Beware Anaerobic Digesters could be a threat to pasture based dairy farms

Anaerobic Digesters could prove to be a real threat to the profits of grass based dairy farmers in the UK. This might seem an odd thing to say when there is so much talk of green renewable energy opportunities. Successive Govt ministers are actively promoting Anaerobic Digesters as a major source of renewable energy. If you haven’t seen an Anaerobic Digester the best description is that it is exactly like a giant rumen. It requires daily feeding of a high energy feed & it needs a liquid mix in the “rumen”. The products of digestion are energy (gas), heat & some waste slurry. The higher the energy values of the feed the more efficient the output of energy. Therefore the preferred feed in Europe is maize silage. In Germany we saw very little dairy slurry being used which was a surprise.
Grass based Dairy farmers in the UK are looking at alternate energy generating opportunities I don’t think Anaerobic Digesters should be one of the viable options.
Firstly pasture based dairy farms simple don’t produce enough slurry that could feed a Digester. Maybe this is an option for a fully housed dairy farm but even then I’m certain they would start feeding it with maize. Second point is that land rentals & cattle feed prices are likely in the future be driven by the owners of Anaerobic Digesters who will buy vast amounts of maize silage. This is likely to create monocultures of maize which is not soil friendly & possibly environmentally unfriendly. Land rentals in Northern Germany are very very high & completely driven by the Anaerobic Digesters securing maize land. The third issue is that to fully capture the efficiency of a Digester you must be able to sell the heat say to a near by village for heating houses. Few ADs in Germany were able to sell the heat so it was lost to the atmosphere. This will only be possible near populated areas perhaps by city councils not farmers. Lastly the Digesters are very expensive to maintain. You have a huge engine running 24hrs a day….this is not cheap. Also the plants/tanks have a build up of sulphur which is very corrosive on all surfaces…this is becoming a major issue. If stones or waste metal are picked up by the maize harvesters this can create havoc with pumps. If Anaerobic Digesters have a place it’s near a city using waste products like vegetables or food waste. We saw a very profitable one near Amsterdam using chicken litter from farms that had NVZ problems. This seemed very sensible & environmentally friendly.
So beware Anaerobic Digesters I don’t think they are the answer. The Anaerobic Digesters we saw in Germany were professionally run by experts but they were struggling to make them pay dispite the feed in tariffs.