Southern on track to surpass CSO target

Southern Water has said it is on track to exceed the 2025 target for permitted combined sewer overflow spills set by the Department for Environment, Food and Rural Affairs (Defra).

Defra set the goal of reducing spills to an annual average of 20 per overflow point by the end of AMP7 as part of its Storm Overflows Discharge Reduction Plan published last year with short and longer term targets for the sector to improve river water quality.

Southern said it should beat that target and is on track to reduce discharges to 18 spills per year by 2025 and a 14% reduction in spills by 2030.

The work is part of the company’s wider approach to minimising the risk of harm to the water environment from the complete wastewater treatment processes, which has three parts. Firstly, it has digitalised its sewer networks with monitors across its pipelines and artificial intelligence detecting blockages and measuring flow rates. This alerts teams to where problems are before they cause flooding or pollution incidents. So far, 22,000 monitors have been added out of a total of 25,000.

Secondly, the company is rolling out enhanced signals and monitoring at its 3,500 pumping stations. Alex Saunders, head of wastewater networks, explained these can get blocked so the sewer digitalisation will vastly reduce the strain by identifying debris and unflushables before they reach pumping stations. Furthermore, additional back-up power supply options are being added to minimise the risk of asset failures due to power outages.

The company has 367 wastewater treatment plants which are attended by staff more than the pumping stations and therefore experience fewer failures as issues are picked up quicker. Saunders said the third stage of Southern’s efforts to reach the pollution reduction targets will ultimately be to digitally link the pipes, pumping stations and treatment plants to understand the geospatial point of view of how they work together.

Southern pulls more than 5,000 tonnes of wetwipes and other plastic out of its sewers each year – with much of this waste getting caught on screens at wastewater treatment plants. It is the only part that cannot be recycled or reused from the treatment process.

Data from event duration monitors (EDMs) showed a fall in the average number of spills from each CSO from 33 in 2020 to 29 in 2021. Southern Water recorded one of the sector’s lowest spill rates.

All companies are required to install EDMs at all overflows points by the end of 2023 to complete the picture of when and where CSOs overflow across the country.