Expert Blog
There is a lot of interest in manure digestion. This makes sense, as livestock farmers can use their manure to produce green gas and make a decent profit from it. In this blog, Willem Dubbelman, biogas expert at Energiefonds Overijssel, explains what manure digestion is, what the advantages and disadvantages are, and why he believes there should be more manure digesters in particular.
What to do with your manure?
‘Manure is waste; it has to go. Dairy farmers can still spread a large portion of their manure on the land. However, regulations regarding what they can spread are becoming increasingly strict, certainly under the influence of the Nature Restoration Law. In addition, manure contains not only nitrogen but also phosphates; these can ‘leach’ and pollute groundwater and surface water.
Furthermore, livestock in the Netherlands generally produces more manure than farmers can spread on the land. Poultry and pig farmers cannot spread their manure on the land at all. They often have to export it abroad. This is, of course, a waste: having to drive hundreds of kilometers just to get rid of your manure. You can also digest it and subsequently turn the residual product into organic synthetic fertilizer.
How does a manure digester work?
A manure digester is a very large, round tank. If you heat the manure slightly—to the temperature of a cow’s stomach—biogas is released. During this process, enzymes naturally present in the manure break down the organic dry matter. The gas released in this process is called biogas. In fact, biogas consists of enzyme farts. You then have to capture that gas and turn it into green natural gas.
Capturing gas
Biogas consists of approximately 57 percent methane (natural gas). By increasing the composition from 57 to 89 percent, you get natural gas that can power a central heating boiler or industry. This can be done by passing the biogas through a membrane, where CO2 is captured, leaving you with 89 percent methane. More and more installations are becoming available that can capture the filtered CO2. Growers can then put that CO2 to good use in greenhouses as a growth enhancer.
Less nitrogen
Digestion does not only provide green gas but also ensures less nitrogen in the environment. Livestock farmers with a manure digester install a special floor in the stable that ensures the manure reaches the digester within a few hours. Without that floor, the manure starts emitting biogas and nitrogen even before it reaches the digester. The manure floor ensures that the manure yields twice as much biogas and also stops nitrogen emissions.
Organic synthetic fertilizer
After digestion, a ‘digestate’ remains. With special technology, you can separate this residual product into dischargeable water and organic synthetic fertilizers. This separation is primarily feasible for larger digesters. Agro Energie in Hardenberg, for example, can already do this. At the regional waste processor Twence, they use an advanced separation system that can even separate it into dischargeable water and a synthetic fertilizer substitute. In doing so, they partially solve the manure problem.
Why so much interest?
Every information meeting about biogas currently draws a full house. This is mainly because you can currently—if you do it right—earn money with digestion. Subsidies on biogas have been increased to 20 cents per KWh for smaller digesters. In itself, the greening of electricity is going quite well: almost half of all power is already supplied by solar and wind. However, only a few percent of gas is currently produced sustainably. By 2030, 20 percent of the gas in the entire Netherlands must be green. Digestion is virtually the only way to produce green gas. Hydrogen also counts, but its production hardly exists yet, and hydrogen does not travel through our gas network. In an attempt to meet the green gas target, the government is therefore stimulating manure digestion with high subsidies.
Small or large digesters?
Then the question remains: as a livestock farmer, is it better to place a digester on your own yard or take your manure to a large digester? Theoretically, every farmer can place a digester on their yard. The big advantage of small-scale digesters is that you keep the manure on your own yard and produce green gas, which reduces the demand for fossil gas. However, small digesters offer a limited solution to the manure problem because you still have digestate left over. This often still has to be transported abroad. I don’t see effective separation happening on a small scale anytime soon. That requires a lot of time and technical knowledge, which is present at large digesters.
Larger digesters more cost-efficient
If you take the manure to a larger digester, it yields less gas (because it reaches the digester later) and the manure must be transported. The advantage is that larger digesters can separate better and are much more cost-efficient. At StartGreen, we also find it important that the digester remains cost-efficient in the long term. If you have to fall back on market prices after the twelve-year subsidy period, that requires a low cost price. And that argues in favor of large-scale digesters.
Hub Holland hub?
The agricultural sector is also frequently talking about hubs now. Many livestock farmers are looking into whether they can produce biogas on their farm and then turn it into green gas at a single location. A hub can be a solution for manure transport: it is then no longer necessary, and moreover, manure can enter the digester fresh daily, which yields more gas. A good idea, then, although the organization of a hub can be very complex and risky and should therefore not be underestimated. Furthermore, a hub requires a great deal of knowledge about digestion, but also about running a business. Good support from parties that bring experience in the development and operation of manure digesters alongside capital is therefore an essential condition.
Will we face gas grid congestion soon?
Furthermore, you must take potential off-take into account. Green gas simply goes through the gas pipe. Small digesters fit on the regular gas connection. Entrepreneurs must inquire in advance whether the gas network has sufficient capacity to accommodate their gas. If more digesters are built, this is something to keep in mind. In that respect, it is similar to the green electricity story: you can’t always get rid of it everywhere.
Plenty of room for digestion
At the moment, less than 5 percent of manure is digested. So there is still an enormous amount of room there. In 2023, over 280 million cubic meters of green gas were produced, and the goal is 2 billion cubic meters in 2030. To reach the green gas target, quite a few larger digesters must be added. And the pace at which new digesters are being built is currently still far too low.
This is mainly because, as a developer, you first have to overcome quite a few hurdles: you have to ensure the manure reaches the digester and the digestate is removed again. Larger digesters also often work with residues from (animal) food and organic waste. In addition, the permit and appeal procedures are so intensive that not many developers want to step into them yet. However, we are seeing an enormous growth in the number of subsidy applications. A few years ago, there were only a handful; now there are already 440 nationwide. That number has more than tenfold in the last ten years due to the higher subsidies.
What is StartGreen’s role in this?
At StartGreen, we now have an enormous amount of in-house knowledge about manure digestion, especially for a financier. Together, the various StartGreen funds have financed 22 digesters to date. For example, PDENH helped build the Sustenso digester, Energiefonds Overijssel has already financed quite a few digesters and helped, among other things, with the development of the one at Agro Energie Hardenberg. Oneplanetcrowd (now Invesdor) has also financed 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 with the manure digester. In that respect, there is a big difference with solar and wind projects: that is so-called deal financing. You set up a solar panel, the sun shines, and you hardly have to worry about it anymore. When you set up a digester, it’s only just beginning. You are, as it were, a chef who has bought a pan and a burner. After that, you have to start buying ingredients and make something of it. There are also risks that you must be aware of and willing to take when you step in. That is why I spend a large part of my time guiding financed entrepreneurs. Also because new developments are being added at a rapid pace, such as new nitrogen separators, a neighbor connecting, et cetera.
Manure digestion is craftsmanship
It should be clear by now that I am very enthusiastic about manure digestion myself. You get green gas and you help reduce the emission of nitrogen and phosphates. If you want to make the livestock sector more sustainable, digestion is a good tool. Moreover, I find it unacceptable that we do not use 95 percent of the manure potential. My ideal vision for the future is that small livestock farmers take their manure away: either to the neighbor’s digester or to a larger digester or hub in the region.
Furthermore, buying out a livestock farmer costs millions. With an investment of a few hundred thousand, he can start digesting, adapt the stable floor, and reduce emissions. From that perspective as well, I support digestion. Above all, it is a beautiful way to make green gas. It is craftsmanship, requiring knowledge and skill to make it a success. I enjoy spending my time on that.’
