Landfill leachate treatment with sequencing batch reactor and membrane bioreactor

Landfill leachate from a composting field of a Finnish municipal waste landfill was treated with sequencing batch reactor (SBR) and a submerged membrane bioreactor (MBR) fed batchwise. The average quality of the leachate was 475 mg/l suspended solids, 1240 mg/l BOD7, 10 mg/l phosphorus, and 210 mg/l ammonium nitrogen. Hydraulic retention times in SBR varied from four to nine days and in MBR from two to five days. Solids retention times in SBR were from 10 to 40 days and in MBR from 35 to over 60 days. The sludge concentration in SBR varied from 6.6 to 10 g/l and in MBR from 7.3 to 9.3 g/l in normal conditions. In SBR, suspended solids concentration in effluent was up to 89% smaller than influent suspended solids concentration. However, sometimes bulking reduced the efficiency. The preliminary results with MBR start-up showed that it is free from bulking problems and compared to feed concentration the retention was over 99% of suspended solids. It also increased the retentions of both BOD7 and ammonium nitrogen to >97% and reduced variations. Phosphorus retention was >88%.