Study On The Migration And Transformation Of Typical Hydrophobicity Emerging Contaminants In Anaerobic Digestion Of Waste Activated Sludge

With the consumption increase of medicines,cosmetics,and health products in China,more and more emerging organic matters enter the municipal wastewater treatment systems,causing problems of emerging containments pollution concerned by current environmrnt field.In particular,hydrophobic emerging containments are difficult to be removed by traditional wastewater treatment technologies due to their high biological toxicity and easy accumulation in the sludge.Anaerobic digestion can realize the stabilization,harmlessness and reduction of sludge and can recover resources through biogas and other forms.Study the migration of hydrophobic emerging containments（the typical antibacterial agent triclosan（TCS）as a representative）in solid and liquid phases is of great significance to the removal of such containments in the process of anaerobic digestion of sludge.This work explored the impact of TCS on the performance of anaerobic digestion,investigated the effects of key factors in the solution of the sludge,properties of the sludge and adsorption sites of sludge on TCS adsorption,and analyzed the rule of TCS migration in anaerobic digestion by using principal component analysis（PCA）.（1）The influences and mechanisms of organic matters,p H,ammonia nitrogen（NH₄⁺-N）and temperature on the distribution of TCS between the solid and liquid phases were evaluated and analyzed.The results showed that protein in the solution combined with TCS through hydrophobic interaction and hydrogen bonding to promote the enrichment of TCS in the liquid phase,and the solid-liquid partition coefficient（K_d）was significantly reduced from 12645.92L/kg to 56.02 L/kg.The increase of polysaccharide concentration reduced K_d from 16026.44L/kg to 8444.06 L/kg.The increase in the concentration of humic acid（HA）reduced the K_dfrom 9034.31 L/kg to 7244.75 L/kg.Polysaccharides and HA were combined with TCS through hydrogen bonding force to increase the concentration of TCS in the liquid phase.Volatile fatty acids（VFAs）can not only be used as organic matter to participate in the adsorption of TCS in the liquid phase,but also can change the p H value of the solution to reduced K_d from 10957.66L/kg to 7833.15 L/kg.K_d increased from 5404.01 L/kg to 8946.43 L/kg in the range of 4-6 of p H,but decreased to 5404.01 L/kg in the range of 6-9.In addition to changing the electrostatic force between the sludge and TCS,p H can also indirectly affect the concentrations of organic matters and the solubility of TCS to affect the distribution of TCS.NH₄⁺-N reduced the electrostatic force between the solid of the sludge and TCS and promotied the formation of hydrogen bonds between the sludge and TCS to increase K_d from 8865.13 L/kg to 12264.93L/kg.Temperature affected the solubility of TCS in the solution directly and affected the concentrations of organic matters in the solution indirectly to reduce K_d from 3858.03 L/kg to1876.32 L/kg.（2）The influence of sludge characteristic on the solid-liquid distribution of TCS and the influence of different sludge structures on TCS adsorption were analyzed,and the results showed that the concentration of organic matters in the sludge had a great influence on the change of TCS solid-liquid partition coefficient,and the difference of organic matter content was the main reason for the different adsorption capacity of sludge adsorption sites on TCS.The total solid content（TS）of primary sludge had positively correlated with the K_dof TCS.The increase in TS of activated sludge and anaerobic digested sludge reduced K_d from 9971.43 L/kg to 4676.87 L/kg and from 3220.39 L/kg to 748.08 L/kg,respectively.The increase in TS of concentrated sludge and dewatered sludge increased K_d from 6285.56 L/kg to 20130.12 L/kg and from 11409.27 L/kg to 14837.02 L/kg,respectively.Additionly,affected by the concentration of organic matter in each adsorption site,TCS was mainly adsorbed in the microbial cells and residuals of sludge,and relative lower in EPSs.The TCS adsorption capacity of S-EPS,LB-EPS and TB-EPS was also different.TCS accounted for the largest proportion in S-EPS of digested sludge,but for the largest proportion in TB-EPS in actavited sludge,concentrated sludge and dewatered sludge.（3）The waste activated sludge（WAS）added with 0,100,200 and 500 mg/kg TCS was anaerobic digested at medium temperature（35±2℃）to investigate the influence of TCS on the organic matter consumption,acid production and methane production.The results showed that TCS can promote the release of organic matter and the process of acid production in the anaerobic digestion of sludge,but inhibit the process of methane production.The maximum VFAs accumulation was recorded in the 500 mg/kg with concentration of 2.51 g/L,while the VFAs concentrations in the 200,100,and 0 mg/kg TCS reactors were 2.13,1.80,and 1.65 g/L,respectively.Compared with the 0 mg/kg TCS control reactor,the methane suppression rates in the reactors with concentrations of 100,200 and 500 mg/kg TCS were 11.11%,21.14%and28.71%,respectively.TCS promoted acid accumulation by enhancing the activities of acetate kinase（AK）and carbon monoxide dehydrogenase（CODH）,but inhibited the activity of coenzyme F₄₂₀ in the process of methanogenesis to inhibit the production of methane.Based on16S r RNA gene sequencing analysis of the microbial community structure,it was found that the addition of TCS increased the relative abundance of typical acid-producing microorganisms such as Romboutsia,Terrisporobacter,Clostridium sensu stricto 13 and Petrimonas.However,it reduced the relative abundance of the methanogenic microorganism such as Euryarchaeota.（4）PCA was used to analyze the factors（p H,SCOD,NH₄⁺-N,polysaccharide,protein,VFAs and VS degradation rate）that can affect the solid-liquid distribution of TCS in the process of WAS anaerobic digestion.TCS tended to migrate from the liquid phase to the solid phase in the first two days of anaerobic digestion due to the consumption of organic matters in the supernatant and the combined effect of NH₄⁺-N and p H.On day 2-6,K_d gradually decreased caused by p H increase,VS degradation rate,TS and VS.After that,the concentration of NH₄⁺-N and VFAs were further changed to enhance the binding force of sludge to TCS,thus TCS migrated to the solid phase again.The reaction stopped at the final stage and keep K_d relatively stable.