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DESIGN OF A BIOLOGICALLY-MEDIATED MANGANESE
REMOVAL SYSTEM WITH ULTRAFILTRATION MEMBRANES
by
CARLOS ANDRES CORREA
A thesis submitted to the
Graduate School-New Brunswick
Rutgers, The State University of New Jersey
in partial fulfillment of the requirements
for the degree of
Master of Science
Graduate Program in Civil and Environmental Engineering
written under the direction of
Dr. Qizhong Guo
and approved by
____________________________
____________________________
____________________________
New Brunswick, New Jersey
October 2011
ii
ABSTRACT OF THE THESIS
DESIGN OF A BIOLOGICALLY-CATALYZED MANGANESE
REMOVAL SYSTEM WITH ULTRAFILTRATION MEMBRANES
by CARLOS ANDRES CORREA
Thesis Directors:
Steve Medlar P.E.
Dr. Qizhong Guo
The purpose of this thesis is to propose an innovative system to integrate biologically-
catalyzed oxidation of manganese with ultrafiltration membranes for drinking water
treatment. The published literature dealing specifically with biological processes in
membrane filtration systems is very limited. The literature review is divided into two
related subthemes. The first part of the literature review concentrates on recent
advances in biologically-mediated oxidation of manganese, while the second addresses
the necessary conditions to operate a membrane filtration system including how
biofouling can affect performance.
Manganese in drinking water causes taste and odor problems as well as other nuisance
problems such as discoloration of laundry and staining of fixtures. Manganese can also
cause severe corrosion problems. Biological manganese oxidation is currently being
explored and evaluated by different researchers and institutions such as the American
Water Works Association (AWWA) and the Environmental Protection Agency (EPA).
iii
Chlorine oxidation of manganese has become increasingly problematic due to the EPA
rule on disinfectant byproducts (DBP), making it necessary to find alternative processes.
Biologically-catalyzed oxidation of manganese is still not fully understood and a
standardized process that can be deployed to treat waters with high concentrations of
manganese has yet to be developed. It is thus necessary to build a pilot system that can
later be scaled up for field application.
Based on findings from studies by other researchers, a full-scale system was designed
based on a 2 million gallon per day (MGD) flow rate in order to understand the footprint
such a system would have compared to a traditional water treatment plant. A pilot-scale
system was designed based on the full-scale system in order to provide a basis for
possible further research and laboratory testing of the system. The pilot-scale design
shows that it is possible to build a biologically-catalyzed manganese removal treatment
system integrated with ultrafiltration membranes with a relatively small footprint.
However, the design presented here is based on many presumptions that remain to be
confirmed once the pilot-scale system is built. With the data from the pilot-scale systems,
adjustments can be made to the system for eventual field implementation.
iv
Acknowledgements
This thesis would not have been possible without the support and encouragement of
many people who generously contributed their time and knowledge.
First, I wish to extend the most sincere gratitude to my thesis directors Mr. Steve Medlar
P.E. and Dr. Qizhong Guo. Their honest insight and extensive knowledge were
invaluable during the course of this thesis. Also, to Sandy Kutzing who generously
offered her time and insight as a member of the thesis panel.
To the professors and instructors from the Department of Civil and Environmental
Engineering and from the Department of Environmental Sciences for sharing their
knowledge and for encouraging my intellectual growth.
To the staff of the Department of Civil and Environmental Engineering who were always
willing to help and answer my questions.
Finally, my utmost gratitude goes to my wife Karen and my family, who with their love
and caring have supported me throughout this process.
v
Table of Contents
Acknowledgements.................................................................................................................... iv
Table of Contents ........................................................................................................................ v
List of Tables .............................................................................................................................. vi
List of Illustrations...................................................................................................................... vi
1 Introduction ........................................................................................................................ 1
2 Summary Background on Manganese.................................................................................. 4
3 Summary Background on Membrane Filtration ................................................................... 8
4 State of the art in biological removal of manganese in membrane filtration systems ......... 12
4.1 Biologically-mediated oxidation of manganese .......................................................... 12
4.2 Operating conditions for membrane filtration systems and biofouling. ...................... 20
5 Problem Statement ........................................................................................................... 25
6 Designing a biologically-mediated manganese removal system ......................................... 26
6.1 Selection of design parameters and equipment ......................................................... 26
6.2 Bioreactor.................................................................................................................. 27
6.3 Intermediate filtration stage ...................................................................................... 33
6.4 Ultrafiltration (membrane filtration) stage ................................................................. 36
7 Designing a pilot scale test system .................................................................................... 39
7.1 Pilot-scale Bioreactor ................................................................................................. 39
7.2 Pilot-scale secondary filtration ................................................................................... 41
7.3 Pilot-scale membrane filtration.................................................................................. 43
7.4 Minor equipment and pump sizing ............................................................................ 44
7.5 Sampling .................................................................................................................... 47
7.5.1 Parameters ........................................................................................................ 47
7.5.2 Sampling interval and methods .......................................................................... 48
8 Discussion ......................................................................................................................... 49
9 Conclusions ....................................................................................................................... 53
10 Further Research ........................................................................................................... 55
11 Bibliography .................................................................................................................. 56
APPENDIX I – Characteristics of bioreactors in reviewed literature ............................................ 59
APPENDIX II – Scaled drawings of pilot scale system .................................................................. 62
vi
List of Tables
Table 1 – Flow rate and type of microorganisms used by some bioreactors in other studies. ..... 19
Table 2 – Summary of bioreactor specifications ......................................................................... 31
Table 3 – Summary of intermediate filtration stage specifications .............................................. 35
Table 4 – Summary of membrane filtration stage specifications ................................................. 38
Table 5 – Summary of pilot-scale bioreactor specifications ........................................................ 41
Table 6 – Summary of pilot-scale intermediate filtration stage specifications .............................. 43
Table 7 – Summary of pilot-scale membrane filtration stage ...................................................... 44
Table 8 – Estimated initial head loss of pilot-scale system ......................................................... 46
Table 9 – Parameters to be measured....................................................................................... 47
Table 10 – Characteristics of some bioreactors in the literature ................................................. 60
List of Illustrations
Figure 1– Manganese oxide covered rock(Photo: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0) ... 6
Figure 2– Hollow fiber membrane module (Photo: Alexdruz, CC- BY) .......................................... 9
Figure 3– Ultrafiltration modules in Waldassen, Germany (Photo: Benreis, CC-BILD BY) .......... 11
Figure 4– Bacteria of the genre Siderocapsa ............................................................................. 14
Figure 5– Plot for equation used for estimating minimum filter depth .......................................... 19
Figure 6– Sketch of proposed full-scale bioreactor .................................................................... 32
Figure 7– Diagram of filtration vessel (based on Cuno Betapure vessel dimensions) ................. 36
Figure 8– Dead-end direct filtration mode of membrane modules .............................................. 37
Figure 9– Side view of pilot-scale system .................................................................................. 45
Figure 10 – Scale side view of pilot-scale system ...................................................................... 63
Figure 11 – Scale plan view of pilot-scale system ...................................................................... 64
1
1 Introduction
Manganese is not considered harmful to human health except at very high
concentrations (US EPA, 2004). However, manganese can cause nuisance problems in
drinking water such as discoloration, staining, rust, taste, and odor. In traditional water
treatment plants, high concentrations of manganese in water have been addressed
mainly through chemical oxidation using chlorine and manganese oxide coated media to
catalyze the precipitation of manganese. Manganese oxide coated media normally also
requires a constant feed of oxidants to maintain its properties.
The second section of this thesis briefly summarizes the problems associated with high
concentrations of manganese and some of the treatment techniques commonly
employed. The third section briefly summarizes what membrane filtration is and the
associated terminology. The fourth section summarizes the current knowledge on
biologically-catalyzed removal of manganese and on optimal operating conditions for
membrane filtration systems. Sections 6 and 7 present the design process of a full-scale
and pilot-scale plant respectively.
In recent years, membrane filtration has emerged as a leading technology for water
treatment because membranes can effectively remove pathogens from water.
Disinfection kills pathogens but leaves them in the water. With the advent of membrane
filtration, a new series of challenges has evolved for treating certain contaminants. For
example, some types of membranes do not tolerate the high or low pH required by
certain processes. Membranes can degrade in the presence of chemicals that have
been extensively used in the water treatment industry (Viessman et al., 2008). In the
2
case of manganese, chemical oxidation requires a high pH. The precipitation of oxidized
manganese particulates can rapidly clog a membrane filtration system. In applications
with limited space, it might not be possible to fit a full chemical oxidation system and the
equipment required to adjust the pH before the membranes. Biologically-catalyzed
manganese removal is known to be effective even at neutral pH but usually requires a
large footprint as can be concluded from the slow flow rates observed in other pilot plant
studies (See Table 1 in section 6).
However one study showed that it is possible to have flow rates above 1 foot per minute
(ft/min) through bioreactors seeded with manganese-catalyzing bacteria (Stembal et al.,
2005). This thesis proposes that with properly sized media of almost uniform size and
high porosity, a biologically-mediated system with a small footprint is possible. The
proposed system is composed of a bioreactor, an intermediate filtration stage, and a
membrane filtration stage. The bioreactor is based on a modified version of the one used
by Stembal et al. (2005) but using media with different characteristics. The constants
used to size the reactor proposed by this thesis can be adjusted once the pilot-scale is
built. However, it was designed with enough tolerance that if the actual velocity or
pressure drop is higher than anticipated, the system will most likely be capable of
handling it.
Section 8 discusses design alternatives that were considered for the proposed system
and the reasons for using the type of bioreactor used in the final design. The alternatives
not used in the final design included ultrasonic disinfection and dual core membranes.
The design chosen is based on proven and tried methods that have been successfully
used for different purposes under laboratory or field conditions. A purely theoretical
3
approach to completely novel technologies would have had too many unknowns, while
the proposed system is likely to work under actual field conditions.
