B. Assefa, D. Abate, B. Leta
First Bio-Innovate Regional Scientific Conference,
Addis Ababa, Ethiopia, 25-27 February 2013
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 Coffee is the world's second most valuable
commodity after petroleum
 Ethiopia
◦ Contributes about 3 % for global coffee market.
◦ Produces about 380,000 tons
◦ About 16% coffee bean is produced by wet process
while 84 % by dry process.
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 The dry processing generates
◦ the solid waste (coffee husk)
◦ piled up in field causing serious
environmental problem
 The wet processing generates
◦ The wastewater released untreated
◦ Solid waste with high moisture content
(pulp and mucilage)
◦ Dispose in the water and field
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 Estimated annual generation of solid
wastes
◦ Husk 430,920 tons/year;
◦ Pulp 72,960 tons/year
 It is huge resources;
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 Characteristics of coffee husk
No Parameters Mean
1 Moisture content (%) 9.63
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2 Bulk Density (mg/cm ) 0.74
3 Volatile matter (%) 82.7
4 Fixed matter (%) 7.65
5 Ash (%) 7.65
6 Total Carbon (%) 53.67
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 Characteristics of the Pulp
Parameters Mean
TS, % 70.13
VS/TS, % 93.0
Moisture Content, % 29.87
Fixed Solid, % 6.99
Total Carbon (%) 50.18
pH 6.8
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 The waste has high organic content
 It can be a good feed stock for biogas
production
 Concern
◦ The biomass might be cellulosic materials
◦ the rate of biodegradability may be low
◦ Tannin, caffeine and phenols could poison
anaerobic bacteria
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◦ Decomposing the biomass using (oyster) mushroom
would improve biodegradility
◦ Reduce the poisoning effect of TCP chemicals using
the use of biomass for mushroom
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 Determination of biogas potential of coffee
husk, coffee husk spent after mushroom
production and pulp
 Comparison of the results against the
hypothesis
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Materials
 The inoculums
◦ brought from an active, food leftover based biogas
plant found in the same institution;
◦ Amount of inoculums: 800 ml (volume);
 Substrates:
◦ Coffee pulp, coffee husk, and spent coffee husk.
◦ The pulp are kept in a deep freezer (less than -
120C)
◦ The spent is brought from a mushroom cultivation
experiment (after three cycle of harvest)
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 Composition of substrate added into the flasks
Substrates TS (%) VS (%)
Husk 87.5 80.8
Spent 27.8 89.8
Pulp 12.1 79.9
Inoculums 2.3 63.3
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Apparatus
◦ Erlenmeyer Flask
— Gas analyzer
◦ Tubes
— Syringe
◦ Water bath (Thermostat)
— Balance
◦ Gas bags
— pH meter
◦ Shredder
— Stop cock
◦ Muffle furnace
◦ Drying oven
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Methods
◦ The samples are added in 1:2 ratio VS of
substrate to inoculum in order maintain
constant food to micro-organism ratio
◦ the experiments were run at 37oC
◦ The temperature is maintained by
thermostat
◦ The pH is measured initially and at the
end of the experimentation
◦ Gas is collected regularly by gas bag
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Measurement
 Mass of substrate
◦ Precision balance is used
 Gas volume
◦ the volume of the gas was measured using syringe
of known volume, 50ml and100 ml.
 Temperature
◦ the temperature of the room is measured regularly
when the gas volume is measured using
(thermometer)thermocouple
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Experimental Set up
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Biogas yield [l/g Methane gas
Items VS] [l/g VS] [%]
Pulp 0.863 0.081 0.460 56
Husk 0.486 0.071 0.266 58
Spent 0.188 0.068 0.090 49
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 Pulp gave output as of comparable to
◦ Organic wastes from food industry : 0.4-
0.8 m3 biogas/kgVS (Gunaseela, 1997)
◦ Fruit and vegetables solid waste and
wastewater 0.2-0.4 m3 CH4/kgVS
 Husk gave output as of comparable to
◦ Crops (straw, beet collars) 0.35-0.4 m3biogas/kgVS
◦ Rice straw 0.2 m3 CH4/kgVS (Dinuccio et al., 2009)
◦ Barley straw 0.2 m3 CH4/kgVS (Dinuccio et al., 2009)
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 Spent substrate gave the lowest
output
◦ It is lower estimated potential all biomass
◦ It seems that the mushroom taken up
significant easily digestible stuff
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◦ Coffee waste can be as a good feed for
biogas production
◦ Coffee husk much higher gas potential
than spent coffee husk
 The use of coffee husk for mushroom
production did not improve gas
production and its rate
◦ The pulp collected from wet processing
gives much higher gas production
coffee husk
◦ Spent coffee husk has still significant
gas potential
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Thank for your
attention
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