Comparison among the Efficiency of Different Bioremediation Technologies of Atrazine–Contaminated Soils

In a previous study by the authors, toxicity screening of Atrazine-resistant soil bacteria from different contaminated soils resulted in 23-soil isolate best grown in the presence of herbicide Atrazine. They were identified according to their 16S rDNA sequencing into Enterobacter (E. cloacae), Bacillus (B. cereus and B. anthracis), Pseudomonas (P. aeruginosa, P. balearica, P. indica and P. otitidis), Ochrobactrum (O. intermedium) and Providencia (P. vermicola). The 23 resistant isolates were enriched in nutrient broth medium amended with 2 folds the recommended dose (RD) of Atrazine. The enrichment technique resulted in the selection of seven bacterial species belong to 4 genera (Enterobacter, Pseudomonas, Bacillus and Providencia) that were superior in their resistance to Atrazine and exhibited remarkable growth stimulation (70.7-88.7%). These four acclimatized and highly Atrazine-resistant strains have been selected and efficiently used for the degradation of Atrazine-contaminated soil. They were employed in different proposed bioremediation technologies including biostimulation (addition of nutrients to enhance the growth and activity of the indigenous microorganisms), bioaugmentation (seeding the most promising indigenous and exogenous Atrazine degraders to accelerate and help the indigenous bacterial population to achieve high and fast remediation of the contaminated soil) and finally a combination of biostimulation and bioaugmentation technologies to investigate the synergistic or suppressive effects of the two techniques. Results proved that bioaugmentation coupled with biostimulation is the most promising bioremediation technology since it is powerful, economical and environmentally friendly technique for decontamination of Atrazine-contaminated soils.