Although this is not exactly a state secret, dairy farmers prefer to keep it quiet: in her working life, a cow produces more than three times as much dung as she does milk!! This means, that every carton of milk in the supermarket is equal to three cartons of that other stuff.
In the case of cheese, it is even crazier. In order to produce one kilogram of cheese, ten kilograms of milk are required, which entails more than thirty kilograms of cow dung. Once upon a time, manure was a by-product of milk, and the cow herself processed it in an aroma-less way in the cow pat. This was a paradise for flies and a myriad of other insects, but nowadays, a cow pat in the meadow is a rare sight indeed. Cows in the meadow use "too much energy by walking about”, which leads to lower milk production, thus less income for the farmer.

With the rise in milk production, dung production has also increased considerably. An average cow needs about three thousand kilograms of milk to feed her calves. In modern dairy farming, any farmer worth his salt can easily extract ten thousand kilograms from his cow. Some farmers even have no trouble in extracting twelve thousand kilograms of milk a year.
The 36.000 kilograms of manure a year produced by such a cow, is becoming a huge problem. For more than 25 years, Dutch farmers have had total disregard for the European manure laws. As manure is no longer processed naturally in the meadow, other means had to be devised to dispose of it.

One of these means, and a profitable one at that, is manure digestion. When manure has been brought to the right temperature, it will digest itself. The addition of maize, chicken manure, grass and the remains of fodder speeds up the digestion process considerably. During this process, gas is formed which can be converted to electricity. This electricity is then sold to the electricity company, which pays 4,1 euro cents per kilowatt hour for it.
For such a price, however, the cow cannot produce manure, so the Dutch dairy farming sector devised the following trick. The sector claims that - because it is a daily process - manure is a sustainable product; so the energy produced after digestion is also sustainable.
Producers of sustainable energy via windmills or sun boilers are paid a further 9,7 Eurocents in subsidy on top of the price paid by the electricity company. So also the owners of manure digesters:  a subsidy guarantee of ten years makes their lives very comfortable indeed.
A medium-sized manure digester costs about 700,000 Euros, so serious amounts of money are concerned here. However, that investment will have been earned back within seven years with an additional yield of 50,000 Euros a year. 

And it gets even better! Interest and repayment entries are reduced to nil and the extra income for the last three years of the contract period rises to 175,000 Euros a year. The Authorities are prepared to go far in their goal to maintain production of sustainable energy. Even the tax authorities cooperate to make the party even more fun: 44 percent of the investment is tax deductable! If you wish, you can spread it out over a period of six years, the choice is entirely yours! So the net investment is brought back to 392,000 Euros, which yields an average net return of almost 21 percent over the first ten years.

However, the problem with manure digesters is, that the ensuing energy is not at all as sustainable as it initially seems. Starting with the cow: her diet consists of grass, maize, supplements and residuary products from the potato industry or beer breweries. The grass normally comes from the farmers own land, but the rest needs to be supplied from elsewhere. A huge quantity of residual energy is used in the production and transport of this.

Chicken manure is full of residual energy. More often than not, the raw materials for fodder in the bio-industry are exported from the other side of the world. Complete rain forests are felled for this purpose. Maize for the digester is not offal, but is grown especially for combustion in the digester, where 1,000 tons of maize is processed each year. For this alone, 2 hectares of land are required and more than 22,000 litres of diesel oil.
The only sustainable product of digesters, would seem to be the riskless and guaranteed earnings for the dairy farmer.