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Cellulose degrading microorganisms
Cellulose degrading microorganisms are ubiquitous and are found in various environments including soils, sediments, compost heaps and the gut of vertebrate herbivores such as the ruminants (Coughlan and Mayer, 1992). They include protozoa, fungi and bacteria, aerobes and anaerobes, mesophiles and thermophiles. In the natural environment, cellulose is mainly oxidized by aerobic fungi and bacteria, producing CO2 and water, while only 10% is converted by anaerobic microorganisms producing methane and carbon dioxide. The anaerobic digestion of cellulose utilising rumen fluid as the inocculum will be discussed in this thesis. The level of microorganisms in the rumen is as high as typically found in any other natural habitat.
These bacteria are adapted to live in a slightly acidic environment between pH 5.5 and 7.0 at a preferred temperature of 39–40 °C. The steady supply of food and continuous removal of fermentation products and food residues maintain relatively constant conditions, in which an extremely dense population develops (Hungate, 1966). The diversity amongst rumen bacteria is striking, which may be due to the complex feed intake by the ruminants. The feed typically contains carbohydrates, proteins, fats and numerous other organic compounds and minerals (Hungate, 1966).
Already in 1832, Karel Sprenger published that decomposition of plant materials in the rumen was known to give rise to volatile substances which, at that time, were assumed to consist of acetic and butyric acids. Hungate in 1966 writes “the ruminant and the rumen microbial population exist in an equally beneficial relationship in which many of the plant materials consumed by the mammalian host are digested and fermented by the rumen microbes to form chiefly carbon dioxide, methane and volatile acids.” The rumen is a complex ecosystem where microorganisms thrive in symbiotic relationship that facilitates fibre digestion. Therefore, anaerobic degradation of plant material can be executed efficiently using the bacteria, fungi and protozoa occurring in the rumen as they produce cellulose fibre degrading enzymes (Lee et al. 2000). Cellulose degradation in anaerobic environments can be carried out by different Clostridium species, producing glucose and cellobiose, which are then fermented to lactate, acetate, ethanol, CO2 and H2. Ljungdahl and Eriksson, (1985) described the fermentation of sugars to produce carbon dioxide and hydrogen according to Equation (2.5) C6H12O6 + 6 H2O 6 CO2 + 12 H2 (2.5)
The hydrogen-utilizing bacteria assimilate hydrogen and use it for the reduction of CO2 to acetate or methane, sulphate to H2S or nitrate to ammonia or N2. The end product of the degradation process depends on the nature of the hydrogen-utilizing bacterium in the second stage, which in our studies will be mainly the SRB, producing hydrogen-sulphide.
The anaerobic species of cellulose degraders comprise Acetivibrio cellulolyticus, Bacteroides cellulosolvens and Fibrobacter succinogenes, Caldocellum saccharolyticum, the Clostridium species, the Erwinia species and the Ruminococcus species. Ruminococci have been isolated from cattle and sheep rumen fluid in Africa, Europe and the USA (Hungate, 1966). Several species of the most primitive group of fungi (anaerobe Chytridomycete) are well known for their ability to degrade cellulose in the gastrointestinal tracts of ruminant animals (Carlile & Watkinson, 1997; Lynd et al. 2002).
CHAPTER 1
1.1 INTRODUCTION
1.2 STUDY OBJECTIVES
1.3 RESEARCH QUESTIONS
1.4 REFERENCES
2. CHAPTER 2 : LITERATURE REVIEW
2.1 SULPHUR CYCLE .
2.2 IMPACT OF MINING AND MINE EFFLUENTS ON THE ENVIRONMENT .
2.3 ACID MINE DRAINAGE (AMD)
2.4 ACID MINE DRAINAGE TREATMENT TECHNOLOGIES .
2.5 REACTOR DESIGN
2.6 MICROORGANISMS IN THE ANAEROBIC BIOREACTOR
2.7 PRODUCTS OF THE MICROBIAL ACTIVITY IN THE RUMEN .
2.8 COMPETITION FOR SUBSTRATE IN THE ANAEROBIC REACTOR
2.9 CARBON AND ENERGY SOURCES FOR BIOLOGICAL SULPHATE REMOVAL
2.10 THE OXIDATION OF ORGANIC COMPOUNDS IN A SULPHIDOGENIC REACTOR
2.11 BIOLOGICAL TREATMENT OF AMD: THE CHALLENGES
2.12 CONCLUSIONS
2.13 REFERENCES
3. CHAPTER 3 : MICROBIAL CELLUOSE DEGRADATION FOR OPTIMAL VFA PRODUCTION AND BIOLOGICAL SULPHATE REDUCTION
3.1 INTRODUCTION
3.2 MATERIALS AND METHODS.
3.2.1 Plant biomass
3.2.2 Microbial biomass
3.2.3 Experimental
3.2.4 Analytica
3.3 RESULTS AND DISCUSSION
3.3.1 VFA production from grass-hydrolysis by natural occurring microorganism on grass
3.3.2 Effect of cellulose degrading anaerobic microorganisms on the VFA production, followed by SO4 reduction
3.4 CONCLUSIONS
3.5 REFERENCES
4. CHAPTER 4 : THE EFFECT OF INCREASED GRASS CONCENTRATION ON THE VFA PRODUCTION AND SUBSEQUENT SULPHATE REDUCTION USING SRB AND RUMEN FLUID AS FERMENTATION INOCULA
4.1 INTRODUCTION .
4.2 MATERIALS AND METHODS.
4.2.1 Study 1.
4.2.1.1 Experimental
4.2.2 Study 2.
4.2.2.1 Experimental
4.2.3 Study 3.
4.2.3.1 Experimental
4.3.1 Study 1. The use of SRB as fermentative and SO4 removing bacteria
4.4 CONCLUSIONS
4.5 REFERENCES .
5. CHAPTER 5 : VFA PRODUCTION AND CONTINUOUS BIOLOGICAL SULPHATE REMOVAL OPERATING A TWO AND THREE STAGE REACTOR SYSTEM FEEDING SYNTHETIC FEED WATER AND FROM ACID MINE WATER.
5.1 INTRODUCTION
5.2 MATERIAL AND METHODS..
5.2.1 Study 1a Two stage reactor system
5.2.2 Study 1b. Three stage reactor system.
5.2.3 Study 2a Effect of AMD on activity of rumen microorganisms
5.2.4 Study 2b. Operating the two stage reactor system using pretreated AMD as feed water .
5.3 RESULTS AND DISCUSSION
5.3.1 Study 1a.
5.3.2 Study
5.3.3 Study 2a..
5.3.4 Study 2b.
5.3.4.1 Sulphate removal .
5.4 CONCLUSIONS
5.5 REFERENCES
6. CHAPTER 6 : PROCESS DESCRIPTION OF THE GRASSCELLULOSE FERMENTATION AND BIOLOGICAL SULPHATE REMOVAL TECHNOLOGY APPLYING MASS BALANCE EQUATIONS
7. CHAPTER 7 : CONCLUDING REMARKS ON BIOLOGICAL MINE WATER TREATMENT TECHNOLOGY USING THE DEGRADATION PRODUCTS OF CELLULOSE
APPENDIX A
