Methane? Burn it!

Farmer Peter van Roessel steps onto the enormous plastic bag behind his farmyard, accidently stepping in a puddle of water. His clogs fill up at once. But he hardly notices, as he eagerly carries on demonstrating the trial taking place on his farm.

The jovial Brabant farmer runs a dairy farm-cum-care farm in the Haarsteeg countryside near Den Bosch. What he is walking over now is a slurry bag of 52 by 26 metres, which can hold up to 1500 cubic metres of slurry. The bag is nearly full of the winter output of his 65 cows, which are in the nearby barn. It’s a strange feeling to walk over the bag, as if you were walking on a waterbed.

Biogas

The slurry bag is connected by two pipes with a much smaller gasbag beside it, which captures the gas formed in the slurry. Pure biogas, explains project leader Roland Melse, a researcher at Wageningen Livestock Research. ‘Biogas consists of 60 per cent methane and 40 per cent CO_2.   The amount of methane generated depends on the temperature and the composition of the manure.’ In standard manure silos and bags, that biogas disappears into the outdoor air through ventilation pipes.

It is not easy to make good use of the methane, explains Melse. ‘The quantities from the manure storage on farms are relatively small, and they are only available for a couple of months a year. In the spring, the manure is spread on the land. The biogas is not enough to make using it to heat water economically viable.’ But you can make the methane less harmful by converting it into CO_2.

That sounds a bit odd: helping the climate by producing CO_2.  ‘But in fact it is climate-neutral,’ says Melse, ‘because this carbon has come from organic matter in the feed, so it is part of the short carbon cycle. By converting the methane into CO_2, you convert a strong greenhouse gas into a much weaker greenhouse gas.’ One kilo of methane contributes 21 times as much to global warming than a kilo of carbon dioxide.

Burping cows

The livestock sector is a horrendous producer of methane. ‘Seventy-five per cent of the methane in the barn comes out of the animals’ mouths,’ explains Karin Groenestein of Wageningen Livestock Research. She and her colleague Ingeborg de Wolf coordinate all the climate pilots currently running in the livestock sector (see inset). ‘The manure is responsible for the other 25 per cent of the methane emissions from the barn.’ The experiments mainly target cows, as they are the major producers.

‘The average cow produces 125 kilos of methane per year in its rumen. Then there is another 40 kilos from emissions from the manure. The average pig produces about 1.5 to 2 kilos internally and 10 to 20 kilos via the manure.’

Animals are not the only methane producers, actually. Roland Melse enjoys demonstrating the sensitivity of the new methane meter that has been acquired for this project. Half of all human beings produce methane too. The apparatus, which resembles an alcohol meter, shows this accurately. Melse’s own gut flora are declared innocent. But in the case of farmer Van Roessel (and, admittedly, that of this reporter), the meter shoots up. ‘A question of genetic makeup,’ Melse reassures us. Luckily, the quantities are minute.

Burning

The pilot is not going particularly well so far. There is very little gas formation, and none has been burned so far. The installation was set up in December, but the gas bag is still as flat as a pancake. Van Roessel and Melse think this is because of current temperatures. It is too cold for the bacteria to produce the biogas. In itself that is good news: the less methane, the better. Van Roessel: ‘But soon, when the sun shines on the manure, the gas production will get going.’

Burning the methane is one of three methods been trialled under Melse’s supervision. Besides this ‘thermic oxidation’, there are two other trials running in which the methane is oxidized biologically (by bacteria). In an above-ground variant, the gas from the manure silo is piped into a basin with a compost biofilter, where bacteria in the compost break down the methane. A soil variant provides a set of underground, perforated tubes that the gas is moved along. Soil bacteria have to do the work of breaking it down. This soil filter still has to be laid down.

The trials are carefully monitored and recorded. ‘The techniques are not new in themselves,’ says Melse. ‘What is new is that they are being demonstrated on this scale on a farm. We want to establish whether they work, how much they cost and what they deliver in the way of CO₂ reduction.’