Interaction of Magnesium–Iron–Carbonic-Layered Double Hydroxides with As(III)

Static granular bed reactor (SGBR) and upflow anaerobic sludge blanket (UASB) reactor were demonstrated at mesophilic condition for the treatment of pulp and paper mill wastewater. The hydraulic retention times (HRTs) were varied from 4 to 24 h following 29-day start-up period. The overall chemical oxygen demand (COD) removal efficiency of the SGBR was higher than the UASB during this study. At 4 h HRT, the COD removal was greater than 70 % for the SGBR and 60 % for the UASB. Biomass yield and volatile fatty acids concentration of SGBR were slightly less than UASB at organic loading rates ranging from 1.2 to 5.1 kg/m³/day. The results indicated that the SGBR system can be considered a viable alternative system for anaerobic treatment for pulp and paper wastewater.     

Biotic and Abiotic Schwertmannites as Scavengers for As(III): Mechanisms and Effects

Arsenic mobility around mining districts is primarily controlled by distribution and abundance of iron minerals. Arsenite-rich mine waters although frequently reported, the interaction of which with schwertmannite is poorly understood despite its high toxicity and mobility. We examined three synthetic schwertmannite types distinguished by surface area (19.9?C227.5?m²/g), Fe/S molar fractions (4.7?C6.6), and saturation index (?1.6?C0.8) towards arsenite retention through controlled batch equilibrium studies at 22?±?2°C and 1 atmospheric pressure in oxic conditions. Sorption isotherms were investigated as a function of dissolved arsenite concentrations (0.13?C1.33?mmol/L) at constant sediment load (10?g/L) and pH (3.0) in order to understand the role of synthesis pathway and physicochemical properties on arsenite immobilization. Multilayer surface coverage with more than one process governs arsenite uptake. X-ray diffractograms, infrared spectroscopy, and high resolution electron microscopic examination revealed new phase formation where schwertmannite underwent morphological and structural degradation. Ionic exchange between schwertmannite SO ₄ ^2? and aqueous arsenite has resulted in an elevated aqueous SO ₄ ^2? that varied according to dissolved arsenite concentrations. Stoichiometric calculations showed that 1?mol of dissolved arsenite can effectively replace 0.12?C0.19?mol of schwertmannite SO ₄ ^2? . This study implies that schwertmannites can be used as potential adsorbents for arsenite treatment where the total uptake will be strongly controlled by both ion exchange and surface precipitation.