Friday, July 31, 2015

Do Anaerobic Digestion Plants Smell?

Anaerobic digestion plant smell is a very highly debated subject, and whenever most new AD (biogas) plants are proposed (and a planning application is submitted) it is a topic of great concern to every local resident. With that in mind, I expected to see any number of articles on this topic when I looked on the web. So, I looked, and I didn't find them.

To my surprise I found that there are numerous website pages written by AD Plant objectors about specific planning applications, and by journalists reporting on what those same AD plant objectors were saying for local papers. But, nowhere did I see an attempt at presenting a rational view on this vexing question. It is an important subject, so I thought that I would write this piece in an attempt to present a "balanced" view on whether anaerobic digestion plants really do smell.

First of all. Let's be perfectly honest, these plants handle organic materials and at times these will already be starting to decompose as soon as they reach the AD Plant site. Once on-site the anaerobic digestion process itself is inherently smelly. Nobody could truly say that there is not a potential odour problem for all biogas plants. Decomposition (rotting) of organic matter produces some of the most offensive odours known to man, and decomposition is what the anaerobic digestion process is all about.

So, anaerobic digestion smells? Well to put a finer point to it, the materials which are fed into a biogas reactor can smell unpleasantly, and the output which is known as "digestate" (simply meaning the liquid and fibre which is left-over after the biogas gas-making reaction has occurred) invariably has a nasty odour, when it is first exposed to the air.

But, that categorically does not mean that an anaerobic digestion PLANT will smell, nor that anaerobic digestion plants are smelly. They can and should be operated responsibly, and with adequate design provisions for covered and air-sealed spaces, where the odour producing activities will take place. The great majority produce less odour than an average Dairy or intensive Chicken rearing farm.

As in all walks of life, some people do fail to run their biogas facilities in a responsible manner, and there are regulations against causing odour nuisance which will always need to be policed alongside other environmental protection legislation. Commercial scale Anaerobic Digestion Plants in the UK, and in most other jurisdictions too, are subject to permitting requirements, and if these are not met, bodies like the UK Environment Agency have powers to close down the AD facility if an odour-nuisance persists.

Odour that is produced by the AD process, can and must be contained and the ventilated air is filtered to remove any odour, before it is blown out through the ventilation system. The technology is routinely available for this, and when correctly applied, the view of many people is that anaerobic digestion plants don't smell. In truth, they routinely create less odour than the farmyard next door.

For any resident who is concerned about a new AD plant planning application being approved, due to their concerns about smells, we would suggest that they conduct some fairly simple research. Find out where there are already biogas plants in your area, and make a visit. Go, get out of your car for a minute, draw a deep breath, and stand on the public roadside, and draw in the air, and smell for yourself.

In my area there are already 4 anaerobic digestion plants within a mile and a half, of where I live and they are all two or more years old, but I have never smelled them outside of the property where each is located. When I have been detected a suspicious odour I have found that the offending odour was in fact the result of general farming activities and not the AD plant.


The anaerobic digestion process has a bad smell, but as long as it is kept sealed in by good practices in the operation of the leachate plant, or other waste disposal method, provided at sanitary landfills, there is no reason for the AD Facility to produce an unpleasant odour.


Patrick Sudlow said...

I tried to convince Manchester Metropolitan University, to build a biodigester, instead of building a biomass incinerator. One of the arguments put forward by those who wanted to gentrify Hulme, was that these plants smell. I did point out, if the plant is build properly, staff trained properly and the plant properly maintained, there should be no problems with smell.
I won my argument against a biomass incinerator, but they built a natural gas-powered energy plant instead, for the zero carbon campus!

Sam Bright said...

Now that might sound crazy - to choose to use natural gas/ fossil fuel. But, there may be a reason for it. If I remember correctly GMWDA has been building at least one anaerobic digestion plant for food waste/ organic household waste? If the food waste will anyway be going to a local AD Plant, it might not make so much sense to build a separate biogas facility on the campus?

Patrick Sudlow said...

That was the excuse they made for going for natural gas. As far as I am aware, Viridor have not managed to get these plants working properly. As someone who worked for Greater Manchester Waste, the reason will be because they were built cheaply and the staff not trained properly. Early this year, planning permission was granted for an AD bio-gester plant to be built at Smithfield Market, Manchester. Manchester Metropolitan University made a big noise, about their zero carbon, zero water, zero waste campus, which in reality runs on fossil fuels and of course produces waste that goes to landfill sites.

Alistair Thomson said...

They may smell but all in all it's helping us become a cleaning world. I recently found this interesting infographic on the whole process from Clean Energies Investment and I thought you and your readership may be interested in it