| For the antimicrobial wastewater treatment,high energy consumption and low efficiency is an emergency technical problem to be solved.The widely used advanced processes?AOPs?has the problem of high processing cost and incomplete mineralization,and the biodegradation of antibiotics is basically impossible in theory due to the nature of antibiotics.Then combining biodegradation with an AOP has been proposed as a more effective means for the antimicrobial wastewater treatment in engineering.For the subsequent biological treatment,obtain specific biodegradable intermediates in the AOP process is a key factor to achieve the purpose of high efficiency and low consumption using this approach.Compared with the traditional process above,the recently developed intimate coupling photocatalysis and biodegradation?VCPB?technology,in which AOPs and biodegradation occur together,has a potential advantage for the antibiotic wastewater treatment.VPCB could avoid the peroxide and improve the mineralization efficiency as biodegradable photocatalytic intermediates are removed as they are formed,focusing the chemical oxidant on the non-biodegradable fraction.However,to the best of our knowledge,VCPB has not been used for antibiotic treatment,in which the compounds are quite complex,and the challenging issue is how bacteria could survive in and respond to antibiotics.In this study,we selected tetracycline hydrochloride?TCH?as a model pollutant and investigated TCH degradation behavior and mechanism of the VPCB protocol by comparing their results with those of photocatalysis or biodegradation individually.We used silver-doped titanium dioxide?Ag/TiO2?as the visible light-responsive photocatalyst.We coated porous carriers with Ag/TiO2 and then cultivated the unacclimated activated sludge to format biofilms on the carriers;thus,intimate coupled photocatalysis and biodegradation?VPCB?system could be set up when illuminating the carriers with visible light.When coupled with biodegradation,the pseudo-first-order simulated kinetic constants for the VPCB protocol were 0.240 ± 0.010 h-1,in comparison with 0.220 ± 0.016 h-1 for the individual photocatalysis?VPC?protocol,suggesting the obviously enhanced degradation efficiency of VPCB.At the same time,the larger ring molecules intermediate accumulated in VPC was utilized by microorganism and achieved further degradation under VPCB.Compared with the biological degradation?B?,the biofilm inside the VPCB carrier was successfully protected.The SEM and SMPs results showed that the photocatalytic oxidation of VPCB could reduce the inhibitory effect of TCH on the biofilm.The new genus Methylibium which could survive in the TCH wastewater,the Runella which had the TCH resistance gene,Comamonas and Pseudomonas which possessed the ability to use the aromatic derivatives,became more abundant,indicating that the biofilm in VPCB could be adapted to the toxicity of TCH through the adjustment of the biological community structure.In addition,VPCB increased the mineralization efficiency of TCH by 23% compared with VPC.Biodegradation of photocatalytic intermediates was a key factor to increase TCH degradation and mineralization in the VPCB system.And then acetate was used as co-substrates to improve the condition of biofilms when encountering TCH,we investigated the effect of additional of acetate on the TCH degradation in the VPCB.After adding acetate as the external electron donor,the living cell ratio increased from 56% to 86%,and the degradation efficiency of VCPB on TCH was improved from 90% to 95% with an increment of the degradation rate constant by 40%,and SCOD removal by 5.2 and 16.1 mg/L respectively.Meanwhile,the adjustment of the biological community structure,which enriched the Thauera,Runella and Pseudomonas,enhanced the degradation of the micromolecular intermediate product which contains ?-? conjugate groups aromatic hydrocarbon structures,as they were not detected in VPCB after the reaction.This suggested that additional NaAc as the electron donor could maintain the biomass and metabolic activity of the biofilm,improve the removal efficiency of TCH by the rapid use of intermediate products and effectively avoid the accumulation of photocatalytic intermediates.In this work,we successfully realized the degradation of the typical antibiotic,TCH,in a visible light induced ICPB reactor for the first time and investigated the degradation behavior and pathway of TCH.The results interestingly revealed that biofilms were not damaged by TCH,but could regulate themselves to degrade photocatalytic generated intermediates by community structure succession,and thus accelerate the TCH photocatalytic degradation.And we found one practicable strategy to improve the degradation and minerlization of TCH was to provide extra metabolic electron donors in VPCB.This work provides an efficient technology for antibiotic wastewater treatment and is beneficial to the further understanding of the process of VPCB with the theoretical and practical significance. |
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