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.
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.