Urban Batch Anaerobic Biodigester

In recent days, the Open Biotecture team has been working to develop a portable bio-digester for urban area.

There is an increasing demand for organic waste management in Kathmandu, and some residents have asked us about cost-effective solutions. Currently, the residents of Kathmandu dispose their organic waste in the streets or pay for door-to-door waste collection services. For the latter, the monthly cost ranges anywhere between 200-500 NPR.

Is Portable Anaerobic Bio-digester a good idea?

Open Biotecture investigated existing solutions for treating organic waste in urban areas. The first consideration was given to aerobic composting, however, the process only produces fertiliser as an output. Also, prejudice regarding bad smells emanating from compost bins was considered a strong disincentive to make composting a valued solution.

Instead, we looked at the possibility of creating portable anaerobic biodigesters to process the waste while producing a certain amount of biogas. To simplify the process, bio-digesters use organic materials such as kitchen waste as input and generate energy source (bio gas) and compost (slurry) as output. The entire system can be made on a budget, and there is demonstrable positive impact in the environment as well.

Organic waste treatment in anaerobic plants has been implemented significantly in rural Nepal by BSP Nepal since the 90s. However, these plants are constructed with building materials such as cement and bricks and are not fit for urban area where space is scarce and waste is not as voluminous as in farms. Compact and portable bio-digesters also address the urban issue of space use.

Several models of urban biogas plants already exist. Notably the ARTI rooftop biodigester, the ITDI portable biodigester and the Biorealis two-phased biodigester. Considering access to material, ease and cost of construction and implementation, we found a simpler solution than all the above. A simple batch biodigester is cheaper and very easy to build, while solving the issue of acid digestion phase conflicting with gas digestion phase which the Biorealis two-phased digester cleverly resolved.

Urban Batch Anaerobic Biodigester

Urban Batch Anaerobic Biodigester

The Urban Batch Anaerobic Biodigester is currently tested by Open Biotecture. A first batch is now being processed. This alpha test will try to bring answer to the following questions:

  • What is the mean production of gas?
  • How long does the digestion of a single batch take?
  • How long do solids take to decay into liquid slurry?
  • How efficient a fertiliser is the slurry output?
  • Can a batch be used to inoculate another batch with anaerobic bacteria?
  • Is a batch system easy of use? Does it appeal to users?
  • What is the cost-benefit ratio of the UBAB?

The UBAB was built in 1h with a total cost of 4253 NPR converting today at 37.75 EUR.

Second Hand Truck Tire Bowel @ 650 * 1 =    650
100L Drum for Gas Holder @ 550 * 1 =    550
50L Drum for Batch @ 300 * 3 =    900
Fittings for Pipe Connections @ 280 * 4 =  1132
50cm Pipe to Connect Tire to Gas Holder @ 90 * 1 =      90
100cm Pipe to Connect Batch to Gas Holder @ 260 * 2 =   520
Valve for Gas Holder @ 260 * 1 =   260
Sealing Tape Roll @ 20 * 1 =      20
Four Way to Connect Pipes @ 111 * 1 =     111
Clamps to Seal Pipe to Bowel @ 10 * 2 =      20
Total = 4253

The approximate price of a gas cylinder in Nepal is of about 3000 NPR and a refill is about 1500 NPR. Waste disposal costs about 250 to 500 NPR a month. The price of fertiliser may depend on the quality produced, which should be compared with the slurry output. With this data, it will be possible to get a better understanding of the cost and benefits of the UBAB.

8 responses to “Urban Batch Anaerobic Biodigester

  1. Pingback: UBAB Urban Batch Anaerobic Digester | Osa Mountain Village·

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  3. Pingback: UBAB version 0.2 | Open Biotecture·

  4. Very neat. Looked into the ARTI before, but I love the intent and approach of this project. Couple questions for clarification:

    1) Is it merely the use of separate containers that solves the acid phase/gas phase digestion issue?

    2) What considerations arise with the use of the truck tire bowel as gas storage (specifically regarding relative pressures between the two containers and regulating the flow rate of biogas out of the system to a stove, etc.)?

    3) Could this system use, or be modified to use human waste as the primary source of organic material?

    Thank you!


  5. Hello Matt, and thanks for your feedback.
    1) The idea behind small batches was portability (we’d imagined a householder transfering the bin from kitchen to roof / balcony). At a later stage it appeared a 25L bin was still too big. (You’ve got to be healthy to carry the full bin around).
    The batch itself seemed a simple solution to the acididy issue. Since we haven’t managed to make the UBAB work (see later posts) we cannot tell if indeed the idea would have been effective.

    2) The bowel as gas chamber was first considered as an option. It was later removed and replaced by a bell system (see later posts). You will find in models around on the Internet, that balloons or bowels are often used as a gas chambers. (See this simple experiment: https://www.youtube.com/watch?v=DC-w1cAo9ks) Methane is lighter than air, so it should always be under pressure. In the first UBAB model, it was set in water for security reasons, and it accessorily provided additional pressure. For the methane to circulate from the digestor to the chamber, the digestor should be strictly air-tight, so the methane would have no way out, other than the chamber, displacing water in the process.

    3)Technically, merging sceptics and organic waste for biodigestion is preferable as far as gas production is concerned. However, this model is not designed for this. Emptying the bins was already an unhygienic nightmare which made us really reconsider the idea of a portable biodigester. I can’t imagine what it would be like to do the same with added human feces in the mixture! Preferably, an underground sceptic tank should be retrofited into a biodigester, adding a leeching system for the slurry. Retrofitting however would be a substential investment.

    Overall, our first attempt at making a UBAB was a failure, but an enriching one. We have had the opportunity to learn a lot about it and we hope to give it another try in the future, but we’re working on more promising projects first.

    Please keep questions, comments and suggestions coming. It is very useful and encouraging to us.


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