Modeling of THM and HAA formation in Missouri waters upon chlorination.

摘要

The more stringent drinking water Disinfection By-Product (DBP) regulations have led utilities to examine and optimize their disinfection processes. Practical models for THM and HAA formation will assist utilities in minimizing DBP formation.; A parallel first-order reaction model was used to fit the chlorine residual data. The results showed that all tested surface waters were kinetically similar. Values of k_R for raw surface waters ranged from 1.25 to 4.09 hr −1 and for treated waters from 1.93 to 3.07 hr−1 . Values of k_S for raw waters ranged from 0.011 to 0.022hr −1 and for treated waters from 0.012 to 0.026. The main kinetic differences among water samples were from the rapid chlorine decay (k _R). Alum treatment substantially increased the rapid reacting fraction functionality for all winter waters with f averaging 24% after treatment.; THM formation rates were initially rapid corresponding with the rapid consumption of chlorine followed by a slower, declining rate of production. On average 65% of the TTHM was formed within 24 hours for all bulk water samples. DCAA, and TCAA were the main species among the nine HAAs. Approximately 50% of the HAA₉ observed after 120 hours actually formed during the first 8 hours. Brominated species were preferentially formed in the early part of the reaction period and maintained the same concentrations after 24 hours.; A new mechanistic model was developed to predict the TTHM and HAA ₉ formation in raw and alum treated waters based on the decay rate constants obtained in the chlorine decay modeling. TTHM yield coefficients ranged from 22.0 to 48.0 μg-TTHM/mg-Cl₂ for all raw and alum treated waters. Alum treatment reduced the TTHM yield coefficient by 14%. HHA₉ yield coefficients ranged from 15.3 to 27.7 μg-HAA9/mg-Cl₂. The yield coefficient was reduced by 33% with alum treatment.; HAA₉/TTHM mass ratio ranged from 0.62 to 0.87 for raw water and from 0.50 to 0.69 for treated water. On average HAA₉ to TTHM ratio was decreased 0.14 by alum coagulation. In the DBP formation processes, a small trend decrease was observed for HAA₉/TTHM ratio with time.; A decrease in the Bromine Incorporation Factor (BIF) values with time in the THMs and HAAs formation processes was observed. The alum coagulation process increased the BIF values of DBP.; Raw waters were fractionated using various size UF membranes. Chlorine decay kinetics, THMs formation potential and formation kinetics in various UF fraction waters were also investigated in this study. UV₂₅₄ value changed with time of UF fractionated waters.; No influences for inorganic compounds (NaHCO₃, NaCl, Na ₂SO₄, MgSO₄, ZnSO₄, CaCl₂, and KBr) were found. Cu(II) and Co(II) did, however, increase the hypochlorite decomposition.