| Pharmaceuticals are a class of compounds manufactured and used in daily life because of their specific physiological effects.In trace amounts,some pharmaceuticals still have reproductive and neurological toxicological effects on humans and aquatic organisms,or have carcinogenic potential.Municipal wastewater is the main receptor for human excretion of pharmaceuticals and their metabolites,and also the main source of pharmaceuticals and their metabolites discharged to natural water bodies.Recently,pharmaceuticals have become a new type of trace organic pollutants due to their huge usage and cannot be completely degraded by existing conventional wastewater treatment plants,which have long-term potential impacts on the ecological environment and bring harm to human health.At present,the research on the removal of pharmaceuticals from wastewater mainly focuses on the removal of the parent compounds,while the transformation products of pharmaceuticals are rarely investigated,though the transformation products of some pharmaceuticals still have certain toxicity.Therefore,qualitative and quantitative analysis of the transformation products of pharmaceuticals in wastewater treatment processes not only plays a key role in clarifying the mechanism of pharmaceutical degradation,but also provides a theoretical basis for the toxicity attenuation of pharmaceuticals in wastewater.In this study,based on the monitoring results of several wastewater treatment plants,a method suitable for the detection of pharmaceuticals and their transformation products was established.A pharmaceutical(trimethoprim,TMP)with removal potential was selected for further study.This study investigated the generation process of TMP transformation products in biological aerated filters by controlling the working conditions,revealed the dynamic process of TMP transformation during wastewater treatment,and analyzed the process and potential reaction mechanisms of the transformation of TMP by the biological aerated filter.This study provides a technical reference for the biological treatment of municipal wastewater containing TMP,and also provides ideas for the study of the transformation mechanism of pharmaceuticals in biological wastewater treatment.The main contents are as follows:(1)Pharmaceuticals in wastewater from three municipal wastewater treatment plants in GZ were monitored using LC-MS methods.The investigated pharmaceutical concentrations were all at the ng/L level,which was at a low level globally.Concentrations of most pharmaceuticals in municipal wastewater showed limited variation over time(RSD < 20%).The removal efficiencies of sulfamethoxazole by the four parallel biological treatment processes were high and stable,indicating that most sulfamethoxazole in wastewater could be removed by the existing anaerobic and aerobic biological treatment processes.While quantifying the target pharmaceuticals in wastewater by the data-independent mass spectrometry acquisition mode,18 pharmaceuticals were preliminarily identified,5 of which were confirmed by standards.39 pharmaceuticals and 7 pharmaceutical metabolites were preliminarily identified by data-dependent mass spectrometry acquisition mode.According to the results,TMP,a typical pharmaceutical with removal potential in actual sewage,was selected as the object of follow-up research.(2)Sequencing batch biofilm reactor(SBBR)and biological aerated filter(BAF)were used to study the removal of pharmaceuticals by biofilm nitrogen removal system and pharmaceutical's effect on the system.The results showed that long-term domestication could improve the removal efficiency of TMP by the system.After 60 days of operation,the removal efficiency of TMP by SBBR was 63%,the removal efficiency of total nitrogen was 73%,and the removal efficiency of ammonia nitrogen was close to 100%.After 128 days of operation,the removal efficiency of TMP by BAF was 97%,the removal efficiency of total nitrogen was56%,and the removal efficiency of ammonia nitrogen was close to 100%.The effect of 1 mg/L TMP on the COD and total nitrogen removal of the biofilm nitrogen removal system was limited.Proteobacteria,Bacteroidota and Gemmatimonadota may help to improve the removal efficiency of TMP by the microbial reactor.According to the results,BAF with a higher removal efficiency of TMP was selected as the object of follow-up research.(3)In order to cope with the difficulty in the detection of trace transformation products in sewage,a method was established to identify the transformation products accurately and efficiently.The identification workflow consists of four steps,namely database establishment,data mining method selection,compound preliminary screening,and compound structure analysis.The transformation pathway of TMP in BAF was speculated according to the molecular structures of the transformation products and the biotransformation mechanism reported in literature.TMP in BAF might either transform to a larger molecule and then degrade into smaller molecules,or directly degrade into smaller molecules,which involves Odemethylation,hydroxylation,demethoxylation,ring cleavage,and redox reactions.In the process of TMP transformation,there might be the production of pyruvate and the transformation of coenzyme A to acetyl coenzyme A,indicating that microorganisms in BAF could use TMP as a carbon source.There was pharmaceutical detoxification in microorganisms exposed to TMP.The result of toxicity assessment based on quantitative structure-activity relationship showed that there were transformation products with higher toxicity than TMP in the transformation pathway of TMP,but the aquatic toxicities of transformation products near the end of the transformation pathway were lower than that of TMP,indicating that biotransformation could reduce the toxicity of TMP-containing wastewater.(4)The initial transformation of TMP in BAF mainly occurred at the beginning of the BAF,and the further transformation of TMP was along the treatment process.A competitive relationship existed between some transformation products in different transformation routes.The primary and secondary transformation products were divided according to their molecular structures and variation of the abundance along the treatment process.BAF could rapidly degrade transformation products with higher toxicity than TMP into transformation products with lower toxicity than TMP.To prevent the formation of highly toxic transformation products from increasing the toxicity in the effluent,the filter material of BAF should have sufficient thickness.TP182,TP168 and TP154 may be the "bottleneck" transformation products of TMP biomineralization.The gas-water ratio had a great effect on some primary transformation products,a certain effect on secondary transformation products,and a limited effect on the removal efficiency of TMP.Excessive gas-water ratio would decrease the removal efficiency of TMP.Increasing the gas-water ratio can facilitate the transformation of TMP to TP276-1 and TP276-2,facilitate the transformation of TP168 to TP154,and inhibit the transformation of TMP to TP232.At high HRT,the total removal efficiency of TMP by BAF was high.The progress of TMP transformation was slowed down by a higher initial TMP concentration.Transformation products that underwent multiple transformations were subject to complex effects.Carbon sources with acetic acid groups may facilitate the transformation of TMP.In addition,the results under multiple working conditions improve the reliability of the speculation on the transformation pathway of TMP. |
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