Preface. PART I: OVERVIEW. 1. Introduction. 2. Bacteria. 3. Methane-forming Bacteria. 4. Respiration. 5. Anaerobic Food Chain. 6. Fermentation. 7. Anaerobic Digestion Steps. PART II: SUBSTRATES, PRODUCTS, AND BIOGAS. 8. Substrates and Products. 9. Biogas. PART III: OPERATIONAL CONDITIONS. 10. Introduction to Operational Conditions. 11. Start-up. 12. Sludge Feed. 13. Retention Times. 14. Temperature. 15. Nutrients. 16. Alkalinity and pH. 17. Toxicity. 18. Mixing. PART IV: PROCESS CONTROL AND TROUBLESHOOTING. 19. Upsets and Unstable Digesters. 20. Foam and Scum Production and Accumulation. 21. Supernatant. 22. Monitoring. PART V: DIGESTERS. 23. Types of Anaerobic Digesters. 24. Anaerobic Digesters verses Aerobic Digesters. References. Abbreviations and Acronyms. Chemical Compounds and Elements. Glossary. Index.

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The Microbiology of Anaerobic Digesters

Contribution of hydrogen to methane production and control of hydrogen concentrations in methanogenic soils and sediments

Mixed culture biotechnology for bioenergy production

https://www.cell.com/trends/biotechnology/pdf/S0167-7799(10)00202-7.pdf

Waste to bioproduct conversion with undefined mixed cultures: the carboxylate platform

Global warming can be slowed, and perhaps reversed, only when society replaces fossil fuels with renewable, carbon-neutral alternatives. The best option is bioenergy: the sun's energy is captured in biomass and converted to energy forms useful to modern society. To make a dent in global warming, bioenergy must be generated at a very high rate, since the world today uses approximately 10 TW of fossil-fuel energy. And, it must do so without inflicting serious damage on the environment or disrupting our food supply. While most bioenergy options fail on both counts, several microorganism-based options have the potential to produce large amounts of renewable energy without disruptions. In one approach, microbial communities convert the energy value of various biomass residuals to socially useful energy. Biomass residuals come from agricultural, animal, and a variety of industrial operations, as well as from human wastes. Microorganisms can convert almost all of the energy in these wastes to methane, hydrogen, and electricity. In a second approach, photosynthetic microorganisms convert sunlight into biodiesel. Certain algae (eukaryotes) or cyanobacteria (prokaryotes) have high lipid contents. Under proper conditions, these photosynthetic microorganisms can produce lipids for biodiesel with yields per unit area 100 times or more than possible with any plant system. In addition, the non-lipid biomass can be converted to methane, hydrogen, or electricity. Photosynthetic microorganisms do not require arable land, an advantage because our arable land must be used to produce food. Algae or cyanobacteria may be the best option to produce bioenergy at rates high enough to replace a substantial fraction of our society's use of fossil fuels.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bit.21875

Opportunities for renewable bioenergy using microorganisms

Anaerobic wastewater treatment

Energetic and reaction-rate interactions between hydrogenic (hydrogen-producing) and hydrogenotrophic (hydrogen-consuming) bacteria were investigated in five perturbation experiments performed on steady-state, mixed-culture methanogenic CSTRs receiving ethanol, propionate, or both hydrogenic substrates. When a large quantity of propionate was suddenly added to a propionatefed CSTR, P(H(2) ) increased to 10(-4) atm and propionate oxidation remained energetically favorable. When ethanol was added to a CSTR receiving ethanol, P(H(2) ) rose to 6.3 x 10(-3) atm within 5 h. In both perturbations, P(H(2) ) remained at levels such that oxidation of the hydrogenic substrate remained energetically favorable throughout the transient. Sudden increase in ethanol concentration in the ethanol- and propionate-fed CSTR resulted in an increase in P(H(2) ) such that propionate oxidation became energetically unfavorable and was blocked. Propionate utilization resumed when the added ethanol was depleted and P(H(2) ) returned to its previous steady-state levels. Ethanol perturbation of ethanol- and propionate-fed CSTRs led to the formation of reduced products, including n-propanol and four-through seven-carbon n-carboxylic acids, when P(H(2) ) was elevated; these products disappeared after P(H(2) ) returned to previous, steady-state levels. The transformations were consistent with reaction energetics. Reduced product formation may have been a sink for reducing equivalents, as an alternative to oxidation for propionate utilization, as indicated by an electron equivalents balance over the time course of experiments.

Energetic and rate effects on methanogenesis of ethanol and propionate in perturbed CSTRs.

Energetic analysis was applied to reduced product formation following perturbation of ethanol- and propionate-fed methanogenic continuous stirred tank reactors (CSTRs). Formation and dissipation of longer-chained n-carboxylic acids corresponded with the variation in Gibbs free energy change associated with beta-oxidation reactions. Formation appeared to occur from acetate and propionate by reductive back-reactions, made energetically favorable by elevated hydrogen partial pressure (P(H(2))), and possibly mediated by biosynthetic enzymes. The formed longer-chained acids dissipated when the P(H(2)) fell and equilibrium shifted to favor beta-oxidations. n-Propanol was found to be produced from propionate in a coupled ethanol oxidation/propionate reduction reaction, mediated by ethanol-oxidizing organisms during high rates of ethanol utilization and elevated P(H(2)). When P(H(2)) declined, n-propanol was oxidized back to its precursor propionate. Both reaction energetics and intracellular diffusion of the electron carrier may effect transient mediation of this coupled reaction.

Reduced product formation following perturbation of ethanol- and propionate-fed methanogenic CSTRs.

A non-steady-state energetic/kinetic model was developed to predict methane production, organic substrate and product concentrations, hydrogen partial pressure, and bacterial mass concentrations in a methanogenic continuously stirred tank reactor (CSTR) receiving ethanol and propionate as organic sub strates for growth. The model was used to simulate a shock-load perturbation of the steady-state CSTR by sudden addition of a large quantity of ethanol and propionate. A cyclic pattern in methane production, corresponding to sequential utilization of substrates and intermediates, was predicted by the model. Ex perimentally measured methane production showed a similar cyclic pattern, but was more erratic due to reduced product for mation which shifted methane production to latter stages in the transient. Res. J. Water Pollut. Control Fed., 62, 58 (1990).

Factors governing methane fluctuations following shock loading of digesters.

The redox control bioreactor (RCB) is a new hollow fiber membrane bioreactor (HFMBR) design in which oxygen and hydrogen gases are provided simultaneously through separate arrays of juxtaposed hollow fiber (HF) membranes. This study applied the RCB for completely autotrophic conversion of ammonia to N(2) through nitrification with O(2) and denitrification using hydrogen as an electron donor (i.e., autohydrogentrophic denitrification). The hypothesis of this research was that efficient biofilm utilization of O(2) and H(2) at respective HFs would limit transport of these gases to bulk fluid, thereby enabling completely autotrophic ammonia conversion to N(2) through the co-occurrence of ammonia oxidation (O(2)-HF biofilms) and autohydrogenotrophic denitrification (H(2)-HF biofilms). A prototype RCB was fabricated and operated for 215 days on a synthetic, organic-free feedstream containing 217 mg L(-1) NH(4)(+)-N. When O(2) and H(2) were simultaneously supplied, the RCB achieved a steady NH(4)(+)-N removal flux of 5.8 g m(-2) day(-1) normalized to O(2)-HF surface area with a concomitant removal flux of 4.4 g m(-2) day(-1) (NO(3)(-))+NO(2)(-))-N based on H(2)-HF surface area. The significance of H(2) supply was confirmed by an increase in effluent NO(3)(-)-N when H(2) supply was discontinued and a decline in NO(3)(-)-N when H(2) supply was restarted. Increases in H(2) pressure caused decreased ammonia utilization, suggesting that excess H(2) interfered with nitrification. Microprobe profiling across radial transects revealed significant gradients in dissolved O(2) on spatial scales of 1 mm or less. Physiological and molecular analysis of biofilms confirmed that structurally and functionally distinct biofilms developed on adjacent, juxtaposed fibers.

Daniel P. Smith

Papers

Anaerobic wastewater treatment

Energetic and rate effects on methanogenesis of ethanol and propionate in perturbed CSTRs.

Reduced product formation following perturbation of ethanol- and propionate-fed methanogenic CSTRs.

Factors governing methane fluctuations following shock loading of digesters.

Redox control bioreactor: A unique biological water processor