Remediation of Fine Fractions of Dredged Sediments by Flotation

Abstract

In the Netherlands, large quantities of contaminated dredged sludge have to be deposited or treated in the near future. Because of the large amounts of small particles involved, successful treatment is difficult. In this study a new flotation method on laboratory scale was used as an alternative remediation technique. Dissolved air was used to create small bubbles. Tests were performed with the finest fractions of sediments of Overschie (Rotterdam) and Petrol Harbor (Amsterdam) sludges contaminated with Polycyclic Aromatic Hydrocarbons (PAH). Several agents and conditions were tested with respect to the flotation efficiency. For Overschie sludge the best results were obtained without collector and SDS as frother. The PAH concentration in the Froth was up to 8 times higher than that in the non-floating fractions. The collected amount of dry matter in the froth was around 13%. With a two step flotation, the PAH concentration of the non-floating “clean” fraction was reduced from 240 mg (kg d m−1) to 99 mg (kg d m−1). For Petrol Harbor sludge the best results were obtained with the alcohol-based frothers Aerofroth and Montanol. The flotation was less selective than with Overschie sediment. Around 50% solids were collected in the froth and the PAH concentration in the Froth was around 2 times higher than in the Settled fraction and 3–5 times higher than in the fraction Remains.