Influence of Chromium Ions on Effectiveness Degradation of Low-molecule PAHs in Sewage Sludges

The aim of the study was to determine the chromium ions influence on removal efficiency of selected polycyclic aromatic hydrocarbons (PAHs) from sewage sludges under aerobic conditions. The studies were carried out using dewatered and biochemically stabilized sewage sludges taken from a small municipal wastewater treatment plant (WWTP). The changes in the concentration of PAHs were conducted in three series: in sludge samples taken after filter press (biotic samples-control samples), in sewage sludge samples amended with added chromium ions and in sewage sludge samples with added sodium azide (abiotic samples). The chromium ions were added into the sludges samples as a solution of chromium(III) chloride. The sewage sludge samples were incubated for 90 days. Determination of PAHs in sewage sludge samples was made at the beginning of the experiment (the initial concentration) and then six times over 15 days. The gas chromatography-mass spectrometry (GC-MS) was used to qualify and quantify PAHs. Six PAHs (2-ring and 3-ring of hydrocarbons) listed by EPA were analysed: naphthalene Naph, acenaphtylene Acyl, acenaphtene Ac, fluorene Flu, phenanthrene Phen, anthracene Antr. In sewage sludges taken from a municipal treatment plant the average PAHs concentration were in the range of 242÷296 μg/kg d.m. The effectiveness of naphthalene was 79 and 81% in the control samples and 78 and 65% in samples amended with chromium chloride carried out in two series, respectively. In abiotic samples the effectiveness removal of naphtalene was 24 and 62% in series, respectively. The average effectiveness of 3-ring PAHs removal ranged 73% in control sewage sludge samples and 56% in sewage sludge amended with chromium(III) chloride, respectively. The effectiveness of removal hydrocarbons in sewage sludge amended with sodium azide (abiotic samples) was 41.5% on average.