Grantee Research Project Results
Final Report: Pilot Studies of the Ozonation/FBT Process for the Control of Disinfection Byproducts in Drinking Water
EPA Grant Number: R826829Title: Pilot Studies of the Ozonation/FBT Process for the Control of Disinfection Byproducts in Drinking Water
Investigators: Masten, Susan J.
Institution: Michigan State University
EPA Project Officer: Hahn, Intaek
Project Period: July 15, 1998 through May 14, 2001 (Extended to August 15, 2001)
Project Amount: $424,734
RFA: Drinking Water (1998) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
The overall objective of this research project was to investigate a combined ozonation/biological fluidized bed treatment (FBT) for the removal of trihalomethanes (THM) and other disinfection byproduct (DBP) precursors from drinking water. The specific objectives of this research project were to: (1) develop an economical and simple processing system for the control of DBPs in drinking water; and (2) develop design criteria for the proposed ozonation/FBT system.
The objectives of this research project were accomplished through bench-scale and pilot-scale studies. The studies were conducted using three very distinct source waters: (1) Lake Erie water collected at the Monroe Water Filtration Plant (Monroe, Michigan); (2) Huron River water collected at the Ann Arbor Water Treatment Plant (Ann Arbor, Michigan); and (3) Lake Lansing water (East Lansing, Michigan). Lake Erie water has a low total organic carbon (TOC) concentration of approximately 2 mg/L. Huron River water has a TOC concentration of 6-8 mg/L and is typical of rivers across the United States. Although Lake Lansing water does not provide source water to any treatment plant, it has been selected because of its high TOC concentration (9-11 mg/L).
Summary/Accomplishments (Outputs/Outcomes):
Several experimental systems were developed to accomplish our objectives. These include a bench-scale ozonation system, a bench-scale biodegradation system, and a pilot-scale ozonation/FBT system.
The bench-scale ozonation system was developed to investigate the kinetics of ozonation of naturally occurring organic matter (NOM) in selected source waters and particularly the effect of ozonation pathways on the formation of both DBPs and biodegradable organic matter (BDOM). The biodegradation kinetics of raw and ozonated waters were studied using bench-scale biofiltration and FBT systems. The pilot-scale ozonation/FBT system was developed to evaluate the performance of the combined ozonation and FBT process for the control of DBP precursors in drinking water.
The effect of ozonation reaction pathways on the formation of both DBPs and biodegradable organic carbon (BDOC) was investigated. The study showed that the production of OH radicals relative to ozone dose adjusted for alkalinity was greatest in water with the lowest TOC concentration (Lake Erie water) and lowest in water with the highest TOC concentration (Lake Lansing water). This suggests that organic matter in selected source waters acted more as a scavenger than a promoter of radical reactions. The study also demonstrated that direct ozone reactions favor the production of BDOC, whereas radical reactions result in the removal of organic carbon. These findings were important in developing optimization strategies for the combined ozonation/FBT system.
In biodegradation studies, we identified several parameters that described the kinetics of the removal of organic matter during biodegradation. These included: (1) empty bed contact time (EBCT)min, which represented the minimum EBCT required to remove rapidly BDOC (“fast” BDOC); (2) BDOCslow, which represented the amount of BDOC that remained after biodegradation at EBCTmin; and (3) Rmax, which was defined as the maximum rate of the biodegradation of “fast” BDOC.
The results of these experiments demonstrated that the source waters selected for this study were very distinctive, not only in terms of the TOC matter content but also in terms of the amount of potentially BDOC. Essentially, all organic matter in Lake Erie water was refractory organics (i.e., not subject to biodegradation). Huron River water contained approximately 20 percent of potentially BDOM, whereas nearly one-half of the organic matter in Lake Lansing could be biodegraded.
The study showed that ozonation of Lake Erie water at doses up to 3 mg/mg C did not result in the production of BDOC. Ozonation of Huron River water resulted in an increase of BDOC concentration from 1.2 mg/L in raw water to 2.8 mg/L in water ozonated at a dose of 1 mg/mg C. The concentration of BDOCslow, however, also increased after ozonation.
