Question

a) Design a septic tank for 10 households, with three 2-bed room houses six 4-bed room houses and one 3-bed room house. The septic tank has a required depth of 1.8 m, and a length to width ratio of 3: 1. The septic tank has a 60 hour hydraulic retention time. b) The septic tank is planned to discharge the water into a soak pit. Site percolation tests conducted in the area indicated an average time of 7 minutes for the test water level to drop by 25mrn. Design and sketch an appropriate soak pit, allowing for a maximum water level to be 500mm below ground level and assuming that all the infiltration takes place through the sides of the soak pit. c) The septic tank is linked up to the household discharge pipes with a 30 m pipeline at a gradient of l: 100. What theoretical diameter is required for this pipe to ensure self-cleansing? Assume the shear stress required for self-cleansing is 4 Pa, the peak flow of all the houses is 2400 1/hour, and the pipe has a Manning coefficient of 0.012.

Answer 1

180 ditcapita do sludge capoy AsSume dary 60 hms Berenuion me 130x 16 toya-s 3.25 depth 3.DS Aoeo 니b . A