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

The biological anaerobic-aerobic treatment of medium-strength municipal lan dfill leachate (COD (chemical oxygen demand) 1500 to 3200 mg l(-1); BOD7 (b iological oxygen demand) 1200 to 1900 mg l(-1); NH4-N 80 to 270 mg l(-1)) w as studied by using a pilot-scale Upflow Anaerobic Sludge Blanket (UASB) re actor (13 to 28 degrees C) and laboratory-scale activated sludge reactors ( 5 to 11 degrees C). In the sequential process, 80 to 90% COD removal was ac hieved 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 degrees C. The aerobic st age served as an ammonium removal and a polishing step. More than 90% of am monium was efficiently removed by nitrification even at 5 degrees C. The an aerobic-aerobic treatment produced effluent fulfilling the official require ments. Furthermore, the sequential process seems sustainable and cost effec tive for leachate treatment at low temperatures. Based on a preliminary des ign, 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 opera tional costs of a transfer sewer are considered.