Application of hydroxypropyl[β]cyclodextrin to evaluation of polycyclic aromatic hydrocarbon losses during sewage sludges composting

Abstract

The aims of the present study were to test the application of the non-exhaustive extraction technique (NEET) with hydroxypropyl[β]cyclodextrin (HPCD) for the evaluation of the content of potentially bioavailable polycyclic aromatic hydrocarbon (PAH) fraction as well as the evaluation of changes in the content of this fraction during composting of municipal sewage sludges. A possibility to apply this method for the forecasting of PAH losses during composting was also studied. Four sludges (from different sewage treatment plants) with varied properties have been selected for the present experiment. The sludges were composted for 76 days. PAH content was determined as extracted with dichloromethane (exhaustive extraction technique) and potentially bioavailable PAH content by means of HPCD (non-exhaustive extraction technique) in both sewage sludges and composts obtained from them. The content of fraction extracted with HPCD ranged from 63.5 to 83.1% depending on the sludge. After composting, a significant lowering of this fraction contribution was noted for 3 sludges. However, in the composts obtained, the fraction extracted with HPCD still constituted 54.7–62.1% of the total PAH content. The composting process clearly influenced a decrease in the bioavailable fraction in the case of 3- and 5-ring PAHs. However, the 4-ring PAHs content of bioavailable fraction did not undergo any significant changes. No satisfactory results were obtained when HPCD was used as a tool to forecast PAH losses. In a number of cases only, PAH remaining after HPCD extraction achieved a value similar to that of PAH after the composting process. In the case of a number of PAH, the method with HPCD application changed the values of the bioavailable fraction.