WASTEWATER TREATMENT OF A BATCH CHEMICAL PLANT EFFLUENT WITH A MEMBRANE BIOLOGICAL REACTOR

The objective of this project was to evaluate the robustness of an aerobic Membrane Biological Reactor (MBR) to fluctuations in wastewater composition from a batch chemical manufacturing plant. Actual plant wastewater was used for a portion of the test program while synthetic wastewater was used for the balance. Both were spiked with a representative mixture of eight compounds to achieve a total organic carbon (TOC) concentration in excess of 1,000 mg/L. The fluctuations included methanol and acetone spikes, tetrahydrofuran (THF) and toluene deletions with add-backs, cold weather operation, short duration (one week) cessation of feed, and overload conditions. The program lasted for 112 days with two lab-pilot MBR systems operating in parallel. The testing confirmed that the design basis used to size equipment and components was sufficient to withstand expected perturbations in wastewater composition while producing an effluent of suitable quality to meet discharge limitations.Reactor A experienced one methanol spike (2X baseline dose) and two acetone spikes (2X and 4X baseline dose). The effluent quality remained within discharge limits during and after each spike. The reactor also experienced a cessation of feed flow for one week followed by a full flow re-start, which did not affect effluent quality. Lastly, operation with spiked plant wastewater for 4.5 weeks showed similar performance to the synthetic water used during the earlier portion of the test. Reactor B experienced two deletions, one for THF and the other for toluene. One week after the THF had been added back to the feed, the effluent showed an elevated TOC concentration, but did not exceed discharge limits during this period. The performance of Reactor B at 12 degrees Centigrade with spiked plant water was poorer than during the ambient operation, but the effluent quality was sufficient to meet discharge limits during this period. A two-stage liquid-phase granular activated carbon (LGAC) system was set up to evaluate carbon polishing of the MBR effluent. A reduction in TOC was measured across the first stage with no additional reduction across the second stage. The only compound that showed signs of break-through was acetone, which was not expected to be removed by LGAC.Respirometry experiments were conducted to assay the impact of various compounds on the microbial activity in the MBR. These experiments showed that activity towards THF can be recovered after a period when no THF was present in the MBR feed. The addition of other organics and salts was evaluated, with most showing no impact on biological activity. A high concentration of Alconox, a cleaning agent, did have a negative impact on activity.