A review on valorization of biomass in heavy metal removal from wastewater

This review summarizes the progress made, in the field of low-cost biosorption of heavy metal ions, over the past few years. It gives a comprehensive summary of the synthesis, performance, modification and regeneration of biosorbent. The review also focused upon optimum operating parameters, isotherm and kinetic studies. Moreover, from an industrial application point of view, fixed-bed column studies have been discussed in this paper. Methods like chemical pretreatment, grafting, immobilization, etc., which improve the biosorbent properties, have been summarized. Operating parameters that affect the biosorption process such as temperature, pH, contact time, agitation speed, etc. have been studied to understand the relationship between factors and removal efficiency. For most of the studies, biosorption process was found to be endothermic, with room temperature being optimum for the process. Grafting was observed to enhance the adsorption capacity of biosorbent enormously. Biosorption process generally followed Langmuir or Freundlich isotherm, whereas mostly the best fit for kinetic model was pseudo-second-order. Desorption process was mostly carried out via acidic eluent. The performance of biosorbents was observed to be appreciable when they were packed into fixed-bed columns.