40 years of progress at Scotland’s largest wastewater treatment plant

Posted on 13 December 2018.

The largest wastewater treatment plant in Scotland is forty years old. A look back at four decades of innovation serving the circular economy – and with Veolia by its side for the last 20 years.

The wastewater treatment plant now produces enough to cover 85% of its electricity needs

Scotland's largest sewage treatment plant is located in Seafield, a neighbourhood of Edinburgh. Owned by Scottish Water - a national water and sanitation utility company - the site treats some 300 million liters of wastewater a day. The equivalent of 121 Olympic swimming pools! This year, the plant celebrates its 40th anniversary. The opportunity to look back at four decades of innovation during which it swapped its processes for ever more ecological solutions inspired by the circular economy.
It all began in 1978 with the opening of the Seafield wastewater treatment plant. The plant was then a primary wastewater treatment plant removing sand and solid waste. The new era began in 1984 when Veolia took charge of managing it through a public-private partnership with Scottish Water. The goal was clear: improve the plant’s energy performance through adopting a circular approach. But how? By transforming the waste produced by the station into new resources.

Recycling and producing

The first idea was to use the sewage sludge - organic matter resulting from wastewater treatment - to produce energy. The plant introduced thermal hydrolysis technology associated with anaerobic digestion. The solution consists of heating the sludge to dehydrate it and thus reducing the volume. It is then placed in an enclosed space that accelerates decomposition and produces methane. This biogas, which compared to diesel reduces greenhouse gas emissions by 80%, powers a cogeneration unit that produces heat and electricity for the plant! Recovering the waste heat emitted by the equipment during operations, the unit produces up to 32,000 kilowatts of sustainable electricity - enough to cover 85% of its needs.

And the circular approach doesn’t stop there: after these treatments, the sewage sludge residues are turned into fertilizer and sold to farmers in the area.

It's possible to go even further, says John Abraham, COO of Veolia's Water business in the UK, "the challenge of the next decade will be to make even greater progress towards energy self-sufficiency in the plant and reduce its carbon emissions".

Wastewater generally has excellent potential. According to some studies, if the energy potential of the 11 billion liters of wastewater produced every day in the UK were exploited, the water sector could become fully self-sufficient in electricity.

The public also has a role to play in improving the energy efficiency of the hydropower industry - primarily by not putting anything such as sanitary products, wipes, cotton buds or food waste such as cooking oils into the wastewater from sinks, showers and toilets.