Repeated fed-batch biological treatment of pre-treated landfill leachate by powdered activated carbon addition

High chemical oxygen demand (COD), high ammonium-N content and presence of toxic compounds such as heavy metals result in low removal efficiencies in direct biological treatment of landfill leachate. Raw landfill leachate was subjected to pre-treatment by coagulation-flocculation and air stripping of ammonia before biological treatment. Pre-treated leachate was subjected to biological treatment in an aeration tank operated in repeated fed-batch mode in the absence and presence of powdered activated carbon (PAC) as adsorbent. Three different cycles of 1×30 h, 3×10 h, and 5×6 h were used in the absence and presence of 2 g l−1 PAC. The results clearly indicated that PAC addition has improved COD removal significantly as compared to PAC-free biological treatment. Repeated fed-batch treatment also resulted in lower effluent COD and higher COD removal efficiencies as compared to single-cycle operation. The feed COD of 7000 mg l−1 was reduced to final COD values of 365 mg l−1 and 875 mg l−1 in repeated fed-batch experiments with 5×6 h cycles in the presence (2 g l−1 PAC) and absence of PAC, respectively. Repeated fed-batch operation with 3×30 h cycle length resulted in percent COD removal and final COD content of 94% and 285 mg l−1, respectively, with 2 g l−1 PAC addition.