The results of biodegradation experiments with ozonated Lake Lansing water were surprisingly different from those with ozonated Huron River water. Unlike Huron River water, for which no significant changes in biodegradation kinetics were observed at doses greater than 0.5 mg/mg C, the biodegradation parameters for ozonated Lake Lansing water were affected by ozone doses to a much greater extent. Ozonation of Lake Lansing water at a dose of 0.75 mg/mg C resulted in an increase in BDOC concentration from 5.04 to 6.06 mg/L. Ozonation at ozone doses of 1.5 and 3 mg/mg C resulted in the formation of additional 0.8 and 1.33 mg/L BDOC, respectively. An increase in ozone dose resulted in an increase in Rmax and a decrease in EBCTmin.
The most striking difference between Huron River water and Lake Lansing water was observed with respect to BDOCslow. The concentration of BDOCslow in Lake Lansing water decreased with an increase in ozone dose compared to Huron River water, in which BDOCslow increased at a dose of 0.5 mg/mg C and leveled off at higher ozone dosages.
The significance of these findings stems from the fact that in the United States, the control of BDOM produced from ozonation usually is accomplished by rapid filtration with an EBCT of 15-20 minutes. Although the results of the experiments suggest that these filters are capable of removing “fast” BDOC from ozonated water, slowly BDOM (BDOMslow) would remain in the filter effluent. This remaining BDOM may cause bacterial regrowth in the distribution system. As such, the control of BDOCslow produced or remaining after ozonation may be critical for the design of water treatment systems employing ozonation.
The ozonation pathways that optimize the formation of easily BDOC were investigated. The pathways by which ozone reacts with NOM are affected significantly by the following parameters: NOM characteristics, initial [O3]/[NOM] concentration ratio, pH, reaction temperature, reaction time, and additives concentration. The effect of operational parameters and the presence and concentration of additives on the concentrations of molecular ozone and the OH radical were determined. The influence of various operational parameters on biodegradability formation was determined. The effect of additives on biodegradability formation also was investigated.
The RCT values calculated allowed us to compare not only the ratio of the OH radical to the molecular ozone concentration at various ozonation conditions but also indicated the reaction rate of the OH radical with tested NOMs. The NOM of Lake Erie reacts with OH radicals more slowly than the NOM present in Lake Lansing, and the NOM of Lake Erie has a capability to promote more OH radical formation than the NOM of Lake Lansing.
The formation of THM and haloacetic acids was independent of temperature over the range from 10 to 40°C (ozone dosage: 1 mg O3/mg C, HRT: 12.5). This was true for both Lake Lansing and Lake Erie waters.
The concentration of ketoacids decreased as pH increased for both water sources. This result indicates that the formation of ketoacids occurs preferentially by a molecular ozone reaction as compared to an OH radical-mediated reaction. An increase in pH resulted in a greater concentration of ketoacids in Lake Lansing water as compared to that in Lake Erie. The lower reaction rate of the OH radical with NOM from Lake Erie water as compared to that with Lake Lansing water may be the cause of this phenomenon.
The concentration of ketoacids in buffered waters was greater than that produced in poorly buffered waters. This was because of the greater concentration of ozone maintained in waters having a greater scavenging capacity because the reaction of the scavenging species with OH radicals consumes OH radicals without producing superoxide anion (O2-), thereby slowing down the decomposition of ozone.
Increases in the concentration of the bicarbonate ion inhibited the reaction of the OH radical with NOM. Carbonate radicals produced from the reaction of the OH radical with carbonate ion, however, resulted in the oxidation of NOM otherwise oxidized by OH radicals.
OH radical concentrations appeared to increase with increasing hydrogen peroxide up to the ratios [H2O2/O3] of 0.3 to 0.5 [g/g] in both water sources. The less important the molecular ozone reaction, the lower the concentration of ketoacids, assimilable organic carbon (AOC), and DBPs produced.
Phosphate ion played a promoter role in ozonation by increasing ozone decomposition to the OH radical. When samples were ozonated in the presence of the phosphate ion (0 to 10 mM added), the level of AOC decreased by 77 percent in Lake Erie water and 22 percent in Lake Lansing water compared to the raw water.
