Applications of biochar in sulfate radical-based advanced oxidation processes for the removal of pharmaceuticals and personal care products

Recently, biochar (BC) has been increasingly used as a catalyst for the degradation of 'emerging pollutants' (EPs). Pharmaceuticals and personal care products (PPCPs), which come under 'EPs', are documented as major pollutants and can cause acute toxicity problems in aquatic ecosystems despite being present in very low concentrations (ng/L-mu g/L). Advanced oxidation processes (AOPs), which produce sulfate radical (SR-AOPs), show a great potential to degrade PPCPs effectively from wastewater. It is mainly due to the higher stability, long half-lives and better non-selectivity of SO4 center dot- compared with AOPs with center dot OH generation. Furthermore, research focus is now given on AOPs coupled with BC-supported catalyst to enhance the degradation of PPCPs due to the quicker generation of radicals (center dot OH, SO4 center dot-) by the activation of persulfate (PS) and peroxymonosulfate (PMS). This article gives a literature review on the catalytic ability of BC after its physical and chemical modifications such as acid/alkali treatment and metal doping. The role of persistent free radicals (PFRs) in the BC for effective removal of PPCPs has been elaborated. Its potential applications in synthetic as well as real wastewater systems have also been discussed.