Application of a membrane sequencing batch reactor for landfill leachate treatment

A bench-scale membrane sequencing batch reactor (MSBR) was used for the treatment of "mature" landfill leachate, originated in the municipal solid waste landfill of Thessaloniki (North Greece). A hollow fiber ultrafiltration membrane module was used for the separation of the biomass from the treated effluent. The average quality of the raw leachate (feed) was 2456 mg/L COD, 375 mg/L total nitrogen (TN) and 8.2 mg/L PO4-P. Hydraulic retention time (HRT) was kept constant at 10 days for most experimental runs whereas the solids retention time (SRT) was practically infinite, as almost no waste sludge removal took place during an overall MSBR operational period of 4 months. The initial concentration of suspended solids in the mixed liquor (MLSS) was 7000 mg/L and it was increased up to 15,300 mg/L. Several operational patterns were investigated in order to obtain maximum organic carbon and nutrients removal. Specific attention was given to the denitrification step. COD removal efficiency was as low as 40% and it was always below 60%. The poor MSBR performance in terms of COD removal was attributed to the high SRT, which had an apparent effect on the activity of the system's drastic biomass. On the other hand, TN removal efficiency was very satisfactory during the most stages of the MSBR operation, reaching a maximum value of 88%. Finally, PO4-P removal efficiency varied between 35 and 45% in the first 50 days of the MSBR operation. The subsequent PO4-P accumulation in the treated effluent was due to the direct addition of KH2PO4/K2HPO4 solutions in the feed leachate, aiming to improve the C:N:P ratio.