Strategies for the design and operation of enzymatic reactors for the degradation of highly and poorly soluble recalcitrant compounds

Enzymatic and non-enzymatic removal of organic micropollutants with spent mushroom substrate of Agaricus bisporus

Water bodies are increasingly contaminated with a diversity of organic micropollutants (OMPs). This impacts the quality of ecosystems due to their recalcitrant nature. In this study, we assessed the removal of OMPs by spent mushroom substrate (SMS) of the white button mushroom (Agaricus bisporus) and by its aqueous tea extract. Removal of acesulfame K, antipyrine, bentazon, caffeine, carbamazepine, chloridazon, clofibric acid, and N, N-diethyl-meta-toluamide (DEET) by SMS and its tea was between 10 and 90% and 0-26%, respectively, in a 7-day period. Sorption to SMS particles was between 0 and 29%, which can thus not explain the removal difference between SMS and its tea, the latter lacking these particles. Carbamazepine was removed most efficiently by both SMS and its tea. Removal of OMPs (except caffeine) by SMS tea was not affected by heat treatment. By contrast, heat-treatment of SMS reduced OMP removal to < 10% except for carbamazepine with a removal of 90%. These results indicate that OMP removal by SMS and its tea is mediated by both enzymatic and non-enzymatic activities. The presence of copper, manganese, and iron (0.03, 0.88, and 0.33 µg L-1, respectively) as well as H2O2 (1.5 µM) in SMS tea indicated that the Fenton reaction represents (part of) the non-enzymatic activity. Indeed, the in vitro reconstituted Fenton reaction removed OMPs > 50% better than the teas. From these data it is concluded that spent mushroom substrate of the white button mushroom, which is widely available as a waste-stream, can be used to purify water from OMPs.

Persistence and impact of steroidal estrogens on the environment and their laccase-assisted removal

Steroidal estrogens are widespread water contaminants with potential carcinogenic and endocrine-disrupting activities. The World Health Organization has listed estrogens as group 1 carcinogens. These contaminants are of substantial concern because of potential threats to human health, and aquatic organisms on long-term exposure. A range of methods, including oxidation, adsorption, electrochemical, and irradiation techniques have been employed for their remediation from aqueous systems. However, inadequate removal, toxic sludge generation, high operating costs, and the requisite for skilled operating and maintenance personnel commercially hampered the application of many methods. An interesting alternative treatment approach based on the use of oxidoreductases, particularly laccases, has recently gained amicability for the biotransformation of emerging pollutants. The use of immobilized enzymes is more cost-effective from an industrial perspective due to improved catalytic stability, reusability, reduction of product inhibition, and easier product separation. This review provides comprehensive knowledge on the use of laccases in the biodegradation of steroidal estrogens, including estrone, 17β-estradiol, and 17α-ethinylestradiol with endocrine-disrupting potency from the environment. After an overview of estrogens and catalytic properties of laccase, the use of free, as well as immobilized laccases with a particular emphasis on estrogens removal by laccase-based fed-batch, packed bed bioreactors, and membrane reactors, is discussed. A comparison of existing treatment technologies with enzyme technology for the removal of estrogens from different environmental matrices is made. Lastly, along with concluding remarks, future research direction aimed at bridging knowledge gaps for estrogenic compounds removal are also proposed in this very important research area.

Bio-based degradation of emerging endocrine-disrupting and dye-based pollutants using cross-linked enzyme aggregates

In this study, manganese peroxidase (MnP) from an indigenous white-rot fungus Ganoderma lucidum IBL-05 was insolubilized in the form of cross-linked enzyme aggregates (CLEAs) using various aggregating agents, i.e., acetone, ammonium sulfate, ethanol, 2-propanol, and tert-butanol, followed by glutaraldehyde (GA) cross-linking. The precipitant type, MnP, and GA concentrations affected the CLEAs activity recovery and aggregation yield. Among precipitants used, acetone appeared to be the most efficient aggregation agent, providing the highest activity recovery and aggregation yield of 31.26 and 73.46%, respectively. Optimal cross-linking was noticed using 2.0% (v/v) GA and 8:1 (v/v) MnP to GA ratio at 3.0 h cross-linking time under continuous agitation at 4 °C. The highest recovered activity and aggregation yield were determined to be 47.57 and 81.26%, respectively. The MnP-CLEAs, thus synthesized, were tested to investigate their bio-catalytic capacity for removing two known endocrine-disrupting chemicals (EDCs), e.g., nonylphenol and triclosan in a packed bed reactor system. The insolubilized MnP efficiently catalyzed the biodegradation of both EDCs, transforming over 80% in the presence of MnP-based system. A maximal of 100% decolorization was recorded for Sitara textile (SIT-based) effluent, followed by 95.5% for Crescent textile (CRT-based) effluent, 88.0% for K&N textile (KIT-based) effluent, and 84.2% for Nishat textile (NIT-based) effluent.

