Adsorption of six organic micro-pollutants from water and wastewater using Graphene Oxide-coated biochars

The objective of this study was to produce regular and Graphene Oxide (GO) coated biochar adsorbents, using two types of biomass as feedstock, i.e. Rice Husks (RH) and Sewage Sludge (SS), in two pyrolytic temperatures (400°C and 600°C). The produced adsorbents were thoroughly characterized in terms of physicochemical properties, where biochars produced from RH at 600°C showed the most favourable results. Specifically, the S_BET values of these samples were up to four times higher compared to biochars produced at 400°C and up to thirteen times higher, compared to the respective SS biochars. Moreover, the metal content of the samples was determined, in order to assess their safety, where all values were under the limits set by the European Union. Finally, biochars were tested as adsorbents for the removal of six organic micro-pollutants, i.e. 2,4-Dichlorophenol (2,4D), Bisphenol A (BPA), Androsterone (ADT), Norethindrone (NOR), Estrone (E1) and Ethinyl Estradiol (EE2), from table water and wastewater, in low (realistic) initial concentrations. The pollutants were successfully adsorbed by biochar, in rates of 40%-97.5% for the RH biochars and 10%-97.5% for the RH biochars, in 1h. GO-enriched RH biochars produced at 600°C were the most effective adsorbents, removing the pollutants in rates higher than 70%, in just 10min of adsorption time.