With more manure digesters, we can meet green gas targets

Expert blog - 27 June 2024

There is a lot of interest in manure fermentation. Logical, because livestock farmers can use their manure to produce green gas and make a nice profit. In this blog, Willem Dubbelman, biogas expert from Energiefonds Overijssel, explains what manure fermentation is, what the advantages and disadvantages are and why he thinks there should be more manure digesters.

Where do you leave your manure?

'Manure is waste, it has to go. Dairy farmers can still dispose of much of their manure on the land. However, regulations on what they can dispose of on the land are getting stricter, especially under the influence of the Nature Restoration Act. In addition, manure contains not only nitrogen, but also phosphates; these can 'leach out' and pollute ground and surface water.

In addition, cattle in the Netherlands generally produce more manure than cattle farmers can dispose of on land. Chicken and pig farmers cannot dispose of their manure on land at all. They often have to export it abroad. That's a shame, of course: having to drive hundreds of kilometres to get rid of your manure. You can also ferment it and then turn the residue into organic fertiliser.

How does a manure digester work?

A manure digester is a very large, round tank. If you heat the manure in it a little - to the temperature of a cow's stomach - biogas is released. During that process, the enzymes naturally present in manure break down the organic dry matter. The gas released in the process is called biogas. In fact, biogas consists of the farts of enzymes. You then have to capture that gas and turn it into green natural gas.

Capturing gas

Biogas consists of about 57 per cent methane (natural gas). By increasing the composition from 57 to 89 per cent, you get natural gas, which can be used to run a central heating system or for industry. This can be done by passing the biogas through a membrane, capturing CO2 and leaving you with 89 per cent methane. There are more and more installations that can capture the captured CO2. Market gardeners can use that CO2  then use it well again in greenhouses as a growth promoter.

Less nitrogen

Fermentation not only provides green gas, but also reduces nitrogen in the environment. Livestock farmers with a manure digester install a special floor in the barn that ensures the manure enters the digester within hours. Without that floor, the manure already starts emitting biogas and nitrogen outside the digester. The manure floor makes the manure produce twice as much biogas and also stops nitrogen emissions.

Organic fertiliser

After fermentation, a 'digestate' remains. With special technology, you can separate this residue into dischargeable water and organic fertilisers. This separation is particularly feasible for larger digesters. Agro Energy In Hardenberg, for example, this is already possible. At the regional waste processor Twence they use an advanced separation system that can even separate into dischargeable water and fertiliser substitute. So in doing so, they partly solve the manure problem.

Why so much interest?

Every information session on biogas currently attracts a full house. This is mainly because - if you do it right - you can currently make money with fermentation. Subsidies on biogas have been increased to 20 cents per KWh for smaller digesters. Because in itself, the greening of electricity is going quite well: already almost half of all electricity is supplied by solar and wind. Only a few percent of gas is still produced sustainably. By 2030, 20 per cent of gas must be green throughout the Netherlands. Fermentation is almost the only way to make green gas. Hydrogen also counts, but that production hardly exists yet and hydrogen does not pass through our gas network. In an attempt to meet the green gas target, the government is therefore encouraging manure fermentation with high subsidies.

Small or large digesters?

This leaves the question: as a livestock farmer, is it better to put a digester on your own yard or take your manure to a large digester? Theoretically, any farmer can place a digester on the farmyard. The big advantage of small-scale digesters is that you keep the manure on your own yard and you produce green gas, thus reducing the demand for fossil gas. However, small digesters offer a limited solution to the manure problem, because you are left with digestate. That often still has to be transported abroad. I don't see effective separation on a small scale happening any time soon. That requires a lot of time and technical knowledge, which is available in large digesters.

Larger digesters more cost-efficient

Taking the manure to a larger digester produces less gas (because it is later at the digester) AND the manure has to be transported. The advantage is that larger digesters can separate better and are much more cost-efficient. That is also important to us at StartGreen: that the digester is also cost-efficient in the longer term. If you have to fall back on market prices after the 12-year subsidy period, that requires a low cost price. And that argues in favour of large-scale digesters.

Hub Holland hub?

The agricultural sector is also now often talking about hubs. Many livestock farmers are looking at whether they can produce biogas on their farms and then turn it into green gas at one location. A hub could be a solution for manure transport: that would no longer be necessary and, moreover, manure could enter the digester day-fresh, producing more gas. So a good idea, although the organisation of a hub can be very complex and risky and therefore should not be underestimated. Moreover, a hub requires a lot of knowledge of fermentation, but also of running a business. Good support from parties who bring not only capital but also experience in developing and operating manure digesters is therefore an essential prerequisite.

Will we soon have gas grid congestion?

Furthermore, you have to consider possible sales. Green gas just goes through the gas pipeline. Small digesters fit the regular gas connection. Entrepreneurs should inquire in advance whether the gas network has sufficient capacity to dispose of their gas. If more digesters come up, this will be something to consider. In this respect, it is similar to the green power story: you can't always put it everywhere.

Lots of room for fermentation

Currently, less than 5 per cent of manure is fermented. So there is still an awful lot of room there. Over 280 million cubic metres of green gas were produced in 2023 and the target is 2 billion cubic metres by 2030. To meet the green gas target, quite a few larger digesters need to be added. And the pace at which new digesters are being built is currently far too slow.

This is mainly because, as a developer, you first have to take quite a few hurdles: you have to make sure the manure gets to the digester and the digestate is disposed of again. Moreover, larger digesters often work with residues from (animal) food and kitchen and garden waste. In addition, the licensing and appeal procedures are so intensive that not many developers want to step in yet. However, we do see a huge growth in the number of subsidy applications. A few years ago, there were only a handful; now there are 440 nationwide. That number has increased more than tenfold in the last ten years due to higher subsidies.

What does StartGreen do in this?

At StartGreen, meanwhile, we have an enormous amount of knowledge about manure fermentation, especially for a funder. Together, StartGreen's various funds have so far financed 22 digesters. For example, PDENH has financed the digester of Sustenso help build, Energiefonds Overijssel has already financed quite a few digesters and helped develop the one of Agro Energy Hardenberg. Oneplanetcrowd (now Invesdor) has also financed about three digesters. This makes us one of the largest financiers in the Netherlands. With every application, we look very critically at the business case: at the permits and at the future.

Intensively involved

Even after financing, we remain intensively involved in the manure digester. In that respect, there is a big difference with solar and wind projects: that is so-called partial financing. You put up a solar panel, the sun shines and you hardly have to worry about it. When you put up a digester, that's when it starts. You are like a cook who has bought a pan and a burner. Then you have to start buying ingredients and making something out of it. There are also risks you have to be aware of and be prepared to take when you get in. This is why I spend much of my time counselling funded entrepreneurs. Also because new developments are coming in at a rapid pace, such as new nitrogen separators, a neighbour joining, et cetera.

Manure fermentation is craftsmanship

It should be clear by now that I myself am very enthusiastic about manure fermentation. You have green gas and you help reduce nitrogen and phosphate emissions. If you want to make the livestock sector sustainable, fermentation is a good tool. Moreover, I find it unacceptable that we don't use 95 per cent of the manure potential. My ideal future vision is, that small livestock farmers take their manure away: either to their neighbour's digester or to a larger digester or hub in the region.

Besides, buying out a livestock farmer costs millions. With a few tonnes of investment, he can start fermenting, modify the barn floor and reduce emissions. From that perspective, too, I support fermentation. Above all, it's a great way to make green gas. It is craftsmanship, which requires knowledge and skill to make it a success. That's what I enjoy spending my time on.'