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.

/pdf/the-microbiology-of-anaerobic-digesters-zycawfpj0t.pdf

The Microbiology of Anaerobic Digesters

This paper presents a literature review of anaerobic digestion of munidpal wastewater sludges. The paper focuses on the fundamentals of anaerobic digestion, setting forth a checklist for review of key process factors including: retention time, mixing, pH, temperature, nutrients, toxic materials, and feed characteristics. Major areas discussed are the microbiology and biochemistry of digestion, kinetics of digestion, environmental factors of concern, process performance indices, product stability, and laboratory and pilot studies on digestion. Although the text is aimed at digestion of municipal sludges, the fundamentals are sufficiently general to permit extrapolation to decomposition of other organics.

Fundamentals of Anaerobic Digestion of Wastewater Sludges

Nitrification and nitrogen removal

Thermophilic aerobic biological wastewater treatment

The effect of dissolved oxygen concentration on nitrification

Renewed interest in the problems cre ated by the d scharge of nitrogenous compounds to receiving waters has focused attention on the form and concentration of nitrogen in wastewater treatment plant effluents. Most wastewater treatment plants are designed, operated, and evalu ated based on the reduction of carbona ceous 5-day biochemical oxygen demand (bod5), rather than on the total bod of the effluent (carbonaceous and nitrogenous). As a result, ammonium is the primary form of nitrogen in domestic wastewater treat ment plant effluents and is commonly found in concentrations up to 20 to 30 mg/1. If a theoretical oxygen requirement for ni trification of 4.5 mg oxygen/mg ammonium nitrogen oxidized to nitrate is assumed, an effluent with 20 mg NH4+-N/1 can exert a nitrogenous oxygen demand of up to 90 mg/1, which is considerably greater than that contributed by the ultimate car bonaceous demand of secondary biologi cal treatment plant effluents (?30 mg/1). The conversion of ammonium to nitrate within a biological treatment plant would, therefore, represent a significant improve ment in effluent quality. The activated sludge process may be used to obtain nitrification if conditions suitable for the retention and accumulation of nitrifying bacteria are maintaned. The conditions necessary for nitrification may be expressed in terms of sludge age, pH, temperature, and dissolved oxygen (do) concentration. The concentration of nitrifying bacteria will depend on their specific growth rate and on the rate at which they are discharged from the system through the effluent and waste sludge streams. Several laboratory, pilot, and full scale investigations have been conducted with nitrifying activated sludge systems and have demonstrated that high efficiencies of nitrification are obtained at sludge ages of approximately 4 days or more.1-6 It is important to note, however, that, at tem peratures less than 20 ?C, the sludge age required to maintain high nitrification ef ficiencies increases markedly. Until the recent application of mathe matical models based on kinetic principles, some of the basic concepts regarding ni trification in the activated sludge process were not clearly understood. Downing et al.1 were among the first to develop a kinetic model for nitrification in the acti vated sludge process. They concluded that consistent nitrification would be expected in activated sludge plants only if the growth rate of the nitrifying bacteria were greater than the rate of loss through the effluent and sludge wasting streams. Using this concept and experimentally determined values for growth rate coefficients, they were able to obtain reasonable predictions of the degree of nitrification in activated sludge plants.7 Although several mathematical models have been developed for the nitrifying ac tivated sludge process,1'3> 8_11 these usually have been steady-state models. Because domestic wastewater treatment plants op erate under time-varying loads, the use of steady-state models to describe these processes is inconsistent with their opera tional nature. In this regard, a full under standing of the kinetics of nitrification and the response of nitrifying systems to dy namic inputs may be necessary before more effective control of nitrification is possible. The primary objective of this research was to develop a dynamic model for nitri fication in the activated sludge process that

Dynamics of nitrification in the activated sludge process.

The grinding of garbage or other organic refuse with subsequent trans port by water to a waste treatment plant is increasing as additional home garbage grinders are installed. This system of disposal also is finding; wider use in commercial establishments, and a number of cities have installed centrally located municipal garbage grinding stations. The use of an exist ing transport system, the sewers, for garbage collection is a promising ap proach to the organic refuse problem. However, use of this disposal method means that increased emphasis must be placed on treatment of these organic solids once they have reached the waste treatment plant. Thermophilic aerobic digestion is a process which appears to have great potential for treatment of these organic solids. One of the major factors to be con sidered in the use of a thermophilic process is the heat energy required to maintain thermophilic temperatures. However, heat can be produced by microbial thermogenesis as evidenced by the autothermal nature of com posting processes which usually operate in the thermophilic range. In indus trial fermentations (1) cooling coils are frequently necessary to remove heat produced by thermogenesis, and Wang

Aerobic thermophilic process for the biological treatment of wastes-simulation studies.

at determining the optimal methods for dewatering digested sludge as well as the subsequent steps for ultimate land disposal. This paper presents the development and application of the mesophilic-thermophilic process, pioneered in New York City at the Rockaway Wastewater Treatment Plant. This was ac complished using a two-stage digestion system, consisting of a mesophilic stage, followed by a thermophilic stage. A part of the digested sludge leaving the thermophilic stage was recycled through the aeration tanks to obtain additional destruction of volatile solids. Results indicate that both the volume and volatile solids content of meso-thermo digested sludge were reduced to the extent that the economics of disposal was significantly im proved. Moreover, the residual sludge was substantially inert and had met the time-temperature requirement for pathogen destruction. The results of tests on the plant effluent are presented to show that recirculation of digested sludge through the aeration tanks does not have any significant adverse effect on accepted parameters (suspended solids (SS), biochemical oxygen demand (BOD), nutrients, heavy metals, oxygen requirements).

John F. Andrews

Papers

Dynamics of nitrification in the activated sludge process.

Aerobic thermophilic process for the biological treatment of wastes-simulation studies.

Effects of multiple digestion on sludge