I read this article and the discussion about safe use of slurry for food production.

I wish to suggest that here the main issue is getting fuel from toilet linked bio gas plant and getting rid of any other fuel for cooking.

In comparison the slurry quantity is so small that its use will be mainly restricted in kitchen garden attached to the house and not in agriculture field so appropriate treatment can be considered at household level..

One of the solution could be to let the slurry in a small fully ventilated drying chamber fof size 3 ft x 3 ft or 4 ft x4t with a closed top having glass which will absorb solar radiation and will help kill the pathogens in few days time due to solar heat and ventilation. This dried and fully sanitized sludge powder can then be safely added as soil conditioner.

Second option coule be to let the slurry in a chamber where earth worms are provided and they will convert all wet and dry waste in to beautiful vermicompost. This can then be given to a kitchen garden.

Our main focus should be the design of bio gas plant and appropriate feed and its composition, to extract maximum bio gas and treat slurry with solar heat and ventilation and then use it as a soil conditioner which will be hundred percent safe for food production,

-- Prof.Shrikant Bhate. Architect and Social Entrepreneur. D-9, Durvankur Society I,Panchavati. Pashan. Pune 411008. R:020-2589 9527 Mobile:91-09890440648

Hi Pawan,

Can I suggest that before recommending the application of biogas plant slurry to food crops, there needs to be further study on helminth destruction? The pilot shows promise but in my mind further study is required, with the purpose of removing risk before promoting use in crops. I look forward to reviewing further evidence as this could indeed be a good solution that breaks the pathogen cycle from human waste, while providing useful products.

cheers
Dean

Dear Dean
Experimental work of Casilla was in Pather Village in Valsad district, Gujarat State, India.
I did monitoring of biogas production rate and constituents of biogas from with and without toilet linked biogas plants continuously for over 35 days in 4 villages ( including Pather) with 5 families in each village for summer and winter seasons. Physico-chemical and microbiological analyses of slurry was conducted for 4 slurry samples from toilet linked biogas plants from 4 villages. Absence of helminthes was found in all the 4 samples. It is quite interesting. However, appropriate explanation is perhaps lacking. The final report is yet to be published.
In case of septic tanks, retention time is normally for 48 hours and there is much less biogas production in comparison to biogas plants where retention time is over 30 days with high rate of production of biogas. That could be reason for destruction of helminthes or coliforms.
Purpose of my work was to demonstrate farmers safe reuse of slurry for agriculture purpose, in addition to enhanced production of biogas when linked with toilet. It helped a lot in dissemination of technology in rural villages.
Regards
Pawan

Hi Pawan,

yes I noted that Casilla reported finding no helminths in the slurry at the outlet of a single domestic scale biogas plant. Could you provide any published reports for the other three biogas plants? I'd note that the definition of "slurry" in this case is anaerobic digested sludge.

I would like to review the credibility of what appears to be a claim that complete destruction of helminths occurs in anaerobic biogas plants. This contradicts what I understand to be contemporary knowledge, that anaerobic digestion does not destroy helminths - meaning that sludge from anaerobic digestion is unsuitable for application in food crops for human consumption. Now, if an anaerobic digester such as a septic tank does not destroy helminths... whereas by adding methane capture, all helminths are destroyed, then this really is an important breakthrough worth reporting!

However, at this point I have to say I remain sceptical, because the experimental design in the one published study available to me (Casilla) is flawed. Evidence of helminth destruction would require samples from the inlet of that plant showing that helminths were present in the influent. Then, if destruction were demonstrated at the pilot scale, this would certainly justify further investigation.

cheers

Dean

pkjha wrote: Helminthes were not found in any wet slurry sample even before dun drying. 4 samples from different biogas plants were analyzed through a reputed Agriculture University laboratory. All samples had the same observation - helminthes not found. It could be due to anaerobic condition inside biogas plant or storage of slurry in pit causing thermophilic condition, raising temperature inside pit or both the possibilities. The concern Professor of the helminthes department was confident of the result and had the opinion that in case of unavailability of alternate hosts, under such condition, chance of survival of helminthes was very low.

Assuming these were non-actively mixed biogas plants, maybe the helminith eggs simply remained at the bottom of the digester due to the way the sludge outlet has been constructed? But also: have there been a measurable number of helminith eggs at the inlet side in the first place? It just seems a bit unlikely that they all just die off like that

pkjha wrote: Faecal coliforms were present (at low level) in wet slurry. As such coliforms are mostly aerobic in nature and can’t survive under anaerobic condition for longer period; their numbers are expected to be nil or very few in case of facultative coliform. However, in sun dried slurry such coliforms were also reported to be absent.

