A HYBRID SYSTEM INCORPORATING A PIPE REACTOR AND MICROFILTRATION FOR BIOLOGICAL IRON, MANGANESE AND ARSENIC REMOVAL FROM ANAEROBIC GROUNDWATER

摘要

In the present work the removal of As(Ⅲ) and As(Ⅴ) from groundwater was studied by the application of biological oxidation of dissolved iron and manganese in a pipe reactor (PR), followed by microfiltration (MF). The examined groundwater (Berlin, Marienfelde) contained average Fe(II) and Mn(II) concentrations of 2.9 and 0.6 mg/L, respectively. Oxidation of these metals provided sufficient adsorption sites and therefore, arsenic species were removed from groundwater very efficiently. From initial arsenic concentrations in the range 20 to 250 μg/L, the residual concentrations were in all cases below 10 μg/L. A significant advantage of this technology is the uptake of oxidized iron and manganese onto recirculated suspended solids which flocculated in the pipe reactor, thus eliminating the need for mechanical cleaning of the membrane, while keeping the Trans-Membrane Pressure (TMP) constantly low. Furthermore, the As(Ⅴ) removal capacity - in terms of μg As(Ⅴ) removed per mg Fe(Ⅲ) - of this hybrid PR-MF unit was found to be significantly higher than that achieved by conventional coagulation - filtration with Fe(Ⅲ). The presence of phosphate at concentrations up to 1.6 mg/L did not exercise any negative impact on As(Ⅲ) removal from initial As(Ⅲ) concentrations of 100 μg/L. Conclusively, the proposed PR-MF process efficiently removes iron, manganese and arsenic without the use of chemical reagents for oxidation or pH adjustment, and without the need for regular regeneration or backwashing, and thus it follows the principles of green chemistry.