Characteristics and treatment of leachates from domestic landfills

The main objectives of this study were to develop a useful database for the leachate quality of Hong Kong landfills, and to compare different experimental trials for the treatment of methanogenic-stage sanitary landfill leachate, which is generally characterized by a low chemical oxygen demand (COD) of 3000 mg L(-1) or less. Extensive chemical analysis data of leachate composition generated from 10 landfills in Hong Kong were collected to identify variations in leachate quality. Variations in COD and ammonia-nitrogen (NH3-N) with time revealed that the rate at which Hong Kong landfills become 'methanogenic' is relatively fast. The transition from phase II (where leachates are characterized by high 5-day biochemical oxygen demand values) to phase III (where high organic strength leachates are converted into methane and carbon dioxide) for the landfills in Hong Kong took less than one year. Several leachate indicator parameters were utilized to assess the stabilization of the landfill. Controlled experimental studies using an aerobic biological treatment process (i.e., sequencing batch reactor) were used to examine its treatment efficiency. Retention times of 20 days and 40 days resulted in a removal efficiency of NH3-N in excess of 99%.