Optimization of a Full-Scale Industrial Wastewater Treatment System at a Former Viscose Rayon Plant – Results From Biological Leachate Treatability Testing

Abstract

As a result of stormwater input, leachate currently accumulates in three surface impoundments that were filled with waste materials from the production of viscose rayon. The objective of this study was to optimize a biological treatment system that is currently treating a wastewater stream (leachate) containing high levels of reduced sulfur compounds. Due to future remediation activities, the performance of the onsite biological leachate treatment system must be improved to more stably treat the leachate and eventually treat more concentrated leachate for direct discharge to a surface water receiving stream. The performance of a hybrid attached growth system, a completely-mixed flow-through system, and a complete mix activated sludge system were compared. The hypothesis was that a hybrid attached growth system would more efficiently and stably treat both sulfide and carbonaceous chemical oxygen demand (COD) in the wastewater stream than the current onsite system, which is a completely-mixed flow-through biological process, modeled in the laboratory using a 12.5 L Plexiglas completely-mixed flowthrough reactor (CMFT). The hybrid attached growth system was created by using moving bed biofilm reactor (MBBR) technology in a 12.5 L Plexiglas reactor with 30% by volume fill with media. A complete mix activated sludge (CMAS) process was operated to determine the feasibility of treating the leachate in a typical industrial wastewater system. Results showed that there was no significant difference between the effluent qualities from the hybrid attached growth system and a suspended growth flow-through system when operated at steady-state. However, the MBBR showed significant operational improvements over the CMFT, when operated under variable loading rates and conditions (DO and temperature). Liquid phase characteristics and gas phase emissions were measured to evaluate mass balance of sulfide and COD in the system. For normal operation with the HRT between 18 and 36 hours, sulfide was near completely oxidized in the reactors, with less than 2% of the influent sulfide level remaining in the effluent and less than 0.05% of influent sulfide in the gas emissions. Under steady-state conditions, removal of COD was 73±9% in both reactors, and 40-50% of the carbonaceous COD (cCOD) was removed.