Zeolites in a permeable reactive barrier (PRB): One year of field experience in a refinery groundwater—Part 1: The performances

This paper describes the performances of zeolites utilized for one year as adsorbents in a permeable reactive barrier (PRB) located under a coastal refinery. The average organic contamination was 5 mg/L of total petroleum hydrocarbons, whose toxic constituents are aromatic (BTEX) and polynuclear aromatic hydrocarbons (PAHs), and 5 mg/L of MTBE, specific gasoline additive, while the average concentrations of more representative inorganic ions were: Na+, 8537 mg/L; Cl−, 10,700 mg/L. The target of the entire process was: Σ hydrocarbons, 350 μg/L; MTBE, 10 μg/L; and BTEX, 1, 15, 50 and 10 μg/L, respectively. Two working tests of six months each were performed. In the first phase two zeolite filters, constituted by ZSM-5 (120 kg) and mordenite (150 kg), were used to treat water with a flow (Q) kept fixed at 4 m3/d. In the second phase next each filter a new one of same material has been added to have a total of four filters, two of ZSM-5 (120 kg each) followed by two of mordenite (150 kg each), while the flow was doubled. In both tests the concentration of the organic contaminants in the outlet water remained constantly under the limits. Between the two phases, the test was interrupted for six months for removing by backwashing the inorganic and biological deposits formed on the filters. The performances of zeolites were evaluated on the basis of the composition of both water sampled at the outlet of zeolite filters (by gas-chromatographic analysis, GC–MS) and contaminants adsorbed in the zeolite channels (by thermogravimetric analysis, TGA and GC–MS).

Figure optionsDownload as PowerPoint slideHighlights
► Zeolites were tested as adsorbents in a field permeable reactive barrier (PRB).
► The field test showed that zeolites can treat refinery's groundwater.
► The level of MTBE, benzene and BTEX contaminants were examined.
► PRB maintained the contaminant concentration consistently below the target levels.