Demulsification Of Oil-in-Water Emulsion In Starlike Latticed Bidirectional Pulsed Electric Field

Oily wastewater has been the focus of environmental protection research because of its wide sources,complex components and enormous environmental harm.The emulsified oil of oily wastewater is difficult to remove and often exists in the stable form of oil-inwater(O/W).Therefore,the research of efficient O/W demulsification method has important practical value to solve the problem of oily wastewater.Since the electric field method has the advantages of high demulsification efficiency,short treatment process,simple equipment and no secondary pollution,therefore,based on the electric field demulsification method in this paper,a starlike latticed bidirectional pulsed electric field(BPEF)was constructed by using rod titanium electrodes and bidirectional pulsed power supply,and its influence on the demulsification effect of O/W emulsion was systematically studied.Firstly,a starlike electrodes arrangement(SEA)was constructed in the vessel of demulsification by rod electrodes,and compared with the traditional parallel electrodes arrangement(PEA)and concentric electrodes arrangement(CEA),the distribution of electric field intensity in the cross section of demulsification space with three electrode arrangements was simulated with the same number of electrodes.The results showed that SEA was superior to PEA and CEA,SEA has the smallest proportion of the low field intensity area and the largest proportion of the high field intensity area.The sum of the proportion of middle and high electric field intensity area formed by the SEA was more than 95%,which could provide an appropriate electric field environment for demulsification of O/W emulsion.Secondly,the motion and coalescence behavior of oil droplets in water under electric field were simulated and analyzed,and the effect of electric field intensity,oil droplets size and oil droplets initial gap on coalescence performance was explored.The results showed that the coalescence process of oil droplets could be divided into three stages:approaching,extruding and merging.The coalescence time of oil droplets decreased with the increase of electric field intensity and oil droplets size,and increased with the increase of oil droplets initial gap.Finally,the effects of electrode parameters,electric field parameters and emulsion phase medium parameters on the demulsification performance of O/W emulsion were investigated respectively.The experiment of electrode parameters included two parts: electrodes arrangement and circumferential electrode-arrays angles.The results show that for the O/W emulsion with initial oil content of 3200mg/L,the oil content of the effluent after the demulsification by SEA was reduced to 24.16mg/L,which was far lower than PEA and CEA.Therefore,the demulsification performance of SEA on O/W emulsion was much better than that of PEA and CEA,which is verified by the electric field simulation results.The rate of demulsification increased with the decrease of the circumferential electrode-arrays angles,but the emulsion current would also increase accordingly.In view of the demulsification rate and the cost of energy consumption,60° could be considered as the optimal circumferential electrode-arrays angles of demulsification performance.The experiment of electric field parameters included three parts: voltage,frequency and duty cycle.The results showed that the demulsification rate ascended with the increase of voltage or duty cycle,and descended with the increase of frequency.The oil content and turbidity of the effluent firstly decreased and then increased with the increase of voltage,frequency or duty cycle.The optimal demulsification performance of O/W emulsion was obtained at the voltage of 500 V,frequency of 50 Hz and duty cycle of 40%,the oil content of the effluent could be reduced to 5.39mg/L.The experiment of emulsion medium parameters included three parts: emulsion conductivity,emulsifier type and emulsifier content.The results showed that the demulsification rate increased with the increase of emulsion conductivity,but the effluent results deteriorated with the increase of conductivity.The demulsification performance of emulsion containing cationic emulsifier was the best,the demulsification performance of emulsion containing anionic emulsifier was the second,and the demulsification performance of emulsion containing nonionic emulsifier was the worst,and the demulsification performance deteriorated with the increase of emulsifier content.