Last week the City of Surrey, British Columbia announced an 80,000 tonne per year anaerobic digester that can turn household organic waste into fuel for vehicles. The facility will be located beside the waste transfer station and will be the largest in North America. It is expected to cost $ 67.6 million, of which 25% is provided by Canada’s taxpayers (http://www.surreyleader.com/news/170582356.html).
Canada has the longest running pilot anaerobic digester in North America – in Dufferin, Ontario. Its a 25,000 tonne per year anaerobic digester that has been operating with household organic wastes since 2003. In a review anaerobic digestion by Arsova (2010), the operations costs for this facility were estimated at $ 185 per tonne of organic waste ( http://www.seas.columbia.edu/earth/wtert/sofos/arsova_thesis.pdf). The proposed expansion of this Dufferin facility to 110,000 tonnes per year was reported to bring the net cost of organic waste processing to approximately $ 130 per tonne. The facility was going to produce 7.8 million cubic meters of biofuel to power city trucks, as per diagram below.
What is the value of the biofuel from an 80,000 tonne per year anaerobic digester? Using the 9 years of Dufferin experience as a guide, we can expect up to 5.67 million cubic meters of biofuel. Assuming an equivalent cost of $ 0.12 per cubic meter of natural gas, we recover a value of $ 680,000 per year. If the anaerobic digester will be a dry digester, we can expect lower biofuel output per tonne because there is less available energy in the yard waste that is required for this process. There are indeed other benefits to anaerobic digestion including greenhouse gas credits, which hopefully will make a substantial difference in the net operating cost.
Another interesting question will involve the 70,000 tonnes per year of material coming out of this biofuel plant. If the plant is a liquid anaerobic digester, we can expect 25,000 tonnes of wet odorous sludge that needs to be further processed , along with some 50,000 tonnes of liquid containing high COD and nutrients (based on the Dufferin plant history). If the plant is a dry digestion facility, there will be approximately 70,000 tonnes of partially decomposed organic material that needs further processing and a home.
This initiative is part of the excitement created by Metro Vancouver’s goal to divert organic waste from landfill by 2015. In the last blog, I discussed Seabird Island’s initiative to compost and capture energy from up to 80,000 tonnes per year of organic material. There is up to 250,000 GJ of potential energy in the 80,000 tonnes of organic waste. Seabird is hoping to capture 10 to 25% of this as heat energy and use it to heat greenhouses, or in organic fertilizer manufacturing. In terms of the economics, at a tipping fee of $ 60 per tonne, and a hauling fee of $ 10 per tonne from the Vancouver area, the total annual cost for 80,000 tonnes is $ 5.6 million, which is still less than the annual capital cost of the anaerobic digester! (If we assume the carrying cost of the capital at 10% per year, that works out to $ 6.7 million annually, or $ 84.50 per tonne of organic material entering the facility).
Perhaps Seabird Island can work with the City of Surrey to further process the residue from the digestion facility can be further processed on Seabird Island, where the valuable plant nutrients can then be recycled to create healthy soil that decreases our need for chemicals and pesticides. There are two potential challenges with this option: 1. the residue from an anaerobic digester has some odor, and 2. the energy value of the organic material is reduced, hence not as valuable for heat energy recovery.
During the next few years, there will be a lot of discussion and digestion of the various organic waste options and costs. One thing that we need to remember is that all of this organic waste contains valuable organic matter and plant nutrients that needs to be recycled back into the soil from which it came. This is important if we continue to strive for local healthy food produced with a minimum of chemicals and pesticides.
In the meantime, communities are welcome to discuss a socially, environmentally and economically sustainable solution to their organic waste with organizations like Seabird Island, where there is a complete recycling of nutrients and organic matter, energy recovery, and the added benefit of additional local sustainable food produced with a minimum of chemicals and pesticides!