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Conversion of Thin Stillage to Methane to Increase the Net Energy Balance of Corn Ethanol

Converting thin stillage (a major byproduct of the dry-mill corn ethanol process) to methane for use in the ethanol production process could increase the net energy balance ratio of corn ethanol at a conventional from dry mill from 1.26 to 1.70, according to a new report published online 5 August in the journal Environmental Science & Technology.

The study by a team from Washington University in St. Louis; Viable Bio-Projects LLC; and GTL Resources evaluated the conversion of thin stillage in laboratory-scale thermophilic anaerobic sequencing batch reactors for conversion to methane. They found that augmentation of cobalt as a growth factor to the thermophilic anaerobic digestion process is required.

After reaching sustainable operating performances, the methane potential in the reactors was 0.254 L CH4/g total chemical oxygen demand (TCOD) fed. Together with a reduction in the mass of solids that needs drying, methane generation translates to a 51% reduction of natural gas consumption at a conventional dry mill, which improves the net energy balance ratio from 1.26 to 1.70.

At the design hydraulic retention time of 10 days, the digesters achieved TCOD, biodegradable COD, volatile solids, and total solids removal efficiencies of 90%, 75%, 89%, and 81%, respectively. We also found that struvite precipitation occurred in the thermophilic digesters during the course of the study, resulting in possibilities for nutrient recovery.


  • Matthew T. Agler, Marcelo L. Garcia, Eric S. Lee, Martha Schlicher, and Largus T. Angenent (2008) Thermophilic Anaerobic Digestion to Increase the Net Energy Balance of Corn Grain Ethanol. ASAP Environ. Sci. Technol., doi: 10.1021/es800671a


Jeff Baker

Grow Algae on Corn Ethanol Waste Products

The anaerobic digestion of waste products into biogas methane used for production power is right on. Now the next step is to grow algae on the nutrient rich digester effluent (leftovers). To break them down faster, use ultrasound fractionation. Also mitigate and exploit the other waste products of corn ethanol production: CO2, waste heat, waste water effluent, exhaust from burning natural gas and biogas. Recycle these to feed nearby algae. When harvesting and processing the algae, use ultrasound fractionation again to separate the components. From the algae oil, produce biodeisel for local farmers, more ethanol from the starch, and animal feed from the protein residues. And or put all or part of the algae in the digester to make more biogas to replace all the natural gas and or to cogenerate electric power. Gasification is also an option in place of digestion.


Good ideas Jeff. I'd like to see an algae/corn pilot plant get up and running. Eventually however these corn ethanol plants will convert to cellulosic, which may be able to utilize your algae suggestions. Presently it looks like misanthcus is the leading energy crop - though good arguments can be made for switchgrass as well.


Thin stillage is worth more as a product than as a fuel. There are better ways to fuel the ethanol process.

Healthy Breaze

Better still, feed it to cows and collect their methane. Then you get the milk, eventually the beef, and some additional ethanol.


@Healthy Breaze

First you have to write a job description, dairy farm fart description. Education: BA udub


Healthy Breeze – Another good idea. What you are describing is an integrated biorefinery, where corn ethanol byproducts are fed to nearby dairy cows or cattle to produce milk and meat. Then their manure is digested into biogas methane for refinery production power. There are several of these plants operating in Texas. This is where the option comes in to grow algae on the leftover digester effluent.


Jeff, those are good ideas, has there been any research done you can point us toward regarding growing algae on digester effluent? The digested thin stillage effluent is fairly rich in nutrients, which may be helpful. One would also hope that digestion of thin stillage would enable increased water recycle within the process, although the feasibility of this remains to be seen.

Paul, you make an important point as well. It is likely that future changes in corn ethanol production will be economically driven. The integrated digestion of thin stillage makes energy-intensive drying of thin stillage unnecessary, freeing that energy (already recycled from other processes) for other uses. Also, the remaining feed that is produced being higher value and the likely continued increase in the cost of natural gas may contribute to better economics. These are issues that should be studied further in an integrated system at scale(along with potentially higher water recycle rates) to know whether these additional benefits make digestion of thin stillage more valuable than drying it as an animal feed.

