Ballasted Flocculation for the Removal of Trace Petroleum Hydrocarbons from Surface Water

Oil spills are likely to occur in regions where oil pipelines are present in close proximity to surface waterbodies. Based on recent case studies, such a spill will introduce toxic and carcinogenic compounds such as benzene that would arrive at drinking water treatment plants (DWTP) at trace concentrations. If oil-spill dispersants are applied as a remediation measure, other dispersant-related compounds with unknown impacts on drinking water quality will also be introduced. Many DWTP in Quebec utilize surface water for potable water generation and employ a physicochemical treatment technology (Actiflo® or Pulsators®), which will serve as the first barrier against petroleum hydrocarbon contamination. This study evaluated ballasted flocculation (or Actiflo®) for its efficiency to remove trace petroleum hydrocarbons from surface water. First, the efficiency of ballasted flocculation for the removal of trace dissolved petroleum hydrocarbons (benzene, toluene, ethylbenzene, and xylenes (BTEX)) was investigated. Due to their relatively high BTEX content, diesel and gasoline were employed to simulate a spill in surface water. Stock solutions of the filtered and dissolved portions of diesel and gasoline were introduced in surface water and agitated for 24 hours. Laboratory ballasted flocculation tests were then carried out using alum and ferric sulfate as coagulants. For each test, water quality parameters – turbidity, dissolved organic carbon (DOC), UVA254, surface tension, zeta potential – and BTEX concentrations were monitored. Results showed that ballasted flocculation alone was not effective to reduce benzene concentrations below 0.5 μg/L (Quebec threshold in drinking water).

Résumé

Les déversements des produits pétroliers à proximité des eaux de surface représentent des enjeux vitaux. Une fuite ou un bris d'un oléoduc situé à proximité de ces eaux peut causer le déversement de divers composés toxiques et/ou cancérogènes tel que le benzène. Selon les études de cas récentes, ces composés arriveraient aux usines de traitement d'eau potable (UTEP) à des concentrations traces. Si les dispersants sont utilisés pour mitiger les effets des déversements, d'autres composés seront introduits dans les eaux de surface. Afin d'assurer la distribution d'une eau de bonne qualité, celle-ci subit un long processus de purification et de contrôle qualité. En effet, les UTEP rendent l'eau potable encore plus sécuritaire par l'implémentation des meilleures pratiques. La plupart des UTEP ont leurs prises d'eau brute dans les eaux de surface et elles utilisent un procédé physicochimique comme barrière principale contre une contamination par les hydrocarbures pétroliers. Ce projet a évalué l'efficacité de la floculation lestée (ou Actiflo®) pour l'abattement des concentrations traces d'hydrocarbures pétroliers.