| Triclocarban?TCC?,as a typical antibacterial agent,has been widely used in various applications,such as soap,toothpaste,shampoo,medical disinfectant,fabrics,leather and other toiletries and household products,due to its effective bacteriostasis and skin compatibility.Amount of TCC have been produced and applied every year since the advent of TCC,which inevitably leads to its environmental release.In fact,TCC is universally detected in terrestrial and aquatic ecosystems at ppb or even ppm level.TCC is reported to have capability of inhibiting the growth and metabolisms of organisms and have certain estrogen effect,thus it has potential risk to the ecological environment and human health.As the last barriers before TCC entering into the natural environment,wastewater treatment plants?WWTPs?remove most of the TCC present in wastewater mainly through precipitation,biosorption,or other biomass mediated processes.However,conventional wastewater treatment plants are used to remove ordinary pollutants,and have not set up units for emerging contaminants removal.TCC in traditional municipal WWTPs cannot be effectively degraded and most of them are absorbed by sludge or remain in wastewater,which brings out a potential influence on the biological sewage treatment and the following sludge stabilization and resource recovery.So far,however,there are no studies to systematically report the toxic effects of TCC on the wastewater-excess sludge biological treatment system.This paper investigated the fate of TCC,the effect of TCC on nitrogen and phosphorus removal,anaerobic fermentation and digest ion of sludge and their mechanism analyses in biological wastewater treatment system and excess sludge system.Firstly,it studied the transformation and degradation of TCC in wastewater treatment and anaerobic sludge system.Conclusions found that most of TCC was removed by activated sludge adsorption and carbanilide,4-chloroaniline and aniline were the main degradation intermediates of TCC in activated sludge system.TCC contained high stability and was not easily transformed and degraded in the anaerobic sludge system,moreover,4,4'-dichlorocarbanilide and carbanilide were major degradation intermediates.Furthermore,the effects of TCC on the physical-chemical properties of activated sludge were investigated.Experimental results showed that there was n o influence on the structure and composition of extracellular polymeric substance?EPS?,settleability,hydrophobicity,effluent suspension,while has slight effect on flocculating ability and dewaterability of activated sludge,under the short-term TCC exposure.It was observed that lower concentration of TCC?10?g/L?showed on impacts on settleability,effluent suspension,hydrophobicity,and EPS in the long-term exposure conditions,however,decreased settleability and dewaterability of activated sludge,increased effluent suspension and contents of EPS,and change of structure and composition of activated sludge were found under the long-term exposure of higher concentrations of TCC?50 and 100?g/L?.Based on the above research,the effects of TCC on operation of activated sludge were further investigated via nitrogen and phosphorus removal efficiency,the transformations of intracellular polymers and the activities of relevant enzymes.It was found that the short-term TCC exposure had no influence on the operation of activated sludge.Under the long-term exposure,the nitrogen and phosphorus removal efficiency,the transformations of intracellular polymers and the activities of relevant enzymes had no obvious variation between lower TCC reactor?10?g/L?and blank reactor.However,higher TCC concentrations?50 and 100?g/L?had severe inhibition on nitrogen and phosphorus removal.Mechanism studies showed that higher TCC long-term exposure impacted the transformations of intracellular polymers and decreased the activities of related denitrification and phosphorus removal?e.g.ammonia oxidizing bacteria?nitrite oxidizing bacteria?polyphosphate accumulating organisms?microorganisms and key enzymes?ammonia monooxygenase,nitrite oxidoreductase,exopolyphosphatase and e.t.?,which finally inhibited the biological processes of nitrification,denitrification,anaerobic phosphorus release,aerobic and denitrification phosphorus absorption.Further,it was analyzed that the effect of TCC on sludge system during anaerobic sludge stabilization.During anaerobic sludge stabilization,the expo sure of TCC has no effect on variation of sludge pH,while its exposure stimulated microorganisms to secrete more protein and polysaccharide from sludge and promoted the VSS reduction,which were beneficial to sludge stabilization and reduction.In addition,the effects of TCC on anaerobic sludge fermentation and digestion were investigated via short-chain fatty acids?SCFAs?,H2 and CH4 production,the sludge decomposition,the specific biological processes,the relevant enzymes activities and microorganism community structure.It was found that the exposure of TCC facilitated SCFAs production,especially acetate,and caused the increasing the percentage of acetate to total SCFAs;moreover,the exposure of TCC not only increased the yield of H2 producing from sludge but also enhanced the hydrogen production rate;while it inhibited the sludge CH4 production.Mechanism researches found that when TCC was introduced into anaerobic sludge system,it significantly facilitated the sludge decomposition,and produced much more organic substances.In addition,it was observed that TCC had no impact on hydrolysis process,and observably facilitated the acidification and acetogenesis processes but seriously inhibited the methonogenesis and homoacetogenesis processes in sludge fermentation or digestion system.Microbial analysis revealed that the exposure of TCC increased the microbial community diversity,and enhanced the abundances of SCFAs?especially acetic acid?and hydrogen producers,also promoted the the activitie s of key enzymes relevant to SCFAs and hydrogen production. |
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