Comparison of the Effects of Ferrate, Ozone, and Permanganate Pre

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Chapter 16

Comparison of the Effects of Ferrate, Ozone, and Permanganate Pre-Oxidation on Disinfection Byproduct Formation from Chlorination Yanjun Jiang,1 Joseph E. Goodwill,1,2 John E. Tobiason,1 and David A. Reckhow1,* 1Department

of Civil and Environmental Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States 2Department of Mathematics, Engineering and Computer Science, Saint Francis University, Loretto, Pennsylvania 15940, United States *E-mail: [email protected]

This study compared the effects of ferrate (Fe(VI)) and ozone pre-oxidation on disinfection byproduct (DBP) formation from subsequent chlorination using batch experiments, and the effects of Fe(VI) and Mn(VII) using continuous flow experiments. In the batch experiments, two natural waters were collected and treated at bench scale under three oxidation scenarios (chlorine, ferrate oxidation followed by chlorination, and ozonation followed by chlorination). The effects of pre-oxidant dose and bromide concentration on DBP formation potentials were also determined. Results showed that ferrate and ozone pre-oxidation were comparable at equivalent doses for most DBP precursor removal. A net decrease in trihalomethane (THM), dihaloacetic acid (DHAA), trihaloacetic acid (THAA), and dihaloacetonitrile (DHAN) yield, while an increase in chloropicrin (CP) yield, were caused by both pre-oxidants. Ozone led to higher formation potentials of haloketones (HKs) and CP than ferrate at the same mass dose. The relative performance of ferrate versus ozone for DBP precursor removal was affected by water quality (e.g., nature of organic matter), DBP species, oxidant dose, and bromide concentration. In continuous flow experiments, the use of Fe(VI) pre-oxidation © 2016 American Chemical Society Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

resulted in improved finished water quality as measured by UV254 absorbance, turbidity and DBPFP compared to waters with no pre-oxidation, or those pre-oxidized with Mn(VII).


Introduction Chlorine is the most commonly used disinfectant in drinking water treatment. However, the formation of potentially carcinogenic disinfection byproducts (DBPs) from the use of chlorine is problematic. Trihalomethanes (THMs) and haloacetic acids (HAAs) are two prevalent DBP groups formed in chlorinated waters and both have been regulated by the USEPA (1). Other unregulated DBPs, e.g., haloacetonitriles (HANs), haloketones (HKs), and chloropicrin (CP), have raised special attention because of their potentially mutagenic and carcinogenic effects (2–4). Pre-oxidants such as ozone can partially oxidize natural organic matter (NOM), including DBP precursors, and thereby decrease DBP formation from subsequent chlorination. The effectiveness of pre-oxidants for controlling DBP formation in finished water has been an active area of research. Previous studies have found that ozone generally decreased the yields of THMs, trihalogenated HAAs (THAAs), and HANs, did not significantly change the dihalogenated HAA (DHAA) yield, and increased the formation of HKs and CP from subsequent chlorination (5–9). In addition, ozone oxidizes bromide producing bromate, which limits the use of ozone in high-bromide waters (10). Ferrate (Fe(VI)) has been proposed as an alternative pre-oxidant in drinking water treatment because it can act as a potent disinfectant and oxidant while producing little or no hazardous byproducts (11–15). Ferrate oxidation was found to decrease the formation of THMs, HAAs, and HANs from chlorination in batch experiments at the bench scale (16–18). In addition, the bromate yield from ferrate oxidation is quite low due to the slow reaction between ferrate and bromide (19). In many ways, ferrate can be considered a simple alternative to ozonation, permanganate, or other strong oxidants (20). However, no research has directly compared the effectiveness of ferrate and ozone pre-oxidation for DBP precursor removal. Furthermore, there have been few continuous flow evaluations of ferrate that also assess DBP formation in the context of conventional drinking water treatment, and compared to other strong oxidants. The overarching goal of this research was to evaluate DBP formation potentials following ferrate pre-oxidation. The primary objectives were to (1) investigate DBP formation under various oxidation scenarios (chlorination alone, ferrate pre-oxidation followed by chlorination, and pre-ozonation followed by chlorination), (2) to compare the effectiveness of ferrate with ozone pre-oxidation for the control of different DBP classes, (3) to examine the effect of oxidant dose and bromide concentration on DBP formation following chlorination, (4) to evaluate the impact of pre-oxidation with ferrate on downstream finished water quality using small-scale continuous flow pilot treatment systems, and (5) to compare pilot system performance with Fe(VI) as a pre-oxidant with Mn(VII) as 422 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

a pre-oxidant. The DBPs analyzed in this study included THMs, HAAs, HANs, HKs, and CP.

