Methods and systems for reducing the concentration of selenium species in water, particularly water containing recalcitrant selenium species. In the methods and systems, water containing one or more selenium species is treated with permanganate to provide permanganate-treated water, which is then contacted with a zero-valent iron treatment system comprising (a) a reactive solid comprising zero-valent iron and one or more iron oxide minerals in contact therewith and (b) ferrous iron.

The present disclosure relates to methods of treating water to remove contaminants, including harmful metal ions, and water treatment plants for practicing such methods. In an embodiment, the process includes adding a sulfur-containing, metal-decreasing agent; an iron (III)-containing, metalloid-decreasing agent; forming a solid precipitate from the contaminated water, wherein the solid precipitate includes a solid metal sulfide, a solid iron metalloid, a solid calcium metalloid, or a combination thereof; and separating the contaminated water from the solid precipitate to form purified water.

Methods and systems for removal of ions from aqueous fluids are provided. In certain embodiments, the present disclosure provides a method of removing one or more oxyanions from an aqueous fluid, including the steps of contacting an aqueous fluid containing oxyanions with an aluminum metal whereby aluminum ions are released from the aluminum metal into the aqueous fluid, wherein the one or more oxyanions in the aqueous fluid react with the aluminum ions to form one or more ettringites; controlling a rate of release of the aluminum ions from the aluminum metal; and removing at least a portion of precipitated ettringites from the aqueous fluid.

Methods for treating water containing a target anion to remove the target anion can include preparing a treatment composition solution that contains a metal treatment agent, adjusting the treatment composition solution to a first pH that is alkaline and then to a second pH that is acidic, and contacting the treatment composition solution with the water that contains the target anion.

A method of reducing selenium contamination in a waste water stream is described herein. The method includes channeling a flue gas stream through an absorber, contacting the flue gas stream with an aqueous alkaline-based slurry, such that any selenium byproduct in the flue gas stream forms a selenium compound within the aqueous alkaline-based slurry, controlling oxidation of the selenium compound in the aqueous alkaline-based slurry, and adding a precipitation agent to the aqueous alkaline-based slurry to cause the selenium compound within the aqueous alkaline-based slurry to precipitate.

Processes are provided for the kinetically efficient reduction of selenate species to selenide species using chromous ions in acidic solution. This reduction may advantageously be carried out in the presence of sulphate species, with selective selenate reduction in preference to the reduction of sulfate. The reduced selenate may be removed from the chromous-treated solution, for example by precipitation of a copper-selenide solid. The chromic ions formed by reaction of chromous ions in the reduction of selenate may also be removed from solution, for example by addition of a base to form an insoluble chromic hydroxide solid. The chromic hydroxide may be recycled to regenerate chromous ions, for example by electrolysis. In this way, systems are provided for continuously removing dissolved selenium from wastewater streams.

Methods are disclosed for treating water containing a target anion to remove the target anion. The methods can include preparing a treatment composition solution that contains a metal treatment agent, adjusting the treatment composition solution to a first pH that is alkaline and then to a second pH that is acidic, and contacting the treatment composition solution with the water that contains the target anion.

A water purification apparatus and a water purification method capable of effectively using a layered double hydroxide and easily being applied are described. A water purification apparatus for removing a polluted substance from polluted water includes a solid-liquid separator that separates the polluted water and a solid material from each other, and a polluted substance remover that removes, by a layered double hydroxide, the polluted substance contained in the polluted water separated by the solid-liquid separator.

Methods for reducing the concentration of one or more contaminants in water using zero-valent iron media. In the method, a mixed aluminum (III) and iron (II) salt solution is added to water containing one or more contaminants that is in contact with a zero-valent iron media that comprises (a) a reactive solid comprising zero-valent iron and one or more iron oxide minerals in contact therewith and (b) magnetite to provide an aqueous reaction medium. The aqueous reaction medium is contacted with the zero-valent iron media for a period of time sufficient to reduce the concentration of one or more of the contaminants.

Systems and methods for treating a metal or metalloid ion-contaminated liquid are provided. The method may include (i) feeding the metal or metalloid ion-contaminated liquid into a bioelectrochemical reactor containing a bacteria selected by the cathode to produce extracellular metal or metalloid nanoparticles; and (ii) operating the bioelectrochemical reactor anaerobically to reduce the metal or metalloid ions in the metal or metalloid ion-contaminated liquid to extracellular metal or metalloid nanoparticles. The method may further include separating the metal or metalloid nanoparticles from the bacteria with no energy input. A bioelectrochemical reactor system for production of extracellular metal and metalloid nanoparticles may include a bioelectrochemical reactor, a separation device, and a tangential flow filtration unit.