Brewery Waste: A look at more effective biofuel production

Dr. Neil Canter, Contributing Editor | TLT Tech Beat June 2011

The principle of anaerobic digestion is used to produce methane for fuel for brewery waste.

KEY CONCEPTS
• Anaerobic digestion of brewery waste is used by the brewery industry to produce methane for use as fuel in applications such as heating boilers.
• Genome sequencing has been used in a study to determine which species of bacteria were unique for each of the nine bioreactors studied and ultimately responsible for most efficiently producing methane.
• The researchers hope to see if these bacteria can be used to produce a series of short-chain and medium-chain carboxylates.

The lubricant industry has had a longstanding negative relationship with bacteria. These microbes extract energy out of lubricants and fuels while generating very harmful byproducts that can accelerate failure.

But there are applications where Bacteria have been found to be beneficial. For example, in a previous TLT article, researchers identified a specific strain of bacteria that excretes exopolysaccharides found to effectively inhibit corrosion (1). Initial testing has shown that the exopolysaccharides form a protective coating that can withstand corrosion, even in the presence of sodium chloride and mineral acid solutions.

Bacteria are also a critical element used in publicly operated treatment works to degrade waste. One process that is proving to be very useful is anaerobic digestion. Largus Angenent, associate professor of biological and environmental engineering at Cornell University in Ithaca, N.Y., says, “Anaerobic digestion is an engineered bioprocess in which an undefined mixed culture of groups of multispecies microbes convert organic waste into the final product, methane. Part of this process is similar to how the bacteria in our intestines help to digest fibrous food.”

The benefit of anaerobic digestion is that methane, which is a major component of biogas, is a fuel that can be used in such applications as heating boilers. Angenent points out that the brewery industry utilizes anaerobic digestion to extract energy from brewery waste. He adds, “Breweries generate a tremendous amount of wastewater that they would normally be very costly to pay for disposal. Instead, they have used bioreactors to generate sufficient methane to offset up to 20% of their natural gas requirements.”

Angenent indicates that anaerobic digestion is used in a number of other industries such as those preparing dairy products, food and ethanol. It is a 100-year-old technology.

The opportunity exists to determine which of the microbes present in the bioreactors will ultimately result in the highest production rates of methane. If those microbes can be identified, then the potential exists to develop microbial communities that can more efficiently produce methane and precursors to other components found in fuels.

A study has now been conducted to identify such species in the brewery waste bioreactors.

GENOME SEQUENCING
A group of scientists led by Angenent used genome sequencing to determine which species of bacteria are present in nine bioreactors used at breweries. Angenent says, “We were very fortunate to have access to a large number of samples, data and statistics that have been compiled by the brewery industry. This industry understands the value of these bioreactors and treats these systems very kindly.”

Figure 3 shows Angenent sitting in front of one of the bioreactors. The researchers were able to use a second-generation Sequencing platform to determine what species of bacteria are present in the bioreactors. Angenent says, “First-generation sequencing work was done in the past but lacked the statistical power to understand the populations of the bioreactors.”


Figure 3. Species of bacteria unique to each of nine brewery waste bioreactors studied have been identified as being responsible for producing methane. (Courtesy of Cornell University)

In a successful bioreactor at breweries, anaerobic bacteria spontaneously form polysaccharide matrixes that have the appearance of caviar granules.

The researchers evaluated more than 400,000 gene sequences of microbes in granular samples from the nine bioreactors which were taken each month during one year. They found that 145 species were unique for each of the nine bioreactors.

Angenent says, “We found that 145 species of bacteria out of 5,000 are predictive and with only these 145 species we can determine from which of the nine bioreactors the sample came from. Our data is 97% accurate based on statistical analysis.”

The bacteria in all of the bioreactors have developed a syntrophic relationship. This means that each species lives off of the metabolic products formed by another species. With this combination, waste can be systematically degraded until a specific microbial group conducts the final step to produce methane. Angenent adds, “The microbial population has formed a unique food web that takes advantage of the available raw material in the waste stream.”

Functional diversity is the most important feature in maintaining a robust microbial community.

Angenent says, “A metabolically diverse bacterial community with as many as 5,000 species is the most important factor. Such diversity means that a large enough gene pool is available to handle a dynamic environment yet also retain a high level of stability. This factor is important to handle any upsets encountered. From a statistical standpoint, such a community needs to be even in its composition.”

In the future, the researchers are looking to see if the bacteria could be used to produce a series of short-chain and medium-chain carboxylates. Angenent says, “We already know that the bacterial community can degrade propionic acid to acetic acid and then to methane. Our hope is to try to make carboxylate that can be used as precursors to the alkanes found in fuels.”

Angenent indicated that a target carboxylate chain length is C6 to C8 carboxylic acids. This also happens to be the ideal chain length for carboxylic acids used in the preparation of polyol esters for use in synthetic lubricant applications. It is conceivable that the work done by the researchers could lead to alternative sourcing for some of these synthetic lubricant precursors.

Additional information can be found in a recent publication (2) and by contacting Angenent at la249@cornell.edu. 

REFERENCES
1. Canter, N. (2010), “Natural Corrosion Inhibitor from Bacteria,” TLT, 66 (11), pp. 8–9.
2. Werner, J., Knights, D., Garcia, M., Scalfone, N., Smith, S., Yarasheski, K., Cummings, T., Beers, A., Knight, R. and Angenent, L, (2011), “Proceedings of the National Academy of Sciences,” 108 (10), pp. 4158–4163.

Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat items can be sent to him at neilcanter@comcast.net.