Subject Categories: Earth & environment
Published online 4 April 2012
Biofuels — fuels derived from corn, vegetables or plants — are a renewable source of energy that leaves less carbon footprint than fossil fuels. In recent years, however, there is a growing concern that the cultivation of plant biomass may increase the usage of nitrogen fertilizers and promote the release of nitrogen oxide — a greenhouse gas — into the atmosphere.
Jie Chang at Zhejiang University in Hangzhou and co-workers have now investigated the possibility of using nitrogen from constructed wetlands to grow plant biomass for biofuel production. Such an approach might not only help tackle the world's energy crisis, but also avoid the wastage of valuable food crop and the release of extra nitrogen into the environment.
A constructed wetland is an artificial ecosystem that uses plants and nitrogen-fixing bacteria to remove pollutants in wastewater. China has built thousands of constructed wetlands in recent years for treating the country's sewage and storm water runoff.
The researchers designed and constructed five experimental wetlands for biofuel production in subtropical China. They assessed the costs and benefits and found that constructed wetlands could generate more energy per year than microalgae, switchgrass, corn or soybean. Although constructed wetlands emit a large amount of greenhouse gases, the amount of carbon dioxide they absorb is more than enough to compensate for the emissions.
Based on their findings, the researchers estimate that if all constructed wetlands in China are used for biofuel production, China could reduce its gasoline consumption by 6.7%.