Everything produces waste and human beings particularly do so.
Because of this, biogas installations are ideal for bring-your-own-infrastructure situations, according to Ryan Dearlove of BiogasSA, a South African biogas technology and equipment supplier There are a number of different biogas technologies, but they all operate by the same principle: biogas production is where you expose decaying organic material in an anaerobic environment and produce a combination of gases which include methane and carbon dioxide. An effluent by-product of biogas systems is generally excellent plant fertiliser.
Dearlove says that biogas digesters exist on the level of inner motorcar tubes which can be operated from the waste of a few cows, upwards to large-scale municipal sewage processing projects.
The gas produced by the digester can be used directly for heating (for instance in a biogas stove) or can power either a turbine or an internal combustion engine to produce electricity.
Unlike LPG (bottled) gas biogas is not pure and is therefore more suited to internal combustion engine use than to turbines (generally, turbines require pure gas).
Although the use of biogas is subject to safety regulations in most jurisdictions, it is a very safe gas because it is never stored under high pressure (unlike LPG gas); explosions are therefore virtually impossible.
Dearlove emphasizes that biogas is a very undeveloped industry with huge potential for development throughout Africa. “For smaller units (for instance 4kVA), it is generally easier and cheaper for a buyer in Africa to simply order a containerised unit from China, where biogas technology is already commonly applied in millions of small-scale projects,” he states. “But for larger and more complex projects, there are considerable advantages in using South African suppliers.”
For the average urban household, installing a biogas digester is not an option because the household is unlikely to produce enough waste (primarily sewage, though garden waste can in certain circumstances be added to sewage).
The likelihood of viability is better for small farmers because of the addition of the waste (faeces and urine) from their livestock. Likewise viability is possible with small businesses like restaurants and food processing concerns.
For larger production units which produce large amounts of waste, however, biogas projects are a “nobrainer” says Dearlove.
There are a number of ways of producing biogas without major investment. Although there have been considerable advances in the efficiency of some biogas technologies, most biogas systems already installed throughout the world have been DIY home-based systems which consist basically of a container and a gas burner.
Most home biogas systems installed in Africa so far have been concrete or brick structures built into the ground and based on the Indian floating dome system.
More favoured by BiogasSA (depending on the application) are plug-flow digesters. In these, unlike the static pool of the lagoon system, the waste is flushed slowly through a tube. Dearlove says his company alone has installed 40 Puxin systems, each costing R20,000-R40,000 ($2,200-$4,400). This includes the construction of a concrete underground cistern. There are a number of suppliers of competing systems, including roto-moulded prefab systems.
BiogasSA is now promoting the biobag which uses a plug-flow system and simplifies the implementation of a rural system. Biobag systems are common in China, Indonesia and lately in countries like Tanzania. The system consists of a cylindrical PVC welded bag. Installation is simple and only requires the excavation of a rectangular ditch and the building of brick and mortar inlet and outlet pits.
The waste material is piped in and flows into the bag with gravity. Retention time is 30-40 days, during which the material moves slowly down the bag. The bags range from 5 metres to 15 metres long and capacities range from 8 cubic metres to 50 cubic metres. The system is modular so expansion can be done easily.
The Biobag system has a number of advantages:
• Low cost of installation.
• Low cost of infrastructure and transport – the supplier sends the system in rolled up form.
• The system produces methane but also (like all biogas digesters) digestate, a green liquid fertiliser.
• The smallest system costs around R9,000 ($1,100) (for an 8 cubic metre system which would provide enough gas for about an hour’s cooking for a family); there are no royalties or intellectual property.
The biobag and other systems are applicable to small projects, but there are many other bigger business opportunities.
“Industrial companies that produce organic waste and larger municipal systems should obviously consider the opportunities. Internationally, waste is a huge issue and producing energy from it is, again, a no-brainer,” says Dearlove.
Opportunities are particularly great in new township developments where, for instance, a few thousand houses could feed into a system which would generate enough gas for its own power needs and for, for instance, public installations like hospitals and street lighting.
“Biogas is low-tech. When high-tech is all the rage, we should not forget the potential of low-tech. The complementary relationship between waste and energy is underappreciated because we have become used to electricity at the flick of a switch. Biogas is not a silver bullet but it is one solution,” he concludes.
• A number of appliances are offered which work off BiogasSA biobagproduced biogas, namely plate stoves (cost: R700/$78), biogas lights (R175/$19), hot water
heaters (R1,990/$222), steam pots (R915/$102), room heaters (R325/$36) and restaurant burners (R750/$83).
BiogasSA, Ryan Dearlove: Tel +27-76- 627-1621; email@example.com
“Biogas technologies have one major advantage over solar and wind technologies – consistency. They can generate electricity 24 hours a day. And biogas can be stored much more easily and cheaply than electricity – normally in plastic or geotextile constructions. The stored gas can then be put through a generator when it is required.” – Ryan Dearlove of BiogasSA