Study On Concentration Process Of Grass Carp Farming Wastewater By Forward Osmosis Membrane

In order to solve the problems of large discharge,low pollutant concentration,and low treatment efficiency for grass carp farming wastewater.A forward osmosis membrane concentration method for treating grass carp farming wastewater with sucrose solution as a draw solution was proposed.Based on three factors of draw solution concentration,cross-flow filtration rate and draw solution temperature,changes of low-concentration organic pollutants in grass carp farming wastewater and water flux effects under process parameters were discussed,response surface optimization design on this basis were carried out,response relationship between different operating parameters and membrane concentration treatment effect were discussed,the change law of membrane fouling under different operating hours and the morphological characteristics of forward osmosis membrane fouling were investigated,the formation mechanism and mutual influence of pollutants in the membrane concentration process were preliminary revealed.(1)In the single factor experiment of different process parameters on the concentration effect of forward osmosis membrane,the concentration of the draw solution is 0.5-2 mol/L,the cross-flow filtration rate is 2.6-21.5 cm/s,and the temperature of the draw solution is 24-36℃,the COD concentration and water flux of grass carp farming wastewater increase with the increase of process parameters.There is a good linear relationship between the COD concentration in the raw material liquid and the process parameters.(2)Based on the single factor experiment,the response surface optimization experiment was carried out,and the secondary response surface model of the concentration of the draw solution,the cross-flow filtration rate,the temperature of the draw solution and the concentration effect of the membrane in the forward osmosis concentration process was obtained.For the COD change multiples,the first term that has a significant impact is the concentration of the draw solution and the temperature of the draw solution,the interaction terms are the concentration of the draw solution and the cross-flow filtration rate,and the second term is the temperature of the draw solution;For the average water flux,the first-order terms that have a significant impact are the cross-flow filtration rate and the temperature of the draw fluid,the interaction terms are the concentration of the draw fluid,the cross-flow filtration rate,the concentration of the draw fluid and the temperature of the draw fluid,and the second term is the draw fluid,the best membrane concentration effect predicted by the model is that the concentration of the extraction solution is 2 mol/L,the flow rate of cross-flow filtration is 155 rpm(18.7 cm/s),and the temperature of the extraction solution is 33.6℃.Under these conditions,the COD concentration of the simulated aquaculture wastewater of grass carp changes by 2.9 and the average water flux is 27.4 L/(m~2?h).(3)SEM-EDS and FTIR to analyze the membrane fouling layer under different operating hours,it is found that the interior is loose and does not have a compacted structure,and has the characteristics of uneven distribution on the membrane surface.The C,O,N,P,and S elements in the membrane fouling layer account for a large proportion.It is speculated that the pollutants are mainly organic matter such as protein.(4)The forward osmosis system with sucrose as the draw solution(the membrane active layer faces the draw solution)is used to treat the actual grass carp wastewater.The concentration of the draw solution is 2 mol/L,the cross-flow filtration rate is 155 rpm(18.7 cm/s),and the temperature of draw solution is 33.6℃,the COD concentration in simulated aquaculture wastewater of grass carp under this condition has a maximum change of 3.5.The main pollutants of the membrane support layer are organic compounds and silicon dioxide;there are not only organic substances on the membrane active layer,but also a small amount of trace elements such as K and Ca.Some substances in the raw material liquid will penetrate the membrane and enter the side of the draw solution.The solute reverse osmosis phenomenon in the forward osmosis membrane system was confirmed by the three-dimensional fluorescence test results.The changing trend of reverse solute flux and water flux is basically the same:the reverse solute flux increases when the water flux increases,and the reverse solute flux decreases when the water flux decreases.Solute reverse osmosis control needs further study.