Effect of humic compounds on bacterial growth in bioremediation of pahs
Polycyclic Aromatic Hydrocarbons (PAHs) are introduced into the environment through natural and anthropogenic combustion processes causing them to be ubiquitous in environment (Menzi et al., 1992; Juhasz and Naidu, 2000 and Nieman et al., 2001). These compounds are potentially carcinogenic, mutagenic and toxic contaminants (Yerushalmi and Guiot, 2001; Verrhiest et al., 2002; Samanta et al., 2002 and Zhang et al., 2005). At present, employing the biochemical abilities of microorganisms is the most popular strategy for the biological treatment of contaminated soils and waters (Semple et al., 2001). The biological strategy is dependent on the catabolic activities of the microflora, optimizing the conditions for growth and biodegradation (Semple et al., 2001). In this manner, bioremediation is one of the best technologies for removing pollutants from the environment (Ewies et al., 1998 and Ramirez et al., 2001). Bioavailability of organic contaminants has been identified as a major constraint for complete bioremediation (Semple et al., 2001 and Park et al., 2002). Researches have been designed to explain and overcome problems of PAHs poor availability (Laor et al., 1996) by using humic substances (HSs). Several mechanisms about the effect of HSs on bioremediation are studied during in recent years and are described as: covalent and noncovalent bounding, adsorption solubility enhancement, microbial activity enhancement, increasing in microbial population and help enhancing production of useful enzymes in biodegradation. Two major technologies using HS are phytoremediation and compost which could stimulate microbial population ability in bioremediation (Alkorta and Garbiso, 2001; Richnow et al., 2000; Gramms et al., 1999 and Van Elsas et al., 1998), but it is not clear whether increased dissipation of PAHs in the system containing humic substances is due to a specific stimulation of PAH degraders in the medium. Hence it is desirable to optimize the activity of degradative microorganisms (Allard and Nielson, 1997). Substrate utilization patterns were shown to vary depending on the both composition and density of the inoculums that is used (Van Elsas et al., 1998).