|M.Sc Student||Barkay-Arbel Yoav|
|Subject||Precursors Removal and Reduction of Disinfection By-Products|
Formation by Enhanced Coagulation and
Sedimentation in the NWC System
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Eran Friedler|
|Professor Emeritus Menahem Rebhun|
|Full Thesis text|
studied the efficiency of the enhanced coagulation and sedimentation process,
with Lake Kinneret water entering Eshkol site, in reducing THMs precursors.
Enhanced coagulation is defined as an intensive coagulation process in which the coagulants doses are significantly higher and coagulation pH is being adjusted to significantly lower values, in comparison to regular coagulation, for the purpose of reducing natural organic matter (NOM) DBPs (Disinfection by-products) precursors (suspended and dissolved).
Previous studies characterized Kinneret's water NOM content (of very low specific ultraviolet absorbance - SUVA, less than 1.0) and other important characteristics such as high bromide concentration (~2 mg/L). Enhanced coagulation processes in other surface waters were reviewed for their efficiencies in reducing DBPs precursor NOM from water. These were linked to raw water quality parameters such as SUVA and specific NOM characteristics.
Three commercial coagulants were tested (doses range of 0 to 3.24 mg-Al/L) with three coagulation pH conditions (6.0 - 7.8) using jar-test apparatus. The enhanced coagulation procedure was followed by constant detention time for sedimentation and effluent analysis for Turbidity, dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UVabs), THMSDS (Simulation of Distribution System) and trihalomethanes formation potential (THMFP, the maximal THMs formation potential).
Optimal experimental conditions obtained when PACL PAX-XL19 or Alum were used, with coagulation pH of 6.0 and doses of 2.44-3.24 mg-Al/L. Maximum DOC and UVabs reduction was 22% and 29% respectively, while THMSDS and THMFP reduction was much lower with values of 4-7% and 16% respectively. The relatively low reductions achieved were attributed to Lake Kinneret's water NOM characteristics- namely: hydrophilic, low molecular weight, higher aliphatic content - which makes it less responsive to enhanced coagulation, in addition to the high bromide concentration in the water which affects heavily the DBPs production chemistry. Additional experiments were performed with humic acid simulative, "Kinneret like", solution, showed much better removal efficiencies in all parameters. In this experiment too, correlation between THMSDS and THMFP reductions (40% and 49% respectively) and UVabs and DOC reduction (97% and 77% respectively) was poor.
The residual (remained in water) DOC, was found to be more reactive in creating THMSDS and THMFP, on a mg-C basis, in comparison to the removed DOC fraction.
Enhanced coagulation and sedimentation of Lake Kinneret water as a measure for THMs precursors reduction is practically inefficient. Although the process removed more DOC and UVabs than expected, THMSDS and THMFP reductions were low due to the specific Lake Kinneret water characteristics.