Materials and Methods


Natural Water Samples Several natural water samples were used as the sources of DBP precursors for this study. The waters utilized in the batch studies were collected from the intake of a drinking water utility in Gloucester (GL), MA and a raw water reservoir in Norwalk (NW), CT. The waters used in continuous flow experiments were untreated surface raw waters from two drinking water utilities (Amherst MA, Atkins supply (AK) and South Deerfield MA (SD)). Table 1 shows the chemical characteristics of the studied waters.

Table 1. Raw Water Characteristics Sample Location

pH

UV254 (cm-1)

DOC (mg/L)

SUVA (L/mg/m)

Bromide (µg/L)

Chlorine demand (mg/L)

Gloucester (GL), MA

6.00

0.24

4.00

6.00

51.2

7.8

Norwalk (NW), CT

7.20

0.11

3.20

3.40

28.7

3.9

Atkins (AK), Amherst, MA

7.10

0.09

3.10

2.90

NA

NA

South Deerfield (SD), MA

6.60

0.06

2.10

2.90

NA

NA

For the batch experimental waters, the dissolved organic carbon (DOC) concentrations of the GL and NW water were 4.0 and 3.2 mg/L, respectively. The UV254 absorbance and specific UV absorbance (SUVA) values were much higher for the GL water than the NW water. This indicated that the GL water contained more hydrophobic and aromatic natural organic matter (NOM) than the NW water. Both waters had low levels of bromide, 51.2 and 28.7 µg/L, for the GL and NW waters, respectively. In addition, the chlorine demand for the GL water was also higher than the NW water, in agreement with its higher DOC and UV254 absorbance. Atkins and South Deerfield waters were used for the continuous flow experiments. These sources were a bit lower in DOC than those used for the batch experiments; 3.1 and 2.1 mg/L, respectively. Both surface waters had the same moderate SUVA value of 2.9 L/mg/m. Bromide was not analyzed (NA) during this subset of experiments. 423 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Experimental Methods In the bench-scale batch experiments, the raw waters were treated under three oxidation scenarios (chlorine, ferrate/chlorine, and ozone/chlorine). For each water, two doses (see Table 2) of ferrate or ozone were added and the pH was monitored and adjusted to 7.0 by dropwise addition of sodium hydroxide or sulfuric acid solution. The ferrate and ozone doses used for the GL water were about twice those for the NW water due to the higher DOC and UV254 absorbance values of the GL water. Ferrate oxidation was initiated by adding K2FeO4 solids to the waters under rapid mixing. For pre-ozonation, an ozone stock solution was prepared by bubbling an ozone and oxygen mixture through deionized (DI) water, and then a certain volume of the ozone stock solution was added to the raw water samples. After ferrate or ozone was depleted through reaction, the samples were filtered (glass fiber filter (GF/F), effective size cutoff of 0.7 μm, Whatman, Clifton, NJ) and preserved for subsequent chlorination. The two drinking water treatment plants at Atkins (AK) and South Deerfield (SD) use cationic polymers as coagulants, and they are both Trident® packaged plants using an adsorption clarifier and then a media filter. Continuous flow experiments were designed to model the full-scale treatment occurring at the sampled water treatment plants (AK and SD). Coagulants and filter media were also obtained directly from the full-scale facilities. Ferrate was dosed as a 1 mM solution made from K2FeO4 of 97% purity (Battelle Corporation), and 40 minutes of contact time preceded coagulation. Coagulant addition and pH control were followed by an inline static mixer and then a course media upflow clarifier, replicating full-scale treatment. Each source water was subjected to two continuous flow experiments; one without ferrate and one with ferrate, to allow for a direct assessment of ferrate impacts. Ferrate preoxidation was not practiced in either full-scale facility. Samples were collected for chlorination following dual-media filtration. Other parameters measured at the filter effluent included UV254 absorbance and turbidity. Chlorination was conducted in 300-mL chlorine demand-free, glass-stoppered bottles. The chlorine doses were determined based on preliminary demand testing of the raw waters. The target residuals were 0.5−1.5 mg Cl2/L after a 72-h incubation time at 20 ºC and pH 7.0 (5 mM phosphate buffer) in the dark. The same chlorine doses were added to the raw water and pre-oxidized water samples and each sample was incubated headspace-free after being dosed with chlorine. In the bench-scale batch study, waters were also spiked with different concentrations of bromide before being treated by the above oxidation scenarios. Table 2 and 3 summarized the experimental conditions used in this study. Analytical Methods The DBPs determined for the batch experiments included four chlorineand bromine-containing THMs, nine chlorine- and bromine-containing HAAs, three dihaloacetonitriles or DHANs (dichloro-, bromochloro-, and dibromoacetonitriles), two haloketones or HKs (dichloropropanone (DCP) and trichloropropanone (TCP)), and chloropicrin (CP). Only THMs and HAAs 424 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


