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Source water and microfiltration plant manganese
control study
Daniel Olin Lewis,1 David A. Ladner,2 and Tanju Karanfil2
1Duke
Energy, Seneca, S.C.
of Environmental Engineering and Earth Sciences, Clemson University, Anderson, S.C.
2Department
A combined field and laboratory manganese study was
conducted for the Startex-Jackson-Wellford-Duncan Water
District in Wellford, S.C. Through source water characterization,
it was found that biochemical processes in the river affected
manganese concentrations more than any processes in the lake
feeding the river. Because measures taken in the lake would not
control manganese at the plant intake, in-plant treatment was
required. Bench-top experiments evaluated three treatment
trains: potassium permanganate (KMnO4) direct oxidation
followed by microfiltration (MF), manganese-coated media bed
before MF, and manganese-coated media bed after MF. All
processes removed manganese, with the media bed processes
consistently achieving < 0.004 mg/L and KMnO 4 oxidation
reaching as low as 0.008 mg/L Mn. Turbidity, organic carbon,
and trihalomethane formation potential removals were
comparable, but the process of media bed following the filter
exhibited the highest rate of membrane fouling. This study
provides a holistic understanding of manganese source and
treatability that should prove useful to utilities with similar
manganese issues.
Keywords: manganese, microfiltration, manganese oxide-coated media, manganese contactor, source water
Manganese adds an undesirable color to drinking water that
undermines consumer confidence in the water provider. A recent
survey of water utilities listed manganese control as one of their
primary concerns (AWWA, 2009). The US Environmental Protection Agency has set a secondary maximum contaminant level
(SMCL) of 0.05 mg/L, but a goal of 0.02 mg/L or less is recommended to avoid customer complaints and maintain consumer
satisfaction (Kohl & Medlar, 2006). Utilities have the following
four manganese control techniques available to achieve this goal.
• Judicious selection of source waters, intake locations, and
active manganese control processes such as lake aeration can
minimize the amount of manganese entering the plant (Gantzer
et al, 2009; Jørgensen, 2005; Zaw & Chiswell, 1999).
• In the plant, strong oxidants (e.g., permanganate, ozone,
chlorine dioxide) may be added to precipitate the soluble manganese for removal through coagulation–flocculation–settling and
filtration (Knocke et al, 1990a).
• Surfaces coated with manganese oxide [MnOx(s)] may be used
to sorb soluble manganese; the sorbed manganese is then oxidized
in place by the addition of an oxidant (Knocke et al, 2010;
Tobiason et al, 2009; Knocke et al, 1990b).
• In the plant, microbial communities capable of oxidizing
manganese may be fostered in an aerobic environment (Burger et
al, 2008).
background
The Startex-Jackson-Wellford-Duncan Water District (SJWD)
is located in Wellford, S.C., in Spartanburg County. SJWD has
observed high manganese concentrations (e.g., 0.06–0.28 mg/L)
in its source waters during summer months (Figure 1). Currently
the 12-mgd SJWD granular media filtration plant efficiently
removes soluble manganese by sorption onto the oxide-coated
media and subsequent oxidation. At the time of the current study,
SJWD was in the process of building a new 8-mgd microfiltration
(MF) plant to meet future demands. Because this new membrane
plant would not have the same inherent soluble manganese
removal capability as granular media filtration, manganese management options needed to be evaluated. Membrane fouling by
manganese was also a concern.
SJWD source water. The primary SJWD source is the Middle
Tyger River, fed by 412-acre Lake Lyman (27 ft deep near the
dam) approximately 8 river mi above the treatment plant (Figure
2). Less than 1 mi below Lake Lyman, Beaverdam Creek enters
the river, contributing 5–30% of the flow in the Middle Tyger.
The secondary SJWD water source is the 137-acre North Tyger
Reservoir, 17 ft deep at the dam. It supplies the new MF plant
and occasionally feeds the older water treatment plant (WTP) as
dictated by demand and the SJWD water management strategy.
Manganese chemistry. The tenth most common element, manganese is a transition metal ubiquitous in the lithosphere. In
well-oxygenated water, the insoluble oxide MnO2 is the most
stable species, but the kinetics of oxidation are very slow, on the
order of days (Morgan, 2005). Under anoxic conditions, the
Mn2+ ion is the most kinetically favored species. As a result,
manganese tends to be cycled across the oxic–anoxic boundary,
mediated by microorganisms. In oxic water bodies, this boundary
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FIGURE 1
Historical manganese concentrations at treatment plant
Parameter
Total
Soluble
0.3
Mn—mg/L
0.2
0.1
0.0
02/01/09
06/01/09
10/01/09
02/01/10
06/01/10
10/01/10
02/01/11
06/01/11
10/01/11
Date
Mn—manganese
will lie in the sediment. Anoxic conditions there lead to manganese reduction, and then the soluble Mn2+ diffuses into the bulk
water, where it is oxidized and returns to the sediment (Zaw &
Chiswell, 1999). However, if the bulk water is anoxic, as often
occurs in lakes in the summer, soluble manganese levels tend to
rise. To minimize this occurrence, the redox potential in the
hypolimnion can be raised by mixing the lake or oxygenating
the hypolimnion (Jørgensen, 2005). Mediation by microorganisms speeds oxidation; the abiotic surface-catalyzed oxidation
rate is approximately 10–3/h, whereas bacterial oxidation ranges
from 10 to 10–1/h (Morgan, 2005).
Oxide-coated media adsorption. The oxidation of manganese is
autocatalytic; surfaces of freshly formed oxides (MnOx) rapidly
sorb Mn2+ ions that are then oxidized to form new precipitates
of MnOx (Morgan & Stumm, 1964). The oxidized manganese is
referred to as MnOx because it has mixed oxidation states ≤ 4
(Knocke et al, 1988.) This occurs in granular media filters when
chlorine (the oxidant) is added over seasoned filter media. The
process is highly effective in removing manganese (Tobiason et
al, 2009), and dedicated manganese contactors have been proposed in the literature. These manganese contactors are similar
to granular media filters, but because particle removal is not the
main goal, they have larger media sizes, higher hydraulic loadings,
and shallower depths (Knocke et al, 2010).
