Study On The Formation Of Halonitromethanes From Algae Solution In The Process Of UV/Chlorine Disinfection

Eutrophication causes algae propagation in water.Intracellular and extracellular organic matter contained in algal organic matter will be released into water during water treatment process.Ultraviolet(UV)/chlorine disinfection can destroy cell structure and change the structure of dissolved organic nitrogen of algal organic matter,resulting in a series of disinfections by-products,which hidden dangers for drinking water safety.Among many disinfection by-products,halonitromethanes had attracted wide attention due to their high toxicity and mutagenicity.In this study,chloronitromethane,dichloronitromethane and trichloronitromethane in halonitromethanes were selected as the research objects.The intracellular and extracellular organic substances of three common algae(chlorella,diatoma and Anabaena)were used as precursors.The formation of halonitromethanes during UV/chlorine disinfection was studied and its reaction mechanism was deduced.This study provides a reference for controlling the formation of halonitromethanes in practical applications.In the experiment,the concentration of precursors,species of algae,chlorine dosage,irradiation intensity and pH value were investigated to study the production of three halonitromethanes in the process of UV/chlorine disinfection of algae solution combing with the change of dissolved organic nitrogen content in the reaction system.The results showed that the organic matter of chlorella,diatom and anabaena had the potential to produce chloronitromethane,dichloronitromethane and trichloronitromethane under chlorine and UV/chlorine disinfection conditions.The potential of formation of halonitromethanes from three algae solutions was chlorella > diatom > anabaena.The formation of trichloronitromethane was significantly higher than that of monochloronitromethane and dichloronitromethane.The formation of three halonitromethanes increased firstly and then decreased.Under the condition of pH=6-8,the production of three halonitromethanes decreased with the increase of pH,and increased with the increase of algal concentration,irradiation intensity and chlorine dosage.Compared with extracellular substances,intracellular substances of algae could produce more halonitromethanes.In the reaction process,dissolved organic nitrogen in the solution firstly increased and then decreased.Based on the experimental results and related references,the pathways of the formation of halonitromethanes in algal organic matter were deduced.Finally,the actual water(filtered water before disinfection)samples from sewage treatment plant were selected to identify the relevant laws.Under chlorine disinfection condition,the amount of trichloronitromethane produced by algae in the samples from sewage treatment plant was still more than that of monochloronitromethane and dichloronitromethane,but the amount of chloronitromethane produced by algae was larger than that in the laboratory simulation experiments.Under the condition of low-pressure UV/chlorine disinfection,the production of monochloronitromethane in the samples from sewage treatment plant increased significantly,and the peak value was at 40 minutes.The production of dichloronitromethane and trichloronitromethane was similar to the laws simulated in the laboratory.The algae contain proteins and other organic substances,which reacted with the substances in the water samples from sewage treatment plant.As a result,the amount of halonitromethanes produced in the UV/chlorine disinfection of the samples from sewage treatment plant after adding algae were less than that produced in the UV/chlorine disinfection of the samples from sewage treatment plant alone.The laws of halonitromethanes formation in the samples from the water supply plant were similar to those in the ultra-pure water in the laboratory.