Freshwater resources are increasingly scarce due to human activities, and the understanding of water quality variations at different spatial and temporal scales is necessary for adequate management. Here, we analyze the hypotheses that (1) the presence of a wastewater treatment plant (WWTP) and (2) a polluted tributary that drains downstream from the WWTP change the spatial patterns of physicochemical variables (pH, turbidity, dissolved oxygen, and electrical conductivity) and nutrient concentrations (reactive soluble phosphorus, total phosphorus, nitrogen series, total nitrogen, and total dissolved carbon) along a mid-order river in SE Brazil and that these effects depend on rainfall regime. Six study sites were sampled along almost 4 years to evaluate the impacts of human activities, including sites upstream (1-3) and downstream (5-6) from the WWTP. The impacts were observed presenting an increasing trend from the source (site 1) towards Água Quente stream (site 4, the polluted tributary), with signs of attenuation at site 5 (downstream from both WWTP and site 4) and the river mouth (site 6). Input of nutrients by rural and urban runoff was observed mainly at sites 2 and 3, respectively. At sites 4 and 5, the inputs of both untreated and treated wastewaters increased nutrient concentrations and changed physicochemical variables, with significant impacts to Monjolinho River. Seasonal variations in the measured values were also observed, in agreement with the pluviometric indexes of the region. Univariate analyses suggested no effect of the WWTP for most variables, with continued impacts at sites downstream, but non-parametric multivariate analysis indicated that these sites were recovering to chemical characteristics similar to upstream sites, apparently due to autodepuration. Therefore, multivariate methods that allow rigorous tests of multifactor hypotheses can greatly contribute to determine effects of both point and non-point sources in river systems, thus contributing to freshwater monitoring and management.

Within this Thesis, a new concept of reactor for UV/H2O2/MW systems without using electrodless discharge lamps was proposed. The reactor allows for the direct comparison of AOPs, with and without the presence of microwave (MW) irradiation, as well as evaluate the effects of such radiation for removing emerging contaminants. To optimize the system, using the Response Surface Methodology (RSM), bisphenol A (BPA, initial concentration of 100 µg L-1) was selected, due to its environmental importance. Selected factors for this study were H2O2 concentration (2 2), flow rate (Q), and MW oven power (P). Initial results showed that MW had a statistically significant effect on the removal of BPA, with a trend of better results at the lower level of the evaluated interval. Optimal conditions for degradation were: 2 2 = 20 mg L-1 , Q = 700 mL min-1 and P = 245 W. With those conditions, there were no significant differences between the UV/H2O2/MW and UV/H2O2 systems. However, with milder conditions of degradation (2 2 = 5 mg L-1 , Q = 600 mL min-1 e P = 245 W), BPA removal increased from 65 to 95% (within 60 min) when the MW was used. Moreover, the initial BPA removal rate doubled (from 0,046 to 0,100 min-1) and the maximal oxidative capacity (MOC) increased from 86 to 100%. In order to evaluate the MW effects without the possible influence of the heating they generate, the MW oven was replaced by a conventional heating system able to mimic the MW heating rate. Both systems were compared, considering the degradation products identified throughout degradation. Different structures were found in both systems, implying the existence of specific effects of MW. To verify whether MW radiation could influence the degradation mechanism of structuralsimilar molecules, four parabens with different alkoxyl radicals were selected (methyl, ethyl, propyl, and isobutylparaben). The 2³ full factorial design (same factors and levels used for the preliminary stage of RSM) showed that the MW had different effects on each paraben, with methylparaben being the only one to benefit from the increment of MW power. Ethyl, propyl, and isobutylparaben had better results with the lower power, being noticed an increase of the intensity of the MW effect for molecules with bigger alkoxyl radicals. Evaluating the degradation products from the systems with MW and conventional heating, it was noticed differences among the intensities of the obtained relative signals for compounds achieved for both reactors, reassuring the hypothesis of the existence of MW-specific effects (in this case, favoring mechanisms and modifying selectivity).

In this paper, the UV/H2O2/MW (microwave) process was compared with the UV/H2O2 one, using bisphenol A (BPA) as a model-pollutant. The proposed experimental setup was operated in batch recycle mode and allows for the direct comparison among different processes: UV only, H2O2 only, MW only, UV/H2O2, UV/MW, H2O2/MW, and UV/H2O2/MW, as well as temperature control to minimize thermal effects. The degradation of BPA at near-environmental concentration (100 µg L−1) was optimized by an experimental design approach (Response Surface Methodology) and its residual concentration was measured by HPLC. Approximately 95% of the initial BPA amount could be removed in 30 min at the optimal conditions (CH2O2 = 20 mg L−1, flow rate = 700 mL min−1, and MW power = 245 W). The experiments designed for comparing the UV/H2O2 and the UV/H2O2/MW processes showed that the use of MW doubled the initial pseudo-first-order degradation rate (from 0.046 to 0.10 min−1) and significantly increased the maximum oxidation capacity of the system (from 86 to 100%). Although the reasons behind those results are still unclear, it seems that the existence of non-thermal effects of the MW irradiation should be considered.