Hi Yashwant,

there are plenty of studies showing impact of digested manure application on agricultural crops. Are you interested in some specific influence? Bacteria, nutrition etc.?

For more exhaustive information use Biogas Handbook: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCMQFjAA&url=http%3A%2F%2Fwww.lemvigbiogas.com%2FBiogasHandbook.pdf&ei=sgCAUNevA4-ShgeJioCIBQ&usg=AFQjCNF5hBhnecF5Emys3-yR9YTuhaoKaQ&sig2=sKtTa5UbgGNkRsLIgvcheQ&cad=rja

Good luck

Pavel

Hi Pavel,

Many thanks for a link for a biogas handbook ! We have just installed some biogas digesters in the selected(sites) rural areas of South Africa. Therefore, we are looking at the use and impact of bioslurry on agricultural and fodder crops, so that we can able to develop a prefect agroforestry model and reduce the dependency on chemical fertilizers.

Kind regards,

Yashwant

Well, send many thanx to Dr Al Seadi et al. the publishers of Biogas Handbook.. :)

Would be great if it helps you. I use it a lot..

Best reg

Pavel

You might also want to have a look at FAO's "Biogas processes for sustainable development" (http://www.fao.org/docrep/T0541E/T0541E00.htm) , it has some content on the usage of digester slurry as fertilizer. Here is a search that yields some results (http://scholar.google.com/scholar?q=anaerobic+digestion+effluent+fertilizer), have a look at for example this article (http://ukpmc.ac.uk/abstract/MED/16784191/)

It does not have any fertiliser value but good as filler value.

Vinayak Gade, could you elaborate on your claim? According to the information I have, manure digestion residues are rather rich in nitrogen and phosphorous and thus have rather good nutritional value.

It is fact that nutrients in substrate are used for growth and metabolism by microorganisms if you are getting good value of nutrients after digestion indicate that your digestion is incomplete the ratio required for anaerobic digestion is 200:30:5 i.e.C:N:P I have worked on this from lab-scale to commercial scale

I disagree; the purpose of anaerobic digestion is to stabilize the waste, to reduce pathogens and perhaps to produce methane, not to reduce nutrients. It is required that there are enough of them to process most of the oxygen demand in the feed, but if there are excess amount of nutrients, they will just go to the effluent. In addition, the form in which nitrogen and phosphorous are met just change form when they are consumed in digestion. Correct me if I'm wrong, but they can be used as fertilizers even in their organic forms — it just takes more time for the organic nitrogen and phosphorous compounds to decompose and to be available to plants.

There is misconception it is not chemical process but biological process there are growth cycles,death cycles and microorganisms doesn't act as a simple catalyst but they use waste as a food for growth and metabolic activities life cycle of methanogenic bacterial is 21 days if you say excess for cattle dung based plants it may true but at industrial scale plants we have to add nutrients to the plant and please keep in mind that end of stabilization process is inert product not a manure or fertilizer best way to get it is composting .

Vinayak,

Unfortunately your statements contain a number of errors, the most serious of which is that when anaerobic digestion is complete, the end product is "inert" (which in your terminology appears to mean that it cannot support the growth of plants). The digestion process, whether aerobic or anaerobic, follows much the same strategy, where complex biochemicals are broken down and energy extracted by microbes. (And by the way, methanogens are not "bacteria": they are archaea, a form of life less similar to bacteria than we are to slime mold.)

The resulting simpler chemicals-- regardless of which pathway was primarily or exclusively responsible for the breakdown-- can easily make rather good fertilizer. Many compost piles will go anaerobic, and likewise the effluent from digesters can be used in making aerobic compost or in such ventures as vermiculture. And after that, or indeed at many points before and between, the material can be returned to the soil and (broadly speaking) it will assist the growth of plants.

That is, the end products of any such biological breakdown can then be used by photosynthetic processes which take solar energy to again build up the complex biochemicals. The circle is never finished, because it is always true, in nature, that whatever life leaves behind serves as food for some other set of organisms in the chain of processes powered by sunlight. If complete breakdown to simple chemicals indeed left something that was "inert", then life itself would be impossible (i.e. the amount of "inert" material would simply increase until nothing was left that would support life), eutrophication could never happen, and aerobic compost would not provide good fertilizer for plants, because it too results in generalized simplification of chemicals which eventually cannot support further life as a continuing result of breakdown.

You must remember that for the vast majority of the history of the earth, life was either absent, or it was anaerobic. (Think of the life at the mid-oceanic volcanic vents...) Free atmospheric oxygen is a rather recent introduction.

In sum, there are indeed various differences in the end product of aerobic vs. anaerobic composting, but many studies and long experience have shown that either will provide excellent fertilizer under the right conditions.

David

Mikko,

You said "the purpose of anaerobic digestion is to... reduce pathogens..." Just a note: mesophilic digestion at ordinary HRTs has little effect on many of the most serious pathogens. Generally speaking, it will reduce the number of parasites, but not pathogens.

David

David, thanks. I'll have to update my knowledge. Could you point me out references where I could learn more about these effects?

Mikko,

One of the better free sources of information which gives a good ("popular" rather than academic) background in the various parasites and pathogens (although it says nothing, really, about AD) is the Humanure Handbook, which is available for download from various sources.

A whole set of resources about the issue, including some information about the use of AD in sanitation, is found from EAWAG (see http://www.eawag.ch/forschung/sandec/publikationen/ewm/index_EN). As well, you may want to consider an excellent WHO publication, Guidelines for the Safe Use of Wastewater, Excreta and Greywater, available at http://www.who.int/water_sanitation_health/wastewater/gsuww/en/index.html

But the key points are two. First, the best means of providing safety for materials suspected of having pathogenic loads when the intention is use as fertilizer for food, pasture, etc. is heat. Thus either thermophilic AD or composting should be used. And second, even mesophilic AD has a place in dealing with sanitation and health issues in urban and other settings, primarily because it will enable control and safe collection of human fecal material, which is not the only source of gut parasites and human pathogens, but it is the most important.

It's a huge subject, however.

Finally please allow me to mention another publication, The Complete Biogas Handbook about the more general subject of AD and biogas, available from completebiogas.com.

David

In one of the comments by Mr Vinayak Gade, it is said the the required ratio fo C:N:P for AD is 200:30:5 whcih indicate that C/N ratio is only around 7. Such a low ration of C/N leads to nitrogen noxicity in the digester and ultimately will affetc the biogas production. It is also experience throgth research that ideal C/N ratio is in the tune of 20-25.

So far as your question on utilisation of digested manure is concerned, I would like to share my experience on using atleast 25 different feed stocks for biogas generation. In case of using single stage digester, the concentration of N in digested manure is found to have good NPK values in all the cases and has also been tested for plant growth.

So the anaerobically digested manure of any orgic biodegradable waste can be used as fertilizer.

Dinesh Pant

Thank you so much for yours invaluable comments and knowledge on the subject......!!!...definitely It would be useful for my study and society as well.

Many thanks !

Yashwant

Pant ji

Can you please send me some literature on biogas particularly using cow dung?

I would greatly appreciate to receive that literature. My email id is [email protected]

thanks

Yashwant

Hello, Dr Rawat.   You may be interested to review the extensive Q&A session with Dr Elaine Ingham which I uploaded to Researchgate at http://bit.ly/2ig2rzw . Her responses to my related questions deal with the implications of aerobic vs anaerobic conditions on pathogens and nutrient value. For example efficient anaerobic digestion will result in losses of N, P and S in the form of ammonia, phosphine and hydrogen sulphide. And lots more insights.