Effect of organic loading rate on the performance of modified anaerobic baffled reactor treating landfill leachate containing heavy metals

Abstract Increasing population, urbanization and changing lifestyle has led to enormous generation of municipal solid waste which is ultimately disposed in sanitary landfills leading to the problem of leachate pollution. Leachate needs to be treated with an effective method before its disposal. Among various options available the treatment using anaerobic technology is preferred in this study. The performance of a modified anaerobic baffled reactor (MABR) treating landfill leachate containing heavy metals at different organic loading rates (OLRs) was investigated in this study. The MABR was seeded with granular sludge taken from an anaerobic digester and fed gradually with landfill leachate at OLRs of 1.4, 1.86, 2.8 and 5.6 kgCOD/m3/d at hydraulic retention time (HRT) of 4,3,2 and 1d, respectively. Experimental results revealed that 76% chemical oxygen demand (COD) removal was achieved at the OLR of 1.4 kgCOD/m3·d. However, when the OLR was increased to 5.6 kgCOD/m3/d, a minor decrease in the COD removal efficiency (70%) was observed. Heavy metals such as arsenic (As), Chromium (Cr), Iron (Fe) and color removal values decreased from 88%, 89%, 88%, and 78% to 8%, 59%,64%, and 37% respectively. Overall Biogas production showed the increasing trend from 0.1, 0.15, 0.32 and 0.4 L/d at OLRs of 1.4, 1.86 and 2.8 and 5.6 kg COD/m3/d, respectively. There was no significant difference in the pH profiles (8.0–8.6) and volatile acids (VA) during the variation of OLRs (1.4–5.6 kgCOD/m3/d). The VA concentration in the effluent (CH4) of the reactor was in the range of 37 to 57 mg/L HOAC, indicating the fatty acids were utilized by the microorganisms. Toxicity caused by heavy metals in the bioreactors is one of the problems of concern in the treatment of wastewaters. This study evaluated the performance of MABR in the treatment of landfill leachate containing arsenic (As), Chromium (Cr), Iron (Fe) and the production of biogas by varying the hydraulic retention time (HRT) and subsequently, organic loading rate (OLR). The study reveals that MABR system can be used efficiently in the treatment of landfill leachate.