Submitted to: Laboratory Solution
Publication Type: Research Notes
Publication Acceptance Date: 1/5/2006
Publication Date: 1/15/2006
Citation: Kim, H., Millner, P.D., Sharma, V.K., Mcconnell, L.L., Torrents, A., Ramirez, M., Peot, C. 2006. Ferrate: nature’s most powerful oxidizer: it’s potential as a disinfection treatment for thickened sludge. Laboratory Solution. 12(6):1-4. Interpretive Summary: Processing and treating wastewater generates large quantities of sludge containing organic and inorganic constituents. Most of the dewatered sludge generated in the US currently is applied to agricultural lands in accordance with US EPA and state rules and regulations. Disinfection helps protect public health and the environment; various strategies are used to reduce the pathogen load in material prior to land application. Ferrate is a powerful, oxidizing chemical that has a higher reactivity and selectivity than traditional oxidants. Ferrate inactivates 99.9 percent of E. coli with 6 mg iron per liter in 7 min. and rapidly inactivates f2 coliphage. Ferrate does not produce any toxic byproducts like other disinfectants such as chlorine, iodine, bromine, chlorine dioxide, and ozone. This report presents results from a pilot-scale experiment designed to evaluate the disinfection efficiency of ferrate produced from an on-site generator (Ferrater-TM) process. Ferrate was applied at 0, 20, 40, 80, and 160 mL per 2 L of thickened sludge (1:1 mixture from gravity and dissolved air flotation thickeners). Treated sludge samples were analyzed for a number of common pathogens to provide an estimate of dosage required to achieve sufficient disinfection for land application. The high pH resulting from the reaction and the oxidation power of ferrate was applied to disinfecting microorganisms in sludge. With only 40 mL ferrate solution per 2 L of thickened sludge, more than 99 percent of all the indicator microbes were inactivated, except for the spore-forming bacterium Clostridium perfringens which was expected to be resistant. Notably, coliforms were completely disinfected at the lowest dosage of ferrate. These results indicate that ferrate has a high potential for use in disinfecting sludge of a range of fecal indicators and pathogens.
Technical Abstract: Throughout the United States, biosolids land application program plays an important role in the management of biosolids. Each year, about 60% of 7-8 million dry tons biosolids generated in the US is land applied as a soil conditioner or fertilizer. However, due to increasing public concern on the risk and safety of land-applied biosolids, the land application program is being opposed. Therefore, various sludge treatment technologies to improve the sludge quality, especially in terms of pathogen content are being developed or are under evaluation. The performance of ferrate [FeVIO42-] as a conditioning agent for sludge was evaluated from the disinfection perspective. With its high oxidizing power, it could disinfect a wide range of microorganisms, i.e., total heterothrophs, enterococci, total coliform, fecal coliform, E. coli, clostridium perfringens and coliphage. At the rate of under 40 mL ferrate solution/2 L thickened sludge (FeO42- content of the solution: 2%; solids content of thickened sludge: 3-5%), more than 99% destruction of the microorganisms was achieved. Therefore, ferrate as an alternate conditioning agent (or disinfectant) is considered promising.