were analyzed in the continuous flow pilot experiments. THMs, DHANs, HKs, and CP were quantified by liquid/liquid extraction with pentane followed by gas chromatography and electron capture detection (GC/ECD) according to USEPA Method 551.1. Haloacetic acids were analyzed by liquid/liquid extraction with methyl-tertiary-butyl-ether (MtBE) followed by derivatization with acidic methanol and analysis by GC/ECD according to USEPA Method 552.2. Mass-based concentrations of all species in a particular group were summed in accordance with the regulatory definition of group summations.

Table 2. Oxidation Conditions in Bench-scale Batch Experiments Conditions

Parameters Ferrate (mg/L)

Ozone (mg/L)

GL water

NW water

2.8

1.4

5.6

2.8

2.2

1.2

4.0

2.3

pH

7.0

Bromide added (mg/L)

0

0.15

Target chlorine residual

0.8

0.5–1.5 mg/L

Disinfectant contact time

72 h

Temperature (deg. C)

20

Table 3. Pre-oxidation Conditions in Continuous Flow Experiments Conditions

Parameters Atkins

S. Deerfield

Coagulant Type

Cationic Polymer

Cationic Polymer

Coagulant Name

Nalco 8100

Chemtrade EC 461

Coagulant Dose (mg/L product)

6.9

5.9

Coagulation pH

6.9

7.5

Ferrate Dose (µM)

25

50

Temperature (deg. C)

20

20

425 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.

Results and Discussion


Effect of Ferrate and Ozone Pre-Oxidation on the Formation of THMs from Chlorination The GL water with higher DOC and SUVA values had higher DBP formation potentials (DBPFPs) than the NW water for most DBP species (see figures below). Without pre-oxidation, the molar concentration of each DBP group did not significantly change with the initial bromide concentration (data not shown), possibly because of the constant number of reactive sites on NOM to react with chlorine and bromine (21). Figure 1 shows that the mass-based THMFPs were increased with bromide concentration for both waters. This is because the formation of THMs shifted from chlorinated species to brominated ones at higher bromide concentrations (22, 23), and the brominated THMs have higher molecular weight (MW) than their chlorinated analogues.

Figure 1. Effect of ferrate and ozone pre-oxidation on THM formation potentials at different bromide concentrations.