Mark M

Ethanol production has never been single product based and nor should it, integrated production is the only way. Distilled dried grains are fed to cattle as a protein feed and the wet stillage can be used for fertilizer. Small scale operators and most of the Brazillian operators work this way. The problem is mainstream media and the 'status quo' don't seem interested in the full story just the sensational headlines and they pick what suits them.
Subsidies also don't encourage integrated production.

Read David Blume's 'Ethanol can be a gas' to learn how it's made, the history and potential.


An earlier post includes an explanation of the energy cost of processing thin stillage to produce low-value animal feed:

"The dry-grind ethanol production process grinds corn kernels and adds water and enzymes. The enzymes break the starches into sugars, which are fermented with yeasts to produce ethanol.
The ethanol is recovered by distillation, but there are about six gallons of stillage—which contains solids and other organic materials—left over for every gallon of fuel produced. Most of the solids in the stillage are removed by centrifugation and dried into distillers dried grains that are sold as livestock feed, primarily for cattle.
The remaining liquid, known as thin stillage, still contains some solids, a variety of organic compounds from corn and fermentation as well as enzymes. Because the compounds and solids can interfere with ethanol production, only about 50% of thin stillage can be recycled back into ethanol production. The remaining thin stillage is currently concentrated by flash evaporation—an energy-intensive process—and blended with DDG, producing DDG with solubles (DDGS).
DDGS is used for livestock feed, but is low in essential amino acids, e.g., lysine, limiting its usage, particularly for hogs and chickens.

At current production levels, eliminating the need to evaporate thin stillage would save ethanol plants up to $800 million a year in energy costs."

In the previous post, the researchers added a fungus, Rhizopus microsporus, to the thin stillage and found it would feed and grow:
"The fungus removes about 80% of the organic material and all of the solids in the thin stillage, allowing the water and enzymes in the thin stillage to be recycled back into production.

The fungus can also be harvested. It’s a food-grade organism that’s rich in protein, certain essential amino acids and other nutrients. It can be dried and sold as a livestock feed supplement. Or it can be blended with distillers dried grains to boost its value as a livestock feed and make it more suitable for feeding hogs and chickens."

It is encouraging to see researchers actively investigating ways to reduce fossil fuel input or increase co-product animal feed output from domestic ethanol production.

Jeff Baker

To MA and others:

(1) Utah State University Biofuels Team using an Andigen digester,. operating successfully in conjunction with dairy operations in Utah, Idaho, and California. “Solar bioreactors can be symbiotically co-located next to commercial anaerobic digesters to sequester CO2, and utilize nutrients and methane from digester effluent to accelerate algal growth and enhance (year round) biofuel production.” Search USU Biofuels Initiative.

(2) Alexandra D. Holland, Chemical Engineering, and Joe M. Dragavon, Chemistry, and Eric M. Stuve, University of Washington, Seattle, WA:
“In this process, the AD methane is used to produce electrical power, and the resulting carbon dioxide is used to enrich the algae reactor. The nutrient-rich AD effluent is fed to the algae, thus by-passing the need to purchase fertilizer.” Search: Bio-Oil Production from Algae Grown on Dairy Anaerobic Digestion Effluent.
“To grow the algae, we are proposing to use AD effluent and carbon dioxide from the AD process as nutrient sources. TAG from the algae will be extracted enzymatically, and used for biodiesel production on the farm.” Search: IGERT Graduate Program :: Student Bios Methane Algae

(3) Methane Digesters for Fuel Gas and Fertilizer by L. John Fry (and Researchers at Berkeley) a working model.

Search: Methane Digesters for Fuel Gas and Fertilizer - Chapter 7-8

(Scroll down to: Sludge-Algae-Methane: Figure 17 Flow Diagram and description under diagram)

(4) Participants will focus on animal waste – using it to grow algae in the production of biodiesel, or anaerobically digesting it to produce methane, for example – and the fuels that can be generated from waste materials. University of Georgia engineering professor K.C. Das and Universidad Autonoma de Coahuila professor Nagamani Balagurusamy in Mexico:

Search: University of Georgia and Mexican Universities Focus on Production of Biofuels In the Agricultural Sector (sci ence dai ly)

(5) Algae being grow successfully on sewage effluent: Old Dominion University: ODU scientist, Patrick G. Hatcher, executive director in association with a newly formed group of university scientists, called the Virginia Coastal Energy Research Consortium.
Search: ODU experiment on turning sewage into algae-based biodiesel is flourishing

(6) Growing wild algae on Marlborough’s NZ municipal sewage effluent. Commercial open pond systems next.
Search: Test Drive of Aquaflows Wild-Algae Biodiesel
Waste and byproducts to digester biogas and power.

