[Digestion] Negative Biogas Press

Mon Feb 14 05:33:01 CST 2011

Dear all,

>From a quick look at the literature out there the problem seems to be that C botulinum spores are not being destroyed in the AD process, but then I think it is also unlikely that a composting process would destroy them either. Pasteurisation at 70 degrees does not remove them and I believe compost temperatures do not exceed this, although the time of heating is obviously longer.

Regarding the soil carbon, there is usually a good amount left in most digestates. The AD process really only removes the more easily degraded carbon which would otherwise be converted to CO2 and/or CH4 and released to the atmosphere during either composting or direct spreading of the waste.

I too am not a fan of the use of maize/grass silage for biogas instead of fodder which is common in parts of Europe and has been created by subsidies. Just remember that not all of Europe does it this way.

Med venlig hilsen / Regards
Alastair James Ward

________________________________
From: digestion-bounces at lists.bioenergylists.org [mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Duncan Martin
Sent: 14. februar 2011 12:11
To: For Discussion of Anaerobic Digestion
Subject: Re: [Digestion] Negative Biogas Press

Hi Alex

There's a lot to respond to here - but I suspect a lot of it is nonsense.

It's true that biogas production removes carbon that could enrich the soil. However, many (most?) AD feedstocks are unsuitable for direct applcn to the soil (for a range of reasons), whereas the digestate is beneficial. So without AD, there could be no enrichment of the soil. With AD, there is substantial enrichment, even if less than some theoretical (but unattainable) maximum.

In the case of a feedstock that can be applied directly, of course, that should be considered. Animals have been 'manuring' the soil since the dawn of time, after all.......

Clostridium spp would not be unusual in AD. I have no idea whether the botulinum toxin is produced in AD. However, I would be surprised if it is stable once applied to the soil - and a 'rest' period should always be allowed after spreading digestate. How long depends on the soil and the crop - longer for salads than for root vegetables or cereals for example.

So any problems of sick cattle might well be caused by poor management: i.e. allowing grazing too soon after application. There is nothing unusual about applying digestate to fodder fields: it has been done for almost 100 years and I have never heard of this problem before.

I don't understand German, so I can't comment on the video clip - but I wonder if this issue mainly relates to grass-fed AD. This is quite common in some German-speaking countries, encouraged by generous prices for electricity from biogas. I wonder if farmers under financial pressure have been tempted to cut corners?

Duncan Martin PhD
Cloughjordan Ecovillage
Ireland
www.thevillage.ie<http://www.thevillage.ie>

On 13 February 2011 23:37, Alexander Eaton <alex at sistemabiobolsa.com<mailto:alex at sistemabiobolsa.com>> wrote:
Hi All,

I have received this from a few people now...it is clearly circulating widely.  I have plenty of comments regarding the soil aspects, and certainly some of the AD sludge contents from industrial or black water plants is a bit beyond my expertise, but I would certainly appreciate some comments from this group, especially any Germans that can comment on the YouTube part. This guy clearly is now against biogas, and it would make sense to have some good responses to this type of thing.

Best

Dear Kamal,
Dear All,

Besides the clear and proven advantages of biogas there are at least two extremely severe problems:

Organic matter that is converted into gas is no longer availabel to produce humus, so there are reports from farmers that the soil is getting less and less producticve. Rich soil may be far more important that the relatively litte amount of gas. Composting expecially with earthworms and additon of some charcoal dust (can easily be made from straw, rice husks instead of the terrible burning) ideally plus stone dust can be far more beneficial with rising productivity for food and more biomass and is simple, too. At TUHH we are now working intensely of also composting urine and mixed excreta stabilised by lactofermenters together with woody wastes to make more soil as I want to work with ecolocical agriculture and not do industrial agriculture with addion of fast fertiliser. Biogas can be a threat for long term food security and you will have to pay for the gas with more and more fertiliser demand, less water reproduction, flooding through compacting soils.

In Germany (see   http://www.youtube.com/watch?v=3cNyyU3zcXY sorry in German) (and probably elsewhere)  there are dramatic problems with the masses of heavily subsidised biogas plants for food to energy producion where Clostridium botulinum is growing rapidly under anaerobic conditions producing the highly toxic substance, there are hundreds of farms where all milk cows are dying and the farmers are ruined, even they became ill sometimes. The reason are fodder fields that are fertilised with the sludge from the biogas plants. The very dangerouos botulinum toxin (misused by people who hate aging by paralysing nerves in the face thus turning it into a mask, then called botox) is only showing effect after many month so the effect is often not related to the cause.

I used to be very positive towards biogas and have planned and built them, I will not do this anymore except for some industrial wastewaters. Maybe also for sanitation in areas where the soils are super humus rich already and botulism can be avoided safely.

Kind regards

Ralf

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Alexander Eaton
Sistema Biobolsa
IRRI-Mexico
RedBioLAC

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