Bioremediation of a PAH-contaminated gasworks site with the Ebiox vacuum heap system

A former gasworks site in the industrial city of Winterthur, Switzerland, was extremely contaminated with polycyclic aromatic hydrocarbons (PAHs); benzene, toluene, ethylbenzene, and xylenes (BTEX); phenols; ammonia; and mineral oils. Three vacuum heaps, with a total volume of 10,500 m{sup 3} of contaminated soil, were bioremediated during 1993/94. Separating excavated soil material into different soil qualities was of particular importance because of the pathway definition of the specific soil material. Excavation of contamination took longer than 10 months, delivering continuously different contaminated soil-type material for bioremediation. Conditioning and subsequent biostimulation of the large soil volumes were the prerequisites for most advanced milieu optimization. The degradation results demonstrated the potential for successful application of bioremediation on former industrial sites. PAH-concentration reductions ranged from 75 to 83% for the soil values and from 87 to 98% for the elution values. Soil and elution target qualities were met within 6 to 12 months, depending on initial PAH-concentration and soil structure. The achieved target quality for the bioremediated soil allowed subsequent reuse as high-value backfill material for the ongoing building project.