Biochar derived from pyrolysis of rice straw as an adsorbent for removal of phenol from water

In the present study, rice straw, an agri-residue, was chemically treated and pyrolysed to produce an efficient adsorbent for removal of phenol from water. The response surface optimization study for removal of phenol from water using biochar was carried out to determine the individual/interactive effects of adsorption parameters and a quadratic equation was obtained. The maximum phenol removal efficiency of 96 % (initial phenol concentration: 100 mg/L) was obtained at an adsorbent dosage of 1.25 g/L in 60 min. The adsorption isotherm and kinetics were best fitted using Langmuir isotherm and pseudo second order kinetic model representing that monolayer chemisorption dominated the adsorption process. The maximum adsorption capacity of biochar was found to be 107.466 mg/g. The adsorption thermodynamics represented an exothermic and spontaneous adsorption process. The fixed bed column studies for removal of phenol from water were also carried out and the column kinetic data was best fitted using Thomas model. The regeneration of adsorbent was studied, and it was found suitable for 8 adsorption cycles. The H - bonding and n - n interaction between phenol molecules and adsorbent surface were the main adsorption mechanism. Further, the batch and column adsorption studies for removal of phenol from industrial wastewater were carried out and the phenol removal efficiency of 97 % was obtained. The estimated cost of treatment was determined and found to be $1.885/m3 of water. The present study, apart from providing an effective, cost-efficient adsorbent for removal of phenol, suggests a sustainable way of managing rice straw.