Volatile organic compounds (VOCs), such as BTEX methanol and other non-phase separable hydrocarbons may be removed from wastewater obtained from oil or gas exploration or production operations by way of a bioreactor. The bioreactor may employ anaerobic microorganisms that metabolize various VOCs. In some embodiments, such a bioreactor may be configured to treat process flow rates of thousands of barrels of wastewater per hour. Such a bioreactor may comprise a large vessel at a larger water treatment site.