Summary: Effluent to algae. Algae to value added products. This is a whole industry in itself. To mitigate waste effluent at dairy farms, feed lots, poultry and hog farms, food processors, sewage disposal plants, municipal solid waste dumps, paper mills, and corn ethanol refineries etc.

Jeff Baker

To Polly and others:

Polly –

Thank you for clarifying what thin stillage is. Basically it is something like 90% to 95% liquid effluent with the rest suspended corn solids. And to retrieve that small percentage of solids is so energy intensive that it is NOT cost effective. Thus, using Thin Stillage as a nutrient rich effluent to grow algae is a way to mitigate the waste. Digester effluent will now become a medium for producing value added products. By equipping corn ethanol refineries with algae production, we will take the industry to a much higher level. Perhaps, to where the energy balance is over 5 to 1 and the current issues have been addressed. One small pilot plant is needed.

How you handle the algae would depend on what you want to use it for. Three categories of algae: (1) A 96% starch variety is suitable for more ethanol production, to add to the corn ethanol stream, with the remaining 4% going to a parallel high protein animal feed supplement sold along side or mixed with distillers grains. (2) A 50% oil variety which is typically the one that researchers are lusting after. Make bio-crude or biodeisel out of this one, which can be marketed regionally, or better yet, sold back to the local corn farmers. The byproduct starch then goes to ethanol, and the residual proteins go to animal feed. (3) A 60% protein variety such as spirulina or chlorella, which would be best if supplying a feed lot or adjacent dairy farm, for example, was the main goal. With the starch going to more ethanol and the oils going to biodeisel. Or throw all or part of the algae back in the digester, and have the option of using more biogas to offset production power, or to co-generate heat and electric power for the plant or for the grid. Or, if your corn ethanol plant is a hybrid plant equipped with a gasifier, then gasify the leftovers. Lots of possibilies.

There are 162 ethanol plants. 1200 landfills, 40% of which have been converted to produce power from biogas methane, with the effluent untapped. Thousands of sewage disposal plants that are paying millions of dollars to dispose of effluent, hundreds of paper mills with waste effluent, thousands of food processors with waste effluent, and thousands of dairy farms, feed lots, poultry and hog farms with waste effluent. Much of this is polluting our waters and constitutes a ground water run-off problem, which can be mitigated by growing algae on the waste effluent. Its a Big Win Win.


Have you contacted any of the researchers to suggest growing algae on the nutrient rich digester effluent?

I recently attended a bio-energy exhibition where companies were showing and selling their products.
There was a company selling an algae growing and harvesting system using large clear plastic pipes in a circuit.
The capital cost was so high that the resulting fuel oil was completely uneconomic.
How close is algal fuel oil to being commercially viable?

Concern has been expressed about the use of fertilizer derived from fossil fuel.
Conventionally, AD effluent is used as fertilizer.
If you used the AD effluent to grow algae, could you provide fertilizer?

Running anaerobic digesters on a farm requires expertise and investment.
Once that investment has been made and the expertise mastered, it would sensible to maximise the productivity of the digesters.
The article states that conversion of thin stillage to Methane will displace 51% (not all) of the natural gas consumption.
I wonder how much methane could be generated by adding the corn stover to the digesters.
As the AD effluent can still be used as fertilizer, there would be no loss of soil condition by digesting the stover instead of plowing it in.

Likewise, it would be interesting to know how much methane can be generated from the manure of the cattle fed by the DDG co-product.

It seems likely that the ethanol industry will gradually move to an integrated bio-refinery system.

