Umberto Cova

Remediation of hydrocarbon contaminants in groundwater using specific zeolites in full-scale pump&treat and demonstrative Permeable barrier tests

Abstract A full-scale pump&treat (p&t) and a demonstrative Permeable Reactive Barrier (PRB) have been successfully working for two years in a gasoline station and for six months in a refinery, respectively. In both cases groundwater presented levels of methyl tertiary-butyl ether (MtBE), BTEX and C 6 −C 28 hydrocarbons to be removed. Different plant designs have been developed in the two sites. P&t at the gasoline station has been carried out with granulated activated carbon (GAC) followed by Mordenite. GAC remove all of hydrocarbons and part of MtBE, while Mordenite reduces MtBE concentration below 10 μ/L. Operative conditions were: 15 m 3 /h average flux with 2.5mg/L BTEX and 2 mg/L MtBE. The PRB at refinery is based on ZSM-5 followed byMordenite. The PRB has treated in the six months about 750 m3 of contaminated water. The outlet contaminant concentrations were constantly held below target limits, in spite of remarkable fluctuations of the inlet concentrations. The GROs (Gasoline Range Organics, C 6 -C 9 ), ranged between 1.3 and 10 μg/L and the DROs (Diesel Range Organics, C 10 -C 28 ) between 0.02 and 0.28 mg/L, while BTEX and MtBE were in therange 0.01–1.8 mg/L and 0.4–4 mg/L, respectively. ZSM-5 removed BTEX and most of MtBE and hydrocarbons, GROs (96% removal), DROs (41%). Mordenite adsorbed higher hydrocarbons escaped from ZSM-5 and maintained MtBE concentrations below the 10 μg/L target. The result obtained have evidenced the excellent efficacy of mordenite for MtBE (adsorption capacity (Q e ) of 24 mg/g) and of ZSM-5 for petrol hydrocarbons (Q e = 120 mg/g).