| At present,renewable energy has occupied an important position in human energy,which also promotes the rapid development of photovoltaic industry.However,in the process of solar cell manufacturing,high concentration of organic wastewater will be produced,which seriously threatens the earth's environment and human health.This study took the workshop wastewater of a practical photovoltaic production plant as the treatment object.The wastewater has a relatively high concentration of thiourea,which is a toxic organic substance that can affect human health and cannot be treated by biological method.In addition,the wastewater has a high salt content,so that new salts cannot be introduced into the subsequent treatment.Therefore,a novel O3/H2O2+BiPO4/UV synergy process was developed for this wastewater,and specific research work was carried out for the treatment of thiourea containing photovoltaic wastewater by this process.?1?Design Expert 8.0 was used to design the experiment,and the experiment data were analyzed by using the response surface analysis and variance analysis.Based on these,we choose the initial experimental conditions as follow:O3 concentration of 55.71 mg/L,hydrogen peroxide initial dosing quantity is 435 mg/L,and pH 9.20.Under this condition,O3/H2O2 process can effectively degrade the thiourea in wastewater,degrade89.14%within 30 minutes,and 100%within 150 minutes.?2?Through the comparison between BiPO4 and TiO2 photocatalyst,it has been found that BiPO4 is more effective in reducing TOC in wastewater and also have higher efficiency of hydrogen peroxide utilization compared with TiO2.During the treatment,BiPO4/UV reduced 30.875 mg/L TOC,and the remaining 74.47mg/L H2O2?from the treatment of O3/H2O2?could be fully utilized within 60 minutes.In addition,it was found that BiPO4 photocatalyst did not change significantly after being used through SEM and FTIR analysis,which proved that it could be reused for many times.?3?We conducted a systematic study on the O3/H2O2+BiPO4/UV synergy process,and found that the O3/H2O2+BiPO4/UV synergy process had better TOC removal effect than other processes,1.8 times of the O3/H2O2 process,1.5 times of the BiPO4/UV/H2O2 process and 1.9 times of the O3/H2O2+UV process.Moreover,it has a better utilization efficiency of hydrogen peroxide,which can fully utilize the remaining hydrogen peroxide within 60 minutes and promote the generation rate of hydroxyl radical.Hydrogen peroxide of 70 mg/L promotes the efficiency of BiPO4/UV segment;however,higher concentration will inhibit the synergy process.In addition,0.5 g/L BiPO4 photocatalyst has the best TOC removal effect and catalyst utilization efficiency.?4?Intermediate products generated in the degradation process were detected by UPLC-IM-QToF-MS and the degradation mechanism and pathway of thiourea were speculated.It was found that thiourea was firstly oxidized by hydroxyl radical generated or directly oxidized by hydrogen peroxide and ozone in O3/H2O2 segment into thiourea dioxide and melamine.The BiPO4/UV segment was then used as the second step to generate holes for hole oxidation of thiourea.The thiourea dioxide and melamine were converted into biuret and further oxidized into H2O and CO2. |
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