|M.Sc Student||Deri Liad|
|Subject||Identification and Quantification of Odorous Compounds in|
the National Water Carrier and the Potential to
Remove them by Activated Carbon
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Yael Dubowski|
|Professor Emeritus Menahem Rebhun|
|Full Thesis text - in Hebrew|
In the last decades the odor in the national water carrier (NWC) was rather low but measurable by common odor panel tests, with short duration but stronger odor episodes in some seasons. For understanding and controlling formation of odors and designing treatment for their removal, it is essential to identify the specific chemical compounds responsible for the odors in water and quantify their concentrations.
Identification and quantification of odorous chemical compounds in water is a challenging task, since their threshold odor concentrations (OTC) may be as low as few nanograms per liter. Five specific odorous chemicals were identified: geosmin, MIB, nonanal, 2-heptenal and 2,4-heptadienal. The concentrations of the strongly odorous compounds (i.e., of low threshold odor concentrations): geosmin, MIB, nonanal were detected and quantified at levels of 2-10 ng/l. Headspace solid phase micro extraction (HSPME) followed by GC/MS analysis was found in this study to be sensitive and reliable method for identification and quantification of the chemical compounds.
A monitoring study of the selected odorous compounds was carried out along the Eshkol site. 17 monthly samples of NWC water were collected at 7 points, covering all seasons and obtaining concentration profiles across the storage and treatment steps. The selected compounds founded mostly under or closed to their OTC level, exceptional was nonanal (Fruity/Rancid odor).
No correlation was found between the concentration of the odorous chemicals, odor level and the present of planktonic algae. This lack of correlation may indicate that the odorous compounds are produced by benthic organisms not monitored in the Eshkol reservoirs.
Adsorption isotherms were obtained experimentally for gesomin and MIB, the most common odors compounds, on 2 powdered and 6 granular activated carbon of bituminous, wood and coconut origins. They could be best fitted to linear type of isotherms. Geosmin was found to be better adsorbed (higher capacity) than MIB for all GAC and PAC tested.
The wood based PAC showed better capacity and kinetics than the bituminous PAC. For the low residence time (7 min) in the mixing flocculation reactor of the Eshkol central filtration plant, PAC dose of 50 mg/l would be needed to remove 80 percent of MIB.
Column experiments of GAC adsorption were carried out in rapid small tests column (RSSCT). The RSSCT run for 15 days represents about 300 days operation in large column. It was found that about 50,000 bed volumes of water can be treated to breakthrough of C/C0~0.5 MIB and geosmin.