Why Build a Biodigester?

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A biodigester converts food waste into methane gas, which can be burned for energy,

and compost, which can be spread on gardens to make the soil more fertile. Every year,

roughly one third of all food produced goes to waste, equating to some 1.3 billion tonnes.

As a result of the energy that goes into overall food production, food waste is a significant

driver of climate change, which cuts to the heart of the problem. Not only is food waste

impactful on the environment, it is preventable, since biodigesters can be used to convert

food waste into fuel and fertilizer.

There is a global shift from rural to city living and, as urban development expands, there is

less room for composting to return organic waste to the land. These energy-valuable food

scraps and other organic residuals are thrown into the landfill where they decompose into

concentrated effluent that increases soil acidity and methane gas that is lost to the

atmosphere as a harmful greenhouse gases. In fact, over 20% of all methane emissions

are attributed to U.S. landfills.

By studying small-scale biodigester technology that can operate effectively within homes

with limited space, this study hopes to develop a sustainable solution for families in

developing countries, particularly those that lack access to energy infrastructure. If a

digester can be made using a 55-gallon drum that produces enough gas to supply the

needs of a family, biogas might begin to replace biomass, such as wood and dung, as an

energy source. Biogas also has the advantage of being useful for electricity generation

as well as cooking and heat. An additional benefit of biodigesters is their production of
fertilizer; families that grow their own food can increase crop yield by using its digestate.

Table 1. Estimated benefits from the installation of a domestic rural biogas plant

Note: Reprinted from Small-Scale Rural Biogas Programmes: a Handbook (David Fulford, 2015).

Biogas generation from food waste demonstrates benefits economic, environmental,

and social equity—what’s known as the triple bottom line. Biogas generation is economically 

feasible since it takes waste streams such as crop residue and food scraps, saves money by

diverting them from landfills, and uses them to produce renewable energy and fertilizer.

This converts a cost to the community into an asset.

This process is also beneficial to the environment in several ways. Firstly, it captures

the methane so that it can be burned, reducing it to energy, water, and carbon dioxide,

a much less potent greenhouse gas than methane. Secondly, it reduces the need to

use chemical fertilizers. This is more sustainable than relying on soil-depleting

fertilizers created from fossil fuels for agriculture. Thirdly, it reduces the need to burn

coal or natural gas for energy, which are nonrenewable fossil fuels. It also reduces the

need to harvest trees to burn as biomass, thus slowing deforestation and the resulting soil

erosion, desertification and drought. 

By Dyllan Furness