Expanding the use of waste to generate bioenergy can neutralize greenhouse gas emissions in São Paulo

Agricultural residues already produce 25% of the electricity used by households in the state. The proportion could jump to 70%, according to researchers who took part in an online seminar on the topic.

By Elton Alisson  |  Agência FAPESP – Increased use of agricultural residues and solid urban waste to generate power could make the Brazilian state of São Paulo net carbon neutral or negative, according to researchers linked to FAPESP’s Bioenergy Research Program (BIOEN).

São Paulo already has one of the world’s cleanest energy mixes, with biofuels for transportation accounting for over 50%. The use of agricultural residues to generate power is growing: the source now contributes 25% of the electricity used by households across the state.

The proportion could jump to 70% if part of the sugarcane trash left in the field after the harvest is used, and to 98% if it is entirely used in cogeneration by sugar and ethanol plants in São Paulo that participate in Renovabio, the federal government’s program to increase production of biofuels, said Gláucia Mendes Souza, a professor at the University of São Paulo’s Chemistry Institute (IQ-USP) and a member of BIOEN’s steering committee, during the online seminar “Valorizing Residues” held on February 24, 2021.

“The potential for generating bioelectricity from residues produced by other segments of agribusiness, such as the animal fat discarded by the meat industry, is as substantial as in the case of sugarcane,” Souza said. “Residues from other types of biomass are available in São Paulo, which has 190,000 square kilometers of croplands, pasturelands, and forests allocated to economic uses.”

During the event, FAPESP and the São Paulo State Department of Infrastructure and the Environment signed a letter of intent to collaborate on strengthening the residue valorization knowledge base and fostering scientific and technological projects in the field.

“The partnership focuses on transforming waste from a problem into opportunities and benefits for society, aiming mainly to promote bioenergy and production of biofuels such as second-generation ethanol, biodiesel, and biogas, as substitutes for oil and other fossil fuels in São Paulo’s energy mix, which is already very special compared with other parts of the world,” said Marco Antônio Zago, President of FAPESP.

For Luiz Eugênio Mello, FAPESP’s Scientific Director, “our partnership with the Department of Infrastructure and the Environment will enable the knowledge produced in laboratories to be transferred to the production environment and be used by society.”

Bioenergy and bioproducts

A methodology developed in recent years by researchers at the University of Campinas’s Interdisciplinary Energy Planning Center (NIPE-UNICAMP) has helped locate, quantify and characterize agricultural and urban waste products for bioenergy production and reduction of carbon dioxide (CO₂) equivalent emissions. 

The methodology, developed by Rubens Augusto Camargo Lamparelli, is based on satellite acquisition of data and maps with a spatial resolution of 250 meters at 16-day intervals. It is used to locate residues in an area and assess the economic feasibility of installing a plant to convert them into bioenergy and bioproducts, for example.  

The method was initially used to assess the potential of the Campinas Administrative Region, which comprises 92 cities. The researchers concluded that the most abundant residues in the region were sugarcane trash and bagasse, and urban solid waste currently dumped in sanitary landfills.  

When they assessed the potential for biofuel production from the organic matter in urban solid waste in landfills, they found it to be similar to that of a plant producing 100 million liters of ethanol per year from sugarcane.

“That doesn’t mean garbage should be used to produce biofuel. It’s just an example of how much we’re wasting valuable raw materials,” said Telma Franco, a researcher at NIPE-UNICAMP, and a professor at the university’s School of Chemical Engineering.

The researchers also assessed the potential for production of biomethane from the organic matter in the urban solid waste sent to more than ten landfills in metropolitan Campinas. “We found that this material could be used to produce more than 120 million cubic meters of biomethane per year,” Franco said.

Alternative to landfills

According to data presented by Yuri Schmitke, President of the Brazilian Waste to Energy Association (ABREN), 40% of the garbage and waste produced in Brazil goes to landfills that capture methane improperly or not at all. Only 50% of the methane produced by urban waste, which accounts for 3%-5% of total greenhouse gas emissions, is captured at landfills. The rest goes into the atmosphere, where it is 25 times more harmful than CO₂.

For these reasons the fifth report of the Intergovernmental Panel on Climate Change (IPCC) recommends heat treatment of urban solid waste as an alternative to landfills, Schmitke said. This will help mitigate global warming by reducing greenhouse gas emissions by a factor of eight.

In addition, heat treatment generates seven to ten times more energy from the same amount of waste. While a landfill generates 65 kilowatts (kW) of biogas per metric ton of solid waste, heat treatment produces 450 kW-600 kW. 

“Landfills also offer risks to the quality of the water available on the planet. Developed countries have chosen heat treatment as an alternative to landfills because of the economic and environmental benefits, including benefits to the climate,” Schmitke said.

There are currently 2,448 waste heat treatment plants in operation worldwide, including 1,063 in Japan, 419 in China, and 209 in South Korea. Plans exist to set up such facilities in South American countries, including Brazil. In São Paulo, for example, there are five projects to build waste heat treatment plants, in Barueri, Mauá, and Diadema in the São Paulo City metropolitan area, and in and near the Port of Santos, for a total of 183 megawatts.

“We’ve been working with all these cities to offer viable waste-to-energy solutions. The Mauá and Santos projects are awaiting environmental licenses from CETESB [the São Paulo State environmental management agency] and have won approval from CONSEMA [the state environmental council]. They will have the capacity to process 2,000 tons of waste per day,” said Marcos Penido, São Paulo State Secretary for Infrastructure and the Environment. 

A complete recording of the webinar can be watched at: www.youtube.com/watch?v=d8kA_Qlfvc8.