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ABSTRACT: Bacillus subtilis is an organism capable of degrading an azo dye, such as p-aminoazobenzene (pAAB), under both aerobic and anoxic conditions. In both cases, pAAB is co-metabolized with a main carbon source and under anoxic conditions denitrification is observed. Kinetic experiments were carried out with a pure culture of B. subtilis and a mathematical model that accurately describes both biodegradation of pAAB under anoxic conditions and the denitrification process under both carbon- and nitrate- or nitrite-limited conditions is developed. Presence of pAAB in culture medium causes an inhibition of bacterial growth and of nitrite accumulation. Bacterial growth and pAAB degradation rates are found to be slower under anoxic conditions compared to the corresponding rates under aerobic conditions. Water Environ. Res., 71, 323 (1999).
KEYWORDS: B. subtilis, p-aminoazobenzene, biodegradation, anoxic conditions, denitrification, kinetic modeling.
Removal of color from wastewater represents a primary environmental concern. Organic dyes cause both organic pollution and a higher coloration of effluent. Dye compounds are difficult to treat because of their ability to resist light and oxidizing agents (McKay et al., 1988). They are not readily degradable and are difficult to remove from water by conventional treatment methods (Anliker, 1979, and Pagga and Brown, 1986). Consequently, they are often hard to biodegrade when present in municipal wastewater. Azo dyes represent the largest group of industrial dyes both in number and amount produced. They are characterized by the presence of nitrogen-to-nitrogen double bonds (-N=N-). The color of azo dyes is attributed to the azo-bond, associated auxochromes, and a system of conjugated double bonds (aromatic hydrocarbons). Although bacterial azo-reduction typically requires anaerobic conditions, there is little information available about biodegradation of azo dyes under aerobic and anoxic conditions (Wurhmann et al., 1980). In a previous paper, Zissi et al. (1997) showed that Bacillus subtilis is an organism capable of degrading an azo dye, such as p-aminoazobenzene (pAAB), under aerobic conditions. A model was developed capable of adequately describing pAAB co-metabolism with glucose (as the carbon source) in the presence of dissolved oxygen. The azo bond was cleaved to give aniline and p-phenylenediamine as products, while the presence of the azo dye caused retardation of bacterial growth rate.
In another publication, Zissi and Lyberatos ( 1996) examined the behavior of B. subtilis under...