Potassium permanganate (KMnO4) oxidation. KMnO4 is a strong
oxidizer that creates a brilliant purple in solution. It is widely used
for manganese oxidation because it has satisfactory oxidation
kinetics over a wide pH and temperature range, does not require
capital-intensive onsite generation facilities (unlike ozone), and
does not form the regulated halogenated disinfection by-products
(DBPs) that free chlorine and chlorine dioxide can cause (Knocke
et al, 1990a). However, the KMnO4 dose must precisely match
the oxidant demand of the water, including dissolved organic
carbon (DOC) demand, in order to create solid MnOx particles
that can be filtered out by MF. Insufficient KMnO4 will not oxidize all of the Mn(II), whereas overdosing leads to unreacted
KMnO4 in the effluent. Overdosing can also produce colloidal
MnOx(s) particles that are difficult to remove with filtration or
sedimentation (Perez-Benito & Arias, 1992).
MF. MF membranes operate on the principle of physical size
exclusion with pores sizes between 0.1 and 0.45 µm. To remove
iron or manganese by MF, the metal must be oxidized to a particulate form larger than the pores. Ellis and colleagues (2000)
oxidized iron and manganese with aeration and KMnO4 and
found that particles formed ranged in size from 1.5 to 50 µm, and
no appreciable iron or manganese remained after 0.2-µm MF.
However, as noted previously, strong oxidant overdosing can
produce colloidal oxides capable of passing through the filter
(Perez-Benito & Arias, 1992).
Objectives and approach
Primary objective. The primary objective of the current study
was to examine different manganese control strategies by combining field observations with laboratory experiments. The field
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FIGURE 2
Overview of the SJWD source water system
Sampling point
Berry’s Millpond
Lake Lyman
Profile sampling
North Tyger Reservoir
Spillway
Bottom gate
Beaverdam Creek
Profile sampling
Granny Mack Bridge Road
Hampton Road
North Tyger
River
Pine Ridge Road
Spartanburg Road
Middle Tyger River
WTP
SJWD—Startex-Jackson-Wellford-Duncan Water District, WTP—water treatment plant
The new microfiltration plant was built next to the current WTP. Water is pumped from the North Tyger Reservoir to the WTP and
microfiltration plant.
study was conducted for SJWD, a water utility in South Carolina
with manganese in its source water, and the laboratory experiments provided controlled evaluations of treatment options under
various conditions. Thus this research serves as both a case study
and a source of generalizable knowledge for water quality professionals with stakes in manganese control.
Secondary objectives. There were two secondary objectives
chosen in order to accomplish the primary aim of the study. First,
to describe the occurrences and trends of manganese and other
important water quality parameters in the SJWD source waters.
It is important to understand manganese speciation as well as
temporal and spatial variations in manganese concentrations in
source waters in order to assess the feasibility of source water
control strategies and guide the utility in source selection.
The other secondary objective was to evaluate two manganese
control strategies—KMnO4 oxidation and manganese-coated
media beds—in an MF treatment train. As detailed by Knocke and
co-workers (2010), the contactor concept offers effective manganese control in a small footprint. In the current study, experiments
were conducted with smaller-sized media than were used in most
of the contactor literature; therefore, this article uses the term
“manganese-coated media bed” to avoid confusion. The smaller-
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Water with manganese in an oxidizing environment was circulated through
this column, darkening the sand as the oxide was formed on it and creating
the oxide-coated media. The sand provided a large surface area on which
manganese oxidation could occur.
sized media may provide some particle removal through a filtration
mechanism. Because little research is available on the performance
of a manganese-coated media bed in conjunction with MF, this
study investigated the effects of the bed both before and after MF.
Placing the media bed before the filter could improve MF
performance by removal of metals before the membrane. Placing
the media bed after the filter was evaluated for comparison purposes because this configuration would prevent interaction
between filterable material and the media bed, where chlorine is
added. Direct oxidation with KMnO4 as a preoxidant (in lieu of
the media bed) was used to inform the utility about the performance of this oxidant and to provide a control for the manganese-coated media bed results. The experimental matrix of the
study included variation of the water source (Middle Tyger River
versus North Tyger Reservoir), season (summer versus fall), water
temperature, and influent manganese concentration.
Materials and Methods
Source water study. Water samples were collected biweekly by
either surface grab or with a van Dorn grab sampler from the
14 sites indicated in Figure 2. Lake samples were collected from
the surface, the middle, and 0.5 m from the bottom at the deepest
location of the lake. Stream samples were collected near the surface. Each sample was immediately split into a glass bottle for
DOC and dissolved nitrogen (DN) analyses and a plastic bottle
for metals analysis. Bottles were chilled for transportation back to
the laboratory. Dissolved oxygen (DO), turbidity, temperature,
specific conductivity, and pH depth profiles were obtained by
lowering a multiprobe sonde1 through the water column. DOC/
DN samples were filtered through prewashed 0.45-µm polyethersulfone (PES) syringe filters2 and analyzed in duplicate on a total
organic carbon/total nitrogen analyzer.3 Ultraviolet absorbance at
254 nm was measured in a spectrophotometer4 with quartz
cuvette. For soluble metals, aliquots were syringe-filtered through
the same filters described previously and acidified with nitric acid.
For total metals, 50-mL aliquots were drawn from shaken bottles
for digestion. To acidify the samples, 1.5 mL of concentrated nitric
acid was added, and the samples were then heated until the majority of the sample had evaporated and the remaining solution was
colorless (approximately 90 min). Samples were then reconstituted
to 50 mL with distilled and deionized (DDI) water. Both total and
soluble metals were measured by Clemson University’s Agricultural
Service Laboratory using inductively coupled plasma atomic emission spectroscopy. Minimum detection limits were 0.007 and
0.002 mg/L for manganese and iron, respectively.
