Removal of refractory organics from saline concentrate produced by electrodialysis in petroleum industry using bone char

In a scenario of hydric scarcity, water reuse is essential to minimize make-up; however, increased salinity comes along with recycling streams. Crystallization has been evaluated to remove dissolved ions; nevertheless, contaminants affect its efficiency. In this context, the removal of residual organics from the saline concentrate from electrodialysis applied for water reuse in a Brazilian petroleum refinery was investigated. Aiming at establishing a sustainable virtuous circle, bone char, a waste from food industry, 0.5–1.4 mm particle size, was used as adsorbent for refractory organics removal. Equilibrium adsorption time of 4 h was determined from batch experiments (through 72 h, at 25.0 ± 0.1 °C, pH 7.6 ± 0.5 and 200 ± 1 rpm, solid/liquid ratio of 10 g kg⁻¹) in a shaker and a removal of 54% for dissolved chemical oxygen demand (COD) was observed. Adsorption kinetics (pseudo-first and pseudo-second order; Elovich equation) and equilibrium isotherms were evaluated. Pseudo-second order model for kinetics (R² = 0.9993; k₂ = 0.0184 mg⁻¹ min⁻¹; q_e = 3.21 mg g⁻¹) and Freundlich isotherm model best fitted to experimental data (R² = 0.995), suggesting physisorption in multiple layers. The adsorbent thermal regeneration was evaluated (at 300, 500 and 700 °C, for 60, 120 and 180 min). Partial thermal regeneration was achieved at lower temperature and time demands (300 °C and 60 min—dissolved COD removal was around 40% after the first cycle of regeneration). Further investigation, including scaling-up and a cost-benefit analysis, is necessary in order to assess its use as a viable low-cost alternative for this type of effluent.