Revealed: the ‘black box’ wastewater trade that rakes in millions for UK utility companies

Exclusive: Firms made more than £340m last year from processing industrial and commercial wastewater at sewage works that are unable to remove many chemical pollutants

Water companies in the UK made more than £340m in revenue last year by pouring billions of litres of industrial and commercial wastewater into sewage treatment works that experts say are not designed to remove most chemicals, leaving pollutants to pass into rivers, seas and farmland.

However, no independent regulator oversees the trade-effluent process and there is no central register, so Watershed Investigations, the Guardian and the campaign group River Action compiled a database of 26,000 consents, providing the first ever national picture of the system.

The permits are issued and enforced by the water companies themselves, with environmental regulators having no direct role. “It’s a bit of a black box,” one industry expert said.

Pollutants that survive treatment are discharged into rivers, lakes and seas as “treated effluent”, while those captured in sewage sludge are spread on farmland as fertiliser. The waste also adds to the overloading of sewer networks that triggers raw sewage spills, which have caused outrage, community protests and calls for the industry to be nationalised so that profits can be reinvested in improving the system rather than going to shareholders.

Thames Water has the largest volume of permitted industrial sewage, at 113bn litres, followed by United Utilities at 105bn litres and Severn Trent Water at 79bn litres.

Across the sector, revenues from receiving industrial and commercial wastewater have risen sharply in five years, with Anglian Water’s increasing by 62%.

The permit regime was very old and not fit for purpose, they added. “Currently the Environment Agency doesn’t know exactly how much of this waste is going into waterworks each year.”

Both the officer and the industry expert identified Davyhulme wastewater treatment works in Manchester, operated by United Utilities, and Avonmouth, operated by Wessex Water, as big receivers of tankered waste. “Carriers will drive [long distances] to dispose of their wastes here … You can see lines of tankers queueing outside Avonmouth,” the expert said.

But “ignorance is no defence”, said the officer. “They should be seeking sufficient information from the producer of that waste to satisfy themselves so they can treat it properly.”

Amy Fairman, the head of campaigns at River Action, said: “Industrial pollution must not become a lucrative business for water companies … Polluters must be held to account and made to pay, rather than passing the costs and consequences down the line.

“Water companies should never profit from pollution,” said a spokesperson for the Department for Environment, Food and Rural Affairs. “We know the water industry hasn’t been working in the public interest for far too long and that’s why we are reforming it, including how wastewater is disposed of.”