Enhancing removal of contaminants by organic waste-derived chars via steam activation and salt treatment.

This study aims to investigate the effects of salt treatment and steam activation on chars derived from biomass wastes (manure, food, and kenaf) and spent tires. Batch sorption experiments were used to evaluate the absorption performance of these chars for benzene, phenol, trichloroethylene (TCE), and arsenate. Steam activation of biochars at 900°C increased their specific surface area, enhancing the sorption of all contaminants. Steam-activated chars exhibited sorption capacities of 25-125 mg/g and 15-70 mg/g for benzene and phenol, respectively, one order of magnitude higher than those of pristine biochars. Further treatment with CaCO3 and CaSO4 decreased the sorption capacity of manure biochar for benzene by 10-30%. In contrast, treatment with CaCO3 and CaSO4 enhanced the sorption capacity of manure biochar for TCE and phenol by approximately 10% and 5-10%, respectively, due to reduced hydrophobicity and the formation of surface functional groups. Similarly, the salt treatment following steam activation slightly increased the sorption capacity for arsenate, reaching up to 1.6 mg/g. These findings suggest that steam activation and surface treatment with CaCO3 and CaSO4 selectively enhance the sorption of various contaminants in natural and engineered systems.Implications: Pyrolysis is widely explored as a final disposal process for various types of organic waste, including agricultural, food, biomass, and thermoplastic wastes, due to its ability to produce valuable by-products, bio-oil, biochar, and syngas as energy sources. Compared to direct combustion with excess air, biochar production may be less cost-effective due to the additional energy required for the pyrolysis process. To overcome this economic disadvantage, improving the properties of biochar via various processes has been proposed to provide additional value to biochar.It has been reported that chemical activation with salt treatment could enhance the porosity and surface area by facilitating carbonization and preventing structural collapse, and that the steam activation could develop micro- and mesopores in carbonized material by gasification of carbon at high temperature using steam. Compared to acid and oxidants, salt treatment is less toxic, easier to remove, and more sustainable. Moreover, compared to CO2 activation, steam is more reactive with carbon, allowing activation at lower temperatures and shorter times. In this study, we investigated the effects of salt treatment (CaCO3 and CaSO4) and steam activation (900 °C) on chars derived from biomass wastes (manure, food, and kenaf) and spent tires. Batch sorption experiments were used to evaluate the absorption performance of these chars for benzene, phenol, trichloroethylene (TCE), and arsenate. Steam activation and salt treatment of char may affect the sorption of contaminants differently, depending on the type of contaminants. Activated char may replace activated granular carbon via steam activation and/or salt treatment. We characterized the properties of steam-activated and salt-treated chars, evaluated their effectiveness as sorbents for various types of contaminants, assessed the role of steam activation and salt treatment, and examined the potential mechanisms involved in contaminant sorption.