MABR: Familiar WWTP Principles Providing Better Results

MABR: Familiar WWTP Principles Providing Better Results

Wastewater treatment plant (WWTP) designers and decision-makers tasked with finding more cost-effective performance for challenging applications want new options.

Here is how flat-sheet membrane aerated biofilm reactor (MABR) technology tweaks the chemical and biological functions of conventional activated sludge (CAS) processes to reduce energy consumption and operating expenses (OPEX) in demanding applications.

The Difference Is In The Design

Wastewater operations challenged by remote treatment locations, growing populations, or tightening effluent requirements are already reaping the potential of flat-sheet MABR in selfcontained treatment plants ranging from 4,000 GPD to more than 300,000 GPD. Based on that proof of concept, the opportunity for retrofitting the same core technology into existing CAS basins for even larger operations is now on the horizon.

Here are the key design principles behind flat-sheet MABR performance that differentiate it fromtraditional CAS installations, in terms of process performance and operating costs:

 

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Figure 1 . The essence of the flat-sheet MABR design is the establishment of an autotrophic biofilm on the membrane to consume ammonia and generate nitrate that in turn oxidizes the wastewater BOD.

 

 

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Figure 2 . Short circulation cycles require very little air to keep suspended solids in the mixed liquor evenly distributed across the face of the membrane.

 

 

How Flat-Sheet MABR Works

Many water industry practitioners have been exposed to the concept of membranes for filtering applications — e.g., ultrafiltration (UF) or reverse osmosis (RO) — designed to let water pass through while particles are filtered out based on the membrane’s nominal pore diameter. Flatsheet MABR flips the focus of the membrane from filtering water to diffusing air. Oxygen passing through the self-respiring membrane envelope to the mixed liquor side of the MABR surface (Figure 3) helps to grow and sustain the biofilm of autotrophic organisms capable of using chemical energy to synthesize their own food from inorganic substances (i.e., ammonia).

When that multi-layered membrane envelope is spiral-coiled around a central core (think of a large roll of paper towels standing on end), it provides an extremely large oxygenated surface area to support biofilm growth in a compact anoxic chamber. The combination of converting ammonia into nitrates and using them to help oxidize BOD leads to a significant decrease in nitrogen and phosphorus levels by the time the flow leaves the anoxic chamber.

 

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Figure 3A (left). Air and water spacers sandwiched between the membrane surfaces allow water and oxygen to circulate freely throughout the spiral-wound unit with maximum surface area for chemical interactions in a minimal volume of space.

Figure 3B (right) . The resulting envelope controls oxygen diffusion to support the growth of an ammonia-consuming biofilm that will eventually cover the entire membrane surface.

 

 

Reaping The Practical Benefits OF MABR

The concept of establishing a biofilm on a physical surface has already been proved in moving bed biological reactor (MBBR) applications for open-aeration basins. Flat-sheet MABR takes that concept to a new level by creating full biofilm coverage across a relatively large membrane surface area in a compact chamber. As a result, MABR technology has gained recognition to the point that it is included as an option in some of the simulation tools for WWTP operations. Documented performance in a series of demanding applications, worldwide, has demonstrated the advantages of flat-sheet MABR across a variety of operating environments:

 

Decentralized Convenience. Treating wastewater at its source minimizes the need for expensive infrastructure to collect and transport wastewater from many small, scattered locations to one large regional WWTP facility. Situating multiple packaged MABR systems that can run independently at local sites, then networking their monitoring and control systems to a central location, enables a single trained wastewater professional to manage multiple facilities. A part-time local maintenance person can handle daily inspections and resupply, while the experienced professional visits every two to three weeks, or as needed