Grantee Research Project Results
2014 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, 2013 through November 30,2014
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:
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:
Progress Summary/Accomplishments:
The project to date has focused on bench-scale testing of ferrate oxidation for small drinking water treatment systems. 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 second project period, we have conducted abbreviated assessments with 2 raw waters and full assessments with 13 additional waters. Most of these have focused on ferrate’s impacts 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 and Lee et al., in 2014 does an excellent job of describing the decomposition kinetics we observe in pure waters, especially those buffered with phosphate. However, natural waters and even pure waters buffered with carbonate show much different decomposition rates. We attribute this to surface reactions that accelerate ferrate decomposition but that are partly quenched by ligands. 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. The observed CT values are high enough to meet criteria for 2 log removal of viruses and Giardia based on the current EPA assessment of ferrate. Higher pHs result in greater ferrate stability and therefore higher CT values.
We also have noted that ferrate will slowly oxidize bromide, forming low levels of active bromine and bromate. This is not expected to cause a serious problem as the levels are quite low. Ferrate rapidly oxidizes 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 preoxidation 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 pre-oxidation with ferrate may be that oxidation and 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. On the other hand, intermediate oxidation with ferrate may result in substantially reduced concentrations of DBPs in the finished water.
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 oxidation and disinfection without producing chlorinated DBPs. Furthermore, it is simpler to apply than ozone, and we expect it will prove to be less expensive and less energy intensive.
Future Activities:
We will continue with the bench-scale tests and lab pilot testing. We continue to look for some problematic waters, especially those with 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.
Journal Articles:
No journal articles submitted with this report: View all 12 publications for this projectRelevant Websites:
UMass project website ExitProgress 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.