There is truth to the saying: “you get out what you put in”. Well-constructed home renovations will withstand extreme weather. You’re able to spend the money you’ve worked hard to gain.
This is no different from the story of advanced biofuels, a renewable energy source capable of using organic waste and lignocellulosic crops as sources of energy. There are a wide variety of raw materials, called feedstocks, which can be used in the production of biofuels. However, in order for advanced biofuels to become a practical and common alternative, their production must be economically favorable relative to crude oil. The production of high-quality final biofuel products must be evaluated to confirm that they are more valuable than the feedstock and energy used to make them.
Nutrients including nitrogen, phosphorous, and potassium often limit both the quality and the yield of the crop. Although many nutrients are found naturally, soil conditions have begun to degrade globally as a result of issues such as climate change, land overuse, and desertification. This in turn, has put a strain on crop production. To replenish nutrients in soil, fertilizers are used. However, this creates an additional problem since fertilizers are both economically and environmentally costly to produce – 1% of the world’s energy is dedicated to fertilizer production (http://www.agronomysociety.org.nz/2011-journal-papers.html). An organic product following the creation of biofuels can act as a substitute for the fertilizer.
Taking on the Challenge of Fertilizing Soil after Choosing Stover as the Feedstock
Dr. Brandon Gilroyed, at Guelph University’s Ridgetown campus, uses anaerobic digestion systems in order to produce renewable fuels from waste products. Biogas, the primary product of anaerobic digestion, can include methane and carbon dioxide, which are transformed by microbes during the digestion process. At the Ridgetown site, this has been applied to waste crop products, called “stover”, which includes the non-edible stalks, leaves, and cobs left over after the grain harvest. Corn cobs are particularly ideal as a feedstock because they have a uniform structure and produce less ash (http://onlinelibrary.wiley.com/doi/10.1002/bbb.1485/abstract). However, corn stover has a low bioenergy yield, which is dependent on both the amount of dry matter that can be produced in a given area, and the ease for microbes to transform sugars into ethanol. This means that in order to get a quality biogas product, more financial and biological input is required. To decrease costs and to mitigate fertilizer use, waste products created by biofuels production, called digestate, can be re-invested into the soil (See Image).
Thus, the feasibility of a closed-loop system has been explored, although some challenges remain.
Schematic Abstract: the type of feedstock for biofuels production is determined by upstream factors such as the amount of nutrients (nitrogen, phosphorous and others) found in the soil.
Closed-loop systems are those in which a product is used for the next generation’s production.
According to an expert at the Ontario Ministry of Agriculture, Food, and Regional Affairs (OMAFRA), one challenge is that waste products containing useful nutrients could potentially be dilute in a liquid state. A product which is capable of improving soil nutrients would require processing, such as densifying the liquid. However, the economics of this have yet to be understood.
Guelph Improving Closed-Loop Biofuels Production
Nonetheless, Gilroyed is still optimistic, stating that “purpose grown bioenergy crops that have a higher bioenergy yield will have a greater chance for success”. He hopes to explore low-input perennial grass crops, which can be planted in areas where food crops cannot. Using these crops as a feedstock – as opposed to crop residues – could reduce production costs and improve output yields.
In New Zealand, Dr. Huub Kerckhoffs and his colleagues have already been exploring purpose-grown biomass crops, specifically on marginal land that has been impacted by drought (http://www.agronomysociety.org.nz/2011-journal-papers.html). Their first goal was to identify a suitable crop for a region similar to Southern Ontario which would be adaptable to frost and shorter growing seasons. Ideally, the feedstock should also be perennial, capable of digestion by microbes, as well as non-woody. Following the original planting process, these perennial plants would require fewer inputs. Jerusalem artichoke is a crop capable of surviving in these conditions as well as producing high biomass yields per hectare.
The picture of the Jerusalem artichoke is labeled for reuse at https://en.wikipedia.org/wiki/Jerusalem_artichoke
Marginal land is unhospitable and can require unsustainable levels of inputs. It often has poor soil composition, climate conditions (ex. droughts), and terrain.
Applying Purpose-Grown Crops in Southern Ontario
The experts at OMAFRA have identified an alternative to recycling nutrients after the production of biofuels. In this case, only part of the crop is removed from the field. For the purpose-grown crop, miscanthus, the harvest occurs in the fall but straws are only removed in the spring. This remaining leaf material can subsequently replenish soil nutrients. The specific amount of grass or crop stover that can be removed is dependent on the region due to many factors, including crop rotation and soil conditions. This is the current challenge that scientists in Southern Ontario are researching.
As policies are put forward and experiments are designed, policy makers and scientists should be mindful of the feedstock they choose, so as to optimize the system by improving the quality of products while decreasing the economic and environmental requirements of soil inputs.
Proposed closed-loop system: Gray boxes indicate inputs and orange boxes indicate end products while arrows show movement throughout. Notably, nutrients such as nitrogen can be added to the crop through fertilizers or digestate from a previous harvest. Digestate is a product following anaerobic digestion of solid material that has not been converted into fuel. It is often rich in compounds containing nitrogen. Another way of closing the system is by using the biofuel product for agricultural equipment or transportation to processing plants.
Acknowledgements: I would like to thank Dr. Brandon Gilroyed and the research team at OMAFRA for participating in email and phone interviews.
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