Why wastewater sludge stimulates and accelerates removal of PAHs in polluted soils?

Wastewater sludge is used worldwide to dissipate hydrocarbon in PAHs-polluted soils. However, little is known about why wastewater sludge stimulates and accelerates the removal of polycyclic aromatic hydrocarbons (PAHs) from soils. Soil of the former lake Texcoco with pH 9 and electrical conductivity 7dSm^-1 was contaminated with phenanthrene and anthracene, and amended or not with wastewater sludge sterilized or not, and with or without polyacrylamide while phenanthrene and anthracene were monitored in an aerobic incubation experiment of 112 days. An agricultural soil from Acolman and wastewater sludge treated in the same way served as controls. After 112 days, the largest dissipation of anthracene and phenanthrene was found in the Acolman soil amended or not with wastewater sludge with or without polyacrylamide. The largest dissipation of anthracene and phenantrene from both soils was found in soils amended with wastewater sludge and polyacrylamide, while the lowest degradation of PAHs was detected in unamended PAHs-polluted sludge and in soils amended with sterilized wastewater sludge. It was found that polyacrylamide accelerated removal of PAHs from soils, while wastewater sludge increased the removal of PAHs from soils but the effect is controlled by the physical, chemical and microbial soil properties, the contaminant and microorganisms in wastewater sludge.