Improvement of biochar capability in Cr immobilization via modification with chitosan and hematite and inoculation with Pseudomonas putida

Modification of biochar using chitosan and hematite made the biochar product more effective for hexavalent chromium (Cr (VI)) reduction in contaminated soils. Release experiment was conducted to examine Cr (VI) reduction in different treatments (control, unmodified biochar and two modified biochars with chitosan or hematite). The results indicated that the application of all treatments significantly decreased the release rate of Cr in comparison to the control treatment. Chitosan-modified biochar application increased Cr (VI) reduction from 28.53% (biochar) to 46.23%. In the case of hematite-modified biochar, it increased Cr (VI) reduction from 28.55% (biochar) to 38.95%. Two kinetic equations including pseudo-first-order and pseudo-second-order models employed to describe the time-dependent Cr release data. Between the kinetic equations estimated, the pseudo-second order best fitted to experimental data. In the presence of Pseudomonas putida, cumulative Cr release rate decreased by 2.38 mg kg(-1) (50.29%) in hematite-biochar and 1.768 mg kg(-1) (39.73%) in unmodified biochar as compared with control (4.43 mg kg(-1)). According to results reported herein, modification of biochar with chitosan or hematite is promising since made biochar more effective in removing Cr from Cr-polluted calcareous soils.