Anaerobic Digestion is today seen as one of the most efficient ways of dealing with biowaste. In simple terms, the process takes organic biowaste to produce renewable energy, biofertiliser and water.
Most of the 20-30 million tonnes of food waste produced annually in England and Wales goes to landfill. However, that's rapidly changing as the UK government has created compelling incentives for renewable energy use, among them, targets for deriving electricity from renewable energy, which is set at 20% by the year 2020.
Anaerobic Digestion is a growing industry with around 100 existing plants in the UK. These plants offer waste producers an alternative to rising landfill costs and other forms of disposal for their food waste - a rich source of material for the process.
However, one of the key challenges is that a considerable amount of the food waste is still in its packaging (especially supermarket waste), far higher than in other parts of Europe. The substrate that feeds the digesters needs to be de-packaged, mixed and blended effectively as substrate composition is a major factor in determining the methane yield and methane production rates from the digestion of the biowaste.
There are a number of de-packaging methods available on the market today. Systems have been designed for the effective separation and processing of organic waste and can form an integral part of an anaerobic digestion plant. The majority of the de-packaging equipment presently available is based on hammer mills or shredding machinery which shred the packaged food waste before passing it through a squeezing process. Some effectively separate and wash the plastic packaging component as well as removing any tins etc.
Larger processing plants have invested in technology such as this costing hundreds of thousands of pounds.
At many other processing plants the food is mixed, shredded and the packaging removed using a static shredder. This involves tipping the food waste into a large pit with an auger (mixer) inside it at the bottom, which turns and pulls the material. A bucket then transfers the materials from the pit into a hopper which starts the digestion process.
Modern processing plants utilise mobile Screening Buckets for the de-packaging process, allowing them to blend the materials, which are then shredded and sorted.
This approach has particular benefits over the static shredder system, as the bucket is mobile and can be used to load the hopper directly. The buckets produce a consistent end product which cuts down on blockages and disruption to the plant. Often an auger gets jammed and it is difficult to get to it, as all the waste material needs removing before repair. With two buckets, there is no down time.
If packaging is not removed effectively and the biowaste is not blended and mixed sufficiently this can course serious issues within the anaerobic digestion process. Blockages of equipment lead to downtime of equipment. Therefore, considering the best de-packaging options is key to successful waste processing