ANAEROBIC TREATMENT OF PETROCHEMICAL WASTE FOR DETOXIFICATION AND SOLIDS REDUCTION

Lab scale studies were conducted to test the anaerobic digestibility of two waste streams acquired from a petrochemical refinery. The waste streams comprised of a float from the dissolved air flotation (DAF) unit and a waste activated sludge (WAS) from the biological treatment unit. Three semi continuous anaerobic digesters (AD) were fed with DAF, WAS and a combination of the two as substrates. Batch bioassays were used as a preliminary tool to determine the toxicity profiles and the biodegradability of the feeds. Out of the three combinations in AD, mono digestion of WAS yielded the highest gas production whereas feeds with portions of DAF showed inhibition in the overall process. Pretreatment of the feeds through ozonation was utilized in the latter phase of the study that exhibited a marked improvement in the mono digestion of DAF when the hydraulic retention time (HRT) was doubled. Both the solids destruction and the biogas recovery increased to 49% and 106 Lbiogas/kgVS respectively. Ozonized WAS saw solids destruction increase by 20% and the biogas recovery was more than double. Whereas ozonized co-digestion led to formation of an emulsified layer which further affected the overall performance and yielded lower biogas. However, pretreatment of influents containing portions of DAF saw substantial removal of volatile organic compounds (VOC) and semi volatile organics (SVOC) going into the lab scale digesters.M.S. in Environmental Engineering, July 201