Studies On The Inhibition And Mitigation Strategies Of Triclosan On Anaerobic Digestion Of Sludge

Triclosan（TCS）,as a typical antimicrobial agent,is widely used in hand soap,disinfectants,and other cleaning products due to its highly effective antibacterial effect.The bacteriostatic and ecotoxic properties of TCS have a potential impact on the biological treatment of sewage sludge,such as anaerobic digestion.After a large amount of TCS is produced and used and enters the wastewater treatment plant with domestic wastewater,finally enriched by sludge adsorption.In addition to the influence of pollutants such as TCS,the sludge itself has problems in digestion such as a slow hydrolysis rate of organic matter,low biotransformation efficiency,and poor stability,which need to be solved.In addition,the digestate and dewatering solution produced in sludge treatment and disposal is also rich in resources but often neglected and needs urgent attention.In this study,the migration distribution pattern of TCS during anaerobic digestion and the mechanism of inhibition of methanogenic performance were firstly investigated with sewage sludge as the treatment object,and then the inhibition effect was weakened and the methanogenic potential of sludge was enhanced by both iron-rich mineral/PMS pretreatment and sludge biochar addition.Finally,the resource recovery of sludge filtrate by cross-linked polymerization method was explored and studied.The main research findings are as follows.（1）TCS in anaerobic digestion of sludge showed migration from the liquid phase to the extracellular polymer before enrichment to the solid fraction of sludge and showed an outward migration process of endocytosis as digestion proceeded.100 mg TCS/kg-TS exposure showed the highest TCS removal efficiency of 36.9%,where the removal of TCS mainly occurred in the solid fraction of sludge.In the early stage of exposure,TCS stimulated the microorganisms to secrete more EPS,mainly producing S-EPS and protein-like substances,and the results of the fluorescence quenching test and UV spectroscopy indicated that TCS was mainly bound to protein-like substances.The lysis effect of TCS on sludge cells was limited,but cell activity was significantly inhibited.The methane production of sludge was inversely proportional to the TCS exposure,and the cumulative methane production was reduced by 55.7%at the highest exposure（250 mg TCS/kg-TS）and the lag periodλwas prolonged by 39.8%.The TCS exposure not only reduced the SCOD degradation efficiency,but also accumulated more NH₄⁺-N in the middle and late stages of digestion.The TCS（50,100 mg TCS/kg-TS）was able to increase the production of SCFAs and promote the production and consumption of acetic acid and butyric acid.The microbial analysis also showed that TCS exposure increased the abundance of acid-producing microorganisms and potential TCS decomposers in the sludge.The vulnerability of methanogenic archaea and the accumulation of acid and ammonia in the digestive system are intrinsic to the inhibition of anaerobic digestion performance by TCS.（2）The pyrite/siderite-peroxymonosulfate treatment effectively cracked the sludge to remove part of the TCS,with 43.9%and 39.9%TCS removal and 51.5%and 60.5%CST reduction under the optimal treatment conditions（Catalyst/PMS=0.36/0.4 mmol/g-TS）,respectively.The iron-rich minerals themselves and the Fe²⁺released by them could catalyze PMS to produce·OH and SO₄^—·,with·OH playing a dominant role,effectively destroying the sludge floc structure and releasing the bound water as well as TCS and organic matter inside the sludge.The rheological analysis demonstrated that pretreatment reduced the rigid structure inside the sludge and significantly improved the mobility of the sludge.Changes in DOM and EPS fractions indicated that pretreatment effectively mineralized complex organic matter and increased the hydrolysis rate of the sludge.The results of EPR and Fe²⁺concentration tests showed that rhodochrosite released Fe²⁺more consistently and thus continued to produce free radicals,allowing siderite/PMS treatment to crack the sludge more efficiently,and siderite did not produce S^2-which is not conducive to anaerobic digestion.This may also be the reason for the superior performance of the siderite-PMS pretreatment.（3）The addition of sludge-prepared biochar significantly alleviated the inhibition of anaerobic digestion of WAS by TCS,which was elevated by 86.5%and 118.1%over the control SBC and SBC_Fe addition,respectively,and even by 36.2%and 59.3%over the blank group.The sludge biochar enhanced the TCS removal rate,which was 64.5%in the SBC_Fe-WAS system and 55.1%in the SBC-WAS,both higher than the 36.9%in the control group.Moreover,the sludge biochar enhanced the hydrolysis process of organic matter,which led to the change from acetic acid type to butyric acid type fermentation in the pre-WAS stage and alleviated the accumulation of isovaleric acid caused by TCS inhibition in the late digestion stage,while reducing the concentration of ammonia nitrogen and improving the buffering capacity of the digestion system.The Fe doping significantly increased the specific surface area of biochar and the microporous structure of the surface,which enhanced the adsorption and microbial loading of SBC_Fe capacity.The microbial analysis showed that the relative abundance of Methanosphaera in the SBC_Fe-WAS system increased to 79.6%,demonstrating that SBC_Feselectively enriched methanogenic archaea.（4）Methyltriacetoxysilane could effectively cross-link and polymerize nitrogen,phosphorus and organic matter in the sludge supernatant,and the separation recoveries of SPS,SPN,TP and TN reached 44.7%,58.5%,48.7%and 76.9%,respectively.The flocculated polymers are rich in organic fraction and nitrogen and phosphorus nutrients,with abundant surface pore size and stable properties,and have the potential to act as a slow-release carbon source,fertilizer and as a soil conditioner.