Small Scale Digesters

BiogasSA specializes in solutions for household scale digester solutions and has a range of products specifically for this type of biogas application which has been developed and adjusted for South African conditions and applications. 

Currently BiogasSA markets 4 micro scale household digesters:

  1. In-situ cast concrete Puxin Digester
  2. DIY Biobag Digester Kit
  3. LGM rotor moulded in-ground household digester
  4. Portable above ground EZ-Digester

 

1.  The Puxin Digester

BiogasSA is the SA agent for the patented in-situ cast concrete digester from Puxin, China.  The design of the Puxin digester not only ensures long term structural and functional integrity due to the high strength solid concrete construction, but also ensures gas is produced under constant pressure.  In the Puxin digester, the gas dome is fixed in position under the water level, which creates around 6kPa of pressure due to the head of water above the dome.  This pressure is sufficient to push the gas up to 70m to point of application and still provide enough pressure for the appliance to operate.

Construction is done using a patented steel mould or shutter system that consists of small bolted steel panels which are erected in the form of an igloo - concrete is placed around the mould to form the actual digester.  The shutter can then be dismantled from the inside and removed once the concrete has gained sufficient strength and used again for the next project.

BiogasSA does not build any fixed dome brick and mortar digester for the simple reason that this type of construction more often than not results in some structural cracks occurring over time due to either poor workmanship, bad material or ground settlement.  This invariably leads to gas and/or fluid leaks which is difficult to repair.  Maintenance is thus the biggest challenge with this type of digester design, especially as most of these digesters are installed in rural locations.  Proof of this fact is that of the 12 million rural fixed dome brick & mortar digesters built over the past 15 years in India, only 4 million are still operational!

The Puxin digester has none of these issues as it is constructed from 25MPa solid concrete and will give maintenance free operation for 30 plus years. 

The Puxin Digester is a standard 10m³ in size which allows it to digest in the order of 80kg - 100kg of organic waste slurry and could potentially produce around 3-5m³ of biogas per day.  Both the digestable quantity as well as the quantity of biogas produced is highly dependent on the actual type of organic waste being fed into the digester.  The same quantity of fatty food waste would for instance produce around 20 times more biogas than cow manure!

The cost of a Puxin DIgester installation is very much dependent on the geographical location of the project and actual soil conditions, but R60 000 would be a budget indication.

BiogasSA Puxin Digesters:

 

  

 

 

 

 

 

 

2.  The DIY Biobag Digester Kit:

The Puxin Digester as well as the common brick and mortar fixed dome digester, both require a certain level of skilled labour to construct and is costly.  A simpler, more practical and considerably more cost effective type of digester is the so-called soft or balloon type digester.  This type of digester has been successfully implemented in countries such as China, Vietnam and India over many years.  The balloon digester is easy to install and requires only semi-skilled labour and is simple to operate and maintain.

BiogasSA has packaged their own DIY Biobag Digester Kit that contains all the components to install a fully operational digester.  The Kit includes a high quality 1000g/m² reinforced, bacteria and UV resistant PVC cylindrical balloon digester, 30m of gas piping and fittings, a desulphurizer, pressure release valve and a small inline gas pressure pump.  Depending on the client's needs, appliances such as stoves, lights, heaters and water geysers can also be supplied as part of the Kit.  A comprehensive Installation & Operational Manual is provided with every kit.  The Kit is compact and is therefore practical to be shipped anywhere.

BiogasSA has experimented with various suppliers and quality of materials for the actual Biobag over the years and the current product will provide long term, maintenance free operations for up to 15 years.

Due to the simplicity of the design and installation requirements, the Biobag Digester is ideal for rural applications were local communities can do the installation and operation of their digesters themselves.  BiogasSA normally provides a one day workshop on biogas basics, including training on how to install and operate the Biobag, as part of larger community projects.  A DVD is also available for those who have access to a computer or laptop and BiogasSA is also working on an APP that will allow the manual to be downloaded on a smart phone.

 

Biobag10 installed in rural KZN
Biobag10 at the Manzini School in Kathlehong
Biobag10 at the Manzini School in Kathlehong

Biobag15 on organic farm in Magoebaskloof
Biobag30 on pig farm in Free State