Evaluation of sequencing batch bioreactor followed by media filtration for organic carbon and nitrogen removal in produced water

Abstract

Produced water contains high concentrations of total dissolved solids (TDS), metals, and organic matter. In areas of high water stress, beneficial reuse of produced water needs to be considered. This study evaluates the treatment capabilities, efficiency, and limitations of a sequencing batch reactor (SBR) to remove organic material and nutrients from produced water. SBRs have been used to facilitate biological organic and nutrient removal from municipal and industrial waste streams. Although the bacteria responsible for the treatment of municipal and most industrial wastewaters cannot tolerate the high TDS concentrations in produced water, the microorganisms native to produced water have the capacity to treat produced water. In a bench scale bioreactor test using produced water from the Denver-Julesburg Basin, the produced water was determined to be nutrient limited with respect to phosphorus. By adding a phosphorus supplement, soluble chemical oxygen demand (COD) removal was increased by over 20 % and ammonia removal increased by approximately 40 %. Various supplements, including KH2PO4, centrate from an anaerobic digester, and activated sludge from a municipal SBR, were added to the bioreactors to determine which of them was more effective. A pilot scale SBR followed by media filtration was used to evaluate the effects of operating conditions on produced water treatment. The hydraulic residence time ranged from 1.67 to 8.3 days during various phases of operation, with no measured effect on treatment performance. Adding 7.5 mg-P/L of KH2PO4 as a phosphorus supplement had the most significant effect on treatment performance of the system. The majority of COD removal switched locations from the filter columns to the bioreactors. Comparing total organic carbon to COD, the biologically available portion of COD appears to be treated in the SBR while recalcitrant carbon and inorganic material may need to be removed via physical or chemical methods.