Home Agriculture Turning methane from rice straw into clean fuel

Turning methane from rice straw into clean fuel

by Admin-Phmp
Published: Last Updated on

Text and Photos by Henrylito D. Tacio

Additional Photos courtesy of SEARCA

Among the greenhouse gases that cause global warming, most reports emphasize more on carbon dioxide. But methane is equally significant. In fact, about 12 percent of global warming is attributed to increases of methane in the atmosphere.

“Methane absorbs heat 21 times more than carbon dioxide and it has 9- to 15-year life time in the atmosphere over a 100-year period,” says Dr. Constancio Asis Jr., a recipient of the 2011 Norman E. Borlaug International Agricultural Science and Technology Fellowship Award.

Methane gas is created naturally as a waste product of anaerobic bacteria (living with little or no oxygen). These bacteria produce methane gas in waterlogged soils and wetlands but also in human-produced environments such as rice paddies and landfills.

The Philippines, being an agricultural country, has contributed a substantial amount of methane in the atmosphere. Most of the methane gasses are released from rice production. The country is among the biggest rice producers. Rice is the staple food for about 80% of the population, the Asian Development Bank reports.

“Rice is a plant that grows best in wet soil, with its roots flooded,” explains L. Hartwell Allen, an American soil scientist at the Crops Genetics and Environmental Research Unit in Gainesville, Florida. “But flooded rice crops emit substantial amounts of methane to the atmosphere.”

There are two products that come from rice when it is harvested from the field: grain (palay) and straw (dayami). Studies conducted by the Laguna-based International Rice Research Institute (IRRI) showed that for every 4 tons of rice grain, about 6 tons of straw are also produced.

“Globally, roughly 800 to 1,000 million tons per year of rice straw is produced, with about 600 to 800 million tons per year produced in Asia,” said IRRI. In the Philippines alone, about 11.3 million tons of rice straw are produced after every harvest.

Unfortunately, farmers consider rice straw as waste as it has little or no commercial value. “Much of this is burnt in open fields or incorporated in the soil in wet conditions during ploughing,” says a policy brief paper published by the Economy and Environment Program for Southeast Asia (EEPSEA).

Based on the five-year study (from 2006 to 2010), it was found that incorporating stubble less than 30 days before crop establishment is responsible for the largest contribution of methane emissions.

Burning rice straw is also not a good practice either. About 60%-80% of rice straw is burned, studies done by the Philippine Rice Research Institute (PhilRice) showed. Burning, they claim, is the most economic and efficient way of clearing the land for the next planting season.

But when done frequently, burning rice straw could reduce the soil’s nitrogen and phosphorus content by 25%, according to Evelyn Javier, supervising science research specialist of PhilRice’s Agronomy, Soil, and Physiology division. “(Burning) also cuts potassium content in soil by 20% and sulphur by 5-60%,” she said.

In addition, some beneficial insects are most likely to be killed when rice straws are burned in the open field. “Useful insects kill some harmful insects which destroy palay and make production less,” she added.

Burning rice straw also causes air pollution as the smoke produces carbon dioxide, carbon monoxide, nitrogen dioxide, and sulphur dioxide. Most of these are also classified as greenhouse gases.

More importantly, burning rice straw is unhealthy – not only to the environment but to people as well. “Rice straw burning is also known to emit particulate matter and other chemicals such as dioxins and furans that have negative impact on human health,” the EEPSEA paper said.

About 90% of the world’s rice crops are grown and consumed in Asia. Across the thickly-populated region, some governments are trying to outlaw the practice of burning rice straw.

However, several burning alternatives – like incorporating the straw into the paddy field, followed by alternate wetting and drying to reduce methane emissions – are recommended but not always possible. Growing rice on uplands is another option because straw can be incorporated into the soil without high methane emissions of flood rice fields, but it results in reduced yields.

In the past, attempts to profitably collect and use rice straw for clean energy have almost all failed. That’s being turned around by Craig Jamieson, whose work has taken him across Africa and Asia, developing bioenergy solutions that enhance rather than compete with food production.

“Rice straw is one of the world’s largest bioenergy resources,” Jamieson, a British national, said in an exclusive interview.

In 2016, with financial support from the United Kingdom government, he established an industrial pilot plant in Laguna making clean fuel from waste rice straw under a company called Straw Innovations (SI) Ltd., where Jamieson serves as its director.

“All around the world, the hunt has been on for a large amount of biomass that can be used for delivering clean energy without competing with anything else and we have millions of tons of it being burnt,” Jamieson was quoted in an earlier interview by World Biogas Association. “That’s a clear indicator that it’s there for the taking – a potentially vast resource that can be used for bioenergy and food production.”

Right now, SI is teaming up with the Laguna-based Southeast Asian Regional Center for Graduate Study and Research in Agriculture (SEARCA) in a three-year project called Rice Straw Biogas Hub.

The project is funded by Innovate UK under the auspices of the United Kingdom Research and Innovation organization. Also involved with it are UK SME Koolmill and UK academic partner Aston University.

