The Influence of Sewage and Sludge Treatment Processes on Polycyclic Aromatic Hydrocarbons Content Changes

The analysis of PAH’s concentration changes in samples of sewage inflowing to urban sewage-treatment plant in Cz stochowa, in sewage after each stage of purification, and in samples of sludge obtained in each (unit process) sewage treatment processes. Average total concentration of analysed PAHs was 5.285 μg/dm in crude sewage, 89.082 μg/dm in sewage after sand trap, 48.252 μg/dm in sewage after primary settling tank, 7.801 μg/dm in sewage after a secondary settling tank, and also 4260,32 μg/dm of d.s.m. in crude sludge, 12853,7 μg/dm of d.s.m. in sludge after SSDC, 6151,6 μg/dm of d.s.m. in sludge after OSDC, and 259,43 μg/dm of d.s.m. in dewatering sludge (only pyrene). Biological sewage treatment with secondary sedimentation decreased PAHs concentration by 83%. It is caused probably by absorption of these compounds on particulates and their decomposition by microorganisms of activated sludge. Highest average total concentration of PAHs was found in digested sludge, which may be caused by biotransformation of organic compounds by microorganisms.After stabilization and filtration of sludge the PAHs content decreased by ca 50% and 95%, which may be caused by volatilizing, oxidation, and photooxidation processes of these compounds or theirs desorption to water over sludge. It can confirmed indirectly the enhanced amount of PAHs in sewage after a sand trap