Wehrle Environmental was contracted by SITA to design and install a treatment system for landfill leachate at their Beacon Hill landfill site near Poole, Dorset. The site has strict leachate quality requirements with licence conditions set at 625 mg/l COD.
SITA operate under a comprehensive ISO 14001 environmental management system and has also adopted its own internal quality environmental monitoring system (QEMS), which demands that higher standards of treatment are achieved than the minimum regulatory requirements.
Wehrle designed and constructed a compact, low maintenance mobile process solution to ensure a sustainable effluent production. It was the first combined membrane bioreactor (MBR) and nanofiltration (NF) leachate treatment system to be used at a landfill site in the UK.
The system receives an average of 60m3/day of leachate at a balance tank, allowing three days storage. Leachate is pumped to three 40m3 biological tanks in series, passing through 800µm stainless steel basket strainers.
Optimal biological nitrification is ensured in the bioreactor tanks by continuous pH control using caustic dosing, and the maintenance of a 100:5:1 C:N:P ratio through the addition of phosphoric acid.
Aeration in each bioreactor operates at a high biomass concentration of 16-20g/l. Continuous dissolved oxygen monitoring allows automatic adjustment of the oxygen feed to maintain treatment whilst minimising power consumption.
Aerated effluent is then transferred a pre-assembled and pre-tested ultrafiltration (UF) system that is housed in a 40' ISO container. A dedicated stainless steel pump effects transfer through three cross-flow tubular membrane modules arranged in series.
The MBR effluent is then polished to meet the requirements set at the site using NF technology. The effluent feed is pressurised before being transferred to two spirally wound NF membrane units. NF reduces divalent ion concentrations, and removes residual organic substances and ultra-fine solids to reduce COD.