Micropollutants clean-up by bio-inspired entrapped laccases

Ardao Palacios, Inés [UCL] Demarche, Philippe [UCL] Nair, Rakesh [UCL] Agathos, Spiros N. [UCL]

(eng) Microbial laccases are powerful enzymes capable of degrading lignin and other recalcitrant compounds. For that reason, there is an increasing interest in these enzymes as biocatalysts for the removal of micropollutants in wastewater, with very promising results so far. However, the establishment of an efficient industrial process greatly depends on the availability of robust, stable and cost-effective immobilized biocatalysts. Recently, a novel immobilization technique based on bio-inspired enzyme entrapment has emerged as a fast and versatile tool for generating robust, cheap and highly stable (nano)biocatalysts, with a very high potential for environmental applications. The enzyme entrapment via bio-inspired mineralization aims to mimic the natural reactions in diatoms, whereby silica precipitation is induced by polypeptides called silaffins. By analogy, different polymers (natural or synthetic) are able to induce the precipitation of different inorganic oxides to form different nanosized structures in which the enzyme is entrapped. Active bio-inspired biocatalysts (150 UABTS, pH3/g) were produced using polyethylenimine as the synthetic polypeptide analogue inducing the precipitation of biotitania on the surface of magnetic particles. The biocatalytic potential of these particles was assessed for the degradation of a variety of micropollutants in wastewater. A 100 mL continuous reactor prototype with magnetic particle retention was set up to test the degradation at laboratory scale of a mixture of 6 micropollutants (bisphenol A, triclosan, nonylphenol, diclofenac, sulfamethoxazole and 17α-ethinylestradiol) at a final concentration of 5 µM each in tap water. In the proof-of-concept experiment, degradation efficiencies of 60% for triclosan and 17α-ethynylestradiol, 45% of bisphenol A and 30% for diclofenac were achieved. Particle aggregation during the reactor run and possible mass-transfer limitations hindered higher degradation efficiencies. An enhanced degradation was observed when the micropollutants are presented in mixture than as single pollutants, thereby suggesting their ability to act as laccase mediators. Additionally, higher enzyme stability, especially at acidic pHs, was obtained with the bio-inspired biocatalysts in comparison with the soluble counterpart.