ABSTRACT
There are two basic types of wastewater collection or sewerage systems, combined and separate. Sewerage is the term to describe the network of pipes or sewers that collects and transfers the sewage, the name for domestic wastewater, to the wastewater treatment plant. Sewer pipes are usually made from concrete and laid 1–3 m below ground. Normally laid on one side of the road away from water mains, the precise depth of the sewer depends on the gradient, geology and road surface loading. Pipe diameters vary in the same way as water mains with individual houses served by 0.15 m diameter plastic pipes that feed into pipes that get progressively larger as the number of connections and area served increase. Sewer pipes up to 3 m in diameter are common within towns with older Victorian sewers constructed from standard bricks. In major cities, such as Tokyo and London, super sewers in excess of 20 m in diameter are being constructed from cast concrete to serve the ever-increasing population and increase in surface water due to increased intensity and frequency of rainfall events. The design of sewerage systems is complex as they must have a minimum gradient to allow the wastewater to move by gravity.
