Flat Sheet Membrane Sequencing Batch Bioreactor for the Removal of Coliforms and Heavy Metals from Stabilized Composting Leachate

Abstract

Treatment process selection for compost leachate is required to carry out a pilot study because of the variability and complexity of this liquid’s composition. The main objective of the present study is to evaluate the removal of coliforms and toxic metals from real compost liquids by a flat sheet membrane bioreactor. To meet this aim, after treatment of the compost leachate in a serially connected process (anaerobic mixed baffled reactor plus anaerobic sequencing batch reactor plus sequencing batch reactor), effluent with chemical oxygen demand (COD)=654 mg/L, biological oxygen demand (BOD5)=54 mg/L, and total suspended solids (TSS)=84.5 mg/L was fed to a membrane sequencing batch reactor (MSBR) that was conducted at the laboratory scale. The membrane was used to enhance the quality of the biological reactor effluent by decreasing the number of total coliform (TC) and fecal coliform (FC) bacteria to below 12 and 5 per 1 mL, respectively. Moreover, increasing pH to 9 resulted in a decrease in heavy metal concentrations. The mean values of toxic metals in the membrane filtrate were Cr=.1–.3, Zn=.4–.8, Ni=.5–.55, Cd=.1–.2, and Pb=1–.2 mg/L. In this study, the biological and chemical parameters measured in the stabilized leachate fell significantly below national standard limits for discharge into the environment. Health risk assessment is needed to evaluate the treated permeates’ capability for beneficial reuse.