Yes, but I would like to note that fecal coliforms might not be the best indicator organism in this case. There is probably a bulk of better scientific literature on this, but to quote from this short fact sheet:

However, fecal coliform bacteria are not always a reliable indicator of the destruction of individual species or groups of pathogens during wastewater treatment processes. For example, during anaerobic digestion, viral pathogens appear to have a greater survivability than fecal coliforms. The rate of inactivation for viruses and fecal coliforms seems to be more comparable for lime stabilization and high heat processes such as composting. In contrast, helminth ova (eggs of parasitic worms such as Ascaris lumbricoides, the large intestinal roundworm) are extremely resistant to chemical treatments such as lime stabilization but can be inactivated by high temperatures. Consequently, the fecal coliform test may be an inadequate indicator of viruses and helminthes in anaerobically digested biosolids, but a good indicator of treatment efficiency during composting. According to the literature, fecal coliform enumeration is most reliable as an indicator of the presence of bacterial pathogens, especially Salmonella sp.

Source: www.des.nh.gov/organization/commissioner...documents/web-18.pdf

Dear Dean
Helminthes were not found in any wet slurry sample even before dun drying. 4 samples from different biogas plants were analyzed through a reputed Agriculture University laboratory. All samples had the same observation - helminthes not found. It could be due to anaerobic condition inside biogas plant or storage of slurry in pit causing thermophilic condition, raising temperature inside pit or both the possibilities. The concern Professor of the helminthes department was confident of the result and had the opinion that in case of unavailability of alternate hosts, under such condition, chance of survival of helminthes was very low.
Faecal coliforms were present (at low level) in wet slurry. As such coliforms are mostly aerobic in nature and can’t survive under anaerobic condition for longer period; their numbers are expected to be nil or very few in case of facultative coliform. However, in sun dried slurry such coliforms were also reported to be absent.
Regards

Pawan

Hi Pawan,

Do you consider sun drying of sludge after storing for a few months sufficient to remove hardy pathogens like helminths? Can you quote any research undertaken on this?

cheers
Dean

Dear Dean
Thanks for your observation.
One of the main objectives of the present study was to demonstrate households in different rural villages about health and economic benefits of using toilet linked biogas plants. Most of the households do not implement toilet linked biogas plants and avoid using biogas for cooking purpose due to inherent psychological taboos. It took considerable time and efforts to overcome such taboos. Since economic condition of most of the households were not better, economic return from toilet linked biogas plants in terms of monthly saving money on LPG for cooking purpose and increase in yields of vegetables and crops helped a lot.
Wetland treatment of sludge from biogas plant is a good option. However, it requires some additional cost. To avoid such cost, sludge was stored for a few months and sun dried before using as manure in agricultural fields. Such fields were mostly near the households and manually transported by the households.. Therefore, transportation cost of sludge to field was also nil. There was considerable economic return on yields of crops/ vegetables, in addition to use of biogas for cooking. The demonstration has helped a lot to farmers in implementing such toilet linked biogas plants in villages.
Best
Pawan

Thanks for the report Pawan.

Some of the objectives were:

• to demonstrate the benefit of using slurry (in agriculture)
• for chemical analysis of slurry (including pathogens)

I don't think anybody would question the positive effect slurry has on growth of vegetables. What interests me is the safety of using such slurry for growing vegetables, in particular those used raw. The slurry is either safe or it isn't.

This report states that "The slurry of the toilet linked biogas plants had no coliforms and helminths.", apparently based on results from a previous report that found low numbers of coliforms and no helminths in slurry after secondary treatment using a sludge treatment wetland (STW).

However, this report does not describe using any sludge treatment wetland, just the first stage biogas plants. Have I missed something?

cheers
Dean

Dear Prof Shrikant and Rajiv
Report is now uploaded. It mentions villages where the experiments were carried out. My email is- This email address is being protected from spambots. You need JavaScript enabled to view it..
regards
Pawan

Dear Mr. Jha,
Interesting topic.
I could not find the report attached.
Can you please check the upload and let me know.

Thanks

Rajiv

Dear Pawan, it is very interesting finding. We are also working in health, sanitation and energy sector.

Will you pl send me the report, your mobile and e mail id. Also pl tell me where is your work located. I would like to visit few plants having toilet linked bio gas plants working. Thanks and regards,



-- Prof.Shrikant Bhate. Architect and Social Entrepreneur. D-9, Durvankur Society I,Panchavati. Pashan. Pune 411008. R:020-2589 9527 Mobile:91-09890440648