Biochar from plant-assisted bioremediation: potential applications for sorptive removal of phenolic pollutants from water

A plant-assisted bioremediation strategy was applied in an area located in Southern Italy, close to the city of Taranto, historically contaminated by polychlorinated biphenyls (PCBs) and heavy metals. A specific poplar clone (Monviso) was selected for its ability to promote PCBs degradation. The harvested biomass was chipped and dried before being processed in a gasification plant to produce energy and biochar (BC), which could be used in agriculture as fertilizer or for environmental purposes as a decontaminating material for water and soil. The gasification has been conducted at a temperature of 850 degrees producing a BC suitable for decontaminating purposes. This work aimed to evaluate the capacity of the BC obtained by the gasification process to adsorb two well-known pollutants possessing endocrine disrupting (ED) properties, namely 4-tert-octylphenol (OP) and bisphenol A (BPA). Both molecules are widespread in water and terrestrial ecosystems as a consequence of increasing anthropic and agro-industrial activity, wastes disposal and the discharge of effluents from sewage sludge treatment plants. BC characterization indicated an organic carbon content of about 68%, a very alkaline pH and an electrical conductivity of about 5 dS/m. Using a batch equilibrium method, kinetics and adsorption isotherms were performed. Adsorption constants were calculated using the linear, Freundlich and Langmuir models. Kinetics data obtained evidenced a very rapid adsorption of both compounds, especially the more hydrophobic OP, onto BC with the attainment of a steady-state equilibrium in less than 1 h. Some differences among the compounds were found regarding the model and the extent of adsorption. Adsorption kinetic data were treated with the non-linear pseudo-first order and pseudo-second order equations in order to investigate the retention mechanisms. Results obtained showed that kinetic data followed preferentially the pseudo-second order model, thus indicating the occurrence of chemisorption between the compounds and BC. The remarkable sorption capacity of this material towards the two ED chemicals suggests its valuable exploitation for decontamination purposes, such as the treatment of wastewater before recycling into the soil and the retainment of pollutants in soil avoiding their entry into the food chain.