How Muscatine, Iowa, turns food scraps and wastewater into clean energy

Posted: September 09, 2026

Cows are ruminants, a suborder of hoofed, cud-chewing mammals. Other ruminants include goats, sheep, and their more exotic cousins like the moose and giraffe. What really typifies the suborder, though, is the rumen, the first chamber of a four-chambered stomach. Here in the rumen, digestion becomes a team sport: one cow plus billions of microbes. Some break down tougher fibers through fermentation; others, called methanogens, consume the resulting compounds and produce methane. Finally, that methane escapes the cow (contrary to popular belief) mostly by way of belching. It’s a process called anaerobic digestion. Grass in, methane out.

Long ago, humans borrowed the idea of anaerobic digestion, first for sewage treatment, later for energy. Today, modern renewable natural gas (RNG) plants harness the same biological process, except at an industrial scale. In place of a rumen, an RNG plant uses what’s called an anaerobic digester—a big vat-like, dome-topped vessel that provides the warm, oxygen-free environment that microbes need to do their best work.

But unlike a cow, which enjoys the simplicity of a fairly narrow diet, modern digesters are increasingly being asked to process a considerably more varied diet. As communities, farms, and industries look for ways to divert more organic waste from landfills and put it to productive use, digesters are taking on feedstocks far more complex than the traditional sewage sludge. Turning an ever-changing mixture of organic waste into consistent, pipeline-quality fuel is where the real engineering challenge begins.

A brief history of anaerobic digestion

Humans have been operating digesters for a surprisingly long time now. The first known digester was built in 1859 at a leper colony in Bombay to treat sewage. By 1895, engineers in Exeter had begun capturing the resulting biogas from the sewage system to light city streetlamps.  Anaerobic digestion had evolved from a sanitation technology into an energy technology, but its diet remained much the same: a single, relatively consistent stream of sewage sludge.

Anaerobic digestion is ancient. Industrial anaerobic digesters are old. What’s relatively new, however, is the rise of a process called co-digestion: feeding a digester more than one type of organic waste at once—food scraps alongside manure, say, or dairy byproduct alongside sewage sludge—rather than a single, consistent input.

That shift brings us to one of the biggest challenges facing modern anaerobic digestion: heterogeneous feedstocks.

The trouble with a diverse diet

Co-digestion may sound like a small shift, but it fundamentally changes the operational challenge. Every organic waste stream arrives with its own chemical makeup—a different balance of sugars, fats, proteins, moisture, acidity, and nutrients. Those differences affect how quickly microbes digest the material, how much methane they produce, and how stable the digestion process remains. The challenge is creating the right conditions for billions of microorganisms to keep doing their work despite constantly changing ingredients.

If you replaced a cow’s usual lunch, for instance, with a novel mixture of ice cream, cooking grease, brewery byproduct, and expired produce, that’s not a healthy rumen, nor a happy cow. Anaerobic digesters are susceptible to the same finickiness. Feed a digester too aggressively and volatile fatty acids can accumulate faster than methanogens can consume them. As acidity rises, methane production falls, microbial communities become stressed, and in more catastrophic cases the digester can fail in spectacularly off-putting fashion, foaming over with a pungent mess of organic slurry.

Every year, the United States generates between 73 and 150 million metric tons of food waste. Much of that waste ends up in landfills, where it decomposes and produces methane anyway, which has a global warming potential roughly 86 times that of carbon dioxide over a 20-year timeframe.

Capturing that methane through anaerobic digestion does two things at once: it prevents emissions that would otherwise escape into the atmosphere, and it transforms an existing waste stream into a valuable source of energy.

The Muscatine project

The project and the players

In the heart of agricultural country, the Iowa Wastewater and Waste to Energy Research Program (IWWERP), led by Craig Just of the University of Iowa’s College of Engineering, is working to make the complex process of co-digestion more predictable, efficient, and reliable.

IWWERP partnered with the City of Muscatine, along with AVEVA, Schneider Electric, and other technology and service providers, on a project at the Muscatine Water Resource Recovery Facility (WRRF). The facility already had two anaerobic digesters, each capable of holding roughly 1 million gallons of slurry. Traditionally, those digesters were fed wastewater sludge produced in the treatment process. This project brings another ingredient into the mix. Actually, many new ingredients: organic waste hauled in from across the region.

