Inorganic Oxide Systems as Platforms for Synergistic Adsorption and Enzymatic Conversion of Estrogens from Aqueous Solutions: Mechanism, Stability and Toxicity Studies

Abstract

Wastewater pollutants now include synthetic hormones. These hormones constitute a dangerous class of pollutants as they impose risks on the reproductive health of ecosystem life and humans via the water, including via drinking water. Traditional methods of wastewater treatment seem to be inefficient. In this work, design and fabrication of a new biosystem made of CaSiO3 and laccase is reported and its application for removal of 17α-ethynylestradiol from aqueous systems is demonstrated. 17α-ethynylestradiol is a syntetic estrogen, known to be robust to degradation. The effect of treatment time, pH, temperature, estrogen concentration and mass of the biocatalytic system was investigated. Removal treatment with 100 mg of biosystem for 12 h at pH 5, 25 °C on 0.1 mg/L of estrogen resulted in 100% removal efficiency. Use of CaSiO3 with deactivated enzyme confirmed a synergistic degradation of estrogen, which appears to occur via simultaneous adsorption and biocatalytic conversion, although with significant predominance of the enzymatic conversion. The efficiency of estrogen removal by the biosystem varied depending on type of cations present in the solution; the estrogen removal efficiency was ~30% higher in presence of Ag+ on the CaSiO3-laccase than with free laccase. After 10 cycles of repeated use, and 20 days of storage, the CaSiO3-laccase biosystem retained ~40% of its initial activity. Application of the CaSiO3-laccase biosystem caused significant reduction of toxicity and estrogenic activity of the solution. The method may pave the way for new efficient approaches for removal of pharmaceuticals and hormones from wastewater.

Keywords: inorganic oxide material, Calcium silicate, Laccase, enzyme immobilization, Biodegradation, Estrogens