A Sewer Line Calculations: Determining Total Sewage Flow
Calculating Total Sewage Flow in a Sewer Line
A sewer line receives sewage from two contributing areas. One area is roughly 13.9 km2 in size and has a population density of only 80 persons per hectare. The average rate of sewage flow from this area is 135 litres per person per day. The second area has a population density of 10 persons per 100 m2, contributing sewage to the sewer pipe at a rate of 45 kL/ha/day. The total coverage of this area is 20.56 km2. If 20% is assigned to infiltration, determine the total sewage flow (m3/min) in the pipe. [20 Marks]
The total sewage flow in the pipe, after accounting for infiltration, is roughly 59.73 cubic meters per minute.
Firstly, let's determine the population for each area based on the density and the area. For the first area, the area is given by 13.9 km2 which is equal to 1,390 hectares. So the population will be 1,390 hectares multiplied by 80 people per hectare, giving 111,200 people. Thus, the sewage flow from this area (not accounting for infiltration) would be 135 litres times 111,200 people, divided by a factor of 1,000 to convert litres to cubic meters, giving 15,012 m3/day.
Similarly for the second area, the given density is 10 persons per 100 m2 which is equivalent to 1,000 persons per hectare. This gives a population of 20,560 people (since the area is 20.56 km2 or 2,056 hectares). The total sewage flow from the second area will be 45 kL/ha/day times 2,056 hectares, which is 92,520 m3/day.
Now, adding the sewage flow from both areas together gives 107,532 m3/day. Taking into account the 20% infiltration, the total sewage flow in the pipe is thus 80% of this value, which equals 86,026 m3/day. Then, we convert this flow rate from cubic meters per day to cubic meters per minute by dividing by the number of minutes in a day (1,440), thus obtaining a flow rate of approximately 59.73 m3/min.
Question:
What is the total sewage flow in the pipe after accounting for infiltration?
Answer:
The total sewage flow in the pipe, after accounting for infiltration, is roughly 59.73 cubic meters per minute.