Occurrence,fate And Ecological Risk Of Biocides In The Wastewater Treatment Plants And Receiving Aquatic Environment

In the past more than ten years,household biocides as emerging organic contaminants have received increasing attention.These compounds have some characteristics of wide use largely,frequent detection with high concentrations,and they show potential ecological environmental risk due to their inherent properties of sterilization,disinfection and antisepsis.Various biocides are prevailingly used in all kinds of pharmaceuticals and personal care products?PPCPs?.After use of these products,a mass of biocides were discharged into wastewater and then reached to wastewater treatment plants?WWTPs?through sewer network.Generally,almost all of biocides cannot be removed completely by conventional treatment technologies,thus these chemicals were released into the receiving aquatic environment through WWTP effluent discharge.But those biocides present in the aquatic environment may cause some adverse effects on aquatic organisms even human beings,such as acute/chronic toxicity,bioaccumulation and endocrine disrupting effects.At present,however,limited knowledge have been recognized about the occurrence,fate and ecological risk of biocides in different WWTPs and the receiving rivers in China.Therefore,this thesis aimed to reveal the occurrence,fate and ecological risk of biocides in different WWTPs and the receiving rivers through the field investigation and laboratorial mechanism research,and the main study contents included:?1?systematacially investigated the occurrence,removal and pollution loads of 19 biocides in ten WWTPs of Guangdong province,South China;?2?systematacially analyzed the contamination profiles,mass fluxes and ecological risks of 19 biocides in the Yangtze River and Dongjiang River?include rainfall runoff?;?3?compared the removal efficiencies of climbazole under ultraviolet?UV?irradiation and the chlorine oxidation,and further studied the photodegradation kinetics,mechanism and toxicity change of climbazole under UV-254 irradiation.The main results of this thesis are given as follows:?1?The concentration levels of 19 biocides in WWTPs and their receiving rivers were measured by using an ultra high performance liquid chromatograph coupled to a triple quadrupole mass spectrometer?UHPLC-MS/MS?,and then,based on the mass balance analysis approach,the removals and pollution loads of 19 biocides in different treatment stages of WWTPs were studied.The results showed that all the target biocides were universally detected in the WWTPs and their receiving rivers,and 19 for liquid samples and 18 for solid samples.The dominated biocides were N,N-diethyl-3-methylbenzamide?DEET?for wastewater and triclocarban for activated sludge and excess sludge,and their mean concentrations in each stage of different WWTPs were 110³93 ng/L and 1170²110 ng/g?dry weight,dw?,respectively.Meanwhile,DEET and triclocarban also showed the highest concentration levels among the 19 biocides in the receiving water?mean: 235 ng/L?and sediment?mean: 339 ng/g?.Most biocides were readily removed from the liquid phase of ten WWTPs,and the mean removal rate to ?19 biocides was up to 75%.The treatment technologies of modified A/O?Anaerobic-Oxic?,MBR?Membrane Bio-Reactor?and Carrousel 2000 oxidation ditch showed excellent removal efficiencies??82%?for total biocides.The removals of target biocides were attributed to biodegradation and adsorption onto activated sludge.The mean input per capita for ?19 biocides based on influent concentrations was 907 ?g/d/person,while the emissions per capita were 187 ?g/d/person for effluent,and 121 ?g/d/person for excess sludge.The total back-estimated usage for ?19biocides on the basis of input per capita and total population was up to 453 t/y in the whole China,and the total estimated emission of ?19biocides discharged to the receiving environment through effluent and excess sludge was also up to 289 t/y.Risk evaluation results based on the detected concentrations and the existing ecological toxicity data showed that some of biocides?e.g.,clotrimazole,carbendazim and triclocarban?posed high ecological risks to the aquatic organisms in the receiving rivers.Therefore,advanced wastewater treatment technologies should be developed and applied to reduce the emission of biocides into the receiving environment,and further to minimize their potential risks to the ecological environment and even human beings.?2?The concentration levels of 19 biocides in the surface water and sediment of Yangtze River and Dongjiang River,even in the rainfall runoff from the cities of Huizhou and Dongguan,were measured by UHPLC-MS/MS,and we estimated their mass fluxes according to the flow of Yangtze River and Dongjiang River,and then assessed the ecological risks of 19 biocides in these two rivers by the risk quotient?RQ?approach.The results showed that all the target biocides were ubiquitous environmental contaminants in the surface water and sediment of Yangtze River and Dongjiang River,even