Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

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Microbial cellulose utilization: fundamentals and biotechnology.

Inhibition of anaerobic digestion process: A review

Pretreatments to enhance the digestibility of lignocellulosic biomass

Principles and potential of the anaerobic digestion of waste-activated sludge

Plant essential oils for pest and disease management

The IWA Anaerobic Digestion Model No 1 (ADM1)

The fundamentals of microbial kinetics and continuous culture models are presented. The kinetics of the anaerobic treatment processes are reviewed recognizing that anaerobic degradation of complex, polymeric organic materials is a combination of series and parallel reactions. Such reactions include hydrolysis, fermentation, anaerobic oxidation of fatty acids, and methanogenesis. The intrinsic rates of each step are reviewed and literature data summarized. Whenever possible, available kinetic information is summarized on the basis of substrate composition (such as carbohydrates, proteins, and lipids). The effect of temperature and inhibitors on the intrinsic kinetic rates is discussed. Stoichiometric and bioenergetic considerations are reviewed. Mass transfer limitations (both external and internal) associated with biofilms and microbial agglomerates, in general, and their effect on the intrinsic kinetic rates are presented. Areas requiring further research are identified.

Kinetics of anaerobic treatment: A critical review

The IWA Task Group for Mathematical Modelling of Anaerobic Digestion Processes was created with the aim to produce a generic model and common platform for dynamic simulations of a variety of anaerobic processes. This book presents the outcome of this undertaking and is the result of four years collaborative work by a number of international experts from various fields of anaerobic process technology. The purpose of this approach is to provide a unified basis for anaerobic digestion modelling. It is hoped this will promote increased application of modelling and simulation as a tool for research, design, operation and optimisation of anaerobic processes worldwide. This model was developed on the basis of the extensive but often disparate work in modelling and simulation of anaerobic digestion systems over the last twenty years.

Anaerobic digestion model No. 1 (ADM1)

Kinetics of Anaerobic Treatment

The biocathode of a microbial fuel cell (MFC) offers a promising potential for the reductive treatment of oxidized pollutants. In this study, we demonstrated biological Cr(VI) reduction in the cathode of a MFC and identified putative Cr(VI) reducing microorganisms. The MFC was continuously monitored for Cr(VI) reduction and power generation. Acetate was provided to the anode compartment as substrate and bicarbonate was added to the cathode compartment as the sole external carbon source. The contribution of biomass decay and abiotic processes on Cr(VI) reduction was minimal, confirming that most of the Cr(VI) reduction was assisted by microbial activity in the cathode, which utilizes electrons and protons generated from the oxidation of acetate in the anode compartment. Relatively fast Cr(VI) reduction was observed at initial Cr(VI) concentrations below 80 mg/L. However, at 80 mg Cr(VI)/L, Cr(VI) reduction was extremely slow. A maximum Cr(VI) reduction rate of 0.46 mg Cr(VI)/g VSS.h was achieved, which resulted in a current and power density of 123.4 mA/m(2) and 55.5 mW/m(2), respectively. The reduced chromium was nondetectable in the supernatant of the catholyte which indicated complete removal of chromium as Cr(OH)(3) precipitate. Analysis of the 16S rRNA gene based clone library revealed that the cathode biomass was largely dominated by phylotypes closely related to Trichococcus pasteurii and Pseudomonas aeruginosa, the putative Cr(VI) reducers.

Spyros G. Pavlostathis

Papers

The IWA Anaerobic Digestion Model No 1 (ADM1)

Kinetics of anaerobic treatment: A critical review

Anaerobic digestion model No. 1 (ADM1)

Kinetics of Anaerobic Treatment

Biological Chromium(VI) Reduction in the Cathode of a Microbial Fuel Cell