| In order to solve the issue of water resources shortage in our country,wastewater reclamation has been considered as one of effective solutions.There are various pollutants in reclaimed water including bacteria and its appendage called endotoxin,it can enter into the human lung through aerosol in the process of reclaimed water use in urban which poses a potential health risk.Recently,some research about endotoxin removal by disinfection process have been published,but most of the studies take the changes of endotoxin activity as the indicator to evaluate the removal efficiency of endotoxin,however it can not reflect the effect on biological toxicity of endotoxin by disinfection process.Therefore,the purpose of this study is to investigate the removal rule and mechanism of endotoxin activity detected by limulus amebocyte lysate method(LAL)and endotoxin induced inflammatory response in the process of chlorination and UV/chlorine advanced oxidation,inflammation is detected using mice inhalation model by making the proportion of polymorphonuclear leukocytes(PMN)in bronchoalveolar lavage fluid(BALF)as the detection endpoint.There are three main contents in this study as follows:Firstly,standard endotoxin was used to make research on its removal performance and related mechanism in chlorination and UV/chlorine advanced oxidation processes.In chlorination process,we found that endotoxin activity did not decrease and presented a trend of increase instead,but the inflammatory response decreased after chlorination,which indicated that chlorination is effective to reduce the health risk of endotoxin inhalation exposure.In UV/chlorine disinfection process,both endotoxin activity and inflammation decreased,the removal efficiency of endotoxin activity was more than 60%,meanwhile inflammatory response induced by endotoxin in mice lung also decreased more than 75%.Endotoxin was oxidized by these two disinfection methods,the size of endotoxin aggregate reduced significantly,which is the main reason that inflammation induced by endotoxin decreased as conjecture.Secondly,bacterial strains isolated from reclaimed water were used to make research on the release and removal of endotoxin.Results showed that after chlorination,bacterial endotoxin activity rise rapidly,while inflammatory response presented a trend of increase at first and then decreased.In UV/chlorine process,bacteria was inactivated which induced the release of free endotoxin,for some gram negative bacteria,the process of endotoxin release was dominant and remove efficiency of the released endotoxin was very low,for some other gram negative bacteria,free endotoxin released rapidly and then oxidized gradually,endotoxin activity and it's inflammation induction in this disinfection process were consistent.Finally,we made research on the removal efficiency of endotoxin in actual reclaimed water by chlorination and UV/chlorine oxidation.In detail,after chlorination for 15 min with 10mg/L chlorine,endotoxin activity and inflammatory response from reclaimed water increased significantly,and then both decreased after chlorination for 1h while they were still higher than that from original reclaimed water.Otherwise,after UV/chlorine oxidation with UV intensity 2.5mw/cm2 and 10mg/L free chlorine,both endotoxin activity and inflammation all rise at first and then decreased in the processe,after contact time of 10 min,endotoxin activity and induced inflammation activity in reclaimed water fell slightly less than the original level.Considering the contact time of UV/chlorine oxidation process is shorter than chlorination and chlorination process is sustained,chlorination may be more conductive to control the exposure risk of endotoxin from reclaimed water.By determining the endotoxin removal and it's mechanism in chlorination and UV/chlorine disinfection processes,this research provides a theoretical basis for the risk control study of reclaimed water inhalation exposure. |
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