Improvement of an Industrial Wastewater Treatment System at a Former Viscose Rayon Plant – Results from Two-Stage Biological Leachate Treatability Testing

Leachate is currently being pumped from three surface impoundments filled with waste material from the production of viscose rayon at the former Avtex Fibers plant. The primary objective of this study was to optimize a two-stage biological treatment process that has the potential to effectively treat a wastewater stream containing high levels of reduced sulfur compounds while also removing organic contaminants. Future remediation activities at the Avtex Fibers Superfund Site warrant the improved performance of the onsite system to more stably treat the leachate for future direct discharge to a surface water receiving stream. A two-stage treatment system used to treat the leachate was comprised of a moving bed biofilm reactor as the first stage for sulfide oxidation with a sequencing batch reactor (SBR) and membrane bioreactor (MBR) operating in parallel as the second stage for COD removal. A moving bed biofilm reactor (MBBR) was chosen for the first stage based on results from an earlier study which was a comparison of different biological processes to treat the leachate. The previous study showed that the MBBR, which is a hybrid attached growth system, was more stable under variable loading rates and conditions and was used in this study to treat the reduced sulfur compounds in the influent. Liquid phase characteristics and gas phase emissions were measured to evaluate mass balance of sulfide and COD in the system. Under steady state conditions sulfide was found to be nearly completely oxidized with less that 0.3% of the influent sulfide remaining in the MBBR effluent and less than 0.1% in the gas phase. The MBR removed COD at 85%, somewhat more effectively than the SBR at 73%. This was likely due to high effluent suspended solids from the SBR as compared to the MBR. Problems associated with high pH and poor biomass flocculation in the SBR may have contributed to the lower COD removal observed. The current BOD5 discharge permit of 30 mg/L was met by the MBR, but the high TSS in the SBR effluent resulted in elevated BOD measurements. Work is continuing with an intermediate pH adjustment step between the two phases of biological treatment.