Treatment tests. Each test was made up of a series of individual
unit operations, arranged to simulate three different treatment
trains (Figure 3). For the direct oxidation process, KMnO4 was
added, a jar test was run to determine the coagulant dose, and
the water was coagulated, flocculated, and settled using that
coagulant dose and then microfiltered. For the other two processes, jar testing was performed to determine the coagulant dose,
and then a single coagulation, flocculation, and settling experiment was conducted. The settled water was then split into two
aliquots. One was pumped through the manganese-coated media
bed and then sent through MF for the media bed–before-filter
process. The other was filtered first and then pumped through
the manganese-coated media bed for the media bed–after-filter
process. The following sections discuss the specific procedures
used in each unit operation.
Feedwater was prepared by collecting samples from the Middle
Tyger River at the SJWD plant intake, from the sedimentation basin
effluent, and from the North Tyger Reservoir sampling tap. The
samples were collected using 20-L polycarbonate bottles5 and were
stored at 4°C until the experiments, which were conducted less than
72 h after collection. Manganese and iron were spiked from 1-g/L
stock solutions of the divalent ion in nitric acid. There were three
levels of target dissolved metals: the unspiked case in which no
metals were added (i.e., Mn and Fe were at their raw water values);
case 1, which was spiked to 0.2 mg/L dissolved Mn and 1.0 mg/L
dissolved Fe; and case 2, which was spiked to 0.45 mg/L dissolved
Mn and 2.5 mg/L dissolved Fe. Hydrogen chloride and sodium
hydroxide were used for pH adjustment when required. The
untreated sample aliquot was taken from this solution.
All tests were begun with coagulation, flocculation, and settling
to simulate a full-scale treatment train. Settled water from the
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FIGURE 3
Manganese control processes
Direct oxidation process
Coagulation
KMnO4
Flocculation
Settling
Microfiltration
Manganese-coated media bed–before-filter process
Coagulation
Flocculation
Settling
HOCl
Media bed
Microfiltration
Manganese-coated media bed–after-filter process
Coagulation
Flocculation
Settling
Microfiltration
HOCl
Media bed
HOCl—hypochlorous acid, KMnO4—potassium permanganate
plant was also used for comparison. The coagulant dose was
determined by a jar test. Six square gator jars were each filled
with 2 L and placed on the jar tester.6 For the KMnO4 oxidation
treatments, the soluble manganese and iron in the samples (0.45µm PES filtered) were measured using iron and manganese measurement reagents and a hand-held colorimeter.7 The required
dose of KMnO4 for oxidation was calculated as 105% of the
stoichiometric dose needed for the measured soluble iron and
manganese. KMnO4 was added to the water from a 1.92-g/L
stock solution (1 mL stock stoichiometrically equivalent to 1
mg/L Mn2+). This was mixed and allowed to stand for at least 15
min before addition of the coagulant, a stock solution of aluminum sulfate octadecahydrate (alum) [5 g/L as Al2(SO4)3]. Alum
was added in the jars with the mixing speed at 100 rpm (root
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In the bench-top setup for the manganese-coated media bed unit operation,
the influent reservoir (left) sits on top of the pump, which forced the water
through the column. The hypochlorous acid (HOCl) pump provided a drip of
HOCl solution into the tee just before the waters entered the column,
providing an oxidizing environment. The column in the center contained the
manganese oxide–coated media, where the large surface area of manganese
oxide sorbed Mn2+ and where manganese removal occurred. After the water
flowed through the column, it was collected in the effluent reservoir.
mean square velocity gradient G = 130 s–1). After 3 min, the speed
was reduced to 30 rpm and then to 20 rpm and 12 rpm at 10-min
intervals for a total of 30 min of flocculation (G = 23, 10.5, 6.5
s–1, respectively). This coagulation–flocculation–sedimentation
procedure was developed by Black and Veatch (headquartered in
Overland Park, Kan.) to simulate the plant conditions at the new
MF plant (Hargette, 2011). G values were taken from correlations
developed by Cornwell and Bishop (1983) for water at 23°C.
After a 5-min settling period, samples were taken from the gator
jar sampling ports. The alum dose was optimized for turbidity
removal. The optimum alum doses were usually found in the
range of 8 to 13 mg/L as Al2(SO4)3; source water pH varied from
6.15 to 6.5 for the Middle Tyger River and 6.4 to 7.15 for the
North Tyger Reservoir. Determination of the optimum coagulant
dose was performed using water that had already been spiked to
the target metal concentrations.
Membrane filtration experiments were conducted using 0.1-µm
polyvinylidene difluoride flat-sheet filter membranes.8 The membrane coupon was cut from the sheet and placed in the filtration
cell9 over a structural backing mesh. A tank of nitrogen pressurized
the vessel containing the sample to be filtered, providing the transmembrane pressure for filtration (target pressure = 10 psi). The
filtrate drained into a flask on a laboratory balance. An attached
personal computer recorded the mass on the balance at 10-s intervals and calculated the membrane flux and the flux decline. Filtrations were run in dead-end mode. A clean water filtration using
distilled water was conducted for at least 10 min to rinse and
establish clean water flux. The clean water was then drained from
the system, the sample was introduced, and filtration of the sample
commenced. The flux curves were adjusted for temperature by
normalizing them to the initial flux, and then flux was plotted
against the specific volume filtered (permeate volume divided by
membrane area—L/m2). Flux decline was quantified as the percentage of initial flux that had been lost after 500 mL/m2; this value
was used to compare the filtration performance among tests.
The manganese-coated media bed was designed using a model
developed by other researchers (Coffey et al, 1993). According
to the model, at a flow rate of 83 mL/min (flow rate determined
by bench-top pump flow rate), 138 mL of media volume is
required to decrease 0.45 mg/L of influent manganese to 0.02
mg/L at pH 6.3 (assuming manganese adsorption site densities
to be 14.8 mol/m3). Transparent 4-cm-diameter tubing was used
to contain the media, resulting in a loading rate of 1.5 gpm/sq ft.
