By Paul Bergeron
Membrane bioreactors (MBRs) utilize a combination of membrane separation processes, such as microfiltration or ultrafiltration, and biological wastewater treatment. They are now being widely used for municipal and industrial wastewater treatment and in an increasing number of ways to protect our dwindling supply of fresh water. They also save time and money.
According to the American Membrane Technology Association (AMTA), an MBR system is a complete and integrated membrane unit with related components necessary to allow the process to function as desired. It is often made up of 10 or 11 subsystems and includes fine screening (headworks), the membrane zone, and, in most cases, some type of post-disinfection process.
The membrane zone can be best described as the initial step in a biological process when microbes are used to degrade pollutants that are then filtered by a series of submerged membranes (or membrane elements), according to AMTA.
The individual membranes are housed in units known as modules, cassettes, or racks, and a combined series of these modules are referred to as a working membrane unit, according to AMTA. Air is introduced through integral diffusers to continually scour membrane surfaces during filtration, facilitate mixing, and, in some cases, to contribute oxygen to the biological process.
AMTA said the benefits of an MBR include a reduced footprint, usually 30 percent to 50 percent smaller than an equivalent conventional, active sludge facility with secondary clarifiers and media tertiary filtration.
The process also produces exceptional effluent quality capable of meeting the most stringent water quality requirements, a modular schematic that allows for ease of expansion and configuration flexibility, a robust and reliable operation, and reduced downstream disinfection requirements, said AMTA.
The Three Main Membrane Types
In general, the market recognizes three main membrane types: hollow fiber, tubular, and flat sheet. According to The MBR Site (thembrsite.com), a resource for the MBR industry, “flat-sheet membranes have planar configuration and are predominantly rectangular.” They are designed to be immersed in the membrane tank and scoured with air to maintain the flow of sludge through the membrane channels.
“The element may be referred to as a sheet, cartridge, or, most commonly, a panel. The panels can either be rigid/semi-rigid (6mm–8mm thick) or flexible, with the flexible panels being thinner (2mm–3mm).”
There is differentiation between rigid flat plates and flexible flat sheets, and further, a delineation between polymeric and ceramic types to broadly distinguish between materials of construction. In the technology used by M|MBR Systems, for example, the cassettes, or modules, can be described as having polymeric, flexible flat-sheet elements.
For the thousands of MBR facilities in the United States, hybrid MBR technologies are making maintenance and upgrades easier. Excluding some industrial markets, hollow-fiber and flat-plate type elements account for most of the membranes installed in MBR systems today. It is generally accepted that hollow-fiber technologies are more space- and energy-efficient than rigid plates. However, hollow-fiber technologies are also generally believed to be more complicated to operate and require more chemical cleaning.
On the other hand, rigid-plate type products are often easier to operate, require more aeration, and need less chemical cleaning. These once black-and-white comparisons are becoming blurry through innovations and with the advent of the flexible sheet.
How It Works
Put simply, an MBR is an activated sludge process that uses membranes for the separation of solids from treated effluent. An activated sludge process amounts to a slurry of living organisms—microbes—that consume biodegradable pollution to form more bugs.
Membranes submerged in the slurry separate out suspended solids so that permeate can be disposed of or reused. The need for disinfection after an MBR is dependent on the application and disposition of the treated effluent.
MBR systems are considered a type of best-available technology because, when properly designed and operated, they can produce the highest-quality effluent and meet the most-stringent permit limits. MBR systems can also be two to four times smaller than conventional activated sludge systems, and they’re highly scalable.
The first MBR patent was filed by Dorr-Oliver in the 1960s. Zenon introduced hollow-fiber membrane technology to the North American municipal market in the 1990s, followed by Enviroquip, which used Kubota rigid flat plates in 2001. In 2012, Ovivo introduced the flexible flat sheet, or hybrid, technology to the U.S.
There are more than 70 technology providers in the market delivering MBR-related products and services. There are also more than 2,000 wastewater treatment plants in the U.S. that use MBR technology, treating roughly 2 billion gallons per day of wastewater.
MBRs Can Handle Four Times More Wastewater
Dennis Livingston, cofounder and technical director of M|MBR Systems, based in Austin, Texas, said, “New MBR wastewater treatment facilities can take 80 percent less concrete than conventional systems to build. Modular MBR solutions take half the time to deploy. And existing infrastructure can be [retrofitted] with MBR technology to increase production capacity by fourfold.”