The proposed system has not been tested under laboratory conditions. The system
should be sufficiently robust to warrant laboratory testing at a later date. This system
could have potential full-scale applications for membrane filtration systems that require
the removal of manganese while maintaining a small footprint relative to traditional water
treatment plants. Traditional water treatment plants can occupy an area up to 8 times
that of a membrane filtration plant (Medlar, 2009). The proposed design would take
approximately one fifth of the space required by a conventional treatment plant using
flocculation and settling. The design proposed in this thesis also offers the advantage of
not relying on chemical processes to remove manganese.
4
2 Summary Background on Manganese
Manganese (Mn) is a commonly found element in water and soils. Manganese plays an
important role in the biogeochemical cycling of carbon and of metals such as lead and
iron (Spiro et al., 2010). Reduction of insoluble Mn(IV) is a naturally occurring process
and is also a well-known mechanism for the oxidation of some organic contaminants in
water. This process occurs in most anaerobic sedimentary environments and is the
major cause for the release of soluble Mn(II) found in many aquifers and surface waters
(Viessman et al., 2008). Normal concentrations of manganese in groundwater ranges
from 0.1 to 1 milligram per liter (mg/L), but it can reach levels of several units in some
settings (Katsoyiannis and Zouboulis, 2004). Due to anoxic conditions common to
aquifers and to the hypolimnion of reservoirs and lakes, soluble manganese is
particularly prevalent in groundwater and in the bottom of reservoirs and lakes
(Viessman et al., 2008).
Manganese can be found in many oxidation states (+2, +3, +4, +5, +6, +7). In nature
manganese is most commonly found in the +2, +4 and +7 oxidation states (Kohl and
Medlar, 2006). In the +2 state, which is commonly expressed as Mn(II), it is highly
soluble in water and must be removed from drinking water down to the treatment
standard of 0.05 mg/L (e-CFR, 1979). Mn(II), however, is unstable and tends to oxidize
and precipitate or dissociate to either Mn (III) or Mn (IV) (Tekerlekopoulou et al., 2008).
In fact, the oxidation of manganese occurs naturally in the environment but at a very
slow rate. A recent study estimated that at neutral pH without catalysts or photochemical
enhancements, it could take up to 500,000 years for the oxidation of Mn(II) to occur
naturally (Spiro et al., 2010). Another recent study concluded that very little oxidation of
Mn(II) can be observed below pH 8 and that in many occasions it proceeds even more
5
slowly in the presence of iron (Hallberg and Johnson, 2005). Given these conditions, the
removal of manganese from waters with concentrations over the secondary treatment
standard of 0.05 mg/L needs to be addressed by promoting more favorable conditions
either through chemical or biological means.
High concentrations of manganese have been observed in surface waters both from
anthropogenic and from naturally occurring sources. A common source of high
manganese concentrations in surface waters is mine drainage from coal mining and ore
extraction. High concentrations of soluble manganese can increase the acidity of mine
drainage waters (Hallberg and Johnson, 2005). Concentrations of soluble Mn in mine
drainage polluted waters has been found to be as high as 90 mg/L (Edwards et al.,
2009) with the added problem that in many cases these waters are acidic in nature
(Hallberg and Johnson, 2005) and Mn oxidation occurs preferentially under alkaline
conditions.
Manganese is not considered a toxic contaminant when ingested at concentrations
below 500 µg/l. However, at levels above 100 µg/l, manganese produces several
nuisance effects such as staining of laundry and fixtures (Tekerlekopoulou et al., 2008)
as well as raising odor, color and taste considerations (Qin et al., 2009). While
manganese is not considered to be toxic at low concentrations, certain studies have
shown a high correlation between high levels of manganese and the toxicity levels of
lake sediment pore water (Hallberg and Johnson, 2005). Apart from the organoleptic and
nuisance considerations, the control of dissolved manganese in drinking water is
important because manganese can oxidize in the presence of oxygen and clog wells and
pipes (e-CFR, 1979) due to the precipitation of manganese oxides and the formation of
catalyzing-bacteria biofilms.
6
The United States Environmental Protection Agency (US EPA) has set legally
enforceable primary maximum contaminant levels in drinking water for contaminants that
pose serious risk when ingested above certain concentrations. US EPA has also set
non-enforceable National Secondary Drinking Water Regulations to regulate
contaminants, such as manganese, that do not pose serious health risks in drinking
water but cause nuisance problems. The secondary standard for manganese has been
set at 0.05 mg/L (US EPA Office of Ground Water and Drinking Water, 2006). According
to Kohl and Medlar (2006), the standard was originally established subjectively. Recent
studies have found that manganese can cause nuisance problems at lower levels than
the current secondary treatment standard and have thus recommended lowering the
allowable concentration of manganese below 0.02 mg/l (Kohl and Medlar, 2006).
It is necessary to remove manganese from drinking water with high concentrations due
to the associated nuisance and health problems. In traditional water treatment plants
that use settling and sand filters, the removal of manganese can be accomplished
through chemical oxidation or through the use of manganese oxide coated media (Islam
et al., 2010). Figure 1 shows a manganese oxide coated rock with characteristic dark
black coloring.
Figure 1– Manganese oxide covered rock (Photo: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0)
7
Oxidation of Mn(II) to the insoluble form Mn(IV) allows for the precipitation of manganese
oxides. Some of the common processes used for the removal of manganese from
drinking water include chemical sequestration, chemical oxidation/filtration, chemical
oxidation/clarification/filtration, ion exchange, lime/soda ash softening, biological
treatment, and ballasted flocculation (Polito, 2011). Chemical oxidation followed by
physical filtration has been used extensively and remains one of the most common
approaches to manganese removal (Kohl and Medlar, 2006). Several oxidizing agents
can be used for the chemical oxidation of manganese including oxygen, ozone,
potassium permanganate, chlorine dioxide, and hypochlorous acid. Chemical oxidation
of manganese requires a high pH (usually above 9.5) and good aeration (Johnson and
Younger, 2005; Viessman et al., 2008). This high pH is not a problem for sand filters and
the pH can be lowered once the manganese has precipitated. The use of chemical
oxidation with chlorine has decreased in recent years because it can cause harmful
secondary byproducts to be formed (US EPA, 2010).
8
3 Summary Background on Membrane Filtration
Membrane filtration is a water treatment method consisting of a synthetic fabric
(membrane) that provides a physical barrier to retain particles exceeding a certain size
or molecular weight. Membranes used in drinking water applications can be either
submersible or encased (AWWA Subcommittee on Periodical Publications of the
Membrane Process Committee, 2008).
Submersible membranes are submerged in tanks containing water to be treated and
filter the contaminants by forcing water to the inside of the membrane, leaving the
contaminants to concentrate in the tank. Submersible membranes are normally operated
under atmospheric pressure and water is forced to pass through the membrane using a
vacuum. This kind of membrane is usually cleaned using air jet pulses in reverse flow
mode. Submersible membranes are more common in retrofits than in new applications
(AWWA Subcommittee on Periodical Publications of the Membrane Process Committee,
2008).
Encased membranes work under pressure and consist of a protective outer encasement
with the membrane itself inside. There are two main configurations found in encased
membranes: hollow fiber and spiral wound (also called flat sheet) (Paul, 2002). Spiral
wound membranes consist of several layers of flat sheets of material rolled around a
central core. Hollow fiber membranes on the other hand consist of thin hollow strands of
material bundled together. Hollow fiber membranes are encased inside a protective
cover. Figure 2 shows a typical hollow fiber membrane module.
9
Figure 2– Hollow fiber membrane module (Photo: Alexdruz, CC- BY)
Encased membranes can be operated either in crossflow or direct filtration mode. The
difference between these two modes of operation is that in crossflow operation, part of
the concentrate is recirculated, while in direct filtration mode, there is no recirculation
(AWWA Subcommittee on Periodical Publications of the Membrane Process Committee,
2008). Encased hollow fiber membranes will be used for practical purposes in this thesis
because they offer certain advantages over submerged and spiral wound membranes
like higher flow rates and better chemical resistance.
In recent years, membrane filtration plants have become more and more common
because they offer certain advantages over other disinfection methods. An advantage of
membrane filtration plants is that they usually have a smaller footprint than traditional
water treatment plants. Membranes can potentially remove bacteria rather than
inactivating them with a disinfectant like most traditional systems do (Viessman et al.,
2008). Finally, since less disinfectant products, such as chlorine, need to be used in
membrane filtration plants, the potential for disinfectant byproducts is reduced. Excess
10
chlorine in water can react with other elements present in the water to form disinfectant
byproducts that are detrimental to human health. Trihalomethanes, haloacetic acids, and
chlorite are among the disinfection byproducts that the EPA has identified as deriving
from chlorine residuals in drinking water (US EPA, 2010).
The removal of manganese can be problematic in water treatment plants that use
membranes. Membranes generally do not tolerate the high pH required for chemical
oxidation of manganese and they can become clogged rapidly with the precipitated
manganese or with microorganisms contained in the water or that migrate from other
points in the treatment system (biofouling). In conventional water treatment systems,
biological oxidation of manganese can occur naturally in sand filters due to the formation
of biofilms of manganese-oxidizing bacteria (Tekerlekopoulou et al., 2008). When
membrane filtration is added to such a system, membranes can quickly be clogged due
to biofouling. One of the goals of this thesis is to propose a system where biological
oxidation of manganese can be used prior to a membrane filtration stage without
causing biofouling of the membranes.
Recent studies have shown that biologically-mediated oxidation of Mn(II) can occur at
much lower pH than purely chemical oxidation. Bacterial oxidation of Mn(II) to Mn (IV)
has been shown to occur at a pH as low as 6.5 and 7.2 (Burger et al., 2008;
Katsoyiannis and Zouboulis, 2004). Manganese is often found together with iron in
groundwater (El Araby et al., 2009) and many of the same bacteria are capable of
catalyzing the oxidation of both elements (Katsoyiannis and Zouboulis, 2004).
