COD-300 – 700 mg/l

BOD-250 – 500 mg/l

O&G-Very high & varies depending on thehouse keeping practices

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Wastewater Disposal Standards
Tolerance Limits for Discharge of industrial effluents in to :
 Inland Surface Waters
 on land for Irrigation Purposes in to Marine Coastal Areas

Parameter

Tolerance Limit

TSS -mg/l

50

pH

6’0 - 8’5

BOD5 - mg/l

30

O & G –mg/l

10’0

COD – mg/l

250

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COMPARISON OF CHEMICAL & BIOLOGICAL SYSTEM CHEMICAL SYSTEM BIOLOGICAL SYSTEM-

Need chemical addition-No chemical addition-Large quantity of chemicalsludge generated-

Small amount of biologicalsludge to be disposed-

Need well trained operator todo the treatment--

Treated water contains trace
amounts of treatment
chemicals

No routine operation otherthan Aerator switch on & off
AND opening & closing ofvalves-No trace chemicals in treatedwaterIndustrial Technology Institute6

Biological Treatment
Conversion of dissolved Organic Compounds in tosimple compounds (CO2 ,H2O, NH3 etc.) by
Aerobic micro-organisms in the presence of O2

COHN +OrganicCompounds

O2

CO2 + NH3+ H2O + New Cells

Aerobic Micro organisms

BIOLOGICAL TREATMENT MECHANISM
 Oxidation
COHN + O2 + Micro organisms(Organic matter)

CO2 + H2O + NH3 + Energy(Bacteria)

 Synthesis
COHN + O2 + Bacteria + Energy

C7H5NO2 (New cell tissues)

 Respiration
C7H5NO2 +(Cell tissues)

5 O2

5CO2 + NH3 + 2H2O

Biological Treatment Process

WW from Vehicle servicing

OIL SEPERATION (Oil trap)
Filtrate

SDB

BIOLOGICAL TREATMENT / Aeration Tank
SludgeREATED WASTEWATERDRIED SLUDGE
FINAL DISPOSAL

Treatment System
Biological Reactor

Aeration Tank
Oil trapOil Trap

Sand BedBiological Reactor

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Aeration Tank function
Micro Organisms that plays the major role of treatment

Favorable conditions for microbial culture Organic Compounds (Food) Oxygen & sufficient Mixing

 pHBiological Reactor sizing

D0.3
h2H

h1

No. of vehicles
Daily discharge
serviced per(Q‐m3)
day (N)
5
0.75
7
110
1.5
15
2.25
203

Diameter
(D)

H (m)

h1 (m)

h2 (m)V (m3)

1.5
1.5
1.5
22

1.2
1.7
2.5
1.9
2.4

0.4
0.6
0.8
0.7
0.95

0.50.81.40.9
1.15

2.25
34.56
7.514

EX: FINAL DISCHARGE QUALITY

ParameterpHBefore
Treatment
5.0‐8.6

After Tolerance
Treatment Limit
6’5 - 8’0

6’0 - 8’5O&G(mg/l)> 10<1010BOD
COD(mg/l)(mg/l)

200‐500
500‐1000<30<25030250

Operational Cost Capital investment ‐Plant construction
 Running cost of Aerator ‐ Plant Operation

Example : Plant Operation Cost
Case : average number of vehicles serviced per day = 5 (= 1m3 of wastewater)
BOD = 350 mg/l
BOD load = 350 mg/l x 1x1000 l/d = 0.35kg BOD/dO2 requirement= 2.3 kg x 0.35 = 0.805 kg O2 / d1.5kW aerator ------ 1 kg O2 /hr,

= 0.805 hrs. (1 hr aeration is sufficient)

01 hour aeration during 20 hrs is not practical. Therefore , assuming 10
minutes aeration for every 1 hr (10 mts x 20 hrs = 3.3 hrs)
Total hrs per month= 3.3 x 31 = 102.3 hrs per month

Need 1.5kW x 102.3 hrs = 153.45 kW hrs per month
Cost= 24 /= /hr x 153.45 hrs. /m= 3682.8/- per month= 3682.8 /5 x25= 29.45/= per vehicle= 30/- per vehicle18

Example : Plant Operation Cost ………
Case : average number of vehicles serviced per day = 5 (= 1m3 ofwastewater)
BOD = 350 mg/l
BOD load = 350 mg/l x 1x1000 l/d= 0.35kg BOD/d

O2 requirement= 2.3 kg x 0.35 = 0.805 kg O2 / d

1.5kW aerator ------ 1 kg O2 /hr,

= 0.805 hrs. (1 hr aeration is sufficient)

10 vehicles

15/= per vehicle

05 vehicles

30/= per vehicle

0.5kW aerator ------ 0.3 kg O2 /hr,

= 0.805 hrs. (4 hr aeration is sufficient)

10 vehicles

08/= per vehicle

05 vehicles

10/= per vehicle
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