Chicken Muck in Anaerobic Digesters
Murcott's Musings: Dispelling the ‘Expert’ Myths of Digesting Chicken Muck
If we could get £120 worth of electricity per tonne of chicken muck (with the UK feed in tariff) via anaerobic digestion, should we be wasting this energy source by throwing it straight onto land as a very inefficient fertiliser?
Some experts say that chicken muck cannot be digested without the addition of large amounts of water, making it unviable to spread as a fertiliser. Other experts say we should only use it as a fertiliser, whilst others say that it should be burnt as a fuel source.
My own experience suggests that we can have all three. We can gain the majority of the energy potential by anaerobically digesting it. The destruction of the dry matter helps to yield a thin, free-flowing liquid as a bio-fertiliser which can be easily and accurately applied (and stored), and using fibre separation can give us a wonderful fibre soil enricher.
By gaining the value of these separate fractions of chicken litter, we can gain far greater benefit from it than any other single-path disposal route. In my experience, chicken litter can be digested with the minimal addition of water and equally it digests extremely well when added to cattle or pig slurry.
There appears to be very little experience with using chicken muck as a feedstock for anaerobic digesters, but I heated my house for 10 years using only chicken muck in the digester. Experts say that this cannot be done because of the high ammonia levels but, after a period of acclimatisation, the digester worked fine.
As I had a day job, the digester was fed at the weekends and took me about half an hour to load – much easier than hauling the amount of wood necessary for the same amount of heating.
A recent report also said that loading more than 6% chicken muck into a digester on a daily basis is not advised. The innovative Fre-Energy digester at Lodge Farm in Wrexham has been running successfully for a long time with at least three times that much chicken muck going into the digester, producing good gas and excellent digestate. The picture below shows a closeup of the digestate. The majority of the rest of the feedstock into the digester is slurry from cows bedded on ash and woodchip – two further feedstocks which apparently cannot work in a digester.
