All the straw from rice in China could get turned into an inexpensive new renewable source of biofuel, new research shows.
In fact, three facilities in China already are making use of the approach.
China is the world's largest producer of rice, a crop that leaves behind roughly 230 million tons of rice straw each year — the stem and leaves are left behind after harvesting the grains. Although there some uses available for rice straw, such as animal feed or papermaking, a significant amount of it remains unused and burned in open fields, boosting air pollution and the risk of disastrous fires.
All that biological matter, or biomass, could in theory get converted into biofuel with the aid of germs that break it down into useful chemicals. An approach like this already is used in more than 30 nations worldwide to help convert corn, sugarcane and other crops into ethanol fuel, a type of biofuel.
Scientists have not tapped rice straw to make biofuel because bacteria cannot easily break down its cellulose, due to the complex physical and chemical structures making up this biomass.
Now researchers in China have developed a pre-treatment for rice straw that increases its potential for biofuel production. They mix the straw with lye, or sodium hydroxide, before giving it to bacteria to ferment. The lye helps make the straw more biodegradable. All this is done at ambient temperature, without need to spend extra energy, and just minimal amounts of water, helping make the process "simple, fast, cost-effective, and environmentally friendly," said researcher Xiujin Li at the Beijing University of Chemical Technology.
All told, the lye technique allowed researchers to boost production of biogas — a mixture of methane fuel and carbon dioxide — by up to roughly 65 percent. Three prototype facilities using this technology have been built in China.
The plan is to build centralized biogas stations for towns, which would feed the biofuel to each household through underground pipelines. The rice straw residues left afterward will go back to the fields as organic fertilizer. "This way, the rice straw will be completely recycled," Li said.
While carbon dioxide is a byproduct of this process — of concern since it traps heat from the sun, leading to global warming — "rice will absorb back the carbon dioxide from air during rice growing," Li said. "The carbon dioxide is actually recycled completely and the net carbon dioxide contribution to global is zero."
Although there have recently been rice shortages worldwide, leading to deadly riots in Haiti, there is so much rice straw around that "we cannot use so much straw using this technology alone at present," Li told LiveScience. "Although the planting area of rice was decreased recently, the reduction was limited, therefore the recent rice shortage will not affect our research."
In principle, this process could be widely used for many different kinds of straw, and therefore "be widely applied in all the countries who plant crops, including both developed and developing countries, and provide renewable and clean energy," Li said.
The scientists are set to detail their findings in the July 16 issue of the journal Energy & Fuels. They were financially supported by the Hi-tech Research and Development Program of China.
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