Study On The Treatment Of The Desorbed Wastewater From Resin With High Concentration From Biologically Treated Sewage Effluent

In this thesis, based on the characteristic properties analysis of printing and dyeing desorbed wastewater from resin saturated by pollutants in biochemical effluent, the wastewater was divided into two parts by nanofiltration(NF) membrane of 200Da-300Da. One was NF permeate dominated by inorganic salts; the other was NF concentrated wastewater containing most organic substances. The concentration ofNF concentrated wastewater was about 5-6 times that of the desorbed wastewater from resin. The results of NF permeate and NF concentrated wastewater analysis by molecular size distributions, hydrophilic and hydrophobic fractionation, UV-visible spectrum and excitation emission fluorescence spectrum analysis showed that NF permeate was with low color and TOC was about 200mg/L, however the pH value of NF permeate was between 11 and 12 and the content of NaCl was as high as 7.39×104mg/L. It was also concluded that NF permeate was with low average molecular weight, high content of Fulvic acid in four fluorescence substances (aromatic protein, Fulvic acid, soluble microbial by-product and Humic acid) detected by EEM. And NF concentrated wastewater was with high color, high organic matter content, high SUVA, high average molecular weight and low BOD5/CODcr ratio. HPO-A content is about half of the organic substances in NF concentrated wastewater and organic acids account for the majority of organic matter. The proportions of four substances was similar to NF permeate. The low BOD5/CODcr ratio of about 0.1 showed the NF concentrated wastewater had a poor biodegradability.Due to the properties of NF permeate, it was considered to be reused as desorption reagent. Experiments results demonstrated that the desorption capacity of NF permeate was about 71%that of fresh NaCl solution by using the same volume. It may reach 80% when adding NF permeate volume of 11mL. It was also found that the desorption capacity of NF permeate equaled to 7.2% NaCl solution. Therefore it can be concluded that NF permeate can be recycled and it decreased the usage of fresh NaCl solution and the cost. According to the characteristics of NF concentrated wastewater, a combined process for NF concentrated wastewater was then proposed. Five different coagulants was selected for treating NF concentrated wastewater, results showed that PFS was not only effective but also low cost. Thus combined PFS coagulation and Fenton oxidation processes was used. The optimum conditions for combined processes were 1000Omg/L of PFS,500mg/L of Fe2+ and the H2O2/Fe2+ molar ratio was between 20 to 30. The treated wastewater contained low content organic matter and the BOD5/CODcr ratio increased from 0.1 to no less than 0.4. These results suggested that the toxicity of the wastewater was greatly reduced and at the same time the biodegradability of the wastewater was improved greatly.It has been proved that l%o of the treated wastewater had no effect on activated sludge biological treatment system. So the combined processes were proved to be feasible. The treated wastewater could be returned to aerobic activated sludge system for further disposal and it realized the recycling of NF permeate and zero discharge of the desorbed wastewater from resin. It may be a promising technology for the treatment of the desorbed wastewater from resin and be instructable for other wastewater treatment.