In this study, the extraction and characterization of aquatic humic substances (AHS) from two blackwater rivers in the Amazon basin was carried out in order to assess the seasonal effects in the AHS structure. In addition, an investigation of the complexing capacities (CC) of the structures containing the metal ions CdII, NiII and PbII was also done. The characterization (of the AHS) was done using UV-Vis, molecular fluorescence, and infrared spectroscopy. AHS from the Negro River showed more aromatic characteristics in its structures and molecular weight, than the AHS from the Carú River. The AHS studied presented a seasonal pattern characterized by higher humification levels during the rainy season. For all the metals, the AHS complexing capacity was higher for the Negro River. The highest complexing capacities were observed for the NiII assays, which were 0.56 and 0.12 µmol NiII mg-1 dissolved organic carbon (DOC), for AHS RN and AHS RC-II, respectively. We concluded that the transport, bioavailability, and toxicity, of these metal species should be higher for Carú River.

Seasonal concentrations of total, particulate and dissolved Al, Cu, Cd, Cr, Fe, Pb and Ni were analyzed in surface water and total metals in sediment samples from black and whitewater rivers within the Itacoatiara City, Central Amazon. Metals concentrations in water and sediment samples demonstrated that even though urbanization and agricultural practices are common in this region. Metal concentrations in sediments samples are acceptable regarding the recommended levels for protection of aquatic life. From this work, which is the first trace elements study in the main tributaries from Itacoatiara region, we conclude that metals are present in a particulate form, being easier to be transported to other aquatic bodies. During flooding periods an increase of Al, Fe and total organic compound (TOC) in almost water sampling points was observed.

The degradation of disperses dyes in aqueous solution and in effluents from textile industry has been investigated by photoelectrocatalytic oxidation using nanoporous thin films electrodes of Ti/TiO2. Samples of dispersil black dye and dispersil blue dye after 300 min of photoelectrolyzed at applied potential of +1.0 V and UV irradiation exhibited 100% of discoloration and 90% and 64% reduction total organic carbon, respectively. The proposed method was applied with success in a textile industry effluent containing residues of these dyes, which after 300 min of treatment leads to reduction of 60% of COD and 64% removal of TOC.

A oxidação fotoeletrocatalítica de solução 0,009% (m/v) do surfactante aniônico comercial, Tamol®, foi investigada em Na2SO4 0,1 mol L-1 empregando-se ânodos de filme fino de Ti/TiO2.Utilizando-se as melhores condições experimentais, potencial de +1,0 V, irradiação UV e pH 2,0 foi possível obter 100% de remoção do dispersante monitorado por espectrofotometria na região do UV e 94% de remoção de carbono orgânico total (COT) após 90 min de fotoeletrólise. O método foi ainda aplicado para remoção do surfactante na presença do corante acido vermelho 151 e após 90 min de tratamento observa-se que o método promove a remoção de 98% da cor concomitante à diminuição de 81% do carbono orgânico total da solução.

The photoeletrocatalytic oxidation of 0.009% (m/v) of commercial surfactant Tamol® in 0.1 mol L-1 Na2SO4 was investigated on thin-film of TiO2 as photoanode.Using the best experimental condition, E = + 1.0 V, pH 2.0 and UV irradiation were obtained 100% of surfactant removal followed by 94% of total organic carbon (TOC) removal after 90 min of photoelectrocatalytic treatment. The method was applied to surfactant removal in the presence of acid red 151 dye. After 90 min of treatment the method promoted 98% of discoloration concomitant to reduction of 81% total organic carbon of the resulting solution.