CWM HARRY LAND TRUST
Food locally grown, food-waste recycled

Processing Food Waste

Composting

Composting of food waste is regulated by the State Veterinary Service and the Environment Agency. Both organizations monitor Cwm Harry’s work and are in regular communication. The company also holds a Waste Management Licence in order to be able to operate both the collection service and the composting process.

The composting takes place undercover, and the building is sealed. Internally, there are ten bays in which to house the compost.

Processing green waste at Cwm Harry

The Process

1. When the material enters the building it is shredded and then mixed with green (garden) waste.
2. This is placed in Bay 1. Temperature probes are now introduced. These monitor the decomposition process. The temperature must rise to a minimum of 60°C for two days in order to kill any pathogens which may be present.
3. The material in Bay 1 is then turned and in so doing it is transferred to Bay 2. Here it must stay at 60°C for a further two days.
4. Over eight weeks the material is turned 10 times in all.
5. At this point the compost still contains pieces of woody material and so it is screened to remove these. The end result is a nutrient-rich compost which is pleasant to handle and smells sweet. At present this is sent to Coleg Powys farm. In time we hope to achieve the PASS 100, at which point the compost can be sold to the public.

Anaerobic Digestion

Food-waste can also be processed anaerobically. It is treated in a sealed container, and the end product is methane which is in turn burned and used to generate electricity.

The nearest AD plant to Cwm Harry is Biogen Greenfinch in Ludlow. Cwm Harry delivers food waste to them on a regular basis.

Biogen in Ludlow [external link]

The process:

1. Waste is delivered to the premises and shredded.
2. It is mixed with water to create a 'soup'.
3. The 'soup' is heated to 40C. This heat is generated through the process of decomposition. Heat is cycled back through the system by drawing off 'soup' from the top layers and re-introducing it at the base of the composting vessel.
4. Methane rises to the top of the composting vessel. It is piped from here to a holding tank.
5. From the holding tank, methane is piped to the engine where it is burned, as any other fuel is burned in an engine. H₂O and CO₂ are produced as bi-products.
6. The energy produced is used to power a generator which produces electricity.
7. The electricity is sold into the National Grid.

The remaining sludge is heated to 72C in order to ensure that all pathogens e.g. salmonella, are killed before the residue is spread on the land. The sludge may be processed to produce a drier residue as well as a nutrient-rich liquid.