| The freezing method is a new type of wastewater treatment technology,which uses the physical phase transition of water molecules in the wastewater under the freezing point temperature,to realize the purification of the wastewater and the concentration of pollutants.Freezing treatment of wastewater has its advantages such as non-selectivity,low corrosion to equipment and structures,low energy consumption,and the ability to recover useful materials from wastewater.In this paper,the effects of suspension crystallization and eutectic freezing crystallization techniques on the treatment of several organic intermediate production wastewater were studied.Inorganic and organic crystalline salts were successfully recovered from these wastewater,and a set of eutectic freezing crystallization pilot plant was designed to treat actual wastewater.Taking olaquindox production waste liquid as the research object,suspension crystallization was used to study the effect of ice formation rate(the percentage of meltwater on the total volume of raw water)on the removal of water quality indicators such as COD,ammonia nitrogen,total nitrogen and conductivity.The results showed that the removal of COD and other indicators decreased as the ice formation rate increased,and had a greater impact on conductivity.When the ice formation rate is 80%,after three-stage freezing treatment,COD,ammonia nitrogen,total nitrogen,and conductivity of raw water decreased from 178341mg/L,356.6mg/L,1920.9mg/L,and 2.02ms/cm to 2504mg/L,6.2mg/L,55.5mg/L,and 83.1?S/cm,the removal were 98.6%,98.3%,97.1%,and 95.9%,respectively.The removal efficiency was significant,and concentration ratios were all above 2.The combustion value of the concentrate increased from 2664J/g to 7449J/g,which meant it could maintain combustion on its own heat during incineration process,and no additional fuel was needed.It is more economically rational to treat olaquindox waste liquid by combination of freezing method and incineration rather than direct incineration.Taking the dichloroethane waste liquid and Na mother liquor as the research objects,eutectic freezing crystallization technology was applied to purify the wastewater while realizing resource recycling.Two-stage freezing was adopted,the ice formation rate of dichloroethane wastewater was 80%.The freezing point of raw water was approximately-22?,and the maximum supercooling degree was 5?.However,due to the increase of the viscosity of Na mother liquor under low temperature,ice crystals and salts were difficult to be separated from the remaining solution.Therefore,we reduced the agitation rate and the primary ice formation rate was set at about 50%.The secondary ice formation rate was 70%.The removal of pollutants was not good as that of olaquindox:For dichloroethane wasterwater,the removal of COD,ammonia nitrogen,total nitrogen and conductivity of final effluent were 75.4%,91.5%,88.8%and 81.4%,respectively,but the concentration ratios of the first three indicators reached about 4.The removal of COD and conductivity of Na mother liquor was 96.2%and 74.8%.About 41.36g of solid could be obtained by treating 1L of dichloroethane wastewater,and about 6.3g of solid could be recovered by treating 1L of Na mother liquor.The main components of the solid material were determined to be NaCl and sodium erythorbate.The recovery value of crystalline salt could largely make up for energy consumption and reduce treatment cost.Based on the eutectic freeze crystallization pilot test,a set of pilot plant was designed for the treatment of actual wastewater from a chemical plant.The designed flow rate was 20t/d.After trial operation and debugging,the removal of COD of primary effluent could reach 80%,also had a good removal effect on the color of the wastewater.But the removal of salt and ammonia nitrogen is still unsteady and further debugging is needed. |
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