Dissipation of phenanthrene and anthracene from soil with increasing salt content amended with wastewater sludge

The removal of PAHs was stimulated by wastewater sludge in an alkaline saline soil of the former Lake Texcoco, but not always to the same extent. We investigated how a varying electrolytic conductivity (EC) affected the removal of phenanthrene (PHEN) and anthracene (ANTHR) from wastewater sludge-amended soils. Soil with EC 6, 30, 80, and 146 dS m^-1 was contaminated with PHEN and ANTHR and amended with or without wastewater sludge, while emissions of CO₂ and concentrations of ammonium, nitrite, and nitrate were monitored. A decrement on the concentrations of PHEN and ANTHR was observed and was faster in soil with EC 6 dS m^-1 than in soil with EC 30 dS m^-1 and 80 dS m^-1, and was slower than in soil with EC 146 dS m^-1. Adding wastewater sludge to soil reduced the concentration of PHEN and ANTHR in soil after 56 days. Spiking soil with PAHs or amending it with wastewater sludge increased the CO₂ emission rate, but decreased at higher EC. The concentration of NO₃ - decreased when soil was spiked with PAHs and amended with sludge, except in soil with EC 146 dS m^-1. It was found that the removal of PAHs was not inhibited by salt content and a principal component analysis indicated that none of the measured soil characteristics, i.e., pH, EC, particle size distribution, water-holding capacity, or organic C content predicted the removal of ANTHR or PHEN from contaminated soil. The application of wastewater sludge increased the dissipation of PHEN and ANTHR after 56 days.