| Oily wastewater refers to various types of industrial wastewater released from industrial processes containing medium-to-high content of oil and other chemicals and solids, such as COD, petroleum organic, volatile phenol, sulfide, ammonia nitrogen, suspended solids, and sulfide. Examples of oily wastewater include produced water, barge/bilge water, machining coolant, washwater with degreaser, lubricant manufacturing wastewater, and oily wastewater from petroleum refinery and petrochemical plants. Conventionally, the wastewater treatment unit has primary and secondary steps that can guarantee compliance with legal and regulatory requirements to discharge into the receiving environmental receptors. Over the past decade, industrial wastewater recycling and reuse, particularly for large water consumption industry like refinery and petrochemical plants, has become a main goal for industrial sectors, not only because more stringent discharge standards are in force, but also in-plant recycling can be especially beneficial for industries competing with municipal, agricultural or other, more essential for industrial users to purchase fresh water. This has led to a pressing need of advanced wastewater treatment technologies. In this study, an integrated process composed of hydrolysis acidification and submerged MBR with PTFE (Polytetrafluorothylene) membrane was designed and utilized to treat oily wastewater. The process was optimized by changing system conditions and control factors.The removal of COD, NH3-N, petroleum pollutant, volatile phenol, and turbidity was investigated under different HRTs and OLRs through the different experiment runs. The results show that a promising treatment performance has been achieved with the treated effluent meeting Class I National Discharge Standard for Industrial Wastewater. Both the hydrolysis acidification process and MBR have played essential roles in treating oily wastewater. PTFE membrane separation is crucial in guaranteeing better water quality. The removal efficiencies of COD, NH3-N, petroleum pollutant, volatile phenol, and turbidity are positively correlated with HRTs and negatively correlated with OLRs. The correlations between membrane separation with HRT and OLR were not observed.The effect of membrane flux, sludge loading and aeration intensity on membrane fouling rate was investigated in the treatment of oily wastewater. It is indicated that the rate of membrane fouling increases with the increase of membrane flux, especially when the membrane flux is above critical flux threshold. Similar result was achieved about sludge loading. However, a nonlinear relationship exists between membrane fouling rate and aeration intensity, and the smallest fouling rate was obtained at23.15L/min. When taking energy consumption into consideration, the optimal solution of energy consumption and membrane fouling could be achieved at15.89L/min. Meanwhile, membrane fouling analysis was also conducted by methods of SEM, FTIR, X-ray. SEM images show that the decrease of membrane permeability is due to the formation of a gel layer on the membrane surface, including carbohydrates, proteins and Ca, Fe, Si, Mg, Al compounds. Its permeability could be recovered to as much as95.11%after a chemical cleaning, showing its superiority in treating oily wastewater. This is also proved by a comparison between PTFE and PVDF for oily wastewater treatment.Through this study, the proposed process combining hydrolysis acidification-membrane bioreactor with PTFE membrane performed very well in oily wastewater treatment, and provide a promising basis for the pilot scale test and industrial field application in the future. |
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