Formation Of N-Nitrosodimethylamine(NDMA) From Algae Organic Matter After Disinfection

N-Nitrosodimethylamine(NDMA), a highly carcinogenic and genetic toxic disinfection by-products formed during the chlorination and chloramination process in drinking water treatment, has drawn much attention. Algae organic matter is an important precursor to form NDMA. Blue-green algae(Microcysti aeruginosa),occurred during summer in most drinking water sources in China, was used to investigate the the N-Nitrosodimethylamine formation potential(NDMAFP) in three kinds of disinfection process such as sodium hypochlorite, monochloramine and UV irradiation. The identification of NDMA precursors in EOM and IOM of Microcystis aeruginosa was also studied.1. NDMAFP of algae organic matter in three kinds of disinfection processesThree kinds of disinfection processes(sodium hypochlorite, monochloramine and UV irradiation) was compared for the NDMA formation potential(NDMAFP)from Microcysti aeruginosa extracellular organic matter(EOM) and intracellular organic matter(IOM). For EOM, the NDMAFP order is: Na Cl O> UV> NH2 Cl.For IOM, the NDMAFP order is Na Cl O > NH2 Cl > UV. 15 N isotope tracer method was applied to track N source of NDMA. It was found out that most N atoms of NDMA was from the algal cells themselves, rather than monochloramine in the process of chloramination. And sodium hypochlorite oxidation is better than a chloramine, therefore the NDMAFP of chlorination is higher than chloramination. For entropywater, there is no NDMAFP elevated risk when monochloramine was used instead of chlorine in the process of disinfection.2. Effects of disinfection conditions on NDMAFPFactors(contact time, disinfectant dosage and reaction p H) that influence the NDMA formation were studied. The results showed that NDMAFP increased at first,and then kept stable in the process of chlorination and chloramination of EOM and IOM as contact time prolonged. With the dosage increasing, NDMAFP increased at first and then balanced. For EOM, NDMA was formed in highest amount at the p H =6 ~ 7 when disinfected with sodium hypochlorite, and at p H = 7 when disinfected by monochloramine. NDMAFP is lower under acidic conditions than that under basic condition during UVirradiation disinfection, NDMAFP stability within the p H range of 6 ~ 9. The p H has a significant influence on NDMAFP from sodium hypochlorite and chloramine disinfection, but little impact on NDMAFP from UV disinfection.3. Characteristics of the NDMA precursorsin algal organic matterIt was the first time that polarity rapid assessment method(PRAM) was applied in the fractionation of nitrosamine precursors in EOM and IOM of Microcysti aeruginosa. In comparison with classical resin method, this method could give more information on the charge distribution of precursors. Moreover, the PRAM method was more simple and reliable. The results showed that the amount of NDMA formed from IOM is much more than that from EOM, but EOM yields more NDMA per DOC after chlorination. The polarity component yield more NDMA than non-polarity component, non-polar component had a higher NDMAFP per DOC during chlorination. The order of NDMA formation from different on charged component of EOM and IOM was uncharged component>positively charged component>negatively charged component. The order of NDMA per DOC in EOM was positively charged>component uncharged component>negatively charged component, and in IOM was uncharged component>positively charged component>negatively charged component.The precursors of NDMA mainly come from polarity, uncharged and positively charged component. Therefore anionic flocculant is a good choice to improve the removal of the precursors.