11
Figure 3– Ultrafiltration modules in Waldassen, Germany (Photo: Benreis, CC-BILD BY)
Bio-fouling can affect the performance of membranes and cause their premature
replacement, adding a financial burden to the operation. Biological oxidation generally
requires a prolonged contact time that is not compatible with the flow rate and pressure
necessary for membrane filtration, and biological treatment systems can have a large
footprint that might not be available or practical where membrane filtration systems have
been implemented.
The objective of this research is to explore how biological oxidation of manganese can
be applied to membrane filtration plants while avoiding the problems that are known to
happen while maintaining a small footprint.
12
4 State of the art in biological removal of manganese in
membrane filtration systems
The literature on removal of manganese from drinking water through biologically-
mediated oxidation is limited and scarce. Most of the existing literature on manganese
removal focuses on chemical oxidation processes like the ones previously mentioned.
Some biological oxidation processes used in wastewater treatment applications are
described in a few journal articles. Presently only one reference was available that
addresses specifically membrane filtration coupled with biologically mediated oxidation
of manganese, but it describes an application with submerged membranes and granular
activated carbon (Suzuki et al., 1998).
Since the availability of references for the topic of biological oxidation of manganese in
drinking water applications is so limited, the literature review revolves around two related
topics: biologically-mediated oxidation of manganese, and membrane filtration systems
and biofouling.
4.1 Biologically-mediated oxidation of manganese
Biologically-mediated oxidation of manganese refers to a process in which
microorganisms are used to help catalyze the oxidation of manganese from a soluble to
an insoluble state (usually from Mn(II) to Mn(IV)). Biologically-mediated oxidation of
manganese has gained popularity in the United States in the last few years, but there
are still many parts of the process that remain poorly understood (Spiro et al., 2010). For
example, the physiological mechanism of bacterial oxidation of Mn(II) is still being
researched, and many of the variables involved (such as the impact of UV light and the
types of viable reactive oxygen, among others) remain to be fully comprehended (Spiro
13
et al., 2010). Additionally, biofilms in drinking water systems are known to contain a wide
diversity of microorganisms and many of them have not been cultured so very little
information on their genetic identity is available (Zhu et al., 2010). The interactions
between different types of microorganisms that might enhance or harm the oxidation
process of manganese are unknown. However, while chemical processes using strong
oxidants such as potassium permanganate or chlorine dioxide can leave residuals or
produce harmful secondary byproducts (Katsoyiannis and Zouboulis, 2004), biologically-
mediated reactions have not been reported to produce known harmful byproducts or
residuals.
Most of the solid phases formed by biologically-oxidized manganese appear to be in the
+4 state, although other oxides such as manganite (MnO[OH]), where manganese is in
the +3 state, have also been observed (Spiro et al., 2010). Once manganese is in a solid
phase, it can be precipitated or filtered and removed from the water. Microorganisms can
contribute to the oxidation process of manganese either by precipitating the manganese
directly or by accumulating manganese oxides on their surface (Spiro et al., 2010) or on
the surface of the biologically active media (Tekerlekopoulou et al., 2008), which in turn
helps the manganese oxidize and precipitate.
According to several studies consulted, there are species of bacteria, algae, and fungi
that are capable of catalyzing the oxidation of Mn(II) to Mn (III) or Mn(IV) and they are
found in nature in many forms (Robbins and Corley, 2005; Spiro et al., 2010). Some of
the microorganisms known to be present in biological treatment systems for manganese
removal are Bacillus sp. Strain SG-1, Pseudomonas putida, Leptothrix discophora,
Pedomicrobium sp, Crenotrix, Siderocapsa, Hyphomicrobium, and Metallogenium
among others (Katsoyiannis and Zouboulis, 2004; Pacini et al., 2005; Spiro et al., 2010;
14
Tekerlekopoulou et al., 2008). The most widely studied manganese oxidizing bacteria
appears to be Leptothrix discophora, which has been demonstrated to be effective for
catalyzing the oxidation process. However, it is not conclusive that this is the most
effective type of microorganism for manganese oxidation, or that, in a biofilm that
contains this species it will be the sole organism responsible for the oxidation process.
For example, in a comparative study conducted in Canada, a filter with an indigenous
biofilm without any presence of L. discophora appeared to perform better than a filter
seeded with L. discophora exclusively (Burger et al., 2008). Further, in field studies it has
been observed that different species can be active in manganese precipitation during
different seasons, and that the microorganisms can even vary from one year to the next
(Robbins and Corley, 2005). It should be noted that in one particular study it was
mentioned that Pedomicrobium manganicum and Metallogenium sp. were particularly
prevalent in high water velocity conditions where Mn deposition was observed (Kohl and
Medlar, 2006).
Figure 4– Bacteria of the genre Siderocapsa
(Photo: David J. Patterson, CC- BY NC)
15
There are several documented methods of biologically-mediated water treatment
systems for the removal of Manganese (Aziz and Smith, 1996; Burger et al., 2008;
Edwards et al., 2009; Gantzer et al., 2009; Ginter and Grobicki, 1997; Hallberg and
Johnson, 2005; Hope and Bott, 2004; Johnson and Younger, 2005; Katsoyiannis and
Zouboulis, 2004; Pacini et al., 2005; Qin et al., 2009; Stembal et al., 2005; Suzuki et al.,
1998; Tekerlekopoulou et al., 2008; Tekerlekopoulou and Vayenas, 2008; Thornton,
1995; Yang et al., 2009; Yoo et al., 2004; Zhu et al., 2010). One method used in mine
drainage waters with very high content of manganese uses a passive treatment method
involving algal ponds and several other passive treatment steps (Hallberg and Johnson,
2005). However, this system is extremely complex and uses a very large land area due
to the high concentration of manganese in acid mine drainage. Given the complexity of
the system and the extremely high manganese content present in acid mine drainage,
the system is not applicable to the treatment of drinking water. The method offers useful
insight on the need to provide a reliable source of carbon for microorganisms to thrive as
well as a suitable media for attachment. In most cases, it has been documented that
enough dissolved oxygen needs to be present for manganese to be successfully
oxidized by biologically-mediated processes (Johnson and Younger, 2005; Pacini et al.,
2005; Tekerlekopoulou et al., 2008). A more suitable method for the removal of
manganese in drinking water applications seems to be the use of bioreactors.
Bioreactors consist of a containment device filled with a type of media that provides
good conditions for biological growth to occur. The media can either be seeded with
microorganisms or allowed to grow a biofilm of naturally occurring microorganisms in the
feed water. As water flows through the media, the biofilm develops. The
microorganisms, in turn, help catalyze the oxidation of manganese and its subsequent
precipitation and deposition on the media. Manganese oxides deposited on the media
16
help further catalyze the oxidation of manganese (Tekerlekopoulou et al., 2008). Several
types of media have been used in biological reactors for manganese removal. These
include sand (Hope and Bott, 2004; Qin et al., 2009; Stembal et al., 2005), polyethylene
beads (Katsoyiannis and Zouboulis, 2004), limestone (Johnson and Younger, 2005;
Thornton, 1995), and gravel (Pacini et al., 2005; Tekerlekopoulou et al., 2008). In all
cases, the bioreactor needs to “mature” and acclimate before reaching its full
manganese-removal potential. Maturation involves passing water with a sufficient
amount of dissolved oxygen through the media and letting the microorganisms develop
on the surface. The microorganisms can either be seeded in the bioreactor from an
external source known to contain manganese-oxidizing organisms, or by allowing the
naturally occurring organisms in the source water to grow. Depending on the method
used and on the conditions of the bioreactor (e.g. availability of dissolved oxygen), the
maturation time can take from a few weeks to several months (Tekerlekopoulou et al.,
2008). The amount of dissolved oxygen available in the bioreactor is often enhanced by
injecting air through mechanical devices. Some studies suggest that the aeration
process itself rather than the added oxygen can aid the oxidation process because the
bubbles created assist the mass transfer of oxygen to the surfaces where reactions
occur (Johnson and Younger, 2005).
The rate at which water can be treated, pH range, dissolved oxygen concentration, water
temperature, effective manganese removal capacity, maturation time, and size and
configuration of the bioreactor varies greatly from one study to another. In a field study
conducted on natural attenuation of acid mine drainage, for example, it was observed
that the amount of precipitation of manganese oxides changed according to the season
and other environmental conditions. Precipitation was more efficient in the summer
possibly due to warmer water temperatures and better oxygenation (Robbins and
17
Corley, 2005). Even with such a high degree of variability and uncertainty in the right
combination of parameters, a number of different configurations of pilot bioreactors have
reported success in reducing the concentration of manganese to drinking water
standards, which has been set at 0.05 mg/L both in the US (e-CFR, 1979) and in the
European Union (The Council of the European Union, 1998). One study in particular
suggests that bioreactors can remove manganese at a higher rate than chemical
processes (Pacini et al., 2005). Table 10 in Appendix I summarizes some of the main
characteristics of the bioreactors in the studies reviewed.
There are many possible configurations of bioreactors that can effectively remove
manganese from drinking water (Aziz and Smith, 1996; Burger et al., 2008; Edwards et
al., 2009; Ginter and Grobicki, 1997; Hallberg and Johnson, 2005; Hope and Bott, 2004;
Johnson and Younger, 2005; Pacini et al., 2005; Qin et al., 2009; Stembal et al., 2005;
Tekerlekopoulou et al., 2008; Tekerlekopoulou and Vayenas, 2008; Thornton, 1995;
Yang et al., 2009; Yoo et al., 2004; Zhu et al., 2010). While some conclusions can be
drawn from the studies, such as the need for a sufficient amount of dissolved oxygen
and the possibility of using water with near neutral pH, many other variables might be
beyond the control of the designer of a treatment system. For example, the initial
manganese concentration will depend on the source water. While one system can be
effective under certain water quality parameters at a set treatment rate, the same system
may not work for another set of conditions. Another variable that might be difficult to
control is the presence of native microorganisms in the water, which can compete with
seeded microorganisms in the bioreactor. The native microorganisms can alter the
chemical and biological balance of the system and affect its efficiency for manganese
removal. Also, other elements or chemicals present in the source water can affect the
18
bacterial population and rate of growth. This will possibly affect how the biofilm will
respond to manganese.
