Wednesday, August 22, 2012
Pluses and Minuses for Anaerobic Digestion vs Aerobic Digestion
For the purpose of this article, in order to avoid complicating the issues unnecessarily, we shall limit our discussion to the case of organic waste processing and not energy crop production.
Reasons In Favor of anaerobic digestion vs aerobic digestion are very significant if you decide to choose just one or the other for your project. However, while reading this please bear in mind that there is no reason why an aerobic digestion system (which is more correctly known as composting) cannot be incorporated on the same site beside the anaerobic digestion (AD) plant. By doing this the owner of a waste can have the best of both worlds very often.
1. Returning to the benefits of anaerobic digestion, probably the most important benefit not available to the "composter" (aerobic digestion plant operator) is the ability to produce a valuable gas, known as biogas. By burning the biogas produced in an anaerobic digestion plant, energy can be used on-site, or the sale of excess energy can be used to generate revenue from the AD plant.
Such projects gain good publicity because they provide sustainable renewable power from plants which are often called Waste to Energy (WTE) Biogas Plants, or may be described as Energy from Waste (EfW) facilities.
2. A second advantage of anaerobic digestion comes from the fact that a liquid portion of the digestate is produced which has high value as a fertilizer.
One additional basis for stating that the liquid digestate fraction is an advantage of anaerobic digestion is in the fact that a liquid portion of the digestate is produced in most of these process variants, which has high value as a fertilizer. This has the further advantage of improving soil structure, that is certain to prevent making the mistake of thinking that the fertilizing effect is the only benefit that digestate gives.
3. Anaerobic digestion when all feed and discharge operations are carried out in a closed building with proper air-filtration systems for expelling de-odorised air can be less odor producing than aerobic composting.
Then there's the fact that as well as spreading the digestate is generally recognized to produce less odor nuisance than spreading manure on farmland, any odor tends to dissipate faster than is the case for fresh manure. That's crucial because it can be very unpleasant for residents close to aerobic digestion plants when odors are producd, and also along with odor there may be tiny aerosol particles present from aerobic composting which can be harmful to health. If you take that into mind, then it makes sense to encourage anaerobic digestion and avoid aerobic digestion.
That is the pros of anaerobic digestion vs aerobic digestion. There is a negative side also. Let us focus on a handful of the negatives.
1. Anaerobic digestion plants cost more to build than a simple open slab (windrow) composting plant.
If you ever thought why anaerobic digestion was not in the past used more than aerobic digestion, that might produce the effect of anaerobic digestion plants cost more to build than a simple open slab (windrow) composting plant.. There is no way that that could be a good thing. It could be enough reason for avoiding doing it at all.
2. Anaerobic digestion needs a consistent supply of organic feed material, and such feed as food waste is hard to obtain.
In the UK until now this has been a problem, but with more and more waste municipal collection authorities now starting to collect source segregated food waste from households, this is less of a problem than it used to be.
3. Not many people know how to efficiently and reliably operate an anaerobic digestion plant compared with the people who know how to operate a composting system, after all composting happens in a garden composting heap without any real control or "operation being needed.
One more cause to avoid anaerobic digestion vs aerobic digestion is not many people know how to efficiently and reliably operate an anaerobic digestion plant but people can, and are being trained quite quickly to learn these skills. I advise everyone to consider this point seriously, because it can result in you becoming a leader in a new trend to make your own energy, if you go for the anaerobic digestion option, or if you go for aerobic digestion (composting) finding out later that your business is considered not to have good environmental credentials as it consumes energy rather than making it. And, if you decide to use and promote anaerobic digestion you are into something growing and destined to get a lot bigger anyway.
So that is that. There are the positives and negatives of anaerobic digestion vs aerobic digestion. So it's actually not what everyone wants and requires. But it will suit and help many. You must look at the info presented to make your personal determination, for or against. You will be able to make an optimal decision influenced by the information provided here in this article.