Green Enzyme Engineering: Bioremediation of Methylene Blue-Contaminated Wastewater Using Hydrogel-Immobilised Enzyme Extract Synthesised from Spent Mushroom Compost

This study aims to synthesise reusable, cost-effective and sustainable spent mushroom extract-alginate beads (SME-AB), investigate its bioremediation abilities of textile dye pollutant, methylene blue (MB), and enhance its removal efficiency ABTS mediation. MB is a toxic, non-biodegradable textile dye. Spent mushroom compost (SMC) waste, has proven its effectiveness in removing a variety of pollutants, including MB, due to its adsorption properties and ligninolytic enzymes like laccase. Recent studies show Pleurotus ostreatus and Hericium erinaceus SME effectively remove dyes and pharmaceuticals, respectively. However, the effectiveness of an SME-mediator hydrogel system in dye removal has not been studied. Enzymes were extracted from SMC by sectioning mycelium, homogenising, centrifuging (10000rpm, 4ºC) and vacuum filtering (pore size 0.2 µm). P. ostreatus SME was 2.25 and 1.32 times more effective than H. erinaceus in decolourising MB at 5 mg/L and 10 mg/L initial MB concentrations, respectively. P. ostreatus SME was immobilised in alginate to improve recovery and enzyme stability and had a swelling degree of 6009.2%, indicating strong mechanical stability. 10.0g SME-AB was added to 200 ml 20 mgL⁻1 MB and placed in a shaking incubator (150 rpm, 35ºC). SME-AB decolourised 26.0% of MB in 24 h, through enzymatic degradation and adsorption, with only an 8.0% drop in removal between the second and third uses. Adding laccase-mediator ABTS to the SME-AB composition further enhanced efficiency by 28.3%. This demonstrates that dried ABTS-SME-AB, repurposed from SMC waste, is a promising low-cost, sustainable technology for textile wastewater treatment.