Ferrate and ozone pre-oxidation both decreased THMFP to similar levels at all bromide concentrations, and the decreases in THM yields were quite uniform across the two oxidants and nearly linear with the oxidant dose (Figure 1). For the two waters at different bromide concentrations, ferrate and ozone decreased the THMFPs by 13.0−28.6 and 10.6−25.4% at the lower doses, and by 29.7−49.0 and 30.0−43.1% at the higher doses, respectively. The continuous flow experiment also demonstrated a decrease in THMFP as a result of ferrate pre-oxidation. Results of THM yield following treatment and chlorination are shown in Figure 2. Also included are results for THMFP for previously unchlorinated filter effluent from the participating full scale facilities. THMFP for Atkins water was higher than the South Deerfield water, in agreement with its higher DOC and raw UV254 absorbance. The addition of ferrate resulted in decreased THMFP for the Atkins water from 105 to 88 μg/L and 50 to 38 μg/L for the South Deerfield water. It should be noted that the ferrate dose was 20 μM 426 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


for Atkins and 50 μM for South Deerfield. The impact of Fe(VI) on DBPFP is known to vary with water quality in batch experiments (16).

Figure 2. Effect of ferrate pre-oxidation on THM formation potentials of two different source waters; (Pilot = Continuous flow experiment without pre-oxidation, Pilot+Fe(VI) = Continuous flow experiment with ferrate pre-oxidation, Full Scale = filter effluent from full scale facility subjected to chlorination protocol in laboratory).

Effect of Ferrate and Ozone Pre-Oxidation on the Formation of THAAs and DHAAs from Chlorination Figure 3 shows that the mass-based THAA yields also increased with the bromide concentration, albeit to a smaller extent than THMs. Pre-oxidation by ferrate and ozone generally decreased the THAA formation potentials (THAAFPs), although there was more variability under different conditions than that observed for THMs. For the GL water, ferrate and ozone decreased the THAAFPs by 2.2−31.0 and 3.1−18.1% at the lower doses, and by 30.0−48.9 and 36.6−43.0% at the higher doses, respectively. At 0 and 0.15 mg/L bromide, ferrate generally achieved better removal of THAA precursors than ozone, whereas at 0.8 mg/L bromide, ozone performed slightly better. For the NW water, ozone led to lower THAAFPs than ferrate under all conditions. Ferrate and ozone decreased the THAAFPs by -8.6−3.4 and 22.6−26.8% at the lower doses, and by 16.7−33.6 and 44.4−49.9% at the higher doses, respectively. 427 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 3. Effect of ferrate and ozone pre-oxidation on THAA formation potentials at different bromide concentrations.

Figure 4 shows that in the GL water, ferrate generally led to lower DHAA formation potentials (DHAAFPs) than ozone at equivalent doses. Ferrate and ozone decreased the DHAAFPs of the GL water by 4.8−19.3 and 4.8−8.0% at the lower doses, and by 22.3−30.4 and 19.5−22.2% at the higher doses, respectively. In the NW water, ferrate only caused greater DHAA precursor removal than ozone at the higher dose and low bromide concentrations (0 and 0.15 mg/L), whereas ozone performed better under the other conditions. Specifically, ferrate and ozone decreased the DHAAFPs of the NW water by -1.3−5.7 and 8.1−16.4% at the lower doses, and by 22.0−29.5 and 18.1−24.8% at the higher doses, respectively.

Figure 4. Effect of ferrate and ozone pre-oxidation on DHAA formation potentials at different bromide concentrations.

Ferrate pre-oxidation also yielded a decrease in HAAs in continuous flow experiments (see Figure 5). For the Atkins water, HAAs with and without ferrate pre-oxidation were approximately 90 and 105 μg/L, respectively. A decrease in 428 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


HAAFP was also observed for the South Deerfield water but to a lesser extent, despite a ferrate dose two times higher than the Atkins water. This generally corresponds to significantly lower raw and finished water UV254 for the South Deerfield water.

Figure 5. Effect of ferrate pre-oxidation on HAA formation potentials for two different source waters; (Pilot = Continuous flow experiment without pre-oxidation, Pilot+Fe(VI) = Continuous flow experiment with ferrate pre-oxidation, Full Scale = filter effluent from full scale facility subjected to chlorination protocol in laboratory).

