America’s Authority in Membrane Treatment

Membrane Bio-Reactors (MBR)

The use of Membrane Bio-Reactors with low-pressure membrane filtration,
(MBRs) in municipal wastewater thus eliminating the need for a clarifier
treatment has grown widely in the past or polishing filter. The membrane
decade. This trend is primarily due to separation process provides a physical
more stringent effluent water quality barrier to contain microorganisms to
requirements, decreasing system costs assure consistent high quality reuse
and improved energy efficiency. water. The ability to cost effectively
Moreover, in response to a changing treat raw sewage for reuse provides a
economic climate, MBR is commonly new reliable, drought proof supply of MBR systems offer a wide range of
viewed as an option for the retrofit, water that can benefit communities by benefits, such as:
expansion and upgrade of aging reducing reliance on over stressed
 MBR is capable of meeting the most
infrastructure to meet new nutrient existing supplies, increase availability
stringent effluent water quality
limits or increase plant capacity. of potable water and improve our
standards. More importantly, the
environment by decreasing discharges
Wastewater treatment plants have effluent quality is highly consistent
of partially treated wastewater to
historically required a significant with the membrane barrier and a
oceans, lakes, rivers, streams and
amount of land to construct the more stable biomass.
creeks.
necessary tanks and infrastructure for
 Combining space efficient membrane
the required levels of treatment. MBR MBR technology is also ideally suited
systems and operation at increased
provides a cost effective viable for an array of municipal and industrial
mixed liquor concentrations
alternative to conventional treatment wastewater applications such as
(commonly 8,000 – 18,000 mg/l);
within a considerably reduced footprint. irrigation, aquifer replenishment,
MBR systems are highly space
Additionally, there is ever increasing wetlands development, industrial
efficient. Commonly, MBR designs
regulation related to pathogens, viruses process water, boilers and cooling
will require only 30 – 50% of the
and other constituents of concern which systems. The scalability and portability
space required for conventional
are not typically reduced to desirable of MBR technology has also created
systems designed to meet the same
levels by conventional treatment new opportunities for satellite and
treatment goals. This improved
processes. scalping treatment plants. Also referred
space efficiency benefits not only
to as point-of-use or decentralized
new facilities, but allows expansion
plants, satellite facilities allow
and upgrade of existing facilities up
communities to remotely treat
to 3-5 times existing capacity without
wastewater, thereby alleviating the
additional treatment volume or site
need for expanding centralized sewage
footprint.
systems and long distance pipelines
which can be disruptive and costly. In a  MBR systems provide this high
related application, scalping plants treat effluent quality in a greatly simplified
New water is not easily created, but
raw sewage from existing regional process, requiring only headworks,
some communities are doing just that,
sewer lines, producing recycled water biological process, membrane
by turning to more advanced processes,
for local use and before sending filtration, and disinfection to meet the
such as MBR systems, which make
residuals back into the sewer system. most stringent water quality
water recovery and reuse possible.
standards. In comparison,
MBR technology combines
conventional process requires
conventional activated sludge treatment
 additional primary treatment, MBR Wastewater Influent Limitation
secondary clarifiers, Enhanced and Pretreatment
Nutrient Removal and media The membranes in a MBR system are
filtration in order to obtain the same made from polymeric organics
effluent characteristics. (PVDF, PE or PES) and assembled into
units (modules, cassettes, stacks) with
 MBR systems are simpler with fewer
high packing density. Raw wastewater
process components and
pretreatment is important to sustain stable
maintenance requirements. Common
MBR performance and fine screening is
maintenance is still required on
an essential operation of any pretreatment
mechanical components, but
system. MBRs have a limited tolerance rotating brush screens, internally-fed
operators can now avoid difficulties
for abrasive and stringy materials, such as rotary drum screens, in-channel rotary
in operation tied to sludge settling
grit, hair and fibrous material. This drum screens and traveling band screens.
and clarifier sludge blankets. MBR
material, if accumulated in the mixed
systems are also easily automated and Oil and grease in the concentrations
liquor to a sufficient extent, can cause
instrumented to measure typically found in municipal sewage have
membrane damage and accumulation of
performance, allowing systems to be little or no impact on the operation of an
solids and sludge between membrane
remotely operated and monitored, MBR, however free oil and grease must
fibers and plates, or clog membrane tube
thus significantly reducing operator be removed as this can prematurely foul
openings. Depending on the type of
attendance. membranes.
