Horse manure as a home heating source? The concept might not be far off, German researchers have found.
Sigrid Kusch and fellow workers at the University of Hohenheim in Germany have been investigating the methane-producing potential of horse manure.
Horse dung: it's a perennial problem. What do you do with it? In the past, townsfolk would follow the cart in hope of collecting some fertiliser for the garden or allotment. Nowadays it is more likely to be considered a health hazard.
For horses kept on small areas, collecting the droppings helps control the spread of parasitic worms. It also increases the area available for grazing by reducing the amount of contaminated pasture.
But, it's all very well collecting the dung from the pasture - what do you do with it afterwards?
And then there is the problem of disposing of faeces and contaminated bedding from the stable.
The researchers at the University of Hohenheim have found they could ferment the manure to produce gas, which could be used for heating.
Their laboratory study employed small-scale reactors, each with a capacity of about 50 litres. Horse dung and straw was used as the substrate for a batch digestion process. The leachate, the liquid that drained out of the substrate, was pumped back to the top of the reactor twice daily. The temperature in the reactor was maintained at about 35ºC.
Initially, the scientists added a solid inoculum (partly digested faeces) to the reactor to start the digestion process. However they found that if they flooded the reactor with liquid collected from an earlier experiment, rather than simply percolating the liquid that leached out of the manure, they did not need to add the solid inoculum.
Flooding the solid matter with liquid led to slightly higher gas production over the six-week cycle than when the water was allowed to percolate through the dung and straw mixture.
If fact, they could even get similar results by using drinking water, without additional bacteria, to flood the reactor, although gas production was lower for the first 10 days. Methane was produced more quickly if the faeces and straw mixture was chopped into pieces about 4cm long before starting the digestion process.
The scientists estimate that if similar techniques were used on a larger scale the expected production would exceed 20m3 biogas /m3 of manure.
Who knows - maybe in the future we will come to look on horse manure as a valuable resource?
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