Polyaluminum chloride with high Al30 content as removal agent for arsenic-contaminated well water.

Polyaluminum chloride (PACl) is a well-established coagulant in water treatment with high removal efficiency for arsenic. A high content of Al(30) nanoclusters in PACl improves the removal efficiency over broader dosage and pH range. In this study we tested PACl with 75% Al(30) nanoclusters (PACl(Al30)) for the treatment of arsenic-contaminated well water by laboratory batch experiments and field application in the geothermal area of Chalkidiki, Greece, and in the Pannonian Basin, Romania. The treatment efficiency was studied as a function of dosage and the nanoclusters' protonation degree. Acid-base titration revealed increasing deprotonation of PACl(Al30) from pH 4.7 to the point of zero charge at pH 6.7. The most efficient removal of As(III) and As(V) coincided with optimal aggregation of the Al nanoclusters at pH 7-8, a common pH range for groundwater. The application of PACl(Al30) with an Al(tot) concentration of 1-5mM in laboratory batch experiments successfully lowered dissolved As(V) concentrations from 20 to 230 µg/L to less than 5 µg/L. Field tests confirmed laboratory results, and showed that the WHO threshold value of 10 µg/L was only slightly exceeded (10.8 µg/L) at initial concentrations as high as 2300 µg/L As(V). However, As(III) removal was less efficient (<40%), therefore oxidation will be crucial before coagulation with PACl(Al30). The presence of silica in the well water improved As(III) removal by typically 10%. This study revealed that the Al(30) nanoclusters are most efficient for the removal of As(V) from water resources at near-neutral pH.

A universal method to assess the potential of phosphorus loss from soil to aquatic ecosystems.

BACKGROUND, AIM, AND SCOPE: Phosphorus loss from terrestrial to the aquatic ecosystems contributes to eutrophication of surface waters. To maintain the world's vital freshwater ecosystems, the reduction of eutrophication is crucial. This needs the prevention of overfertilization of agricultural soils with phosphorus. However, the methods of risk assessment for the P loss potential from soils lack uniformity and are difficult for routine analysis. Therefore, the efficient detection of areas with a high risk of P loss requires a simple and universal soil test method that is cost effective and applicable in both industrialized and developing countries. MATERIALS AND METHODS: Soils from areas which varied highly in land use and soil type were investigated regarding the degree of P saturation (DPS) as well as the equilibrium P concentration (EPC(0)) and water-soluble P (WSP) as indicators for the potential of P loss. The parameters DPS and EPC(0) were determined from P sorption isotherms. RESULTS: Our investigation of more than 400 soil samples revealed coherent relationships between DPS and EPC(0) as well as WSP. The complex parameter DPS, characterizing the actual P status of soil, is accessible from a simple standard measurement of WSP based on the equation [Formula: see text]. DISCUSSION: The parameter WSP in this equation is a function of remaining phosphorous sorption capacity/total accumulated phosphorous (SP/TP). This quotient is independent of soil type due to the mutual compensation of the factors SP and TP. Thus, the relationship between DPS and WSP is also independent of soil type. CONCLUSIONS: The degree of P saturation, which reflects the actual state of P fertilization of soil, can be calculated from the easily accessible parameter WSP. Due to the independence from soil type and land use, the relation is valid for all soils. Values of WSP, which exceed 5 mg P/kg soil, signalize a P saturation between 70% and 80% and thus a high risk of P loss from soil. RECOMMENDATIONS AND PERSPECTIVES: These results reveal a new approach of risk assessment for P loss from soils to surface and ground waters. The consequent application of this method may globally help to save the vital resources of our terrestrial and aquatic ecosystems.

The origin of aluminum flocs in polluted streams.

About 240,000 square kilometers of Earth's surface is disrupted by mining, which creates watersheds that are polluted by acidity, aluminum, and heavy metals. Mixing of acidic effluent from old mines and acidic soils into waters with a higher pH causes precipitation of amorphous aluminum oxyhydroxide flocs that move in streams as suspended solids and transport adsorbed contaminants. On the basis of samples from nine streams, we show that these flocs probably form from aggregation of the epsilon -Keggin polyoxocation AlO4Al12(OH)24(H2O)12(7+)(aq) (Al13), because all of the flocs contain distinct Al(O)4 centers similar to that of the Al13 nanocluster.