membrane technology selected and
 The modular nature of the membrane specific project drivers, some Pretreatment of industrial wastewater
system allows more efficient phasing combination of coarse screening, varies from case to case because some
of facilities. Membrane modules can grinders, grit removal, primary industrial wastewater may have high
be delivered on a “just in time” basis, clarification and fine screening is COD (>10,000 mg/L), high temperature
reducing the need for large and costly generally recommended as pre-treatment (> 40°C), high TDS (>20,000 mg/L) or
initial construction to meet long-term for MBRs. However, pre-treatment high content of inorganic solids. Without
projections. requirements can vary widely between proper pretreatment, these wastewaters
technologies and treatment objectives. In may jeopardize MBR applicability or
 The cumulative advantages of MBR
fact, recent innovations in membrane economic feasibility. Most industrial
are increasingly translating into lower
equipment design are geared toward wastewaters do not require fine screening
total installed costs as compared to and some may need physical-chemical
reducing pre-treatment requirements and
conventional activated sludge and pretreatment, such as flocculation/
equipment sensitivity to damaging
SBR technologies. Cited cost coagulation and/or dissolved air flotation
debris.
savings often include reduced (DAF).
concrete, space and building sizes MBR suppliers normally specify a fine
among other factors. screening requirement of <3 mm mesh or MBR Effluent Water Quality
hole opening (with <2 mm preferred), Capability
 The ability of MBR systems, One of the most important advantages of
while side stream MBRs will typically
Microfiltration or Ultrafiltration, to MBR over conventional biological
have a tighter requirement for fine
produce effluent with very low solids technologies is the superior quality and
screening. Fine screens are sized for peak
(SDI < 2) makes them well suited as consistency of the produced effluent.
flow with one screen out of service to
RO pre-treatment. Historically, MBR operations have
prevent overflow or bypass of unscreened
wastewater. Washing and compaction of proven that the effluent quality can
screening solids are recommended where exceed the world’s most stringent
practical to reduce the water and organic wastewater treatment standards,
content of the screenings. Fine screens in including: California’s Title 22 reuse
many different configurations are standards, European bathing water
available, each uniquely fitting a standards, US Coast Guard,
particular need and application. Typical United Nation’s International convention
fine screen configurations include for prevention of pollution from ships
and Alaskan marine discharge standards.
Not only do MBRs ensure an effluent Facilities greater than 1 MGD typically
free of solids due to the positive barrier see some efficiencies and economies of
for suspended solids and colloidal scale, with equipment costs of
materials, but also overcome the $0.75 - $1.50 per gallon of plant capacity
operational problems associated with and complete plant construction from
poor sludge settling in conventional $3.00 - $12.00 per gallon of plant
activated sludge processes while capacity. Operational costs for these
maintaining a considerably higher MLSS plants generally range from $300 - $500
concentration and sludge retention time. per million gallons treated. Through
Consequently, both soluble and improved products and more efficient
particulate organics in waste streams are design and construction, these costs
effectively oxidized, and nutrient removal continue to decline globally.
can be readily accomplished through
biological nitrification, denitrification and
chemical or biological phosphorus
removal.
MBR Capital/O&M Ranges
MBRs have the capability to consistently
As a result of widely varying
achieve the following effluent quality:
conditions, costs for MBR systems can
BOD5: <3 mg/L vary greatly. For both capital and
TSS: <1 mg/L operating costs, numerous factors will
NH3-N: < 0.5 mg/L impact any particular project including:
Total Nitrogen: <3 mg/L
- Membrane technology selected
Total Phosphorus: < 0.05 mg/L
Turbidity: < 0.2 NTU - Local construction costs
The consistent high quality effluent - Redundancy requirements Other Considerations
produced by MBRs is suitable for a For owners and utilities, there are a
- Hydraulic peaking factors
variety of municipal, industrial and number of key factors to consider when
commercial reuse purposes and can be - Local power costs contemplating selection of an MBR
applied in environmentally sensitive - Project specific needs for the site, system. Capital costs for a typical MBR
areas. MBR effluent is also an excellent including plant buildings and enclosure system have become more competitive
water source for reverse osmosis and in many cases less than conventional
applications to produce higher quality - Project size tertiary or re- use, but still remain
water for ground water recharge or - Materials of construction marginally more expensive depending on
industrial pure water reuse. evaluation criteria and comparison
However, to provide general guidelines
methodology. However, MBR can
we have made some general assumptions.
