Beating Back Bad Bugs

Bacterial contamination is one of the banes of ethanol production. Producers spend a considerable amount of money on sanitation and antibiotics trying to control bacteria in their fermentation tanks. A new system will not only reduce bacteria in the fermentation tanks, but also prevent re-infection. As a bonus, the new system leaves distillers grains free from antibiotic residues.
By Jerry W. Kram | July 08, 2008
To make ethanol, producers must create a pleasant environment for a living creature, yeast, which does the heavy lifting of converting sugars to alcohol. Unfortunately, other organisms also find the inside of a fermentation tank to be hospitable and compete with yeast and inhibit their growth. That lowers an ethanol producer's efficiency and production.

To combat the growth of bacterial invaders such as Lactobacillus and Acetobacter which produce organic acids that inhibit ethanol production, plants have resorted to dosing their tanks with antibiotics.

Different plants have various levels of contamination problems depending on their age, design and maintenance practices. In some large plants more than a half-million dollars can be spent per year on antibiotics to control infection problems and the resulting organic acid levels. However, this is a short-term fix that allows tanks to become re-infected and leaves residues in the distillers grains that has made some feedlot operators uneasy.

A New Approach
PureMash is a system developed by Resonant BioSciences LLC, which greatly reduces bacterial contamination in ethanol plants without leaving antibiotic residues in the distillers grain, says company President Allen Ziegler. The system is based on a water purification technology that uses chlorine dioxide (ClO2) and hydrogen peroxide to kill bacteria. Yeast turned out to be resistant to the chemicals' antiseptic properties. "We came across this technology a few years ago when I was working for a major brewer," Ziegler says. "When they went to aseptic brewing they started having all kinds of infection problems. We found that yeast could stand up to the chemicals to a high degree where the other microbes could not. We also found [the chemicals] can stand up to a high organic matrix."

The PureMash system is designed to produce ClO2 without unwanted byproducts such as chlorine and chlorites. ClO2 also attacks biofilms which coat the insides of tanks, pipes and other equipment. "Where we found most of the infections coming from in these plants is actually the heat exchangers," Ziegler says. "A lot of the antibiotics will not get [those infection sources]." Bacteria in the biofilms are more resistant to antibiotics and antiseptics and can be a source of re-infection in an ethanol fermentation tank. "Because of production reasons, ethanol plants don't go through the levels of cleaning you find in a brewery, so they wind up leaving lots of biofilm in the heat exchangers," he continues. "When we directed our technology to the heat exchanger and then the fermentor we were able to clean up that heat exchanger and a lot of the source of the infection.

"What we try to do is not just clean the common areas you treat but our standard package also goes into the CIP (clean in place) loop. As we've proved in breweries, PureMash does a good job in removing biofilms. What they do now is a caustic wash that isn't very effective against biofilms. But adding our system to the final rinse gets to the problem at the source and doesn't treat just the symptoms."

The system is integrated into a plant's distributed control system allowing full control and monitoring of the process. It also gives the plant a paper trail to go back and investigate in case any problems crop up. "It helps you run the plant too," Ziegler says. "From an engineering and operations standpoint, it really lets you look to see where you have any issues in real time. So it is really like looking at a whole other way of running and operating a plant while dealing with unwanted microbiology."

The PureMash system is mounted on a pallet-sized skid, which makes it easy to integrate into the water systems of existing plants. The input chemicals are relatively safe and the system generates the ClO2 on-site, unlike systems using chlorine gas. "You cannot ship or package chlorine dioxide," Ziegler says. "The chemistry is much like (generating) ozone. Some people are concerned because it has chlorine in the name. Even though it has chlorine in the name it has nothing to do with chlorine chemistry and doesn't react like chlorine."

It is also an improvement on ozone or chlorine as a disinfectant because it is much more selective. ClO2 doesn't react with organics such as starch and sugar or compounds such as ammonia, like pure chlorine does, so it can be used directly in the fermentation process. "Chlorine dioxide is better because ozone wants to react with everything," Ziegler says. "But they have similar chemical characteristics. They are both dissolved gases and are not chlorinating agents." Ziegler says the company has also worked closely with engineering firms to confirm that the ClO2 doesn't harm stainless steel pipes, tanks and other equipment.

