Bioremediation of PAH-Contaminated Soil via In-Vessel Composting

This study is being conducted to investigate the biodegradation of polycyclic aromatic hydrocarbons (PAHs) present in contaminated soil using composting technology. Pyrene, a four-ring aromatic hydrocarbon, was chosen as a model PAH compound for the study. Preliminary investigations were carried out to assess the feasibility of soil composting by monitoring (a) carbon to nitrogen (C/N) ratio, (b) microbial consortia diversity, (c) coefficient of permeability and (d) moisture content. The soil was augmented with composted sludge, which was used as a bulking agent and nutrient supplement, in quantities ranging from 0-50% dry weight basis. Tests were conducted in both batch and continuous composters. In the batch composter, forty grams of soil/sludge mixtures in different proportions were spiked with 13.5 mg/kg (dry weight basis) of unlabeled pyrene. The batch composters were aerated and placed in a constant temperature water bath for a period of 21 days. Samples were soxhelet extracted and analyzed on the High Performance Liquid Chromatograph to determine the reduction in pyrene concentration. Analysis of these samples is in progress. In the continuous composter, the soil/sludge mixtures are spiked with both labeled and un-labclcd pyrene to obtain a total radioactivity of 13.5 µci. This process is being monitored for temperature, moisture content, volatile solids and microbial population. Mineralization of pyrene is assessed by quantifying ¹⁴CO₂ produced.