A network of anaerobic digesters could power the city and be cost-effective, according to the study
FROM Paolo Travis
Biogas from grass, when is it appropriate?
Produce biogas from grass clippings It is possible and the topic is not entirely new. In fact, already about ten years ago, a European project GR3 – From grass to green gaswas devoted to utilization waste grassi.e. coming from a mowing park or agricultural area, as a raw material for the production of clean gas. At that time, in a European project in which Veneto also participated, there was an attempt to to develop a suitable technology to produce this mixture of gaseous methane and carbon dioxide is produced by oxygen-free fermentation of organic matrices, (anaerobic digestion); in nature, this process occurs in the digestive system of animals and in the transformation of organic material in the absence of oxygen.
Biogas production from grass: a process
The natural process of biodegradation of organic matter without oxygen can be reproduced using the so-called anaerobic digesters, tank-like, in which biogas is converted into a fuel that can replace gas derived from fossil fuels, but also can power generators and produce fertilizers. However, after ten years of research, the energy potentially produced by wood shavings is still grossly underutilized throughout Europe and the United States. Reason? More than one: certainly because AND‘insufficient knowledge of appropriate technologies for mowingconservation and anaerobic digestion of grass residues, as well as and‘lack of cooperation between supply chain operators, to which a non-secondary topic is added: poor economic viability. As a result, plant residues from mowing, despite their interesting potential, are either not used or are marginally used.
A new option from America?
However, the topic returns to interest after the American researcher from Iowa State University, Lisa Schulte Moorehas spent the last few years studying how to efficiently convert harvested grass into affordable renewable gas for farmers who decide to convert parts of their land into prairies from which they will cut grass for energy use.
“We are looking at existing markets where there is already demand, leveraging existing infrastructure to reduce the cost of energy transformation and create benefits across categories. We want benefits for farmers, benefits for businesses, benefits for municipalities and benefits for societysaid Schulte Moore, professor of ecology and natural resource management. “To replace natural gas with resources that will revive sustainable agriculture, we need to be able to quantify how much energy we can produce and show that it can be cost-effective and environmentally sustainable.” added Mark Mba-Wright, associate professor of mechanical engineering and co-author of the studies.
American model 10 anaerobic fermenters: how much does the produced biogas cost?
In a study published in BioEnergy ResearchAmerican scientists have developed a model based on a network of 10 hoods located both in and around the city of Ames, fed not only by grass feed but also lfarmyard manure, biofuel by-products, food waste and wastewater. The analysis showed that fermenters could produce biogas at a break-even price $0.011/kWhelectricity at a balanced price from 0.025 to 0.039 dollars/kWh AND fertilizer at a price ranging from $0.035 to $0.055/kWh; The cost of producing biogas is higher than traditional gas, but the study found that the largest municipalities in Ames would be able to reduce costs by using economies of scale to reduce capital costs and optimize infrastructure to minimize waste while providing enough power to mitigate peaks in demand, although the research refers to future studies to evaluate the actual feasibility of these use cases.
Instead, a second American study, published in GCB Bioenergydeveloped another model to evaluate the economic and environmental impact of two digesters for the processing of grass biomass; according to the analysis, they would generate a profit over their lifetime, estimated at 20 years more than $400 million thanks to 45 million gigajoules of renewable natural gas produced over two decades and they should a83% lower carbon footprint than natural gas derived from fossil sources. But in the study, to calculate the profitability of the biogas produced by the two fermenters, the researchers also took into account existing programs and bonuses at the national and federal level that promote energy production with a low environmental impact, while taking into account prairie grass on land of non-productive agricultural crops.