Use of a Novel Bio-Nano-IX Process to Remove SeO₄^2– or Se(VI) from Contaminated Water in the Presence of Competing Sulfate (SO₄^2–)

Abstract

Removal of trace concentrations of selenium, mostly present as selenate or SeO4 2–, from contaminated water and wastewater or SO4 2– presents a formidable challenge that remains unsolved. A new hybrid bio-nano-ix process presented here provides a synergy where selenate (SeO4 2–) is first biologically reduced first to selenite (HSeO3 –) under a relatively mild anoxic condition without producing H2S. Selenite, thus produced, is a relatively strong ligand and has a much higher sorption affinity for hybrid anion exchangers (HAIX-NanoFe) than competing sulfate anions. Extensive laboratory studies provided convincing evidence that the two-step bio-nano-ix processa fixed-film biological unit followed by a HAIX-NanoFe sorption columnmay very selectively remove Se­(VI) or SeO4 2– in the presence of competing sulfate. HAIX-NanoFe is also amenable to efficient regeneration and reuses without any loss of selenite sorption capacity for multiple cycles. The sorbed selenium could thus be concentrated and recovered, thus posing no environmental threat of future contamination.

CO2 Utilization for Water Treatment: Ion Exchange Nitrate Removal Driven by CO2 without Producing Spent Brine Regenerant

“…Nitrate removal was not affected by the doped ZrOnp because of the dual functionality of NSR-NanoZr, where the tributyl quaternary ammonium groups in the host NSR beads functioned independently from the ZrOnp sites . Similar resins as NSR-NanoZr have been reported for selectively removing arsenic, silica, phosphate, and selenium. − Thus, the results with NSR-NanoZr indicate the system versatility by potentially adopting different selective anion exchangers in different decontamination applications. Due to the much longer treatment cycle (over 1000 BVs) of fluoride removal than nitrate removal, fluoride regeneration required a much lower frequency using conventional chemicals such as 1–5% NaOH .…”

Direct air capture (DAC) and sequestration of CO 2 : Dramatic effect of coordinated Cu(II) onto a chelating weak base ion exchanger

“…), is essentially a ternary complex in which coordination numbers of Cu(II) are partly satisfied by nitrogen donor (N-donor) atoms in the polymer phase, while its two positive charges and remaining coordination numbers are satisfied by carbonate and water. Previous studies have demonstrated that the hybrid metal-ion exchangers, once appropriately designed, are suitable for selective removal of target contaminants, such as arsenic, phosphate, ammonia, fluoride, and others (26)(27)(28)(29)(30)(31). However, their applications so far have been limited only to aqueous phase separations.…”

Resilient Nitrate Removal by a Biological Nitrate-Selective Ion Exchange (BIO-NIX) Process

“…The ceramic material (BIO-DN cubes, Metamateria, Columbus, OH) contains hierarchical pore structures and is highly porous (average surface area of >20,000 m 2 /m 3 ) compared to widely used plastic host materials, which enhances water flow rates and improves denitrification kinetics (details in Table S2). , A nitrate-selective resin (A520E, Purolite) was used in the NIX column, which has tributyl quaternary ammonium functional groups (−((CH 2 ) 3 CH 3 ) 3 N + ) in a polystyrene–divinylbenzene matrix. The tributyl groups significantly enhance the nitrate selectivity compared to typical strong base anion exchange resins (details in Table S3).…”

“…However, both techniques face challenges as stand-alone processes. The BIO process uses bacteria to convert nitrate to nitrogen gas, which represents one of the most sustainable decontamination methods without demanding extensive energy and chemicals. , However, BIO lacks the resiliency in handling impulsive fluctuations in influent and system parameters (e.g., flow rate). − The kinetics of the BIO process is also slow compared to physical–chemical methods such as NIX . NIX uses nitrate-selective ion exchange resin to remove nitrate by exchanging it with innocuous ions such as chloride. , NIX is kinetically fast and resilient in handling influent fluctuations and system parameter changes. , However, regenerating nitrate-selective ion exchange resin requires high-concentration brine (e.g., 10–15% NaCl solution). , The intensive chemical consumption of NIX makes the technique unsustainable in the carbon-neutral era due to associated energy penalties and carbon emissions in chemical production and transportation. ,, Additionally, brine disposal has led to increasing bans in many regions such as California due to its potential contributions to salinity elevation in the watershed .…”

“…9−11 The kinetics of the BIO process is also slow compared to physical−chemical methods such as NIX. 12 NIX uses nitrate-selective ion exchange resin to remove nitrate by exchanging it with innocuous ions such as chloride. 13,14 NIX is kinetically fast and resilient in handling influent fluctuations and system parameter changes.…”