Organic Waste Recycling

Aquatic weeds and their utilization 379

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7.10 Exercises

7.1 From Equations 7.1 and 7.2, derive the following equation:

ln 2

Doubling time =

ln x

where x = daily incremental factor.

7.2 It is estimated that water hyacinths have a doubling time of 10 days in
natural freshwater. Determine how much time is needed for initially 10
water hyacinth plants to cover 0.4 ha of a natural freshwater surface The
average density of water hyacinths in water bodies is about 150 plants/m^2.

7.3 Design a constructed wetland system to treat a raw wastewater with the
following characteristics:

Flow rate = 500 m^3 /day

BOD 5 = 200 mg/L

COD = 300 mg/L

The effluent BOD 5 concentration after treatment should be less than 10 mg/L.