Aerobic transformations

FIGURE 10.45 Aerobic transformation of (a) quercitin and (b) genistein. (From Neilson, A.H. and Allard, A.-S., The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, Heidelberg, 1998. With permission.)... 

The most broadly studied organic nitrogen compound is probably quinoline however, most studies report biodegradation. As we have seen from Table 14, quinoline is representative of the organonitrogen compounds present in the diesel cut. Its transformation has been studied in both, anaerobic and aerobic conditions. Several metabolic pathways have been proposed to explain the aerobic transformations however, no pathway has been proposed for quinoline metabolism under anaerobic conditions. 

Reaeration in sewer networks the presence of dissolved oxygen in wastewater of sewer systems determines if, and to what extent, aerobic and anaerobic processes proceed. The air-water oxygen transfer (the reaeration) determines the potential of aerobic transformation and corresponding removal of wastewater components in many sewer... 

Fundamentally, the extent of the aerobic transformations of organic matter in a sewer depends on the presence of an active heterotrophic biomass, electron donors and the electron acceptor. The continuous supply of the electron acceptor, oxygen, is, in this respect, crucial. The reaeration process often limits the transformations and is a key process. 

Although experimental studies under sewer conditions are subject to high variability, it can be concluded that the removal of the components shown in Table 5.1 is mainly attributed to the activity of the heterotrophic biomass. Theoretical considerations and a number of studies like the one performed by Almeida (1999) clearly demonstrate that the heterotrophic biomass is central for understanding aerobic transformations. Studies by Stoyer (1970), Stoyer and Scherfig (1972), Koch and Zandi (1973), Pomeroy and Parkhurst (1973) and Green et al. (1985) have also focused on removal of organic matter in sewers, primarily in terms of BOD and COD. 

The heterotrophic biomass in wastewater is typically not a limiting factor for the aerobic transformations in a sewer. The limitation is typically caused by the supply of the electron acceptor (oxygen), i.e., the reaeration. Contrary to what has been proposed by several authors, it would typically serve no useful purpose to inject biomass (sludge) in a sewer line to enhance the treatment processes unless a significant amount of oxygen is continuously supplied to the wastewater (cf. Example 5.1). 

A gravity sewer pipe with a diameter D=0.5 m and a slope s=0.003 m m-1 is flowing half full under stationary conditions, i.e., the DO concentration is constant and equal to about 0.3 g02 m-3. The pipe is made of concrete, and the roughness is 1.0 mm. The sewer is an interceptor and serves a separate sewered catchment. The wastewater originates from domestic sources and has a temperature of T= 15°C. The characteristics of the wastewater are approximately as depicted in Figure 3.10, i.e., the potential process rates for the aerobic transformations are relatively high. Only aerobic processes in the water phase are considered in the example. 

The aerobic transformations are considered limited by the reaeration, and Equation (6) in Table 4.7 is used to calculate the rate of oxygen supply. Based on the formula of Colebrook and White for a full-flowing circular pipe, the flow and velocity of the wastewater are determined as follows for the half-filled pipe ... 

Anaerobic processes — related to both the sulfur and the carbon cycles — are, therefore, important in sewers. The interaction between these processes and the aerobic transformations of the wastewater may be even more interesting for the functioning of the urban wastewater systems. 

The difference between aerobic and anaerobic transformations of wastewater organic matter is crucial. From a basic point of view, however, still related to the sewer systems, aerobic and anaerobic microbial processes have been dealt with in Chapter 3. The aerobic transformations and a corresponding conceptual model were the main subjects of Chapter 5. 

The sewer model is designed from a conceptual point of view and has potential for further applications. In Section 4.3.3, it was concluded that the occurrence of sulfide can be used as a pragmatic measure of malodors. Therefore, the sewer process model also has potential for the prediction of odor problems. Furthermore, as dealt with in Section 8.5.2, the model also predicts the aerobic transformations of suspended sediment particles in sewers (Vollertsen and Hvitved-Jacobsen, 1998, 1999 Vollertsen et al 1998, 1999). The model is also a potential tool for simulation of the impacts from combined sewer overflows. 

