Control of PAHs degradation process under reducing conditions

The paper presents the results of the study that determined the changes in the concentration of selected polycyclic aromatic hydrocarbons (PAHs) in the sewage sludge during the incubation of sewage sludge under reduction conditions (anaerobic conditions). The sewage sludge was incubated for 16 d at 37°C ± 1°C in the dark. The value of oxidative and reduction potential ranged from –300 to –400 mV. The studies were conducted using sludge differing in their initial PAH content. PAHs were determined in the beginning of process and after 4, 6, 12, and 16 incubation days. The quantification of the three-ring PAHs (acenaphthylene, acenaphthene, fluorene, phenanthrene, and anthracene) was carried out simultaneously in the sewage sludge (solid phase [SP]) and supernatants (liquid phase [LP]). Control of the course of changes in PAH concentrations indicates fluctuations in concentration of these compounds in sludge and supernatant liquids under reduction conditions. The efficiency of three-ring PAH decomposition in sewage sludge was in the range from 33% to 75% and was not correlated with the initial concentration of these compounds. The mass balance of PAHs in SP and super-natant liquids confirms biodegradability of these compounds: their mass loss was within the limits of 13 and 21 μg for 1 L of hydrated sludge incubated for 16 d under reducing conditions. The half-life of PAH decomposition in sewage sludge ranged from 3 to 65 d and in supernatant liquids from 3 to 26 d.