Containerized MBR Vs. Conventional Activated Sludge: What Is the Difference?

When there are multiple wastewater treatment technologies that employ similar biological processes but use different equipment configurations and operating parameters, selecting the appropriate process can be challenging. Membrane bioreactor (MBR) and conventional activated sludge are two approaches that are frequently used.

The difference isn't just in the use of more modern equipment. Both are based on the use of microorganisms to treat the wastewater, but the separation of biological solids from treated water is different. In the case of containerized water treatment systems, this is important because it can assist the buyer in determining space requirements, treatment goals, system layout, and the day-to-day operation.

How Does Containerized MBR Differ From Conventional Activated Sludge?

The major difference is the solid/liquid separation process.

In conventional activated sludge, the microorganisms in the biological reactor decompose the wastewater's biodegradable pollutants. The mixed liquor then is passed into a secondary sedimentation tank. The sludge settles, the effluent flows out, and some of the sludge is returned to the biological treatment process.

An MBR plant includes a biological treatment stage, but solid-liquid separation is provided by membranes. Activated sludge and solids are retained by the membranes, and treated water can cross the membranes as permeate. This means the membrane module takes the place of the secondary sedimentation stage for solid-liquid separation.

What Changes When MBR Is Put in a Container?

Containerization does not change the biological process of treatment but changes the physical configuration and deployment of the treatment system.

A containerized MBR can utilize the biological treatment equipment, membrane modules, pumps, piping, valves, instruments and controls in a standardized container. Rather than building each significant process unit individually on location, a significant portion of the equipment can be fabricated in a modular fashion and shipped as a package.

QILEE's wastewater range includes containerized wastewater treatment systems, such as A/O + MBR and A²/O + MBR. They combine biological treatment and membrane separation and are designed for uses where a compact, integrated treatment arrangement is beneficial.

There is a difference between 'MBR' and 'containerized' – the latter refers to how the treatment equipment is packaged and deployed, the former to the treatment process itself.

MBR vs. Conventional Activated Sludge: Key Differences

The most significant difference is the separation step that takes place in the membrane.

Why Does the Separation Method Matter?

The separation method can impact the retention of biological solids during treatment.

In the conventional activated sludge system, the secondary clarifier must have good settling characteristics to keep the biological solids out of the treated effluent. The sludge characteristics, hydraulic flow conditions, or settling performance can thus influence the clarification stage.

An MBR uses membranes as a physical barrier. The membrane holds back activated sludge and suspended solids while allowing treated water to go through. Proper system design and operation can result in very low suspended solids and turbidity levels in the treated water stream.

The difference also impacts plant design. An MBR is not required to have a traditional secondary clarifier to achieve the same solid-liquid separation purpose, so the treatment facility arrangement may be smaller.

Which System Needs Less Space?

When a wastewater treatment plant needs to be installed at an existing facility or on a limited site, space can be a determining factor.

An MBR may be able to minimize the space required for the clarification step, and containerization may be able to fit several treatment units into a standardized unit. QILEE describes its containerized MBR systems as compact solutions and has standard 20-foot and 40-foot container sizes for various treatment capacities.

But a smaller piece of equipment does not equal no site preparation. However, space will still need to be allocated for connections, utilities, access, pretreatment if necessary, sludge handling, and maintenance.

The question is then not just about the MBR being smaller. Purchasers should evaluate the full treatment plan needed for their unique wastewater flow and treatment objective.

What About Effluent Quality?

MBR systems are able to produce treated water with very low suspended solids and turbidity due to their physical separation barrier. This can be beneficial if the project requires discharge or water reuse.

Activated sludge treatment may also be effective in conventional systems, with clarification occurring at the end. Other treatment stages can be added to the traditional biological treatment if further polishing or a higher level of treatment is needed for a project.

Process selection should not be based on effluent quality alone for either process. All of the conditions listed above must be considered in combination.

When Should Buyers Consider a Containerized MBR?

A containerized MBR can be a viable option when a project has limited space or requires a modular system, or the treatment system must fit in a compact container.

It can also be useful for decentralized facilities, for remote locations, and for industrial sites and/or projects where fast equipment deployment or future modular expansion is needed. The containerized wastewater systems from QILEE are available for various treatment configurations for municipal, industrial, decentralized, and other applications.

Where adequate land is available for conventional treatment units, and the treatment goals can be achieved through biological treatment and secondary treatment, conventional activated sludge might be acceptable.

The selection of equipment format should thus start with the wastewater and not the equipment itself.

What Should Buyers Compare Before Choosing?

However, prior to choosing MBR vs. conventional activated sludge, a potential buyer must compare:

• Influential: What pollutants, concentrations, and changes in flow will the system receive?
• Treatment objective: What must the discharge or reuse requirements be?
• Space available: Does the site have sufficient room for biological treatment, clarification, sludge handling, and supporting equipment?
• Operation: How much operator involvement and maintenance is feasible?
• Modular or relocatable system: Is a modular or relocatable system necessary for this project?
• Future needs: Will there be a need to expand treatment facilities in the future?
• Biological sludge and other residues: How will they be managed?

These factors should not be considered individually by a qualified water treatment systems manufacturer or supplier but rather together as a whole.

Conclusion

The main difference between a containerized MBR and a traditional activated sludge system is the separation of the biological solids from treated water. In conventional activated sludge, secondary sedimentation is used, while in MBR, membrane filtration is used. Containerization then changes the way the treatment equipment is packaged and deployed.

In projects where space, modular deployment, and/or membrane-based solid-liquid separation are critical, it may be practical to consider containerized water treatment systems with MBR.

For projects with traditional treatment facilities, conventional activated sludge might still be appropriate.

The starting point isn't so much the technology label as the wastewater characteristics, treatment target, site conditions, and operating requirements.