Extracting methane from rice straw to produce clean fuel

In the past, attempts to profitably collect and use rice straw for clean energy have almost all failed. That’s being turned around by a man who is developing bioenergy solutions that enhance rather than compete with food production.

By Henrylito D. Tacio

Almost everyone on the planet now knows what climate change is. It refers to long-term shifts in temperatures and weather patterns. These shifts may be natural, such as through variations in the solar cycle. But since the 1800s, human activities have been the main driver of climate change, primarily due to burning fossil fuels.

Burning fossil fuels generates greenhouse gas emissions that act like a blanket wrapped around the Earth, trapping the sun’s heat and raising temperatures.

“Emissions continue to rise,” the United Nations claim. “As a result, the Earth is now about 1.1°C warmer than it was in the late 1800s. The last decade (2011-2020) was the warmest on record.”

Among the identified greenhouse gasses, most reports emphasize more on carbon dioxide, which comes from using gasoline for driving a vehicle or coal for heating a building. Deforestation also releases carbon dioxide.

Methane, another greenhouse gas, is equally significant. Although methane has a much shorter atmospheric lifetime than carbon dioxide (around 12 years compared with centuries for carbon dioxide), it is a much more potent greenhouse gas, “absorbing much more energy while it exists in the atmosphere,” says the US-based International Energy Agency (IEA).

As such, methane has important implications for climate change. “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.
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Close up of dried palay (Jay-Rness Ceria)

The IEA says the annual global methane emissions are around 570 million tons. This includes emissions from natural sources (around 40% of emissions), and those originating from human activity (the remaining 60%, known as anthropogenic emissions).

“The largest source of anthropogenic methane emissions is agriculture, responsible for around a quarter of the total,” the IEA says.

The Philippines, being an agricultural country, has contributed a substantial amount of methane to 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.

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 gasses.

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.

Across the thickly-populated region of Asia, where about 90% of the world’s rice are grown and consumed, some governments are trying to outlaw the practice of burning rice straw due to the reasons cited above.

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 successful. 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 (Photo by Henrylito D. Tacio).JPG
The waste after harvesting rice (Henrylito D. Tacio)

“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.”

Just recently, the SI teamed 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 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, 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 level 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 introduces 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,” Jamieson 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 is 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.
This is how the rice is harvested (Jay-Rness Ceria)

“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.

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

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.

In last year’s fourth quarter, the SI ventured its first commercial combine harvesting in two locations in Nueva Ecija. “We found that there was a difference in the harvesting conditions between the two locations, but we were able to adapt to some challenges we encountered during our first operation,” reports Jay-Rness Ceria, SI’s farmer relations manager.

Photo by Henrylito D. Tacio