Abstract
This study attempted to investigate the feasibility of volatile fatty acid (VFA) production from coffee pulp hydrolyse, and further to determine the potential of methanization of both the pre-acidified effluent and the coffee wastewater. The experiments were carried out in 2 completely mixed reactors, each one with a working volume of 4 litres. Coffee pulp was used as substrate in the acidogenic reactor and different mixtures of pulper and wash-water and pre-acidified effluent in the methanogenic one. The acidogenic and methanogenic reactors were operated at an organic loading rate of 5 COD g x l(-1) x d(-1) and 0.5 COD g x l(-1) x d(-1). The total, soluble and VFA's effluent COD concentrations of the acidogenic reactor present average values of 57.75, 17.00 and 13.92 g x l(-1) respectively. Under these experimental conditions, 23% (COD based) of coffee pulp was hydrolysed with a rate of 1.32 gCOD x l(-1) x d(-1) and the soluble fraction was transformed to VFA's with an acidification efficiency of 82%. Total VFA's concentration reached a value of 13.9 gCOD x l(-1), and acetate, propionate, butyrate and valerate represented 52%, 28%, 9% and 11% respectively of the liquid phase COD. In the methanogenic reactor, COD removal and methanization of fresh coffee wastewater, pre-acidified effluent and both combined occur with an efficiency of 85% to 95% respectively, with a characteristic biogas composition of 80% CH4 and 20% CO2. These results show that a humid coffee "Beneficio" processing daily 23 tons of cherry coffee (fresh fruit), equipped with a two stage anaerobic digestion process could generate at least 1,886 CH4 m3 x d(-1). This represents an increase in methane production by a factor 3 to 5 compared to a "Beneficio" using anaerobic digestion only for the treatment of its wastewater.
Published Version
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