Apple Energy: Too Valuable to Waste

By Sunny Lewis for Maximpact

CAMPINAS, Sao Paulo, Brazil, February 17, 2023 (Maximpact.com Sustainability News) – Brazilian scientists have successfully produced biogas from the pulpy waste remaining after apples have been crushed to extract their juice. The biofuel produced from this waste, called apple pomace, could help reduce the use of climate-warming fossil fuels, the scientists say in research published this week.

Biofuel is energy derived from living matter – both plants and animals. Bioethanol, biodiesel, and biogas, different types of biofuels, are considered renewable sources of energy. While not perfectly sustainable as they take land to grow the raw materials, they do emit less greenhouse gases and pollutants than fossil fuels like coal and oil, and could bridge the gap to a low-carbon world.

An article describing the research done by scientists at the State University of Campinas (UNICAMP) and the Federal University of the ABC (UFABC) in São Paulo state, is published in the journal “Biomass Conversion and Biorefinery” under the title, “Valorization of apple pomace for biogas production: a leading anaerobic biorefinery approach for a circular bioeconomy.”

The central concept is that of a circular economy, a system of closed loops designed to reduce costs, recover resources from waste, promote reuse and recycling, and maximize use of bioenergy and biomaterials.

Vegetable and fruit factories are prime candidates. They generate massive volumes of waste that impact landfills, producing 80 percent sugars and hemicellulose, nine percent cellulose, and five percent lignin. They produce methane and leachates and have high chemical and biochemical oxygen demands since they are biodegradable, leading to increased recovery costs.

According to the Food and Agriculture Organization of the United Nations, global apple production totaled almost 86.5 metric tons in 2020. The main producers were China (46.85 percent), the United States (5.38 percent) and Turkey (4.97 percent).

“Biorefining with dry anaerobic digestion produces electricity and thermal energy, reduces greenhouse gas emissions, and valorizes waste via conversion to organic fertilizer,” said Tânia Forster Carneiro, the principal investigator in the Brazilian study. 

Carneiro earned a PhD in industrial process engineering from the University of Cadiz in Spain in 2004 and is currently a lecturer in bioengineering and biotechnology at UNICAMP’s School of Food Engineering.

Anaerobic digestion, she explained, is a microbiological process involving consumption of nutrients and production of methane. Dry anaerobic digestion, with total solids in the reactor exceeding 15 percent, is considered an efficient method of recycling solid organic waste, far more environmentally appropriate than landfill disposal.

The scientists’ results pointed to a yield of 36.61 liters of methane per kilogram (kg) of removed solids, potentially generating 1.92 kilowatt hours (kWh) of electricity and 8.63 megajoules (MJ) of heat per ton of apple pomace.

The recovered bioenergy could supply 19.18 percent of the electricity and 11.15 percent of the heat used to operate the anaerobic biorefining reactor designed by the researchers.

They conclude that biofuels and electricity generated by them, including biogas from apple pomace, can contribute to public policy, reduce fossil fuel consumption and cut the greenhouse gas emissions from organic residues.

Energy Transition Underway

The Sao Paulo research group found the greenhouse gas emissions avoided by burning the biogas produced from apple pomace corresponded to 0.14 kg of carbon dioxide equivalent (CO2e) in the electricity and 0.48 kg of CO2e in the heat generated per ton of apple waste.

“Anaerobic digestion is a stable technology and can be implemented in small to medium plants, assisting the circular economy transition and offering an added-value alternative to disposal of fruit residues as waste that benefits the entire supply chain,” Carneiro said.

The other authors of the article are Larissa Castro Ampese, William Gustavo Sganzerla and Henrique Di Domenico Ziero, PhD candidates at FEA-UNICAMP; Josiel Martins Costa, currently a postdoctoral fellow at FEA-UNICAMP; and Gilberto Martins, a professor at UFABC’s School of Engineering, Modeling and Applied Social Sciences. 