In some studies, it has been noted that the effective surface area of the media is critical
to the success of the biofilter (Tekerlekopoulou et al., 2008). A larger surface area
translates into more places for the microorganisms to attach. However, a larger effective
surface area also means smaller grain sizes in the media for a given filter volume. The
filter can clog more rapidly (Tekerlekopoulou et al., 2008). An important operational
consideration is to control the biofilm thickness in order to prevent filter clogging and the
associated head loss which consequently affects the treatment flow rate. Frequent
backwashing may be necessary to control this variable (Zhu et al., 2010). The
maturation time for bioreactors using different microorganisms is difficult to predict as
can be seen from the large variations presented in Table 10 (Appendix I). In general, the
maturation time involves passing aerated water through the filter column for a certain
amount of time until the formation of a biofilm is observed on the media (Hope and Bott,
2004).
An equation for the concentration profile for mass-transfer has been proposed by
researchers from the University of Zagreb for estimating the size of a bioreactor for
manganese removal (Stembal et al., 2005):
����� = exp− �� ��
Where, CA is the target concentration of manganese, CA0 is the initial concentration, u is
the flow velocity, L is the depth of the media, K is the treatability factor, and n is a factor
19
related to the media characteristics; these two last factors are obtained experimentally
(Stembal et al., 2005). This sizing formula can be a good starting point for a bioreactor
design, but specific site characteristics will ultimately play an important role. For
example, turbidity and the presence of other contaminants might affect the performance
of the bioreactor.
Figure 5– Plot for equation used for estimating minimum filter depth
with target concentration of 0.02 mg/L and flow velocity of 15 m/h (0.82 ft/min)
0
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Min
imu
m F
ilte
r D
ep
th (
m)
Initial Concentration (mg/L)
20
Table 1 – Flow rate and type of microorganisms used
by some pilot and bench-scale bioreactors in other studies.
Type of bioreactor Source of microorganisms Flow rate Flow rate
(gpm)
Trickling filter with silicic
gravel
Seeded with sample from
wastewater plant
500 to 2000 ml /
min 0.53 gpm
Up-flow filtration columns
with PE beads Leptothrix ochracea from sludge 7 m / h 0.11 gpm
Down-flow bioreactor
Coated stones taken from
stream – Phoma herbarum and
Pleosporales identified as main
catalysts
N/A N/A
Down-flow bioreactor. One
with manganese sand and
one with siliceous sand
Filter sand from old sand filter of
existing plant – Leptothrix
identified
3.9 L/h 0.017
gpm
Down flow sand filter Leptothrix discophora SP-6 N/A N/A
Pressure sand filters
Leptothrix discophora SP-6 and
indigenous biofilm from
microorganisms in the source
water.
1 mL/min 0.000264
gpm
Limestone-filled tanks Indigenous biofilm from existing
ponds 3.8 L/min 1 gpm
Dolomite substrate with a
bentonite and MnO2 basal
layer.
Indigenous biofilm – not
attempted to identify bacteria 5 mL/min
0.00132
gpm
Quartz sand 0.5 to 2 mm Siderocapsa from operating
plant 22 m/h 12 gpm
Gravel 10-15 mm Galionella – biofilm allowed to
develop spontaneously 12 m/h N/A
Hybrid MF membranes with
PAC and sludge
Sludge from wastewater
treatment plant – leptothrix
ochracea and siderocapsa
0.00625 m/h N/A
4.2 Operating conditions for membrane filtration systems and biofouling.
There are 4 types of membranes that can be used for drinking water applications:
microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO)
membranes. Nanofiltration and reverse osmosis membranes are typically used in
desalination or to treat brackish waters. Nanofiltration and reverse osmosis membranes
21
can remove Mn (II) but will likely foul with Mn (IV). Nanofiltration and reverse osmosis
membranes need high pressures to operate (200 to 500 psi typically) given their reduced
pore size and high osmotic pressure. Most common in the drinking water treatment of
surface and ground waters are microfiltration and ultrafiltration membranes, which are
often referred to as low pressure membranes (AWWA Membrane Technology Research
Committee, 2005). While microfiltration membranes typically have a pore size of 0.1
microns (µm), ultrafiltration membranes have a typical pore size of 0.01 µm (Paul, 2002).
Giardia and Cryptosporidium have typical sizes larger than 3 µm, so both types of
membranes will remove them. However, many viruses have smaller sizes than
protozoan organisms and can bypass microfiltration membranes; but they are typically
retained by ultrafiltration membranes (AWWA Subcommittee on Periodical Publications
of the Membrane Process Committee, 2008). The removal of microorganisms by
membranes is usually measured in logs. There are studies that have shown up to 7 logs
(99.99999%) removal of protozoans by ultrafiltration membranes (AWWA Subcommittee
on Periodical Publications of the Membrane Process Committee, 2008).
According to the available literature, membranes offer certain advantages over other
methods of pathogen removal, especially with respect to the regulations on disinfectant
byproducts, due to their capacity to remove pathogens without depending on chemical
treatment (AWWA Membrane Technology Research Committee, 2005). Disinfectant
byproducts are formed when residual disinfectants react with other chemicals in the
water to form different substances, some of which are detrimental to human health and
aquatic flora and fauna.
22
Several materials can be used for MF and UF membranes, the most common in drinking
water applications are polyvinylidene fluoride (PVDF), polyethersulfone (PES),
polysulfone (PS), and cellulose acetate (CA) (AWWA Subcommittee on Periodical
Publications of the Membrane Process Committee, 2008). Given the limited number of
membrane manufacturers, it is typical for each one to have a proprietary technology and
choose a suitable material. For example, Koch’s ultrafiltration membranes are spiral
wound membranes that use PES with a polyester backing material (Koch Membrane
Systems Inc., 2011). Toray, on the other hand, uses hollow fiber membranes
constructed of PVDF with a Polyvinyl Chloride (PVC) casing for their ultrafiltration
applications (Toray Industries Inc., 2011). CA membranes were common in the past but
have slowly been replaced by PVDF membranes due to their propensity to biological
attack and hydrolysis (AWWA Membrane Technology Research Committee, 2005).
However, PVDF membranes are not without their faults; they have low mechanical
resistance so they tend to be more fragile than membranes built from other materials
(AWWA Membrane Technology Research Committee, 2005).
The amount of water that can pass through a membrane is measured as flux, which is
the flow per unit area (AWWA Subcommittee on Periodical Publications of the
Membrane Process Committee, 2008). Some common units for flux are gallons per
square foot per day (GFD) or cubic meters per hour per square meter of membrane area
in the SI system. In some cases, flux can also include units of pressure since the flow
going through the membranes is proportional to the pressure of the system. The flux of a
system will impact the fouling rate, the durability of the membranes and the operating
costs among other variables (Freeman et al., 2006). Membrane systems can be
designed to work either at constant pressure or at constant flux using variable speed
23
drives for the pumps to compensate for the loss in flux caused be fouling (AWWA
Subcommittee on Periodical Publications of the Membrane Process Committee, 2008).
Fouling can be caused by suspended particles, organic matter or biological
contaminants (biofouling). Fouling can be either reversible or irreversible. Biofouling in
membranes can become irreversible due to the attachment of microorganisms and the
formation of biofilms (AWWA Subcommittee on Periodical Publications of the Membrane
Process Committee, 2008). While several methods such as surface modification have
been tested in an attempt to minimize membrane fouling, the additional hydraulic
resistance created by these surface modifications is a handicap to the practical
application of the modified membranes. Also, since fouling is normally associated to
several processes and materials (e.g. NOM, inorganic compounds, organic colloids), it is
very difficult to create a type of membrane that will resist fouling across a wide enough
spectrum of conditions (AWWA Membrane Technology Research Committee, 2005).
Backwashing in combination with chemical cleaning can be used to partially control
fouling (AWWA Subcommittee on Periodical Publications of the Membrane Process
Committee, 2008). However, part of the fouling will be irreversible and the membranes
will eventually need to be replaced. Biofouling needs to be controlled in order to keep
irreversible fouling under control. Usually the particles rejected by the membranes will
form a cake layer on the membrane surface and in many cases reduce the flux of water.
Air sparging is commonly used to encourage mass transfer of accumulated material
away from the surface, thus restoring part of the lost flux (AWWA Membrane Technology
Research Committee, 2005). However, the material that is not removed or becomes
permanently attached will create irreversible fouling. Also, certain microbial substances
tend to modify the adhesive strength of the membrane surfaces which can promote more
24
bacterial attachment, sometimes resulting in the formation of a biofilm (AWWA
Membrane Technology Research Committee, 2005).
From the specifications data sheet of ultrafiltration membranes from two manufacturers
(Koch Membrane Systems Inc., 2011; Toray Industries Inc., 2011), commercially
available ultrafiltration membranes used in drinking water processes typically operate
between 30 and 60 psi and up to a temperature of 50 °C. The maximum continuous free
chlorine to avoid deterioration is 2 mg/L. The presence of iron or other catalyzing metals
in the presence of chlorine can cause the membrane to degrade prematurely. In the
case of manganese removal that concerns this research, any chlorine would need to be
added after the water passes through the membranes. Design pH levels are between 1
and 10 and the maximum design turbidity in the feed water is 1 NTU, but it is
recommended not to exceed 0.2 NTU in order to avoid a high cleaning frequency. The
design flux of the membranes is between 10 and 22 GFD for the Koch membranes and
21 to 65 GFD for the Toray (where GFD = Gallons per square Foot of membrane area
per Day). The transmembrane pressure is typically kept between 7 and 30 psi (AWWA
Subcommittee on Periodical Publications of the Membrane Process Committee, 2008).
25
5 Problem Statement
In order to successfully implement a biologically-mediated manganese removal system
in membrane filtration applications, it is necessary to find a way to avoid fouling of the
membranes while keeping the system small and without the addition of high doses of
chemicals.
