|M.Sc Student||Roni Greenberg Eitan|
|Subject||Removal of Trihalomethane Precursors by Nanofiltration in|
the National Water Carrier System
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Dubowski Yael|
|Dr. Lili Heller Grossman|
|Professor Emeritus Rebhun Menahem|
|Full Thesis text|
Disinfection with chemicals is used for protection against photogenic microorganisms, however powerful disinfectants may react with dissolved organic matter and generate disinfection by-products (DBP) that may pose a health risk. One of the most prevalent DBP group is trihalomethanes (THMs), which are believed to be carcinogenic. One promising way to reduce THMs formation is by the removal of their precursors using nanofiltration (NF). High THM formation is usually associated with organic matter characterized by high SUVA value (ratio between absorbance at 254nm (UVA254) and dissolved organic carbon), such as aromatic humic substances. In the national water carrier (NWC), however, the water shows high THM formation potential although it mainly contains low molecular weight (MW) hydrophilic organic matter with low SUVA.
Previous studies mainly focused on removal of high MW organic matter with high SUVA. Additional research is needed regarding the removal of small and hydrophilic organic matter, as in Israel's NWC and which is believed to be harder to remove.
In the present study NF removal abilities were tested on NWC water (before chlorination) in spiral wound membranes at cross flow, batch system. The rejections and flux were tested as a function of pressure (recovery aspires to zero), recoveries (constant pressure) and type of membrane (NF 90, NF 270 and DL). The feed and permeates TOC, UVA254, THM formation (THMF) and THM formation potential (THMFP) as well as alkalinity, conductivity, hardness, and concentrations of Ca, Mg and Cl- were tested in order to evaluate rejections/reductions following filtration. The results show that NF can remove well NWC organic matter and reduce THM formation, thus improve water quality. At low water recovery, NF 90 and NF 270 membranes showed average reduction of about 85% and 83% in THMFP and THMF. DL membrane results were lower with average reductions of 75% and 70% in THMFP and THMF. Elevating water recovery to 85% resulted in lower average reductions in THMF and THMFP: 60%-70% and 70%, respectively, for NF 270 and NF 90. These reductions are still high and product quality is well below Israel total THM concentration permitted in drinking water. DL at 70% recovery reduced THMF and THMFP by 54% and 60%, respectively, lower average reductions but still acceptable.