The media (16/30 filter sand with an effective size of 0.65 mm10)
was coated with MnOx(s), according to the procedure published
by Merkle and colleagues (1997) in which a solution of Mn2+ is
oxidized onto the media with hypochlorite. The media adsorption
capacity was measured using the procedure set out by Islam and
colleagues (2010). The media prepared for this study had an
adsorption capacity of 0.016 mg/g Mn as is (measured after some
use) and 0.041 mg/g Mn adsorption capacity after overnight
regeneration with strong chlorine—i.e., hypochlorous acid
(HOCl) solution. In use, a peristaltic pump supplied 80 mL/min
of water for treatment while a second pump introduced 0.7 mL/
min of 350-mg/L HOCl solution into a tee just above the manganese-coated media bed inlet. Raw water was pumped through
the media bed with a chlorine feed for a period of days in order
to simulate media in use for some time. The manganese-coated
media bed pump and chlorine-drip flow rates were checked by
graduated cylinder and stopwatch. Before each experiment, the
manganese-coated media bed was rinsed and regenerated with
DDI water and HOCl drip. The supply pump inlet was then
moved from DDI water to the sample, which was kept in an ice
bath when low temperatures were needed. The first 500 mL
discharged were discarded, and the balance was collected in a 3-L
The jar tester was used to simulate the coagulation–flocculation–
sedimentation unit operation in the full-scale plant.
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FIGURE 4
Total and soluble manganese profiles for SJWD water sources
Species
Site
Total
Middle Tyger River at WTP (primary source)
Soluble
North Tyger Reservoir, middle depth (secondary source)
0.3
Mn—mg/L
0.2
0.1
0.0
06/01/10
08/01/10
10/01/10
12/01/10
02/01/11
04/01/11
06/01/11
08/01/11
10/01/11
Date
Mn—manganese, SJWD—Startex-Jackson-Wellford-Duncan Water District, WTP—water treatment plant
glass jar. Analytical methods were identical to those described
previously for the source water study with two exceptions: turbidity was measured by turbidity meter11 and trihalomethanes
(THMs)—the selected regulated disinfection by-product (DBP)
for this study—were measured using method 551.1 (USEPA,
1995) with quantification by gas chromatograph.12
The same experimental treatments were repeated several times,
but variations in source water from day to day and in optimum
alum dose prevented these from being true duplicates. Some variability in the filtration flux existed, even from day to day. A
Student’s t-test was used to determine the statistical significance
(p value) of differences in treatments.
RESULTS AND DISCUSSION
Source water study. Results regarding seasonal variations in
source water manganese levels are reported subsequently in a
comparative fashion, followed by discussion of spatial variations.
The results of this portion of the study were used to inform the
SJWD water management strategy.
Comparison of Middle Tyger River versus North Tyger Reservoir. Soluble manganese was generally lower at the North Tyger
Reservoir intake than at the Middle Tyger River intake (Figure
4). By late summer, however, high manganese concentrations were
observed in the reservoir, suggesting a change in the redox potential. Historical data show manganese levels > 0.4 mg/L in the late
summer. However, as long as the anoxic hypolimnion does not
rise to the elevation of the intake structure in the reservoir, the
summer and fall manganese concentrations (both total and soluble) in the reservoir are generally lower than the manganese
concentrations in the river at the influent of the WTP. Iron profiles mimicked the trend seen for manganese; i.e., iron concentrations were generally lower in the North Tyger Reservoir (mean =
0.21 mg/L soluble Fe) than in the Middle Tyger River (mean =
0.95 mg/L soluble Fe).
Unlike typical reservoirs, the North Tyger Reservoir showed
increased soluble manganese concentration in the late winter and
into spring. The high soluble manganese concentration was found
not merely at the middle depth but throughout the reservoir. DO
profiles taken in early spring showed the lake was well oxygenated, which should favor manganese oxidation.
Comparison of the two Middle Tyger River sources: Lake
Lyman and Beaverdam Creek. SJWD’s primary source, the Middle
Tyger River at Lyman, S.C., is fed by Lake Lyman and the tributary
Beaverdam Creek (Figure 2), which contributes 5–30% of the flow
(USGS, 2011a, 2011b). The river drainage basin is quite narrow at
this point, and there are no other considerable water sources. Figure 5 shows the concentrations of manganese in Lake Lyman and
Beaverdam Creek. Lake Lyman samples were taken 200 yd downstream of the dam, allowing contributions from the spillway and
the bottom gate to mix completely. When results were considered
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FIGURE 5
Total and soluble metals in Middle Tyger River tributaries
Fe—mg/L
Mn—mg/L
E
Month
Month
Fe—iron, Mn—manganese
Figure shows data from June 3, 2010, to Oct. 6, 2011, with monthly totals averaged.
on a mass basis, Lake Lyman dominated the manganese loading
in the summer, and mass contributions between the two sources
were roughly equal during the winter. Therefore, control measures
applied in Lake Lyman could decrease the manganese load during
summer but would be less efficacious in winter.
Manganese profile for Middle Tyger River. A mass balance was
performed on the Middle Tyger River to compare the inputs from
Beaverdam Creek and Lyman Lake to the output of the Middle
Tyger River at the WTP. US Geological Survey (USGS) gauging stations on Beaverdam Creek and the Middle Tyger River at the WTP
provided the necessary flow data. Manganese concentrations at the
influent of the WTP did not match the concentrations measured
upstream (Figure 6). Results showed that in the summer the manganese concentrations were attenuated in the river before reaching
the plant. Conversely, in the winter the manganese concentrations
at the plant intake were higher than in the reservoirs. Two phenomena were observed here: a net loss of manganese during summer
and a net gain during winter months, both shown in Figure 7.
Manganese loss during the summer was assumed to be attributable to oxidation. The rate was first order and was calculated
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to be 0.083±0.03/h using a simplistic travel time model of the
river as a prismatic channel. (Flow was known from USGS station
02157510 for the Middle Tyger River near Lyman, S.C., and
distance was measured via satellite photography.13) This rate is
comparable to the ~ 0.1/h rate estimated for microbial oxidation
of manganese and is considerably faster than abiotic oxidation
with a surface catalyzed oxidation rate estimated at 10–3/h (Morgan, 2005), suggesting that microorganisms are the responsible
agents. Increases in soluble manganese concentrations occurred
along the entire stretch of river during the winter and in the last
2 mi before the treatment plant during the summer. DO and pH
river profiles taken in summer 2010 showed that conditions
favored oxidation throughout the river reach. The source of the
manganese is not known.
Manganese contributions from settling basins. Samples taken
at SJWD during the summer (water temperature = 26.3–27.1°C)
indicated that solids management in settling basins would be
important in maintaining low manganese concentrations. Settling
basins can develop anoxic zones, which allow settled particulate
manganese to become reduced and diffuse back into the bulk
water, raising the soluble manganese concentrations. Figure 8
FIGURE 6
Microfilter membranes used in the microfiltration unit operation show cake
formation. Color differences reflect the different water sources and different
treatments. (Cake flaking occurred after drying and not during filtration.)
Total and dissolved manganese at the confluence of Beaverdam Creek and the Middle Tyger River and at the SJWD WTP
River flow—cfs
Parameter
15.2
Total Mn
50.0
Soluble Mn
100.0
150.0
205.3
Confluence of Beaverdam Creek and Middle Tyger River
Mn—mg/L
0.6
0.4
0.2
0.0
Middle Tyger River at WTP
Mn—mg/L
0.6
0.4
0.2
0.0
06/01/10
09/01/10
12/01/10
03/01/11
Date
Mn—manganese, SJWD—WStartex-Jackson-Wellford-Duncan Water District, WTP—water treatment plant
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FIGURE 7
Downstream manganese profiles in the Middle Tyger River
Parameter
Total Mn
Mn—mg/L
0.6
Soluble Mn
January
July
February
August
March
September
April
October
May
November
June
December
0.4
0.2
0.0
Mn—mg/L
0.6
0.4
0.2
0.0
Mn—mg/L
0.6
0.4
0.2
0.0
Mn—mg/L
0.6
0.4
0.2
0.0
Mn—mg/L
0.6
0.4
0.2
0.0
Mn—mg/L
0.6
0.4
0.2
0.0
0
2
4
Distance—mi
6
8
0
2
4
6
8
Distance—mi
Mn—manganese
Figure shows data from June 3, 2010, to Oct. 6, 2011, with monthly totals averaged. Distance is measured as miles downstream from Lake Lyman dam.
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FIGURE 9
FIGURE 8
Increase in soluble manganese concentrations after
settling basins
0.20
0.15
Soluble Mn—mg/L
shows that soluble manganese was considerably higher after the
settling basins than at the intake. With SJWD’s existing granular
media filtration plant (which could sorb and oxidize soluble
media), solids management was not a great concern, but it could
pose a challenge with the new MF facility unless steps were taken
to ensure that anoxic pockets would not develop in settling basins.
Bench-top treatment study. As shown in Figure 9, manganese
was effectively removed to below the SMCL by all three treatment processes evaluated in laboratory experiments, i.e.—direct
oxidation, manganese-coated media bed before the filter, and
manganese-coated media bed after the filter. However, some of
the direct oxidation experiments resulted in high manganese
concentrations; this result was attributed to overdosing of
KMnO4 (as verified by a pink color in the MF permeates from
those experiments). Small changes in the manganese adsorption
capacity of the media bed across the duration of the test did not
appear to affect the results because the media bed removed
manganese well in all cases. Iron was also effectively removed
to below the SMCL; however, the iron results must be qualified
with the recognition that much of the dissolved iron was
removed during coagulation. This was hypothesized to be attributable to oxidation (from higher DO levels caused by pouring
water between vessels) and removal of complexed iron. DOC
removal was the same for all three processes because most of
the removal occurred in coagulation, flocculation, and sedimen-
0.10
0.05
0.00
Treatment
Plant Intake
WTP East
Filter Influent
WTP West
Filter Influent
Sampling Location
Mn—manganese, WTP—water treatment plant
Raw water concentrations and manganese (A) and iron (B) removal for different manganese control strategies
A
B
0.6
2.5
0.5
2.0
Fe—mg/L
Mn—mg/L
0.4
0.3
1.5
1.0
0.2
0.5
0.1
USEPA SMCL
USEPA SMCL
0.0
0
Raw
(Total)
Filtered Raw
Direct
(Soluble)
Oxidation
Media
Media
Before Filter After Filter
Raw
(Total)
Treatment Process
Filtered Raw
Direct
(Soluble)
Oxidation
Media
Media
Before Filter After Filter
Treatment Process
Fe—iron, Mn—manganese, SMCL—secondary maximum contaminant level, USEPA—US Environmental Protection Agency
Box-and-whisker plots show minimum, maximum, median, and 25th and 75th percentiles with points showing each experimental result.
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FIGURE 10
Effect of permanganate dose (as µmol/L
above stoichiometric requirement) on effluent
manganese
KMnO4 dose—µmol/L
4.85
6.00
8.00
10.00
12.00
14.00
15.82
3
2
0.10
0.05
USEPA SMCL
1
0.00
Process Effluent Mn—µmol/L
Process Effluent Mn—mg/L
0.15
0
0
5
KMnO4 Overdose—µmol/L
10
reduced metals concentrations, the stoichiometric oxidant dose
based on dissolved metals concentrations served well, resulting
in no excess manganese. When higher metals concentrations
necessitated higher KMnO4 doses, excesses KMnO4 was present. Figure 10 shows that when KMnO4 was overdosed, a fraction of the manganese showed up in the finished water and the
amount increased with KMnO4 dose. It was expected that some
additional oxidant would be required to overcome oxidant
demand posed by dissolved organic material (Knocke et al,
1987). In fact, less than the stoichiometric dose may be required
because of the ability of the resulting oxide to sorb manganous
and ferrous ions (Stumm & Morgan, 1967) or possibly because
of iron oxidation in the time interval between concentration
measurement and oxidant dosing.
Seasonal effects. No considerable differences were observed in
membrane filtration or overall treatment performance for July
and August (summer) compared with water from October for the
parameters manganese, iron, DOC removal percentage, and flux
decline versus turbidity.
Temperature effects. Lower temperatures would be expected
to slow the reaction between HOCl and manganese in the manganese-coated media bed. The pH was 5.8, the initial manganese
was 0.433 mg/L for one experiment and 0.177 mg/L for the other,
and the temperature was < 6°C. The effluent manganese levels
were 0.008 mg/L (unfiltered) and 0.001 mg/L (filtered), showing
that the manganese-coated media bed was capable of removing
manganese, even at low temperatures. However, although these
tests demonstrated that manganese could be adsorbed, they were
not extensive enough to show long-term maintenance of the
regeneration ability. Further work would be needed to demon-
Mn—manganese, KMnO4—potassium permanganate, SMCLsecondary maximum contaminant level, USEPA—US Environmental
Protection Agency
Negative values signify a dose less than the stoichiometric
requirement.
FIGURE 11
Representative microfiltration flux data for two sets of
experiments
Treatment
Direct oxidation
Media before filter
Media after filter
1.0
Fraction of Initial Flux—J/Jo
tation. The manganese-coated media bed and membrane processes are not expected to offer additional benefits for removing
DOC or DBP precursors.
The two manganese-coated media bed processes resulted in
much lower turbidities (0.15±0.18 ntu for media before filter and
0.16±0.13 ntu for media after filter) than the direct oxidation
process (0.45±0.43 ntu). Higher direct oxidation turbidities were
attributed to the oxidation of excess KMnO4 after filtration,
which resulted in a brown tint to the water. When placed before
the filter, the media bed removed turbidity to < 0.25 ntu by a
filtration mechanism. A full-scale manganese-coated media bed
would likely be constructed using larger media and larger loading
rates and would not have the solids-removal capability observed
in the lab-scale column.
Sensitivity of KMnO4 oxidation dose. As in other studies
(Carlson & Knocke, 1999; Knocke et al, 1990a), the effluent
manganese concentration observed here after KMnO4 oxidation
dosing was quite sensitive to the KMnO 4 dose. With low
Middle Tyger River Water
North Tyger Reservoir Water
0.8
0.6
0.4
0.2
0
500
1,000
Specific Volume—L/m2
0
500
Flux values (J) were normalized by the initial flux (Jo).
2013 © American Water Works Association
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Specific Volume—L/m2
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FIGURE 12
decline. Lower temperatures decreased the absolute magnitude
of flux as expected, but the normalized flux decline was not
affected. Manganese concentration also did not make a difference; flux declines were similar for natural waters and those
spiked with 20 and 45 mg/L manganese.
The parameter that did significantly affect flux decline was
treatment procedure. As shown in Figure 13, the media-afterfilter treatment showed more rapid flux decline than the other
two treatments (although there was significant spread in the
data). To isolate the effects among the treatments and control for
interset variability, the flux decline was normalized by the average
flux for each experimental set (i.e., the set composed of the three
processes having the same experimental treatment and same
water source) to evaluate the relative flux decline, shown in Figure 14. The plot in this figure more clearly shows that the mediaafter-filter treatment exhibited, on average, significantly more
flux decline than the other treatments.
Flux decline versus turbidity
Source
Treatment
North Tyger Reservoir
Direct oxidation
Middle Tyger River
Media before filter
Media after filter
Flux Decline After 500 mL/m2 Filtered
0.6
0.4
0.2
FIGURE 13
Flux decline by treatment
0.7
0.0
0.5
1.0
1.5
2.0
Turbidity—ntu
0.6
0.5
Flux Decline After 500 L/m2
strate regeneration capability at lower temperatures, which may
affect the long-term manganese removal in practice.
Membrane filtration results. Figure 11 shows representative
flux data for the MF portion of the experiments. Curves similar
to those shown in the figure were observed for each filtration (43
filtrations in all), and the data were summarized by recording the
percent flux decline at 500 L/m2 (thus a larger percent decline
indicates greater fouling). North Tyger Reservoir water resulted
in significantly greater flux decline than Middle Tyger River water
(p < 0.02, calculated using percent flux decline values for a simple
homoscedastic t-test). Although none of the other water parameters measured in these experiments was significantly correlated
with flux decline, it is noteworthy that the two water sources
exhibited very different relationships between fouling and turbidity. (The filter influent turbidity is plotted against filter flux
decline in Figure 12, where the points are coded both for treatment and water source.) Compared with water from the North
Tyger Reservoir, Middle Tyger River water caused significantly
less fouling for the same amount of turbidity (p < 0.01). The lack
of correlation between turbidity and fouling indicated that suspended or light-scattering material was not the major contributor
to fouling; this was consistent with findings that a fraction of
DOC (e.g., 3–20 nm material) is primarily responsible for fouling
in natural water (Howe & Clark, 2002). However, overall DOC
was not correlated with fouling.
Flux data were evaluated to determine temperature and seasonal effects, but neither parameter was a strong predictor of flux
0.4
0.3
0.2
0.1
0.0
Direct
Oxidation
Media
Before Filter
Media
After Filter
Treatment Type
Box-and-whisker plots show minimum, maximum, median, and 25th and
75th percentiles with points showing each experimental result.
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Relative flux decline
180
160
120
Average flux decline for each experiment
80
60
FIGURE 15
40
TTHM concentrations for three treatment scenarios
Uniform Formation
Conditions
Formation Potential
20
Middle
Tyger River
Middle Tyger
River
North Tyger
Reservoir
Media
After Filter
200
Treatment Type
100
50
Treatment Scenario
TTHM—total trihalomethane
Error bars show data range.
2013 © American Water Works Association
Media After Filter
Media Before Filter
Raw
Direct Oxidation
Raw
Media After Filter
Media Before Filter
Raw
Direct Oxidation
Media After Filter
0
Raw
The differences in the observed flux declines were hypothesized
to be a result of foulant sorption before filtration. The mediabefore-filter process and the direct oxidation process both provided opportunities for DOC or other foulants to be sorbed onto
metal oxide particles, which have large surface areas and are
excellent adsorbents (Stumm & Morgan, 1967). Although oxidant addition is also coincident with lower flux decline, physical
removal was considered a more likely cause of fouling reduction
than any chemical changes to these colloids caused by the relatively small oxidant doses.
THM formation results. Two DBP formation tests were used.
The first, the formation potential (FP) test, indicates the quantity
of DBP precursors present by providing very high chlorine concentrations for 24 h. The second, the uniform formation condition test, mimics distribution system conditions to measure the
quantity of DBPs that would likely form in the distribution system over a 24-h period.
150
Average TTHMs—µg/L
Relative flux decline is defined as the flux for each treatment relative to
(normalized by) the average flux decline for each experimental set of
treatments. Shaded boxes show the second and third quartiles.
Media Before Filter
Media
Before Filter
Direct Oxidation
Direct
Oxidation
North Tyger
Reservoir
Media After Filter
100
Media Before Filter
Relative Flux Decline—% of average
140
THMFP test results (Figure 15) indicated considerable
removal of total THM (TTHM) precursors over the raw water
and that the effluent from the three treatment processes had
very similar TTHMFPs. This was not surprising, given that the
treatment processes all had approximately the same amount of
DOC in the effluent. Two TTHMFP data sets were collected for
each water, which explains the wide span of the error bars.
Removals ranged from 5.8 to 71.3%, with a mean removal of
36.0%. The THM removals observed were hypothesized to be
primarily attributable to precursor removal in coagulation,
filtration, and sedimentation. Although KMnO4 preoxidation
is known to improve THM precursor removal, this is a result
of complexing by particulate or colloidal MnOx (with Ca2+ ions
forming bridges to bring these ions together), improving removals during coagulation (Zhang et al, 2009).
UFC test results also showed less TTHM formation in the
treated water than the raw water (average of 30.4%, range of
15.8 to 37.7%). The direct oxidation process had the lowest
TTHM yields in both waters. This was expected because of the
KMnO4 THM removal benefit and because no chlorine is used
in this process, unlike the other two processes; chlorine would
be expected to cause higher DBP yields. Any differences were
within experimental variation, however. The decrease in the
Direct Oxidation
FIGURE 14
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TTHM-to-DOC ratio over treatment showed that the TTHM
precursor fraction of the DOC was preferentially removed in
the Middle Tyger River. Ratios of specific ultraviolet absorbance
(SUVA) to DBP ratios mirrored the SUVA/DOC trends, suggesting that the TTHM precursor fraction of the DOC was preferentially removed.
CONCLUSIONS AND RECOMMENDATIONS
Source water study conclusions. Manganese concentrations at
the plant are controlled by conditions and processes in the river,
not by the manganese inputs from Lake Lyman or Beaverdam
Creek. The study found a large overall net loss of soluble manganese in the summer months and a small increase in soluble
manganese observed in the last two river miles in the summer.
Because river conditions are the controlling factor for manganese
levels, manganese management measures in Lake Lyman (the
river source) would not solve the manganese concentration challenges at the plant intake. Rate studies suggested that soluble
manganese loss in the Middle Tyger River is attributable to
microorganism-mediated oxidation.
In the summer the North Tyger Reservoir generally has lower
manganese levels than the Middle Tyger River unless the anoxic
hypolimnion rises to the level of the intake. The reservoir also
has soluble manganese concentrations in the range of 0.1 to
0.2 mg/L from January through June, which was unexpected
for a lake.
Treatment study conclusions. The manganese-coated media bed
was effective at removing manganese to low levels (< 0.004
mg/L) in both North Tyger Reservoir and Middle Tyger River
water. Manganese was also effectively removed by KMnO 4
oxidation; however, the difficulty involved in matching KMnO4
dose to oxidant demand of the water prevented high removal
efficiencies from being consistently achieved. All three processes
proved comparable in removing turbidity and organic carbon
and minimizing DBPFP. These results provide support for the
use of the manganese-coated media bed as a simple, reliable
process with a small footprint that is capable of removing manganese to very low levels.
The manganese-coated media bed–after-filter process demonstrated significantly greater filter flux decline (i.e., more
fouling) than either of the other two treatment processes. The
improved membrane filtration performance may have resulted
from the sorption of colloidal foulants onto metal oxides
(either the media in the bed or freshly formed oxides after
oxidant addition). When the two water sources were compared,
North Tyger Reservoir water exhibited more flux decline than
Middle Tyger River water for the same turbidity (p > 0.01).
Although these data provided valuable insights into filtration
performance, the experiments here did not evaluate the reversibility of the fouling; that information would be important in
the design of an MF facility.
Utility recommendations. Water utilities are advised to conduct
a comprehensive evaluation of their options for manganese control at both their water sources and treatment plants. By characterizing manganese dynamics and levels in the source waters,
utilities obtain useful information for selecting waters for treat-
ment and developing and assessing strategies for manganese
control at the source. In this study, results indicated that an
understanding of manganese dynamics in source waters may help
utilities select a low-manganese source; however, additional
actions will still be necessary at the treatment plant in order to
develop a more robust manganese control strategy.
Study recommendations. Recommendations for further study
include using a backwashable MF module to more closely match
the MF plant configuration and evaluate longer-term performance, separating the irreversible fouling from the flux decline
that can be recovered by backwashing. Additional analytical
tools should be used to arrive at a better understanding of fouling mechanisms.
Acknowledgment
This study was funded and supported by the Startex-JacksonWellford-Duncan Water District, Wellford, S.C.
About the authors
Daniel Olin Lewis is a system engineer with
Duke Energy in Seneca, S.C. He holds a
master’s degree in environmental engineering
and science from Clemson University,
Anderson, S.C. David A. Ladner is an
assistant professor in the Department of
Environmental Engineering and Earth
Sciences at Clemson University. Tanju
Karanfil (to whom correspondence should be addressed) is a
professor and chair of the same department, 342 Computer
Ct., Anderson, SC 29625; [email protected].
peer review
Date of submission: 10/21/2012
Date of acceptance: 05/30/2013
Footnotes
1Hydrolab
Datasonde 4, Hach, Loveland, Colo.
Pall, Ann Arbor, Mich.
Shimadzu, Tokyo, Japan
4Varian Cary 50 Bio UV-Vis, Agilent Technologies, Santa Clara, Calif.
5Nalgene, Rochester, N.Y.
6Phipps & Bird, Richmond, Va.