Membrane filtration offers an excellent alternative to conventional water treatment
models because it can reduce the amount of disinfectant byproducts, reduce the surface
area of a water treatment facility, and completely remove bacteria and viruses.
Biologically-mediated manganese removal can be an alternative to purely chemical
processes and can also avoid the addition of chemicals that can potentially lead to the
formation of harmful byproducts. Further, in membrane filtration systems, using
biologically-mediated removal of manganese could avoid fouling of the membranes
caused by flocculation and sedimentation processes associated with chemical treatment
systems. However, coupling biological treatment systems and membrane filtration poses
several challenges. On one hand, biofouling can cause the membranes to clog
prematurely and cause a shortened life span that can potentially drive up operating
costs. Biofouling of the membranes could be driven by migration of microorganisms from
the bioreactor stage or by other microorganisms that pass through the system. On the
other hand, most biological remediation systems require a long contact time and thus
low water velocities which translate into large system footprints, while membrane
filtration systems are known for having a small footprint and high water output when
compared to traditional systems. Given that one of the advantages of building a
membrane filtration plant can be the efficient use of space, having a large footprint
biological remediation system attached to it would be inconvenient.
26
6 Designing a biologically-mediated manganese removal system
6.1 Selection of design parameters and equipment
The calculations for the proposed system will be based on parameters for a full scale
water treatment plant and later scaled down to pilot scale size. The design was planned
this way to have an estimate of the footprint of a full scale system. Hydraulic scaling can
be problematic but having an initial full scale design will provide useful data so the pilot
scale system will replicate as closely as possible the conditions of a full scale system.
The design will assume a 2 million gallon per day (mgd) water treatment plant. The
membranes used will be Toray HFS-2020 Ultrafiltration membranes (specifications
available at http://www.toraywater.com/america/en/Home.aspx). These membranes are
some of the most common in water treatment plants and have excellent chemical
resistance and mechanical properties. The filtration rate will be calculated in the next
sections based on manufacturer recommendations and on the performance expected
from the system.
From the literature review, it was observed that Siderocapsa was the microorganism of
choice in the only study where bioreactors were successful in removing manganese with
high flow rates (Table 1). For this reason, it will be assumed that the bioreactor will be
seeded with this genre of bacteria. It might be necessary to isolate and culture this type
of microorganisms in order to conduct the experiment or to identify a nearby wastewater
treatment facility with sludge that contains it. In the study cited, the bacteria observed
came from sludge from a wastewater treatment plant used to seed the plant and the
specific strain was not identified (Stembal et al., 2005). The substrate used for the
bioreactor will be gravel with a nominal diameter of 4 mm. The original experiment by
27
Stembal et al. (2005) used quartz sand ranging from 0.5 to 2 mm; however, it is believed
that by having a larger pore size, the flow rate per unit area can be increased.
An intermediate filtration stage will be included between the bioreactor and the
membrane filtration stage. The filters used for this stage will be the Cuno Betapure NT-T
Series (specifications available at http://www.cuno.com/) with an absolute rating of 2
microns, which should minimize the bacteria migrating to the final membrane filtration
stage. These filters are constructed of polypropylene and have a high chemical
compatibility. Also, their price is much lower than that of the Toray membranes (more
than 50 times less for the same flow rate), so fouling and replacing of these elements will
be less expensive than having to replace fouled membranes. The filters will be paired
with a Cuno Express Series Filter Housing constructed in 316 L Stainless Steel
(specifications available at http://www.cuno.com/). The sizing of this unit will be
determined in subsequent sections.
The raw water manganese concentration used for this study will be around 1 mg/L,
which is a reasonable assumption of what could be encountered under field conditions
(Viessman et al., 2008). It will be assumed that the source water used will be either
surface or ground water with an average concentration close to 1 mg/L.
6.2 Bioreactor
As mentioned previously, the bioreactor will use 4 mm nominal diameter gravel as the
substrate. Other substrates such as anthracite and limestone could be used, but due to
the high velocities that the system will operate at, gravel should offer the mechanical
properties and roughness that shall allow the microorganisms to attach firmly. A previous
28
study showed that a similar setup can effectively remove Mn at a rate up to 1.2 ft/min (22
m/h) (Stembal et al., 2005). The gravel will have to be sorted carefully in order to
maintain the particle size as uniform as possible. This will allow having a high porosity
and thus keeping the bioreactor small. The initial calculations will be based on a rate of
0.8 ft/min but this velocity would be ramped up during laboratory testing in order to
determine the maximum velocity at which the system could still be effective for removing
manganese down to 0.02 mg/L.
A total flow of 2 mgd translates approximately to 185.67 ft3/min. So with a rate of 0.8
ft/min, the surface area of an empty pipe to convey the flow would be:
� = 185.67���/���0.8��/��� = 232.1��!
However, since the bioreactor contains gravel, the actual flow area consists of the
openings between the gravel particles. Given the large nominal size of the gravel being
used and the uniformity in size expected, it will be assumed that the total porosity of the
setup will be around 50%. With this porosity, the effective surface area of the bioreactor
would be:
�" = 232.1��!0.50 = 464.2��!
If a circular bioreactor is used, the radius of the bioreactor would be:
29
$ = %464.2��!& = 12.15��
Given that there is a large margin of tolerance for the velocity, and that a 24 foot
diameter could pose problems for the construction and water distribution through the
surface, an array of 4 bioreactors with a 12 foot diameter each will be proposed. With
this adjusted diameter, the velocity of water passing through the system will be 0.82
ft/min keeping the total flow at 2 mgd.
The minimum filter depth can be calculated by rearranging the concentration profile
equation (Stembal et al., 2005):
� = −'� � ( ln ' �����(
Since the values of K and n in the previous equation are determined experimentally,
there is no way of knowing what their value will be before running laboratory or pilot
scale testing. Using K=30.2 and n=0.74 as found by Stembal et al. (2005) in their study,
using u = 0.82 ft/min = 15 m/h, and setting a target concentration of 0.02 mg/L in order to
minimize problems, the equation becomes:
� = −'15+.,-30.2 ( ln 0.021 � = 0.96m = 3.15ft
This is the minimum depth required for the bioreactor to be able to remove the
manganese down to the target level. However, given that the constants used were not
30
specific to the media being used and that they will have to be adjusted when the pilot
scale system is built, a depth of 12 feet of gravel with a 4 mm average diameter will be
used for the design. This will also facilitate the construction of the bioreactors and insure
a good contact time between the water and the microorganisms.
The 4mm gravel layer will be supported on a 2 feet thick layer of gravel with an average
diameter of 6 mm. The head loss through each layer of the filter can be estimated using
the Kozeny equation (Viessman et al., 2008):
ℎ3 = 45(1 − 7)!9:!;7�<!
The grains used are going to be assumed to be semi-spherical with an S shape factor of
6.5, the J constant will be assumed to be 7 since the flow will not be in the laminar flow
region and it can be assumed to be closer to that observed in that of unidirectional fiber
arrays (Chen and Papathanasiou, 2006), the water temperature will be assumed to be
held around 15 °C, so the kinematic viscosity v will be assumed to be 1.139 X 10-6 m2/s,
the porosity was defined earlier to be 50%, the approach velocity V is 4.17 x 10-3 m/s.
For effects of this estimate, the two layers will be defined with average diameters of 4
and 6 mm respectively. With this numbers, the head loss through the clean bioreactors
is calculated as 0.23 feet. It is expected to backwash the bioreactor when the pressure
drop reaches between 10 and 12 feet, however, given the large diameter of the
substrate used and the low head loss expected in the system, backwashing will be
considered unnecessary for the bioreactor except as a measure to control biofilm
thickness.
31
Table 2 – Summary of bioreactor specifications
Effective surface area: 232.1 ft2
Porosity: 50%
Total surface area: 464.2 ft2
Minimum filter depth: 3.15 ft.
Bioreactors: 4
Diameter per bioreactor: 12 ft
Filtration rate: 0.82 ft/min
Filter depth (4 mm gravel) 12 ft.
Supporting layer (6 mm gravel) 2 ft.
Head loss through bioreactor: 0.23 ft.
Active microorganisms: Siderocapsa
A peristaltic pump will be connected near the top of the bioreactor in order to insure that
the Dissolve Oxygen (DO) of the water passing through the bioreactor is kept high to
keep aerobic conditions throughout the process.
32
Figure 6– Sketch of proposed full-scale bioreactor
33
6.3 Intermediate filtration stage
The intermediate filtration stage aims to minimize the amount of biofouling in the
ultrafiltration membranes. Its main objective is to retain microorganisms migrating from
the bioreactor. This stage is particularly important in this system given the high flow rate
of the bioreactor.
There is no available information on the rate at which microorganisms are expected to
migrate from the bioreactor to subsequent stages. However, it is known that most
bacteria are over 5 microns in size, so this stage will be planned with cartridge filters
rated at 2 microns. It is expected that these cartridges will retain most of the biological
residue that passes from the bioreactor in the effluent. Several manufacturers of
industrial equipment produce cartridges for use in the food, beverage, pharmaceutical,
and oil industries among others. Given that this system will be used to produce drinking
water, cartridges normally used for the production of bottled water and drinks will be
used. Most commercially available cartridge filters from different manufacturers have
similar characteristics. In fact, in many cases a filter cartridge manufacturer will produce
cartridge filters that can be used in the vessels of other manufacturers. For practical
purposes, it will be assumed that Cuno Betapure cartridges will be used for this design.
However, FSI and GAF, among others, produce equivalent cartridges and vessels that
could be used instead.
