Biodegradation of Naphthalene, Benzene, Toluene, Ethyl Benzene, and Xylene in Batch and Membrane Bioreactors

Produced water is the liquid waste that is generated during coal bed methane and oil explorations. Treatment and management of produced water pose a great challenge to the sustainable operation of oil, gas, and coal bed methane operations. Proper treatment of produced water leading to its reuse can provide a sustainable water management strategy for produced water. Presence of polyaromatic hydrocarbons and benzene, toluene, ethyl benzene, and xylene (BTEX) compounds in produced water is of particular concern because these contaminants are recalcitrant and slow to degrade. In this article, we report the results of biological treatment of these compounds in laboratory-scale batch and membrane bioreactors. Naphthalene was considered a model compound to represent polyaromatic hydrocarbons. The strategy employed involves the enrichment of bacteria capable of degrading naphthalene and BTEX in separate batch reactors and study of their degradation kinetics. A membrane bioreactor was initiated with seed from the enriched batch reactors. In all biodegradation experiments, glucose was also used to simulate the presence of easily biodegradable organics that are generally present in the produced water. Results indicate that the removal efficiencies of naphthalene and BTEX were more than 95% with initial concentrations of about 10mg/L in batch reactors. Kinetic coefficients of biodegradation were determined assuming pseudo-first-order kinetics. Naphthalene showed the greatest degradation kinetics. Cloning and sequencing results revealed the enrichment of Pseudomonas-related organisms in naphthalene-fed batch reactor, whereas Bdellovibrio-, Propionibacteriaceae-, Stenotrophomonas-, and Wolinella-related organisms were enriched in the BTEX-fed reactor. Naphthalene and BTEX were undetected in the final effluent of the membrane bioreactor. The membrane bioreactor also showed more than 90% COD removal consistently and enabled good effluent quality in terms of solids removal.