Study On Salt Recovery And Utilization Of Pickle Wastewater

The production and sales volume of Sichuan pickles increased year by year,which not only brought economic benefit growth,but also resulted in a large number of high-salt wastewater with more than 10%salt content due to pickles.The pickles wastewater produced in the process of pickles production has the characteristics of high COD,high organic matter,high chloride ion,high nitrogen and phosphorus.If not treated,the discharge will cause great pollution to the water body,and the high nitrogen and phosphorus in the wastewater will also cause eutrophication of the water body,pollution of surface water and groundwater,and excessive salt will also cause soil salinization.In addition,a large amount of salt in pickle brine wastewater is not recycled,which is not only difficult to be treated by conventional biological method,but also causes a waste of resources.In this experiment,the high salt wastewater produced by a pickle production enterprise in Meishan City was used as the base water sample to achieve salt removal and pollutant removal by membrane separation technology.The use of microfiltration membrane to remove COD,suspended matter and total phosphorus in all kinds of wastewater has a preliminary effect.The use of ultrafiltration membrane to intercept most suspended matter and organic matter with large molecular weight in water can effectively extend the life of the back-end nanofiltration membrane and reduce the membrane pollution.The nanofiltration membrane can intercept most of the bivalent ions,and let the monovalent ions in the wastewater pass through the filtration membrane.The main impurity cationic calcium ions and other pollutants in the salt-containing wastewater can be effectively intercepted by the nanofiltration membrane,so as to achieve the goal of separating the salt in the high-salt wastewater.Finally,the effluent from nanofiltration membrane can be condensed and crystallized through evaporation to obtain the crystalline salt which can be used for further industrial use.In the whole process,the salt is recovered by evaporation and crystallization through membrane treatment,and the effluent from the last stage is treated by hydrolytic acidification+air flotation+A~2/O process,which can realize the goal of resource utilization and standard discharge of high salt wastewater.The main research results of this paper are as follows:(1)According to the test conditions,the two kinds of microfiltration membranes in the front-pretreatment:flat membrane and curtain membrane were compared to compare the removal effects of the two kinds of microfiltration membranes on COD,total phosphorus and suspended matter and the changes of membrane flux with time;It is concluded that the overall removal effect of curtain membrane on the three pollutants as well as the maximum flux and stable running flux are better than that of flat membrane.Curtain membrane should be selected as the front microfiltration membrane for the primary treatment of saline wastewater in the subsequent treatment.(2)The influent p H was adjusted by neutralizing the regulating tank,and the influence of p H on the curtain membrane flux was observed.The optimal influent p H of the microfiltration membrane was determined to be 7.5～8.Taking the operating temperature of the equipment and the pressure difference before and after the membrane as experimental factors,and the flux of nanofiltration membrane as measuring index,the optimum processing conditions of nanofiltration membrane were determined as follows:the set operating temperature of the equipment was 40℃,the set operating pressure difference was 0.3MPa,and then the flux of nanofiltration membrane stabilized at 70L/h and 52L/h.(3)The removal rates of COD,suspended solids and total phosphorus in the front-stage pretreatment system are 3.6%～8.2%,56.4%～72.3%and 29.0%～62.0%,respectively.The front-stage pretreatment system has an ideal effect on the removal of suspended solids and total phosphorus,especially for the removal of suspended solids.It can meet the requirements of reducing the subsequent plugging of ultrafiltration/nanofiltration system.The overall recovery rate of the system is66.1%～70.0%.The interception rates of COD,suspended matter,total phosphorus,calcium ion,ammonia nitrogen and chroma are 92.1%～94.7%,89.6%～93.3%,90.5%～99.1%,92.2%～95.0%,20.2%～30.7%and 98.0%～99.0%.It can be seen that in addition to the ammonia nitrogen interception effect of the double membrane system,The removal rate of other pollutants is above 89%,which has an obvious effect on the removal of pollutants in saline wastewater.The post-stage biochemical treatment process is selected according to the field investigation and analysis of kimchi related enterprises,and the hydrolytic acidification+air flotation+A2/O process is adopted to treat the mixed wastewater produced by subsequent enterprises.After the whole process treatment,the main pollutants in the wastewater of the enterprise can be effectively removed,and the final expected effluent of the plant sewage station can meet the level 3 discharge standard of the Comprehensive Sewage Discharge Standard(GB8978-1996),and meet the conditions for discharging into the park municipal sewage network.(4)The salt recovery rate of evaporated crystal salt is about 72.0%,and the salt quality of evaporated crystal salt from MED device reaches the second grade standard of“Industrial salt”(GB/T 5462-2015),which can be directly recovered and utilized,to realize the goal of utilization of pickle saline wastewater.In this pilot project,38.3tons of industrial salt can be obtained by evaporating and crystallizing in one year,and 27.22 tons of chloride ion can be reduced every year.The social and environmental benefits are remarkable.