From the technical information available from the manufacturer (Cuno, 2011), the
specific pressure drop per 10” cartridge length for a 2 micron rating would be 0.87
psi/gpm/cps. To calculate the initial pressure drop for the system, the following formula is
provided by Cuno (2011):
34
�3=>�∆@@A� = (BC�>3ADA�=�;@�)(9�AECA��DE@A)(A@=E���E@$=AA�$=<$C@)(#C�=G��5>3=��A��;3=3=�;�ℎE>$�$�<;=A��ℎC�A��;)
By setting the clean differential pressure target to be between 5 and 10 psi and
rearranging this equation, it is possible to find the number of equivalent single length
cartridges in the housing:
HG��5>3=���>$�$�<;=A = (1389;@�)(1E@A)(0.87@A�/;@�/E@A)5@A� = 242
HG��5>3=���>$�$�<;=A = (1389;@�)(1E@A)(0.87@A�/;@�/E@A)10@A� = 121
The viscosity in cps is assumed to be 1, since this is the approximate value for water at
20 °C (68 °F) (Viessman et al., 2008).
Using a double open end cartridge configuration and the available information on
standard filter housings, two units with a capacity of 18 forty inch filters each one will be
chosen. These units have a diameter of 14 inches each one and can each handle the
flow coming from 5 bioreactors. Even though it would be viable to have only one unit
with 36 filters to handle all the flow, it is considered prudent to have two units in case
there are problems in the system that require one of the filtration units to be shut down. It
will also be helpful for routine maintenance so the system does not have to be shut down
completely. With these specifications, the new initial pressure drop can be calculated as:
35
�3=>�∆@@A� = (1389;@�)(1E@A)(0.87@A�/;@�/E@A)(144) = 8.4@A�
The head loss in feet through the intermediate filtration stage would thus be 19.4 ft. The
maximum head loss recommended by the manufacturer is 115 ft (50 psi) at 86 °F (Cuno,
2011). Pump calculations for the system will need to consider that the filters will be
changed when they reach a maximum head loss of around 60 feet. Manufacturers of
these type of filter normally do not recommend backwashing them in order to avoid
compromising the pore size and due to their low cost, so it will be assumed that they will
not be backwashed but changed when they get clogged. However, if pilot-scale testing
shows excessive clogging due to the characteristics of the source water or of a high rate
of biofouling, it might be necessary to evaluate how they perform with backwashing, and
also how many times they could be backwashed without damaging the media.
Table 3 – Summary of intermediate filtration stage specifications
Filtration Vessels: 2
Vessel diameter: 14 inches
Filters per vessel: 18
Filter length: 40 inches
Filter rating: 2 microns
Clean ∆ p 19.4 ft.
Maximum head loss: 60 ft.
36
Figure 7– Diagram of filtration vessel (based on Cuno Betapure vessel dimensions)
6.4 Ultrafiltration (membrane filtration) stage
There are several manufacturers of membranes suitable for treating water. However,
given that the characteristics of the membranes vary widely between manufacturers, it is
imperative to choose a specific type of membrane for purposes of designing the system.
The membranes chosen for this system are the Toray HFU series ultrafiltration
membranes with a rating of 150,000 Daltons. The module model used will be the HFU-
2020 with a surface area of 775 ft2 and a design flux of 2.6 to 8 m3/hr (92 to 282 ft3/hr).
They are 7 feet in length and are composed of PVDF hollow fiber membranes contained
37
in a PVC casing (Toray Industries Inc., 2011). These membranes will be used in dead-
end direct filtration configuration.
Figure 8– Dead-end direct filtration mode of membrane modules
The flux specified for the design needs to balance the high operating costs of using a
high flux with the high capital expense of using a low flux and thus more membranes.
For this design, since it is a small facility, a design flux of 140 ft3/hr (25,135 gpd) will be
chosen. Given that these membranes are used in a dead end configuration, the recovery
rate is expected to be close to 90%. However, a conservative estimate of 80% will be
used for the design. The actual total output of the system will thus be 1.6 mgd instead of
2 mgd. This could be addressed by increasing the capacity of the previous stages, but
for the purposes of this thesis will not be modified. The pilot scale system will provide
more accurate data to determine the recovery rate of the system. With the chosen
parameters, the amount of membrane modules needed would be:
38
2,000,000;>3/<>D25,135 ;>3<>D /�C<�3= = 79.57�C<�3=A ≅ 80�C<�3=A
Table 4 – Summary of membrane filtration stage specifications
Membrane type: Toray HFU-2020
Rating: 150,000 Daltons
Surface Area per module: 775 ft2
Membrane Material: PVDF
Casing Material: PVC
Filtration Modules: 80
Flux per module: 140 ft3/hr
Incoming flow: 2 mgd
Recovery Rate: 80%
Permeate: 1.6 mgd
Filtration mode: Constant flow
39
7 Designing a pilot scale test system
7.1 Pilot-scale Bioreactor
Given that the main goal of the pilot scale test will be to analyze the manganese removal
capability of the system, it will not be considered imperative to conserve strict hydraulic
scaling. In fact, the gravel size for the bioreactor and pore sizes for the intermediate
filtration stage and ultrafiltration modules will be kept constant. The flow rate used for the
pilot scale testing will correspond to around 1% of the flow of the full-scale system. The
full scale system will be operated at 2 mgd, so the pilot scale system will operate at
20,000 gal/day, or equivalently 14 gpm.
The pilot-scale bioreactor stage will consist of four 15-inch internal diameter bioreactors.
The bioreactors will preferably be constructed of acrylic in order to facilitate visual
monitoring of the media. If acrylic tubes in this diameter are not available, PVC tubes
could be used instead. It is assumed that the piping used to build the bioreactors will be
half-inch thick, so the nominal diameter of the piping will be 16 inches. Table 5
summarizes the calculations and assumptions for the construction of the pilot-scale
bioreactors.
Given that the equation for the minimum depth of the bioreactor is not going to vary from
that of the full scale model, it is known that the minimum depth shall be around 3 feet. In
order to facilitate the construction of the pilot system, the length of the columns used will
be half of those in the full-scale model. Each of the four bioreactors will be loaded with a
different type of media for a first run aimed at detecting the optimal type of media for the
40
hydraulic conditions of the system. The four types of media to be tested will be: 1) 4 mm
gravel supported on 1 foot of 6 mm gravel; 2) 0.5 to 2 mm sand with the same particle
size distribution as that used by Stembal et al. (2005); 3) crushed limestone with an
average diameter of 5 mm.; 4) crushed dolomite with an average diameter of 5 mm. All
of the bioreactors will be seeded with sludge known to contain Siderocapsa and left to
mature for at least 8 weeks. It will be assumed for now, that the porosity of all the
substrates will be close to 50%. However, this will be reevaluated upon testing and the
diameter of the particles will be adjusted as necessary to try to maintain similar hydraulic
conditions across all bioreactors.
Based on the results of the first run, a second run would be performed with the media
chosen from the previous test but seeding each bioreactor with a different type of
microorganism. The microorganisms to be tested are: 1) Siderocapsa, 2) Leptothrix
Discophora, 3) Sludge from a nearby wastewater treatment plant with unknown microbial
composition, 4) Not seeded, control bioreactor to observe if microorganisms naturally
occurring in the source water can catalyze the oxidation of manganese. As with the
previous run, the filters will be left to mature for at least 8 weeks.
The pressure loss across the bioreactor will be assumed to be half of that calculated for
the full-scale system, which equates to approximately 0.12 feet of clean filter head loss.
This head loss only takes into account the media itself, but the supporting metal grid for
the gravel and the friction against the walls of the bioreactor will add head loss so the
initial head loss will be adjusted to 0.6 ft. However, it is known that for the test run with
41
different types of media, it is likely that each bioreactor will have a different head loss
depending on the porosity and hydraulic characteristics of the media.
Table 5 – Summary of pilot-scale bioreactor specifications
Flow rate: 1.87 ft3/min
Velocity in bioreactor: 0.80 ft/min
Area of empty bioreactor: 2.34 ft2
Porosity: 50%
Area of bioreactor with media: 4.68 ft2
Radius of single bioreactor: 1.22 ft
Number of bioreactors: 4
Area per small bioreactor: 1.17 ft2
Radius of small bioreactors: 0.61 ft
Diameter of small bioreactors: 14.64 in
Standard size available: 16 in
Inner diameter of std size: 15 in
New bioreactor area: 1.23 ft2
Adjusted velocity: 0.76 ft/min
Initial Head loss: 0.6 ft
The bioreactors will be equipped with sampling ports spaced 1 foot apart along the
height to allow for sampling of water passing through the bioreactor.
7.2 Pilot-scale secondary filtration
Using the same cartridge filters selected in the full-scale plant (Cuno Betapure), the size
of the secondary filtration stage can be calculated. The first step is to determine the
amount of filters to maintain the pressure between 5 and 10 psi:
42
HG��5>3=���>$�$�<;=A = (14;@�)(1E@A)(0.87@A�/;@�/E@A)5@A� = 2.4
HG��5>3=���>$�$�<;=A = (14;@�)(1E@A)(0.87@A�/;@�/E@A)10@A� = 1.2
From the calculations above, it can be seen that 2 10” cartridges will need to be used for
the pilot-scale system. The initial pressure loss for the secondary filtration stage can thus
be calculated as:
�3=>�∆@@A� = (14;@�)(1E@A)(0.87@A�/;@�/E@A)(2) = 6.09@A�
The initial pressure loss for the pilot scale system will thus be slightly lower than that of
the full-scale system. However, given that the system is evaluating primarily the capacity
of the system to remove manganese; this will have a negligible effect in the study. 6 psi
is equivalent to approximately 14 feet of head loss. Given that in the original system the
filters will be changed when the differential pressure reaches 60 feet of head loss, it can
be assumed that this pilot scale system will be backwashed at 55 feet of head loss to
account for the difference in initial head loss.
In order to maintain similarity with the full-scale system, 2 separate 10-inch filters will be
used. Given the reduced scale of the pilot-scale system, the filter housing will be in-line
43
instead of with perpendicular inlet and outlet ports as the full-scale system. However,
this should not affect the performance of the system.
Table 6 – Summary of pilot-scale intermediate filtration stage specifications
Filtration Vessels: 2
Vessel diameter: 3 inches
Filters per vessel: 1
Filter length: 10 inches
Filter rating: 2 microns
Clean ∆ p 14.05 ft.
