Laccase immobilization in polyelectrolyte multilayer membranes for 17α-ethynylestradiol removal: Biocatalytic approach for pharmaceuticals degradation

Ultrafiltration and composite microfiltration biocatalytic membrane activity and steroid hormone micropollutant degradation at environmentally relevant concentrations

Biocatalytic degradation of micropollutants has been extensively explored in both batch and membrane reactors in µg/L to mg/L concentrations and variable water compositions. The degradation of micropollutants by biocatalytic membranes at environmentally relevant concentrations of ng/L range found in natural surface water matrices has not yet been investigated, presumably because of the challenging concentration analysis. This study investigated the limitations of biocatalytic degradation of estradiol (E2) micropollutant at environmentally relevant concentrations by a biocatalytic membrane. The contributions of solute flux, hydraulic residence time (HRT) and water matrix composition on reaction kinetics, the apparent rate of disappearance (or reaction rate) and enzyme activity were examined. Two biocatalytic membranes were used: i) laccase entrapped in an ultrafiltration (UF) membrane support (namely UF-SNPs) and, ii) laccase covalently bound to the nanofiber matrix of a composite microfiltration (MF) membrane. The three main findings are reported. Firstly, the apparent rate of E2 disappearance decreases significantly by four orders of magnitude at a low micropollutant concentration of 0.1 µg/L, resulting in undetectable degradation during filtration, irrespective of the biocatalytic membrane. Secondly, the solute mass transfer and HRT control the biocatalytic degradation through the membranes resulting in different E2 removal. For the UF-SNPs membrane, a removal of 31 % is achieved only by increasing the concentration to 3000 µg/L and at a flux of 60 L/m².h (HRT of 4.5 s) due to an increase in solute flux by an order of magnitude similar to the apparent rate of disappearance. In contrast, the nano-MF membrane is ineffective in achieving biocatalytic degradation regardless of E2 concentration, as the HRT is approximately seven times lower (0.6 s) than that of the UF-SNPs, and thus insufficient for E2 to reach the catalytic site. Thirdly, the composition of the aqueous matrix plays a crucial role in the control of laccase activity irrespective of the membrane. Indeed, laccase is inactivated predominantly by chloride ions in synthetic carbonate buffer, since the typical NaCl concentration is about two orders of magnitude higher than E2 concentration. This study highlights that the slower kinetics achieved in the biocatalytic UF-SNPs and MF membranes are ineffective in removing steroid hormone micropollutants at realistic concentrations in surface water matrices. Further research is suggested to accelerate the reaction kinetics at such low concentrations and prolong the residence time within the membrane.

Progress towards Stable and High-Performance Polyelectrolyte Multilayer Nanofiltration Membranes for Future Wastewater Treatment Applications

The increasing demand for nanofiltration processes in drinking water treatment, industrial separation and wastewater treatment processes has highlighted several shortcomings of current state-of-the-art thin film composite (TFC NF) membranes, including limitations in chemical resistance, fouling resistance and selectivity. Polyelectrolyte multilayer (PEM) membranes provide a viable, industrially applicable alternative, providing significant improvements in these limitations. Laboratory experiments using artificial feedwaters have demonstrated selectivity an order of magnitude higher than polyamide NF, significantly higher fouling resistance and excellent chemical resistance (e.g., 200,000 ppmh chlorine resistance and stability over the 0-14 pH range). This review provides a brief overview of the various parameters that can be modified during the layer-by-layer procedure to determine and fine-tune the properties of the resulting NF membrane. The different parameters that can be adjusted during the layer-by-layer process are presented, which are used to optimize the properties of the resulting nanofiltration membrane. Substantial progress in PEM membrane development is presented, particularly selectivity improvements, of which the most promising route seems to be asymmetric PEM NF membranes, offering a breakthrough in active layer thickness and organic/salt selectivity: an average of 98% micropollutant rejection coupled with a NaCl rejection below 15%. Advantages for wastewater treatment are highlighted, including high selectivity, fouling resistance, chemical stability and a wide range of cleaning methods. Additionally, disadvantages of the current PEM NF membranes are also outlined; while these may impede their use in some industrial wastewater applications, they are largely not restrictive. The effect of realistic feeds (wastewaters and challenging surface waters) on PEM NF membrane performance is also presented: pilot studies conducted for up to 12 months show stable rejection values and no significant irreversible fouling. We close our review by identifying research areas where further studies are needed to facilitate the adoption of this notable technology.

Study of Membrane-Immobilized Oxidoreductases in Wastewater Treatment for Micropollutants Removal

The development of efficient strategies for wastewater treatment to remove micropollutants is of the highest importance. Hence, in this study, we presented a rapid approach to the production of biocatalytic membranes based on commercially available cellulose membrane and oxidoreductase enzymes including laccase, tyrosinase, and horseradish peroxidase. Effective enzyme deposition was confirmed based on Fourier transform infrared spectra, whereas results of spectrophotometric measurements showed that immobilization yield for all proposed systems exceeded 80% followed by over 80% activity recovery, with the highest values (over 90%) noticed for the membrane-laccase system. Further, storage stability and reusability of the immobilized enzyme were improved, reaching over 75% after, respectively, 20 days of storage, and 10 repeated biocatalytic cycles. The key stage of the study concerned the use of produced membranes for the removal of hematoporphyrin, (2,4-dichlorophenoxy)acetic acid (2,4-D), 17α-ethynylestradiol, tetracycline, tert-amyl alcohol (anesthetic drug), and ketoprofen methyl ester from real wastewater sampling at various places in the wastewater treatment plant. Although produced membranes showed mixed removal rates, all of the analyzed compounds were at least partially removed from the wastewater. Obtained data clearly showed, however, that composition of the wastewater matrix, type of pollutants as well as type of enzyme strongly affect the efficiency of enzymatic treatment of wastewater.