compete economically with secondary
For smaller facilities, not including
treatment technology when nutrient limits
package plants and less than 1 MGD,
are specified, space is limited, concrete is
expected equipment costs should be
expensive or capacity is phased in over
$1.00 - $6.00 per gallon of plant capacity,
time. Regarding operating costs, although
with complete plant construction costs
it is well documented that MBR systems
ranging between $5.00 and $22.00 per
are more energy intensive than their
gallon of plant capacity (depending on
conventional treatment equivalents,
design). Operating expenses for the
significant gains in energy efficiency
combined biological and membrane
have been achieved in the last decade.
systems, including power, chemicals, and
membrane replacement should range The hydraulic capacity of membranes in
from $350 - $550 per million gallons an MBR process is based on design flow
treated. rate criteria and temperature. Typically
maximum day or peak hour flows at the Membrane systems are highly automated treatment. Building on numerous system
expected coldest temperature will dictate processes and as such redundancy and innovations, the technology is considered
the membrane surface area required for a reliability need to be evaluated through by many industry professionals to be “the
treatment plant. The design flux (unit the design process. There are many treatment technology of choice”
flow per membrane surface) is the single approaches to build redundancy into an regardless of the size or application.
most important design parameter as it MBR process including specification of
This type of support, coupled with
will dictate the surface area of membrane redundant trains, influent equalization
industry improvements in the technology,
installed, impact membrane air scour (relevant for smaller facilities), stand-by
will take MBR to the next level to
requirements, chemical cleaning power and, in some cases, hot back-up
become “not just an alternative” but “the
requirements, membrane replacement and PLCs. The level of redundancy required
treatment of choice” in the next few
warranty costs. Design flux is very site is site specific and should properly
decades.
dependent and needless to say, requires account for available storage, overall
careful consideration. In the past, MBR number of process trains, reliability of
peak factors were limited to roughly power, and type of plant (end of pipe vs.
twice the rated (nominal) capacity of the water reuse facility) among other factors.
plant but suppliers are now employing
Years ago, when MBR was first
novel approaches to storm flow
introduced to the market, a perceived
management that can, in some cases,
advantage was the decoupling of the
allow for much higher peaking factors.
biological process from solids removal.
A number of membrane configurations However, after more than two decades
are commercially available and include and based on nearly 6,000 installations
hollow fiber (both reinforced and worldwide, it is clear that mixed liquor
non-reinforced), flat plate or tubular. The characteristics can significantly impact
differences between each of these types membrane performance. Significant
of membranes are significant and include flexibility exists with the biological
materials of construction, chemical design associated with MBRs. Sound
cleaning, pore size (ultrafilter vs. biological design such as maintaining
micofilter), air scour requirements, adequate DO concentrations in aerobic This material has been prepared as an
hydraulic configuration and membrane reactors and proper selection of SRT is educational tool by the American Membrane
tank volume. Selecting the appropriate critical for overall good membrane Technology Association (AMTA). It is
membrane configuration also requires performance. Biological process designed for dissemination to the public to
careful consideration of robustness, configurations options are extensive and further the understanding of the contribution
operating flexibility, influent systems can be designed for very low that membrane water treatment technologies
wastewater characteristics and operating total nitrogen applications as well as can make toward improving the quality of
costs for a given application. biological phosphorus removal in water supplies in the US and throughout the
addition to more conventional world.
Like all membrane facilities, periodic
nitrification/denitrification systems.
cleaning must be performed to remove For more information, please contact:
biological and inorganic foulants. Future of MBR
Initially, many MBR systems were Market trends indicate MBR technologies American Membrane Technology
submerged in the aeration basin requiring will be increasingly utilized as part of Association (AMTA)
removal of the membrane elements or wastewater treatment, water reuse 2409 SE Dixie Highway
units for cleaning – this was very labor programs to conserve our natural water Stuart, Florida 34996
intensive, particularly as plant capacities resources and to provide new water
Phone: (772) 463-0820
expanded. The current trend is toward sources. There are roughly 600 operating
Fax: (772) 463-0860
fully automated, in-situ cleanings and plants in the U.S. and 6,000 worldwide.
even chemical free technologies that From small, point-of-use plants to large Email: admin@amtaorg.com
minimize or eliminate the need for 40 MGD municipal plants, MBR systems or visit our website at:
routine cleaning. are now considered mainstream and www.amtaorg.com
widely accepted as best available
(FS-13) Dec. 2013