From the design and manufacture of three scale bioreactors, it was found that the ideal proportion to produce bioethanol or bio-fertilizer with these organic residues would be a mixture of 70% cassava peel and 30% banana
UNAL/DICYT This was determined by the civil engineer Diana Murcia Velasco, from the Resilience and Environmental Sanitation Research Seedbed (Sirsa) of the National University of Colombia (UNAL), who highlights that the efficiency of this mixture can be improved with modifying agents such as molasses and oil vegetable.
His research proposes an alternative to improve the management and treatment of organic waste in rural areas of Colombia, taking advantage of the waste that is most produced in these places to produce biogas and bio-fertilizer.
The Murcia engineer explains that, after the diagnosis of environmental sanitation in the municipalities of Morales, Puerto Wilches and Yondó, in the Magdalena Medio valley, they proposed an alternative to improve the management of organic waste that would result in the production of biogas using Cassava and banana peel, high-generation waste in those municipalities.
According to the researcher, “between 1940 and 2013, Colombia went from having 8.5 million inhabitants to 47.7 million, which meant that the growth in the countryside was 35 percent while in urban areas it was 500 percent.
The country produces about 12 million tons of solid waste each year, that is to say that each Colombian is responsible for about 0.76 kilos of solid waste per day, and although most of these are organic matter, only 17 percent is used .
As the main methods of garbage disposal are landfills or open dumps, an alternative would be to take advantage of organic waste to generate energy through bioreactors. These use organic solid waste and animal excreta to produce biogas and bio-fertilizer for soil fertilization, through chemical reaction processes.
The different phases of these reactors allow to obtain as a final product a combination of methane –considered as an ecological fuel– and carbon dioxide.
Three treatments
“In each bioreactor designed for the study, a different mixture was treated: in the first, water, manure, cassava peel and banana were used; molasses was added to another, and vegetable oil to the third ”, indicates the researcher Murcia.
Variables such as the quantification of methane with sodium hydroxide were monitored and measured at the UNAL Environmental Engineering Laboratory. “What happens is that the hydroxide absorbs the CO2 and displaces an equivalent volume of methane to that produced in the reactor. Imagine a bottle full of water turned upside down: if air enters it, it displaces the water and you can see the bubble, this would be the amount of biogas produced, if there is no bubble, there is no gas ”, details the engineer Murcia.
The researchers found that in the municipality of Yondó there is a sanitary landfill for the management of solid waste, in Puerto Wilches they use that of another nearby municipality and in Morales there is an open dump. In the latter, the cleaning service has limited coverage in the urban area.
In the rural areas of the three municipalities there is no or limited cleaning service, and only in Yondó were recycling strategies identified, which would open the possibility of using these wastes that do not have an adequate treatment.
Methane generation
The highest generation of this gas occurred for the treatment to which vegetable oil was added with 15,309 ml of methane produced after 40 days, that is, 239 percent more compared to the treatment without any modifying agent, and the lowest production was for the which had molasses with 4,271 milliliters. “What we saw is that in this reactor the pH was much more acidic, and this would explain why the anaerobic digestion was not continued and why the amount of methane was less” adds the researcher.
The conclusion of the UNAL engineer is that the way in which waste is being disposed of in these three municipalities would be causing environmental and socioeconomic problems, so it considers that generating biogas and bio-fertilizer would be an option that the inhabitants explore to achieve a better waste management without depending on the precarious existing cleaning service.
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