Browsing by Author "Kivaisi, Amelia Kajumulo"

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    Anaerobic degradation of cereal residues by a rumen derived process
    (University of Dar es Salaam, 1990) Kivaisi, Amelia Kajumulo
    The conversion of lignocelluloses into biogas in a Rumen Derived Anaerobic Digestion (RUBAD) process was studied. Anaerobic degradation of lignocelluloses in conventional digesters is a slow process mainly due to low enzymatic activity present and lignin protects the degradable polysaccharides against enzymatic attack. On the contrary, the rumen degrades lignocelluloses efficiently because ruminants employ many highly cellulolytic microbial species. Hence the RUDAD-process has a potential to degrade lignocelluloses. However, lignin has been shown to inhibit rumen microorganisms in vitro. To examine the performance of rumen microorganisms in degrading lignocelluloses, various materials with lignin contents between 0 and 34% of total solids were tested in batch cultures and in the RUDAD-process. An increase in lignin content resulted in decrease of degradability. The effects of externally added lignin or lignin monomeres on in vitro degradation of filter paper cellulose by rumen micro-organisms and on their cellulose activity were studied in batch cultures. Addition of these compounds in concentrations comparable to natural conditions showed minor inhibitory effects. It appeared that the decrease of degradability with increasing lignin content was caused by lignin forming a physical barrier to enzymatic attack on the degradable polysaccharides. Rumen micro-organisms were further tested for degrading various cereal residues in a one-phase process. Under standard rumen conditions, and loading rates varying between 9.8g of volatile solids per litre per day, total fibre degradation efficiencies were in the 42-57% range irrespective of the loading rates applied. Optimum degradation of barley straw fibre (16% lignin) was obtained under conditions similar to those found in the rumen in vitro. In all of the experiments 40-60% loss in lignin was observed based on fibre analysis. The degradation efficiency of the straw in a two-phase process was 50%. The fermentation products of the first phase were converted to biogas in the second phase. The two-phase process was demonstrated to be stable for over three months with straw as the sole substrate for anaerobic digestion. To check if lignin was solubilized during the degradation of lignocelluloses the presence of soluble lignin derived compounds in the reactors fed barley straw was determined by Ultraviolet Spectral Characteristics and Pyrolysis Mass Spectrometry. Most of these compounds were shown to be released from the cell walls by the action of rumen micro-organisms. Determination of the association between rumen ciliates and methanogenic bacteria on the bias of coenzyme F42O-2 was attempted. The ease of extracting and quantifying the coenzyme makes the assay a much better method of assessing the extent of association than direct microscopically enumeration of methanogens.