Aqueous ibuprofen sorption by using activated walnut shell biochar: process optimization and cost estimation

Abstract

Ibuprofen is a widely used non-steroidal anti-inflammatory, anti-pyritic, and analgesic drug with occurrence in the aquatic systems of 47 countries. The presence of ibuprofen in aquatic systems poses a threat to flora and fauna. Therefore, this study developed walnut shell activated biochar (WSAB) using H₃PO₄ immersion and 450 °C pyrolysis as a 3-dimensional adsorbent for aqueous ibuprofen remediation. WSAB was characterized using elemental analysis, ATR-FTIR, XRD, SEM, SEM-EDX, TEM, BET surface area and pore size measurements. The S_BET surface area, pore volume, and pore density of the WSAB were 686 m² g⁻¹, 0.38 cm³ g⁻¹ and 0.87 g cm⁻³, respectively. Batch sorption studies were performed from pH 2 to 10 at ibuprofen concentrations from 10 to 120 mg L⁻¹ and temperatures from 25 to 45 °C. Maximum sorption (80%) occurred at pH 4 at an IBP concentration of 50 mg L⁻¹ and a WSAB dose of 1.0 g L⁻¹. Sorption followed second order kinetics well (R² = 0.999). The sorption isotherms remained almost constant with an increase in temperature as shown by Langmuir adsorption capacities [Q°_25°C = 69.7 mg g⁻¹, Q°_35°C = 68.0 mg g⁻¹, and Q°_45°C = 66.9 mg g⁻¹]. WSAB provided an efficient ibuprofen sorption capacity (30.08 mg g⁻¹) in fixed-bed sorption studies (column parameters: initial Ibuprofen concentration = 7.5 mg L⁻¹; pH = 4.0; WSAB dose = 2.0 g; bed length = ∼4 cm; hydraulic flow rate = 2.5 mL min⁻¹). Sorption of ibuprofen to WSAB involves H-bonding, pore filling with complexation and hydrophobic π–π donor–acceptor attractions likely participating. An estimated cost of US$ 6.93 kg⁻¹ together with excellent sorption capacity makes WSAB an efficient low-cost adsorbent for ibuprofen removal. Thus, this study describes a sustainable waste walnut shell management strategy as well as treatment of ibuprofen contaminated water.