Bioremediation of a Light NAPL (Toluene) Contaminated Soil under Different Environmental Conditions

Abstract

LNAPLs are a common contaminant in the environment. When a LNAPL infiltrates the soil, it leaves behind a trail of immobile ganglia in the pore spaces. When the groundwater table is reached, the LNAPL forms a film on top of the groundwater, where it generally migrates laterally, subjected to the groundwater flow. LNAPLs are toxic to humans by ingestion, adsorption through skin and inhalation. The combination of mobility and toxicity classify the contamination as a high risk. However, soil microorganisms are able to remediate LNAPLs. The rate of this remediation depends on several factors like temperature, soil moisture content, initial concentration and soil type. The objective of this study was to investigate the impacts of the environmental factors on the rate of bioremediation of a LNAPL. The BTEX component toluene was used as a representative for this group of contaminants. Numerous batch experiments were performed under controlled conditions to reach these objectives. The batches contained soil, groundwater spiked with toluene stock and sufficient headspace to prevent oxygen deficiency. The biodegradation rate of toluene increased with increasing temperature up to 21° C. No significant increase in biodegradation rate was observed at 30° C. The biodegradation rate also increased with increasing moisture content, when sufficient headspace was present. As for the dependence on initial toluene concentration, the initial biodegradation rate increased with increasing toluene concentration reaching its optimum around 100 mg/L. The soil type comparison showed that the biodegradation rate of toluene was high in a soil containing organic matter compared to clean sand.