Anaerobic Digestion: an option for the milk production sector

Nicole Miranda's picture

Last Friday 9th of March, 3 members of the EPG Group (Dr. Malcolm McCulloch, Andrew Alkiviades and myself) and Barbara Hammond (Oxfordshire Low Carbon Hub) visited Mapledurham Estate. Located in the north west of Reading and owned by John Eyston, this Estate includes a variety of activities such as: tourism and planning events, cultivation of crops milk production and hydropower generation.

In fact, the first hydropower turbine built on the river Thames (2011) is in Mapledurham Estate. This shows the commitment of the Estate towards building sustainable energy systems and now a new step is being studied to obtain electricity and heat from the milk production process.

     

a) Mapledurham cows     b) Old mill that has been replaced by hydropower generator

Currently there are 500 cows in Mapledurham Estate to produce milk. The animal slurry are currently put back into the grown as source of nitrogen for maize growth. The maize is fed to the cows and it seems to be a close system, yet there is lost in carbon efficiency that is released into the atmosphere after the slurry in the field undergoes aerobic reactions leading to CO2 production. Manure is a source of biomass that may be processed, for example, by gasification or anaerobic digestion to obtain syngas (a mixture of H2 and CO) or biogas (a mixture of CH4 and CO2), respectively. These gases may then be used in the generation of electricity, using combined cycle. In these chemical processed, carbon contained in CH4, CO2 or CO is used with lower environmental impacts.

    

a) Collection of manures          b) Milk tank

At the same time, this source of biomass is uncompetitive with food/energy land designation as its products are both. Considering that milk is already in a steady state production, energy production is a secondary, yet very important, by-product.

Anaerobic digestion (AD) is the main option for this case as degistate (remaining solid material) may be obtained as co-product of anaerobic digestion and used as fertilizer, as well as recovery of energy that may be used for electricity and heat in the Estate.

The EPG is now working on modelling technologies that may suit better Mappledurham. Experimental work (production of biogas in the lab) will also be carried out and results, such as environmental and electricity generation analysis will be shared with you in the near future.