Not just a load of manure

In my continuing research of sustainable energy sources, I could not resist sharing portions of this article from Sustainable Agriculture Research and Education (SARE) outreach, a decentralised grants and education programme operating throughout the USA. Since 1988, SARE’s competitive grants programme has supported farmers, ranchers, researchers and educators who are improving the sustainability of agriculture in the USA.

Capturing fuel from animal manure

Converting animal and plant waste into energy can be a triple-hitter: it not only helps reduce waste going to landfills or from being released as gas into the atmosphere, but it saves energy and money. Waste materials, ranging from animal manure for methane to wood chips for direct heat, to waste vegetable oil for straight use or conversion to biodiesel, also have a positive energy and carbon balance. That is, more energy is derived from the fuel than is spent converting it. Therefore, no net CO2 is generated.

Nature has always used anaerobic digestion – bacteria breaking down organic material in the absence of oxygen – to recycle waste. Modern anaerobic digester systems on livestock farms work on the same principle: the solids in manure are converted by bacteria into biogas, primarily methane, which can then be used to generate electricity.

Blue Spruce dairy, a member of Vermont’s Cow Power programme, uses an anaerobic digester to turn manure into methane, which is used to generate electricity. Anaerobic digesters have traditionally been geared towards large livestock confinement operations, which produce a lot of manure. The digester’s broader-use potential, however, has spurred manufacturers to explore scaling down the technology for small- and mid-sized farms. China and India have long promoted smaller digesters. Digesters resolve multiple problems simultaneously:

  • When the liquids and solids are separated and treated, odour is reduced. The liquid portion is much easier to apply as fertiliser and is often mixed directly with irrigation water.

  • The odour- and pathogen-free solids can be sold as compost or reused as bedding, either generating new revenue streams or saving producers money on purchased bedding.

  • Fly populations in and around the manure storage systems are reduced, as are weed seed populations in the compost.

  • Biogas is captured and burned to power the farm and/or generate electricity to be sold back to the power supplier. Capturing and using the methane prevents its discharge to the atmosphere, where it has 21 times more global warming potential than CO2.

A unique partnership between an investor-owned utility and several Vermont farms is making ‘cow power’ more feasible for a number of growers by allowing customers to choose sustainable energy. It currently takes about 500 milking cows to produce enough energy for cow power to be economically viable, so a number of small-scale farms are considering combining their manure to become eligible.

It brings to mind our family allotment, where we grew our own vegetables during WW2. One of my duties was to follow horse riders in the adjacent park and collect the ‘horse apples’ for manure!

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