Civil Engineering License Review, Fifteenth Edition
Including essay and multiple-choice exam problems, this review book offers a detailed discussion of the Civil Engineering/Professional Engineer Exam and how to prepare for it.
TABLE OF CONTENTS Civil Engineering License Review, Fifteenth Edition
Chapter 9: Wastewater Treatment
Kenneth J. Williamson
WASTEWATER FLOWS
Wastewater flows are comprised of domestic and industrial wastewaters, infiltration, inflow, and storm water. Most modern sanitary sewers are separated from storm water systems so these flows are treated separately. Modern sewers are constructed so that inflow rates are assumed to be negligible.
Domestic Flows
Domestic flows are determined from water use rates. Typical values are 150 gallons per day per capita. Peak daily and hourly rates can be determined from historical data; typical values are 1.8 and 2.7 times the annual average flow, respectively. Peaking factors vary with the size of the area being served such that larger values are used for lateral as compared to interceptor sewers.
Industrial Flows
Industrial flows vary widely. Specific data are required, based upon industry and production rates.
Infiltration
Infiltration rates for new sewers vary from 5 to 20 m 3/ha-d with smaller values for larger areas being served. Infiltration from existing old sewers is estimated from historical data.
Storm Water Flow
Storm water flow rates are estimated by using the rational formula as reviewed in the Civil Engineering: License Review hydrology chapter.
SEWER DESIGN
Hydraulics of Sewers
Sewers are designed as open channels, usually with a circular cross section. Flows in sewers are modeled using Manning's Equation, as
where V = velocity (fps), n = Manning coefficient (0.013 is a common design value), R = hydraulic radius (ft), and S = slope of the energy grade line.
The relation between...
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