Urban wastes to remediate industrial sites: a case of polycyclic aromatic hydrocarbons contamination and a new process

The objective of the present paper was to investigate the potential of urban wastes derived soluble bioorganic substances (SBO) to perform as auxiliaries for enhanced washing of urban soil contaminated by industrial activities. The second objective was to show how the SBO could be used for remediating the environmental impact caused by industrial activities and, at the same time, be compatible with the real-world situation demanding zero waste processes. The SBO, isolated from four urban biowastes, were characterized for their lipophilic/hydrophilic (LH) and aliphatic/aromatic C ratios, and for their surface activity properties. Soil, containing about 0.45 % w/w polycyclic aromatic hydrocarbons (PAHs), was sampled from a dismissed coal gasification site. The efficiency of the SBO for washing the contaminated soil was investigated. The most lipophilic SBO, in spite of the highest surface activity, was the least efficient. The products having lower LH, poorer surface activity, but higher concentration of aromatic C were more efficient. All SBO allowed developing a two steps process. This comprised soil washing, and the recovery and chemical treatment of the washing solution, to yield a PAHs-SBO precipitate and the clean water phase to recycle to further soil washing. Data were obtained under the same experimental conditions using Triton X-100 commercial surfactant. The results indicated that, although the commercial surfactant is the most efficient in the soil washing step, it does not allow removal of PAHs from the recovered washing solution. On the contrary, 95-99 % PAHs removal from the recovered SBO washing solutions is attained.