Efeitos da irradiação ultravioleta na eficiência das microalgas na biorremediação

Abstract

The aims of this study were to evaluate the capacity of native microalgae in the remediation of wastewater derived from cleaning process of smoked cigarette butts (CB), and to assess the use of artificial ultraviolet B (UV-B) radiation as a possible inducer of antioxidant activities in microalgae to alleviate the negative effects of CB wastewater pollutants. To this end, different experiments were performed at laboratory scale and the obtained results were discussed in two chapters. In Chapter 2, six natural isolates of microalgae were screened for the remediation of organic pollutants in wastewater derived from smoked CB cleaning process. The strains were one from the family Scenedesmaceae, two Chlamydomonas debaryana and three Chlorella sorokiniana. Microalgal cultures were exposed to different CB wastewater dilutions to identify the toxicity levels reflected in the alteration of microalgal physiological status and to determine the optimal conditions for an effective removal of contaminants. The results demonstrated that CB wastewater could impact on microalgal chlorophyll and carotenoid production in a concentration-dependent manner. Moreover, the resistance and remediation capacity did not only depend on the microalgal strain, but also on the chemical characteristic of organic pollutants. In detail, nicotine was the most resistant pollutant to removal by the microalgae tested and its low removal correlated with the inhibition of photosynthetic pigments affecting microalgal growth. Concerning the optimal conditions for an effective bioremediation, this study demonstrated that the Chlamydomonas strain named F2 showed the best removal capacity to organic pollutants at 5% CB wastewater maintaining its growth and photosynthetic pigments at control levels. In Chapter 3, it was selected the best strains with the highest biomass production under the strongest CB condition (i.e., 25%) according to the Chapter 2. It included three Chlorella sorokiniana strains named F4, R1 and LG1. These strains were treated with UV-B for 3-days prior to receiving CB wastewater and then incubated for 4-days in absence or maintaining UV-B. UV-B-untreated microalgae were used as control. Comparative physiological responses, including photosynthetic pigments and non-enzymatic antioxidants, as well as nicotine and nicotyrine removal were evaluated at 7-days culture. UV-B caused eustress as it did not negatively impact on algal chlorophyll and carotenoids production. UV-B acclimation was straindependent, correlating with native environment adaptions and genetic constitutions. UV-B as pretreatment had long-term positive effects on non-enzymatic antioxidant capacity. However, LG1 needed more time to readjust pro-oxidants/antioxidants balance as it was the most UV-B sensitive. Phenolic compounds played an important role in the antioxidant system to UV-B, while flavonoids did not contribute to total antioxidant capacity. Among strains, R1 was the only one in that UV-B seemed to have a synergistic effect on crossresistance to the most persistent and toxic CB pollutants (i.e., nicotine and nicotyrine), where their UV-B exposed cells may not only gain protection against pollutants but also may improve the catabolic pathways involved in the removal of these alkaloids.