A Ca-alginate particle co-immobilized with Phanerochaete chrysosporium cells and the combined cross-linked enzyme aggregates from Trametes versicolor

For improving stability of immobilized white-rot fungus to treat various effluents, Phanerochaete chrysosporium cells and the combined cross-link enzyme aggregates (combi-CLEAs) prepared from Trametes versicolor were co-immobilized into the Ca-alginate gel particles in this paper. The activity yields of obtained combi-CLEAs were 42.7% for lignin peroxidases (LiPs), 31.4% for manganese peroxidases (MnPs) and 40.4% for laccase (Lac), respectively. And their specific activities were 30.2U/g as combi-CLEAs-LiPs, 9.5 U/g as combi-CLEAs-MnPs and 28.4 U/g as combi-CLEAs-Lac. Further, the present of the combi-CLEAs in the particles extremely improved their ability to degrade the dyes. Compared to the immobilized Ph. chrysosporium without the combi-CLEAs, the co-immobilized particles enhanced the decolorized rate of Acid Violet 7 (from 45.2% to 93.4%) and Basic Fuchsin (from 12.1% to 67.9%). In addition, the addition of the combi-CLEAs improved the adaptability of the white-rot fungal particles to adverse environmental conditions.

Degradation of estrogens by laccase from Myceliophthora thermophila in fed-batch and enzymatic membrane reactors

Several studies reported that natural and synthetic estrogens are the major contributors to the estrogenic activity associated with the effluents of wastewater treatment plants. The ability of the enzyme laccase to degrade these compounds in batch experiments has been demonstrated in previous studies. Nevertheless, information is scarce regarding in vitro degradation of estrogens in continuous enzymatic bioreactors. The present work constitutes an important step forward for the implementation of an enzymatic reactor for the continuous removal of estrone (E1) and estradiol (E2) by free laccase from Myceliophthora thermophila. In a first step, the effect of the main process parameters (pH, enzyme level, gas composition (air or oxygen) and estrogen feeding rate) were evaluated in fed-batch bioreactors. E1 and E2 were oxidized by 94.1 and 95.5%, respectively, under the best conditions evaluated. Thereafter, an enzymatic membrane reactor (EMR) was developed to perform the continuous degradation of the estrogens. The configuration consisted of a stirred tank reactor coupled with an ultrafiltration membrane, which allowed the recovery of enzyme while both estrogens and degradation products could pass through it. The highest removal rates at steady state conditions were up to 95% for E1 and nearly complete degradation for E2. Furthermore, the residual estrogenic activity of the effluent was largely reduced up to 97%.

Combined cross-linked enzyme aggregates from versatile peroxidase and glucose oxidase: production, partial characterization and application for the elimination of endocrine disruptors

Versatile peroxidase (VP) from Bjerkandera adusta was insolubilized in the form of cross-linked enzyme aggregates (CLEA®s). Of the initially applied activity 67% was recovered as CLEA®s. Co-aggregation of VP with glucose oxidase from Aspergillus niger led to an increased activity recovery of 89%. The combined CLEA®s showed higher stability against H(2)O(2) and exerted VP activity upon glucose addition. The elimination of the endocrine disrupting chemicals bisphenol A, nonylphenol, triclosan, 17α-ethinylestradiol and the hormone 17β-estradiol (10 mg L(-1) each) and the removal of their estrogenic activity by combined CLEA®s were tested in batch experiments. Within 10 min, the combined CLEA®s were able to remove all the endocrine disruptors except triclosan (residual concentration 74%). The removal of the estrogenic activity was higher than 55% for all compounds, except triclosan. A membrane reactor continuously operated with combined CLEA®s could almost completely remove bisphenol A (10 mg L(-1)) for 43 h.

Oxidation of pharmaceutically active compounds by a ligninolytic fungal peroxidase

Pharmaceuticals are an important group of emerging pollutants with increasing interest due to their rising consumption and the evidence for ecotoxicological effects associated to trace amounts in aquatic environments. In this paper, we assessed the potential degradation of a series of pharmaceuticals: antibiotics (sulfamethoxazole), antidepressives (citalopram hydrobromide and fluoxetine hydrochloride), antiepileptics (carbamazepine), anti-inflammatory drugs (diclofenac and naproxen) and estrogen hormones (estrone, 17β-estradiol, 17α-ethinylestradiol) by means of a versatile peroxidase (VP) from the ligninolytic fungus Bjerkandera adusta. The effects of the reaction conditions: VP activity, organic acid concentration and H(2)O(2) addition rate, on the kinetics of the VP based oxidation system were evaluated. Diclofenac and estrogens were completely degraded after only 5-25 min even with a very low VP activity (10 U l(-1)). High degradation percentages (80%) were achieved for sulfamethoxazole and naproxen. Low or undetectable removal yields were observed for citalopram (up to 18%), fluoxetine (lower than 10%) and carbamazepine (not degraded).