After You Own It: Cutting OpEx and Scaling Legacy Plants with Modern MBR Technology
You bought the plant. Now it’s on you.
The 24/7 performance, the operating budget, the compliance record—it all becomes your responsibility after the ink dries. For private utility owners and operators, legacy infrastructure isn’t a sunk cost. It’s an opportunity. And with the right retrofit strategy, that aging wastewater treatment facility can become a stable, revenue-generating asset.
Here’s how modern membrane bioreactor (MBR) technology makes it happen.
Start with the Blowers
Energy is usually the biggest line item on the OpEx sheet, and blowers are the main culprit, often chewing up a significant portion of a plant’s electricity. Most systems still run on coarse-bubble diffusers and fixed-speed motors, wasting energy all day long.
The upgrade path is straightforward: swap in fine-bubble grids and tie variable frequency drives (VFDs) to real-time dissolved oxygen (DO) sensors. You’ll see cost savings right away. And if you’re dealing with shallow basins that were never designed for efficient oxygen transfer, a move to high-MLSS MBRs can shrink your basin volume and drop blower horsepower even further.
Imagine a small 0.3 MGD sequencing batch reactor (SBR) in the Rockies, one that might retrofit to a modular MBR: even with the addition of membrane scour blowers, the plant will save money in its first year because basin volume will drop considerably. This is how you turn inefficiency into leverage.
Trim the Chemical Waste
In legacy wastewater treatment plants, clarifiers are often propped up with coagulants to keep suspended solids (sludge) from floating. Problem is, dosing becomes guesswork. Influent strength fluctuates, operators change, and before long you’ve got chemical “creep”—more alum, more polymers, and no clear reason why.
MBRs sidestep this entirely by using membrane filtration instead of gravity settling. That alone cuts coagulant use dramatically. Combine that with ORP-controlled disinfection, and many facilities report a major reduction in chemical costs. Less guesswork. More precision. Better margins.
Half the Sludge, Half the Headaches
A major hidden cost in wastewater operations is solids handling—and it adds up fast in remote or resort communities where trucking and disposal are both expensive and logistically complex. One of the most compelling benefits of switching to an MBR is the significant reduction in biosolids yield.
In a conventional activated sludge (CAS) system treating 250,000 gallons per day, you might waste 12,000 gallons daily of liquid sludge with 0.5–1% solids. An MBR operating at a longer solids retention time (SRT) can cut that in half—to around 6,000 gallons per day—without sacrificing performance. If the facility has a press that thickens to 16% solids, you’re still dealing with around 1,000 gallons per day of concentrated material. Further dewatering to cake could produce roughly 3 to 4 cubic yards per day of dry biosolids—and that’s still less than what a CAS system would generate.
That volume difference has real-world impacts. Solids handling costs can, in some cases, be cut in half or more through a combination of reduced biosolids yield, less labor, the reduction or elimination of polymer dosing, and fewer truckloads out of the plant.
One Operator, Many Plants
Labor is getting harder to find and harder to afford.
SBRs often need manual DO adjustments multiple times per shift, which doesn’t scale when your most experienced operators are heading for retirement.
Modern MBR skids come with PLC-based control, automated clean-in-place (CIP), and full SCADA dashboards. That means one licensed operator can manage multiple plants with a tablet—checking transmembrane pressure (TMP) trends, tweaking setpoints, and handling alarms without leaving their truck. You get modern staffing flexibility without sacrificing compliance, effluent quality, or treatment efficiency.
Don’t Guess. Model the Financials.
Retrofits live or die on financial modeling. Run a 20-year net present value (NPV) comparing your options:
- Stick with the lagoon: Energy bills climb, chemical use spikes, and new nutrient limits loom.
- Upgrade clarifiers and add tertiary filtration: You’re into it for $2 million (or more), and the chemical spend doesn’t go away.
- Convert to modular MBR: CapEx may hit a few million, but OpEx drops considerably and each treatment plant capacity doubles.
When you can pencil in a seven-year payback and pair it with interest-only construction financing, it’s not a tough call.
Turn Reuse Into Revenue
Treat to Title 22 and you’ve got a product—one you can sell. In California (and similar states), Title 22 of the California Code of Regulations sets the standards for using treated water for non-potable purposes such as irrigation, industrial uses, and dust control. If you treat to this standard, the effluent is officially considered “recycled water” and can be sold or distributed for permitted uses.
Golf courses will seek you out. They often prefer recycled water due to irrigation restrictions.
Data centers use large amounts of water for cooling; many in water-stressed regions and will pay for recycled sources for their cooling tower supply.
Construction companies will pay for recycled water for dust control and concrete mixing, especially in drought-prone regions..
We’ve seen industrial wastewater treatment and municipal wastewater treatment utilities in arid counties generate major revenue opportunities year over year simply by monetizing recycled water that used to be a disposal problem. That revenue is considered non-rate (i.e., not from ratepayers), which can improve financial stability and fund infrastructure upgrades.,.
Track the Metrics That Matter
In the first year post-acquisition, focus on the KPIs that directly impact performance and profitability. Start with these five::
- Blower Efficiency: Are your blowers hitting their kWh/BOD removal target? Inefficiency here can quietly drain your O&M budget.
- Polymer Usage: Is your polymer dose drifting? Time to check the influent; variability could signal upstream issues.
- Sludge Hauling: Are you hauling more than projected? Reassess and optimize wasting strategies and sludge thickening.
- Permit Compliance: Is any permit parameter creeping past 80% of its rolling-quarter threshold? Get ahead of violations before they cost you.
- Reserve Capacity: How much reserve capacity do you really have for new connections? Validate it before committing to growth.
Monitor these monthly. They’ll drive smarter ops decisions and give you the data backbone to justify uture CapEx, staffing, or rate adjustments.
Legacy to Leverage
An aging sewage treatment plant doesn’t have to be a liability.
With the right combination of smart energy upgrades, MBR retrofits, and automation-driven staffing, you can flip the script—cutting OpEx, hitting compliance targets, and creating long-term revenue opportunities through water reuse.
At IWS, we build small footprint, modular MBR packages and design retrofit strategies that make these results predictable. You bought the plant. Now let’s make it perform.