Converting wastes to resources
posted on December 9, 2010 2:00pm
Waste. It’s all around us, a reality of life, and perhaps more importantly, a potential resource. The generic term “waste” may have a negative connotation since it typically represents an unpleasant but inevitable end-product or consequence of an action or individual’s metabolism. Waste
products, along with their removal, transport and disposal, receive even greater scrutiny these days in terms of conserving and protecting the environment and finding innovative ways to recycle and reuse them.
Various methods exist for managing waste. These range from the traditional—wastewater treatment—to the more contemporary methods, such as converting waste products into energy to create a value-added product. Anaerobic digestion falls into this second category and, even though it sounds state-of-the-art, it’s anything but. Anaerobic digestion is a natural process of breaking down complex waste materials, such as waste produced by food processing plants or animal waste (manure), into its simplest form: methane gas and carbon dioxide. The beauty of using high-tech digester equipment is that the process occurs in real time as opposed to geological time, a process occurring naturally over thousands to hundreds of thousands of years.
Take manure for example. Animal waste is awkward to manage in its unprocessed state because of its high water content. According to the lead researcher on anaerobic digestion at Michigan State University, associate professor of biosystems and agricultural engineering Steve Safferman, digestion enables the waste to be separated efficiently into solids and water, thereby readying the components for further processing.
“Waste is a highly unstable product, and even if it’s stored and properly handled in a lagoon system, there are still the issues of odor, greenhouse gas emissions, and handling and disposal to contend with,” he explains. “It’s not efficient or economical to move liquid manure any great distance from where it’s produced. Once the separation takes place, you’re left with virtually liquid-free phosphorus manure with the consistency of dirt that can be easily and economically transported off-site. The resulting liquid can be spread on cropland providing it with nitrogen.”
Safferman notes that even though the effect on global warming is reduced 21-fold simply by burning off the methane that’s produced naturally through the digestion process, recycling it into energy presents a value-added opportunity.
“Investing in a digester is extremely expensive, but it leads to opportunities beyond just being able to manage manure more easily and protect the environment,” he says. “Methane is a valuable by-product that can be used for energy. Excess energy can be sold for profit, and producers can earn and sell carbon credits and receive renewable energy credits.”
The food processing industry, in its quest to safeguard the environment, has embraced highly engineered digester technology as a system for treating end-product pollutants from the food processing cycle for quite some time. Juice is the most common by-product from food processing. It has a high
pollution content but generally contains a lot of energy with little to no nutrients so additives are needed to complete the process.
Safferman and his colleagues are researching how blending farm and food processing wastes together could ultimately lead to more economical and efficient energy production. Partnering with a farm could eliminate the need to add these synthetic buffers and nutrients to food processing wastes, instead relying on the naturally occurring nutrients present in manure.
“There’s great potential for blending wastes, for putting two wastes together to produce so much more energy than either could alone, but our biggest challenge is determining the right ratios to use,” Safferman says. “This is a key piece of the puzzle, and we’re still a long ways off from being able to consistently predict the digestibility of blends without first conducting laboratory and pilot-scale studies.”
Another mission the researchers would like to tackle is to develop a centralized digester, one that can serve multiple biomass (waste used to generate fuel or energy) residuals producers, including smaller organizations.
“The (digestion) process doesn’t rely on size. The challenges are not in the process itself or the microbiology, but in the logistics and how to make it work economically,” Safferman says. “Smaller businesses are more at risk because it’s harder for them to conform because of the economies of scale. Just imagine if a small farm was able to extend its growing season by being able to heat its hoop house, or a small farm was able to use the energy to open a cheese factory? The question is: how can we create a new revenue stream by creating a renewable energy source?”
Safferman would also like to study the feasibility of fueling vehicles with gas originating from digester production.
“Instead of using the energy for electricity, can it be used to fuel a natural gas engine in a semi-truck or tractor?” he asks. “We know the science behind converting it into vehicle-grade fuel, but we first need to reduce the cost and simplify the logistics. More research is needed so that someday we can offset diesel fuel use, a substantial cost-savings to farmers.”
For the time being, reducing the cost of investing in a digester is one of the most obvious challenges facing North American innovators as compared to Europe which has upwards of 8,000 digester units in operation and economic incentive programs in place to minimize the payback period.
“There is great potential for digesters as part of a diversified system, but more work has yet to be done,” Safferman says. “I have no doubt that we’ll come up with advancements to reduce installation and implementation costs, but how does one really put a price tag on providing for a healthier environment?”
