Dear all,

I got the attached presentation sent by Heinz-Peter Mang and thought it could be useful for people working with biogas digesters and reuse of digestate in agriculture. It is not so easy to geld hold of such information from China.

The ppt is about the application of the digestate as fertiliser.

It is a short version of USTB/CSES training ppts which were used in a IDCOL-NDBMP training seminar on digestate utilisation in Bangladesh in 2012 (with support by KfW).
Before anyone asks: I also don't know what IDCOL-NDBMP is...
But USTB/CSES is epxlained in the ppt: Centre of Sustainable Environmental Sanitation
University of Science and Technology Beijing , P.R.China

I have two questions for Heinz-Peter:

(1)
The presentation talks about digested effluent and shows a slide (number 12) where people are spraying something that looks like water but the slide says "anaerobic digestate". I thought what comes out of such a digester is a slurry that is difficult to settle - so how can it be sprayed through such nozzles?

(2)
Secondly, the presentation mentions on slide 8:
What are the required hygienic standards? From my understanding, biogas digesters are not particularly strong on destroying pathogens. The helminth eggs may settle well but wouldn't you still find them in the slurry? By which mechanism would they get killed in a digester?

Regards,
Elisabeth

Meanwhile, I got some replies from Heinz-Peter mang about the bioslurry use in China (see my questions above), which I have translated into English and copied below:

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From Heinz-Peter Mang:

a) IDCOL = Infrastructure Development Company Ltd.
     NDBMP = National Domestic Biogas and Manure Programme

b) Anaerobic digestate consists of (i) BIOL = Bioliquid and (ii) BIOSOL = biosolids (see chapter on the GTZ biogas film from 1992, it has been scientifically developed in Peru, then first applied in Bolivia, China, Nigeria), separation occurs by post-composting (leachate of the compost pile = BIOL), by sedimentation or filtration or drainage beds (subject to the requirements of further reuse application). BIOL will normally be further diluted with water for foliar fertilization, seed treatment, and used as biopesticides in the corn and fruit or flowers in the production. BIOSOL is used mostly for soil improvement or for fungal cultures.

c) The Chinese standard GB7959 requires that for the (co-) treatment of human faeces in biogas plants, a post-composting (which is usually the standard applied) or thermophilic fermentation is used. A non-authorised translation of the Chinese standard GB into English is attached below.



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For the mentioned video see here:
www.susana.org/lang-en/videos-and-photos...mp;type=3&id=130

Or direct link:


I know it seems a bit odd to watch a biogas movie from 1991 but the funny thing about biogas technology for human and animal excreta is that it was peaking in the 1990s and the publications from then are still pretty valid (I am told)!

Regards,
Elisabeth

And I had one more question about pathogen kill in anearobic digesters:
I had asked (above):


Answer by Heinz-Peter Mang (thank you!!):
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The question with the helmith egg was answered already in the GIZ-ecosan-Technology review "Biogas sanitation" (www.susana.org/lang-en/library?view=ccbk...mp;type=2&id=877). "Helminth" means parasitic worm, including : Ascaris lumbricoides (sometimes called just "Ascaris"), and hookworm (Anclostoma duodenale and Necator americanus). In the table "Effects of anaerobic sanitization on selected pathogens and parasitic ova as well as on E-Coli indicator (source: Zhang Wudi, BRTC, China 1985)" it is explained that these ovas (eggs) have 98.8 to 100% fatality after 10-36 days in mesophilic conditions and 53-90% fatality after 30-100 days in ambient temperature fermentation.

As we have in conventional simple biogas sanitation systems a separation of a long sludge retention time through sedimentation and scum formation vs. a short liquid retention time, settled ovas are treated. This differentiation of the hydraulic rentention time does not happen in Completely Stirred Tank Reactors (CSTR). And as explained in the Technology review: "Chinese, and Dutch as well as German studies showed that there is a complete inactivation of the pathogenic test organisms through aerobic post composting process." See also some confirming new research work from Nigeria (attached) and from SANSED.
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Most basic digesters that I know of in developing countries operate at ambient temperatures or at the most mesophilic (35 °C). This means we get some helminth egg kill (according to the above 53-90%) but not total. It would in fact be better to quote the log reduction, I guess. That's fine by me, it means that the WHO multi-barrier approach still needs to be applied.

Elisabeth