Cutting operating costs in wastewater treatment requires a broader perspective than just pure energy consumption. While traditional cost analyses often focus on kilowatt-hours per cubic meter, the real savings come from optimizing sludge management, chemical usage, labor, and compliance. 

Membrane Bioreactor (MBR) systems consistently outperform conventional activated sludge processes (ASP) in these areas, lowering total operational expenses while delivering higher-quality effluent.

While energy is one of the largest cost drivers—often accounting for nearly half of a plant’s budget—it’s only one piece of the puzzle. MBRs optimize overall operational expenses by eliminating secondary clarifiers, minimizing sludge production, cutting chemical treatment needs, and streamlining maintenance through automation. These advantages often outweigh the higher kilowatt-hour demand per cubic meter.

For plant operators focused on total efficiency, the key question isn’t just how much energy an MBR system consumes. The important data is found in how that energy translates into lower long-term OPEX and a more future-proof treatment facility.

MBR Energy Demand Sets Up Long-Term Cost Savings

A conventional ASP system consumes between 0.3 and 1.2 kWh per cubic meter of treated wastewater. Most of that goes toward aeration.

An MBR system, by comparison, falls in the range of 0.8 to 1.5 kWh per cubic meter. The additional energy demand comes from two primary sources:

• Membrane aeration and scouring. MBRs need extra airflow to keep membranes from fouling.
• Higher pumping requirements. Unlike gravity-based clarification, MBRs rely on transmembrane pressure to filter water, which increases pumping energy.

At face value, it seems pricey. More kilowatt-hours, higher costs. But that’s only part of the picture.

How MBR Offsets Its Higher Energy Demand

Consider the below chart, with notional cost figures representing a facility’s given expenses on wastewater treatment. 

By optimizing sludge retention, eliminating unnecessary chemical treatments, and integrating advanced automation, MBR improves effluent quality while ultimately lowering long-term costs in ways traditional treatment methods cannot.

Less Sludge, Lower Costs

MBRs operate at a higher solids retention time (SRT), typically 20 to 60 days compared to 5 to 15 days in an ASP. That extended retention time allows for better biological breakdown of solids, meaning up to 30 to 50% less waste sludge is produced.

Less sludge means lower costs across the board—less dewatering, hauling, and disposal. Sludge management is a major operational expense, and reducing the volume of waste significantly cuts down on ongoing costs.

Fewer Chemicals, Simpler Process

MBR’s membrane filtration produces high-quality effluent without the need for additional clarification steps. That reduces or eliminates:

• Coagulants and polymers used in ASP secondary clarifiers
• Tertiary filtration chemicals for additional treatment
• Disinfection costs, since MBR effluent has lower pathogen loads and requires less chlorine or UV treatment

Cutting back on chemical dependency reduces both costs and process complexity, making operations more predictable and efficient.

Lower Labor and Maintenance

MBRs integrate easily with automation and advanced process control systems. Conventional ASP systems require frequent monitoring of clarifier performance and sludge settlement rates, leading to higher labor costs. MBRs, by contrast, can be run with fewer manual adjustments and better real-time optimization.

Membranes do require maintenance, but modern designs now last 7 to 10 years with proper operation. That’s a significant improvement over earlier systems and puts their lifecycle costs well within the range of conventional clarifiers, which require frequent repairs and operational oversight.

Optimizing MBR Energy Efficiency

Even though MBRs require more aeration, there are ways to cut down on energy use:

• Fine-bubble aeration increases oxygen transfer efficiency, ultimately reducing blower energy demand.
• Variable frequency drives (VFDs) on blowers and pumps dynamically adjust airflow and transmembrane pressure, reducing unnecessary power consumption.
• Automated dissolved oxygen (DO) control optimizes aeration setpoints, preventing over-aeration without compromising treatment.

Beyond aeration, MBR sludge—being more concentrated—is ideal for anaerobic digestion and biogas recovery, offering another pathway to offset energy costs.

Some treatment plants are now integrating renewable energy sources like solar or combined heat and power (CHP) systems to further reduce net power draw. In some cases, MBR plants are approaching net-zero energy consumption by pairing process efficiencies with onsite energy recovery.

Long-Term Cost Efficiency: More Than Just Energy

Upfront capital expenditures for an MBR system are typically higher than a conventional ASP system, yes. But that gap shrinks quickly when looking at total lifecycle costs, and that’s how responsible budgets are built.

MBR’s advantages include:

• Lower sludge disposal costs
• Reduced chemical consumption
• Fewer labor-intensive operations
• More consistent effluent quality, avoiding regulatory fines or retrofits
• Higher potential for water reuse applications

As regulations tighten on nitrogen, phosphorus, and suspended solids, conventional plants will need costly upgrades to meet stricter discharge limits. MBRs already meet those standards without additional modifications, making them future-proof against compliance changes.

When Does MBR Make Financial Sense?

MBR’s higher kilowatt-hour consumption doesn’t tell the full story. 

When wastewater plants factor in sludge handling, chemical reductions, labor automation, and long-term regulatory compliance, MBR’s energy trade-off often results in lower total OPEX.

This is ideal for facilities facing:

• High sludge disposal costs
• Tightening effluent regulations
• Land constraints that limit expansion
• The need for future water reuse capabilities

Looking at this through this lens, MBR is a long-term cost-saving strategy that doubles as a highly efficient and sustainable wastewater management solution for the future.

At the end of the day, the decision shouldn’t hinge on energy consumption alone. The real calculation is total efficiency, and on that front, MBR delivers.