Complete mineralization

Triazines pose rather more of a problem, probably because the carbons are in an effectively oxidized state so that no metaboHc energy is obtained by their metaboHsm. Very few pure cultures of microorganisms are able to degrade triazines such as Atrazine, although some Pseudomonads are able to use the compound as sole source of nitrogen in the presence of citrate or other simple carbon substrates. The initial reactions seem to be the removal of the ethyl or isopropyl substituents on the ring (41), followed by complete mineralization of the triazine ring. 

Carbamates such as Aldicarb undergo degradation under both aerobic and anaerobic conditions. Indeed the oxidation of the sulfur moiety to the sulfoxide and sulfone is part of the activation of the compound to its most potent form. Subsequent aerobic metaboHsm can completely mineralize the compound, although this process is usually relatively slow so that it is an effective iasecticide, acaricide and nematocide. Anaerobically these compounds are hydrolyzed, and then mineralized by methanogens (61). 

The synergistic potential in mixtures with other surfactants as well as with other functional ingredients The high solubility in aqueous solution The superior biodegradability down to complete mineralization... 

Abiotic hydrolysis generally accomplishes only a single step in the ultimate degradation of the compounds that have been used for illustration. The intervention of snbseqnent biotic reactions is therefore almost invariably necessary for their complete mineralization. 

Another specific and important aspect to consider is the possibility that an environmentally heterogeneous photocatalyst can lead to the undesirable formation of reaction intermediates which are more toxic than the starting reagents. For instance, the Ti02-based photodegradation of ethanol, a relatively innocuous air pollutant, occurs through its transformation into the more toxic acetaldehyde. Condensation reactions can also lead to the formation of traces of methyl formate, ethyl formate, or methyl acetate. Catalyst design is therefore important to increase the overall oxidation rate to ensure complete mineralization (formation of C02 and H20). 

Because of UV filters are substances designed to absorb solar energy, photolysis and photocatalysis have been tested as a feasible treatment to degrade the recalcitrant compounds. To date, very few studies have examined UV filters response under UV radiation when exposed in aqueous samples [41-44], Results indicate that the extent of degradation is quite variable, from no photodegradation of BP3 to complete mineralization of BP1 after 24 h of UV light irradiation. 

A pathway reported in the organism Brevibacterium strain DO is more interesting due to complete mineralization of the substrate DBT [129,140,141], This pathway is shown in Fig. 9. 

Bacillus fusiformis Disperse Blue 79, Acid Orange 10 The dyes were completely mineralized within 48 h [60]... 

As stated earlier, the biodegradation of azo dyes requires an anaerobic and aerobic phase for the complete mineralization. The required condition can be implemented either by spatial separation of the two sludge using a sequential anaerobic-aerobic reactor system or in one reactor in the so-called integrated anaerobic-aerobic reactor system. In recent years, combined anaerobic-aerobic treatment technologies are extensively applied in the treatment of azo dye-containing wastewaters. Table 1 lists the systems based on combined anaerobic-aerobic treatment in separate reactors. Table 2 lists SBR based on temporal separation of the anaerobic and the aerobic phase. Table 3 lists the other systems, either hybrids with aerated zones or micro-aerobic systems based on the principle of limited oxygen diffuse in microbial biofilms [91]. 

Factors Affecting the Complete Mineralization of Azo Dyes 3.1 Oxygen Availability... 

---