Exploring the potential of a waste-derived bone char for pharmaceuticals adsorption in saline-based wastewater

In this study, the effect of salinity in wastewater on the adsorption capacity of a bone char material prepared through pyrolysis of tuna bones at 1000 °C was investigated for two pharmaceuticals, tramadol (TRA) and venlafaxine (VNF), both contaminants of emerging concern. This is the first time that the adsorption efficiency of a bone char-type material was tested in such conditions. The Tuna Bone Char (TBC) was composed of calcium phosphate (hydroxyapatite), and graphitic carbon. The TBC is a nanostructured material (particle size 30–60 nm), with a surface area of 100.67 m²/g (higher than other waste-derived type materials), and a total pore volume of 575.2 mm³/g. TBC capacity to adsorb TRA and VNF, individually or combined, was evaluated in batch experiments using different aqueous matrices: water, non-saline wastewater, and wastewaters with different salinity levels (7.5 and 12 g/L). For individual pharmaceuticals, the TBC had a higher affinity for TRA than VNF. The presence of salts in wastewaters led to a decrease in the TBC adsorption capacity but it was still effective for pharmaceuticals adsorption. Indeed, for the individual pharmaceuticals, the TBC adsorption capacity (q_t) was 0.72–2.14 and 0.77–1.70 mg/g for TRA and VNF respectively, depending on the aqueous matrix. With both pharmaceuticals present, lower q_t values were experimentally obtained for TRA and VNF. The potential of the TBC, a material derived from a by-product of the fish industry, to be used for environmental remediation in different environments, such as saline wastewaters was demonstrated, widening the range of its potential applications.