Biogas yield potential of by-products from primary coffee processing

Publikations-Art

Kongressbeitrag

Autoren

Chala, B; Latif, S; Oechsner, H; Müller, J

Erscheinungsjahr

2016

Veröffentlicht in

Book of abstracts

Seite (von - bis)

13

Tagungsname

24th EUBCE 2016

Tagungsort

Amsterdam, Netherlands

Tagungsdatum

6 - 9 June 2016

Schlagworte

Biogas yield potential, Coffee by-products, Ethiopia, HBT

Coffee is a ‘black gold’ to many developing countries which particularly receive their export earnings from sale of green coffee beans. Moreover the sector provides livelihood for millions of households and absorbs huge workforce in its chain from coffee growers to exporters. In Ethiopia, coffee is not merely an export item, but it has significant implication in daily social and cultural practices. About half of the total coffee produced is consumed domestic. Primary coffee processing, which is mostly undergoing in coffee growing countries, eventually produces green coffee beans, both for export and domestic consumption. There are two coffee processing methods to produce green bean, the wet and dry one. Regardless of the methods followed, both methods generate considerable amount of by-products like the pulp, parchment, husk and mucilage. Theses by-products are considered waste, so causing adverse impact to the environment. Wet coffee processing method consumes about 80 litre of water per kilogram of green bean, hence competing humans and animals water demands. Moreover, wet processing liquid by-product is polluting nearby streams by high organic load so degrade water quality and aquatic life. However, these by-products could be converted to renewable energy carriers if proper conversion technologies would be applied. One promising energy technology to convert the by-products is anaerobic fermentation, to recover biogas.

All coffee by-product samples were obtained from a coffee processing farm in Jimma zone, Ethiopia. The pulp and mucilage was collected after processing and sun drying in the farm, while the husk and parchment were taken as it was. The samples were packed and transported to Germany for lab analysis. In the present study, biogas and methane yield potential of pulp, husk, mucilage and parchment was determined following the Hohenheim biogas yield test (HBT) protocol, for 35 days. The digestion was undergone at 30oC and 37oC digestion temperature using inoculum adapted with respective temperatures. Each sample was tested in each of the digestion temperature and inoculum source. Two standard substrates (with known biogas/methane yield) and blank inoculums alone were also run along with each digestion mode to verify the correctness of the systems.

The methane yield from pulp, husk, parchment and mucilage was 0.245, 0.159, 0.031 and 0.294 mN3/kg oTS respectively while digested at 37oC and 0.235, 0.157, 0.025 and 0.287 mN3/kg oTS while digested at 30oC. Hence, the methane yield from all by-products digested at 37oC was higher than those digested at 30oC. In general, the highest methane yield was obtained from mucilage, followed by pulp and husk. The methane yield from the parchment was significantly low, thus not promising for biogas production.

Special fractions of the coffee processing by-products were promising regarding methane yield and can contribute to the energy supply of households or processing facilities of coffee growers while maintaining the environment safe and improving livelihoods.