Because the system is integrated into the regular operation, plants don't have to go off-line to be disinfected. "You don't have to break everything down," Ziegler says. "You don't get it all right away, but within a week or two you see an effect."

Successful Tests
Resonant BioSciences tested the process in a fermentation laboratory in Montreal. In the summer of 2007, the company tested the system in plants that had bacterial contamination problems. Some of the plants had been having recurring problems for several years. The results were dramatic. "The plant we went into gave us their worst fermentor," Ziegler says. "It had [organic acid levels] a good 30 [percent] to 40 percent higher than the other three fermentors. In a period of just three fermentations, we took that fermentor that was notorious over the past three or four years and got its [organic acids] down to 30 percent lower than the other three fermentors. They had spent years and a lot of money trying to address the problem. We were able to do it in one week."

The company is conducting tests in plants that have minimal problems with bacterial contamination to confirm the system's ability to increase ethanol production in clean plants. "The first plant we went into had some mild infections and we were able to demonstrate significant ethanol gains," Ziegler says. "Even in the lab in experiments with no organic acids present we're seeing an ethanol gain. What we are trying to do is quantify those gains. We have four plants signed up for much more indepth studies. Two of the plants are very clean and the other two have some challenges. We know what we can get out of an infected plant, but we're not sure what we can give you out of a very clean plant."

The speed of the PureMash system will also be one of its selling points, according to Ziegler. But the real gains come from the higher, more consistent levels of production that
come from running a consistently clean system. The test plants using the PureMash system had more consistent levels of ethanol production even if they didn't suffer from noticeable infection problems. "If you have an infection, this will take it out immediately as opposed to antibiotics," Ziegler says. "It gives you a way to rid yourself of antibiotics, and it gives you a much better performing plant. You can address infections in all areas of the plant, not just where it is obvious. We try to go to the source of the infection and not just treat the symptoms all the time."

With the positive results from the testing, PureMash received U.S. EPA registration in February and is now commercially available to dry-grind ethanol producers through Ethanol Technology of Milwaukee, Wis. Ten plants signed up to have the system installed in the first few months that it was available. The system can be purchased through a leasing arrangement with monthly payments, Ziegler says. "It is one monthly fee and for that fee we take care of the equipment, we provide the chemicals and service, and also provide 24/7 emergency service," he says. "There is no capital purchase. We do ask for a three-year commitment but we include a performance guarantee. If it doesn't work for some reason, we will pull it out."

Factoring in the increased and more reliable production from the ethanol plants, the cost of the system is comparable with using antibiotics to control bacterial contamination. "The plants we are going into, we are matching their antibiotic pricing," he says. "But [the plants] are showing higher ethanol production and much less variation in ethanol production.

They don't see the wild swings in ethanol production anymore. With a little more history under our belt I think we will be able to put a better number on the real cost of our system.

But we should be right in the middle of what an average plant spends on antibiotics."

Clean Distillers Grains
An added benefit of the PureMash system is the only traces of the chemical left in the distillers grain is in the form of chloride, which is a component of common table salt. The level of chloride left in the mash is well within the acceptable limits set by federal regulations. That allows companies that use the PureMash system to sell their distillers grains as antibiotic free. "That seems to be one of the primary drivers of interest in the system," he says. "It doesn't leave a residue in the distillers grains. We have forwarded all this to the [U.S. Food and Drug Administration] and [U.S.] EPA and they are very interested that we can take the bacteria out and still leave natural or organic grain behind."

PureMash has been approached by some ethanol producers not because they have production problems, but because they would like to market their ditillers grains as being free of antibiotic residues. Ziegler says a number of the plants that have installed the PureMash system have been able to command a significant premium for their distillers grains by marketing them as natural or organic. "There is a lot more interest in the system than we expected from the market looking for an antibiotic alternative," Ziegler says. "I think they are looking for something that is a little better. We are certainly seeing interest from the engineering firms."

While cutting the use of antibiotics is a definite selling point for PureMash, Ziegler takes a broader view of the system's benefits. "Yes you can say you are replacing antibiotics, but I really don't look at it like that," he says. "It is really a better systems approach to maintaining and treating your plant like a lot of food facilities do now. What we are doing is updating that technology and bringing it into the ethanol plant."

Jerry W. Kram is an Ethanol Producer Magazine staff writer. Reach him at or (701) 738-4962.