A biosystems engineering professor from the University of Manitoba says anaerobic digestion by itself will not reduce phosphorous output from hog operations.
The province has referred to anaerobic digestors as being part of the solution to reducing the amount of phosphorous entering waterways from livestock operations.
"Anaerobic digestion is not a silver bullet in any way. In some cases you might argue it makes things even more difficult," explains Nazim Cicek. "Digestion does not really do anything to phosphorous, except it makes it more mobile. It releases some of the phosphorous from the organic material into the liquid, which in return makes it more recoverable."
"So you could envision having an anaerobic digestion system coupled with a struvite recovery system which would allow you to reduce the phosphorous content in your final product," he says. "If one combines it with a phosphorous recovery strategy, it could certainly help with rebalancing the nitrogen-phosphorous ratio in your manure."
Cicek says with cheap, green energy, a cold climate and minimal government support, it's tough to make the case for anaerobic digestion in Manitoba.
"It's certainly feasible in a place like Germany where there are several hundred large scale plants. The reason for that is both subsidies, and also the fact that electricity is expensive, so when you do make electricity on site you can sell it for a premium," he says.
"The research we do might be longer-term in nature, so in that sense there's some hope, but currently it is not feasible," he says. "Unless there are substantial subsidies in place, it's difficult seeing this technology taking off."
The province's new "Save Lake Winnipeg" Act bans any new hog industry construction or expansion unless technologies that protect water quality are used. When asked what kind of technologies that may include, Conservation Minister Bill Blaikie has mentioned anaerobic digestion.
Again, Cicek says the province cannot expect anaerobic digestion alone to solve the nutrient issues surrounding hog production.
"If you can find technologies that can rebalance the nitrogen-phosphorous ratio in manure and provide agronomically sound strategies, then Lake Winnipeg's issues will be somewhat alleviated," he says. "The question of how big this impact might be is still up there. There are lots of different sources of phosphorous into the lake."
"Without trying to take any sides on the political spectrum, it's important that we realize single technologies might not work everywhere and might not address all these issues simultaneously."
What is anaerobic digestion?
"The term refers to the breakdown of organic material when there's no oxygen available," explains Cicek. "There are a variety of environments where it naturally occurs, such as bogs where you have no oxygen, or in the guts of most animals."
"It requires a microbial community that breaks down large organic molecules into smaller ones and ultimately into the final end products of biogas."
"The primary objective in the past has always been to use anaerobic digestion to make energy," he says, noting there are records of ancient Chinese using biogas for heating over 3000 years ago. "It has moved to the point where biogas can also now be converted to other energy sources related to electricity, or you can even purify it to the point where its similar to natural gas."
He explains the digested material can also be used as organic fertilizer. Some people have also found technology for extracting pure fertilizer, such as struvite, from the digested product.
Anaerobic digestor at Glenlea
Cicek has been key in the development of a pilot-scale digestor at the U of M's Glenlea Research Station. The digestor is housed within a greenhouse, which minimizes the cost of heating the digestor. With traditional methodology, digestion requires temperatures of at least 35 degrees Celsius.
"We're trying to establish substrates that could be added to boost biogas yields, amendments such as glycerol or distiller grains or chopped up wheat straw, things of that nature that would allow us to increase biogas yields. By a virtue of increasing those yields, you establish a better energy balance...this allows you to make this process more feasible. Our ultimate goal is to make it work economically for folks in Manitoba and Canada."