Suitability of low cost pristine and iron modified biochars for removal of arsenic in drinking water [MSc thesis]

Arsenic contamination of drinking water is a major problem in the world. Arsenic has been identified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). According the World Health Organization guidelines, the maximum permissible arsenic level in drinking water is 10 μg/L. To maintain this very low limit of arsenic in drinking water, adsorption is one of the least expensive methods for arsenic removal. Biochar is one of the promising low cost adsorbents for treating polluted water. Therefore, this study aimed at investigating the effect of iron modification and pyrolysis temperatures on arsenic removal efficiency. Pristine and iron modified Cocoa shell biochars produced at 650 ℃ (COSH-650 and COSH-Fe-650) and two Miscanthus biochars produced at 400 ℃ and 650 ℃ (MISC-400 and MISC-650) were investigated. The effect of the iron modification, pyrolysis temperatures, adsorbent dosage, and adsorption kinetics on arsenic adsorption efficiency was evaluated by screening batch experiments. The ash content of the biochars under investigation ranges from 9.6% to 30.3%. BET surface area showed that they have good surface properties as an adsorbent and MISC-400 (928±174 m2/g) has the largest surface area. Further, it was observed that the zeta potentials of all biochars were negative with average value of -18.1 mV and unfavourable for anion adsorption. Furthermore, phosphate leaching from the Cocoa shell based biochars was observed. Generally, all biochars were ineffective in removing arsenic from water (< 30% removal efficiency). However, COSH-Fe-650 showed comparable removal efficiency to other biochar studies. (i.e. removal efficiencies of As(III) and As(V) were 24.2% and 22.9%, respectively). The effect of pyrolysis temperature on Miscanthus biochar showed that low pyrolysis temperature biochar was better arsenic removal than high pyrolysis temperature biochar. Washing of biochars strongly improved As(V) and As(III) removal efficiency of pristine Cocoa shell biochar, while this washing procedure did not effective for iron modified Cocoa shell biochar and two Miscanthus biochars. Furthermore, COSH-Fe-650 biochar was selected as the promising adsorbent for arsenic removal and the experimental results of COSH-Fe-650 fitted well with the pseudo-second-order and the Elovich kinetic models. This revealed that the main adsorption process associated with As (III) adsorption appeared to be chemisorption