Improving Organic Reduction and Overcoming Challenges of a Membrane Bioreactor (MBR) Treating Wastewater from Plastic Production

The Chesapeake Bay Watershed Initiative (CBWI) of 2010 required many wastewater treatment plants discharging to affected waterways to meet progressively lower effluent contaminant levels. While the initiative’s impact was felt most profoundly by municipal plants that now had to meet lower nutrient limits, it also affected many of the area’s industrial dischargers. One such industry – the world’s leading producer of polyester films – produces polyethylene terephthalate (PET) at its Chester, VA facility. During the manufacturing process, the plant produces 0.03 – 0.055 MGD of wastewater, which is treated on-site and discharged to an internal outfall. When tighter limits were imposed on the amount of 5-day biological oxygen demand (BOD5) in the discharge, plant management realized they would have to modify the original treatment scheme – aeration basins, clarifiers, and sand filters – in order to comply with the new requirement. They looked at four options that involved adding basins, filters, and/or membranes to their existing system and one option that entailed converting the system to a membrane bioreactor (MBR). Because the MBR option would provide a positive barrier to suspended solids (including insoluble BOD5) and wouldn’t require additional space or concrete, they chose to go with this alternative. Two systems were piloted, and the successful system – the Aqua-Aerobic MBR – was purchased, installed, and placed on-line in July of 2014. The system ran extremely well for about 6 months, at which time trans-membrane pressures (TMPs) started to climb and the flow through the membranes gradually stopped. Through extensive investigation and troubleshooting, it was determined that the cause was a specific extracellular polymeric substance (EPS), either created in the bioreactor by stressed microorganisms or accidentally/inadvertently placed in the wastewater stream. This paper describes the membrane pilot and full-scale systems, details the membrane fouling and troubleshooting sequences, and explains the system recovery and lessons learned.

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