A small community is building a lagoon determine surface are

A small community is building a lagoon, determine surface area of primary cell and volume of secondary cell

      Design Criteria

1.      BOD₅ loading rate < 22 kg/ha*day Primary Cell

2.      Detention time >180 days Secondary Cell

3.      250 people 450 litres per capita per day; 77 grams BOD /capita-day

Solution

Loading Rate < 22 Kg/ha/day

Detention time > 180 days

BOD₅ = 77 g/capita/day therefore for 250 people it will be,

BOD₅ = 77 * 250 g/day = 19250 g/day = 19.250 Kg/day

Area (ha) = BOD₅/Loading Rate

Area(ha) > 19.250/22 ha = 0.875 ha = 2.1622 Acre

Flow = 450 L/capita/day therefore for 250 people flow will be,

Flow overall =450*250 L/day = 112,500 L/day

Detention Time = Volume/Flow

=> Volume, V = Detention Time * Flow

=> V > 180 * 112500 L = 20,250,000 L