Instead of going to the landfill, organic waste—from sources ranging from local restaurants and grocery stores to large food and beverage manufacturers—is diverted to regional organic recycling centers. Food-processing byproducts, off-spec batches pulled from production lines, unsold fast-food meal deals, dog-biscuit rejects, the contents of the diner’s grease trap—it’s all hauled to the recycling center, depackaged as necessary, prepared, and transported to the WRRF, where it’s blended with the wastewater sludge into a high-strength waste slurry. Then it’s off to the digester, and from the digester: biogas.

Today, the WRRF uses some of this biogas onsite to fire its boilers, reducing its costs and its carbon footprint. Meanwhile, the city is working with regional energy partners to upgrade the biogas to RNG, which can be injected into a natural-gas pipeline or compressed for use as vehicle fuel. The city might use this RNG in any number of ways: as fuel for municipal vehicles, or to generate electricity in a microgrid; it can sell it into pipelines for added revenue, or sell it as vehicle fuel and help stabilize rates.

For the project team, the opportunity was to bring all these existing resources together: existing digesters and wastewater infrastructure, existing sludge, and a steady regional stream of organic waste that might otherwise have gone to the landfill.

How the system works

First, incoming organic slurry travels into the digester via a pump. Mounted on that pump is a spectrometer, a type of optical sensor that uses visible and infrared light to measure the slurry’s spectral signature. The system takes a new measurement every minute. Software translates those spectra into estimates of the slurry’s composition—how much fat, protein, carbohydrate, and other material it contains, as well as how concentrated the waste is.

A second sensor monitors conditions inside the digester itself. Together, the sensors provide a picture of both sides of the process: what operators are putting in and how the digester is responding. The project also brings in the facility’s existing SCADA data, including hauled-waste flow, sludge flow, biogas production, and other operating conditions.

All this information comes together in CONNECT, where data from the facility and the University of Iowa can be shared and analyzed in the cloud. Operators can see it laid out as time-series charts and tables. A high concentration of volatile fatty acids? That tells operators that they should dose the reactor slowly. A more alkaline effluent? That lets operators know they have a healthy buffer against sudden pH swings.

Still, these dashboards are only as useful as an operator’s ability to read them. Without additional training, the visualizations resemble a mess of squiggly lines. That’s where the system’s machine-learning and advanced-analytics models come in, combining feedstock composition, SCADA data, lab measurements, and digester history into a direct recommendation for how much high-strength waste to feed into the reactor, and how quickly.

Operators can accept the recommendation, adjust it, or disregard it based on their own read of the facility. The system doesn’t cut the human operator out of the loop; it informs, narrows, and improves the decisions they make every day.

What’s next for IWWERP and Muscatine?

High-strength waste is so high-strength that effectively managing the digestion process can require adjustments several times a day, or even hourly. No matter how experienced the operator, there is a practical limit to how much information one person can monitor and how quickly they can respond. That’s why, ultimately, IWWERP’s vision is to connect the predictive model directly to the digester’s controls.

This is the pathway to an operational digital twin. The digital twin model would maintain a continuously updated picture of the physical digester, taking in information about the incoming feedstock, conditions inside the reactor, and the facility’s other operating data. Rather than simply telling an operator what might happen next, it could determine the appropriate response and adjust the feed pump accordingly.

Operators would continue to oversee the system, set boundaries, review recommendations, and intervene when necessary. The point is to let the system handle routine adjustments at a frequency that human operators can’t otherwise sustain.

From natural process to industrial scale

The rumen is a wonder, a natural bioreactor perfected by millions of years of evolution. Over the centuries, humans have iterated on the idea and scaled it from small digesters treating sewage to industrial facilities processing millions of gallons of organic waste. Now, by getting better at managing co-digestion, we may be able to take that process further, not by building bigger digesters, but by unlocking more value from the capacity we already have.

All around the country, there are municipalities like Muscatine with anaerobic digesters already built and much of their capacity going unused. The EPA estimates that, on average, existing digesters are only operating at about 41% capacity. In other words, the infrastructure is there. With real-time platforms like the one IWWERP and its partners are developing, we could put it to use, diverting more waste from the landfill, rerouting it to existing facilities, and turning it into renewable natural gas.

Muscatine offers a model other cities and towns can adopt and adapt to rethink organic waste, reducing landfill emissions, lowering energy costs and carbon footprints, all while creating new revenue. The result is a circular approach that transforms unpredictable waste streams into a manageable, valuable resource.

To learn more about how IWWERP is using cloud-based machine learning to tackle the challenge of heterogeneous feedstocks, watch Craig Just’s full presentation at AVEVA World Milan.