TREATMENT OF PRODUCED WATER WITH A MEMBRANE BIOREACTOR

摘要

The oil and gas industry in the United States generates more than three billion tons ofrnwastewater annually. This ‘produced water’ is characterized by saline water containing arnvariety of pollutants, including water soluble and immiscible organics as well as manyrninorganic species. Several of the dissolved contaminants, namely benzene, toluene,rnethylbenzene, and xylenes (BTEX), are known to be hazardous at low concentrations.rnAlthough most produced water is disposed of via re-injection, the remaining amounts that arerndischarged on the surface are significant. In order to reuse produced water, removal of bothrnthe inorganic dissolved solids and BTEX is necessary. Reverse osmosis (RO) membranernfiltration is a promising treatment option, especially for inorganics, but fouling of thernmembranes, due to the organic content in produced water could result in marked reductionsrnin the flux rates. Therefore, pre-treatment is generally required for cost-effective operation.rnThe focus of the current research was, therefore, to evaluate the effectiveness of a membranernbioreactor (MBR) to simultaneously remove both organic acids and hazardous BTEXrnconstituents from produced water.rnThe laboratory scale MBR was operated at a 9.6 hr hydraulic residence time with a 10 L/minrnaeration rate to treat synthetic produced water containing 430 mg/L of organic acids andrn10.25 g/L of inorganic ions which are representative of saline produced water. Resultsrnindicate that the MBR system degraded 92% of the organic acids (100% acetate and 85%rnmalonate) in synthetic produced water. The biomass levels (MLVSS) that developed in thernMBR system treating high-TDS produced water (1.0 g/L) were lower than those thatrndeveloped in an identical MBR system treating a low-TDS water (4.5 g/L). This resultrnsuggests that the produced water may minimize the rate of biofouling that occurs on thernmembrane. Though inorganic precipitates did clog the membrane system, controlling the pHrnof the water was found to minimize this problem as well. When BTEX was simultaneouslyrnintroduced into the MBR system (1800 mg/day) with organic acids, 80% overall removal viarnbiodegradation was observed. During this period, organic acid removal was maintained atrnthe previously high levels and was not affected by the addition of BTEX. These resultsrnsuggest that simultaneous bio-degradation of both BTEX constituents and organic acidsrnfound in produced water may be possible.