The Study On Conductance Method Of Salinity In High Salinity Wastewater

Shandong Province Environmental Protection Agency revised ?Comprehensive discharge standard of water pollutants along the line of the South to North Water Transfer in Shandong Province? four river basin water pollution discharge standards and increased the total salt content in 2014. The method of detecting total salt content is gravimetric method.However, the total salt content using gravimetric method has great error and it is time-consuming. It can not be monitor the total salt content of wastewater on-line, so the standard of total salt content is difficult to enforce. Measuring total salt content using EC is short-time, so it meets the demand of online monitoring. This article focuses on thermoelectric, printing and dyeing, paper making and pesticide four industries that discharge more high salinity wastewater. The article bases on seven kinds of inorganic salt to simulate four high salinity wastewater. The article studies the effect of concentration, temperature and pH on EC of single inorganic salt solution and the effect of concentration, temperature, COD and pH on EC of mixed inorganic salt solution. The article compares salinity error of conductivity method and gravimetric method.Finally, the article get four equations of seeking salt content by conductivity method.The results of article are as follows:(1) The effect of concentration on EC:Both the EC of single salt solution and mixed salts solution were highly significant linearly related to their respective total salt content and confidence reaches 99.9%. When the quality is the same,KCl make the greatest contribution to EC and Na3PO4 make the least contribution. When the molar mass is the same, the order of cation EC is:K+>Na+>Mg2+ and the order of anionEC is:Cr>SO42->CO32->SiO32->PO43-.(2) The effect of temperature on ECThe conversion of EC at different temperature to the EC at 25? of both single salt solution and mixed salts solution can use formula as follows: K25=K/[1+0.02(t-25)] In the formula:K25-the conductivity at 25?;K-the conductivity at t?.And the average error is less than 5%.(3) The effect of COD on EC:When add COD (500mg/L) into the waste water of printing and dyeing, paper making and pesticide, the EC of printing and dyeing wastewater do not change and the EC of paper making wastewater decrease 2.3% and the EC of pesticide wastewater decrease 1.1%. Overall, when the concentration of COD is less than 500mg/L, the effect of COD on EC can be neglected.(4) The effect of pH on EC:When the pH is 6-9, the effect of pH on EC of thermoelectric, printing and dyeing, paper making and pesticide wastewater can be neglected.(5) The salinity error of conductivity method and gravimetric method:The salinity error of conductivity method of thermoelectric, printing and dyeing, paper making and pesticide isl.1%?0.8%?0.9% and 0.9%. The salinity error of gravimetric method of thermoelectric, printing and dyeing, paper making and pesticide is21.3%?1.3%?27.8% and3.3%. So, the salinity using conductivity method is more accurate. When wastewater contains a lot of MgCl2 and Na2SiO3 like thermoelectric wastewater and printing and dyeing wastewater, the salinity error of gravimetric method is too large.(6) When the concentration is 2g/L-40g/L and the temperature is 0?-45? and the pH is 6-9 and the concentration of COD is less than 500mg/L, the article establishes formulas of four industries to solve salinity by conductance method.The formula of thermoelectric industry is as follows: y=0.0036{K/[1+?(t-25)]}2+0.5812{K/[1+?(t-25)]}-0.0614The formula of printing and dyeing industry is as follows: y=0.0028{K/[1+?(25-t)]}2+0.6749{K/[1+?(25-t)]}-0.1823The formula of paper making industry is as follows: y=0.0036{K/[1+?(25-t)]}2+0.3965{K/[1+?(25-t)]}+0.1534The formula of pesticide industry is as follows: y=0.0030{K/[1+?(25-t)]}2+0.5768{K/[1+?(25-t)]}-0.1493 In the formula:K-the conductivity at t?;?-temperature correction coefficient(0.02);y-Total salt content of conductivity method(g/L).