Up to now, it has been difficult to take advantage of slaughterhouse waste from cattle in an efficient way. Some biogas is produced from the waste in Sweden, but production is not as efficient as it could be. In other places such as Cuba – Jhosané Pagés Díaz's native country –, the waste is just piled up to rot. The high protein and fat content is good for biogas production, but to make the process more efficient and stable, the protein and fat need to be supplemented with other materials. Jhosané Pagés Díaz has studied different mixtures of slaughterhouse waste, types of cereal, manure and household waste and has found the ones that are most efficient and allow the largest-scale, most stable biogas production in the shortest length of time.
“It turned out that the same mixtures are good no matter where you use them”, she says. The climate does not seem to have as much impact and this knowledge can therefore be used to help Sweden to use slaughterhouse waste in a more efficient way and to start up biogas production from it in Cuba.
The most successful mixture contains around one third slaughterhouse waste (consisting of soft parts, i.e. no parts of skeletons), a tiny amount of mixed cereals and just under two thirds mixed household waste.
More than half the animal's weight becomes waste
The slaughterhouse waste she uses in her research comes from cattle. Usually half the waste from an animal in beef production is left over. A large proportion of that waste can be used and, with the aid of bacteria, converted to biogas and bio-fertilisers.
Jhosané Pagés Díaz will shortly travel back to Cuba to continue her research and to teach. She will also have a meeting with the Ministry of Agriculture to discuss her results and possible ways of using them.
“We had a meeting before I started the project and they were very interested”, she says. Much can be gained by taking advantage of slaughterhouse waste. It creates renewable energy that can be used for electricity, cooking, heating and fuel for vehicles. Another by-product is liquid biological fertilisers. Greenhouse gases form if slaughterhouse waste just lies there and rots in the open. However, if we process it, we can use it for something we need.
Jhosané Pagés Díaz has conducted her research at a University in her home city of Havana and at the University of Borås. Most of the laboratory research was carried out in Borås. In a complicated process, she mixed slaughterhouse waste with different mixtures of cereals, plant residues, manure and household waste and studied the impact on biogas production in terms of efficiency, stability and time.
“To be honest, dealing with slaughterhouse waste was quite disgusting”, she says. But I think it's so important for these methods to be developed that I just had to ignore it. We must find more ways of creating renewable energy and we need to find ways of reducing pollution. Here we have found both, and that is very exciting!"
Thesis: “Biogas from Slaughterhouse Waste: Mixture Interactions in Co-digestion”
Postgraduate student: Jhosané Pagés Díaz at the University of Borås
Main supervisor: Ilona Sárvári Horváth, Assistant Professor at the University of Borås
Public defence of the thesis: 10 December 2015 at the University of Borås
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