Optimization of an Industrial Wastewater Treatment Plant through Implementation of a Membrane Bioreactor and Reverse Osmosis System for Reuse

Stone Brew Co. in Escondido, California, built a brand new brewing facility with a simple wastewater treatment system adjacent to a restaurant and one acre beer garden in 2005. After some significant production growth, the City threatened to significantly increase the water rate to be able to accommodate the higher organic strength and solids content in the water. This resulted in the installation of an aeration tank to meet biochemical oxygen demand (BOD) limits and a dissolved air flotation (DAF) unit to meet total suspended solids (TSS) limits in 2008. By doing this, the City agreed to leave the water rate at the existing value. Typical influent water quality to the WWTP was 12,000 mg COD/L, 7300 mg TSS/L at a pH of 5.4. The issues with running an industrial WWTP with a rudimentary design quickly became apparent. Due to the degree of difficulty in treating the brewery wastewater, which consists mostly of sugars, proteins, carbohydrates and yeast, the DAF was not able to achieve sufficient solids removal or facilitate consistent BOD removal required to meet the local limitations. Issues included excessive process control problems such as the need to haul away sludge that could not be separated by the DAF unit, foaming events and overflows, high chemical consumption, multiple mechanical failures and trouble with sludge dewatering. These factors caused breaches in water quality restrictions, costly repairs and time consuming labor. Since the WWTP was on-site next to a restaurant and outdoor beer garden, there were also concerns with the unpleasant odors created from poor biological performance and sludge handling becoming visible to customers. After a little over a year of operation with the problem-riddled system, the plant decided it would be advantageous to change the treatment scheme to something better suited for their particular wastewater. The decision to replace the DAF with a membrane bioreactor (MBR) system was mainly motivated by the guarantee in TSS removal via membrane filtration. Other reasons included enhanced BOD removal and the possibility to reuse the effluent water within the plant. The MBR system was commissioned in January 2010 and was designed to process 60,000 gpd. It utilized two HYDRAsub-MBR HSM500 modules, each containing 500 m of surface area. Upon stabilization of the system, various benefits of the MBR were soon realized. First of all, TSS in the effluent was drastically reduced and COD removal was greatly improved. Process control was enhanced so that all activated sludge could be treated and recycled back to the aeration tank, not hauled away. The simplistic and almost fully automatic operation of the system resulted in low maintenance and labor time compared to the DAF. The chemical usage and cost for separating solids and sludge dewatering decreased significantly. Finally, as soon as the MBR system was stabilized, a reverse osmosis (RO) system was commissioned to further treat the effluent for reuse purposes. The installation of a RO system allowed the plant to reuse 30,000 gpd of reclaimed water within their facility. Prior to commissioning the MBR-RO system, 25,000 gpd was discharged to the sewer. Postcommissioning, 10,00015,000 gpd was discharged to the sewer and no activated sludge was hauled from the facility. The ability to reuse their wastewater combined with reduction in chemical costs and hauling fees saved the company hundreds of thousands of dollars, completely covering the capital cost of the MBR and RO systems in the first year of operation.