Evaluation of a sequencing batch reactor followed by media filtration for organic and nutrient removal from produced water

Abstract

With technological advances such as hydraulic fracturing, the oil and gas industry now has access to petroleum reservoirs that were previously uneconomical to develop. Some of the reservoirs are located in areas that already have scarce water resources due to drought, climate change, or population. Oilfield operations introduce additional water stress and create a highly complex and variable waste stream called produced water. Produced water contains high concentrations of total dissolved solids (TDS), metals, organic matter, and in some cases naturally occurring radioactive material. In areas of high water stress, beneficial reuse of produced water needs to be considered. Sequencing batch reactors (SBR) have been used to facilitate biological organic and nutrient removal from domestic waste streams. Although the bacteria responsible for the treatment of domestic sources cannot tolerate the high TDS concentrations in produced water, the microorganisms native to produced water have the functional potential to treat produced water. In a bench scale bioreactor jar test using produced water from the Denver-Julesburg Basin, the produced water collected 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 tested to see how treatment changed with phosphorous type. 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 on the system. The majority of COD removal switched locations from the filter columns to the bioreactors. Comparing total organic carbon (TOC) to COD, the biologically available portion of COD appears to be treated in the SBR treatment train while recalcitrant carbon and inorganic material may need to be removed via physical or chemical methods.