Obtaining Biogas from Nopal- a Mexican Approach to Use of Waste

Author: Sofía Arriaga (Junior Alumni)

Since the middle of the last century, oil has led our progress as a society, changing radically our lifestyle; and irreversibly, our environment. From oil, the most profitable business in the world, we obtain products like solvents, polymers such as PVC, etcetera. However, the most relevant use is its combustion as a way to generate over 40% of the worldwide energy, and not only is its extraction and versatility the problem, but the combustion itself what truly damages the environment.

That is why a viable option, among others, for the obtention of energy is biogas; a term used to describe gas produced by organic matter decomposing. The great majority of the gas produced is considered to be of great quality and release over 95% fewer greenhouse gases than the use of regular oil as a fuel. A biogas station produces said gas by anaerobic co-digestion tanks, and as a waste, a biofertilizer useful for increasing the production of the original fields waste products were obtained, creating a sustainable cycle. This biogas can be used for electricity, heat and fuel options, in a similar way as oil.

A great example of crops that produce a lot of waste is nopal; a type of cactus endemic to America and some parts of Africa that is vastly found in Mexico’s traditional medicine, cosmetic uses, as well as a food resource; as erosion and water container in several kind of landscapes, and is even present in our culture as part of our national flag and important pre-Hispanic myths. However, because of the spiky nature of the plant and fruits, the outer part of the nopal has to be removed to process it as desired, making it ideal to be incorporated into the biogas obtaining structure.

Usually the process takes a few weeks to get it complete and use up all the energy stored into the waste and obtain perfectly useful fertilizer as well as a biogas concentration up to 96%; but it needs no external source of water as other organic matter put into biodigestors. Nowadays this special biodigestors can be found in two of the 32 states in Mexico; both coming from the people for the people.

The first one named SUEMA (short for Sustainability in Energy and Environment Conditions in Spanish) is located in Mexico’s capital, Mexico City, proposed a recollection center inside one of the biggest producers markets in the skirts of the city, were farmers obtain fertilizer in exchange for their waste. The plant receives over 10 tons of nopal waste daily, used to supply the markets needs, the biodigestion plant itself and even the small village surrounding the market.

The second plant is located near the southern-west cost of Mexico run by a small family in charge of a large nopal crop center as well as a tortilla shop (tortillas are flat, circular pancakes made out of mainly corn, that are the main food source in the country). The idea was born as gas and oil bills were too high for the owners to pay them, so they slowly built their own biogas plant that nowadays process over 8 tons of nopal waste daily, that later propel the crops equipment, the tortilla shop, and a truck that transports nopal to several markets in important cities.

With this in mind, biogas plants turn out to be not only a viable option for some communities in Mexico, but for other communities that have to deal with large amounts of food waste as well. Even if this project has been tested for nopal waste, it is easily modifiable for other types of food waste and it definitely represents a Mexican approach to an issue that concerns all of us.