The company is fitting the new engines at Gravesend in Kent, Goddards Green in Sussex, and Millbrook, Fullerton and Budds Farm – all in Hampshire.
All five sites will have replacement combined heat and power (CHP) engines fitted, and two sites – Budds Farm and Millbrook – will have additional engines installed.
After the engine upgrades Budds Farm will generate 95 per cent of its power demand and Millbrook will be completely self-sufficient.
Southern Water currently generates 17 per cent of its electricity from 16 CHP sites. This puts the company ahead of its target to increase the proportion of renewable energy it uses to 16.5 per cent by 2020.
The latest investment in CHP at five key sites will allow the company to produce even more electricity from renewable sources.
Southern Water energy manager Martin Ross said: “The capturing of biogas is a double win because not only do we collect free fuel but we also prevent the release of methane which has a global-warming potential 25 times more potent than carbon dioxide.
“Last year, we generated 77GWh of power through CHP – equivalent to powering over 20,000 homes for a year and saving the equivalent of 40,000 tonnes of carbon dioxide.”
CHP takes biogas – primarily methane – created during the wastewater treatment process and uses it as a fuel to produce electricity.
Yesterday, Southern published its interim financial report for the six months to September 2016. The firm reported a 2.1 per cent rise in revenue for the period to £409.2 million, principally resulting from an increase in its charges linked to RPI.
Operating costs for the first half of the year were £277.2 million, up 2.6 per cent on the previous year. This increase mainly resulted from inflation, an increase to the company’s bad debt charge and initiatives to improve its customer services performance.
Operating profit for the period increased by 1.1 per cent to £133.5 million.