The Green Leap Forward 绿跃进

One of the themes of Chinese energy policy is the use of renewable, distributive energy solutions to aid rural development. One of the more successful rural energy development strategies is the use of biogas digesters, which involves a process whereby organic material such as agricultural or animal waste are broken down by specific types of bacteria by anaerobic digestion, releasing carbon dioxide and methane gas. For the chemistry geeks out there, here is the chemical equation:

C₆H₁₂O₆ → 3CO₂ + 3CH₄

The resulting methane gas burns more cleanly than say wood, coal or kerosene, and is channeled indoors to run fire stoves for cooking or to run gas lamps. The use of biogas, especially in rural areas, provides a multiplicity of benefits that has made the popularization of biogas systems a cost-effective rural energy development strategy:

• Health.  Indoor air quality is improved as methane burns more cleanly than existing stove fuels such as coal, wood or dung.
• Time.  Much time (as much as 3 to 4 hours a day) otherwise used for wood collection is saved and can be devoted to economically productive activities.
• Money.  Money otherwise spent on fuel is saved as the raw ingredients needed for biogas systems consist of agricultural, animal and human waste that is generated by the household anyways.
• Fertilizer.  The residual slurry from the anaerobic digestive process makes for an ideal fertilizer for the farmer’s crops, reducing the need to purchase, and the demand for, petrochemical-based fertilizers.
• Reduced Deforestation.  Deforestation (and its ecological implications such as soil erosion) is reduced as the demand for wood as a fuel is made unnecessary.
• Climate Protection.  Methane gas, which is a greenhouse gas with a global warming potential that is over a period of a hundred years some 25 times that of carbon dioxide, that might otherwise be leaked into the atmosphere through natural anaerobic decomposition is channeled towards productive uses.

Case Studies around China

The Shaanxi Mothers’ Environmental Protection Volunteer Association (Shaanxi Mothers) were recipients of an Ashden Award in 2006 for its efforts in spreading a biogas system that is dubbed in the following video as “four-in-one system.”

A true “four-in-one system,” however, consists of a greenhouse (an element missing in the above video), pigsty, human toilet, and anaerobic digester. This set up is favored in the colder northern regions as the greenhouse increases agricultural crop yields while keeping the pigs warm as well. For more information on “four-in-one systems,” click here, here and here.

The southern province of Yunnan (云南) (hat tip to China’s Green Beat)…

…and southwestern province of Guangxi (广西)…

… are also adopting their own variation of biogas digesters. The warmer climates in these regions make the economic case for integrating greenhouses less compelling, but similarly rely on closing the loop on human and animal waste and creating a circular flow of waste-to-energy to create a sustainable and renewable energy system.

An International Model for Rural Development?

The adaptability of Chinese biogas systems to other developing countries may be challenging. According to Village Earth:

Attempts to replicate the Chinese results outside the PRC have yielded very uneven results. Building materials, such as cement, lime and quarried stones which are produced locally on Chinese communes are unavailable or very expensive in many other countries. Also, the Chinese skill and diligence in construction (particularly for the vaulted dome designs) and maintenance may be difficult to find or develop elsewhere.

There is in fact a question on the veracity of reports on costs and gas yields of Chinese systems:

One observer notes that the Chinese digesters are very similar to septic tanks, and that their gas yields per unit volume may be only a fraction of large-scale sewage digesters—meaning the gas production may be significantly lower than commonly assumed. It should also be remembered that virtually all reports on the Chinese successes have come from the Chinese themselves, so that data on construction costs and gas yields need further confirmation.

That being said, there appears to be biogas success stories in places like Nepal and Rawanda.

Related:
General Electric has announced that it will provide its proprieatary Jenbacher gas engines for a biogas project that will convert methane generated from the anaerobic digestion of chicken waste into electricity in northern Beijing.  The project is expected to qualify for clean development mechanism (CDM) financing by reducing an equivalent of 95,000 tons of carbon dioxide-equivalent per year.

Tags: anaerobic digester, biofuel, biogas, China, circular economy, clean development mechanism, climate change, GE, rural development, rural energy