According to Biomass Magazine (yeah, I read that) Europe has over 8,000 anaerobic digesters (and this number is quickly rising: projected to increase to 25,000 by 2020!!!). Meanwhile, the US has fewer than 200.
Anaerobic digesters (AD) take in organic waste (food, yard waste, manure, etc.) and create biogas (methane + carbon dioxide), otherwise known as natural gas. They generate revenue from three main sources: selling their energy to the grid, tipping fees for the organic waste they take in, and selling the ‘digestate’ (leftover mush) as fertilizer.
So what is the potential for this energy sector in the US? The US generates 36 million tons of food waste annually and 31 million tons of yard waste. Digesting 1 ton of food waste can generate about 300 kWh, and according to the EPA, if half of our food waste were anaerobically digested, this would produce enough energy to power 2.5 million homes for 1 year. Add to this the energy potential from sewage and farm manure, and organic material has the potential to supply a not insignificant portion of our energy needs.
What’s the reason more people haven’t tapped into this energy source already? In the US, cheap landfill tipping fees, combined with cheap energy are tough to compete with. But Harvest Power is one company trying to beat the odds.
Harvest Power is a for-profit company that operates over 30 composting facilities in North America – these facilities collect food and yard scraps and convert them to mulch, compost, and nutrient-dense soil supplements. In 2013 Harvest also began operating two power plants in Canada that run off collected organics (the company calls these plants Energy Gardens). And its first US-based power plant opened in Orlando late last year. The facility is a co-generation plant, using energy both from solid and liquid organic waste, and is connected with a theme park in the state… guesses as to which one, anyone??
Does Harvest Power have the potential to be competitive in the waste management and energy sectors? The company claims that its waste collection fees are actually lower than those offered by most landfills, which is impressive. While its energy prices are cheaper than prices for most renewable energy sources, they are still more expensive than average prices for natural gas-powered electricity (one of their Canadian plants currently sells for 13cents/kWh).
I’ve posted before about the major push waste management companies are making to categorize landfill gas as a ‘renewable’ energy source. I find this type of categorization murky, at best, as it suggests that the landfill gas is produced intentionally, and that landfills should thus be lauded as environmentally friendly. Instead, the methane produced from landfills is simply a byproduct of burying organic materials. In addition, landfill gas collection systems are woefully inefficient, where as anaerobic digestion is a process set up with the intention of capturing off-gassed methane, and is significantly more efficient.
In addition, nutrients caught up in organic materials are lost when these are buried in landfills. Soils are further stripped, leading to more need for fertilizers. In anaerobic digestion none of these nutrients are lost and the leftover ‘digestate’ is a nutrient-rich soil enhancer.
In Europe renewable energy sources are subsidized, and landfill tipping fees are made higher. This allows energy from anaerobic digestion to be more competitive. Though energy from anaerobic digestion may not strictly be the cheapest from of energy in the present, I often think that we offset future costs onto the future – i.e., landfills are cheap now but may lead to exorbitant costs in future water treatment due to groundwater contamination. I believe the same is true for energy from food waste – though it may be cheaper than coal in the present, what are the future costs of burning coal? and are these offset by anaerobic digestion?