Peat moss-derived biochars as effective sorbents for VOCs' removal in groundwater

Peat moss-derived biochars were produced at the pyrolytic temperatures of 300, 500, and 700 °C and were tested for evaluating the removal efficiency of volatile organic compounds (VOCs) from waters. As the pyrolytic temperature increases, the carbon contents were increased from 66 to 84%, and the contents of hydrogen and oxygen were decreased from 4 to 1% and from 19 to 4%, respectively. The surface areas of the biochars were 2 m² g^-1 at the pyrolysis temperature of 300 °C and were increased to 200 and 300 m² g^-1 at 500 and 700 °C, respectively. Results of FTIR analysis showed that functional groups such as hydroxyl, nitro, and carboxyl groups were observed in the biochar produced at 300 °C; however, the functional groups were removed in the biochars produced at higher temperatures. Sorption kinetics and equilibrium experiments were conducted with selected six VOCs of benzene (BZN), toluene (TOL), ethylbenzene (EBZ), p-xylene (pXYL), trichloroethylene (TCE), and tetrachloroethylene (PCE), which are the most common VOCs found in contaminated groundwater of South Korea. Sorption equilibrium was attained in 6 h with the constants of first order kinetic rate of 0.5 h^-1 for the VOCs tested. Freundlich isotherm well described the adsorption of VOCs to the biochars. Biochar produced at 500 °C showed the highest sorption capacity for all VOCs with an average K_f of 7692 (±2265), although biochars produced at 300 °C (K_f = 3146 ± 629) and 700 °C (K_f = 2776 ± 2693) showed the similar sorption capacity. The biochars produced at 500 °C can be an excellent remover of VOCs in contaminated groundwater.