As far as organic matter transformations are concerned, the process rates are significantly slower compared with aerobic transformations. Basically, readily biodegradable organic matter is preserved and even, to some extent, produced opposite to the situation when aerobic processes proceed. The sulfur cycle, until now included in the sewer process model, is relatively simply described following empirical expressions for sulfide formation. Other important processes in this respect, e.g., hydrogen sulfide emission and sulfide oxidation, still need to be included, however, and, most of all, investigated from a conceptual point of view. 

Figure 8.3 shows that the sewer is full flowing at 775 m3 h 1 (215 L s 1). It also shows that the reaeration and the DO concentration vary considerably with the flow conditions. At rather low flow rates, the DO concentration is about 2-4 g02 m-3, a level that is significantly reduced even at flow rates that are below those corresponding to a half-full flowing pipe. Example 8.2 shows that it is possible to control the magnitude of the aerobic transformation of the wastewater by the selected level of the flow compared with the capacity of the sewer. 

The predicted treatment in the interceptor is supported by corresponding aerobic transformations of the wastewater in the tributaries. In general, the slopes in the tributaries to the interceptor are relatively steep, and a number of sewer drops exist. The wastewater in these tributaries typically flows under aerobic conditions, and heterotrophic processes proceed. Field studies that have been undertaken by Almeida (1999) have shown that these transformations are in agreement with the results shown in Table 8.2. 

Incomplete aerobic transformations may involve cometabolic transformations and reactions resulting in recalcitrant dead-end metabolites. Cometabolic o-hydroxylation of MCPs and DCPs by a phenol monooxygenase has been shown, for example, in a Pseudomonas sp. (Knackmuss Hellwig, 1978) and by the toluene dioxygenase reaction in Pseudomonas putida (Spain Gibson, 1988 Spain et al., 1989)- Cometabolic transformation of CPs is also possible in aerobic mixed culture systems. Phenol- and toluene-enriched cultures completely removed 2,4-DCP, and the toluene enrichment also removed 2,4,6-TCP and PCP (Ryding et al., 1994). This PCP attack by the toluene enrichment involved an o-hydroxylation. 

Ogawa, J., Matsumura, K., Kishino, S., Omura, Y., and Shimizu, S. 2001. Conjugated linoleic acid accumulation via 10-hydroxy-12-octadecaenoic acid during micro-aerobic transformation of linoleic acid by Lactobacillus acidophilus. Appl. Environ. Microbiol., 67,1246-1252. 

To grow the cultures, the inoculated nutrient broths are agitated on a rotary or reciprocal shaker. Shaking prevents sedimentation of solid constituents of the nutrient medium and of the growing culture, and favors homogeneous growth. The vessels arc closed with wadding closures for conventional aerobic transformations, which allows sufficient sterile air to enter the incu-... 

OECD (2000). Simulation test - Aerobic Transformation in Surface Water. Draft proposal for a new guideline. May 2000... 

Aerobic Transformation of TNT by Bacteria and Their Major Products... 

Valkova, N., Lepine, F., Valeanu, L., Dupont, M., Labrie, L., Bisaillon, J. G., Beaudet, R., Shareck, F. and Villemur, R., 2001. Hydrolysis of 4-hydroxybenzoic acid esters (Parabens) and their aerobic transformation into phenol by the resistant Enterobacter cloacae strain. Applied and Environmental Microbiology 67, 2404-2409. 

This enzyme catalyzes the aerobic transformation of proto-catechuic acid to p-carboxymuconic acid (equation 26 (501)). The... 

Aerobic transformation of uric acid to allantoin (equation 119) is catalyzed by uricase, an enzyme widely distributed throughout the phylogenetic scale, which participates in the final degradation of purines (246,472). It catalyzes oxidation of uric acid only (396) substituted uric acids are not attacked. The course of oxidation is complex, the number of products and their relative proportions being dependent upon conditions of reaction. A summary of these reactions is given in Figure 33 (36,43,96,130-132,181,592). 

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