Formation And Removal Of Disinfection By-Products From Chlorination Of Microcystis Aeruginosa

Algal organic matter(AOM) has become important precursors of disinfection by-products(DBPs). However, studies on the formation of DBPs from AOM were limited. In this study, Microcystis aeruginosa was selected as a representative alage during algal blooms. This study investigated the characteristics of AOM, the formation of nitrogenous DBPs and carbonaceous DBPs from chlorination of AOM under different chlorination conditions(including pH, chlorine dosages, reaction time and bromide concentrations), and removal efficiencies of AOM and DBPs by enhanced coagulation and activated carbon adsorption.AOM was highly hydrophilic, low aromatic and contained relatively low molecular weight organic matters. AOM was divided into intracellular organic matter(IOM) and extracellular organic matter(EOM). IOM contained a TON/TOC(total organic nitrogen/total organic carbon) rate of 0.102. The EEM fluorescence spectra analysis indicated that IOM contained chlorophyll a, phycocyanin, aromatic proteins and humic-like material. The TON/TOC of EOM was 0.074. The EEM fluorescence spectra of EOM indicated it contained humic-like material.IOM and EOM generated sililar species and levels of halomethanes(THMs) and haloacetonitriles(DHANs). Higher pH generated higher levels of chloroform and lower levels of dichloroacetonitrile from IOM and EOM. Bromide concentration and pH generated more significant influences on EOM than on IOM.Without the presence of bromide, the formation of chloroform increased with reaction time, while formation of dichloroacetonitrile, trichloroacetonitrile, 1,1-dichloroacetone and 1,1,1-trichloroacetone followed an increasing and then decreasing pattern. Higher pH resulted higher levels of chloroform, but lower levels of other DBPs. Increasing chlorination dosages increased the formation of these DBPs.Without the presence of bromide, the total concentration of THMs was maximum at pH 7.5, and bromine substitution factor was maximum at pH 8.5. Increasing chlorination dosages increased the total concentrations of THMs and DHANs, reduced the bromine substitution factor of DHANs, and has little effects on species of THMs. Increasing bromide concentrations increased the total concentrations of THMs and DHANs, as well as the incorporation of bromine into DBPs.AOM was difficult to form big flocs and had poor settling performance. When the polyaluminium chloride dosages were 15~25mg/L(r1=100r/min, t1=30s), the concentration of dissolve organic carbon(2.9~3.9mg/L) was reduced by 47%~52%. Coagulation had different removal efficiencies on different DBPs. Activated carbon adsorpotion had a low removal efficiency for AOM. With activated carbon dosages of 10~30mg/L and adsorption time of 10~30min, the concentration of dissolve organic carbon was reduced by 12%~32%, chloroform was reduced by 15%~25% and dichloroacetonitrile was reduced by 15%~70%.