Effect of Ferrate and Ozone Pre-Oxidation on the Formation of DHANs from Chlorination Figure 6 shows that in the GL water, ferrate achieved similar or slightly greater DHAN precursor removal than ozone. Ferrate and ozone decreased the DHAN formation potentials (DHANFPs) by 17.0−30.6 and 11.9−25.8% at the lower doses, and by 27.0−51.5 and 28.4−47.0% at the higher doses, respectively. In the NW water, ozone led to greater decreases in DHANFPs than ferrate. Ferrate and ozone decreased the DHANFPs of the NW water by 7.2−14.1 and 7.8−16.3% at the lower doses, and by 22.9−30.1 and 29.3−40.4% at the higher doses, respectively. 429 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 6. Effect of ferrate and ozone pre-oxidation on DHAN formation potentials at different bromide concentrations.

These results show that the relative performance of ferrate versus ozone for DBP precursor removal depended on water quality (e.g., nature of NOM), DBP species, oxidant dose, and bromide concentration. Ferrate generally achieved greater DBP precursor removal than ozone in the GL water which had more hydrophobic and high MW NOM. In the NW water, ferrate performed better at the higher oxidant dose to bromide concentration ratios, whereas ozone was more effective for DBP precursor removal at the lower oxidant to bromide ratios (21). Ferrate was found to preferentially remove hydrophobic/transphilic NOM fractions and high MW molecules (24). This might explain the better DBP precursor removal by ferrate in the GL water. In the NW water with NOM of a different nature, the lower dose of ferrate was not able to fully destroy the DBP precursors and the newly formed organic byproducts might still be precursors to DBPs such as THAAs and DHAAs, especially at high bromide levels. Hua and Reckhow (6) found that ozone also had limited effects on the THM and THAA yields, and increased the DHAA formation potentials in waters with low SUVA values.

Effect of Ferrate and Ozone Pre-Oxidation on the Formation of Haloketones (HKs) and Chloropicrin (CP) from Chlorination Figure 7 shows that ferrate led to lower HK formation potentials (HKFPs) than ozone under all conditions. At the lower doses, ferrate slightly increased the HK yield from chlorination by 0.3 and 8.8% for the GL and NW water, respectively, whereas at the higher doses, ferrate decreased the HKFPs by 26.4 and 3.6%, respectively. Previous studies also showed small and site-specific effects of ferrate oxidation on HK precursors (16, 18). In contrast, ozone oxidation enhanced HK formation under all conditions. The low and high doses of ozone increased the HK yield by 17.4 and 22.8% for the GL water, and by 24.2 and 53.0% for the NW water, respectively. Ketones are known ozonation byproducts and HK precursors (25). Ozone oxidation might have produced more ketones than ferrate, which caused higher HKFPs. 430 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


Figure 7. Effect of ferrate and ozone pre-oxidation on HK formation potentials. Figure 8 shows that pre-ozonation led to much higher CP yield than ferrate, and the CP formation potential (CPFP) greatly increased with ozone dose but not with ferrate. The low and high doses of ferrate increased the CPFP by 28.6 and 25.0% for the GL water, and by 26.3 and 19.7% for the NW water, respectively. With ozone, the lower doses increased the CP yield by 18.3 and 86.3%, and the higher doses increased the CPFP by 226.5 and 831.1% for the GL and NW water, respectively. Compared to ferrate, ozone might have produced more CP precursors by oxidizing amine groups to nitro groups (26, 27). In addition, the hydrophilic fractions of NOM were determined to be major halonitromethane precursors (28). This might explain the much higher CP yield in the NW water than the GL water at high ozone doses. In addition, the CPFP was also slightly higher for the NW water than the GL water without pre-oxidation.

Figure 8. Effect of ferrate and ozone pre-oxidation on CP formation potentials. Effect of Ferrate Pre-Oxidation on Other Drinking Water Quality Parameters The formation of bromate after ferrate and ozone oxidation (without chlorination) was determined at bench scale for the Gloucester (GL) water. At equivalent doses, the bromate yields from ozonation were 2.5−4.5 times those 431 Sharma et al.; Ferrites and Ferrates: Chemistry and Applications in Sustainable Energy and Environmental Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 2016.


