How Membrane Aerated Bioreactors (MABR) Could Change Wastewater Design
A new technology that can cost-effectively improve energy and treatment efficiency is poised to change the way we design and operate wastewater treatment facilities.
The new technology also can help existing facilities expand—in fact it’s ideal for retrofits. Membrane aerated bioreactors (MABR) is being piloted right now.
In conventional wastewater treatment, it’s common to use the activated sludge process. This process uses large aerated tanks. Inside these tanks, air is bubbled through the wastewater to provide oxygen to suspended microorganisms (or microbes). These microbes break down excess nutrients in the wastewater. The mixture is then separated in a clarifier, where the heavier microorganisms settle to the bottom. Clear water from the top of the clarifier continues in the treatment process and then is discharged to the environment. The leftover microbes are recycled back to the aeration tanks to continue their jobs. This is a proven and effective technology.
MABRs are more efficient than the activated sludge process. They deliver oxygen more effectively to the microbes. There also is a higher density of microorganisms present within the process. MABRs achieve this by blowing air through small membrane tubes that allow layers of microbes, or a biofilm, to form on the surface of the membrane.
The traditional way of supplying air consumes a high amount of electrical energy, and a large amount of oxygen in the air simply exits the system before it can be used. About half of the energy consumption at conventional wastewater treatment plants is used to blow air into the biological tanks. But MABR technology can reduce this amount by half. This results in annual savings in the tens of thousands of dollars for medium-size wastewater plants, with greater savings for larger plants.
MABRs can also help facility owners and managers achieve the desired capacity and treatment capabilities in a smaller plant footprint. This is extremely important as many wastewater facilities are landlocked; building out may not be possible. Expanding the footprint of the facility is also very expensive. Frequently, nearby sensitive environmental features, such as rivers and lakes, can also hamper expansion. This is concept illustrated in the Hespeler WWTP Upgrades.
Stantec is designing headworks, thickening and clarification upgrades at the Hespeler facility to meet future flow and treatment requirements. In parallel, a conceptual design is being completed for an MABR process to provide significant energy savings at the current facility capacity. The MABR conceptual design will look at achieving these energy savings by the installation of the membranes either within the existing tankage or in compact new tanks as shown. Both MABR options take significantly less space than a conventional upgrade!