Performance evaluation of an activated sludge system for removing petroleum hydrocarbons from oilfield produced water

Abstract

During crude oil and natural gas exploration and production, large volumes of petroleum hydrocarbon containing ‘produced water’ are concurrently recovered. Produced water is the largest volume waste stream in the exploration and production processes of oil and gas. During onshore oil recovery, the petroleum hydrocarbon/water mixture is processed through various separation units where the water extract is either discharged into above ground storage facilities, or re-injected into a subsurface formation as a permanent disposal/secondary recovery process. In offshore or coastal oil recovery operations, produced water is either discharged through shore side outfalls or coastal rim releases (within 4 miles from shore). In many cases, current disposal practices such as these have caused severe environmental petroleum hydrocarbon contamination to surface, ground and coastal waterways. Therefore, a research project was conducted to evaluate the performance of a field (continuous-flow) activated sludge treatment system for removing petroleum hydrocarbons from Southwestern US oilfield generated produced water. Petroleum hydrocarbon removal efficiencies were determined using gas chromatography/mass spectrometry (GC/MS) and total petroleum hydrocarbon (TPH) analysis. The activated sludge treatment unit maintained a TPH removal efficiency of 98–99% at a solids retention time (SRT) of 20 days and a mixed liquor suspended solids concentration (MLSS) of 730 mg/l. Incurred energy costs were $0.17 per barrel (or $0.004 per gallon) of produced water treated.