| Pickle production is the main stream of the agricultural economy of Meishan, whose Dongpo District is known as the "hometown of Chinese pickle". In recent years, through establishing vegetable production bases, standardizing leading enterprises, strengthening the large-scale development and branding strategy, the pickle industry have been being developed rapidly. The2008sichuan pickle annual output reaches100million tons, of which meishan pickle accounted for70%. However, it has been estimated that in meishan region, at least7000thousand tons of wastewater is produced each year by this industry, which are characterized by high concentration of salt, nitrogen and organics. Notably, the nitrogen and phosphorus compounds, richly contained in pickle wastewater, are the main causes of eutrophication nutrient. With a salinity between2%to15%, pickle wastewater can induce serious soil salinization after local direct emissions. In view of that, in this study, membrane separation technology was used to treat meishan pickle wastewater. As wastewater in fermentation process of pickle contains large amounts of sugar, protein and amino acid, etc, using the membrane separation technology can effectively intercept the useful substances. By microfilter, pickle wastewater could be effective filtered asepticly to achieve a pretreatment for ultrafiltration process, while ultrafiltrating membrane can intercept macromolecular organic matters, such as protein, colloid, etc. Reverse osmosis was then used to intercept salt in order to achieve the purpose of waste recycling:the concentrated salt reserves intercepted can be again for pickle production. And the main results of this study are as following:1. According to the test conditions, the coagulation effects of PAFC, PAS, PAC, FeCl3and AL2(SO4)3were compared, among which PAFC showed a significant treatment effect on pickle wastewater. Removal rates of COD, NH3-N and TP were79.7%,47.3%,88%respectively, thus the PAFC was selected as the best flocculating agent to deal with the pickle wastewater.2. Taking pH, temperature, and adding amount of PAFC and PAM as testing factors, removal rates of COD, NH3-N and TP as measured indicators, a Lg(34) orthogonal experiment was conducted. The result showed that the optimum conditions of flocculation for disposing comprehensive emissions of pickle wastewater were:pH for9, temperature for35℃, PAFC for120mg/L, PAM for90mg/L. Removal rates of COD, NH3-N,TP were83.9%.47%and92.5%respectively. The best conditions of flocculation to dispose saline pickle wastewater were:pH for9, temperature for40℃, PAFC for600mg/L, PAM for90mg/L, generating removal rates of COD, NH3-N and TP83.9%.47%and92.5%respectively.3. Micro filtration membranes with0.24m2membrane square and different core diameters were used to carry out comparative tests and to evaluate the influence of operation pressure, pH, velocity of membrane flux. Results showed that the best conditions were:microfiltration membrane aperture for200nm, operating pressure for0.15MPa, pH for8, and membrane surface velocity for1.6m/s. After microfilter processing, pickle comprehensive discharging achieved the level3of national emissions standards, which means direct emissions could be conducted. When Microfiltration membrane aperture was200nm, operating pressure at0.21MPa, pH at8, membrane surface velocity at2.5m/s, removal rates of COD NH3-N, NTU and chroma of pickle saline wastewater achieved66.7%,48.5%,83%and75%respectively.4. Ultrafiltration membrane with1.77m2membrane square and different intercept molecular weights were selected to conduct comparative tests and to assess the influence of operation pressure, pH, velocity of membrane flux. The test results showed that treatment effect of ultrafiltration membrane with intercept molecular weight of2000Dal is superior to that of ultrafiltration membrane with intercept molecular weight of8000Dal. Removal rates of ultrafiltration membrane with intercept molecular weight of2000Dal for COD, NH3-N, NTU, protein and coloring in pickle saline wastewater reached57.2%,69.2%,97.8%,91%and85%respectively, among which protein and coloring removal is especially significant.5. Reverse osmosis membrane with1.77m2membrane square, which is suitable for dealing with industrial material liquid, was employed and under different osmotic pressures the temporal changes of flux were investegated. The test results showed that when the pressure difference was2.4MPa, membrane flux was0.100m3/m2.h and stayed in a relatively stable condition. Removal rates of reverse osmosis membrane for COD, NH3-N, salinity, protein and coloring in pickle salt wastewater reached98%,93.2%,97.5%,100%and100%respectively, among which proteins and coloring removal is especially significant. The wastewater treated by reverse osmosis membrane can be recycled in the production of pickle. |
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