Natural attenuation, biostimulation and bioaugmentation in 4-chloroaniline contaminated soil

Abstract

4-Chloroaniline has been widely used in various industries. It is also the main intermediate accumulated in the environment as a result of microbial degradation of phenylurea herbicides. Due to its toxicity and persistence in the environment, a remediation technology to reduce and clean up 4-chloroaniline is necessary. Bioremediation which is a natural, safe and complete degradation process is a useful technique to clean up 4-chloroaniline. The objective of this study was to evaluate the best bioremediation technique for 4-chloroaniline treatment. Bioremediation consisting of natural attenuation, biostimulation and bioaugmentation (with bacterial pure culture and bacterial consortium) were carried out to degraded 500 ppm 4-chloroaniline in two soil types; loam soil and sandy clay loam soil. The greatest 4-chloroaniline degradation was observed with biougmentation with bacterial consortium (96%) after 28 days of incubation at room temperature in loam soil. The biostimulation (addition of 1 mM aniline) and bioaugmentation with pure bacterial culture showed 87% and 84% of 4-chloraniline degradation, respectively, while natural attenuation showed 67% of degradation. For sandy clay loam soil, there was no significant difference of 4-chloroaniline degradation in each treatment. The highest percent of 4-chloroaniline degradation was only 58% after 2 months of the incubation. Sandy clay loam soil was acidic soil therefore pH was a factor that should be considered. When pH of sandy clay loam soil was adjusted to neutral pH, bioaugmenttion with bacterial consortium showed the greatest 4-chloroaniline degradation (95%) after two months of incubation. The biostimulation and bioaugmentation with pure bacterial culture showed 63% and 64% of 4-chloroaniline degradation, respectively, while natural attenuation showed 29% of degradation. The increasing total microbial activity was detected with bioaugmentation in loam soil while it could not be detected in sandy clay loam soil. The bacterial community shift during each treatment was monitored using the denaturing gradient gel electrophoresis (DGGE). The result showed that the bacterial community in biostimulation and bioaugmentation was changed and some bacteria become dominant when the 4-chloroaniline was utilized.