Biorremediação de fármacos por microalgas

Abstract

The contamination of water by emerging pollutants (EPs) has become an environmental concern, due to the toxicity effects on the aquatic environment and on human health. For the most part, these micropollutants are not removed or degraded in conventional water treatment plants, persisting even after treatment. In this context, the bioremediation of PEs via microalgal metabolism becomes a promising alternative. The processes by which microalgae remove PEs from water or wastewater include mechanisms of bioaccumulation, bioadsorption and biodegradation. After the bioremediation crops, the generated biomass and the wastewater from these crops can be used in other applications, such as in the production of biofuels or in the use of fertigation, respectively. The objective was to carry out the bioremediation of the drugs fluoxetine, paracetamol, diazepam, acetylsalicylic acid, and caffeine through the microalgae Spirulina platensis, Scenedesmus obliquus and Chlorella homosphaera, and to evaluate the possible uses of biomass and wastewater after cultivation. This work was divided into 3 stages. In the first step, the microalgal growth and the effects on the composition of the biomass were evaluated in media with the presence of the drugs separately, at different concentrations (100, 70, 50, 30, 10, 5 and 1 mg.L-1). In the second stage, the drugs were inserted together, considering the resistance results observed in the first stage. Growth parameters were monitored for 20 d, and ecotoxicity on plant bioindicators with the culture supernatant were evaluated every 5 d of cultivation. In the third step, every 5 d, 20 g.L-1 of each drug was added to the culture medium containing 10% (v/v) of effluent from the conventional post-treatment of sanitary sewage. Microalgae growth parameters were analyzed for 30 d, and chromatographic analyzes were evaluated every 5 d. In the first stage, the maximum tested concentration of the drugs caffeine and cetylsalicylic acid did not present a toxic effect in the three tested strains. Exposure to fluoxetine, paracetamol and diazepam resulted in cell death or reductions in the maximum specific growth rate and biomass concentration in the cultures, mainly at concentrations above 30 mg.L-1. The least resistant microalgae was Spirulina platensis, followed by Chlorella homosphaera, with Scenedesmus obliquus being the most resistant strain. The enzymatic hydrolysis tests of the biomass cultivated in the presence of the drugs showed hydrolysis efficiency equal to the biomass cultivated in standard medium without the drugs. In step two, the tests with fluoxetine and paracetamol caused reductions in the growth of microalgae. There was no toxic effect in the ecotoxicity tests of the supernatant of Scenedesmus microalgae cultures, obtaining germination rates above 80%. The supernatant of Spirulina cultures obtained germination rates below 10%, a factor related to the toxicity of the culture medium. In step 3, drug biodegradation was observed, with reductions of 39% in caffeine concentrations and almost 80% in fluoxetine concentrations, in addition to quantifying the presence of drug degradation by-products. Therefore, it is possible to verify that the microalgae can perform the degradation of emerging pollutants via biodegradation mechanism. Also, cultivated biomass can be used to produce biofuels, mainly bioethanol, and wastewater from crops can be used in fertigation processes.