Oxidation Pond

SOLUTION

1. 1 MLD of wastewater with influent soluble BOD 5 (S o ) = 75 mg/L is to be treated in an oxidation pond such that effluent soluble BOD 5 (S) is 5 mg/L. Calculate the oxidation pond surface area, assuming the depth of the pond to be 0.5 m. Calculate oxygen requirement for microbial respiration and oxygen supplied by algal growth, and check adequacy of the design by assuming that 50 percent of the oxygen produced by algal growth is available for microbial respiration. Neglect oxygen input into the pond by mass transfer from atmosphere

Data:

• K = 0.1 L/mg/d,
where K is the first order microbial substrate utilization rate ( )
• Y T = 0.5 mg/mg; K d = 0.05 /d

•  Average intensity of solar radiation: 150 calories/cm 2 /d

•  Solar energy utilization efficiency for algae: 6 percent

•  Energy content of algal bio-mass: 6000 calories/g algae

•  Equation for algal photosynthesis:

Solution:

We know, ;

Therefore,

Also,

Also, , or,

Sludge Production ( ) = Q.X =

Volume of Oxidation Pond =

Assuming depth to be 0.5 m, Surface Area (A) =

Algae production =

Total algal production = (15).(10000) = 150 kg/d

Assuming 1.3 Kg oxygen production per Kg algal production,

Oxygen Production = (1.3).(150) = 195 Kg/d

Since oxygen available is more that oxygen requirement for microbial respiration, the design is adequate.