The Aerobic Process

A two-step microbial process yields a dilute 5-12 % solution of acetic acid (vinegar) from a crude carbohydrate-containing mash. The first step is the production of ethanol fi om sugars by an anaerobic fermentation, usually by the yeast Saccharomyces cerevisiae or alternatively by a bacterium such as Zymomonas mobilis 

The second step is the oxidative conversion of ethanol to acetic acid carried out by an Acetohacter strain. These bacteria catalyze an interesting incomplete oxidation where characteristically their capacity to oxidize ethanol and lactate far exceeds the oxidation of acetic acid to CO2. During the incomplete oxidation of ethanol, the reducing equivalents are transferred to oxygen  

Surprisingly, the microbiology of the modern vinegar fermentation is not entirely worked out as to the exact taxonomy of the participating Acetobflcter species. It is still state of the art to 

Organic Acid and Soivent Production Acetic, Lactic, Giuconic, Succinic, and Poiyhydroxyaikanoic Acids 

lovaniensis Growth and acetic acid produced at 37-40 °C SaekI et al. (1997b) 

---

In the aerobic process, organic contaminants such as gasoline releases are broken down by bacteria to produce new biomass (bacteria) and other byproducts ... 

U.S. EPA has shown that 90% of process water can be recycled to the front end of the system for slurry preparation, and the rest must be treated on site or transported to an off-site facility.80 During the aerobic process, some contaminated air may be formed and emitted from the reactor. Depending on the air characteristics, a compatible air pollution control device may be used, such as activated carbon. Slurry biodegradation has been shown to be successful in treating soils contaminated with soluble organics, PAHs, and petroleum waste. The process has been most effective with contaminant concentrations ranging from 2500 mg/kg to 250,000 mg/kg. 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

All subsystems influence the integrated in-sewer processes, although the water phase processes are typically most important. Reaeration is a process that, when there are low DO concentrations in the wastewater, limits the rate of the aerobic processes (cf. Example 5.1). The relative importance of the processes in the suspended water phase and in the biofilm may vary, e.g., determined by the area/volume ratio of the sewer pipe. 

Nitrification is the aerobic process by which microorganisms oxidize ammonium to nitrate and derive energy. It is the combination of two bacterial processes one group of organisms oxidizes ammonia to nitrite (e.g., Nitrosomonas), after which a different group oxidizes nitrite to... 

Recall In which steps of the aerobic processing of pyruvate is CO2 produced ... 

Aerobic metabolism is a highly efficient way for an organism to extract energy from nutrients. In eukaryotic cells, the aerobic processes (including conversion of pyruvate to acetyl-GoA, the citric acid cycle, and electron transport) all occur in the mitochondria, while the anaerobic process, glycolysis, takes place outside the mitochondria in the cytosol. We have not yet seen any reactions in which oxygen plays a part, but in this chapter we shall discuss the role of oxygen in metabolism as the final acceptor of electrons in the electron transport chain. The reactions of the electron transport chain take place in the inner mitochondrial membrane. 

Aeration and agitation plays a significant role in the SSF process because it faces two fundamental problems O2 demand in the aerobic process, and heat and mass transport phenomena in a heterogeneous system [24, 26]. O2 demand in SSF can be satisfied with relatively low aeration levels. Agitation may also break the mycelia-substrate bed depending on the nature of the solids, which can disrupt the growth and metabolism. However, there is always a compromise between the rate of aeration, microbial growth, and product formation. Several authors continue to study aspects related to aeration in different kinds of reactor setup in SSF [27, 28]. 

---