Concurrent microscopic observations and activity measurements of cellulose hydrolyzing and methanogenic populations during the batch anaerobic digestion of crystalline cellulose

This study compares process data with microscopic observations from an anaerobic digestion of organic particles. As the first part of the study, this article presents detailed observations of microbial biofilm architecture and structure in a 1.25-L batch digester where all particles are of an equal age. Microcrystalline cellulose was used as the sole carbon and energy source. The digestions were inoculated with either leachate from a 220-Lanaerobic municipal solid waste digester or strained rumen contents from a fistulated cow. The hydrolysis rate, when normalized by the amount of cellulose remaining in the reactor, was found to reach a constant value 1 day after inoculation with rumen fluid, and 3 days after inoculating with digester leachate. A constant value of a mass specific hydrolysis rate is argued to represent full colonization of the cellulose surface and first-order kinetics only apply after this point. Additionally, the first-order hydrolysis rate constant, once surfaces were saturated with biofilm, was found to be two times higher with a rumen inoculum, compared to a digester leachate inoculum. Images generated by fluorescence in situ hybridization (FISH) probing and confocal laser scanning microscopy show that the microbial communities involved in the anaerobic biodegradation process exist entirely within the biofilm. For the reactor conditions used in these experiments, the predominant methanogens exist in ball-shaped colonies within the biofilm. (C) 2005 Wiley Periodicals, Inc.

Fermentation methods for dextransucrase production

Several fermentation methods for the production of the enzyme dextransucrase have been employed. The theoretical aspects of these fermentation techniques have been given in the early chapters of this thesis together with a brief overview of enzyme biotechnology. A literature survey on cell recycle fermentation has been carried out followed by a survey report on dextransucrase production, purification and the reaction mechanism of dextran biosynthesis. The various experimental apparatus as employed in this research are described in detail. In particular, emphasis has been given to the development of continuous cell recycle fermenters. On the laboratory scale, fed-batch fermentations under anaerobic low agitation conditions resulted in dextransucrase activities of about 450 DSU/cm3 which are much higher than the yields reported in the literature and obtained under aerobic conditions. In conventional continuous culture the dilution rate was varied in the range between 0.375 h-1 to 0.55 h-1. The general pattern observed from the data obtained was that the enzyme activity decreased with increase in dilution rate. In these experiments the maximum value of enzyme activity was ∼74 DSU/cm3. Sparging the fermentation broth with CO2 in continuous culture appears to result in a decrease in enzyme activity. In continuous total cell recycle fermentations high steady state biomass levels were achieved but the enzyme activity was low, in the range 4 - 27 DSU/cm3. This fermentation environment affected the physiology of the microorganism. The behaviour of the cell recycle system employed in this work together with its performance and the factors that affected it are discussed in the relevant chapters. By retaining the whole broth leaving a continuous fermenter for between 1.5 - 4 h under controlled conditions, the enzyme activity was enhanced with a certain treatment from 86 DSU/cm3 to 180 DSU/cm3 which represents a 106% increase over the enzyme activity achieved by a steady-state conventional chemostat. A novel process for dextran production has been proposed based on the findings of this latter part of the experimental work.