Application of modified walnut shell adsorbents in oily wastewater treatment

Oil spills are of great concern because oily wastewater disrupts the aquatic ecosystem, causes animal mutations, contaminates surface water resources, and causes diseases such as human cancer. Current efforts are geared towards recovering spilled oil from marine environments and ensuring the effective separation of oil and water in the collected emulsion. After oil separation from the emulsion, a polishing step is required to treat the residual oil in the water before discharging the effluent into the aquatic environment. Adsorption using natural materials as adsorbents is seen as an attractive option due to its simplicity, cost-effectiveness, accessibility, and eco-friendliness. Recent adsorption studies have focused on modifying eco-friendly materials to enhance their adsorption potential. This study investigated a two-step modification of walnut shells (WS) to treat oily wastewater. Firstly, WS was modified with sodium hydroxide (NaOH) via the wet impregnation method to attain WS/NaOH. Then, tetrabutylammonium bromide (TBAB) was introduced as a co-adsorbent to enhance the oil removal potential of WS/NaOH. The surface morphologies and chemical composition of the WS and WS/NaOH were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. A one-factor-at-atime experimental design was employed in this study. Findings from this research project indicated that raw WS and WS/NaOH are excellent adsorbents for the treatment of oily wastewater, with a removal efficiency of 81 % and 88 %, respectively. They generated adsorption capacities of 201 mg/g and 220 mg/g, respectively. However, with the introduction of TBAB as a co-adsorbent, an efficiency and capacity of 91 % and 226 mg/g, respectively, were achieved, proving the effectiveness of TBAB. Adsorption isotherm and kinetic studies were conducted to understand the adsorption mechanism of the proposed adsorbent. It was concluded that the Freundlich and Pseudo second-order model best represents the experimental results, as they show higher R² values of 0.9695 and 0.9998, respectively. This research project presents an eco-friendly and highly efficient adsorbent from modified WS to treat oily wastewater, offering a sustainable, scalable alternative to traditional methods by utilizing agricultural waste to remove oil pollutants in petrochemical wastewater treatment efficiently.