Enzymatic treatment and subsequent toxicity of organic micropollutants using oxidoreductases - A review

Organic micropollutants like pharmaceuticals, personal care products, pesticides and industrial chemicals have received an ever growing attention due to their adverse ecological effects in natural water bodies. A promising technology to remove the micropollutants from the wastewater is biocatalytic treatment using oxidoreductase enzymes. In order to improve removal efficiency and feasibility, the focus has been on developing enzyme-mediator systems and immobilisation techniques. Nonetheless, since oxidoreductase enzymes often promote coupling reactions, enzymatic reactions do not necessarily result in simpler compounds. Thus transformation products, which might be in equally or even more hazardous pollutants, can be still present in the wastewater after treatment. Therefore, the toxicity and ecological effects of the reaction products have to be investigated rigorously to ensure that the treatment mitigates the environmental and health related impacts. The objective of this paper is to give an overview of research carried out with oxidoreductase enzymes to treat different organic micropollutants and their mixtures along with real wastewater and to collect available information on different techniques, transformation products and toxicity. Though in most cases the reviewed enzymatic treatment methods resulted in less toxic effluent, the application of mediators, while facilitating higher transformation rates, increased the level of toxicity. Hence, it was concluded that the suitability of biocatalytic methods should be assessed from the perspective of toxicity beside the removal efficiency in order to allow the upscaling of the technology to a feasible and sustainable wastewater treatment solution. (C) 2019 Elsevier Ltd. All rights reserved.