Bioremediation of PAH-contaminated sites: From pathways to bioreactors

Pouli, Maria [UCL] Agathos, Spiros N. [UCL]

Polycyclic aromatic hydrocarbons (PAHs) are widespread pollutants found in industrial sites linked with petroleum, gas production or other activities involving incomplete combustion of organic matter. These compounds constitute a priority for treatment of contaminated soils and sediments due to their toxicity and carcinogenicity. Microbial degradation represents an important mechanism of PAH removal and can be used for the treatment of contaminated sites by in situ or ex situ bioremediation. This technology is taking advantage of a few established peripheral catabolic pathways converting different PAHs into a limited number of central intermediates. Peripheral pathways are typically initiated by dioxygenases, oxidizing PAHs into dihydroxylated intermediates, which, in turn, are catabolized further and degraded via central pathways into TCA cycle metabolites. However, both the hydrophobic characteristics of most PAHs as well as the physicochemical properties of soils diminish the bioavailability of these pollutants and thus limit the degradation capacity of naturally occurring microorganisms for bioremediation of contaminated sites. The success of biotreatment interventions can be enhanced by measures promoting bioavailability (e.g. addition of surfactants or solvents) and/or boosting microbial activity (e.g. by biostimulation or bioaugmentation). The same strategies can be further optimized by implementing appropriately designed bioreactors for faster and more complete removal of recalcitrant PAHs from contaminated soils and sediments