Maximum head loss: 55 ft.
7.3 Pilot-scale membrane filtration
Using the same design flux of 140 ft3/hr (25,135 gpd) chosen for the full-scale system,
the computation for the amount of modules needed to handle the pilot-scale flow of
20,000 gpd would be:
20,000;>3/<>D25,135 ;>3<>D /�C<�3= = 0.8�C<�3=
Since a whole module is to be used, the design flux would be adjusted to 20,000 gal/day
per module, or equivalently 111 ft3/hr, which is still within the range stated by the
manufacturer. Assuming an 80% recovery rate as in the full-scale system, the filtrate
flow will be 16,000 gallons per day (11 gpm).
44
The initial pressure loss for the system is assumed to be close to 14 psi (32 ft) since this
is the initial clean pressure flow estimated by the manufacturer in its specifications.
Table 7 – Summary of pilot-scale membrane filtration stage
Membrane type: Toray HFU-2020
Rating: 150,000 Daltons
Surface Area per module: 775 ft2
Membrane Material: PVDF
Casing Material: PVC
Filtration Modules: 1
Flux per module: 111 ft3/hr
Incoming flow: 20,000 gal/d
Recovery Rate: 80%
Permeate: 16,000 gal/d
Filtration mode: Constant flow
Assumed initial pressure loss: 32 ft
7.4 Minor equipment and pump sizing
Apart from the three major components of the system (bioreactor, secondary filtration,
membrane filtration), other minor components such as a solution feed pump, solution
preparation feed tank, static mixer, peristaltic air pump, pump for the membrane filtration
stage, and backwashing pumps will be needed. Figure 4 shows the layout of the pilot-
scale system with all major and minor components to be used. The side and plant view
can be seen at scale in Appendix II.
45
Figure 9– Side view of pilot-scale system
For the pilot-scale system it will be assumed that only one pump is to be used for the
whole system. However, it must be considered that depending on how the system
performs, it could be necessary to add a storage tank after the bioreactor and secondary
filtration stages and an additional pump before the ultrafiltration stage. Given that at this
time it is unknown if the source water will be coming from ground water, surface water or
an elevated reservoir, calculations for the pump will not be provided. However, once the
location of the pilot plant is identified, this should be straightforward given that the
pressure loss through the system has been calculated.
It can be seen from the diagram that the system will include 3 ball valves to isolate
sections of the system for backwashing. It must be noted that the secondary filtration
stage is assumed not to be backwashed since it is assumed that these cartridge filters
are disposable and the cost of down time and backwashing will exceed the cost of
replacing them during actual operation. However, if considered necessary during the
46
pilot testing, a simple modification of the piping would allow backwashing these filtration
elements.
In order to maintain aerobic conditions in the system, a peristaltic pump with a capacity
of 0.5 mL/min will be feeding air into the system before the bioreactors. This should be
enough to maintain saturated dissolved oxygen conditions within the pilot-scale system.
A one-way valve will be installed so water does not feed back into the air pump.
A rough calculation of the pressure loss through the pipes using the Hazen-Williams
equation with a friction coefficient of 140, gives approximately 6 feet of head loss. With
this, the total for the clean system would be approximately 53 feet of head loss. This
however does not take into account the pressure loss or gain from the source to the
pump. A summary of the expected initial pressure loss is shown in Table 8.
Table 8 – Estimated initial head loss of pilot-scale system
COMPONENT hL Unit
Bioreactor 0.6 ft
Sec filters 14 ft
Membranes 32 ft
Pipes and minor components 6.3 ft
TOTAL HEAD LOSS 52.9 ft
47
7.5 Sampling
In order to evaluate the performance of the system, it will be necessary to take samples
of the water passing through the system. Aside from dissolved manganese, other factors
that affect the oxidation of manganese such as dissolved oxygen and pH will be
evaluated. Samples will be taken before and after before each of the three treatment
stages (bioreactor, secondary filtration, membranes) as well as from the bioreactors from
sampling ports spaced a foot apart along their lengths.
7.5.1 Parameters
The parameters to be measured and range of possible values are summarized in Table
9 below.
Table 9 – Parameters to be measured
PARAMETER Max Min
Dissolved manganese 2.0 mg/L 0.0 mg/L
Dissolved iron 10.0 mg/L 0.0 mg/L
Dissolved oxygen 8.0 mg/L 1.0 mg/L
Water temperature 50 °C 0 °C
Absolute pressure 300 psi 14 psi
pH 14 0
Turbidity 9.99 NTU 0.00 NTU
48
7.5.2 Sampling interval and methods
Absolute pressure will be monitored daily using permanently installed gages before and
after each stage. There will thus be 3 pressure gages installed. This will give an
indication of the total pressure within the system and of the head loss at each stage of
the system to allow backwashing in a timely manner.
Full water sampling at all sampling ports will be carried out once a week. However,
during startup of the system, daily sampling will be conducted at the top, center, and
bottom of each bioreactor in order to monitor if the system is maturing as expected.
Once a steady state is reached, only weekly samplings will be conducted.
pH, temperature, DO and turbidity will be measured immediately as the sample is taken
from the system. Also, the influent and effluent at each stage of the system will be
sampled and analyzed. A calibrated digital pH meter will be used to take both pH and
temperature readings at once. Several manufacturers of laboratory equipment offer
equipment with these characteristics. Dissolved oxygen will be measured using a
suitable DO meter and probe, and turbidity using a suitable calibrated turbidity meter.
Dissolved manganese will be measured using the ASTM method D858-07. All water
samples will be collected in acid washed bottles and prepared according to the
requirements of the method. Dissolved iron will be measured using the ASTM method
D1068 – 10 for measuring iron in water.
49
8 Discussion
Several design alternatives were pondered during the course of this research. From
double core membrane filters to ultrasonic disinfection, there is a wide range of
possibilities that could allow biological removal of manganese to be coupled with
membranes while maintaining a small footprint. However, most of these innovations are
only in the theoretical stage or in the first stages of development.
In the case of a double core membrane module for example, it was considered to
propose a central core of spiral wound membrane made of acetate or PES and an outer
core made of anthracite or silicic gravel for the microorganisms to attach. However, there
are many foreseeable problems with such a design. For example, controlling the
migration of microorganism to the inner membrane layer and controlling their growth to
avoid biofouling could be difficult. Another problem could be that changes in temperature
that might arise during field conditions could affect each core and in turn affect the
performance of the module (e.g. gaps between layers due to difference in expansion and
contraction rates). The added resistance to flow from the second layer might require the
system to operate under very high pressures that could affect both the capital and
operational costs. Finally, since performing actual laboratory testing is out of the scope
of this thesis, the answers to these questions would be based on assumptions given that
there is no literature mentioning any attempt to do something similar.
As for using ultrasonic disinfection as an intermediate stage between the bioreactor and
the membrane filtration stage to avoid biofouling, this could allow maintaining a small
footprint. However, ultrasonic disinfection is still under development and in the very early
stages of development. It is unknown if the system would be robust enough to provide
50
the amount of protection required to avoid biofouling. There is simply not enough
information to proceed with a theoretical design of such system.
Another option that was considered was attempting to isolate microorganisms that have
been identified to cause manganese-related corrosion in piping under pressure, and
designing a system that would promote the growth of this biofilm in metallic pipes.
Several problems were foreseen with such a system so it was discarded. For one part, it
would be difficult to control the amount on manganese being deposited in the pipes. For
another, given the high velocity in the pipes and the high pressure to which they are
subjected during system startup, it would be likely to have some of the deposited
manganese migrate with every system shut down for maintenance. Finally, as the pipes
corrode, they would tend to fail and to clog, making it very difficult to predict when to
change them and risking structural failure.
The design components chosen are proven and tried methods that have not been used
in conjunction before. The proposed system, however, uses large diameter gravel as
the media instead of sand or other materials because the goal of the bioreactor is not to
retain a large number of particles so much as to help the manganese precipitate. The
bioreactor is based on that used by Stembal et al. (2005) in their study, the intermediate
filtration stage has been successfully used in the food and drink industry for years, and
the membrane filtration systems have become ubiquitous in the past few years for
drinking water treatment. The intermediate filtration stage should be robust enough to
retain most of the precipitated manganese that passes from the bioreactor stage and
most of the biological material that could potentially foul the membranes.
51
It is unknown how changing media and flow conditions within the bioreactor would affect
the migration of microorganisms, but several studies have successfully used limestone
and other coarse material in bioreactors for removing manganese. The smaller pore size
available with the sand media could aid in holding the bacteria in place and the larger
surface area might allow a smaller bioreactor by providing more places for
microorganisms to attach. If laboratory testing is performed in the future, this is a
variable that is most certainly valuable to explore further. In fact, having a media surface
that also provides a source of carbon could provide added benefits like some of the
studies mentioned in the literature review suggest.
The array of bioreactors could have any number of units. Four units were chosen to
keep a small enough diameter to allow for water to be distributed evenly over the surface
and for ease in constructing or purchasing the tanks. However, a more thorough analysis
would be required both in terms of balancing costs and of the optimal relationship
between diameter and depth to allow manganese to be removed adequately by the
bioreactor. Another point of concern is that the head loss through the bioreactor is based
on several gross assumptions such as the constants used, which would need to be
verified through experimental procedures.
It is unknown if the Siderocapsa bacteria will be available or even present in samples of
wastewater sludge available in proximity to a potential test site. From the literature
review it was not possible to determine if Siderocapsa has been isolated and cultured
yet or if it will be necessary to find an adequate wastewater sludge source that contains
this specific type of bacteria.
52
As for the intermediate filtration stage, it is unknown if it will be effective in preventing the
biofouling of the ultrafiltration membranes. To optimize the operation of the system, it
would be ideal to coordinate backwashing of the membranes, bioreactors and cartridge
filters replacement simultaneously. However, there is not enough information at the
present time to know if this is feasible. Also, it might be necessary to have completely
separate backwashing systems for the bioreactor and the membranes to avoid cross
contamination and to avoid excessive migration of microorganisms to the membranes
during the backwashing cycles. The theory behind using an intermediate filtration stage
is that this cartridge filters cost a fraction of what the membrane modules cost, so they
will reduce operational costs by protecting the ultrafiltration membranes. Only laboratory
and pilot testing will allow determining the ultimate benefits of this filtration stage.