7DR890, Hach, Loveland, Colo.
8VVLP membranes, Millipore, Billerica, Mass.
9Amicon stirred cell 8040 and 8010, Millipore, Billerica, Mass.
1016/30 FilPro Columbia filter sand, US Silica, Frederick, Md.
112100N turbidity meter, Hach, Loveland, Colo.
126890 GC-ECD, Agilent Technologies, Santa Clara, Calif.
13Google Earth, Google, Mountain View, Calif.
2Acrodisc,
3TOC3201,
References
AWWA, 2009. Committee Report: A Survey of the “Other” Inorganics. Journal
AWWA, 101:8:79.
Burger, M.S.; Mercer, S.S.; Shupe, G.D.; & Gagnon, G.A., 2008. Manganese
Removal During Bench-scale Biofiltration. Water Research, 42:19:4733.
Carlson, K.H. & Knocke, W.R., 1999. Modeling Manganese Oxidation With KMnO4.
Journal of Environmental Engineering, 125:10:892.
Coffey, B.M.; Gallagher, D.L.; & Knocke, W.R., 1993. Modeling Soluble Manganese
Removal by Oxide-Coated Filter Media. Journal of Environmental
Engineering, 119:4:679.
2013 © American Water Works Association
E495
Lewis et al | http://dx.doi.org/10.5942/jawwa.2013.105.0108
Journal - American Water Works Association
Peer-Reviewed
Cornwell, D.A. & Bishop, M.M., 1983. Determining Velocity Gradients in
Laboratory and Full-scale Systems. Journal AWWA, 75:9:470.
Kohl, P. & Medlar, S., 2006. Occurrence of Manganese in Drinking Water and
Manganese Control. AwwaRF, Denver.
Ellis, D.; Bouchard, C.; & Lantagne, G., 2000. Removal of Iron and Manganese
From Groundwater by Oxidation and Microfiltration. Desalination,
130:3:255.
Merkle, P.B.; Knocke, W.R.; & Gallagher, D.L., 1997. Method for Coating Filter
Media With Synthetic Manganese Oxide. Journal of Environmental
Engineering, 123:7:642.
Gantzer, P.A.; Bryant, L.D.: & Little, J.C., 2009. Effect of Hypolimnetic Oxygenation
on Oxygen Depletion Rates in Two Water Supply Reservoirs. Water
Research, 43:6:1700.
Morgan, J.J., 2005. Kinetics of Reaction Between O2 and Mn(II) Species in
Aqueous Solutions. Geochimica et Cosmochimica Acta, 69:1:35.
Hargette, P., 2011. Personal communication.
Howe, K.J. & Clark, M.M., 2002. Fouling of Microfiltration and Ultrafiltration
Membranes by Natural Waters. Environmental Science & Technology,
36:16:3571.
Islam, A.A.; Goodwill, J.E.; Bouchard, R.; Tobiason, J.E.; & Knocke, W.R., 2010.
Characterization of Filter Media MnOx[s] Surfaces and Mn Removal
Capability. Journal AWWA, 102:9:71.
Jørgensen, S.E.; Löffler, H.; Rast, W.; & Straskraba, M., 2005. Lake and Reservoir
Management. Elsevier Science, Amsterdam, the Netherlands.
Knocke, W.R.; Zuravnsky, L.; Little, J.C.; & Tobiason, J.E., 2010. Adsorptive
Contactors for Removal of Soluble Manganese During Drinking Water
Treatment. Journal AWWA, 102:08:64.
Knocke, W.R.; Van Benschoten, J.E.; Kearney, M.; Soborski, A.; & Reckhow, D.A.,
1990a. Alternative Oxidants for the Removal of Soluble Iron and Manganese.
AwwaRF, Denver.
Knocke, W.R.; Occiano, S.; & Hungate, R., 1990b. Removal of Soluble Manganese
From Water by Oxide-Coated Filter Media. AwwaRF, Denver.
Knocke, W.R.; Hamon, J.R.; & Thompson, C.P., 1988. Soluble Manganese Removal
on Oxide-coated Filter Media. Journal AWWA, 80:12:65.
Knocke, W.R.; Hoehn, R.C.; & Sinsabaugh, R.L., 1987. Using Alternative Oxidants
for Removal of Dissolved Manganese From Water Laden With Organics.
Journal AWWA, 79:3:75.
Morgan, J.J. & Stumm, W., 1964. Colloid–Chemical Properties of Manganese
Dioxide. Journal of Colloid Science, 19:4:347.
Perez-Benito, J.F. & Arias, C., 1992. Occurrence of Colloidal Manganese Dioxide in
Permanganate Reactions. Journal of Colloid and Interface Science, 152:1:70.
Stumm, W. & Morgan, J.J., 1967 (2nd ed.). Aquatic Chemistry. Wiley-Interscience,
New York.
Tobiason, J.E.; Knocke, W.R.; & Goodwill, J.E., 2009.Characterization and
Performance of Filter Media for Manganese Control. AwwaRF, Denver.
USEPA (US Environmental Protection Agency), 1995. Method 551.1, Revision 1.0.
Determination of Chlorination Disinfection Byproducts, Chlorinated Solvents,
and Halogenated Pesticides/Herbicides in Drinking Water by Liquid–Liquid
Extraction and Gas. National Exposure Research Laboratory, Office of
Research and Development, Cincinnati.
USGS (US Geological Survey), 2011a. National Water Information System. USGS
02157510 Middle Tyger River Near Lyman, S.C. USGS, Reston, Va.
USGS, 2011b. National Water Information System. USGS 02157490 Beaverdam
Creek Above Greer, S.C. USGS, Reston, Va.
Zaw, M. & Chiswell, B., 1999. Iron and Manganese Dynamics in Lake Water.
Water Research, 33:8:1900.
Zhang, L.; Ma, J.; Li, X.; & Wang, S., 2009. Enhanced Removal of Organics by
Permanganate Preoxidation Using Tannic Acid as a Model Compound—Role
of In Situ Formed Manganese Dioxide. Journal of Environmental Sciences,
21:872.
2013 © American Water Works Association