Population Equivalent Estimates

Population equivalents that are used to calculate hydraulic and organic loadings for domestic wastewater treatment if actual operating information is not available are as follows:

BOD5 = 0.17 lbs./capita/day
TSS = 0.20 lbs./capita/day
Phosphorus = 0.0048 lbs/capita/day
Flow = 100 gallons/capita/day
Note – Capita is the same as Person

Estimate the population served if a treatment plant is processing .885 MGD.

The number of people can be determined by dividing the flow by the population equivalent. Change MGD into gpd.

# of people served = (885,000 gal/day) / (100 gal/day/person) = 8,850 people

Ideal nutrient requirements for biological stabilization of organic matter result in the following ratio:

Carbon/Nitrogen/Phosphorus = C/N/P = 100/5/1

Another way of viewing this nutrient balance is to consider the BOD5 as the carbon source so that for every 100 ppm of BOD5 removed, there would have to be 5 mg/L of nitrogen and 1 mg/L of phosphorus available for cell synthesis. The units of measure, if the same, do not matter because it is the ratio that is important.

Sewers

Sewers are hydraulic conveyance structures that carry wastewater to a treatment plant or other authorized point of discharge. A typical method of conveyance used in sewer systems is to transport wastewater by gravity along a downward-sloping pipe gradient. In some areas, sanitary sewers are separate sewer systems specifically for the carrying of domestic and industrial wastewater, and are operated separately and independently of storm drains, which carry the runoff of rain and other water which wash into city streets.

Sewers are usually pipelines that begin with connecting pipes from buildings to one or more levels of larger underground trunk mains, which transport the sewage to sewage treatment facilities. Vertical pipes, called manholes, connect the mains to the surface. The manholes are used for access to the sewer pipes for inspection and maintenance, and as a means to vent sewer gases. They also facilitate vertical and horizontal angles in otherwise straight pipelines.