| Based on the problems of high COD,high salinity,high toxicity and difficult disposal of pesticide wastewater,the concentration and gasification technology of high-salt organic wastewater was carried out with simulated wastewater and representative pesticide wastewater as the research objects,to realize safe disposal and resource utilization of high-salt organic wastewater.Firstly,the laboratory investigation of evaporation preconcentration was carried out with simulated wastewater and typical pesticide wastewater.Variables such as organic species,salinity,evaporation temperature were changed to study the precipitation rate of organic compounds,salt mobility and evaporation rate in evaporation preconcentration process.The results show that more than 98%of the salinity remains in the concentrated solution and it is feasible to separate salt by evaporation preconcentration process.On the basis of laboratory research,a pilot scale experimental platform for thin-layer preconcentration was set up to preconcentrate simulated wastewater and typical pesticide wastewater.It is found that the moisture content of preconcentrated salt slag decreases with the increase of preconcentration temperature and increases with the increase of feed rate.The Box-Behnken Design response surface methodology was used to fit the relationship between moisture content of preconcentrated salt slag and energy consumption ratio with conduction oil temperature,roller speed,NaCl thickness and material COD.The results from experimental study shows that the main and secondary factors affecting the moisture content of preconcentrated salt slag,which were conduction oil temperature,material COD,roller rotating speed and NaCl thickness in turn.The operating parameters of the experiment table were optimized by simulated wastewater to obtain the optimum technological conditions as follows:the temperature of conduction oil is 180?,and the roller speed is1.00 r.min-1.The preconcentrated salt slag from pesticide wastewater and its characteristics of gasification and detoxification were analyzed.The characteristics of preconcentrated salt slag,volatile constituents of gasification,filter residue,recrystallized salt were analyzed using GC/MS,TG,IR and XRF.The results show that a large number of pesticide intermediates remained in preconcentrated salt slag which is still hazardous wastes.However,the original toxic pesticide intermediates in preconcentrated salt slag had been volatilized or decomposed after gasification at 500?under nitrogen conditions.61.1%of organic matter in pesticide wastewater migrated to evaporative condensate during preconcentration process,33.7%of organic matter migrated to gasification vapor during gasification and detoxification process,only 5.2%of organic matter remained in filter residue of recrystallization process.The gasification temperature was 600?,and the TOC content in recrystallized salt could meet the standard of sodium chloride by-product of glyphosate?TOC<0.03g/100g salt?.A small amount of salt in pesticide wastewater was carried by steam in the preconcentration stage,and more than 98%remained in recrystallized salt.Numerical simulation by Fluent software was used to numerically analyze the experimental parameters such as nozzle height,number of nozzles and feeding rate.The results show that choosing appropriate nozzle height,nozzle number and increasing feeding rate have effectively improved the utilization efficiency of internal heat source,which also improved the recovery rate of preconcentrated salt slag.The optimum conditions were obtained as follows:nozzle height was 33 cm,the number of nozzles was 2 and feeding rate was 6 L·h-1. |
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