Oxidation Pond 6g322

OXIDATION POND

OXIDATION POND

OXIDATION POND • Oxidation Pond or Waste Stabilization Pond (WSP) are the simplest biological systems available for the treatment of wastewater. • These are of great use for two basic purposes:1) when the high quality effluent is not required 2) the availability of power source is not abundant • The ponds are generally constructed in earthwork with relatively very small depths as compared to their large areas.

TYPES OF WSP 1) AEROBIC PONDS These ponds are generally 0.3-1.5m deep and have further been classified as low rate and high rate aerobic ponds. While low rate are used for reducing soluble BOD5 and aerobic conditions are maintained throughout the pond depth. High rate aerobic ponds are used for production and harvesting of algal cultures. 2) Anaerobic ponds These ponds are generally 2.5-5.0 m deep in which anaerobic conditions prevail throughout the pond depth except for a surface zone of few cms.

TYPES OF WSP 4) Maturation pond these ponds are generally 1.0-1.5m deep and normally used after facultative ponds with the prime objective of destruction of pathogens. 3) Facultative ponds These ponds are generally 0.9-2.5m deep and three zones exist throughout the pond depth viz. aerobic zone at the surface, anaerobic zone at the bottom and facultative at the mid depth.

PRINCIPLES • In these types of ponds special relationship exist between algae and aerobic microorganisms, and also between aerobic and anaerobic microorganisms. • Algae during photosynthesis releases oxygen which is consumed by the aerobic microorganisms to carry out the decomposition of OM resulting in the formation of biomass which is further utilised by the algae as nutrient. • Anaerobic microorganisms produces gases (CO2, CH4) which is utilized by aerobic microorganisms as the source of energy and biomass formed during the aerobic decomposition settles to get utilized as nutrients by the anaerobic microorganisms. • Overdosing of the pond may result in odour problem which is avoided by adding sodium nitrate which act as both oxidising agent and nutrient for the algae.

EXISTING WSP

EXISTING WSP

ADVANTAGES • • • •

Very cheapest option Very high removal of pathogens Operation and maintainance is very simple. No skilled labour is required. Good resistance to shock hydraulic and organic loading

DESIGN DATAS parameter s

aerobic

facultative

anaerobic

maturation

Depth(m)

0.3-1.5

1.0-3.0

2.5-5.0

1.0-1.4

Detention time(d)

4-40

5-30

15-50

5-18

OLR(kg/ha/d 40-160 )

15-150

200-500

0-15

BOD removal efficiency (%)

80-95

50-80

60-80

80-95

OLR A/C LATITUDE LATITUDE (N)

OLR (kg/ha/day)

36

150

32

175

28

200

24

225

20

250

16

275

12

300

DESIGN STEPS Present population- 20000 Rate of growth- 2% Design period 15 yrs So population after 15 yrs- 26917.367 Let the water consumption be 150 lpcd So, total water consumption- 4037650.5 80% of it getting on as sewage, so sewage production= 3230120.4 Let us take sewage production of 3.5 MLD The influent BOD5= 300 mg/l The effluent BOD5= 30 mg/l

DESIGN STEPS Step-1 Calculation of limiting HRT t= 1/k*log(L/L-Y) Where K= BOD removal rate constant L= BOD load applied to the pond Y= BOD load satisfied And K is temperature dependent as:• In summer K35 = K20(1.047)^35-20 So if K20 =0.1 day^-1 Then K35= 0.2 day^-1 t limiting summer= 5 days

DESIGN STEPS • during winter K15 = 0.08 So t limiting winter = 12.5 days Let us assume detention time of 20 days. STEP-2 Calculation of volume Volume= influent rate of sewage* detention time = 70000 m^3 STEP-3 Calculation of surface area Let us assume depth of the pond as 2 m So S.A= 35000 m^2 = 3.5 ha But S.A must be <= 3 ha

DESIGN STEPS Let us take 2 ponds of 1.75 ha each STEP 4 Check for OLR( kg/ha/day) OLR = BOD applied/hydraulic loading OLR = 280 kg/ha/day As per IS 5611 the OLR for eight states through which latitude es is between 140 to 335 kg/ha/day STEP 5 Dimension calculation assume L:B ratio = 3:1 so B = 76.37 m Take B= 77 m L = 231 m Thus provide 2 WSPs of 231 * 77 * 2 m with detention time of 20 days