Bioremediation of pah polluted soils: Column studies

Abstract

Background. Due to spills, discharges and leakage, the gaswork site at Husarviken in Stockholm is today the largest (36 ha) creosote-contaminated site in Sweden. The main pollutants are creosote, lead and mercury. The remediation costs are estimated to be as high as US $125 million. It is thus of great interest to find more cost effective remediation methods. Objectives. The aim of this study was to investigate i) if the addition of NTA, EDTA, nitrate, iron and dry yeast would enhance the bioremediation rate of a complex organic pollutant like PAH and, if so, at what concentrations they would be most efficient, ii) the effect on PAH reduction when larger dimensions of the column is used to diminish the effect of water passing along the sides of the column, iii) long-term effects on the reduction of PAH in field-contaminated soil with high concentrations. Creosote-contaminated soil from the Husarviken gaswork site was treated with aerated water in column experiments at room temperature. Three column experiments were performed in 2 and 100 L of homogenised soil samples percolated by recircula ting flushing water. Fluoranthene was analysed as a representative of the overall degradation of PAH in the columns. The PAH concentration (total 16 Priority USEPA PAH) was reduced from 129 mg/kg to at most 33 mg/kg in the 2-litre columns. A total of four PAH in the soil were reduced from 1330 mg/kg to about 400 mg/kg in the 100-litre columns. Generally, a 70% reduction of PAH concentration can be achieved by bioremediation technology. The transformation and/or degradation of fluoranthene were fast at the beginning of the experiment and then gradually slowed down. This mirrors the impact of the bioavailable fluoranthene, which is initially large, but reaches zero after 200 days. A simulation model using the fluoranthene data shows that the effectiveness of PAH degradation is, above all, dependent on the bioavailability of PAH. A reduction of 70% of PAH in the soil is applicable to soil containing <200 mg/kg to meet the Swedish recommendations of 60 mg/kg. At Husarviken, soil with <200 mg/kg corresponds to 80% of the polluted area.