Research into utilizing waste products has benefited several industries in recent years, improving their sustainability. Writing in the journal Energies, a team of scientists from Armenia and Poland has investigated the use of waste coffee and alcohol products to produce biofuels.
Study: Biogas and Biohydrogen Production Using Spent Coffee Grounds and Alcohol Production Waste. Image Credit: koya979/Shutterstock.com
Sustainable Biofuels: Overcoming Issues with Hydrocarbon Use
Hydrocarbons have played a key role in driving societal and industrial progress over the course of recent history. Whilst they have provided the energy needed to grease the wheels of production, their exploitation has caused a huge environmental burden. Their use in heavy industry, energy generation, and transportation is helping to cause climate change on an unprecedented scale.
To mitigate the environmental damage caused by our over-reliance on fossil fuels, research has turned in recent decades to sustainable biofuels. Biogas and biohydrogen have been developed to help meet net zero carbon emission targets. Biohydrogen only emits water vapor after combustion and has a 3.5x higher energy content than oil.
Biogas is composed of methane and carbon dioxide, and is cleaner than conventional hydrocarbons such as coal, although it is not completely pollution-free. This sustainable fuel is composed of methane and carbon dioxide, with some nitrogen, ammonia, hydrogen, water vapor, and hydrogen sulfide.
Phasing out conventional hydrocarbon-based fuels is a key aim of several governments and international bodies. Switching to sustainable biofuels offers environmental benefits such as reduced carbon emissions and exploitation of virgin resources. Additionally, it provides several economic benefits.
Producing Biofuels from Waste Materials
Utilizing lignocellulosic biomass for biofuel production holds vast potential for the future of the economy and environmental remediation strategies. This waste biomass is produced in staggering amounts, with the total global production estimated to be in the region of 120 x 109 annually. Around 2.2 x 1021 J of energy is contained in global lignocellulosic biomass, which can comfortably meet global energy needs.
The alcoholic and non-alcoholic beverages industries are major contributors to worldwide waste. In distilleries, for example, 88% of raw materials become waste, making them a major polluter. Global spirits consumption is predicted to exceed thirty-eight billion liters by 2025. In the beer industry, 38.6 x 106 tons of brewer’s spent grain is produced annually.
Non-alcoholic beverages such as tea and coffee generate vast quantities of waste materials. By-products of the beverages industry include coffee grounds, sugarcane bagasse, rice straw, wheat straw, brewer’s spent grain, and sorghum leaves. Many studies have already reported the use of these waste materials in biofuel and industrial chemical synthesis.
Amongst the various proposed methods for biofuel production, anaerobic digestion and dark fermentation have shown noteworthy promise. However, currently, technical challenges exist with using these techniques for the conversion of waste biomass into valuable alternative fuels. Treatment technologies have been explored in recent years, including physical, chemical, thermal, and hydrothermal treatments.
The new paper in Energies has considered the use of anaerobic digestion for converting alcohol waste and spent coffee grounds into biohydrogen and biogas. The authors have explored preparation methods and pretreatments, along with gas analysis and the use of reagents.
Data were calculated and processed using three experiments. Standard errors were considered in the research. Reactors containing only feedstock and inoculum were used to observe the amounts of produced gas.
Sewage sludge from wastewater was used as the microbial inoculum in batch cultures. The authors note that there are several variables that must be accounted for, such as varying composition and concentration of microbial communities which occur seasonally or daily. Volatile and total solids in samples were determined prior to digestion using oven drying.
Study Results and Conclusions
The authors demonstrated that alcohol waste and spent coffee grains are promising high-organic content substrates. Utilizing these waste products could improve the efficiency and cost-effectiveness of biofuel production in the future. Untreated waste yielded enhanced methane and biogas production, whereas pre-treated waste yielded higher amounts of biohydrogen.
The highest biogas yields were observed using spent coffee grounds inoculated at pH 7.5. Good yields were also observed for untreated alcohol waste. Different methane yields were obtained depending on inoculum and treatment method. Due to the enhanced methane yields observed using these substrates, the authors have stated that they are promising for commercial biogas production.
For biohydrogen production, results indicated that spent coffee grains are more suitable, with data suggesting that the fermentation of alcohol waste, either treated or untreated, is not efficient for the production of this biofuel.
Biohydrogen yield obtained from spent coffee grounds is comparatively higher than using cotton waste but inferior to some other types of lignocellulosic waste. Results indicated a correlation between increased lignin removal and soluble sugar.
The authors concluded that acid hydrolysis treatment is beneficial for biohydrogen synthesis, whereas it is not important for biogas synthesis. Overall, the study has demonstrated the benefits of using spent coffee grounds and alcohol waste for the production of different biofuels and the effects of treatment technologies. The paper is valuable for future research in the field of sustainable biofuel production.
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Vanyan, L, Cenian, A & Trchounian, K (2022) Biogas and Biohydrogen Production Using Spent Coffee Grounds and Alcohol Production Waste Energies 15(16) 5935 [online] mdpi.com. Available at: