MABR provide simultaneous nitrification-denitrification (SND) in anoxic conditions in new and upgrade wastewater treatment projects

One of the most talked-about new wastewater treatment technologies is the membrane aerated biofilm reactor (MABR), which is revolutionizing the field.

MABR is being heralded for its high treatment efficiency, low operating expenses, low maintenance, scalability, and its neighborly low noise and odor levels. What’s discussed less is exactly what goes on inside an MABR module.

MABR’S low-pressure, passive aeration offers significant energy savings over conventional, high-pressure aeration. The unique MABR process provides highly efficient biological nutrient removal, which results in operational savings and minimal footprint requirements.

At the most basic level, MABR enables highly efficient biological treatment. In traditional aerobic treatment, the process is fed with air bubbles created by aerators. This traditional method is not only energy-intensive, but also inefficient because most of the air in the bubbles rises to the surface before the bacteria have a chance to use it.

Simultaneous Nitrification and Denitrification

One interesting thing about MABR is that the membrane configuration allows multiple processes to occur simultaneously in the same tank, something that used to require multiple chambers.

Fluence’s MABR uses a spirally wound, self-respiring membrane envelope that supports the formation of an aerobic biofilm in an anoxic environment, resulting in simultaneous nitrification and denitrification (SND). The semi-permeable membrane is submerged into a wastewater tank while low-pressure air is blown through the air side of the membrane. Oxygen is constantly supplied to the fixed nitrifying biofilm that develops on the wastewater side of the membrane, while denitrification occurs in the anoxic bulk liquid.

The Connecticut Water Pollution Abatement Association describes the nitrification and denitrification process:

Nitrification is the conversion of ammonia (NH₃) to nitrate (NO₃). […] This is a two-step process that is done with oxygen and two types of bacteria, Nitrosomonas and Nitrobacter, known collectively as the nitrifiers. […] Denitrification is the conversion of nitrate (NO₃) to nitrogen gas (N₂) […] Heterotrophic bacteria utilize the nitrate (NO₃) as an oxygen source under anoxic conditions to break down organic substances.

These nitrifying bacteria thrive as a biofilm on the membrane as it continuously delivers oxygen to them at the molecular level without bubbles. As air flows through the membrane walls and into the wastewater, aerobic bacteria cling to it, form a nitrifying biofilm, and thrive, converting dissolved ammonia into nitrate.

The oxygen levels near the membrane in an MABR are high, but the levels are lower between the membrane sheets and in the rest of the tank, so denitrifying bacteria use oxygen from the nitrate. The nitrate is broken into nitrogen gas, which is discharged to the atmosphere, and into oxygen, which induces further digestion of carbon-based organic contaminants in the wastewater.

The biofilm-based SND used in MABR is a very stable and resilient process, with high resistance to environmental shocks. It works well in lower temperatures and its reactors are smaller than others that perform similar treatment work. Because no nitrate recirculation is required, energy is saved on pumping.

Here, Leon Downing of Black & Veatch explains the evolution of MABR, which began with the idea of aerating wastewater treatment with air in a permeable membrane, in effect, a “stationary bubble.”

Air Use Inside an MABR Module

It is important to clarify that although the energy-intensive process of pressurizing air to force it through diffusers is not required with MABR modules as it was in legacy aerobic water treatment facilities, the air must still be pumped into the membrane envelopes. The pressure required to do so, however, is negligible. Because the membrane walls of the envelopes are held separate by a specially designed air spacer, fanning the air through the membrane envelopes is done at close to atmospheric pressure.

The wastewater within an MABR module must be mixed periodically, and, in fact, bubbles are used in periodic cycles to mix the wastewater to avoid the drawbacks of mechanical mixing, but the pressure required is also negligible.

Take a look inside an MABR module in this short video:

Fluence MABR Applications

Fluence supplies MABR in two product lines:

• Aspiral™, which packages MABR modules in standard shipping containers
• SUBRE, which uses arrays of MABR modules to retrofit existing activated sludge plants

Aspiral Smart Packaged MABR

In a decentralized model, treatment is brought to the point of use, eliminating much of the significant expense of building pipelining infrastructure. As part of a decentralization strategy, Aspiral’s compact nature opens up a world of possibilities for remote communities, resorts, factories, corporate campuses, schools, and more.

Aspiral’s low energy requirement makes off-grid operation on alternative energy sources viable. And, for small- and medium-scale applications, Aspiral is highly scalable: Units can be used in tandem to increase capacity, and relocated or sold in case of decreased demand.

One such decentralized application is a Fluence project in China to commission 80 Aspiral units for plants at rest stops every 50 kilometers on a Hubei Province highway system, thus avoiding long, costly pipelines.

Moreover, Smart Packaged Aspiral units can be installed with little site preparation or construction. They’re supplied in weatherized steel containers that are specially coated for corrosive environments and rated for hurricane-force winds, making them ideal for coastal applications.

Learn more about Aspiral MABR technology in this short video:

SUBRE for Retrofitting Existing Plants

With increased urbanization putting pressure on existing wastewater treatment systems, SUBRE can come to the rescue, increasing nutrient removal, energy efficiency, and treatment capacity at an existing plant.

With SUBRE, towers of stacked MABR modules are simply lowered into an existing aeration basin after a partition is set up between the anoxic MABR zone and the aerobic zone. This can be done in basins with capacity ranging from 2,000-100,000 m³/d. SUBRE enhances treatment with minimal disruption to operations.

SUBRE reduces the need for coagulants and carbon sources, and reduces an existing plant’s energy needs by 20-30%.

Learn more about SUBRE MABR technology here:

The Future of Wastewater Reuse

MABR combines new membrane polymer technology and old wastewater treatment principles into an ingenious package that efficiently and simultaneously performs many functions within one small footprint.

And, with all indicators pointing to decades of deepening groundwater depletion and water stress, wastewater reuse is becoming more and more necessary. Christopher Gasson, publisher of Global Water Intelligence, said that water reuse seems to be “on the verge of a golden decade,” lacking only technological advances to change the paradigm.

MABR, with its revolutionary approach to wastewater treatment, could hold the key to ushering in more widespread water reuse. Contact Fluence for more information about MABR technology or to learn how it can benefit your wastewater operation.