## 4 Bioremediation of PAH-Contaminated Soil by Composting  
Composting technology is categorized as ex situ technology, which has been used for the treatment of contaminated soils. During the last few decades, the process received more attention, as it has proved its high efficiency in degrading various organic contaminants like, among others, PAHs, pesticides, explosives, and chlorophenols [55; 56; 57; 58; 59; 60]. Essentially, the process relies on the addition of compost or organic co-substrates/amendments to the contaminated soil, and while the co-substrate matures, due to the action of various microbial populations within the mixture, the target pollutants  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**PAH**} & **Number** & **Molecular** & **Aqueous** & **Vapor** & **Log** \\  & **of Rings** & **Weight** & **Solubility (mg/L)** & **Pressure. (Pa)** & \(K_{ow}\) \\ \hline Naphthalene & 2 & 128 & 31 & \(1.0\times 10^{2}\) & 3.37 \\ Acenphthylene & 3 & 152 & 16 & 0.9 & 4.00 \\ Acenaphthene & 3 & 154 & 3.8 & 0.3 & 3.92 \\ Flourene & 3 & 166 & 1.9 & \(9.0\times 10^{-2}\) & 4.18 \\ Phenanthrene & 3 & 178 & 1.1 & \(2.0\times 10^{-2}\) & 4.57 \\ Anthracene & 3 & 178 & 0.045 & \(1.0\times 10^{-3}\) & 4.54 \\ Pyrene & 4 & 202 & 0.13 & \(6.0\times 10^{-4}\) & 5.18 \\ Flouranthene & 4 & 202 & 0.26 & \(1.2\times 10^{-3}\) & 5.22 \\ Benzo(a)anthracene & 4 & 228 & 0.011 & \(2.8\times 10^{-5}\) & 5.91 \\ Chrysene & 4 & 228 & 0.006 & \(5.7\times 10^{-7}\) & 5.91 \\ Benzo(b) & 5 & 252 & 0.0015 & - & 5.80 \\ flouranthene & & & & & \\ Benzo(k) & 5 & 252 & 0.0008 & \(5.2\times 10^{-8}\) & 6.00 \\ flouranthene & & & & & \\ Benzo(a)pyrene & 5 & 252 & 0.0038 & \(7.0\times 10^{-7}\) & 5.91 \\ Dibenzo(a,h) & 5 & 278 & 0.0006 & \(3.7\times 10^{-10}\) & 6.75 \\ anthracene & & & & & \\ Indeno(1,2,3-cd)pyrene & 6 & 276 & 0.00019 & - & 6.50 \\ Benzo(ghi)perylene & 6 & 276 & 0.00026 & \(1.4\times 10^{-8}\) & 6.50 \\ \hline \hline \end{tabular}  
* \({}^{*}\)Kow: octanol–water partition.  
\end{table}
Table 1: Selected properties of the 16 USEPA PAHs.  
are degraded [57, 61]. Thus, treatment of PAH-contaminated soil combined with composting of organic waste could be an interesting option and a sustainable method with much increasing attention. It would enable eco-friendly disposal of such waste and enhance the biodegradation rate of PAHs [7, 60, 62]. The biodegradation process efficiency depends fundamentally on the bioavailability of the substrates, environmental conditions (pH, moisture, temperature), the presence of oxygen, and the availability of nutrients [38]. Remarkably, the bioremediation of PAH-contaminated soils through composting has confirmed this technique's capability to overcome most obstacles that might hinder reaching its goal, which is the removal of contaminants [63, 64, 65, 66, 10, 67].  
As the process is based on mixing the contaminated soil with organic co-substrates, any failure may result in producing much greater quantity of contaminated material, and this is recognized as the main concern of using such approach. This weakness, and the general scarcity of information on the toxicity, distribution, and bioavailability of such contaminants in compost-amended soils, may therefore result in the drawing up of excessively stringent soil assessment measures with remediation cost implications [68].