from ferrate oxidation. The highest yield of bromate, 10.2 µg/L, was produced by 4 mg/L ozone at 0.8 mg/L bromide. The bromate yields from ferrate oxidation were below 4 µg/L under all conditions (data not shown). The use of continuous flow experiments with small-scale pilot treatment systems allowed for the assessment of ferrate impacts on other parameters of importance in drinking water treatment, including turbidity and UV254 absorbance. Results for filter effluent turbidity and UV254 absorbance are shown in Figure 9. In general, the addition of ferrate decreased both UV254 absorbance and turbidity of the finished water as compared to the no ferrate conditions, thus improving water quality. For the Atkins water, UV254 and turbidity improved by approximately 10 and 35%, respectively. For the South Deerfield water, UV254 and turbidity improved by approximately 20 and 5%, respectively. The improvements in UV254 are similar in magnitude to improvements in DBPFP. Results indicate that, in addition to decreasing regulated THMs and HAAs, ferrate pre-oxidation also improved other important water quality parameters. Ferrate also did not have a negative impact on filter performance with respect to headloss development, or residual iron concentrations (29). However, ferrate resultant particles likely require additional destabilization prior to effective clarification and filtration (30) Lower turbidities and improved organic removal resulting from ferrate pre-oxidation and coagulation have also been observed for bench-scale batch experiments (31, 32).

Comparison of Ferrate and Permanganate Pre-Oxidation on Regulated DBPs Results from continuous flow studies on South Deerfield water that directly compared Mn(VII) and Fe(VI) pre-oxidation are included in Figure 10. An improvement in DBPFP was observed with Fe(VI) over no pre-oxidation and Mn(VII) oxidation. In general, DBPFP decreased approximately 20% with Fe(VI) and there was not a significant decrease with Mn(VII). It should be noted that the Fe(VI) dose was significantly higher than Mn(VII) on a molar basis. Higher permanganate dosages led to Mn(VII) and colloidal Mn(IV) in the filter effluent (data not shown). Thus 10 μM represents the highest possible Mn(VII) dose for the South Deerfield water. This points to an advantage of Fe(VI) over Mn(VII) in that it will undergo autodecay in waters with otherwise lower oxidant demands, and thereby allow for higher applied pre-oxidation dosages with greater potential for DBP precursor oxidation. Like Mn(VII), Fe(VI) is also effective at oxidizing inorganic contaminants such as As(III) and Mn(II) which may be present in raw water (14, 33, 34).



Figure 9. UV254 absorbance and turbidity impacts of ferrate pre-oxidation in continuous flow experiments.



Figure 10. Effect of pre-oxidation with ferrate or permanganate on regulated disinfection byproducts on South Deerfield Water. (Fe(VI) = 50 μM, Mn(VII) = 10 μM, no hatching = THMs, hatching = HAAs, Poly Only = no pre-oxidation)

Conclusions In bench-scale batch studies, ferrate and ozone generally achieved comparable decreases in THM, THAA, DHAA, and DHAN yields from chlorination, whereas ozone led to higher HK and CP formation potentials than ferrate. The relative performance of ferrate versus ozone for DBP precursor removal was affected by water quality, oxidant dose, DBP species, and bromide concentration. At an equal mass dose, ferrate was more effective for DBP control in high-SUVA waters and at high oxidant to bromide ratios, whereas ozone performed better than ferrate in waters with lower SUVA value and at lower oxidant to bromide ratios. These factors need to be taken into consideration when selecting the better pre-oxidant for DBP precursor removal in drinking water treatment. In continuous flow experiments, the addition of ferrate as a pre-oxidant improved finished water quality with respect to UV254 absorbance, turbidity, and DBPFPs. No negative impacts on coagulation or filter performance were noted as a result of ferrate addition. Results for both batch and continuous flow experiments suggest that ferrate is a viable alternative to other strong oxidants commonly used in drinking water treatment, such as permanganate and ozone.


Acknowledgments


Funding for this research was provided by USEPA Grant No. 83560201. The authors gratefully acknowledge the support of Battelle Memorial Institute for providing the potassium ferrate product used in this work, and Richard Ross of WesTech Inc. for his guidance in the construction and operation of the continuous flow experimental apparatus. The authors also thank the numerous utilities that provided water and other support for this research.

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