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The efficacy of potassium ferrate as a chemical disinfectant on E. coli, Vibrio cholera, human adenovirus, and Giardia lamblia - Abstract
Boczek, L., J. Hoelle, M. Ware, M. Elovitz, AND H. Ryu. The efficacy of potassium ferrate as a chemical disinfectant on E. coli, Vibrio cholera, human adenovirus, and Giardia lamblia - Abstract. Presented at AWWA Water Quality Technology Conference, Salt Lake City, UT, November 15 - 19, 2015.
Research results on effectiveness of ferrate as a disinfectant
Introduction: Drinking water and wastewater effluents go through numerous treatments to remove microorganisms and other contaminants in the United States. One of many processes along the treatment train is disinfection, and to date the most common disinfectants still remain chemical disinfectants such as sodium hypochlorite and chloramines. One of the big disadvantages of using these disinfectants is the formation of disinfection by products (DBPs). Due to the problem with DBPs, alternative methods for disinfection are always being sought. Disinfection with potassium ferrate as an alternative to chlorine based disinfectants has the potential to revolutionize the disinfection of drinking water and wastewater. This is mainly due to the fact that ferrate (VI) (FeVI: HFeO4-/FeO42-) is a strong oxidant and the by-product formed is ferric ion, which is a non-toxic product. Potassium ferrate has not been used widely as a disinfectant due to cost constraints, and the stability of the product, as well as the lack of accurate CT tables. More recently, newer potassium ferrate products have been introduced into the market. In this study, we attempted to evaluate the disinfecting capability of ferrate against a variety of waterborne microorganisms under different pH and water temperatures. Methods: Classic bench-scale disinfection studies measuring the CT of the disinfectant and the log-inactivation of several different microorganisms were conducted by using stock solutions of potassium ferrate as the ferrate source. Experiments were conducted at pHs of 7, 8, and 9, and at 5C and 25C. The testing microorganisms included waterborne bacteria (three strains of Escherichia coli including pathogenic O157 strain and three strains of Vibrio cholera), protozoan parasite (Giardia lamblia cysts), and enteric virus (human adenovirus type 2). Membrane filtration, animal infectivity using Mongolian Gerbils, and tissue culture infectivity assays were used for the detection of the respective test microorganisms. Residual ferrate was measured during the experiments using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid). Results: More than 4 log inactivation of E. coli and Vibrio cholera was achieved under all the testing conditions (i.e., three different pHs and two temperatures) with a CT of 4.7 mg-Fe*min/L, whereas G. lamblia cysts showed the highest resistance to ferrate (700 mg-Fe*min/L to achieve 2-log inactivation). For human adenovirus type 2, a maximum of over 4 log inactivation was achieved with as little as 0.5 mg-Fe*min/L under optimum performance conditions (i.e., at pH=7 and temp=25C), whereas less than 2-log inactivation with the same CT value was shown at pH=9, 25C. For all test microorganisms, the microbial inactivation rates increased at lower pH and higher temperature, which is consistent with other studies showing the greater oxidation potential of the HFeO4- acid/base species, and a considerable temperature dependence of many ferrate reactions. Compared to the tested bacteria and G. lamblia, human adenovirus is relatively susceptible to ferrate inactivation, requiring orders of magnitude lower CT values to achieve the same level of log inactivation. Conclusions: Overall, ferrate demonstrated sufficient inactivation of the testing microorganisms with relatively low CT values. Given these promising results on ferrate’s disinfecting capability, we suggest further study on the evaluation of its coagulation property as synergistic treatment efficiency during water treatment processes.