Jeff Baker


There are now over 70 companies, universities and labs doing R&D on Algae. Three companies have announced commercial size projects. Hopefully these 3 will be successful. And more will be rolling out their technology. There will be new and better ways of digesting, producing algae, processing the algae, and implementing the highest use for the algae. Bring the optimal components together, and algae could be commercially viable right now. You will see algae configured in different ways. For example, one company grows a thousand times more algae in the dark by feeding it sugar. Could you leverage corn sugar at an ethanol plant to grow algae at night? Or maybe even 24 hours a day? Maybe digester effluent enhanced with corn sugars can be used to feed algae, and then hundreds of times more fuel will be made from the algae instead of the corn. This is something we should experiment with. Very exciting.

The fertilizer research is also important. I’m sold on ultrasound fractionation, which breaks the effluent up into smaller particles which should speed-up digestion. This will also speed-up the absorbtion of the nutrients by the algae or other crops. An ultrasound fractionated slurry of processed effluent and algae would possibly make a very good fertilizer. But it would also make a very good fuel component, without even being refined as a conventional fuel is refined. And whats unique is, at a corn ethanol plant, equipped with a biogas digester, you have onsite methane and onsite ethanol to mix with the slurry. Imagine if you could power the plant on a vaporized blend of 75% waste water and 25% algae slurry enhanced with digester methane.

Regarding the use of stover, I think 50 miles may be too far to truck it. Maybe within a radius of 5 or 10 miles it could work. You have to load it, truck it, unload it, store it, reload it and then processes it. I’m not sold on that. Maybe pyrolize it in the field, and make bio-crude out of it, which would be easier to ship and store. But pyrolisis is an extra process, and you still have to handle the stover, pump the bio-crude, truck it, store it, and pump it again for refining. Pulverizing the stover in the field, then shipping it, then adding it directly from the field to the digester as you need it might work. But above all, I like onsite algae production much better. Grow it onsite. Use it as you make it.

Yes, the industry must integrate to evolve. You have a lot of insight. POB 18902 AZ 85731

Henry Gibson

There is not enough corn plus biomass of any kind to make a substantial contribution to the US energy market and not enough land. Though waste organic materials that would go into a landfill should be converted to fuels first instead of getting methane out of landfills.

The soil needs organic and inorganic chemicals as fertilizer. There are microbes that need organic materials to supply energy to fix nitrogen from the air. Every atom of potassium in the corn comes from the soil. Put all of the left over stuff on the fields.

I can understand making corn ethanol for people to drink. Corn ethanol was made in the 1700s because it was too expensive to transport corn to market. High taxes on the stuff led to the whiskey rebellion.

If you drink ethanol there are many dollars of tax per gallon on it. If you put it in your car there is at least a dollar of subsidy on it. I wonder if there is a law against extracting ethanol from gasoline to drink.

Most commentary is that butanol is a better fuel for common cars and that butanol can be made from the same feed stocks. Butanol can even be burned in diesel engines better than ethanol.

The US economy would get more for its money if coal or natural gas were made into methanol. ..HG..

Account Deleted

Few months back, I met one of my friends, who are an owner of a Distillery in Bangladesh. They produce Ethanol by their factory using corn starch. I think they mix many other things with Corn starch (maybe urea and other chemicals) and make a fermentation and then produce the Ethanol to produce Alcohol (however I am not very sure what they mix for the fermentation, but all I know is they put lots of Corn Starch to it).

Since the owner of the factory is my friend, he told me to take out the entire waist (Stillage/ Sludge- I think it is called yeast Stillage from Distillery Fermenters, for free f charge. He told me this could be use as Poultry Feed (Chicken or Cattle).

Friends, All I want your help is to the above process. I saw in your documentary that this can be used as to produce a DEMAND PRODUCTS as methane. Sir, please tell me a way, what and how we could do a production from the sludge. Moreover I saw this sludge of my friend’s factory and the thickness is not there. It is almost 02 milk powder spoons mix with a glass of water. So this is how this sludge looks like.

I hope you understand my efforts and I hope you will give me the full support. I need to talk to you regarding this business and I need your assistance to start this project from a minimum investment. We will talk this further and discuss how we could win this together. My email is:

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