Impacts Of Particles On Microorganisms In Drinking Water Under Disinfectant Stress

A large number of suspended particles exist in drinking water,not only causing water turbidity,adsorbing microorganisms and organic substances,but also providing shelters for microorganisms to resist disinfection,thus threatening the safety of drinking water quality.While the protection role of particles for has been widely reported,the mechanism of disinfection-stressed protection effects of particles on microbes remains unclear yet.This study aims at investigating chorination-stressed protection effects of suspended particles on drinking water cells through analyzing microbial physiological characteristics,surface features and aggregation behaviors.This study is expected to provide theoretical guidance and new ideas for the control of microbial growth in drinking water systems.The main results are as follows:Firstly,the effect of goethite on drinking water microbes was examined.Results showed that goethite dosage had little impacts on the logarithmic inactivation rate of drinking water microbes in the absence of chlorine.When confronted with chlorination stress(0.5 mg/L),increasing goethite concentration from 0 to 20 mg/L yielded the logarithmic inactivation rates decreasing from 1.266±0.154 to 0.880±0.083.However,an increase in chlorine concentration resulted in reduced protection of goethite on microbes.Microbial aggregation behavior analysis revealed that goethite promoted microbial aggregation in both bulk water and biofilm phase,particularly at 0.5 mg/L chlorine.Therefore,the presence of goethite encouraged microbial aggregation behaviors and chlorine decay process,thus playing a protective role and shaping distribution characteristics when facing chlorination stress.Secondly,the role of extracellular polymeric substances(EPS)in the effects of goethite on microbes was investigated.The results showed that,in the presence of disinfectant(0.5 and 1.0 mg/L chlorine),the increase in goethite dosage(0-20 mg/L)led to an increase in the EPS excretion,especially exopolysaccharides,from 0.35±0.11 ?g/m L to 0.56±0.11 ?g/m L.The removal test of polysaccharide showed that the removal of polysaccharides weakened microbial aggregation ability in bulk water and biofilm phase,thereby regulating the cell survival and distribution characteristics.It indicated that goethite may shape microbial aggregation behaviors through modulating EPS secretion and accordingly varying the surface characteristics.Finally,the effect of kaolin on microbial protection was studied.The results showed that,in the presence of disinfectant(0 and 0.5 mg/L chlorine),goethite dosage had little impacts on the logarithmic inactivation rate of drinking water microbes.When confronted with chlorination stress(1.0 mg/L),increasing kaolin concentration from 0 to 20 mg/L yielded the logarithmic inactivation rates decreasing from 1.17±0.021 to 0.780±0.020.Enhancing kaolin concentration also resulted in the increase of microbial aggregate size.It indicated that,in the presence of chlorine,kaolin promoted EPS secretion and microbial aggregation behaviors.Meanwhile,kaolin supported resistance ability from disinfection and thus shaping,thereby shaping cell survial and distribution characteristics,particularly at the chlorine of 0.5 mg/L.