Home Environment Turning methane from rice straw into clean fuel

Turning methane from rice straw into clean fuel


Text and Photo by Henrylito D. Tacio

Our planet is getting warmer each year. In fact, the days are hotter even if Christmas season is fast approaching. In the past, during the so-called “ber” months, the weather started to get cooler. 

But not anymore. Experts claim that this may be due to climate change, which refers to long-term shifts in temperatures and weather patterns. Climate change is caused by the increase of greenhouse gasses (GHGs) emitted into the atmosphere.

The hot weather these days is caused by the continuous increase of release of GHGs, particularly carbon dioxide, methane, and nitrous oxide. We fail to keep on the objective of the Paris Agreement. The goal of the legally binding international treaty on climate change is to limit global warming to well below 2, preferably 1.5 degrees Celsius, compared to pre-industrial levels.

“We are still nowhere near the scale and pace of emission reductions required to put us on track toward a 1.5 degrees Celsius world,” Simon Stiell, executive secretary of the UN Climate Change, said in a statement.

What is even more alarming is that atmospheric levels of three main greenhouse gases mentioned earlier all reach new record highs in 2021, according to a new report released by the UN’s World Meteorological Organization (WMO).

Take the case of methane whose concentrations last year reached 190.8 parts per million, the value of which constitute 262% of pre-industrial levels before human activities started disrupting the natural balance of this gas in the atmosphere.

“The continuing rise in concentrations of the main heat-trapping gases, including the record acceleration in methane levels, shows that we are heading in the wrong direction,” WMO Secretary-General Petteri Taalas was quoted as saying.

Methane is the second largest contributor to climate change and consists of a diverse mix of overlapping sources and sinks. That’s why scientists have difficulty in quantifying emissions by source type.

Scientists also don’t know what causes the recent increase of methane emissions but some research indicates that a large amount is coming from “biogenic sources,” such as wetlands and rice paddies.

A possibility explored by WMO’s Greenhouse Gas Bulletin is called “climate feedback,” which means that as it gets warmer, organic material decomposes faster in tropical wetlands, thus increasing emissions.

That’s really bad news, particularly for Filipinos who eat rice more than three times a day. Being a staple food, rice is grown extensively in the country; in fact, the Philippines is one of the world’s largest rice producers.

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, which are left in the open field.

In the Philippines alone, about 11.3 million tons of rice straw are produced. Most farmers leave rice straw in the open field; others burn them immediately or later. When left in the flooded fields, decomposed rice straw generates methane-emitting bacteria. Most of the produced methane is released into the atmosphere.

Methane is primarily used as fuel to make heat and light. So, why don’t we use the waste rice straws in producing clean fuel? Is this possible?

Yes, according to Craig Jamieson, the director of Straw Innovations (SI) Limited.  In 2016, with financial support from the United Kingdom government, he established an industrial pilot plant making clean fuel from waste rice straw in tandem with the Laguna-based Southeast Asian Regional Center for Graduate Study and Research in Agriculture (SEARCA).

The three-year project, called Rice Straw Biogas Hub, 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 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, 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 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.

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 in an exclusive interview. “(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.

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