| With the increase of population and the increasing degree of global industrialization,the gap of water resources expands increasingly.In this situation,the regeneration and reuse of sewage are becoming more and more widely.However,more consideration is given to whether the conventional indicators reach the limit in the reclaimed water treatment and reuse process,and the detection and analysis of trace organics is rare.Therefore,in order to guarantee the safety of the reclaimed water reuse,it is urgent to study and evaluate the changes in the occurrence and migration of trace organics in the process of reclaimed water reuse.And then,we have to comprehensively evaluate the change regulation about the reduction and change of trace organics in the process of reclaimed water,as well as the health risks caused by the reclaimed water.It provides theoretical basis and data support for the change of trace organics and health risk control in wastewater reclamation and reuse.This paper takes Siyuan Sewage Plant in Xi'an as the research object,sampling and monitoring the water at the influent,MBR effluent and back to the lake of Siyuan college respectively.The trace organic compounds in 3 kinds of water were detected and analyzed by GC/MS and UPLC/MS/MS,and the concentration and variation of each index were analyzed in detail.According to repeated analysis and detection,there are four types of 58 trace organics detected in the system,including 13 polycyclic aromatic hydrocarbons,3 pesticides,16phenols,and 26 pharmaceuticals.In the sewage treatment section?fromthe fine screens to MBR effluent?,the removal rate of PAHs is only 14.81%,which is the lowest,Because PAHs are stable and difficult to decompose.Phenols own the highest removal rate?98.20%?among four types of micropollutants,just due to the fact that the alkylphenols in the raw water accounted for 91.49%of the total,was highly removed in this process.For the three pesticides,although the removal rate of the other two substances was low,dichlorvos,which has the largest concentration,was effectively removed in the process,and the total removal rate reached the second highest level of 81.21%.The removal rate of pharmaceuticals and personal care products?PPCPs?in this process was also unfavorable,at 56.85%.In the reclaimed water reuse section of the MBR effluent to the artificial lake,the concentration of PAHs increased conspicuously.The concentration in the lake water was 1.7 times of the MBR effluent,and the ratio of the PAHs and the characteristic parameters were calculated.Volatilizes for diesel.The chlorophenols in the phenols changed the former state,and the removal rate increased a lot,but the concentration of alkylphenols increased significantly,resulting in a negative total removal rate of phenols.For the three pesticides,the concentration of atrazine increased slightly,but the removal rate of the other two pesticides reached 100%,so the total removal rate of pesticides also reached 67.18%.The highest removal rate of PPCPs in this process was 85.66%.It can be seen that longer residence time and more sediments and suspended matter are of great benefit to the removal of pharmaceuticals in this process.After analyzing the concentration variations of each pollutant at each stage,combined with its hazardous toxicity parameters and exposure parameters,the maximum exposure conditions are selected according to the"most adverse principle"of risk evaluation,and the four-step method of risk assessment is used to evaluate the health risk.The results shows that there are 8 kinds of definitive carcinogens.The carcinogenic risk are 3.69×10-8,5.80×10-9and 4.66×10-99 in raw sewage,MBR effluent and artificial lake respectively.It can be seen that the risk of carcinogenesis decreases obviously in the sewage treatment stage?from raw sewage to MBR effluent?.The analysis shows that dichlorvos is the decisive factor for removing the carcinogenic risk in this process.While in the reclaimed water reuse section,the concentrations of polycyclic aromatic hydrocarbons which have a high proportion because of the carcinogens,increased in this process.Therefore,although the risk of carcinogenicity of other substances was further reduced,the overall risk of carcinogenicity decreases slightly.In general,however,the carcinogeni risk of the eight carcinogens in the three types of water is less than the threshold of 10-6,and the risk of carcinogenic risk is negligible.According to the non-carcinogenic risk assessment of the remaining 50 substances,their non-carcinogenic risks in raw sewage,MBR effluent,and artificial lake were 6.61×10-3,5.65×10-4,and 1.40×10-4,respectively.In the sewage treatment section,Non-carcinogenic risk decreased by 10 times,mainly due to the fact that the effectively reduce of Non-carcinogenic risk of PPCPs,which the persentage oftotal risk is 93.34%.In the reclaimed water reuse section,removal of PPCPs with a risk ratio of 95.19%in the MBR effluent at this stage is still a decisive factor in the reduction of non-carcinogenic risk.The proportion of non-carcinogenic risk of PAHs and pesticides in the three types of water is relatively small.The non-carcinogenic risk caused by 50 trace organics in the entire system was also less than the corresponding risk threshold 1.In a word,the non-carcinogenic risk and carcinogenic risk caused by the 58 trace organics detected in this research system were all less than the corresponding thresholds,the risk level was very low,and the reuse was relatively safe. |
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