Polycyclic aromatic hydrocarbons (PAHs) have been recognized as a heterogeneous group of persistent con- taminants, due to their toxic, carcinogenic and mutagenic properties and high recalcitrance to different types of degradation (Ockenden et al., 2003; Mohan et al., 2006). They are widely distributed in environments such as soil, sediment, water and air as results of both natural and an- thropogenic processes, and therefore have known harmful effects on humans and wildlife (Keith, 1979; Eibes et al., 2006).
Bioremediation is a low-cost and environmentally- friendly alternative for decontamination of PAHs-contaminated soils. Recently, numerous studies investigating the application of bioremediation to treat PAHs-contaminated soils using a variety of plant (Liste and Alexander, 2000; Fismes et al., 2002; Fan et al., 2008) or microbial species (Gomes et al., 2005; Wu et al.,
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[email protected]2008) or plant-microbe combinations (Tam and Wong, 2008) have been carried out. However, the effectiveness of in-situ bioremediation of aged PAHs-contaminated soils is always limited, because the residual components of PAHs in aged soil have poorer water solubility and are more strongly adsorbed by soil particles, which leads to a lower biodegradation effectiveness compared with fresh PAHs-contaminated soils (Leonardi et al., 2007; Hwang and Cutright, 2002). Furthermore, PAHs-contaminated soils are often nutrient- and organic matter-deficient so that a low PAHs degradation capability is exhibited due to the low number and activity of indigenous microbial population (Kobayashi et al., 2008).
Organic wastes, such as animal manure, straw, compost and sewage sludge, have often been used to improve soil quality, by altering the physical properties (soil aggrega- tion), ameliorating soil organic matter (SOM) quantity, increasing nutrient availability, and other soil functions (Debosz et al., 2002; Celik et al., 2004; Courtney and Mullen, 2008). Based on the introduction of microorgan-