Mechanistic approach for removal of cyanide and phenol from coke- oven wastewater by green nano zero-valent iron mediated adsorption-biodegradation treatment system

Abstract

Abstract Cyanide and phenol represents the most hazardous combination of wastewater due to their synergistic toxicity. The present study investigated the efficacy of a hybrid treatment based on green nanoscale zero-valent iron (nZVI) mediated adsorption followed by biodegradation for removal of cyanide and phenol from synthetic coke-oven wastewater. The nZVI particles were characterized using FESEM, EDX, DLS, XRD and FTIR. Response surface methodology based optimization showed 99.88% removal of cyanide (50mg/L), thereby facilitating subsequent biodegradation of phenol. Adsorption process was found to follow Langmuir isotherm model (maximum adsorption capacity = 178.8mg/g) and pseudo-second order kinetic model, suggesting cyanide adsorption is controlled by chemical ion exchange mechanism. Furthermore, biodegradation of the residual phenol was attempted by isolated bacterial strain (Pseudomonas BSPS_PHE2) that was found to be capable of 98.98% removal of phenol (1000mg/L). The metabolic pathway of phenol biodegradation was elucidated from GC-MS analysis. This study has for the first time presented a green technology based adsorbent for cyanide removal that not only provides high adsorption capacity, but also improves the biodegradability of recalcitrant coke-oven wastewater.