Bioremediation of two persistent pesticides in biomixtures: Role of pre-exposed soils, biochar and bioaugmentation

Composition and properties of biomixture are crucial for the success of the bio-purification system. The present study evaluated the effect of pre-exposed soil, wheat straw biochar (WBC), and bio-augmentation on glyphosate and tricyclazole degradation in a rice straw-compost biomixture. Degradation of both pesticides followed first order kinetics. Glyphosate pre-exposed soil with recent history of application significantly enhanced herbicide's and metabolite aminomethylphosphonic acid (AMPA) degradation in biomixture, while no effect of tricyclazole pre-exposed soil was observed on fungicide's degradation. Effect of WBC varied with the nature of pesticide and its dose. Compared to the control, WBC (1 %) enhanced glyphosate and AMPA degradation and decreased half-life (t_1/2) of glyphosate (4–12 %) and glyphosate + AMPA (22–25 %). However, WBC (5 %) increased t_1/2 by 17–20 % (glyphosate) and 14–75 % (glyphosate + AMPA). Both, 1 and 5 % WBC enhanced tricyclazole degradation in biomixture and compared to control t_1/2 values decreased by 8 and 44 %, respectively. Compared to control, augmentation of glyphosate degrading Bacillus piscis significantly enhanced glyphosate/AMPA degradation and t_1/2 were reduced by 45–48 % (glyphosate) and 43–52 % (glyphosate + AMPA). However, white rot fungi Phanerochaete chrysosporium failed to enhance glyphosate and tricyclazole degradation. Pre-exposed soil, WBC and bio-augmentation increased microbial biomass carbon (MBC), dehydrogenase and fluorescein diacetate activities in glyphosate treated biomixtures, while WBC increased MBC and dehydrogenase activity in tricyclazole treated biomixtures. This study suggested that pre-exposed soil, biochar, and bio-augmentation can be used/utilised for better glyphosate and tricyclazole degradation potential of bio-purification systems.