Magnetic Spent Tea Leaves as a Sustainable Carrier for Laccase Immobilization in Brilliant Green Removal from Aqueous Solution

Abstract

Synthetic dyes released into waterways through industrial effluents remain a major environmental concern because of their persistence and potential ecological effects. This study evaluated magnetic spent tea leaves (MSTL) as a low-cost and sustainable carrier for laccase immobilisation and assessed the performance of the resulting material (MSTL-LI) for Brilliant Green removal from aqueous solution. Laccase was immobilised onto MSTL, achieving an activity of 106.4 U/g and demonstrating successful enzyme attachment to the support. The effects of contact time, initial dye concentration, and adsorbent dosage on dye removal were investigated. Dye removal increased with contact time and reached 86.30% at 48 h for 100 ppm Brilliant Green using 50 mg of MSTL-LI, with only marginal improvement at 60 h, indicating that equilibrium had been approached. At the optimized contact time, the highest removal efficiency was obtained at the lowest tested dye concentration (100 ppm), while removal efficiency decreased progressively as the initial concentration increased from 200 to 400 ppm. Increasing the adsorbent dosage from 50 to 200 mg improved removal efficiency from 87.98% to 95.31%, although only marginal additional improvement was observed beyond 150 mg. These findings suggest that MSTL-LI is a promising waste-derived support for dye removal. Nevertheless, further studies involving material characterisation, reusability assessment, and mechanistic investigation are required to further evaluate its practical applicability in wastewater treatment.