Remediation of Aged Crude‐Oil–Contaminated Surface Water From Okerenkoko Creeks, Southern Nigeria, Using Process‐Optimized Lignin Isolated From Sandbox ( Hura crepitans ) Seed Capsules

ABSTRACT

Petroleum hydrocarbon contamination of aquatic environments in the Niger Delta region of Nigeria requires remediation approaches that combine effectiveness, simplicity, and the utilization of renewable materials. This study investigated the application of unmodified lignin isolated from sandbox ( Hura crepitans ) seed capsules for the remediation of aged crude‐oil–contaminated surface water from Okerenkoko creeks in Delta State, Southern Nigeria. Lignin was isolated by alkaline extraction, followed by acid precipitation, and characterized using UV–Visible spectroscopy, Fourier‐transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface‐area analysis, and Thermogravimetric/differential thermogravimetric (TGA/DTG) analysis. Batch remediation experiments were conducted by varying the adsorbent dosage, pH, temperature, and agitation rate, whereas total petroleum hydrocarbon (TPH) removal kinetics were evaluated using pseudo‐first‐order, pseudo‐second‐order, Elovich, intraparticle‐diffusion, zero‐order, first‐order, and second‐order models. The alkaline extraction yielded 46.20% lignin. The isolated lignin showed a BET surface area of 4.4 m ²  g ⁻¹ , pore volume of 0.015 cm ³  g ⁻¹ , and an average pore diameter of 8.7 nm. FTIR analysis revealed characteristic lignin functional groups, whereas SEM showed an irregular and heterogeneous surface morphology. TGA/DTG analysis indicated the thermal stability and multistage decomposition behavior of the lignin. Optimum treatment conditions were achieved at an adsorbent dosage of 0.8 g, pH 5, a temperature of 25°C, and an agitation rate of 300 rpm. Under these conditions, the maximum observed TPH removal at 180 min was 68.82%, corresponding to an adsorption capacity of 23.53 mg g ⁻¹ . The pseudo‐second‐order model provided the best kinetic description of TPH removal, with a high coefficient of determination ( R ²  = 0.981), indicating that the adsorption process was predominantly controlled by interactions between the lignin surface and petroleum hydrocarbon constituents. The intraparticle‐diffusion model showed a non‐zero intercept, indicating that intraparticle diffusion was not the sole rate‐controlling mechanism. The findings demonstrate that unmodified H. crepitans lignin can serve as a renewable and effective bio‐based adsorbent for the treatment of aged crude‐oil–contaminated creek water under near‐ambient conditions. Its availability, simple preparation, and measurable TPH‐removal performance highlight its potential as a low‐cost and environmentally compatible material for petroleum hydrocarbon remediation in the Niger Delta region of Nigeria.