In this study, four biochars prepared from different crop residue waste i.e. sugarcane bagasse (SBB), coconut shell (CNB), paddy straw (PDB), and distilled waste of lemongrass (LGB) were evaluated for removal of Remazol Brilliant Blue R from the aqueous system. The RBBR adsorption capacities of biochar were 97–79% for SBB, 99.9–99.47% for CNB, 66.1–48% for PDB, and 78–68% for LGB, dominantly controlled by their aromaticity and mineral content. The Langmuir and Freundlich isotherms and pseudo-second-order kinetic models have described the chemisorption of RBBR on biochar surfaces. The thermodynamic data suggested that adsorption was spontaneous and endothermic. These biochars demonstrated excellent reusability (till four cycles with 50–61% regeneration). The purified water and biochar dye sludge demonstrated no phytotoxicity. The findings obtained in this study may provide supports for the potential of biochars for anionic dye removal from water and utilization of generated sludge for zero waste-producing technologies in the future.

For the application of biochar in restoring pesticide-contaminated soils and minimizing the risk associated with their uptake in plants, it is crucial to understand the biochar impact on soil biological activities and dissipation and accumulation of pesticides in plant and soil systems. In this study, the effect of Mentha-distilled waste-derived biochar was investigated on chlorpyrifos and atrazine contaminated sandy loam soil. The four application rates of atrazine (2, 4, 6, and 8 mg kg⁻¹) and chlorpyrifos (2, 4, 6_, and 12 mg kg⁻¹) and a single application rate of biochar (4%) were used in this study. The degradation of pesticides, the diversity of the bacterial community, and enzymatic activities (alkaline phosphatase, dehydrogenase, arylsulfatase, phenol oxidase, urease activity and N-acetyl glucosaminidase) were examined in soil. The uptake of two pesticides and their effect on growth and stress parameters were also investigated in plants (A. paniculata). The dissipation of chlorpyrifos and atrazine followed simple first-order kinetics with a half-life of 6.6–74.6 and 21–145 days, respectively. The presence of deisopropyl atrazine desethyl atrazine (metabolites of atrazine) and 3,5,6-trichloro-2-pyridinol (a metabolite of chlorpyrifos) was observed in soil and plant tissues. Biochar application significantly (p = 0.001) enhanced the degradation rate of chlorpyrifos and atrazine leading to the lower half-life of chlorpyrifos and atrazine in soil. A significant reduction (p = 0.001) in the uptake of chlorpyrifos and atrazine and alteration in their binding affinity and uptake rate in plant tissues was observed in biochar treatments. The incorporation of biochar improved chlorpyrifos/atrazine degrader and plant growth-promoting bacterial genera such as Balneimonas, Kaistobacter, Rubrobacter, Ammoniphilus, and Bacillus. The upregulation of functional genes associated with nucleotide, energy, carbohydrate, amino acid metabolism, xenobiotic biodegradation, and metabolism: atrazine degradation was observed in biochar treatments. The biochar amendments significantly (p = 0.001) reduced the plant’s uptake velocity (Vmax) and affinity (Km) of chlorpyrifos and atrazine. These results delineated that Mentha-distilled waste-derived biochar can potentially remediate chlorpyrifos and atrazine contaminated soils and ensure the safety of plants for consumption. Graphical Abstract