A scientific paper just published by four Brazilian and two American scientists reports the increase in electrical and thermal energy produced when spent brewing grain (barley mash), a rich waste product generated in the beer industry, is sonicated prior to anaerobic digestion, a microbiological process. . involving organic matter consumption and methane production.
Pretreatment generated biogas with 56% methane, 27% more than the share obtained without the use of ultrasound. After methane treatment, biogas can be used as an automobile fuel with very low carbon emissions compared to conventional fossil fuels. Moreover, in cogenerators, methane can be burned in the brewery to produce electricity and heat. The final waste can be used as biofertilizer instead of mineral fertilizers. The methodology is described in detail in the article published in Journal of Clean Production.
The innovative process was developed at the Bioengineering and Water and Waste Treatment Laboratory (Biotar) of the School of Food Engineering of the State University of Campinas (FEA-UNICAMP). The head of the research team, Tanya Forster-Carneiro, is the principal investigator of the FAPESP-supported project.
Food processing plants have treatment facilities as required by law, but do not always treat solid organic waste, which is usually sent to controlled or sanitary landfills or used to produce animal feed. “Research that adds value to solid organic waste is important to industry and society as a whole,” Forster-Carneiro said. “Specifically, in this study we pre-treated the waste with ultrasound, a rudimentary technology that is usually only applied in the laboratory, and thus obtained a higher rate of methane production. The results were very positive.”
PhD student Luz Selene Buller and Ph.D. candidate William Sganzerla, both holders of FAPESP fellowships, are also members of the research team.
As Sganzerla explained, brewery waste is lignocellulosic (containing lignin, cellulose, and hemicellulose), and the microorganisms involved in anaerobic digestion cannot easily penetrate cell walls. “Feeding an anaerobic digestion reactor with lignocellulosic feedstock produces low levels of methane because the microorganisms do not consume this biomass, which must be broken down in pretreatment.”
The study also analyzed energy recovery pathways throughout the process, concluding that the electricity produced by biogas offsets 80% of the energy required for pre-treatment by sonication and anaerobic digestion, and generates 50% more excess thermal energy than excess heat, which will be obtained without the use of ultrasound.
“The technological challenge is how to apply a sustainable pretreatment that consumes little energy,” Sganzerla said. “Pretreatment with high energy consumption is not suitable for industrial scale applications. Therefore, the electricity generated by burning the biogas will be used for ultrasound. The resulting heat can be used in industry for various processes that require thermal energy. All of this is in line with the principles of the circular economy for low-carbon food production.”
Nutrient recycling and local renewable energy production are key to sustainable development and decarbonisation of food production, according to Buller.
Detailed calculations
For Forster-Carnaire, the very detailed measurements made in the study are the main reason the paper has attracted so much attention from the scientific community. “We calculated the mass and energy balance in all the input and output streams. We have shown in detail that 0.23 megawatt-hours of electricity can be produced for every metric ton of processed barley husk,” she said.
The study also shows the potential of renewable energy production to reduce greenhouse gas emissions. Forster-Carneiro has collaborated with Michael Timko, the paper’s penultimate author, for more than five years. Timka is a professor at the Worcester Polytechnic Institute in the state of Massachusetts (USA) and a specialist in waste valorization. “The research was great,” she said. “Very few research projects describe in detail the calculations for generating energy from methane.”
This experiment, among other things, arose from the good relationship between FEA-UNICAMP and the local brewers, which was manifested in technical visits and the donation of solid household waste. A suitable brewery produces 120-250 metric tons of barley bagasse per week. “The plant does not currently process this waste. It just gives them away to be used as animal feed, but it can process the pulp and produce energy at the same time,” Forster-Carneiro said.
In this context, Sganzerla noted the implications of Brazil’s national solid waste policy (Law 12305, passed in 2010). “The time will come when all producers will be obliged to deal with the waste they produce,” he said. “They will have to use available technology. Technically speaking, it is already possible. In our research, we point to various possibilities. Currently, no producer is doing this on a large scale, because anaerobic digestion exists and is a viable technology for liquid and solid waste, more in-depth research is required for solid and lignocellulosic waste.’
Rich in nutrients
Brazil is one of the top five beer producers in the world. In 2019, 14 billion liters were produced, according to the article. In the production of 100 liters of beer, about 20 kg of barley pulp is obtained, thus, about 2.8 million tons are produced in Brazil every year. In 2020, Forster-Carneiro and her team patented the use of this organic waste in anaerobic reactors for brewers to treat wastewater.
The article by Forster-Carnaire, Sganzerla, Buller and Solange Mussat, of the Department of Biotechnology and Biomedicine, Technical University of Denmark, is published in Journal of Clean Production in March 2021, a detailed assessment of the economic benefits of waste valorization, including fertilizer production, is presented.
” anaerobic digestion the process treats waste with a high organic load, resulting in nutrients. The solid fraction remaining in the reactor, known as biodigest, consists mainly of treated lignocellulosic material rich in nitrogen, phosphorus, potassium and other minerals. Malted barley bagasse is high in nitrogen as well as protein, making it a good biofertilizer that can replace NPK [mineral fertilizer containing nitrogen, phosphorus and potassium]”, Sganzerla said.
Forster-Carneiro and her team are also investigating hydrothermal pretreatment of barley pulp. “We feed waste into a reactor that hydrolyzes biomass under certain conditions of temperature and pressure [breaking down the molecules] to obtain a hydrolyzate [liquid] with soluble nutrients. It is very useful for fermentation processes. However, more in-depth research is needed so that we can find an effective and sustainable solution for the treatment of lignocellulosic waste,” said Sganzerla.
Additional information:
Luz Selene Buller et al., Ultrasonic Pretreatment of Brewery Spent Grain for Anaerobic Digestion: Biogas Production for Sustainable Industrial Development, Journal of Clean Production (2022). DOI: 10.1016/j.jclepro.2022.131802
William Gustavus Sganzerla and others. Feasibility assessment of the production of bioenergy and fertilizers by anaerobic fermentation of spent brewing grain in the concept of biorefinery, Journal of Clean Production (2021). DOI: 10.1016/j.jclepro.2021.126600