Biological treatment for removal of organic material and ammonium from leachate at low temperatures

The biological anaerobic-aerobic treatment of medium-strength municipal landfill leachate (COD (chemical oxygen demand) 1500 to 3200 mg l^-1; BOD₇ (biological oxygen demand) 1200 to 1900 mg l^-1; NH₄-N 80 to 270 mg l^-1) was studied by using a pilot-scale Upflow Anaerobic Sludge Blanket (UASB) reactor (13 to 28°C) and laboratory-scale activated sludge reactors (5 to 11°C). In the sequential process, 80 to 90 COD removal was achieved with an effluent COD of 250 to 350 mg l^-1 and a BOD₇ of < 10 mg l^-1. Most of the organic material was removed during anaerobic pretreatment, and more than 50 COD removal was obtained at 13°C. The aerobic stage served as an ammonium removal and a polishing step. More than 90 of ammonium was efficiently removed by nitrification even at 5°C. The anaerobic-aerobic treatment produced effluent fulfilling the official requirements. Furthermore, the sequential process seems sustainable and cost effective for leachate treatment at low temperatures. Based on a preliminary design, leachate treatment costs were estimated at 3.1 to 3.3 EUR m^-3 in the sequential process. This compares with the option of discharging leachates into a sewer system. Both the discharge fee and the construction and operational costs of a transfer sewer are considered.