Influence of treatment conditions on the oxidation of micropollutants by Trametes versicolor laccase

Abstract

Many organic compounds present at low concentrations in municipal wastewater, such as various pharmaceuticals and biocides, are recalcitrant in conventional wastewater treatment plants (WWTPs). To improve their biodegradation, oxidoreductase enzymes such as laccases were tested. The goal was to find optimal conditions for the transformation of two anti-inflammatory pharmaceuticals (diclofenac (DFC) and mefenamic acid (MFA)), one biocide (triclosan (TCN)) and one plastic additive (bisphenol A (BPA)) by Trametes versicolor laccase. Experiments were conducted in spiked solutions at different pH values (from 3 to 9), enzyme concentrations (70-1400 Ul(-1)), reaction times (0-26 hours) and temperatures (10, 25 and 40°C) following a Doehlert experimental design. A semi-empirical model was developed to understand better the combined effects of the four factors and to determine optimal values. This model was able to fit well the experimental data (R(2)>0.97) and showed good predictive ability. All four factors had a significant effect on the micropollutant oxidation with the greatest influence shown by pH. Results for single compounds were different from those obtained for mixtures of micropollutants. For instance, DFC transformation occurred at much higher rates in mixtures under alkaline conditions. Optimal conditions were compound-dependent, but were found to be between pH 4.5 to 6.5 and between 25°C to more than 40°C. A laccase concentration of 730 Ul(-1) was sufficient to obtain a high removal rate (>90%) of the four individual compounds (range of times: 40 min to 5 hours), showing the potential of laccases to improve biodegradation of environmentally persistent compounds.

Sulfamethoxazole and isoproturon degradation and detoxification by a laccase-mediator system: Influence of treatment conditions and mechanistic aspects

“…As shown in previous studies [23,34], pH has a strong influence on the laccase activity, with higher activities (for T. versicolor laccase) under acidic conditions (pH 4-6) and almost no activity in alkaline solutions (pH > 7.5-8). It was therefore expected that LMS oxidation would also be strongly influenced by pH, especially during the first stage of the mediator oxidation by laccase.…”

“…The laccase activity was determined using a colorimetric assay by measuring the oxidation of 0.5 mM ABTS in an oxygen-saturated acetate buffer (0.1 M) at pH 4.5 and 25 • C as described by Margot et al [23]. A sample aliquot containing laccase was added to the solution and the increase of absorbance at 420 nm was monitored with a temperature-controlled spectrophotometer (U-3010, Hitachi, Tokyo, Japan).…”

Fungal Bioremediation of Emerging Micropollutants in Municipal Wastewaters

“…On the contrary, the presence of diclofenac decreased BPA and mefenamic acid conversion probably due to competition phenomena for the active site (Margot et al 2013). …”

“…Moreover, the operative parameters can affect conversion rates and can completely switch off the system. For example, pH, temperature, loaded enzymes concentration and contact time greatly affected (ranging from 0 to 100%) the removal of 4 EDCs (Margot et al 2013). …”

“…Laccase-catalyzed system was studied over a pH range 5-9 and set at 6 for natural estrogens (estrone, 17β-estradiol and estriol) and synthetic estrogen (17α-ethinylestradiol) (Auriol et al 2007). The optimal pH range of 4-6 was observed for the transformation of dymron (Maruyama et al 2006), TCS Nicell 2006a, Margot et al 2013), sulfonamide antibiotics (Weng et al 2013), anti-inflammatory pharmaceuticals (Margot et al 2013) and BPA Nicell 2006b, Margot et al 2013).…”