The Environment Agency has decided to vary the Permit for Wanlip Sewage Treatment Works (STW) operated by Severn Trent Water, as a result of an application made by the water company.
The application is one of eight submitted by Severn Trent Water to update their Permits - the water company has applied for all eight sites to increase their permitted quantities of waste processed via anaerobic digestion (AD).
The AD plant is co-located at Wanlip STW where Severn Trent also carries out treatment of effluent received via the sewerage network under the Urban Waste Water Treatment Directive. UWWTD-derived sludge from the STW is also treated in the AD plant via co-digestion.
The original AD plant Permit for Wanlip was issued in 1994 and the original combined heat and power (CHP) Permit in 2007.
The new permit only relates to the treatment of imported tankered waste including UWWTD derived sludge from other sewage treatment works , either owned by Severn Trent or from third party plants. The anaerobic digestion of UWWTD-derived sludge from Wanlip STW itself does not form part of the permit. The permit, which only covers the import of the waste not the subsequent treatment.
The Environment Agency decision document says the changes will allow for greater business flexibility and allow the utility to divert imported tankered waste to the most appropriate site for treatment.
The Industrial Emissions Directive increased the number of activities that require an Installations permit. These are predominantly regulated as “waste operations” and include biowaste treatment – recovery and/or disposal and independently operated wastewater treatment works serving industrial activities subject to the Directive.
The permit issued is a result of ongoing discussions between Severn Trent and the Environment Agency – the water company has proposed to categorise European Waste Catalogue (EWC codes) into three groups of lower, medium and higher risk which they deemed to be reflective of the risk of the waste stream.
All anaerobic digestion plant operators are required by the Environment Agency to produce an odour management plan (OMP). The Wanlip site does not currently have an OMP - an improvement condition has been added to the permit for one to be submitted. In addition, no drainage plan currently exists for the site. The Agency has also added an improvement condition to obtain one. The completion date has been set so that Severn Trent has time to coordinate drainage plan reviews across the eight sites.
Severn Trent has waste acceptance procedures in place and uses various testing methods to ensure that the waste streams are suitable to be added to the anaerobic digestion treatment process. Only when it is confident that the imported wastes will not have a detrimental impact on the biological treatment process will they be added to the digesters.
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