The performance of a Multi-Stage Hybrid Reactor to treat real wastewater: Benzophenone and Diethyl Phthalate removal

Abstract

One of the consequences of the increasing diversity of new chemical compounds used in industrialized products is the release of these compounds as micropollutants (MPs) in the environment around the world, particularly in aqueous matrices. Benzophenone (BP) and Diethyl Phthalate (DEP), two MPs of environmental concern due to their potential toxicity are widely used and found with considerable concentrations mostly in wastewaters. Information about the efficiency of biological treatment in removing DEP from the wastewater is scarce and until recently, there was no information on the removal of BP. Due to the risks these substances pose to the human and environmental health there is a worldwide demand for the improvement of biological treatment plants with focus on the removal of these and other MPs, since conventional Wastewater Treatment Plants (WWTP) have very limited capacity to remove them and advanced treatment steps (e.g.: ozonation, photocatalysis, ultrafiltration.) increases substantially the treatment costs. A promising biological treatment approach for the removal of MPs combines fixed and suspended biomasses in the same reactor (hybrid reactors) and includes multiple compartments with different redox conditions. The objective of this study was to assess the performance of a new Multi-Stage Hybrid Reactor, focusing on the removal of Benzophenone (BP) and Diethylphthalate (DEP). The pilot system has seven units (anaerobic, anoxic 1, aerobic, anoxic 2, re-aeration and 2 sedimentation tanks) and it was installed at a large Municipal WWTP in Rio to treat real domestic wastewater. The total volume was 400 L and 50% of the aerobic tank (120 L) was filled with carriers (support media). The reactor’s efficiency was evaluated during two periods: (a) one with predominantly suspended biomass and (b) another one with predominantly fixed biomass in the aerobic tank. The highly variable composition of the affluent, affecting the organic load, caused fluctuations in the treatment performance. Even though, multi-stage hybrid bioreactor was able to remove up to 69.6% of BP and up to 74.5% of DEP, being the highest removal efficiencies achieved during the period when the aerobic tank had predominantly fixed biomass.