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Title: Anaerobic digestion of solid wastes : fundamental studies on the factors governing microbial hydrolysis reactions
Author: Siegert, Irene
ISNI:       0000 0001 3409 1674
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2004
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The effect of different physical-chemical conditions on the anaerobic digestion of paper with low lignin content was studied. Experiments were conducted at the one-liter and five-liter scale, and included both batch and semi-continuous digestion. The conditions tested were microbial and substrate conditions, pH, nutrients content, particle size, temperature and volatile intermediates concentrations. Emphasis was placed on the first step, cellulose hydrolysis, by measuring the enzymatic activity of the hydrolytic bacteria under the conditions applied. Different inoculum and substrate concentrations were tested with 40% inoculum and 14.8g cellulose.1⁻¹ showing to be necessary to achieve efficient cellulose digestion and an appropriate process for the study of the other conditions in batch mode. An improvement in cellulose digestion was observed in semi-continuous systems when gradually increasing the solids loading during the acclimatisation period. The use of dilution medium compared to tap water showed a higher cellulose removal and cellulolytic activity, and more pH stability providing more buffering capacity. Various pH and temperatures were tested with optimums found to be 7 and 35°C, respectively. In the pH and temperature range tested, more cellulolytic activity and cellulose digestion was obtained at slightly lower pH and temperature. An inverse relationship was obtained between the cellulolytic activity and the size of the paper particles, once the paper has been partially hydrolysed, enzymatic activity proceeds at similar levels. In general, the rate of hydrolysis/acidogenesis was higher than the production of biogas, leading to the rapid accumulation of volatile fatty acids even at optimum conditions, and therefore, the inhibition of methanogenesis. The effect of volatile fatty acids was also studied on cellulose hydrolysis, in batch and semi-continuous systems, by using a synthetic mixture. A decrease of the cellulolytic activity was observed from 2,000mg VFA.1⁻¹ added with the effect being more severe in batch systems compared with the semi-continuous tests. The decrease in cellulose hydrolysis observed in single-phase reactors due to the accumulation of volatile intermediates was alleviated by means of a hydraulic flush carried out to obtain a liquid retention time of 2 days. The removal of VFAs from the system produced a stimulation of the cellulolytic activity, improving the rate of cellulose removal.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available