Citation:

Boczek, L., J. Hoelle, M. Ware, M. Elovitz, M. Rodgers, AND H. Ryu. The efficacy of potassium ferrate as a chemical disinfectant on E. coli, Vibrio cholera, human adenovirus, and Giardia lamblia. Presented at WQTC, salt lake city, UT, November 15 - 18, 2015.

Impact/Purpose:

This presentation will outline the ferrate disinfection work on a variety of microorganisms. This information will be beneficial to individuals that are interested in alternative forms of disinfection. This is the first publication that discusses CT values of ferrate as a disinfectant on a wide variety of microbes.

Description:

Introduction: Drinking water and wastewater go through numerous treatments to remove microorganisms and other contaminants one of many processes along the treatment train is disinfection. There are different ways to disinfect these waters, however to date the most common disinfectants still remain chemical disinfectants. The most common chemical disinfectants used in water and wastewater are sodium hypochlorite and chloramines. Each of these disinfectants has advantages and disadvantages with respect to treatment; one of the big disadvantages is the formation of disinfection by products. Due to the problem with disinfection by-products 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 water and wastewater. This is mainly due to the fact that it is a strong oxidant and the by-product formed is ferric ion, which is a non-toxic product that the water industry currently uses in coagulation methods. 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. Newer potassium ferrate products have recently been introduced into the market, and as such should be evaluated for their disinfecting properties. In this study, we attempted to evaluate the disinfecting capability of ferrate against a variety of waterborne microorganisms under different pH and water temperature. Methods: Controlled bench scale disinfection experiments were used with potassium ferrate as the disinfectant. The efficacy of potassium ferrate as a disinfectant was determined using several different microorganisms. These 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) (ABTS). Experiments were conducted at three pHs of 7, 8, and 9 and were performed at 5C and 25C 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 (ferrate concentration (mg/L)*contact time (min)) of 10, whereas G. lamblia cysts showed the highest resistance to ferrate, resulted in a CT of 1500 to achieve two log inactivation. For human adenovirus type 2, a maximum of over 4 log inactivation by a CT of 1 under optimum performance conditions (i.e., at pH=7 and temp=25C) was achieved, whereas less than 2 log inactivation with the same CT value was shown at pH=9. Compared to the tested bacteria and G. lamblia, human adenovirus is relatively susceptible to ferrate, resulted in few orders of magnitude lower CT values to achieve the same level of log inactivation. The microbial inactivation rates increase with decrease in pH at warmer temperature which is comparable to other studies. 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 strongly suggested further study on the evaluation of its coagulation property as synergistic treatment efficiency during water treatment processes.

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