The project is expected to make clean energy accessible to remote and underserved rural communities. “(It) will generate biogas as clean energy from waste rice straw and provide an innovative package of technology services for rice farmers,” said Dr. Glenn B. Gregorio, SEARCA Director.

The clean fuel is used for drying the grains and milling thereafter. “We asked farmers and their preference was to use the energy for productive purposes rather than domestic use. So, that’s what we are doing,” Jamieson explained.

According to Jamieson, his UK-registered group has established a rice drying service through the combustion of biogas from rice straw.

Drying is the most critical operation after harvesting a rice crop. When rice is harvested, it contains up to 25% moisture. The goal of rice drying is to reduce its moisture content to meet the recommended levels for sale and long-term storage.

“It is important to dry rice grain as soon as possible after harvesting – ideally within 24 hours,” IRRI explained. “Delays in drying, incomplete drying or ineffective drying will reduce grain quality and result in losses.”

IRRI said high moisture levels during storage can lead to grain discoloration, encourage development of molds, and increase the likelihood of attack from pests. If the grains are used for seeding purposes, the germination rate is greatly decreased.

But before drying, rice has to be harvested first. Here, the SI is introducing a rice harvesting system that it has developed over five years. “The main problems are in getting the rice straw out of the field and to a place where it can be used,” he said.

The solution: the 5-in-1 harvesting technology, referring to a machine which is said to be the first of its kind in the world. “Our machine performs in one pass of the field and performs the five separate operations in conventional straw collection – harvester, chopper, rake, densifier, and collection. It’s more efficient and, critically, it works even in wet conditions (muddy or flooded fields),” Jamieson pointed out.

The collected palay are then brought to another machine where the grain is separated from the rice straw. “At the biogas hub, a dryer dries the rice grain with energy from the rice wastes, another removes the husk and another mills the grain to remove the brain, thus giving the final product,” Jamieson said.

The dryer takes about 12 hours for the grain to dry, Jamieson said. “The technology innovation is to use rice straw to power the process,” he said. “We give farmers the option to retain ownership of their grains throughout the process.

“In some of today’s cases, farmers only get 4% of the purchase price of rice. In our model, farmers can use our harvesting, drying, and milling services and then sell the finished products to the public. We just take our cut after the sale….”

To produce methane in the hub, water is added with the rice straw. The methane gas is a direct substitute for diesel or kerosene in conventional dryers.

“In the past, the government tried to give out free rice dryers but as soon as something broke, the dryers were no longer used,” Jamieson said. “Our business model is to own and operate our equipment and offer it as a service to farmers. They pay us a service fee but don’t need to buy or operate our equipment.”

During the process, the rice straw gets broken down into fertilizer, which can be used to fertilize the rice. Or, it can be applied as organic fertilizer for crops, vegetables and fruits. “It can be used for anything,” he said.

Dr. Gregorio said the Rice Straw Biogas Hub demonstrates efficient removal of waste rice straw from farmers’ fields and conversion into eco-friendly and commercially viable products, focusing on biogas and fertilizer.

“With this, it is envisioned that farmers could triple incomes while protecting the environment,” Dr. Gregorio stressed. “Through an affordable, value-adding commercial business model, farmers will avoid buying and maintaining expensive equipment.”

The clean fuel produced in the biogas is only used for drying rice grains. Because that’s what the farmers in the area need. Jamieson, however, said the fuel can also be used for cooking. “If that’s what those concerned farmers and communities want, why not?”

Dr. Gregorio, an academician with the National Academy of Science and Technology (NAST) added that the biogas hub will engage farmers in a working model for income resilience. “SEARCA will help measure and establish the impact of the hub on farmer incomes, equality of opportunity, food security and decarbonization benefits, and will also be involved in formulating recommendations for policymakers,” he pointed out.

For its part, Koolmill will showcase its energy-efficient rice milling technology, packaged in a pay-per-use business model. As for Ashton University, it will conduct surveys in Laguna and major rice-growing areas across the country to assess attitudes toward and socioeconomic impacts of the hub and proposed business models.

Jamieson is very hopeful about the Rice Straw Biogas Hub. “This new project will demonstrate how rice straw can be used to supplement manure and other wastes in biogas production,” he said.

The British innovator believed the biogas hub can prevent the burning of millions of tons of rice straw as waste across the region each year. “The hub has exciting potential to bring clean energy access to the 150 million small-scale rice farmers who need it to process their crops and generate new income opportunities,” he said.

Dr. Gregorio is also very optimistic. “Rice straw biogas is an innovative way to increase our efficiency in producing rice and maximize the utilization of its by-products like straw for energy,” he said. “(It’s) a good example for a circular economy – nothing goes to waste. This is carbon-wise rice farming.”

Jamieson is hoping the project will help address energy challenges faced by developing countries like the Philippines. He argued however that what his group is doing is not the only way to use rice straw for energy; it’s just showcasing one route among many. “Once we have harvested and collected the rice straw, the choice of end use will be site specific to some degree,” he pinpointed.

Just recently, Straw Innovations Ltd. was one of the three successful companies recommended by Shake Climate Challenge for £100,000 of investment.

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