The South Brazilian Bight (SBB) is a hydrographically dynamic environment with strong seasonality that sustains a diverse planktonic community involved in diverse biogeochemical processes. The inherent optical properties (IOPs; e.g., absorption and scattering coefficients) of optically actives constituents of water (OACs; phytoplankton, non-algal particles–NAP, and colored dissolved organic matter–CDOM) have been widely employed to retrieve information on biogeochemical parameters in the water. In this study conducted in the SBB, a cross-shelf transect was performed for biogeochemistry and hydrographic sampling during a summer expedition. Our research aimed to determine the distribution and amount of the OACs based on their spectral signature, in relation to the distribution of water masses in the region. That allows us to get insights into the biogeochemical processes within each water mass and in the boundaries between them. We observed a strong intrusion of South Atlantic Central Water (SACW) over the shelf, mainly driven by the wind action. With that, phytoplankton development was fueled by the input of nutrients, and increased chlorophyll-a (Chl-a) concentrations were observed within the shallowest stations. Colored dissolved organic matter did not follow the distribution of dissolved organic carbon (DOC). Both CDOM and DOC presented high values at the low salinity Coastal Water (CW), as an indication of the continental influence over the shelf. However, CDOM was inversely correlated with salinity and lowest values were observed within Tropical Water (TW), whereas DOC values within TW were as high as within CW, indicating an autochthonous DOM source. Additionally, a deep Chl-a maximum (DCM) was noticed in the boundary between the TW and SACW. Along with the DCM, we observed the production of fresh, non-colored DOM attributed to the microbial community. Finally, our results suggest that CDOM is photodegraded at the surface of CW. This is mainly due to the Ekman transport effect over the region that traps CW at the surface, making it longer exposed to solar radiation.

Mining of sulfide minerals produces acidic effluents rich in soluble metals and sulfate. The effluents pose a risk to the environment and must therefore be treated prior to their release. Conventionally, effluents are neutralized, and remaining metals are precipitated as hydroxides by means of alkaline minerals or industrial chemicals. The process leads to a formation of large amounts of disposable sludge containing valuable metals. Efforts are needed for more sustainable and resource efficient water treatment in the spirit of circular economy. Nanofibrillated cellulose (NFC) adsorbents are a promising and sustainable alternative to conventional treatments as cellulose is the most abundant natural polymer. In addition, NFC can be prepared from industrial byproducts and its surface properties can easily be modified to adsorb pollutants with different chemical properties. Understanding the adsorption mechanisms is essential for the rational development and use of NFC in water treatment and environmental protection in the future. Based on previous studies, anionic NFC retains metal cations and sulfate anions simultaneously from aqueous solutions. However, the adsorption mechanisms in conditions comparable to e.g. authentic mining water with high metal salt concentrations are poorly understood. In this Master’s Thesis work, adsorption experiments with pure metal salt solutions of increasing metal concentrations (0-800 mM) were carried out to investigate the adsorption mechanisms of metal cations and anions. Based on previous studies five cations with different chemical properties were chosen: Na⁺, Mg²⁺, Mn²⁺, Al³⁺ ja Fe³⁺. The adsorption was examined in both metal chloride and sulfate solutions to also elucidate the co-adsorption of counter ions and their possible effects on metal adsorption on NFC. The Freundlich adsorption isotherm model was utilized to analyze the adsorption of metals. In addition, removal percentages were calculated for both metal cations and their counter anions. NFC was observed to retain all metal cations equally regardless of their different properties and pH-values of the metal salt solutions. The removal percentage of both cations and anions ranged mainly between 14–20 % and the removal capacity of NFC decreased only slightly with increasing initial concentrations. No remarkable differences were observed in the adsorption isotherms of different metals and the adsorption was almost linear in the whole concentration range. Despite the relatively low removal percentages, the amounts of metals adsorbed by NFC (mmol/g dry weight) were tenfold compared to those previously obtained in many studies. According to the results, NFC adsorbed cations non-specifically with weak interactions and the dominating adsorption mechanism resembles physical rather than chemical adsorption. Upon the adsorption of cations, an equal amount of negative charge was co-adsorbed and hence the adsorption of anions was deemed electrostatic in nature.