Due to its widespread use and its ubiquity, phenol is a major pollutant of the environment. Industries that produce or use phenol may at some point release this compound into the environment. It is therefore not surprising to find that phenol is a commonly found waste by-product in many industries, including petroleum refining, petrochemical, coke conversion, pharmaceutical, and resin manufacturing plants. Phenol concentrations of up to 10,000 mgl-1 have been reported in industrial wastewaters (Fedorak and Hrudey, 1988). Without proper treatment, industrial waste-waters would become potentially important sources of anthropogenic phenol into the environment.
Phenol and its structurally related compounds are toxic at relatively low concentrations and are listed as priority pollutants by the US Environmental Protection Agency (Ghisalba, 1983). Phenol can be toxic to some aquatic species at concentrations in the low mgl-1 range (Brown et al., 1967) and causes taste and odor problems in drinking water at far lower concentrations (Rittmann and McCarty, 2001). Hence the removal of phenol from wastewater is of obvious interest.
Phenol can be removed by solvent extraction, adsorption, chemical oxidation, incineration, and other non-biological treatment methods, but these methods suffer from serious drawbacks such as high cost and formation of hazardous by-products (Loh et al., 2000). Biological degradation is generally preferred due to lower costs and the possibility of complete mineralization. However, phenol-containing wastewater is difficult to treat because of substrate inhibition, whereby microbial growth and concomitant biodegradation of phenol are hindered by the toxicity exerted by high concentrations of the substrate itself.
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