Fates of pahs in sewage sludge under aerobic and anaerobic conditions

The objective of that researches was to follow the changes of the PAH content in the sludge under anaerobic (fermentation process) and aerobic conditions. Samples of raw, digested as well as dewatered sewage sludge taken from municipal treatment plant were used in this study. In serie I- the fermentation process was carried out in closed bioreactors for 22 days. 16 PAHs according to US-EPA list were analysed both in solid phase and supernatants over 0, 13 and 22 days. Serie 11 - the representative sludge sample was divided into four parts. Two samples were sterilised to obtain abiotic conditions. Then one of them was supported with a standard mixture of 16 PAHs'. Moreover the standard mixture was also added to one of those not sterilised ones. Samples without sterilization and without standard mixture were treated as a control ones. Afterwards the sludges were incubated within 45 days in laboratory conditions at 20 degrees C in the darkness and with not limited oxygen access. Extraction process for samples with methanol, cyclohexane and dichloromethane mixture as solvents was carried in ultrasonic bath. Extracts were then purified using SPE columns packed with silica gel. Qualitative and quantitative analysis was done using gas chromatography with mass spectrometry detector. PAHs recoveries were also determined in order to evaluate extraction method efficiency. The total PAHs concentration in sewage sludge samples before digestion was 1308 mu g/kg (dm) and in the supernatants - 5 mu g/L, respectively. Concentration of PAHs' in sludge samples and in supernatants samples taken from bioreactor during fermentation process (after 13 days) was higher. The results of this experiment confirm the hypothesis that PAHs' might have been released from organic matter during the hydrolysis of complex organic compounds. These compounds that concentration increased less than 2 times could have been degradable during digestion, as 2-times decreased of dry matter of sludge was observed during the digestion process. PAHs' concentration in samples supported with the standard mixture in abiotic and biotic samples was 95 048 mu g/kg (dm) and 106 001 mu g/kg (dm), respectively. In control sample 16 PAHs' concentration reached 1 798 mu g/kg (dm). The total PAHs' concentration was lower after 45 days. The insignificant difference in PAHs decrease results in small participation of biological processes in PAHs' degradation. During sludge storage under laboratory conditions PAHs' diminish was over 5-times lower in control samples than in sludge supported with the standard mixture.