Strategic utilization of groundnut shell (Arachis hypogaea) immobilized bacterial consortium for enhanced 4-nitrophenol remediation: statistical optimization, kinetic modeling, and reusability

This study reports the utilization of raw agricultural biowaste groundnut shell (GS) as a potential immobilization matrix for an isolated bacterial consortium as a sustainable means to remove 4-nitrophenol (4-NP). Optimization of five parameters such as immobilization matrix size, matrix dosage, pH, temperature, and agitation and their three levels was done through Taguchi Orthogonal Array approach by Qualitek-4 software. Taguchi methodology indicated the optimum reaction conditions to be (in order of their significance) agitation speed (100 rpm), immobilization matrix dosage (4 g), matrix size (800 µm), pH (9), and temperature (32 °C), resulting in an overall enhancement of 57.30% 4-NP removal efficiency under the optimized conditions. GS-immobilized cells exhibited an improved substrate removal efficiency and high substrate tolerance over free cells, indicating the synergistic effects of adsorption and biodegradation on the removal process. The GS immobilized cells could remove 1000 mg l −1 of 4-NP as opposed to only 700 mg l −1 by the free cells. Biodegradation kinetics were analyzed using various substrate inhibition models, and Haldane model fitted the experimental data reasonably well. GS immobilized cells retained a stable activity of 85.5 ± 3.48% for 45 days when stored at 4 °C and could be efficiently reused for 4 consecutive cycles. Thus, utilizing untreated agricultural wastes like GS will be a cost-effective alternative to conventional immobilization matrices in small-scale industries and can be a step towards sustainable agro-waste management and contaminated wastewater treatment.