Graduate's green idea turns cactus into biogas

Francis Merinyi uses chaff cutter to crash opuntia stricta to produce a porridge-like substance that is put into bio digester for fermentation. [Jacinta Mutura, Standard]

Nearly a decade after scientists introduced a method to kill Opuntia stricta, an invasive cactus that has colonised large sections of Laikipia North, pastoralists continue to lose livestock at an alarming rate.

But now Francis Merinyi believes his idea of using the cactus to produce bio gas for households could be the solution to the 50-year-old menace.

The University of Nairobi Environmental Science graduate explained how he chopped up the entire plant into small pieces before crushing it to produce a porridge-like substance.

The thick liquid is diluted with water, transferred into a bio-digester tank and left to ferment for three weeks.

“Bacteria work on the green substance and the end product is let out while the gas is collected through a pipe connected to a storage tube,” said Merinyi. He said the by-product can be used as manure.

Merinyi, who hails from Makurian village in the county, says he would sometimes add cow dung to the green substance to catalyse the fermentation process.

He says the process produces three types of gases - carbon dioxide, sulphur and methane, adding that his biggest challenge is how to store the methane.

Merinyi is optimistic that if his method is replicated in homesteads in the infested regions, it may finally eliminate the cactus, which has displaced more than 100 families after the death of their animals.

Laikipia National Environment Management Authority Director Fanuel Mosago says Merinyi's idea is viable because biogas is clean energy that does not emit pollutants.

“We encourage the project because it poses no threat to the environment, and it will go a long way to help pastoralists get pasture for their livestock,” said Mosago.

Felix Magaju from the Kenya Climate Innovation Center said they planned to offer financial support to enable residents replicate the project at home.