Continuous Biotransformation of Estrogens by Laccase in an Enzymatic Membrane Reactor

Abstract

Although the removal of steroid estrogens by enzymatic treatment with free fungal enzymes has been already demonstrated in previous batch experiments, the main limitations associated to this system are the low productivity and degradation yield, typical of batch operations, as well as the unfeasibility of reusing the enzyme. With the aim of overcoming these drawbacks, an enzymatic membrane reactor (EMR) was designed for the continuous removal of estrone (E1) and estradiol (E2) by a commercial laccase from Myceliophthora thermophila. The use of an ultrafiltration membrane allowed the separation of the enzyme according to its high molecular weight while the degradation products could pass through it. Not only the continuous operation was proved, but also different operational parameters were assessed for their relevance on the efficiency of the process. Accordingly, the effects of laccase activity (500-1,000 U/L), hydraulic residence time (1-4 h) and oxygen frequency supply (2-8 pulses of oxygen each HRT) were investigated. Removal efficiencies between 64-100 % and degradation rates of 0.96-2.92 mg/(L·h) were attained. Furthermore, the residual estrogenic activity of the effluent was largely reduced up to 97 %. The present work proves the feasibility of using a laccase- mediated reactor for the continuous removal of estrogenic compounds.