Occurrence and mass balance of polycyclic aromatic hydrocarbons in the Thessaloniki sewage treatment plant

The occurrence and the mass balance of the 16 EPA. polycyclic aromatic hydr ocarbons (PAHs) were investigated in a conventional activated sludge treatm ent plant. Polycyclic aromatic hydrocarbon concentrations were determined i n wastewater and sludge samples from different treatment stages. The concen trations of PAHs in raw sewage were statistically analyzed to examine wheth er temporal factors (sampling period, day and hour of sampling) had a signi ficant effect on the observed variance. Sampling period was the only factor that showed a significant impart. Principal component analysis (PCA) was u sed to assess similarities of the wastewater PAH pattern with possible sour ce matrices (domestic effluents, urban runoff, and atmospheric particulates ). The composition of wastewaters was found to be particularly similar to t hat of domestic effluents. Mass balances of PAHs were calculated for indivi dual stages of wastewater treatment (primary treatment, secondary treatment , and chlorination), as well as for the whole treatment process. Relatively good mass balances were calculated in the primary clarifier for most PAHs. Lower molecu lar weight PAHs (Np, Ace, Ph, An, and Fl) showed substantial losses (>40%), in the secondary treatment probably due to biodegradation an d volatilization. Good closures for all PAHs were found in the chlorination stage. Total mass balances indicated that only the lower PAHs are effectiv ely removed, whereas the heavier compounds are rather resistant to the trea tment process. Sorption was found to be the dominating removal process of P AHs-especially of the heavier ones-during primary treatment, while their re moval during the secondary treatment is also governed by other processes, s uch as biodegradation and/or volatilization.