Strategies for Bioremediation of Soil from an Industrial Site Exposed to Chlorinated and Nitroaromatic Compounds

As technological advances allow the development of new products, the number of synthetic chemical compounds released into the soil, surface water and groundwater increases, posing a threat to the environment. Therefore, treatability studies to improve bioremediation strategies (biostimulation and bioaugmentation) were applied to samples of soil containing nitro and chlorinated aromatic compounds from a former chemical manufacturing site in Brazil. Native microorganisms were stimulated to degrade compounds including dichloroanilines, dichloronitrobenzenes, 2-chloronitrobenzene, and 1,2-chlorobenzene, through oxygen exposure and pH (6.0-8.4) and moisture content (13-23%) adjustments. For the inoculation of soil samples, a culture enriched from site groundwater was developed. The aeration alone stimulated the indigenous microbes to degrade some of the compounds. However, reinoculation with an enriched culture and moisture content adjustment increased the attenuation rates by 3.6 and 1.4 times, respectively. The pH values in the range of 7.6 and 8.4 seem not to harm microbes' activity and moisture content higher than 16% is recommended to enhance biodegradation. Based on the findings, it is likely that natural attenuation is happening in aerobic zones at the site. Results indicate both bioremediation strategies (biostimulation and bioaugmentation through reinoculation with enriched culture mainly composed of organisms from the Diaphorobacter genus) are promising strategies to enhance bioremediation. However, considering the applicability of the strategies on a field scale, further experiments will broaden the understanding of biodegradability of compounds, such as their inhibitory effects when in higher concentration (>150 mg/kg), individually or combined.