May, 2015 - Industry Article

Cow’s producing CNG

Hard to believe maybe, but waste increases in value and is becoming a valuable raw material. How? Cow manure is one of the examples and is easily available on the market. It contains valuable minerals such as nitrogen and phosphorus both needed for plant growth.  Apart from these minerals, manure also contains organic material. This material contains energy that can be released by bacteria in the form of methane; a ground source for Compressed Natural Gas. For what? Yes, driving. It’s possible to drive up to 9,000 km on the yearly manure production of one cow!

Producing manure
producing manure is not a very difficult task. Dairy cows produce manure every day. As all living animals, the manure of the cow is based on his nutrition. Cows are very efficient in how they use their food, but still some organic material cannot be digested by the animals. On average, a dairy cow produces 27 m3 of manure per year.

So how is it possible to drive on this manure?

Well, the manure of cows can be fermented by bacteria. This process produces biogas and takes place in an anaerobic digester. The digester is supplied with manure from cows on a daily basis. On average, manure remains in the digester for about 60 days during which time most of the organic material is converted into biogas. The gas in this digester roughly contains 50% of methane and about 50% of CO². To be able to drive on it the CO² has to be separated from the methane. The biogas needs to be upgraded.

Biogas upgrading

In order to drive on biogas, the gas from a digester needs to be upgraded. As stated before, the CO² needs to be separated from the CH⁴, the methane. Biogas can be upgraded using different techniques. One of the most efficient ways to do so, is by using membranes. The biogas is pressed trough very small spaghetti‘s through which the methane is defused from the CO².  The CO² can be used to produce soft drinks or to stimulate plant growth in greenhouses. It can also be used to inject into an algae culture to support the production of this biomass. The methane, or natural gas, can be fed in into the national grid or can be used to drive on; CNG, Compressed Natural Gas, the cleanest car fuel today.

Driving around the globe

Per cow, a total of 260 kg CNG can be produced per year.  An average car can drive around 30 km per kg CNG. So if we do the math, 260kg a year per cow, means that you can drive almost 8.000km on the manure of one cow per year! On the manure of 7 cows you could drive around the world. Not only is it the cleanest fuel today, with this manure of these 7 cows enough Nitrogen and Phosphorus is produced which is needed for 3ha of high producing wheat corps.

There are many different ways to produce more biogas. Together with the manure other organic materials can be used to digest and produce even more methane and fertilizers. For instance, organic waste from cities and grass from nature reserves could and are used to produce methane and minerals like nitrogen and phosphorous, of which phosphorous is the most important. This procedure would prevent the yearly loss of for instance millions of kg of phosphorous through Dutch cities. And it would imply the return of excess minerals, which are nowadays emitted from arable land to nature reserves. Moreover, more biogas will be available and more kilometres can be made on the cleanest fuel available today.