To help educate and support industry players, M|MBR Systems has created the MBR Technology Hub, which combines veteran water treatment professionals with a deep and varied list of potential product solutions. The purpose of the hub is to serve as a universal resource center for all MBR projects using several types of polymeric flat-sheet membrane products.
For new greenfield projects, MBR’s biggest benefit is that it can handle four times more wastewater in the same footprint compared to older treatment methods while producing the highest-quality effluent for reuse purposes.
In fact, the discharge from properly designed and operated MBR wastewater treatment plants can meet the most-stringent regulatory standards, even those in California. Because MBR systems use filtration in place of sedimentation, they are also more scalable and more easily transportable. MBR solutions can be phased in over time to keep pace with growing demand or be delivered as modular systems.
Newer, flexible flat-sheet membranes are a hybrid of the original hollow-fiber and flat plates. These hybrid products have performance specifications that are somewhere between fibers and plates but lean toward the plate side of the comparison.
Livingston said that flexible flat-sheet technologies are typically easy to operate like their flat-plate predecessor. They are found to be two to four times more efficient, greener by requiring 10 times less material to make, less susceptible to clogging, and five to 12 times easier to remediate.
The biggest benefit of the flexible sheet design, in a module with open sides, is the reduced impact of clogging. These benefits are not necessarily brand specific, but exact performance metrics vary by product.
Livingston said this hybrid technology “is a game changer” for the industry. “For existing facilities, our manufacturing partners have introduced adaptable, customizable components that are backward compatible with most legacy MBR systems.”
Livingston said that “MBR systems are one potential remedy to water scarcity problems in some areas because they produce better, cleaner effluent that can serve more reuse purposes. They also treat wastewater to higher standards, and reusing it can offset the demand for potable water while also protecting the environment and human health.”
MBR’s Exponential Demand Growth
According to market research company IMARC, the global membrane bioreactor market reached a value of $3.3 billion in 2021. IMARC expects the market to reach $5.8 billion by 2027, exhibiting a compound annual growth rate (CAGR) of 10.31 percent from 2022 to 2027.
According to Transparency Market Research (TMR), the global MBR systems market will expand at an exponential and robust 14.31 percent CAGR from 2021 to 2031.
An increase in demand for clean water and tightening regulations regarding the treatment of wastewater and industrial discharges are some of the major factors projected to give significant push to the global MBR systems market.
There are more than 16,000 permitted plants treating wastewater in the U.S. today, and “many are candidates to be converted into MBR systems,” Livingston said. Most systems are owned and operated by local governments. Some of the smaller plants are privately managed. Many are interested in improving their operational efficiency, according to Livingston.
“The challenge now,” he said, is “getting that technology to projects, to customers, in time.”
Cost- and Energy-Efficient Systems
In part, the protection of lakes, rivers, aquifers, and streams from damaging pollution relies on the strategic use of membrane bioreactor solutions and systems, Livingston said.
TMR reported a significant increase in the production of wastewater that is now treated through MBRs across residential, commercial, and industrial complexes.
“Additionally, the development of submerged MBRs is acting as another growth-inducing factor,” according to TMR. “These systems are cost- and energy-efficient, compact, lightweight, and can create aeration to generate tangential liquid flow around the membranes.
“Apart from this, the increasing utilization of environment-friendly water and wastewater management technologies across industries, including chemical, pharmaceutical, power, food and beverage, and textile, is also contributing to the market growth.
“Other factors, including rapid industrialization and the implementation of favorable government policies for upgrading the existing wastewater treatment plants with MBRs, are projected to drive the market further.”
These improvements include the increased use of remote monitoring platforms. “Dashboards and analytics help those running the systems make better decisions,” Livingston said.
A Competitive Landscape of Providers
“There are no equipment standards in the MBR market like there are in the reverse osmosis market,” Livingston said. “Most MBR membrane suppliers use their own unique, proprietary specifications and dimensions. Commoditization—the open-platform approach to membrane delivery—is a long way off for MBR technology providers.
“But flexible flat-sheet products solve the challenge in a different way because they are highly adaptable and often compatible with legacy MBR systems,” he said.
“Customers have quickly seen results after they deployed membrane solutions,” Livingston said. “They not only save money and improve filtration capacity from the same plant, but they can also repurpose assets and people resources onto other projects or find new efficiencies within existing projects.”
About the author
Paul Bergeron has been a multi-industry reporter for 30 years, covering energy and sustainability, property management, global HR trends, small business, technology and horse racing. He currently is Executive Editor for his self-operated content marketing company, Thought Leadership Today in Herndon, VA.