Assignment 3a
(To be submitted on the 17 May 2019)

1. Design a constructed wetland to treat domestic wastewater from a small town of 6000 population. Wastewater generation is at 160 litres per capita per day. The initial BOD of the primary treated wastewater is 180 mg/l and the treated wastewater needs to conform to a BOD standard of 30 mg/l. Fine and medium sized gravel are as substrate material for wetland bed of depth 0.6 m. Assume the water depth is 0.4 m and the hydraulic gradient is 0.003. Further assumptions are porosity of 40% and hydraulic conductivity of 10.2 x 10-2 m/sec. Annual average temperature of water is 27oC.

2. Calculate the volume of rain tank required for Rain Water Harvesting. The area of the roof is 100 m2. Assume the average ddemand is =50 L/person per day. The house is occupied by four people. The monthly rainfall is summarised in the table below.

Jan Feb Mac Apl May Jun July Aug Sep Oct Nov Dec
103 117 131 127 123 128 98 81 68 76 83 78

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