A just-published scientific paper by four Brazilian and two American scientists reports gains in electrical and thermal energy by sonicating spent brewer’s grain (barley bread), an abundant waste product of the beer industry, prior to anaerobic digestion, a microbiological process. involves the consumption of organic matter and the production of methane.
During pretreatment, biogas with 56% methane is produced, which is 27% higher than the rate obtained without using ultrasound. After purification in methane, biogas can be used as a vehicle fuel with a very low carbon footprint compared to traditional fossil fuels. Moreover, in cogenerators, methane can be burned by the brewery to produce electricity and heat. The latter waste can be used as biofertilizer instead of mineral fertilizer. The methodology is detailed in a journal article Clean Manufacturing Journal.
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, Tânia Forster-Carneiro, is the principal investigator of the FAPESP-supported project.
Food processing plants have wastewater treatment facilities as required by law, but do not always treat organic solid waste, which is usually sent to controlled or sanitary landfills or used for animal feed production. “Research that adds value to organic solid waste is important for industry and society as a whole,” said Forster-Carneiro. “In this study, we pre-treated the waste with ultrasound, a new technology usually only applied in the laboratory, and thereby obtained higher methane production. The results were very positive.”
Luz Selene Buller and PhD candidate William Sganzerla, both candidates receiving fellowships from FAPESP, are also members of the research team.
As Sganzerla explains, brewery waste is lignocellulosic (composed of lignin, cellulose, and hemicellulose), and microorganisms involved in anaerobic digestion cannot easily penetrate cell walls. “Feeding an anaerobic digestion reactor with lignocellulosic feedstock produces low levels of methane because microorganisms do not consume this biomass, which must be broken down by pretreatment.”
The study also analyzed energy recovery pathways throughout the process, concluding that electricity produced by biogas replaces 80% of the energy required for pretreatment with ultrasound and anaerobic digestion, while generating 50% more heat energy than waste heat. . can be obtained without the use of ultrasound.
“The technological challenge is how to implement sustainable pretreatment that consumes less energy,” Sganzerla said. “Pretreatment with high energy consumption is not suitable for industrial-scale applications. Thus, the electricity produced by burning biogas will be used for ultrasound. The heat produced can be used for various processes that require thermal energy in industry. All this is in line with the principles of the circular economy for food production with low carbon emissions.”
According to Buller, food recycling and local energy production from renewable sources are key to the sustainable development and decarbonisation of food production.
Detailed calculations
For Forster-Carneiro, the highly 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 of all incoming and outgoing flows. We have shown in detail that it is possible to generate 0.23 megawatt-hours of electricity from every metric ton of barley bread processed.
The study also presents the potential of generating energy from renewable energy sources to reduce greenhouse gas emissions. Forster-Carneiro has collaborated with Michael Timko, the paper’s penultimate author, for more than five years. Timko is a professor at Worcester Polytechnic Institute in Massachusetts (USA) and an expert in waste assessment. “The study went great,” he said. “Very few research projects detail the calculations for generating energy from methane.”
This experience stems from the good relationship between FEA-UNICAMP and local brewers, reflected in technical visits and solid waste donations, among others. The brewery in question produces 120-250 metric tons of malted barley per week. “Currently, the plant does not recycle this waste. It’s just giving it to use in animal feed, but it can also treat bagasse and produce energy,” Forster-Carneiro said.
In this context, Sganzerla noted the effects of Brazil’s national solid waste policy (Law No. 12,305, enacted in 2010). “There will come a time when all manufacturers will have to clean up the waste they produce,” he said. “They will have to use existing technologies. Technically, this is already possible. We point to various possibilities in our research. Currently, no producer is doing this on a large scale because although anaerobic digestion is available and a viable technology for liquid and solid waste, more in-depth research is required for solid and lignocellulosic waste.”
It is rich in nutrients
Brazil is among the top five beer producers in the world. The article says that 14 billion liters were produced in 2019. The production of 100 liters of beer produces about 20 kg of barley bread, so about 2.8 million tons are produced in Brazil every year. In 2020, Forster-Carneiro and his team patented the use of this organic waste in anaerobic reactors operated by brewers to treat wastewater.
The article by Forster-Carneiro, Sganzerla, Buller and Solange Mussatto of the Department of Biotechnology and Biomedicine at the Technical University of Denmark is published in the journal. Clean Manufacturing Journal March 2021 presents a detailed assessment of the economic benefits of waste assessment, including fertilizer production.
“The anaerobic digestion process cleans waste with a high organic load, resulting in nutrients. The solids remaining in the reactor, known as biodigest, consist mainly of treated lignocellulosic material rich in nitrogen, phosphorus, potassium and other minerals. Malted barley bread has a high proportion of nitrogen as well as protein, making it a good biofertilizer that can replace NPK. [ mineral fertilizer containing nitrogen, phosphorus and potassium ]”said Sganzerla.
Forster-Carneiro and her team are also investigating hydrothermal pretreatment of barley bread. “We feed the waste to a reactor that hydrolyzes biomass under certain temperature and pressure conditions [ breaking down the molecules ] to produce a hydrolyzate [ liquid ] with soluble nutrients. It is very useful for fermentation processes. However, more in-depth research is needed before we can come up with an efficient and sustainable solution for processing lignocellulosic waste,” said Sganzerla.
Reference: Buller LS, Sganzerla WG, Lima MN, Muenchow KE, Timko MT, Forster-Carneiro T. Ultrasonic treatment of brewers’ spent grains for anaerobic digestion: Biogas production for sustainable industrial development. J Pure Product. 2022;355:131802. doi: 10.1016/j.jclepro.2022.131802