Performance of an on-site UASB reactor treating leachate at low temperature

A pilot-scale UASB reactor was used to study treatment of municipal landfill leachate (COD 1.5–3.2 g l−1) at low temperatures (13–23°C) and in on-site conditions for 226 days. The reactor was successfully operated by decreasing the process temperature as leachate temperature decreased in winter. Despite changes in leachate quality, 65–75% COD and up to 95% BOD7 removals were achieved at 18–23°C with organic loading rates (OLR) of 2–4 kgCOD m−3 d−1. At 13–14°C, 50–55% COD and 72% BOD7 removals were obtained with OLRs of 1.4–2 kgCOD m−3 d−1. Methane yield averaged 320 mlCH4 g−1 CODremoved. Excessive solids washout was not observed despite low process temperatures. Inorganic material accumulated in the reactor sludge throughout the study. The main precipitants were calcium and iron which, at the end of the run, accounted for 24% and 7% of total solids of the sludge, respectively. The specific methanogenic activity (SMA) of the mesophilic (37°C) inoculum used in the study increased 7 fold at 11°C and 3 fold at 22–24°C during the run. Yet SMA at 11°C (0.05 gCH4-COD gVSS−1 d−1) remained one third of that at 22–24°C.