Wastewater treatment in Wales 2024: data for 2022

Without treatment, urban wastewater has significant adverse impacts on our water environment. This is because it:

• contains nutrients which, when in excess, can speed up the growth of certain plants, disrupting natural processes and harming wildlife
• can be contaminated with harmful chemicals and bacteria which present risks to human health and the wider ecology of our water bodies

The Urban Wastewater Treatment (England and Wales) Regulations 1994 aim to protect the environment from the adverse effects of untreated urban wastewater. The main requirements of the regulations are:

• the establishment of systems to collect wastewater from urban ‘agglomerations’ (towns and cities)
• the secondary treatment of collected wastewater
• the identification of sensitive areas (for example, areas susceptible to eutrophication)
• more stringent treatment of wastewater discharged to sensitive areas

The regulations implement the European Union Urban Wastewater Treatment Directive (91/271/EEC). This publication fulfils the requirement under section 12A of the regulations to regularly publish a situation report on the treatment of urban wastewater, disposal of sludge in Wales, reasons for non-compliance and proposed measures to achieve compliance.

Treatment of urban wastewater

In 2022, 99.6% of Wales’s generated load from wastewater treatment works (WWTW) was compliant with the Urban Wastewater Treatment Regulations (UWWTR).

There were 113 agglomerations generating more than 2,000 population equivalent (PE) of wastewater:

• 109 agglomerations, generating 3,519,711 PE of wastewater, complied with the requirements of the regulations
• 2 agglomerations, generating 15,054 PE of wastewater, did not comply with the requirements of the regulations

For the 113 agglomerations generating more than 2,000 PE of wastewater, there were 113 urban wastewater treatment plants with a total design capacity of 3,534,765 PE:

• 113 plants were equipped with technology for primary and secondary treatment
• 41 plants were equipped with technology for more stringent treatment than secondary treatment
• 99.6% of the collected wastewater load was compliant with secondary treatment requirements
• 99.1% of the collected wastewater load was compliant with more stringent treatment requirements

100% of wastewater load was confirmed connected to a collecting system or to individual and appropriate systems.

Disposal of sludge

In 2022, water companies produced 37,084 tonnes of sludge. 100% of sludge was reused for soil and agriculture in Wales.

Reasons for non-compliance & proposed measures to achieve compliance

In 2022, 2 wastewater treatment plants were non-compliant. Rhuddlan WWTW had a biochemical oxygen demand (BOD) sampling shortfall and a non-compliant UWWTR upper tier chemical oxygen demand (COD) limit. The monitoring programme was reviewed and amended to ensure an even spread of BOD sampling throughout the year. The COD failure was caused by a blocked bell mouth. A high turbidity telemetry alarm triggered operator attendance. Amroth consistently exceeds 2000 PE but UWWT permit conditions were not applied for and no UWWT samples were supplied. Both these plants became compliant in 2023.

Population equivalent

The unit of measure used in the Urban Wastewater Treatment Directive for assessing the polluting potential of wastewater discharges. 1 population equivalent (PE) means the organic biodegradable load having a 5-day biochemical oxygen demand (BOD5) of 60g of oxygen per day. This means the oxygen used, largely by bacterial organisms, in breaking down the organic matter in wastewater.

Agglomerations

An agglomeration is an area where the population and/or economic activities are sufficiently concentrated for their wastewater to be collected and conducted to a wastewater treatment plant or to a final discharge point.

Eutrophication

Eutrophication means the enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned.