BIOLOGICAL IRON AND MANGANESE REMOVAL, PILOT AND FULL SCALE APPLICATIONS

BIOLOGICAL IRON AND MANGANESE REMOVAL,
PILOT AND FULL SCALE APPLICATIONS
Brian Gage, Aqua Technical Sales Inc.*
Dr. Dennis H. O’Dowd, BOD Consulting
Paul Williams, ONDEO Degremont Ltd.
Presented at the Ontario Water Works Association conference, May 3rd , 2001
INTRODUCTION
Both manganese and iron are found in surface and ground waters at varying
concentration levels. When present even at low concentrations they can be linked to the
following problems: discolouration, turbidity and taste problems or form slime and iron
oxide or manganese dioxide accumulations in pipes. Both metals promote the growth of
certain types of chlorine tolerant micro-organisms in water distribution systems. This
biota, as in Walkerton, can provide protected sites for noxious organisms and
consequently, vastly increase the costs of cleaning and sterilizing systems that contain
organisms dangerous to human health. Although there is little evidence that the
consumption of water with natural concentrations of these metals have adverse effects on
public health, and they are in fact essential elements for human diet, they do remain
problematic from an aesthetic, technical and economic point of view. The Guidelines for
Canadian Drinking Water has a recommended limit for aesthetic reasons for iron of 0.3
mg/l and an objective concentration target of 0.05 mg/l. The recommended limit for
aesthetic reasons for manganese is 0.05 mg/l and the objective concentration is 0.01
mg/l.. Ontario drinking water objectives have aesthetic objectives of 0.05 mg/l or
manganese and 0.30 mg/l for iron.
Conventional iron and manganese removal plants typically rely on physical-chemical
reactions using manganese greensands, intense aeration or chemical oxidation (with O3 ,
KMnO 4 or ClO 2 ). These processes provide treatment but they can have operating
problems and they do not always provide an effluent that meets the water quality
objectives.
C l2 / O 3 o r
K M n 0 4
Filter
Media or
Greensand
R a w
W a t e r
Figure 1
Conventional Treatment Plant
C l2
C l2
Biolite S
Filter
Media
Static Mixer
Treated Water
Air for Backwash
Raw
Water
Air
Figure 2
Biological Treatment Plant
Due to the limited success of traditional treatment methods, Ondeo Degrémont has
investigated the use of biological iron and manganese removal for municipal drinking
water in Canada. They are doing so because biological iron and manganese remova l
systems can sometimes have the following advantages: smaller plants because of higher
applied filtration rates, (sometimes in excess of 50 m/hr versus 10 – 15 m/hr) or because
aeration and filtration can take place simultaneously in the same vessel; longer filter runs
because the iron or manganese retention in the filter due to the formation of more dense
precipitates and the use of a more course media; denser backwash sludge that is easier to
thicken and de-water; higher net productions due to less water being required for
backwashing and being able to use raw water for the backwash; require no chemical
addition; and no deterioration of water quality over time; lower capital and operating
costs through the elimination of chemicals, less frequent backwashing, fewer
components, etc.
Development of Biological Manganese and Iron Removal
Iron was the first element for which biological removal techniques were developed
because water rich in iron is more common and also because iron is more readily
removed biologically. It was noticed that in some physical-chemical iron removal
plants, in spite of raw water quality that was not well suited for conventional iron
removal, that satisfactory iron removal occurred anyway. Large amounts of bacteria,
either stalked species such as Gallionella ferruginea, or filimentous ones such as
Leptothrix orhracea were found present in the backwash sludge and those bacteria were
in fact found to be responsible for removing the iron. In addition it was noticed that when
iron or manganese was complexed with substances like humic acids, polyphosphates ,
silica etc., which normally interfered with the ability of physical chemical treatment
plants to work, that the bacteria could still remove the metals. It was realized that these
bacteria could be used for iron removal in water treatment plants before the water enters
the municipal distribution system. These bacteria which can remove iron or manganese,
are referred to as ‘Iron Bacteria’. In general, these bacteria are found wherever there is a
detectable level of iron or manganese in water.
Figure 3 Common Forms of Iron Bacteria
1. Leptothrix ochracea
2. Gallionella ferruginea
Biological Iron and Manganese Removal Process
In anaerobic ground water, iron and manganese may remain in their soluble forms of Fe2+
and Mn2+. Physical chemical removal processes require the oxidation of this water in
order to sufficiently raise the oxidation-reduction potential (ORP) of the water so that the
iron and manganese present will be converted into their insoluble oxidized forms. The
ORP or rH of the water is directly related to the pH and the Eh, (the potential energy
expressed in volts, of a substance compared to that of hydrogen, to proceed in a reduction
reaction, calculated from an equation rH = Eh/0.029 +2pH =(A +or- Ehg) /0.029 +2 pH
).
The metabolic activities of iron bacteria are not fully understood but it is believed that the
same oxidation of iron is carried out by some variation to the physical chemical reaction:
4Fe 2+ + O2 + 10H2 O ? 4 Fe(OH)3 + 8H+ + Energy
Whatever the metabolic pathway for the iron oxidation reactions, the biological process is
catalytic in nature and causes a rapid oxidation. The red insoluble precipitates formed are
all slightly hydrated iron oxides that, beneficially, are more compact forms than the
precipitates formed when using physical chemical processes. This feature partially
explains the greater iron retention capacity between backwashes of biological filters
when compared to physical chemical treatment filters.
Manganese is also oxidized by ‘iron bacteria’ but at higher rH, or oxidation reduction
potential (ORP) values than that for iron, according to some variation of the following
three step reaction:
Mn2+ + 02 ? MnO2 + Energy
Mn2+ + MnO2 ? ?MnO2 o Mn2+
MnO2 o Mn2+ + O2 ? 2MnO2
Oxidation of manganese by oxygen alone is slow but the reaction is catalyzed by the
presence of previously oxidized manganese. The ion in its reduced form is adsorbed by
the manganese dioxide which allows the normally slow oxidation reaction to go to
completion.
As with iron oxidation, the manganese dioxide, or some hydrated variant, remains as a
black precipitate trapped within the filter media until a backwash is carried out. The iron
bacteria species of particular interest for manganese removal are Leptothrix, Crenothrix,
Hyphomicrobium, Siderocapsacaes, Siderocystis, Metallagenium and Pseudomonas
manganoxidans.
It is important to recognize that iron bacteria catalyze the oxidation reactions under
conditions of pH and Eh that are intermediate between those of natural groundwater and
those required for conventional treatment. The field of activity of catalyzed oxidation for
iron bacteria thus straddles the theoretical boundaries between the fields of Fe2+ and Fe3+
stability expected strictly by chemical thermodynamics. This can be visualized in a
stability diagram, using pH and Eh as ordinates, as shown in Figure 4.
EH vs. pH
EH (mV/H
800
2
)
MnO
600
2
Manganese
Removal
Field
400
Iron
Removal
Field
200
Fe(OH)
Fe
Mn
Mn
2
0
3
2+
3
2+
0
6
Figure 4
7
8
9
pH
Stability Diagram for Biological Iron and Manganese Removal
By aerating the raw water and raising the dissolved oxygen concentration, the raw
water’s rH or ORP can be increased into the pH and Eh range where biological oxidation
can take place. By controlling the quantity of air supplied, the ORP or rH can be
adjusted to a level which is either ideal for iron or for manganese removal. When both
iron and manganese are present the iron must be removed first through one aerationfiltration step, and then the manganese with another after raising the pH by stripping
carbon dioxide. In some cases, if the pH is below 7.0, chemical addition may also be
necessary in order to raise the pH to make manganese removal possible.
Once a biological iron or manganese removal plant is constructed, the system must be
given time to ‘seed’ with bacteria naturally present in the water source. This seeded
biomass is naturally and continuously regenerated during the life of the plant and is
periodically partially removed through backwashing. For iron removal plants, the
seeding period is quite short requiring anywhere from a day to about one week. For
manganese removal plants the seeding time can be considerably longer, anywhere from 3
weeks to 3 months. At the end of the seeding period, the metal concentration in the
effluent falls to near detection levels. The seeding period is affected by the temperature
of the water source, and is generally longer for cold water sources.
Iron bacteria are generally robust, and because of the variety of species involved, one
type or another is able to thrive under most environmental conditions. Given the correct
pH, between 6 – 8, and Eh, the bacteria are normally able to oxidize iron at temperatures
ranging from 5 ?C to 50 ?C. Inhibition of the biological process can however be caused
by the presence of H2 S, Chlorine, NH4 +, and some heavy metals normally not present in
water sources. Under certain conditions of alkalinity and hardness, it can also be
impossible to raise the ORP sufficiently for biological manganese removal even with a
theoretically sufficient quantity of dissolved oxygen. It is therefore critical to have a
complete and accurate analysis of the influent water because a biological removal system
will only be effective if the proper water conditions are present.
PILOT STUDIES
Pilot Plant
ONDEO Degremonts’ pilot plant for biological iron or manganese removal consists of a
transparent filtration column that operates in a down flow mode through what ONDEO
Degremont calls “Biolite S” growth media. One column is necessary for removal of a
single metal while two columns must be used in series if removal of both iron and
manganese is desired.
The pilot filter columns have the following dimensions:
Diameter:
100 mm
Height:
2000mm
Normal Media Height:
1500mm
On the top and bottom of each unit are small stainless flanged columns that permit
connections for the influent and effluent water as well as to accommodate pressure
gauges. The bottom of the column is equipped with a special nozzle designed to prevent
loss of the “Biolite S” during filtration.
A raw water peristaltic pump with a variable speed motor provides the process and
backwash water for the system. A positive displacement piston type compressor provides
both the process and backwash air for the system. Flow indicators and manual control
valves for both the air and water are all centrally located on a panel at the front of the
pilot unit. Two pressure gauges measure the pressures on either side of the media to
provide the differential pressure or head across the filter. Normal head is 3-5 psi and at
15 psi the filter should be backwashed .
Woodstock Mangazur Pilot
The town of Woodstock New Brunswick is located about 100 km north of Fredericton on
the St. John River and the town draws its drinking water from wells located below the
adjacent river. Unfortunately this water contains a significant quantity of manganese and
the town noticed a dramatic increase in its’ concentration in recent years. The manganese
concentratio n in the well water during the summer of 1997 was 0.67 mg/l or fourteen
times the provincial recommended maximum limit of 0.05mg/l for drinking water. The
town tested physical-chemical removal systems but they were dissatisfied by the
inconsistent effluent quality, high chemical costs and the degree of operator attention
required. After an analysis of the raw water, ONDEO Degremont suggested that the
town consider a biological manganese removal plant. It was agreed that a pilot plant was
necessary before building a full size system because this technology had never before
been tried in Canada, to prove the feasibility of the system for their water source, and to
facilitate the design of a full scale system. The iron concentration in the water source
was very low so iron removal was unnecessary.
Data available from a previous analysis that had been carried out by RPC laboratories in
Fredericton indicated that the pH, ORP, and manganese concentration made biological
manganese removal feasible. Because the water is drawn from a well approximately 50
metres deep, the water temperature remains between 9 ?C and 10 ?C year round.
Although this temperature is low, it is within the temperature ranges of some iron
bacteria and was sufficient for biological manganese removal. Temperature analysis was
carried out using an Orion 250 hand held pH meter. Dissolved oxygen, being the key to
the process was an important parameter that was measured frequently. The influent raw
water had an oxygen content close to 0 mg/l. The oxygen analyses were carried out using
a Hanna 9143 membrane dissolved oxygen probe.
Influent and effluent manganese concentrations were measured daily to monitor the
manganese reduction during the seeding and operations phases. These analyses were
carried out using a Hach DR2000 spectophotometer and the appropriate chemical
reagents. The results were confirmed with independent tests carried out at RPC
laboratories in Fredericton.
After site testing began the pH was found to be between 7.6 – 7.7 which confirmed that
the pH of the water was sufficient for the Mangazur. Initial analysis indicated that the
raw water had an ORP that was also high enough to make the process feasible. Testing
of the ORP by the pilot operator was at first problematical. Unfortunately reliable
readings in samples that have a low dissolved oxygen concentration, or low total ionic
strength or low temperature are difficult to obtain and the meter often needs 30 minutes
to stabilize. The raw water at Woodstock had all of these inhibiting characteristics. As a
result, for day to day operation of the pilot, ORP measurements were not taken because
the pH was high enough that the ORP was not seen as a likely impediment to the process.
ORP and pH readings were taken with a hand held Orion 250 pH meter and an Orion
ORP platinum electrode.
A hydrogen sulfide test was carried out to ensure the absence of this interfering
substance. Results confirmed that H2 S concentrations were below detectable limits.
Because the influent water came directly from the pumps at the water source, there was
no risk that chlorine or other contaminants could enter the water before treatment.
The pilot plant was installed in the Woodstock pumping station and connected to their
water supply directly at the source on June 25 1997. After the pilot began operating, a
sample of the influent and effluent were collected and sent to the laboratory in
Fredericton for a complete water analysis. They confirmed the accuracy of the D.O., pH,
and Mn tests being carried out on-site, (samples cannot be sent to a laboratory for ORP
testing).
On-site testing was used for the day-to-day operation of the pilot plant because these tests
are more accurate (especially for pH and D.O. tests that are sensitive to water
temperature) and to allow instantaneous adjustment of system parameters when
necessary. The operator carried out the following tests on a daily basis on-site: dissolved
oxygen concentration; pH; temperature; manganese concentration
During the first phase of the pilot study, a filtration rate of 15m/h (6.1 USgpm/ft2) was
maintained. After the column was properly seeded and the effluent manganese
concentration was below the desired limit of 0.05mg/l, the speed was increased to 25 m/h
(10 USgpm/ ft 2). The flow was then further increased to a velocity of 37 m/h (15 USgpm/
ft2) without any deterioration in effluent quality. The system was tested at this speed only
to determine if the unit could handle this high filtration rate. At a 37 m/h filtration speed,
filter headloss was significant and more frequent backwashes were required. (The full
scale system was designed to operate between 20 and 30 m/h.)
The day-to-day operation of the pilot required little operator attention. During the start
up phase it was necessary to adjust the airflow to obtain the appropriate quantity of
dissolved oxygen, but once adjusted, pilot operation required only water testing and
backwashing. The operation protocol required backwashing to be carried out after a head
loss increase (? P) of 1.5m or every 5 to 10 days. During the seeding phase, the first
backwash was carried out four weeks after the start-up because it was feared that a
backwash would remove the biomass that had accumulated. Immediately after the first
backwash, the manganese concentration dropped in the effluent by approximately 25%.
It was clear that backwashing was necessary during the seeding phase even if the desired
increase in head loss had not been achieved. In theory, backwashing removes dead
biomass and allows for fresh or endogenous bacteria growth. During the seeding phase,
the period between backwashes should not be more than ten days to help ensure that the
biomass is in a healthy and hungry growth phase much like our teenage years.
Backwashing is carried out using an air scour, then a simultaneous air and water wash,
and lastly a water rinse. This process fluidizes the bed and allows the removal of the
accumulated manganese dioxide.
Woodstock Results
The pilot plant was producing water that had a manganese concentration below 0.05mg/l
after six weeks as shown in Figure 5. The water quality remained between 0.02 and
0.03mg/l consistently after this time even just after backwashing, increased filtration rates
and a pilot shut down. As long as backwashing is carried out regularly, the system can
run for an indefinite period without any replacement or regeneration of the growth
media.
After 15-20 minutes following backwash, the effluent water quality returned to levels
below the required level of 0.05 mg/l Mn. In the full-scale system the effluent produced
following backwashing is filtered to waste. Because the biological process produces large
floc, the turbidity of the effluent is also low immediately following backwash.
Woodstock Pilot Study Results
0.8
[Manganese] mg/l
0.7
0.6
0.5
0.4
I
0.3
0.2
Influent Mn
Effluent Mn
9/10/1997
9/3/1997
8/27/1997
8/20/1997
8/13/1997
8/6/1997
7/30/1997
7/23/1997
7/16/1997
7/9/1997
7/2/1997
0
6/25/1997
0.1
Date
Figure 5 Manganese Concentration in Woodstock Pilot Effluent
During the pilot test the system was completely shut down for a period of six days to test
the effect on the system’s operation as this type of interruption will occur during the
operation of a full- scale system. During the period of time when the system was stopped,
the filter was drained. Iron bacteria can survive intermittent system interruptions as long
as 6 months and this has been demonstrated during the normal operation of several plants
in France. The pilot was restarted after six days and the effluent manganese
concentration was below the acceptable concentration of 0.05 mg/l within 15 minutes.
The town of Woodstock had the opportunity to test biological, greensand and intensive
oxidation manganese removal systems for its drinking water. The biological system was
shown to be superior to the others in terms of treatment efficiency, cost, flexibility and
system life. The biological system could operate at higher filtration rates (>30 m/h),
required less frequent backwashing, used no chemicals other than oxygen from the air,
and provided consistent water quality when compared to the other systems. The
biological system also used less water for backwashing and produced a smaller quantity
of sludge than other treatment methods. Backwashing could also be carried out with
untreated water and this increased the net production capacity of the plant.
If the raw water quality were to change significantly the biological system would under
some circumstances need minor modifications (a possible pH adjustment, an additional
iron removal step, H2 S removal etc.), but this is unlikely given the fact that the wells used
provide water of highly consistent quality. Based on the results of the pilot it was
determined that a system designed to operate at a filtration rate of 20-25 m/h would serve
the towns’ current and future treatment requirements. Although the system could run at
higher filtration rates (up to 35 m/h), a speed of 20-25 m/h provided an acceptable margin
of safety, a more stable system and a reserve if the town were to have some temporary
increase in demand.
Woodstock Mangazur Full Scale Start Up
Influent
Date
Effluent
Guideline
November 18th , 1998.
Figure 6 Manganese Concentration in Full Scale Plant Effluent
Seeding of the plant took 34 days to get the effluent concentration down to below the
acceptable level of 0.05 mg/l of manganese. This compares well with the 40 days taken
to seed the pilot filter. The initial flows through the filters were limited to rates below the
design flow rate of 20 m/h (8.2 Usgpm/ft2). Operating at flow rates of 9.6 - 14.3 m/h the
full-scale plant has, as shown in Figure 6, demonstrated consistent manganese removal to
levels below the guideline objective of 0.05 mg/l. Since April of 1999 the plant flow rate
has been increased to the design rate of 20 m/h or 1200 USgpm.
The frequency of backwash has remained as low as once every 3 - 4 weeks based on
headloss. This extended time between backwashes was subsequently reduced to once
every 2 weeks based on the desire to keep the biomass fresh. Backwashing utilizes
untreated well water and, as no chemical is added to the water, the backwash water is
discharged directly to the St. John River.
When compared to the original estimates for the water treatment plant, the total installed
cost for the plant was about 60% less than a physical che mical type plant, (about
$800,000 versus $1,460,0000). Chemical costs were eliminated which saved an
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05 mar. 99
19 fev. 99
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30 dec. 98
23 dec. 98
21 dec. 98
17 dec. 98
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Woodstock Mangazur Full Scale Start Up
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
26 nov. 98
[ Manganese] mg/l
As a result of the successful pilot study an order was placed with ONDEO Degremont for
a full-scale plant. The full-scale plant utilized automatic valves, in- line ORP and Oxygen
meters, magnetic flowmeters and PLC controls to provide automatic operation of the
filter backwash and the filter-to-waste cycles. The two filters are each 3 M diameter
which at the design flow rate of 272.5 m/h (1200 USgpm) provides a conservative
filtration rate of 20 m/h. The plant was built and installed in 1998 and began operation
additional $7,000 to $ 16,000 per year. Offsetting the elimination of the chlorine or
potassium permanganate costs was the need for
aeration blowers to supply air (oxygen) upstream of the filters. Sludge handling costs
were almost non-existent due to the fact that the sludge had no chemical addition and the
filters used raw water for backwash.
Barrie, Ontario Ferazur Pilot
Located north of Toronto on the shores of Lake Simcoe, the City of Barrie draws its’
water from a number of wells that have unacceptable levels of iron. The wells are
located on glacial till that due to changing ancient shorelines, has a number of aquifer
“blisters” which can cause significant changes in raw water quality. Levels of iron,
manganese and oxygen can vary significantly depending on the weather and the rates of
withdrawal. These conditions were considered appropriate for testing the strengths and
weaknesses of the ONDEO Degremont Ferazur Biological Iron Removal Filter. As a
result of the need of the City of Barrie PUC to test various alternate technologies and the
desire on the part of the Ontario Ministry of the Environment to test a biological iron
removal filter, side by side with conventional greensand and electromedia filters, funding
was allocated by the Ministry and the City for a pilot test at Well # 3 at 55 Anne Street in
downtown Barrie. BOD Consulting of Toronto was retained to perform the pilot testing,
led by Dr. Dennis H. O’Dowd, PhD. Dr. Anthony Edmonds, PhD of the Ministry of the
Environment has overseen the pilot study on behalf of the City of Barrie and the OMOE
and will be issuing a comprehensive report in the near future that covers the results from
all of the technologies tested.
The well pump was operated 24 hours per day and a water head reduction device
consisting of a plastic line with a tee discharge into a pail provided the transition from the
pump pressure down to 20 kPa (3 psi) for the auto samplers. An on site lab in the pump
house was equipped with a Hach Dr 2000 with reagents for testing for all forms of iron,
manganese, chlorine and other strong oxidizers, a lab scale, pH meter, oxygen meter with
built in temperature compensation , a lap top computer with Hach link and other
instrument programs, a computer driven electron microscope (to 600 x) for particle
viewing and microphotography and a Hach Colourimeter. Testing was
Barrie Ferazur Pilot Seeded Start
0.6
0.4
0.3
0.2
0.1
Date
Fe raw
Figure7
Fe totalRw
Fe fini
Fe tot fin
Barrie Ferazur Initial Start Up with Seeded Media
performed twice a day, (4.30-5.30 a.m. and 4.30-5.30 p.m.) seven days a week by Mr.
Roy Symes, a federally certified water treatment plant operator for 25 years. The
standard tests performed twice daily were: raw and finished water oxygen, temperature,
pH, total iron, free iron and manganese (irregularly): finished water chlorine and visual
turbidity, odour and color observations. All microbiological sampling was performed by
Dr. O’Dowd and shipped on ice to Barbara J. Butler, PhD, University of Waterloo
Groundwater Microbiology, Department of Biology.
The ONDEO Degremont Ferazur pilot unit was installed and started up on August 25,
2000. The pilot was initially operated at a filtration rate of 22 m/hr. With raw water levels
averaging approximately 0.5 mg/l of ferrous iron, Fe2+, the level of ferrous in the effluent
was below 0.05 after two days. This rapid start up partially the result of seeding of the
filter with media from an earlier pilot unit. Although the immediate results were good,
the practice of seeding the pilot to shorten the start up is not a good idea. Not only does it
prevent a proper evaluation of the time needed to seed the filter, it also presents a remote
but very real possibility that should the feed pump discharge check valve fail, the biota in
the filter could contaminate the existing aquifer with new bacterial “pests” like a sulfur
fixer that could significantly alter the aquifers’ water quality.
Sept 8 -0420
Sept 7 1715
Sept 7, 0545
Aug 30 ,1700
Aug 30 ,0450
Aug 29,1700
Aug 29,0445
Aug 28,1700
Aug 28, 0500
Aug 27,1630
Aug 27, 0600
Aug 26, 1640
Aug 26, 0700
Aug 25,1815
0
Aug 25, 0430
[ Iron ] mg/l
0.5
Due to the fact that the well being tested shared its’ draw down zone with two other old
wells, the influent had a large amount of fine particulate oxidized iron that had been
accumulated around the old wells. These particles which contributed approximately 70%
of the iron going to the well would be filtered by the Ferazur and would have shown up in
the total iron removal. This highlights the importance of performing an analysis of both
ferrous and ferric iron and not just total iron.
Barrie Ferazur Pilot Unseeded Re-Start
0.8
0.7
[ Iron ] mg/l
0.6
0.5
0.4
0.3
0.2
0.1
Date
Fe raw
Figure 8
Fe totalRw
Fe fini
Fe tot fin
Barrie Ferazur Second Start-Up with Unseeded Media
Raw water oxygen levels varied from 0.0 to 1.2 mg/l. Interestingly, as the weather
cooled, the average oxygen dropped. Manganese levels were low, about 0.01 to 0.03,
with excursions to 0.05 but usually only slightly or occasionally above the target level of
0.01 mg/l.
Shortly after the initial start up, microbiological analysis showed an elevated level
bacteria in the effluent. Whereas the raw water had on average about 50 organisms per
ml, the effluent had 3500. To compare this result with the conventional plants, samples
were taken from an existing manganese-greensand plant in Ontario. Although not as high
as the levels seen in the effluent of the Ferazur, the levels were above the Ontario MOE
guideline level of less than 100. The significance of this finding is that both conventional
and biological filters are discharging chlorine tolerant bacteria into the distribution
system and although they are not pathogenic they are pest bacteria which will proliferate
in the distribution system so long as the proper nutrients, Fe2+ and Mn2+, are passed
along.
Oct 3 - 0445
Oct 2 - 0445
Oct 1 - 0600
Sept 30 - 0625
Sept 29 - 0445
Sept 28 - 0445
Sept 27 - 0445
Sept 26 - 0500
Sept 25 - 0445
Sept 24 - 0600
Sept 23 - 0700
Sept 22 - 0500
Sept 21 - 0445
Sept 20 - 0445
Sept 19 - 0500
Sept 18 - 0445
Sept 17 - 0700
Sept 16 - 0530
Sept 15 - 0500
Sept 14 - 1645
Sept 13 - 1720
Sept 12 - 1705
Sept 11 - 1705
Sept 10 -1705
Sept 9 - 1700
Sept 8 -1720
0
The backwash from the Ferazur appeared the same colour as that from the competing
technologies but the live protein count is too high for the MOE to allow its’ disposal back
to a river and must go to the sewer. Another concern is the potential for a failure of the
biofilter due to an attack by a viral bacteriophage. As phages are usually specific for only
one type of bacterium or metabolic pathway, the chances of a complete failure
comparable to those found in the cheese industry is remote due to the diverse community
of species normally co-existing in the filter at any one time.
Some things that were expected by Dr. O’Dowd that apparently did not happen included
not finding a proliferation of pathogens in the biofilter. Although two molds and 2
gelatinous saprophytes were found, molds, mildews and fungi were not present in large
quantities. It was also expected that there would be a cyclical shedding of bacteria as
colony forming units (CFUs) are sent downstream and a consequential decrease in
removal efficiency. Although CFUs’ may be migrating, again, due to the community of
bacteria present in the filter at anyone time, there was no apparent difference in shedding
from one day to the next as reflected in the iron removal efficiencies.
Barrie Ferazur Pilot Post Sterilization
0.8
0.7
[ Iron ] mg/l
0.6
0.5
0.4
0.3
0.2
0.1
Date
Fe raw
Figure9
Fe totalRw
Fe fini
Fe tot fin
Barrie Ferazur Pilot after Sterilization Showing Oxygen Effects
As can be seen in Figures 9, 10 and 11 the effluent levels of Fe2+ and total iron shot up
following an extended period of over oxidation. The ferrous iron was being oxidized in a
physical chemical reaction and the faculative bacteria were starved of food. It took 4
Nov 18 - 0630
Nov 16 - 1700
Nov 15 - 0445
Nov 13 - 1345
Nov 12 - 0530
Nov 10 - 1330
Nov 9 -0445
Nov 7 - 1700
Nov 4 - 1400
Nov 6 - 0445
Nov 1 - 1700
Nov 3 -0445
Oct 31 - 0445
Oct 29 -1500
Oct 28 - 0500
Oct 26 -1700
Oct 25 -0430
Oct 22 - 0530
Oct 23 - 1620
Oct 20 -1645
Oct 19 -0445
Oct 16 -0520
Oct 17 -1700
Oct 14 -1415
Oct 13 - 0415
Oct 11 -1700
Oct 10 -1710
Oct 9 -0530
Oct 7 -1600
Oct 6 -0450
0
Date
Nov 22 - 1700
Nov 20 - 1715
Nov 18 - 1445
Nov 16 - 1700
Nov 14 - 1700
Nov 12 -1300
Nov 10 - 1330
Nov 8 - 1700
Nov 6 - 1700
Nov 4 - 1400
Nov 2 -1700
Oct 31 - 1700
Oct 29 -1500
Oct 27 -1845
Oct 25 -1700
Oct 23 - 1620
Oct 21 -1440
Oct 19 -1700
Oct 17 -1700
Oct 15 -1450
Oct 13 -1645
Oct 11 -1700
Oct 10 -0445
Oct 8 - 0545
Oct 6 -0450
[ Oxygen ] mg/l
days for the biofilter to revive. A full explanation hopefully will be provided in the
report as to what exactly was being tested over the last couple of weeks of the study.
Oxygen Applied
8
7
6
5
4
3
2
1
0
Barrie Ferazur Post Sterilization
Concentration mg/l
10
1
Oct 6
-0450
Oct 8
0545
Oct
10 0445
Oct
11 1700
Oct
13 1645
Oct
15 1450
Oct
17 1700
Oct
19 1700
Oct
21 1440
Oct
23 1620
Oct
25 1700
Oct
27 1845
Oct
29 1500
Oct
31 1700
Nov
21700
Nov
41400
Nov
6 1700
Nov
81700
Nov
10 1330
Nov
12 1300
Nov
14 1700
Nov
16 1700
0.1
0.01
Date
oxy finish
Figure 10
Fe raw
Fe fini
Barrie Ferazur Raw and Final Oxygen Levels
As can be seen there is a close relationship between applied oxygen and filter
performance. The pilot plant has a primitive rotameter that made control of the air supply
very rough. In addition there was a period several weeks when the stainless float in the
rotameter was lost.
DISCUSSION
Although it may not be apparent from the information provided in this paper, the author
believes the following recommendations are justified.
1.
Biofilters should not be seeded with media from another aquifer.
2.
Ensure that the aquifer can not be contaminated with backflow from any filter.
3.
Ensure that the biofilter can be isolated and sterilized in case of a phage attack.
4.
Consider having a certified, FDA or Health Canada approved culture of bacteria
to seed the filter initially and also as backup in the unlikely event of system failure
due to a phage attack.
5.
Ensure that the biofilter operator has a background in biological treatment and
understands that the effects from any process modifications are delayed .
6.
Look for applications for iron removal with high pH values, i.e. above 8 where the
chemical costs for conventional treatment begins increase significantly.
7.
Consider using a biofilter as a pretreatment for manganese- greensand filters in
retrofit applications where an increase in capacity is required.
8.
Consider biofiltration for manganese removal due to its operating costs
advantages over conventional treatment.
ACKNOWLEDGEMENTS
Nov
18 1445
The author would like to thank the City of Barrie and the Ontario Ministry of the
Environment for funding the Barrie pilot study. I would also like to acknowledge the
support provided by Dr. Dennis O’Dowd of BOD Consulting in providing the basic data,
much background information on the microbiology of groundwater, and many of the
insights gained from the pilot at Barrie.
BIBLIOGRAPHY
Bergel, J.Y. & Mouchet, P. Unpublished Paper. “Biological Filtration for Iron and
Manganese Removal: Some Case Studies”.
Bergel, J.Y. & Trudel, J.P. Unpublished Paper. “Operating Results of Canada’s First
Biological Manganese Removal System”.
Krimbein, W.E. (editor). 1983. “Microbial Geochemistry”, ISBN 0-632-00683-8..
Ministry of Environment and Energy. 1994. “Ontario Drinking Water Objectives”.
Government of Ontario Report.
Mouchet, Pierre. 1992. “From Conventional to Biological Removal of Iron and
Manganese in France”. Journal of American Water Works Association. Vol. 84, No. 4,
April 1992.
O’Dowd, D. Unpublished Paper. “Iron (Fe) and Manganese (Mn) Removal Trials at
Barrie Ontario”.
O’Dowd, D. Unpublished Paper. “Project 2000. The Barrie Iron and Manganese
Removal Trials”.