Advanced Treatment Of Bilge Oily Wastewater In Ship With Ultrafiltration

As the complex oil composite,high emulsification level,variable water quantity,high oil concentration,and high salinity of the bilge oily water,conventional water treatment processes cannot separate water and oil effectively.Aimed to decrease the oil concentration lower than 5mg/L in the discharge water,the ultrafiltration technology has been applied in this study to treat the bilge oily wastewater.The permeate flux and treatment efficiency of the ultrafiltration process has been investigated,and fouling mechanism and cleaning method were studied as well.This research has been carried out from following aspects:1.The characters of the modified polyvinylidene fluorid(PVDF)ultrafiltration membrane have been investigated through the pure water ultrafiltration.The single factor ultrafiltration of wastewater was conducted to research the permeate flux and rejection rare.Based on the crossover experiment results,the permeate flux and economic prediction model were created to optimize the operation parameters of modified PVDF ultrafiltration process of bilge oily wastewater.The results showed that transmembrane pressure(TMP),flow velocity(v),oil concentration and p H could affected the permeate flux and rejection rate of the ultrafiltration process of bilge oily wastewater with modified PVDF ultrafiltration membrane,in which the TMP and v affected greater significantly.A high rejection rates of oil and turbidity has been obtained by the ultrafiltration.The oil concentration was lower than 2mg/L and the turbidity was lower than 1NTU.The removal rates of oil and turbidity were over than 85% and 90% respectively.The optimal operation parameters of ultrafiltration process of bilge oily wastewater with modified PVDF ultrafiltration membrane were v=3.0m/s,TMP =0.18 MPa.2.In order to investigated the fouling mechanism of ultrafiltration of bilge oily wastewater with modified PVDF ultrafiltration membrane,scanning electronic microscopy(SEM)and atomic force microscopy(AFM)were utilized to analysis the morphology properties of the surfaces of original membrane,fouled membrane and cleaned membrane.The fourier transform infrared spectroscopy(FTIR)and energy dispersive spectrometry(EDS)were applied to analysis the substance compositions and molecular structures of those types of membrane.The results suggested that the main pollutants of the fouled membrane were oil,suspended solids and salt.Under the function of hydrogen bond between the oil and membrane,a mess of oil accumulated on the surface of membrane which led to the formation of gel layer.The suspended solids reacted with salts to form complex inorganic salt compounds which accumulated on the membrane surface and in the membrane pores.3.According to the fouled mechanism of membrane,three cleaning methods,namely“ water flushing + 8%(mass fraction)sodium hypochlorite flushing + water flushing”,“water flushing + 0.5%(mass fraction)sodium dodecylbenzene sulfonate flushing + water flushing ” and “ water flushing + 1%(mass fraction)sodium hydroxide flushing + water flushing” were used to clean the fouled membrane.The results showed that “ water flushing + 8%(mass fraction)sodium hypochlorite flushing + water flushing” was the optimal cleaning method.