Browsing by Author "Shadrack, Eliapenda"

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    Application of rumen microorganisms for the production of biofuels and chemicals from various agroindustrial lignocellulosic wastes.
    (University of Dar es Salaam, 1993) Shadrack, Eliapenda
    Degradation of various agroindustrial wastes by a mixed population of rumen microorganisms was tested in batch cultures and in an artificial rumen reactor. Within a pH range similar to that of the rumen and a substrate concentration of 20 g per litre, fibre degradation efficiencies after 168 h batch incubations were in the range of 20 - 52%. A strong correlation between degradation and lignin content of the materials was observed. Specific productions of volatile fatty acids (VFA) and methane per gram of fibre digested varied between 8.35 and 10.35 mmol. and 0.050 and 0.068l, respectively. The conclusion was that the less lignified materials are potential substrates far an anaerobic digestion process employing rumen microorganisms. The effects of varying pH, substrate concentration, initial acetate concentration and incubation time an fibre degradation were examined. A pH range between 6.5 and 7.5 appeared to be optimal. Fibre degradation was limited at a substrate concentration above 40 g.l-1. Extension of fermentation period from 168 to 336h increased fibre degradation by 10 - 15 % and at an initial acetate concentration above 160mmol.1-1 fibre degradation, and VFA and methane formations were markedly reduced. It was concluded that degradation and fermentation products can be increased by optimizing fermentation conditions of agroindustrial wastes. The effect of some chemical and physical pretreatments were tested. With hydrochloric acid, sodium hydroxide and ammonium hydroxide as chemical pretreatments, conversion of bagasse and coconut fibres was significantly increased. Substrate particle size reduction from 5mm to less than 0.85mm (physical pretreatment) improved fibre degradation and increased VFA formation by 29 and 24% for bagasse and coconut fibres, respectively. Methane production was increased by 33 and 28% for bagasse and coconut fibres, respectively. By comparing the tested chemical and physical pretreatment methods it was concluded that the chemical pretreatment methods used are more effective than the tested physical methods for improved conversion of lignocellulosics. In an artificial rumen reactor bagasse and maize bran were tested for digestibility at varying loading rates and solid and hydraulic retention times of 60 and 19h, respectively. Total fibre degradation efficiencies were in the range of 54 69%. In all the experiments, 29 - 39% apparent loss in lignin was observed. Mean VFA and biogas productions per gram of substrate digested per day varied between 6.45 and 7.75 mmol. and 0.06 and 0.19, respectively. It was concluded that maize bran and bagasse are potential substrates for large scale biogas production in artificial rumen system.