Understanding the Complexity and Strategic Evolution in PAH Remediation Research

Abstract

The development and improvement of society through industrialization and urbanization comes with the cost of consistent deterioration and degradation of the natural environment through generation of toxic and hazardous pollutants. Polycyclic aromatic compounds (PAHs) are a major class of such persistent organic pollutants, posing serous threat to terrestrial and aquatic ecosystems due to their intrinsic low aqueous solubility, higher binding affinity toward soil organic matters, and higher chemical stability, making them less susceptible toward remediation process. Two key issues are covered in the review. First, the severity of contamination and its implications are addressed with reference to source, distribution, and toxicity of PAHs. Second, a detailed overview on significant and systematic changes that have ever been observed in remediation methodology of PAH contaminants in past decades is presented. The remediation and treatment time, contaminant composition and load, site characteristics, and desired degree of cleanup are the decisive factors guiding selection of proper in situ or ex situ remediation technology. It has generally been observed chemical oxidation is the method of choice for rapid reduction (within minutes to couple of hours) of recalcitrant PAHs (e.g., benzo[a]pyrene) load in a more heterogeneous system (e.g., soil) with an efficiency from ∼10% to 100%. On the other hand phytoremediation can effectively handle 3- and 4-ring PAHs (phenanthrene, pyrene) in aged and spiked contaminated soil and sediment system with a similar degree of conversion, but in a long or extended period of time (a couple of months to years). The times scale for ex situ microbial remediation systems in liquid phase are in days to weeks and contaminant load that can effectively be treated varies with the nature and concentration of additives (e.g., surfactants, solvents). Finally, the authors offer general insight about biological treatment methods, with a wider focus into the recent developments in the process.

KEY WORDS:

• biodegradation
• PAH remediation
• PAH toxicity
• surfactant
• TPPB