Disclosed are systems and processes for the removal and conversion of pollutants in water. A system includes a set of electrodes with at least one electrode having an integrated catalyst material. The system is operatable in a first, electrodialysis mode in which one or more pollutants are separated from a feedwater stream, and a second electrolysis mode in which the separated pollutant(s) are catalytically converted into benign products by way of the catalyst material of the electrode. Electrodialysis and electrolysis are therefore carried out using the same unit.

The object is to provide a wastewater treatment method and a wastewater treatment system that reduce the total selenium concentration of treated water while reducing cost compared to conventional methods of removing selenium by oxidation. In the wastewater treatment method according to the present disclosure, an iron agent is added to waste water containing selenium and cyanogen to form a first coagulated substance, the first coagulated substance is removed by solid-liquid separation to obtain first treated water, a second iron agent is added to the first treated water, an acid is added to the first treated water to obtain acidic water, an oxidizing agent is added to the acidic water to oxidize the selenium, a coagulant is then added to form a second coagulated substance, and the second coagulated substance is removed by solid-liquid separation to obtain second treated water.

A method of treating water to remove selenium and/or mercury that is dissolved in the water. The method includes adding an acid to the water to reduce the pH, adding a metal reagent to the water that is effective to reduce the selenium and/or mercury to a lower oxidation state, and then removing the reduced selenium and/or mercury from the water.

An organic polymer composition (OPC) comprising guanidinium-containing A units interconnected with B units of the formula *—R*).sub.r, wherein each asterisk (*) in A units denotes a connection point with an asterisk in B units; R is a hydrocarbon linking group containing at least one carbon atom; r is an integer of 1, 2, or 3; and the composition necessarily includes an anionic species X.sup.m− with a magnitude of charge m of at least 1, wherein the sum of negative charge provided by anionic species X.sup.m− counterbalances the total positive charge provided by the A units. Also described herein is a method for removing one or more oxoanions from an aqueous source by (i) contacting the aqueous source with the above described OPC to result in absorption of the oxoanion into the OPC to produce an oxoanion-containing OPC; and (ii) removing the oxoanion-containing OPC from the aqueous source.

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.

Systems and methods for removing heavy metals such as selenium from wastewater with zero valent iron media. Air may be introduced directly into a reaction zone of a fluidized bed reactor filled with the media to catalyze treatment.

The present invention is directed to a ligated metal-organic framework (MOF) for use in removing both anionic and cationic species from a liquid or liquid stream. The present invention also provides methods for placing the MOF on a substrate to form a MOF-containing product that can be used in the removal of certain species from a given fluid. The MOF may be a Zr-based MOF, such as NU-1000, for removal of certain anions, such as oxy-anions, or having an attached thiosulfonyl-thiol (—SO.sub.2—S—R.sub.2—SH, where R.sub.2 is an alkyl group) ligand for complexation with certain cationic species in addition to the anions. The substrate may be any substrate to which a given MOF may be attached, including inert polypropylene polymer resin beads, a macroscopic fabric such as a mesh material or mesh filter, and a molecular fabric.

The description relates to a composition and a method for reducing the concentration of selenium in water. Contaminated water is contacted with a kaolinite clay characterized by a removal efficiency for selenatearsenate of at least 40 wt % at ambient temperature. The adsorption process is fast. Following sufficient contact, the water is separated from the kaolinite clay. In a preferred form, the kaolinite clay has high surface acidity.

Methods and systems for reducing the concentration of selenocyanate in water. In the methods and systems, water containing selenocyanate is treated an oxidant to provide oxidant-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.

A method of removing cations from water and a process arrangement for performing the method, wherein the method includes containing cations selected from a group consisting of Se, As, Sb, Cr, Mn, Mo, W, V, Te, P, Si including preparing an iron precipitate-containing sludge by electrochemical water treatment, wherein the water is led through an electrochemical water treatment unit, wherein electricity dissolves iron from an anode to the water thereby forming an iron precipitate-containing sludge to which cations to be removed are adsorbed/co-precipitated, adsorption and co-precipitation enhancing to provide a very high density sludge having an iron precipitate concentration of 50-400 g/l thereby further adsorbing cations contained in the water, and separating solids from the obtained sludge thereby producing treated water having a reduced cation content and solids comprising iron precipitate compounds and adsorbed/co-precipitated cation compounds.