In 2003, Cleanaway decided to investigate treatment options available to reduce ammonia concentrations in the leachate that is discharged from Ockendon landfill site to the sewer and subsequently treated at the local water company’s wastewater treatment works.
The local water company restricted the concentration of ammonia that could be received into the sewer system from the Ockendon site to 100kg/day in order to meet stringent Environment Agency consents for release of ammonia from treatment systems.
Based on an average leachate production of 135m3/day, the ammonia loading restriction imposed by the water company equated to an average permissible concentration of 750mg/l. The ammonia concentrations were known to fluctuate up to 1100mg/l in the leachate, making it impossible for Cleanaway to send all their leachate for remote treatment.
To resolve this problem, Cleanaway selected Wehrle Environmental as one of two companies to undertake pilot trials to determine the treatment process required.
Using one of their advanced pilot test systems, Wehrle undertook a detailed investigation of the flow variations and composition of the leachate. After running pilot trials with various membrane types (from a range of suppliers) and configurations at Ockendon, they concluded that the most cost-effective solution was to treat the leachate using MBR technology that incoporated a specific ultrafiltration (UF) membrane selected to facilitate removal of COD and ammonia.
During the three-month evaluation, Wehrle were also able to make a detailed assessment of specific site conditions, which included a restricted footprint and a 3m height constraint.
Based on their pilot evaluation, Wehrle proposed a cost-effective and efficient membrane solution that would enable the Cleanaway to reduce significantly the ammonia loading of the leachate to well below the consent levels.
The order for the system was awarded to Wehrle Environmental in early 2006, and the plant officially opened in October 2006. The leachate treatment system was the first of its kind to be operational in the UK.
To meet space constraints, the membrane component of the system was supplied fully assembled and pre-tested in an adapted 40' ISO container.
Special concrete tanks were provided to meet strict Environment Agency requirements and the biological treatment tank was constructed with 70% of the capacity below ground level in order to meet planning height restrictions.