The Application Of Dynamic Membrane In The Separation Of Oil-in-water Emulsions

The oily emulsion wastewater is a kind of wastewater which is very difficult to separate. Membrane technology is one of the most effective methods for oil-in-water emulsions separation in comparison with the traditional separation methods.However,membrane fouling is a main drawback in the practical application in oil-in-water emulsions separation. Preparation and selection of the hydrophilic membrane to separate oil-in-water emulsions is necessary.Dynamic membrane(DM) technology is a novel and simple method for membrane modification.Dynamic membrane has many advantages,for example,simple preparation,low cost,great flux,strong retention ability,rich material and so on.Recent years,precoating the low-coat filtration medium by using some special particles has been proved as an interesting and potential alternative for wastewater treatment.Titanium dioxide dynamic membranes formed on carbon tube support via crossflow microfiltration and their performances in separation of oil-in-water emulsions are experimentally studied.The effect of operating conditions on dynamic membrane preparation is investigated.The orthogonal experiments are conducted and the results of variance analysis show that the effect of operating conditions on oil-in-water emulsions separation is not significant.Experiment analysis results in the following optimum conditions of preparing, such as suspension concentration is 0.5g/L,preparation pressure is 0.10MPa,cross-flow velocity is 1.13m/s.The surface of the prepared titanium dioxide dynamic membrane is relatively smoothly and uniform and the particles arranged neatly.Titanium dioxide particles can fill up the defects of support in the separation of oil-in-water emulsions.Dynamic membrane layer can change the hydrophilic-hydrophobic property of the support,and it has an asymmetric structure with the support.Dynamic membrane has a narrow diameter distribution.The effects of feed concentration,trans-membrane pressure,cross-flow velocity, temperature and pH on oil-in-water emulsions separation are investigated.Experiment results show that oil rejection efficiency of the prepared dynamic membrane is more than 98%and oil concentration of permeate solution is less than 8.3mg/L,which meets the requirement of national drainage control regulations.Based on the experiment results,a novel concept,"steady flux decay ratio"(FDR) of dynamic membrane is proposed,and types of dynamic membrane are identified based on the concept.In addition,flux decline mechanism of the intermediate blocking filtration is investigated.Analysis displays that the FDR increases at first then decreases with the increase of the support pore size,and microfiltration type of dynamic membrane transits from full blocking filtration to intermediate blocking filtration.When support average pore size is similar to titanium dioxide particle size,FDR can reach 90%,and dynamic membrane is full blockage filtration type.Medium blockage filtration dynamic membrane has a blockage turning point in the separation of oil-in-water emulsions.After the turning point,the slope of the J^-1-t fitting straight line decreases with the increase of the pore size of the support, namely flux decay become slowly with the increase of the pore size of the support.