Carneiro and Sganzerla recently published a separate article on anaerobic digestion to produce methane from malting barley bagasse in the beer industry. They detailed the gains in electricity and heat in terms of the balance of mass and energy in all inbound and outbound flows. This article shows that it is possible to produce 0.23 megawatt-hours of electricity for every metric ton of barley bagasse processed. For more details visit: agencia.fapesp.br/39093. 

Both the apple pomace and beer research studies are supported by the São Paulo Research Foundation (FAPESP), a public institution that supports scientific research by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. 

Apples are among the most widely consumed fruits worldwide, both fresh and processed as juice, vinegar and cider. But today the apple processing industry throws away as much as 20–35 percent of the fresh weight of the apple fruit. The pomace is a mixture of peel, core, seed, calyx, stem, and pulp.

Keeping Apples Out of the Waste Stream

Polish and Turkish scientists have found that, “If not managed properly, such bio-organic waste can cause serious pollution of the natural environment and public health hazards, mainly due to the risk of microbial contamination.”

Their research, published by the U.S. National Institutes of Health in February 2022, shows that apple pomace can be successfully reused in different industrial sectors as a source of energy and bio-materials, turning waste into sustainable products. 

Raw or processed forms of apple pomace can be feedstocks for bioenergy applications, such as biogas and pyrolysis oil, bioethanol, and materials like biochar and activated carbon.

The recovered active compounds from apple pomace also can be used as preservatives, antioxidants, anti-corrosion agents, wood protectors and biopolymers, or as a sustainable, low-cost raw material to make valuable food additives that offer health advantages such as nutraceuticals, citric acid and pectin.

Apple pomace is considered as a good source of nutrients since it is rich in carbohydrates, crude fibers, minerals and polyphenols. 

Polyphenols work as antioxidants in the body. They can combat environmental harm such as UV damage and pollution. In addition to their antioxidant activity, research shows that diets rich in polyphenols offer protection against development of certain cancers, cardiovascular diseases, diabetes, and neurodegenerative diseases.

“Apple pomace has strong antioxidant properties due to the presence of phenolics like epicatechin, its dimer, quercetin glycosides, chlorogenic acid, phloridzin and 3-hydroxy-phloridzin [4]. The phenolics rich extract of pomace were found to exhibit anticarcinogenic activity by preventing colon cancer,” wrote a team of scientists from the CSIR-Institute of Himalayan Bioresource Technology in Himachal Pradesh, India. Their study is published in the journal “Food Science and Human Wellness” Volume 4, Issue 4, December 2015.

Apple pomace also has been used as a substrate of various microorganisms including bacteria, fungi, and yeast, in both solid and liquid fermentation arrangements. 

Finding Wasted Treasure

With the inefficient use of raw materials and the rise in waste production, waste management has shifted from emissions reduction to the reconsideration of waste as valuable when used as raw materials for the production of new goods, explains a group of Malaysian and UAE scientists published this year in the journal “Sustainability.”

The value of limiting natural resource consumption is related to a decrease in greenhouse gas emissions. Agroindustry wastes are important on a global scale because they are linked to greenhouse gas pollution from processing, use, and disposal and can result in natural resource depletion as a result of an ever-increasing global population, they write. 

Since apple pomace is produced in large amounts and includes a large percentage of water, it presents storage issues and requires prompt care to avoid putrefaction. However, with new discoveries adding to the usefulness of apple waste alongside ancient uses such as animal feed, more of it can be kept out of landfills.

“Processing garbage into value-added products could reduce the waste and become a viable option for the global community. Pomace has long been utilized as an animal feed source for cows, buffaloes, sheep, and goats. Its potent antioxidant capacity, antibacterial and antiviral properties are also beneficial and could be used in future extraction processes, particularly in the nutraceutical and pharmaceutical industries,” the Malaysian/UAE scientists wrote. 

Under the biorefinery model, concepts such as “circular economy” and “cradle to cradle” aim to create a world in which wastes from specific industrial processes can be used as sustainable raw materials for other products and commodities. These concepts would raise both critical economic and environmental issues that can prevent the use of non-renewable resources.