Synthesis and application of recycled carbon fibre-based adsorbents for the removal of antibiotics from freshwater aquaculture environments

Abstract

The growing environmental impact of end-of-life carbon fibre composites and the rising use of antibiotics in aquaculture present two critical sustainability challenges. Carbon fibre reinforced polymers, widely used in aerospace and automotive industries, generate significant waste. While aquaculture is a major source of pharmaceutical pollution. Antibiotics such as ciprofloxacin and oxytetracycline are commonly used in fish farming and have been linked to the emergence of antimicrobial resistance in aquatic environments. This research aimed to develop high-performance, sustainable carbon-based adsorbents using recycled carbon fibres recovered from Carbon fibre reinforced polymer waste, and to optimise their use for the removal of ciprofloxacin and oxytetracycline from water. A systematic approach was applied to optimise each stage of the adsorbent development process including chemical activation, surface modification, adsorption, and regeneration. Design of Experiments techniques were used to identify optimum process parameters. Initial testing with sodium hydroxide-activated recycled carbon fibres yielded low adsorption capacities (16.84 mg/g for methylene blue), indicating incomplete activation. Process optimisation employing potassium hydroxide significantly improved adsorbent performance. The optimum conditions were identified as an activation temperature of 670 °C, impregnation ratio of 1:10 (CF:KOH) and hold time of 0.5 h, achieving methylene blue adsorption capacities above 450 mg/g and yields exceeding 70%. Surface-modified samples utilising 10 M nitirc acid, 16 h contact time at 28 °C, resulted in increased acidity and mesoporosity. However, it was found that additional modification was not essential to maintain high antibiotic removal. Optimised adsorption conditions were identified to be an adsorbent dose of 0.8 g/L, pH of 2 and initial concentration of 2 mg/L, which resulted in removal efficiencies above 95% for both CIP and OTC. Regeneration studies using 0.1 M potassium hydroxide demonstrated strong reusability, with regeneration efficiencies remaining above 75% over seven cycles. The results confirm that recycled carbon fibre-derived adsorbents are effective, reusable, and environmentally sustainable materials for removing antibiotic contaminants from aquaculture wastewater.