Effect Of Bromide Ion On The Formation Of Halonitromethanes From Algae Solution Under UV/Chloramine Disinfection

The rupture of algae cell can produce a large number of algal metabolites.Algae organic matter（AOM）released through algal metabolic activities contains amino acids,carbohydrates and proteins,which are the main precursors to produce disinfection by-products（DBPs）.As a typical nitrogen-containing disinfection by-products（N-DBPs）,the toxicity of HNMs is stronger than of Trihalomethanes（THMs）and Haloacetic Acid（HAAs）.In this paper,three algal solutions（Chlorella,Microcystis aeruginosa,Diatom）were selected as the precursors of HNMs.The law of HNMs formation in the presence of bromide was studied under UV/chloramine disinfection.The changes of nitrogen and HNMs toxicity were analyzed,and the reaction mechanism was deduced.Finally,the law of HNMs formation in laboratory was verified by actual water samples.This study can provide a theoretical basis for controlling the generation of HNMs under UV/chloramine disinfection.Firstly,the rule of HNMs formation from algae solution was studied under UV/chloramine disinfection in this paper.The experimental results showed that Chloronitromethane（CNM）,Dichloronitromethane（DCNM）,Trichloronitromethane（TCNM）could be generated by Chlorella,Microcystis aeruginosa and Diatom.With the increase of reaction time,the concentration of CNM,DCNM and TCNM showed a trend of increasing firstly and then decreasing.The concentration of CNM,DCNM and TCNM increased with the increase of chloramine concentration,initial concentration and light intensity,while the increase of p H inhibited the formation of HNMs.The concentration of HNMs produced by intracellular organic matter（IOM）was higher than that of extracellular organic matter（EOM）.Secondly,the effect of bromide iron on the HNMs formation under UV/chloramine disinfection was studied in this paper.The experimental results showed that Chlorella could produce TCNM,Bromonitromethane（BNM）,Bromodichloromethane（BDCNM）,Dibromochloronitromethane（DBCNM）and Tribromonitromethane（TBNM）.The HNMs produced by Microcystis aeruginosa did not detect Bromochloronitromethane（BCNM）.Diatoms produced BNM,BDCNM and TBNM.With the increase of bromide iron,the concentration of Chloronitromethane（Cl-HNMs）formation from three algal solutions showed a decreasing trend,and the concentration of Bromonitromethane（Br-HNMs）increased firstly and then decreased.With the increase of chloramine concentration,the concentration of TCNM,BNM,BDCNM and TBNM from Chlorella showed an increasing trend.The concentration of DBCNM produced by Chlorella increased firstly and then decreased.The concentration of CNM,DCNM,TCNM,BNM,TBNM and BDCNM from Microcystas aeruginosa showed an increasing trend with the increase of chloramine concentration.The concentration of Dibromonitromethane（DBNM）and DBCNM increased firstly and then decreased.The concentration of BNM and TBNM from diatoms increased with the increase of chloramine concentration.The concentration of BDCNM increased firstly and then decreased,with the increase of p H,the HNMs produced by three algaes showed a decreasing trend.With the increase of light intensity,the concentration of HNMs in the three algal solutions increased.The formation of HNMs produced by EOM was lower than that of IOM.With the increase of Br^-concentration,the Bromine Incorporation Factor（BIF）values of the three algal solutions showed an increasing trend.The order of cytotoxicity calculated by LC₅₀was Chlorella>Microcystis aeruginosa>Diatoms.After UV exposure,the fluorescence intensity of protein-like,Soluble Microbial Byproducts（SMP）and humic acid in Microcystis aeruginosa IOM decreased.The fluorescence intensity of SMP in Chlorella and Diatom IOM decreased.Compared with chloramine disinfection,the concentrations of total nitrogen（TN）and organic nitrogen（DON）decreased more with reaction time under UV/chloramine disinfection,while the concentrations of ammonia nitrogen（NH₃-N）and nitrate nitrogen（NO₃-N）increased more under UV/chloramine disinfection.Finally,the experiments were carried out with real water samples under the conditions of UV/chloramine and UV/chloramine（with bromine）to verify the law of the formation of HNMs in laboratory.By comparing the experimental results of laboratory and real water samples,it was found that the types and rules of HNMs formation were similar,but the size and the time of the maximum HNMs formation were different due to the more complex composition of real water samples.