| The treatment of highly concentrated organic wastewater with high salinity for the dye industry has become a bottleneck restricting the sustainable development of the dye industry due to its large emissions,complex components,high salinity,high toxicity and poor biochemical properties.In view of the lack of effective pretreatment technology for the current highly concentrated dye organic wastewater with high salinity,in this paper,the advanced oxidation process optimization and process mechanism for the typical refractory organic dye wastewater were studied systematically,which aimed at recycling the waste salt in the dye industry.For the more,the effects of organic matter in wastewater on salt crystallization were analyzed.The main progress made in this paper were as follows:(1)The simulated dye wastewater was degraded by sodium hypochlorite method,hydrogen peroxide method and sodium persulfate method.The results showed that the degradation effects of three oxidation methods at normal temperature conditions were as follows:the treatment effect of sodium hypochlorite method was the best,COD removal rate was 88%,followed by hydrogen peroxide method,COD removal rate was 70%;sodium persulfate method was the worst,COD removal rate was only 50%.Sodium hypochlorite oxidation method had the best degradation effect under microwave,ultrasound and water bath heating conditions,when 50 mL of simulated dye wastewater with a mass concentration of 1440 mg/L was treated,the COD removal rate could reach 95%under the conditions of sodium hypochlorite input was 4.1 mL,the pH of solution was 3.0 and reaction time was 30 minutes,respectively.The kinetics of the degradation process of degrading simulated dye wastewater by sodium hypochlorite showed that the reaction accorded with the first-order kinetics,y=0.0118t+1.5677,R2=0.9978.(2)The feasibility analysis of the degradation pathway of rhodamine b in dye wastewater at molecular level was investigated with the density functional theory combined with GC-MS and mass spectrometry.The atomic net charge,the highest occupied orbital,the lowest unoccupied molecular orbital and its energy were calculated,it was found that,atoms with enough negative charges were easily attacked by hydroxyl radicals,it leaded to the breaking of chemical bonds.The main degradation pathway of rhodamine b essence was supposed as two aspects.One was the ring-opening oxidation of rhodamine b essence under the attack of hydroxyl radicals,and the other was deethylation reaction.(3)The influence of organic matter concentration on the salt crystallization of wastewater was carried out.The optimum evaporation conditions of mixed solution of sodium chloride and sodium sulfate with different concentrations were discussed.The results show that the purity and crystallization yield of sodium chloride and sodium sulfate crystals decreased with the increase of organic matter concentration in dye wastewater.Sodium chloride crystal was strongly affected by the concentration of organic matter.When the mass concentration of organic matter was increased from 50 mg/L to 5000 mg/L,while the purity of the crystal decreased linearly from 97%to 87%,and the crystallization yield decreased from 82%to 40%. |
