Influence of activated sewage sludge amendment on PAH removal efficiency from a naturally contaminated soil: application of the landfarming treatment

The removal of polycyclic aromatic hydrocarbons (PAHs) from a naturally co-contaminated soil by PAHs and heavy metals with an initial concentration of 620 mg of total PAHs kg(-1) dry soil was investigated. The efficiency of landfarming in removing phenanthrene, pyrene, benzo(a) pyrene and the group of total 16 US EPA PAHs was evaluated. The process was biostimulated by adding centrifuged activated sewage sludge (SS) as an organic amendment. The tested ratios of contaminated soil to SS were 1:2, 1:1, 1:0.5 and 1:0 as wet weight basis. The process performance was monitored through chemical, microbiological and ecotoxicological analyses during 105 days of incubation. The results of analyses demonstrated that the treatment without centrifuged SS achieved a significantly higher total 16 US EPA PAH removal efficiency (i.e. 32%) compared to treatments with amendment. In the same treatment, the removal efficiency of the PAH bioavailable fraction was 100% for phenanthrene, benzo(a) pyrene and the group of total 16 US EPA PAHs, whereas 76% for pyrene. Ecotoxicity test performed with bioluminescent bacteria Vibrio fischeri confirmed the effectiveness of landfarming. Finally, the results showed that indigenous microorganisms under certain and controlled operating conditions have greater potential for PAH biodegradation compared to allochthonous microorganisms.