Pathogens in Traditional Biogas systems linked to Toilets


  • apurvasahu
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Pathogens in Traditional Biogas systems linked to Toilets

Dear Members,

I am master's student of Sanitary Engineeing at Unesco-IHE (The Netherlands)* and currently working for my thesis in India on "Enhanced die off of pathogen in slurry from (traditional) biogas digester linked to Toilets". This research work is intended to identify safe and sustainable sanitation solution by promoting reuse of slurry (after reducing / removing pathogens in slurry) for agriculture purpose, use of biogas as cooking fuel, use of biogas for electrification.

For reduction of pathogen concentration the slurry from digester is mixed with lime or urea, and thereafter applied on unplanted drying bed to make it transportable. This master thesis is application of use of urea or lime to digester slurry instead of proven use in domestic waste-water (as per literature review).Being pilot scale implementation here slurry's solid concentration varies on daily basis. (Attached pictures show varying concentration of slurry in 2 different digester).

Lime is expected to affect the pathogen concentration by temp. and pH variation, whereas with urea it is expected by NH3 toxication.

Also below please find links of similar research but with constructed wetland.

With this post i would like to seek inputs and feedback from everyone in forum and all who are working in similar area.

I would also like to post a Query, and seek guidance from all members.

1. Being at pilot facility, TSS measurement is not quickly available hence difficult to feed/mix lime or urea according to TSS concentration, what other alternate can be adopted ?

Apurva Sahu
MSc. Student
Sanitary Engineering

* See here for an explanation on the program:
Apurva Sahu
Sr. Engineer
M.Sc Sanitary Engineering
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Re: Pathogens in Traditional Biogas systems linked to Toilets

Apurva, lime stabilization has long been practiced to stabilize wastewater sludges. As you note, it is generally attributed to the high pH. However, the actual effect could be as you indicate for urea, by NH3 toxicity. This is because ammonia is predominantly in the form NH4+ until the pH is raised to >> 9.4.
The criterion used for lime stabilization in wastewater sludge stabilization is simply by pH measurement. Rules such as pH>12.5 for 30 minutes, or pH>12 for two hours, have been used. So a simpler operating criterion for you would be to take some supernatant from the slurry and measure pH, easily and inexpensively done with litmus paper. This is a much better rule than dosing by TSS, which can only be an indirect factor.
The only other note is that lime should be mixed in quite well, so there are no pockets or clumps of material that have not been sufficiently treated.

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