Surface modified mesostructured iron oxyhydroxide: synthesis, ecotoxicity, and application.

Mesoporous iron oxide, particularly amine-functionalized FeO(x) and FeO(x), was investigated for the removal of toxic heavy metal anions of arsenic and chromium from an aqueous solution. As a control experiment for these toxic compounds, adsorption tests were also performed on Fe3O4 as their counterpart bulk chemical. The mesostructures were confirmed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscopy (TEM). In addition, we prepared stock suspensions of meso-FeO(x), amine-functionalized meso-FeO(x) and Fe3O4 particles, and compared their acute toxicity against Daphnia magna. The 24 h-EC50 values of the amine-functionalized meso-FeO(x), meso-FeO(x) and Fe particle suspensions used in this study were 1682, 2549 and 95 mg/L, respectively. Organism toxicity caused by spills of adsorbents can be negated when the amine-functionalized meso-FeO(x), up to 1500 mg/L, is used as the adsorbent for heavy metal treatment. The adsorption of arsenic and chromium by the three adsorbents were examined, and different adsorption models were used to describe the equilibrium and kinetic data. The amine-functionalized meso-FeO(x) adsorbent was found to give the maximum adsorption capacities for arsenic and chromium (33.51 and 25.05 mg/g, respectively). This research gives promising results for the application of modified meso-FeO(x) as an adsorbent of toxic heavy metal anions from aqueous solutions.

Structural, physicochemical and microbial properties of flocs and biofilms in integrated fixed-film activated sludge (IFFAS) systems.

Integrated fixed-film activated sludge systems (IFFAS) may achieve year-round nitrification or gain additional treatment capacity due to the presence of both flocs and biofilms, and the potential for multiple redox states and long solids retention time. Flocs and biofilms are distinctive microbial structures and characterization of the physicochemical and structural properties of these may provide insight into their respective roles in wastewater treatment and contaminant removal in IFFAS. Flocs and biofilms were examined from five different pilot media systems being evaluated for potential full scale implementation at a large municipal wastewater treatment plant. Flocs and biofilms within the same system possessed different surface characteristics; flocs were found to have a higher negative surface charge (-0.35 to -0.65 meq./g VSS) and are more hydrophobic (60%-75%) than biofilms (-0.05 to -0.07 meq/g VSS; 19-34%). The EPS content of flocs was significantly higher (range of 2.1-4.5 folds) than that of biofilms. In floc-derived extracellular polymeric substances (EPS), protein (PN) was clearly dominant; whereas in biofilm-derived EPS, PN and polysaccharide (PS) were present in approximately equal proportions. Biofilm EPS had a higher proportion of DNA when compared to flocs. Biofilm growth was preferential on the protected internal surfaces of the media. Colonization of the external surfaces of the media was evident by the presence of small microcolonies. The structural heterogeneity of the biofilms examined was supported by observed differences in biomass content, thickness and roughness of biofilm surface. The biofilm on the interior surface of media was found to be patchy with clusters of cells connected by an irregular arrangement of interconnecting EPS projections. Biofilm thickness ranged between 139 µm and 253 µm. The pattern of oxygen penetration is expected to be complex. Nitrifiers and denitrifiers were predominantly associated with the biofilms, and the latter were found to be dispersed throughout the film and arranged in micro-clusters, suggesting partial oxygen penetration.