Sustainable biochar adsorbents for dye removal from water: present state of art and future directions

The wastewater generated from the industrial activities are considered as one of the prime sources of water contamination. The yearly production of synthetic dyes are ~ 700 tons worldwide. Synthetic dyes have detrimental effects on the human as well as animal health. Therefore, there is an urgent need to treat the water containing synthetic dyes. Dye treatment methods can be divided in to three categories namely; chemical, physical, and biological. The chemical procedure includes; photocatalytic degradation, ozonation, fenton reagent, and aerobic and anaerobic degradation are the examples of the biological procedures. However, the physical procedures consists of filtration/coagulation, adsorption, ion exchange etc. Further, these techniques may have its own drawbacks including generation of hazardous sludge and expensive to operate along with high maintenance cost. The most appealing techinque for abatement of dye from the contaminated water is adsorption owing to its ecofriendly, flexibility, affordability, sustainability, and abundant availability of raw materials to produce adsorbents. It has been noticed that over 80% of dye adsorption processes on adsorbent surfaces were endothermic in nature which means the adsorption processes were self-sustaining in terms of energy consumption. In present review paper, the discussion has been focused on the removal of anionic dyes from water using low-cost biochar adsorbents which is not reported in any previous review papers. Further, it will significantly help to the budding researchers to develop continuous water treatment system (in column mode), if wish to work of anionic dyes remediation from water.