|M.Sc Student||Fridman-Bishop Noga|
|Subject||Minimization of Bromate Formation as Part of the Operation|
of a Non-Thermal-Plasma Method for Oxidation of
Refractory Organic Compounds
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Ori Lahav|
|Full Thesis text|
Advanced oxidation processes (AOP) are developed for the removal of refractory organic compounds from the aqueous phase. Non-thermal-plasma is an emerging AOP technique. In this method, due to a strong electric discharge, a large amount of radicals and reactive molecules are created and used to oxidize target pollutants.
Bromate ion (BrO3-) might form during strong oxidation of tap water containing bromide ions (Br-). The EPA has set the maximum bromate concentration allowed in drinking water at 10 mg/l.
The mechanism of bromate formation is described in the literature as a combination of oxidation of bromide by ozone and hydroxyl radicals. It is known that bromate formation depends on both water quality and system operation parameters.
Most of the information on bromate has been acquired in the context of ozonation processes. Only a few works addresses the issue of bromate formation in AOP but none with respect to non-thermal-plasma based AOP.
The main goal of the research was to reveal the mechanism of bromate formation and to define an optimal set of parameters for operation of a non thermal plasma reactor which results in both minimal bromate formation, along with maximal oxidation efficiency.
Bromate formation was found to be higher at higher bromide concentrations, higher pH values and lower water temperatures. The presence of organic contaminants in the solution and the required degree of degradation also affected bromate formation. In general, with respect to the organic contaminants tested in this work, the affinity of the oxidants formed in the plasma reactor was found higher to the organic contaminants than to the bromide ion. Thus, the presence of organic matter inhibited bromate formation. The higher the organic matter concentration was, the lower were the bromate concentrations formed. This effect depended on the organic contaminant itself: higher affinity of the organic matter to O3, OH? and HOBr\OBr- appears to absorb the oxidants thereby reducing the bromate formation rate. Turning an inherent "injection" unit, used to inject rich-O3 gas to the water, off, resulted in lower bromate formation.
Based on the experimental results, a dominant bromate formation pathway was proposed.
Bromate will probably not exceed the 10 μg/l MCL in water containing bromide concentrations lower than 0.5 mg/l and concentrations higher than 0.5 mg/l phenol or 10mg/l CSB. If required, a low ammonia dosage or a combination of chlorine and ammonia were found sufficient for minimizing bromate formation to below the MCL value.