Study On The Formation Of Brominated Halonitromethane From Algaes In The Process Of UV/Chlorine Disinfection

During the growth of algae,algae metabolites will be released into the water,which it is difficult for the traditional water treatment process to effectively remove,resulting in a series of nitrogen-containing disinfection by-products during the chlorination disinfection process.Halonitromethanes(HNMs)are typical representatives of nitrogen-containing disinfection byproducts.When bromide ions are present in the water,brominated HNMs are easily formed during the disinfection process.Their cytotoxicity and genotoxicity are at the forefront of HNMs.It will cause hidden danger to water quality.In this paper,it explored the photodegradation rules and reaction pathways of bromonitromethane(BNM)and bromodichloronitromethane(BDCNM)in HNMs under low-pressure ultraviolet light irradiation.Simultaneously,the intracellular organic matter(IOM)of three common algae(Chlorella,Anabaena and Synedra)was used as precursors to study the laws and influencing factors of the algae generating brominated HNMs during the UV/chlorine disinfection in the presence of bromide ions.In addition,the actual water samples were used to verify the influencing factors and regularity of brominated HNMs generated by the laboratory-simulated IOM of algae during UV/chlorine disinfection.The results of this paper could provide theoretical basis and basic data for controlling the production of brominated HNMs during the UV/chlorine disinfection process.Firstly,the photodegradation characteristics of HNMs were studied under UV irradiation.In the experiment,BNM and BDCNM were selected as the research objects.The effects of light intensity,initial concentration,free chlorine concentration,bromide ion concentration and pH value were investigated on the photodegradations of BNM and BDCNM,and the kinetics of their photodegradation were also analyzed.Based on relevant references and experimental results,the photodegradation pathways of BNM and BDCNM were deduced.The results showed that BNM and BDCNM hardly degraded under dark conditions,but could degrade rapidly under UV irradiation.The photodegradations of BNM and BDCNM under UV irradiation fitted the first-order reaction kinetics model.Their photodegradation rates increased with increasing light intensity and pH,and decreased with increasing initial concentration.Adding free chlorine could significantly promote the photodegradation rates of BNM and BDCNM and accompanied by the formation of other HNMs during the photodegradation process.Bromine ion could slightly promote the photodegradations of BNM and BDCNM.The experimental results in this chapter could provide a reference for controlling the production of brominated HNMs,and at the same time provided an explanation for the phenomenon of increasing first and then decreasing of the concentration of brominated HNMs from the IOM of algae under UV/chlorine disinfection.Secondly,the laws of brominated HNMs formation from the IOM of algae were studied under UV/chlorine disinfection with the presence of bromine ions.The experiments selected the IOM of Chlorella,Anabaena and Synedra as the research objects,investigated the effects of free chlorine concentration,bromine ion concentration,initial concentration,light intensity and pH value on the formation of brominated HNMs and analyzed the variations of different forms of chlorine and nitrogen in the IOM of algae under UV/chlorine disinfection.The results showed that the IOM of Chlorella,Anabaena and Synedra could produce brominated HNMs during the UV/chlorine disinfection process with the presence of bromine ions.The production of brominated HNMs increased firstly and then decreased with the extension of the reaction time.The potential formation of brominated HNMs from three algae was Chlorella > Anabaena>Synedra.The IOM of Chlorella could produce BNM and BDCNM while the IOM of Anabaena and Synedra could produce BNM,bromochloronitromethane(BCNM)and BDCNM under UV/chlorine disinfection.The BNM produced by the IOM of Chlorella increased with the increase of free chlorine concentration and BDCNM showed a trend of increasing first and then decreasing with the increase of free chlorine concentration.The BNM and BDCNM produced by the IOM of Anabaena and Synedra first increased and then decreased with the increase of free chlorine concentration and BCNM increased with increasing free chlorine concentration.With the increase of bromine ion concentration,the amount of BNM and BDCNM produced by the IOM of Chlorella,Anabaena and Synedra d showed a trend of first increasing and then decreasing under the UV/chlorine disinfection.The BCNM produced by the IOM of Anabaena and Synedra increased with increasing bromine ion concentration.The productions of brominated HNMs in the IOM of Chlorella,Anabaena and Synedra increased with the increase of light intensity and initial concentration,and decreased with the increasing of pH under UV/chlorine disinfection.Finally,the actual water samples were selected after filtration and before disinfection in the sewage plant and water supply plant to verify the law of laboratory simulation.It simultaneously studied the law of the formation of brominated HNMs under UV/chlorine disinfection after adding bromide ion and IOM of algae in the actual water sample.The results showed that the trend of the production of brominated HNMs in the UV/chlorine disinfection process of the actual water sample was similar to that of the brominated HNMs when the IOM of algae was used as the precursor.The variation trend of the formation of brominated HNMs from the IOM of algae in the actual water sample was similar to that in the laboratory ultrapure water simulation.However,due to the complexity of the components in the actual water sample,the productions and peak time of the formation of brominated HNMs were different.The results of this paper can provide a reference for controlling the formation of HNMs in the process of UV/chlorine disinfection.