The main objective of the study was to define the interaction between the solid retention time (SRT) and the contaminant loading rate on a membrane bioreactor's efficacy in removing contaminants frequently detected (chemical oxygen demand (COD), NH4+, total phosphorus and metals) above the discharge criteria in waste-originating leachates. The rates and coefficient calculated from this study's experimental data can be used for the design of membrane bioreactor treating wastewaters, even beyond the scope of this experiment. Over a period of 152 days, SRTs of 28 and 47 days and HRTs of 13, 25, 36 and 52 h were studied using a real leachate with a constant composition. Results showed that membrane bioreactors can efficiently treat >1850 mg COD L-1 d-1 of highly to moderately biodegradable COD, with the SRT having no significant impact on the removal of recalcitrant COD. Overall ammonium removal rates of >740 mg NH4-N L-1 d-1 can be achieved as long as a residual alkalinity of 200 mg CaCO3 L-1 and an adequate dissolved oxygen concentration (6-7 mg L-1) are both maintained. Overall phosphorus removal rates are independent of the phosphorus loading rate. However, the highest overall phosphorus removal rate (39 ± 2 mg P per g of total suspended solids) was obtained at the lowest SRT (28 days) due to an increased extracellular polymeric substance production. Finally, membrane bioreactor's metal removal capacity is mostly dependent on the metals' affinity to both the leachate's recalcitrant COD as well as sludge concentrations.
Keywords: Extracellular polymeric substances; Leachate treatment; Membrane bioreactor; Nitrification; Process design.
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