Grantee Research Project Results
2012 Progress Report: Use of Ferrate in Small Drinking Water Treatment Systems
EPA Grant Number: R835172Title: Use of Ferrate in Small Drinking Water Treatment Systems
Investigators: Reckhow, David A. , Tobiason, John , Rees, Paula
Institution: University of Massachusetts - Amherst
EPA Project Officer: Page, Angela
Project Period: December 1, 2011 through November 30, 2014 (Extended to November 30, 2015)
Project Period Covered by this Report: December 1, 2011 through November 30,2012
Project Amount: $497,078
RFA: Research and Demonstration of Innovative Drinking Water Treatment Technologies in Small Systems (2011) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
To test the ability of ferrate oxidation to solve a wide range of water quality and treatment problems faced by small systems. The general working hypothesis is that ferrate is: (1) more effective and less detrimental than existing conventional oxidative technologies such as chlorination, chloramination, and permanganate oxidation, and that it is (2) comparable in performance to advanced technologies such as ozonation or chlorine dioxide oxidation that are more costly, more hazardous or require specialized expertise to operate.
Progress Summary:
The project to date has focused on bench-scale testing of ferrate oxidation for small drinking water treatment systems. This required a substantial amount of preliminary assessment and testing, resulting in new protocols for lab-scale ferrate treatment and process evaluation. The lab-scale studies have examined the direct effect of ferrate oxidation and its impact on subsequent coagulation, flocculation, settling and filtration. As of the end of this first project period, we have conducted abbreviated assessments with two raw waters and full assessments with eight additional waters. Most of these have focused on the impacts of ferrates on residual iron, manganese, natural organic matter, and a range of disinfection byproduct (DBP) precursors. The DBP compounds (and their precursors) being studied include the trihalomethanes (THMs), all nine haloacetic acids (HAAs), the haloacetonitriles (HANs), the haloacetamides (HAMs), the halonitromethanes (HNMs), and the haloketones (HKs).
Bench-scale testing has shown that ferrate decomposition reactions are more complicated than previously recognized. The kinetic model proposed by Carr in 2008 does an excellent job of describing the decomposition kinetics we observe in pure waters buffered with borate. However, natural waters and even pure waters buffered in carbonate show much slower decomposition. We attribute this to radical reactions that accelerate ferrate decomposition but that are partly quenched by scavengers such as bicarbonate ion. This is good news for possible applications of ferrate in water treatment as it means that the ferrate species will persist longer than previously predicted, resulting in higher CT values for disinfection.
We also have noted that ferrate will rapidly oxidize iron, manganese and DBP precursors in most waters. The net result is conversion of soluble iron and manganese to particulate and colloidal forms. The latter are easily removed in conventional treatment (coagulation and filtration). The impact of ferrate oxidation on natural organic matter (NOM) and DBP precursors is similar to that observed for ozonation. At typical doses, destruction of THM precursors ranges from 15-30%. Considering the HAA precursors, destruction is higher for the trihalogenated species (i.e., 10−50%) than the dihalogenated compounds (i.e., 0−20%). These ranges are typical of what has been observed for ozonation.
After subsequent coagulation and filtration, we note that the overall impact of ferrate pre-oxidation on DBP precursors is somewhat diminished. The direct precursor destruction noted above is partly mitigated by the fact that many of these oxidized precursors would have been removed by coagulation anyway. The net impact is a small benefit in ultimate formation of regulated DBPs (i.e., THMs and HAAs). Therefore, the greatest benefit of ferrate treatment may be that pre-oxidation and pre-disinfection can be achieved without formation of regulated DBPs and with modest decreases in these DBPs after final chlorination. Ozone, by comparison, can result in elevated levels of bromate and brominated DBPs.
Our broad perspective so far on ferrate for use in small utilities is still quite positive. It offers a very attractive alternative to ozonation, providing pre-oxidation and pre-disinfection without producing chlorinated DBPs. Ferrate is capable of oxidizing regulated DBP precursors, as well as Fe and Mn with an effectiveness similar to ozone. Furthermore, it is simpler to apply than ozone, and we expect it will prove to be less expensive and less energy intensive. Use of ferrate with coagulation results in lower DBP levels in some waters under similar chlorination conditions.
Future Activities:
We will continue with the bench-scale tests and initiate our lab pilot testing. The first pilot tests will be on the Stockbridge Massachusetts system. Bench-scale tests will incorporate waters with high levels of some problematic contaminants such as sulfide, arsenic, wastewater organics and pesticides. Plans for a full-scale assessment as outlined in the proposal have been temporarily suspended as the only full-scale installation in the United States (in Florida) currently is not operating. Instead, the team is looking at options for extended pilot testing in New England.
References:
Journal Articles:
No journal articles submitted with this report: View all 12 publications for this projectSupplemental Keywords:
oxidation, costs, NOM, DBPs, PPCPs, kinetics, decomposition, iron, manganese, water quality, drinking water treatmentRelevant Websites:
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.