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Advantages and Disadvantages of In-vessel Composting Food Waste


11 March 2011
Written by: Steve Symes


The in-vessel composting of food waste is being carried our increasingly, particularly in the United Kingdom, with the prime purpose being to divert this waste from landfill, in order to comply with the EU requirements for the reduction in organic materials being placed in landfills. In this discussion, the advantages of in-vessel composting will be compared with the alternatives of windrow composting and anaerobic digestion (which produces biogas/energy in addition to a liquid fertilizer and a fibrous soil improver).

Advantages: Factors in support of the in-vessel composting food waste are:

1. The high control ability of in-vessel system ensures that the food waste, which may be seasonal in its quality will always be composted to high quality standards, and produce a consistently high quality compost with excellent properties when applied to the ground both in the release of nutrients and as a soil structure improver.

 Deerdykes In-vessel Composting Plant
In-vessel Composting Plant showing ventialtion fans. (Image courtesy: Hytech-Water Ltd

Of course, every one of these options is better than sending these wastes to landfill, as was being done in the past. In a landfill it would produce landfill gas and ammoniacal nitrogen (to name just a few) and stay in the landfill for a very long time, as a result the organic nutrients in the waste are a threat to the environment should they escape in an uncontrolled way to the groundwater, or surface water streams.


2. Some food wastes are potentially a risk to livestock from vectors infectious diseases they might contain. For example, it is thought to have been sausages discarded by passengers from a flight into a UK airport which were included in pigs swill which infected the first UK farms with Foot and Mouth Disease in the 1990s. As a result, pig swill and other livestock feeding methods using animal by-products, are no longer permitted.

Another good reason for the in-vessel composting of food waste is the enhanced capability of in-vessel composting to be certain that the temperature is elevated sufficiently and for long enough, through the whole body of the compost material, to comply with the UK Regulations for Animal By-products, which contain strict requirements for the pasteurisation of potentially infectious food wastes.

Advantages and disadvantages of in-vessel food waste composting

Aeration pipes used in commercial in-vessel composting carry substantial air-flows, requiring pumping energy.

This contains the extra benefit of adding confidence to all those who will buy and use the compost, that there is as far as is possible, no risk of infection from it. That will protect against making the error of producing a compost product which farmers and horticulturists won't use due to fear of biological contamination being passed to their plants or livestock through use of the compost product.

3. It is easiest also to obtain PAS100 certification for high quality, highly marketable and sought after compost using in-vessel composting techniques

Then there's the speed of the composting process which is increased by using and in-vessel rather than a windrow composting method. That is certainly very important because it can easily take three or more months to windrow compost in cold winter climates, and in some cases composting plants then require very large windrow areas and may even run out of space by the end of the winter. After you take that under consideration, then it makes sense to use in-vessel composting of food waste.

That is the good side of the advantages and disadvantages of in-vessel composting food waste. There's a bad side as well. Let me examine some of the downsides.

Downsides: Reasons Against the in-vessel composting of food waste

1. Capital and running costs are much higher than carrying out composting entirely by a windrow slab method.

If you ever consider the cost effectiveness of in-vessel composting food waste versus windrow you will likely see that in-vessel methods are substantially more expensive, that might produce the effect of pricing the compost product out of the market if competing with sellers of compost who are carrying out composting entirely by a windrow slab method. There is no way that could be a good thing. In fact, it may well be a good enough reason to avoid it completely.

2. In-vessel composting requires the use of aeration and fans to pump air through the compost pile while it is in the composting vessel. The source of the power is usually the local electricity grid and therefore the power is from non-sustainable (mostly fossil fuel based sources). Therefore, in-vessel composting is not very sustainable.

The sustainability of a process is becoming more and more important these days.

3. Aerobic composting whether by windrow or accomplished in a vessel, bears a disadvantage over Anaerobic Digestion (AD) in that it does not produce any energy (power) in the way that AD plant does.

One more cause to avoid the in-vessel composting of food waste is that it will become more expensive over time, as the cost of energy rises and experts in energy supply say that power costs will continue to rise even above current prices, over time. Everyone ought to consider this point with great care, considering the fact that it can result in a big financial impact a few years from now.

So, if you want to carry out the in-vessel composting of food waste it is still better than windrowing and you could add an AD Plant later, anyway.

So that is it. We have now looked at the pluses and minuses of in-vessel composting food waste. 

Source: http://waste-technology.co.uk

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