Effluent sewer
Effluent sewers also currently serve fewer people than septic systems, which also use septic tanks, but simply dispose of the effluent by draining it into a leach field. About one quarter of United States homes dispose of their wastewater with septic tanks. However, effluent sewers are being looked at as a sewage treatment solution in areas where gravity sewer systems are not well-suited or when the high capital cost to build a gravity system is prohibitive. Areas that are less than ideal for gravity systems include areas that are large, but extremely flat and areas that require long-distance pumping, such as where homes are widely spread out or when several small villages or towns connect their sewage systems so that a centralized plant can be built.
Lee Tunnel
This long tunnel, of diameter , running from deep at Abbey Mills down to deep at its terminus at Jenkins Lane, East Ham, will capture , or 16 million tonnes, of sewage annually from the single largest polluting CSO in London. This sewage would otherwise flow straight into the River Lea, the Thames Tideway and eventually the Thames Estuary. However, the sewage is now pumped up to the Beckton Sewage Treatment Works – the largest sewage treatment works in Europe – and the resultant clean water emptied into the River Thames. The reason for starting at −75 m is to be ready to collect sewage from the lowest point of the Thames Tideway Tunnel, which is under construction and intended to connect.