Biodegradation Of Three Typical UV-filters (BP-3,BP-4 And Lawsone) In Biological Aerated Filter:Efficiencies,Mechanisms And Major Intermediates Investigation

UV-filters have been considered as the emerging environmental micropollutants,which are widely detected in surface water,ground water and even aquatic organisms,posing adverse effects on the safety of ecosystem and human health.Therefore,it is urgent to develop effective techniques to degrade UV-filters in water for the protection of the aquatic environmental safety.In the present study,the biodegradation efficiencies,mechanisms and major intermediates of three typical UV-filters(e.g.,2-hydroxy-4-methoxy benzophenone(BP-3),2-hydroxy-4-methoxy-5-sulfonyl benzophenone(BP-4)and 2-hydroxy-1,4 naphthoquinone(Lawsone))in simulated wastewater in biological aerated filter(BAF)were investigated.The major results obtained in this study are summarized as follows:Firstly,the biodegradation of BP-3 and BP-4 in simulated wastewater in BAF reactor were investigated.The results showed that at hydraulic retention time(HRT)of 12 h,the removal efficiencies of BP-3 and BP-4(initial concentration of 500 μg L-1)in the BAF reactor reached 99.5%and 98%,respectively.When decreasing the HRT from 12 h to 4 h,the removal efficiencies of BP-3 and BP-4 still reached 95.7%and 89.8%,respectively.It was found that the removal mechanism of BP-3 in the BAF reactor included both adsorption and biodegradation;whereas the removal mechanism of BP-4 was mainly ascribable to the biodegradation and the adsorption removal of BP-4 was quite minimal.Additionally,the results showed that nitrifying bacteria played a major role in biodegrading BP-3 and BP-4.The major intermediates of BP-3 and BP-4 were identified by using a high performance liquid chromatography-time of flight mass spectrometry(HPLC-QTOF-MS).Six intermediates were identified during the biodegradation of BP-3,including(2-(2,4-dihydroxybenzoyl)phenolate,2-hydroxy-4-methoxybenzoic acid,3-methoxy-9H-xanthen-9-one,(E)-3-formyl-4-(2-hydroxy-4-methoxyphenyl)-4-oxobut-2-enoic acid,(E)-4-(2,3-dihydroxy-4-methoxyphenyl)-3-formy]-4-oxobut-2-enoic acid and(2E,6Z)-3-formyl-8-methoxy-4,5,8-trioxoocta-2,6-dienoic acid).Seven intermediates were identified during the biodegradation of BP-4,including(3-benzoyl-2,4,5-trihydroxy-6-methoxybenzenesulfonic acid,(2,4-dihydroxyphenyl)(phenyl)methanone,2-hydroxy-4-methoxy-5-sulfobenzoic acid,2,3,4-trihydroxy-6methoxy ’benzenesulfonic acid,3,4-dihydroxy-2-methoxycyclopenta-1,4-diene-1-sulfonic acid,5-hydroxy-4-methoxy-2-oxotetrahydrofuran-3-sulfonic acid and 2,3,4,5tetrahydroxy-6-methoxybenzenesulfonic acid).These results indicated that the biodegradation mechanisms of BP-3 and BP-4 included hydroxylation,methylation,hydrolysis and desulfurization pathways.Moreover,the results showed that the abundance of these intermediates of BP-3 and BP-4 decreased gradually by increasing the HRT,indicating that these intermediates could be further degraded in the BAF reactor.Secondly,the degradation efficiency of Lawsone in the BAF reactor was further investigated.The results showed that the removal efficiency of Lawsone(initial concentration of 500 μg L-1)reached 99.9%at HRT of 12 h.When decreasing the HRT from 12 h to 4 h,the removal efficiency of Lawsone still reached 97.6%.Four major intermediates were identified during the biodegradation of Lawsone by HPLC-QTOF-MS,including(2-hydroxybenzoic acid,5,8-dihydroxynaphthalene-1,4-dione,5,6,8-trihydroxynaphthalene-1,4-dione and 4,7,7’-trihydroxy-(2,2’-binaphthalene)-5,5’,8,8’-tetraone).Additionally,the removal efficiencies of the mixture of Lawsone,BP-3 and BP-4 in the BAF reactor were further evaluated at HRT of 6 h,and the results showed that BP-3 and Lawsone were still removed efficiently(e.g.,>98%),whereas the removal efficiency of BP-4 was strongly limited(e.g.,<5%).Moreover,the results showed that the dominant microbial communities in the BAF reactor included proteobacteria(69.4%),Planctomycetes(10.3%),Actinobacteria(7.0%)and Chloroflexi(6.0%).The dominant bacterial colonies were identified as Methylotenera(12.9%)and Hyphomicrobium(11.1%).In summary,the obtained results of this paper can provide guidance for the efficient treatment of UV-filters in municipal sewage,which has great significance in both theoretical and practical application.