Pilot-scale studies of the 1 gpm ozonation/FBT system were initiated on November 28, 2000, at the Monroe Water Treatment Plant in Monroe, Michigan. Unfortunately, we were behind schedule because of unforeseen problems with the firm originally awarded the contract for the construction of the pilot-scale system. The new contract was awarded to Ace Technologies, Cincinnati, Ohio, a small minority-owned business. They constructed the system and installed it in November 2000.
We tested the system at Monroe until May 2001. As expected, because of very little formation of BDOC after ozonation of Lake Erie water, the ozone/FBT system was not effective in removing organic carbon and DBP precursors (which were low to begin with). This, however, allowed us to establish the lower threshold for the process effectiveness.
We started testing at the Ann Arbor, Michigan, plant in December 2001. The system was installed at the plant pump station in June 2001, which had no around-the-clock personnel, and we had to address numerous operational issues to ensure continuous nonsupervised system operation.
In Ann Arbor, we maintained ozone dose at a level of approximately 0.5 mg/mg C and a retention time in the FBT column of about 5 minutes. The ozone/FBT system allowed us to reduce turbidity to the level that could be acceptable for subsequent direct filtration. We could not, however, achieve any appreciable reduction in TOC and DBP precursors. This was expected based on our earlier in-house pilot testing with the Huron River, which suggested that at least 30 minutes retention time was needed to achieve 30-40 percent TOC removal. When we started adding an easily biodegradable carbon source (acetate), we were able to remove up to 40 percent of organic carbon and DBP precursors.
Subsequent operation allowed for further optimization of parameters for ozonation and biodegradation to increase the efficiency of the combined ozonation/FBT system and to develop design criteria for a large-scale pilot system.
The results of the study also showed that the system would be most effective for the treatment of contaminated source waters having a TOC concentration of 4 mg/L and higher.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 14 publications | 4 publications in selected types | All 4 journal articles |
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Flanders C. Dec J. Bollag JM, Horseradish-Mediated Binding of 2,4-Dichlorophenol to Soil, Bioremediation Journal 2010:315-321. |
R826829 (Final) |
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Yavich AA, Masten SJ. Modeling the kinetics of the reaction of ozone with natural organic matter in Huron River water. Ozone: Science & Engineering 2001;23(2):105-119. |
R826829 (2000) R826829 (Final) |
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Yavich AA, Masten SJ. Use of ozonation and FBT to control THM precursors. Journal of the American Water Works Association 2003;95(4):159-171. |
R826829 (2000) R826829 (Final) |
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Yavich AA, Lee K-H, Chen K-C, Pape L, Masten SJ. Evaluation of biodegradability of NOM after ozonation. Water Research 2004;38(12):2839-2846. |
R826829 (Final) |
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Supplemental Keywords:
drinking water, ozone, biological treatment, geographic area, water, analytical chemistry, environmental chemistry, environmental engineering, disinfection, disinfection byproducts, DBPs, DBP precursors, DBP risk management, Region 5, Wyoming, WY, Ann Arbor, community water system, Detroit, drinking water system, drinking water contaminants, fluidized bed treatment, FBT, Huron River, Lake Erie, Lake Lansing, Michigan, MI, microbial risk management, Monroe, naturally occurring organic matter, NOM, organic matter, ozonation, public water systems, regulated DBP, surface water, treatment, trihalomethanes, THMs,, RFA, Scientific Discipline, Water, Geographic Area, Environmental Chemistry, Analytical Chemistry, Drinking Water, Environmental Engineering, EPA Region, public water systems, lake erie, trihalomethanes, disinfection by-products, detroit, monroe, ann arbor, disinfection byproducts (DPBs), regulated DBP, organic matter, biological treatment, michigan, community water system, fluidized bed treatment, DBP precursors, surface water, huron river, treatment, NOM, microbial risk management, naturally occurring organic matter, Wyoming, DBP risk management, water quality, drinking water contaminants, water treatment, DBPs, Region 5, drinking water system, disinfection, ozonation, THMsProgress 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.