Adsorptive removal of dye using biochar derived from residual algae after in-situ transesterification: Alternate use of waste of biodiesel industry

The primary aim of this present study was to utilize the residual biomass (DB) of Spirulina platensis algae, left after in-situ transesterification, for biochar preparation. This is a solid waste residue of biodiesel industry. The biochar (BC) prepared was examined for its capacity to adsorb congo red dye from the aqueous solution. The results were compared with other adsorbents used in the study such as commercial activated carbon (AC), original algae biomass (AB) and DB. The results of proximate analysis of BC showed the decrease in the percentage of volatile matter and an increase in fixed carbon content compared to DB. The physico-chemical properties of BC were studied using elemental analysis, SEM, FTIR and XRD techniques. The AC and BC adsorbents showed better performance in removing 85.4% and 82.6% of dye respectively from solution compared to AB (76.6%) and DB (78.1%). The effect of initial dye concentration, adsorbent dosage and pH of solution on the adsorption phenomena was studied by conducting the batch adsorption experiments. The highest specific uptake for biochar was observed at acidic pH of 2 with 0.2 g/100 ml of adsorbent dosage and 90 mg/l of initial concentration. The equilibrium adsorption data were fitted to three isotherms, namely Langmuir, Freundlich and Temkin. Freundlich model proved to show the best suited results with value of correlation coefficient of 99.12%. Thus, the application of DB for production of biochar as potential adsorbent supports sustainability of algae biodiesel. •Promising approach of utilizing residual algae biomass for biochar preparation.•Adsorption properties of biochar comparable to commercial activated carbon.•High adsorption capacity of biochar effectively treats dye contaminated wastewater.