Effect Of Triclosan On Short-chain Fatty Acid Production In Peroxymonosulfate Combined With Alkaline Fermentation System Of Sludge

In recent years,a large amount of waste activated sludge（WAS）has been generated in the sewage treatment process of wastewater treatment plants（WWTPs）.In order to avoid the harm to the environment and human body,proper treatment and disposal of WAS is a hot issue to be solved.As a broad-spectrum fungicide,triclosan（TCS）is widely added to daily personal care products.After TCS is used,it will enter the sewage treatment plant with wastewater.Most of the TCS in the sewage treatment process is adsorbed on the surface of WAS due to its hydrophobicity.TCS in WAS will promote the formation and spread of drug-resistant bacteria and drug-resistant genes,which may threaten ecological security and human health.The alkaline fermentation of WAS can stabilize the sludge and realize the recovery of short-chain fatty acids（SCFAs）.Peroxymonosulfate（PMS）can promote the acid production process of WAS and the removal of refractory substances.The effect of TCS on the sludge anaerobic fermentation process is unknown at present.In this paper,the effect of TCS concentration on SCFAs production of WAS in alkaline fermentation system（pH10）and peroxymonosulfate combined with alkaline fermentation system（pH10+PMS）was explored at 30°C;the effect of PMS concentration on SCFAs production of WAS was studied respectively;the mechanism on TCS affecting SCFAs production in peroxymonosulfate combined with alkaline fermentation system system was studied;high-throughput sequencing method was used to analyze the microorganisms in the system and the removal of TCS was analyzed.The main conclusions were as follows:（1）Effect of TCS concentration on alkaline fermentation system of WAS was studied.Experiments showed that the proper concentration of TCS could promote the production of SCFAs of WAS.The maximum SCFAs production was achieved when the TCS concentration was 400 mg/kg TSS on the 5th day of fermentation.The concentration of SCFAs was 2900.37 mg COD/L（i.e.,304.89mg COD/g VSS）.The proportion of acetic acid reached largest（36.73%）.Meanwhile,when the TCS concentration was 400 mg/kg TSS,the concentration of NH₄⁺-N released from system was the highest.TCS degradation rate was 49.91%and VSS reduction rate was 40.50%after fermentation of 10 d.（2）When the TCS concentration was 400 mg/kg TSS,the effect of PMS concentration on sludge anaerobic fermentation in PMS combined with alkaline fermentation system was studied.Experiments showed that the proper concentration of PMS could promote the production of SCFAs.When the PMS concentration was 0.11 g/g TSS,the maximum SCFAs concentration reached3332.81 mg COD/L,and the corresponding fermentation time was 5 d.The proportion of acetic acid was the largest（47.14%）.Meanwhile,when the PMS concentration was 0.11 g/g TSS,the concentration of NH₄⁺-N released from system was the highest.The degradation rate of TCS was 68.45%and the organic matter reduction rate was 47.05%after fermentation of 10 d.The solid-liquid partition coefficient（K_d）of TCS was reduced after adding PMS,which was beneficial to the removal of TCS.When the concentration of PMS was 0.11 g/g TSS,the effect of TCS concentration on sludge anaerobic fermentation in PMS combined with alkaline fermentation system was studied.The results showed that the proper concentration of TCS could promote the production of SCFAs from sludge anaerobic fermentation.When the TCS concentration was 400 mg/kg TSS,maximum SCFAs production was achieved（3453.27 mg COD/L）,and the corresponding fermentation time was 5 d.The proportion of acetic acid was the largest（47.20%）.Meanwhile,when the TCS concentration was 400 mg/kg TSS,the concentration of NH₄⁺-N released from system was the highest.TCS degradation rate was 68.07%and VSS reduction rate was 47.16%after fermentation of 10 d.（3）In alkaline fermentation and PMS combined with alkaline fermentation systems,the addition of TCS could promote the solubilization,hydrolysis,acidification of WAS and improve the activities ofα-glucosidase and protease,leading to increased production of SCFAs（4）The high-throughput sequencing technology was used to analyze the microbial community structure of the five groups of samples.The results showed that the microorganisms of the five samples were different.Different levels of dominant flora were found at the level of phylum,class,and genus.The microorganisms that degrade TCS were described.At the phylum level,increasing the proportion of Firmicutes and Actinobacteria and reducing the proportion of Proteobacteria were the reasons for the highest acid production in the pH10+PMS+TCS group.At the class level,the main dominant microorganisms were Clostridia,Actinobacteria,and Alphaproteobacteria.Among them,the proportion of Clostridia in pH10+PMS+TCS reached the highest to 41.34%,which was beneficial to the accumulation of SCFAs.At the genus level,Acetoanaerobium,Proteinivorax and Tissierella the main dominant bacteria.The three genus belong to the Firmicutes phylum,and its improvement was beneficial to microbial acid production.Finally,TCS-degrading microorganisms were analyzed,including Nitrosomonas,Pseudomonas,Alcaligenes,Novosphingobium and Sphingomonas.Studies showed under the condition of pH10,adding PMS could increase the relative abundances of TCS-degrading bacteria and help to improve the degradation rate of triclosan.In summary,in order to obtain higher SCFAs yield and increase the degradation rate of TCS during anaerobic fermentation of WAS,under the conditions of TCS=400 mg/kg TSS and PMS=0.11 g/g TSS and long-term adjustment of pH=10,the sludge anaerobic fermentation after 5 days of fermentation had the best acid production performance and TCS was removed.