Multifunctional in-situ ferrate treatment and its removal mechanisms of membrane bioreactor residual pollutants

Abstract

Membrane bioreactors (MBRs) integrate the technique of membrane separation with biologically activated sludge and produce high-quality effluent that can be used for water reclamation. However, removal of residual pollutants, including phosphorus, non-biodegradable organic matter, and microorganisms, is necessary for water reuse in areas with high human exposure to water, necessitating further water treatment. In this study, ferrate (VI) was used to remove various residual pollutants that can be contained in the MBR effluents, and the removal mechanisms were studied by comparing with ferric chloride (FeCl3). Optimal ferrate production using the in situ wet oxidation method in the synthetic MBR effluent occurred at pH 7.0 and Fe3+:OCl- = 5, with a ferrate yield of 1.8 mg L-1. Based on the results of the jar test, the optimised ferrate dosage was 7.5 mg L-1, which removed 90% of total phosphorus, 20% of dissolved organic matter, and 90% of microorganisms in the real MBR effluent. Ferrate was more effective than FeCl3 even at a lower dosage (~25%). The simultaneous oxidising, coagulating, and disinfecting properties of ferrate are expected to reduce the number of post-treatment steps for water reclamation, thus reducing the capital and operational expenses.