Finally, the ultrafiltration stage will be affected by the intake water quality and by the
effectiveness of the previous stages. Thus, it is unknown if the actual operating
conditions will resemble the theoretical performance on which the proposed system is
based.
53
9 Conclusions
A new design for a biologically-catalyzed manganese removal system with membrane
filtration was proposed. The new design is based on existing technology and on previous
studies published by other researchers. The bioreactor itself is based on a modified and
adjusted version of the one proposed by Stembal et al. (2005), but pilot-scale testing will
allow further improving the design by trying different substrates for the biofilm to form
and different types of microorganisms. For example, it might be possible that either
limestone or dolomite might cause less compaction in the long term and still allow
enough porosity to keep a high flow rate through the bioreactor.
The proposed design has a high probability of success if built as laid out in this thesis.
However the pilot-scale plant would allow changing and analyzing how varying
parameters such as temperature, pH, flow rate, and substrate; to name a few; can affect
the performance of the system. It is possible that during pilot-scale testing, a new
substrate could be found to work better for the selected microorganisms or that an even
higher flow rate could be tolerated thus allowing making the bioreactors smaller.
It was assumed that it would be possible to achieve a porosity of 50% with carefully
selected and sorted media. While this is believed to be possible under controlled
conditions, it will be necessary to monitor the process carefully to determine how the
porosity and flow vary as the system reaches steady state and manganese oxides start
to be deposited on the substrate. This will also be crucial in order to determine the
backwashing rate necessary to keep a balance between biofilm thickness and downtime
for backwashing.
54
By using a proven and tried technology from the beverage industry (cartridge filters rated
at 2 microns), it is believed that the system will be capable of operating cost-efficiently
and effectively for the removal of manganese. However, it remains to be seen if the 2-
micron rated cartridges will prevent both biological contamination and manganese-
induced fouling in the membrane ultrafiltration stage.
It is believed that the proposed system is an effective solution to the problem of
removing manganese without the use of chemicals while keeping a small footprint.
When the proposed pilot-scale system is built, the system can be refined further and an
even more robust system is expected to emerge.
55
10 Further Research
The physiological aspects of biologically-mediated removal of manganese still remain to
be completely understood, as well as the interaction between different microorganic
populations that can contribute simultaneously to the removal of manganese. In regards
to Siderocapsa, which is used in this study, it remains to be seen if it can be isolated and
cultured to allow seeding a bioreactor.
Standardized constants for the depth equation to size a bioreactor could be researched
for different types of substrate. This could be achieved by running a bioreactor with all
parameters constant and varying the type of media used. A formula using porosity
and/or density could be developed to allow for media with different conditions to be used
in modeling a bioreactor.
A mathematical model for migration of microorganisms in relation to flow rate and media
characteristics could be developed in order to aid in the design of future bioreactors.
Also, different filtration devices, configurations and materials can be tested for the
intermediate filtration stage to minimize biofouling of the membranes. Backwashing rates
to maintain optimal microbial balance and biofilm thickness in the bioreactor remains to
be investigated. The influence of grain size in the media and how it relates to bioreactor
efficacy are still not fully understood and warrant further research.
Many unknowns remain to be elucidated regarding the use of biologically mediated
oxidation of manganese with membrane filtration technology. However, as more data is
generated and the bioreactors refined, the potential for full-scale application increases.
56
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Hallberg, K. and D. Johnson, 2005. Biological Manganese Removal from Acid Mine Drainage in Constructed Wetlands and Prototype Bioreactors. Science of the Total Environment 338:115-124.
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Islam, A., J. Goodwill, R. Bouchard, J. Tobiason, and W. Knocke, 2010. Characterization of Filter Media MnOx(s) Surfaces and Mn Removal Capability. Journal of the American Water Works Association 102:71-83.
Johnson, K. and P. Younger, 2005. Rapid Manganese Removal from Mine Waters Using an Aerated Packed-bed Bioreactor. Journal of Environmental Quality 34:987-993.
Katsoyiannis, I.A. and A.I. Zouboulis, 2004. Biological Treatment of Mn(II) and Fe(II) Containing Groundwater: Kinetic Considerations and Product Characterization. Water Research 38:1922-1932.
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59
APPENDIX I – Characteristics of bioreactors in reviewed literature
60
Table 10 – Characteristics of some bioreactors in the literature
Authors of the
study
Type of
bioreactor
Maturation
Time
Source of
microorganisms
Water
temp pH
Water
treatment
rate
Initial Mn
C (mg/L)
Mn
Removal
%
D.O.
(mg/L)
Redox
Potential (V)
Backwash rate
and time
Tekerlekopoulos et.
Al
Trickling
filter with
silicic gravel
5 months
Seeded with
sample from
wastewater plant
25 ± 1 ° C Inlet: 7 – 7.3
Outlet: 8 – 8.3
500 to
2000 ml /
min
0.6 to 2 100 to
54% 7 to 8 0.3 to 0.5
Air: 10 L/min for
30 min.
Water: 12 L/min
for 30 min.
Katsoyannis and
Zoubolis
Up-flow
filtration
columns
with PE
beads
8 months
Leptothrix
ochracea from
sludge
N/A 7.2 7 m / h 0.4 95% 3.8 0.34
Every 3 days with
3 L of treated
water.
Mariner et al. Down-flow
bioreactor N/A
Coated stones
taken from
stream – Phoma
herbarum and
Pleosporales
identified as main
catalysts
5-30 ° C 3.5 - 6 N/A N/A N/A N/A N/A N/A
Qin et al.
Down-flow
bioreactor.
One with
manganese
sand and
one with
siliceous
sand
7 days
Filter sand from
old sand filter of
existing plant –
Leptothrix
identified
N/A 7.2 3.9 L/h 1.5 to 2.25 60% 5 N/A 5 L/m2 s for 8
minutes
Hope and Bott Down flow
sand filter 3 months
Leptothrix
discophora SP-6 26 ° C 7.3 N/A 4.7 97% 8.2 N/A N/A
Burger et al. Pressure
sand filters 6 weeks
Leptothrix
discophora SP-6
and indigenous
biofilm from
microorganisms
in the source
water.
N/A 6.5 – 7.5 1 mL/min 0.5 90% N/A 481 N/A
61
Thornton Limestone-
filled tanks 3 weeks
Indigenous
biofilm from
existing ponds
N/A 6.43-7.55 3.8 L/min 3.15 88% 6.9 – 7.1 N/A N/A
Johnson and
Younger
Dolomite
substrate
with a
bentonite
and MnO2
basal layer.
8 weeks
Indigenous
biofilm – not
attempted to
identify bacteria
As low as
4 °C 7 5 mL/min 20 97% N/A N/A N/A
Stembal et al. Quartz sand
0.5 to 2 mm 3 to 4 weeks
Siderocapsa from
operating plant
11.2 – 14.6
°C 7 – 8.09 22 m/h .224 – 1.06 99% N/A N/A N/A
Pacini et al. Gravel 10-
15 mm 8 weeks
Galionella –
biofilm allowed to
develop
spontaneously
N/A 7.1 12 m/h 1.35 95% 8.1 N/A 50 m/h for 10
minutes
Suzuki et al.
Hybrid MF
membranes
with PAC
and sludge
90 days
Sludge from
wastewater
treatment plant –
leptothrix
ochracea and
siderocapsa
18 °C
(average) N/A 0.15 m/d 0.31 69% 3.09 N/A
Backwash and air
scrubbing every
30 mins with 40 to
80% of volume of
treated water
62
APPENDIX II – Scaled drawings of pilot scale system
2 cartridge
filters in parallel
4 bioreactors
in parallel.
6 ft - media
1 ft - supporting layer
1 membrane
module (7 ft)Pump
Backwash
Pump
Water inlet
Air
pump
Filtrate
Concentrate/reject
Ball
valve
Ball valve
Ball
valve
Backwash
Outlet
Backwash
Inlet
Check
Valve
8'-4"
9'-10"
5'-6" 4'-2"
1" pipe
1/2" pipe
1/2" pipe
1" pipe
Pressure
Gauges
Pressure
Gauges
Pressure
Gauges
Pressure
Gauges
Sampling ports
Sampling
valve
Sampling
valve
Design of a biologically-mediated
manganese removal system with
ultrafiltration membranes
Figure 5
Pilot-scale system
SIDE VIEW
Prepared by:
Carlos A. Correa
SCALE 1/4" = 1'
0 2'4' 6'
PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCTP
RO
DU
CE
D B
Y A
N A
UT
OD
ES
K E
DU
CA
TIO
NA
L P
RO
DU
CT
PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCTP
RO
DU
CE
D B
Y A
N A
UT
OD
ES
K E
DU
CA
TIO
NA
L P
RO
DU
CT
Ball
valvePump
Air pump
90° Elbow
Backwash
Outlet
1'
1'
Flow Meters
(at outlet)
Bioreactors
1" Pipe
90° Elbows
1/2" Pipe
1" cross
1" to 1/2" reducers
1" tee
Ball valve
Backwash Outlet
Cartridge Filters
Ball valve
Sampling
valve
Backwash
Pump
Membrane
module (7 ft)
Design of a biologically-mediated
manganese removal system with
ultrafiltration membranes
Figure 6
Pilot-scale system
PLAN VIEW
Prepared by:
Carlos A. Correa
SCALE 1/4" = 1'
0 2'4' 6'
PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCTP
RO
DU
CE
D B
Y A
N A
UT
OD
ES
K E
DU
CA
TIO
NA
L P
RO
DU
CT
PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCTP
RO
DU
CE
D B
Y A
N A
UT
OD
ES
K E
DU
CA
TIO
NA
L P
RO
DU
CT
