Physicochemical Behaviour of Polynuclear Aromatic Hydrocarbons in Primary Sedimentation. I. Batch Studies

Abstract

In this, the first part of a combined laboratory/pilot plant study into the behaviour of Polynuclear Aromatic Hydrocarbons (PAH) during waste water treatment, laboratory experiments were conducted to investigate the effect of primary sedimentation on PAH removal from raw sewage. Losses of 14 PAHs due to settlability, volatilisation and photodegradation were quantified. PAH particle size distributions in sewage are also reported. Sedimentation resulted in PAH removal rates from raw sewage ranging from 35% for acenaphthylene to 86% for benz(a)anthracene. Removal rates increased with increasing molecular weight and the association of a PAH with sewage particulate matter was found to correlate with the compound's log Kow value. Association of PAH with sewage particulate matter was greatest for the smallest particle size fraction (0.45 to 53 µm). PAH associated with the dissolved/colloidal phase in raw sewage (the size fraction <0.45 µm) were enriched in the compounds with the lowest molecular weight. The removal of PAH from raw sewage by volatilisation or photodegradation over the comparitively rapid process of primary sedimentation is minimal compared to sedimentation.