Reduction in Effluent SS from UASB/EGSB Reactors Treating Beverage Wastewater

Anaerobic treatment technologies are commonly used in treatment of high strength wastewaters. Of the several anaerobic technologies available, granular sludge technologies and filters are generally used for treating high strength wastewaters with low suspended solids concentration, typical of that from beverage bottling companies. The Upflow Anaerobic Sludge Blanket (UASB) and the Enhanced Granular Sludge Bed (EGSB) are two of the most commonly used granular technologies. Several factors, such as pH, temperature, reactor configuration, wastewater characteristics, nutrients, recycle, etc., affect effluent quality from UASB/EGSB reactors. Wastewater characteristics play an important role in the process flow schematic chosen to meet effluent criteria. When treating high strength wastewaters, a portion of the effluent is typically recycled and combined with the reactor influent for beneficial reasons. Typical treatment flow schemes offer several opportunities where the recycle can be combined with the influent. Recycle locations that have been used in the past include the equalization tank, inline or a separate tank. This paper presents a case history highlighting the importance of the location where the recycle stream is combined with the influent wastewater.Wis-Pak Central Inc. (Wis-Pak) owns and operates a beverage bottling facility in Mankato, Minnesota. Wis-Pak retained the services of Triad Engineering Inc. (Triad) to conduct a feasibility study to evaluate wastewater minimization and disposal options at this facility. Pretreatment was deemed viable. The pretreatment system selected consisted of an EGSB reactor followed by an aerobic sequencing batch reactor (SBR) for polishing to meet design COD and SS limits of 300 mg/L and 150 mg/L respectively. The anaerobic system was designed to achieve 89 percent COD reduction with minimal SS reduction. The pretreatment system was designed to achieve 96 percent BOD and 94 percent COD reduction. At the completion of the feasibility study, Wis-Pak retained Triad to implement the pretreatment system under a Design/Build project delivery approach. The pretreatment system consists of an influent pump station, an equalization/conditioning tank, EGSB reactor, SBR, pH adjustment, nutrient feed, and associated equipment. A portion of the anaerobic effluent was recycled back to the equalization/conditioning tank.The pretreatment system was started up and put into operation in December 1996. The overall system performance has been excellent, although high anaerobic effluent SS concentrations inhibited/impaired performance of the SBR. Immediately after startup, steady state monthly average anaerobic effluent SS ranged from a low of 598 mg/L to a high of 1,609 mg/L. Following several months of operation during which anaerobic effluent SS was over 1,000 mg/L, Triad implemented several changes to the flow scheme to modify the location where the recycle stream combined with the influent wastewater. This paper highlights changes made to the system (inline recycle, addition of a rapid mix tank) and briefly discusses the effects of these changes, both theoretically and observed performance through data analysis. These changes resulted in a significant decrease in EGSB effluent SS, thereby improving system performance. Steady state monthly average EGSB effluent SS following the changes ranged from a low of 364 mg/L to a high of 491 mg/L. This represents an anaerobic effluent TSS reduction of nearly 80%.