Uses of nopal biomass as a source of energy and biofertilizers

Abstract

The nopal (Opuntia ficus-indica), cultivated by smallholder farmers, is traditionally used for production of fruits, industrial products, forage and “cochinilla”. Cladodes can also be used for a number of other purposes. We evaluated other uses of nopal cladodes. One of the uses is for biogas production from anaerobic bio-digestion. The daily energy need for a rural family of five people can be met from 3.61 m3 day(‑1) biogas. Considering that 10 t ha(‑1) year(‑1) dried cladodes are produced and that 3 kg dried cladodes produce 1 m3 biogas, it is possible to obtain the biogas needed annually by the family from a 0.4-ha cactus plantation. This amount of biogas has an economic value of US$1078, using the price of commercial gas as a reference. Solid materials and liquid biofertilizer that contain nutrients and material can be obtained in biogas systems. One tonne of solid biofertilizer is equivalent to 40 kg urea, 50 kg potassium nitrate and 94 kg triple superphosphate. Assuming an average price of US$0.32 kg(‑1) fertilizer, each tonne of biofertilizer would be worth US$58.80. Also, dried and crushed cladodes can be used for direct burning or in combination with coal. It is also possible to obtain ethanol from the cladodes, but the production technology is more complex. On a larger scale, 8.6 L ethanol could be produced from 100 kg dried cladodes and 24.7 L ethanol from 100 kg dried fruits, for concentrations of ethanol above 98%. Another bioenergy use is the extraction of fatty acids from fruit seed residues and their transformation into biodiesel. Each fruit has between 150 and 300 seeds, and the oil content ranges between 98 and 139 g kg‑1 seed.