Anaerobic Digestion Case Studies
Source-Separated Kitchen Waste
The concept of harnessing the AD process to treat kitchen wastes is a relatively new one. Too wet and “gooey” for normal aerobic composting it is excellent for AD. To capitalise on this the Greenfinch AD Company ran a trial in South Shropshire. Taking the source-separated waste from 1,200 households over an 18 month period over 310 tonnes of waste were diverted away from landfill. The AD process safely digested all food waste including meat, bones, vegetable peelings and cooked food. With the addition of pasteurisation (70°C for one hour) pathogens were eradicated.
Ryegrass as an Energy Crop
Most biomass to energy work has been on “woody” material, converted to useful energy by means of a thermal process, e.g. combustion or gasification. One disadvantage of this is that most nutrients in the crop are lost to the atmosphere.
As the UK has one of the best climates in the world for growing grass (along with farmers and the machinery to do it) why not harness this for energy production through AD? The DTI Renewables Programme is supporting Greenfinch to undertake the research for this.
It is the objective of the study to achieve a minimum biogas yield of 11,000 m3 per hectare per year, which when converted to electricity on a commercial scale would generate 2.5 kWe/ha. providing a significant return to the farmer.
Farm Wastes
Since the 1980’s the UK has been using onfarm digesters to treat and stabilise manures and generate both heat and electricity. Whilst doing this it reduces the pollution potential and aids the storage and stabilisation of valuable nutrients for use on the farm.
There are individual farm based digesters in the Marches and a large-scale co-operative farm waste digester was installed in Holsworthy, Devon. The plant will process 146,000 tonnes of liquid slurry each year from 50 dairy farms, and generate approximately 1.4 megawatts of electricity. .
