The country town with service area of 150 ha described in Question 3 is sewered, and the main outfall sewer is laid on a grade (slope) of 0.003 m/m to a treatment plant. Effluent from the treatment plant is at present discharged via an open channel to the river. At the end of the design period (20 years), wastewater from a proposed dairy industry (average wastewater flow of 0.5 ML/day, BOD5 = 1500 mg/L, and service area = 25 ha) and from a nearby food processing industry (average wastewater flow of 300 m3/day, BOD5 load of 68 kg/day, and service area = 25 ha.) are also expected to be discharged into the main outfall sewer. Assume that the average wastewater contribution from the community is about 300 L/(person. day) and each person contributes 70 g BOD5/day.
(a) Estimate the ultimate mean dry weather flow, peak dry weather flow, peak wet weather flow and the minimum dry weather flow.
(b) Calculate total organic load reaching the plant per day and the population equivalent based on BOD5 of the combined wastewater flow for ultimate development condition (ie. end of the design period).
(c) Determine the pipe size required at the ultimate development stage for the main outfall sewer.