in the rainfall runoff from the cities of Huizhou and Dongguan.For the Yangtze River,14 biocides were detected,with the highest concentrations up to 166 ng/L for DEET in surface water,and 54.3 ng/g for triclocarban in sediment.The predominant biocides were DEET and carbendazim for surface water,while triclocarban and methylparaben for sediment,with their detection frequencies of 100% in both phases.Based on the mass fluxes,an estimate of 152 t/y of 14 biocides was carried by the Yangtze River to the East China Sea.For the Dongjiang River,19 biocides were all detected in the surface water and sediment.The predominant biocides were methylparaben,climbazole and DEET for surface water,among them,climbazole occurred with a highest concentration of 276 ng/L;while those for sediment were climbazole,triclosan and triclocarban,and triclocarban showed a highest concentration of 656 ng/g.An estimated mass flux of 17 biocides in the section of Shilong?Dongjiang River?was 3434 kg/y.In the rainfall runoff from Huizhou and Dongguan,all the target biocides were extensively detected,with carbendazim and DEET as primary biocides,and the highest concentration of them were up to 2572 ng/L and 1629 ng/L occurred in the rainfall runoff from farmland and street,respectively.Meanwhile,based on the precipitation of Huizhou and Dongguan,the total estimated mass loads of this two places for DEET and carbendazim were respectively up to 2815 kg/y and 2380 kg/y,which easily caused the contamination of DEET and carbendazim to the receiving rivers of Dongjiang River basin.Moreover,the results from redundancy analysis?RDA?suggested that the distribution of biocides in the aquatic environments was significantly correlated to Gross Domestic Product?GDP?,total phosphorus?TP?and total nitrogen?TN?,so the dominant input source of biocides in rivers was come from the domestic wastewater of cities along the river;and the monitoring results from rainfall runoff revealed that the rainfall runoff was an important source for some special biocides?DEET and carbendazim as insecticide?in rivers.A preliminary risk assessment showed high ecological risks to aquatic organisms posed by some biocides?including clotrimazole,carbendazim,triclosan,etc.?existed largely in the Yangtze River and Dongjiang River.Therefore,proper measures should be taken to reduce the input of biocides into the river systems,for example,reducing the usage of biocides and developing the removal efficiency for biocides in wastewater.?3?A inside-irradiation photoreactor and a homemade experimental device were used to compared the degradation behaviour of climbazole?CZ?under ultraviolet radiation and chlorine oxidation.The concentrations of climbazole during the experiment were monitored by a high performance liquid chromatograph system equipped with a diode array detector?HPLC-DAD?,while the photodegradation by-products of climbazole were identified and confirmed by an ultra high performance liquid chromatograph coupled to the quadrupole time-of-flight mass spectrometer?UHPLC-Q-TOF?and an UHPLC-MS/MS.Moreover,the toxicity change of the climbazole photodegradation system was evaluated by duckweed toxicity test and software prediction.The results revealed that the degradation efficiency of climbazole under ultraviolet radiation?UV-225⁴25 and UV-225?was obviously faster than chlorine oxidation.Under the irradiation of UV-254,the photodegradation half-life of climbazole in pH=7.5 aqueous solutions was 9.78 min,and the process of photodegradation followed pseudo-first-order kinetics.There was no obvious relationship between the pH values and the photodegradation rate constants and quantum yields of climbazole.Compared to the control of ultrapure water,the photodegradation of climbazole in the tap water,river water and secondary effluent from WWTP showed a significant inhibition effect,which was a combined result of the coexisting constituents in natural waters,such as Fe3+,NO3– and HA.The addition of different radical scavengers also inhibited the photodegradation of climbazole due to the reduction of reactive oxygen species?ROS?,which contributed to the photodegradation of climbazole.The absence of O₂ have no influence on the generation of the ROS,while the absence of H2 O significantly inhibited the forming of ·OH.Climbazole underwent direct and self-sensitized photolysis involving ROS,and transformed to five photodegradation by-products?CZ-BP1^CZ-BP5?.Based on the results of identification and semi-quantitation of photodegradation by-products,the proposed pathways mainly included hydroxylative dechlorination,dechlorination,de-pinacolone,etc.Moreover,toxicity evaluation using duckweed found significant toxicity reduction in the photodegradation system of climbazole after the irradiation of UV-254,and the remaining by-products did not pose extra toxicity compared with climbazole itself.These findings from present study suggest that the azole fungicide like climbazole presented in the effluent of WWTPs could be further reduced by applying UV disinfection treatment.