Modular Advanced Oxidation Process Enabled by Cathodic Hydrogen Peroxide Production

Hydrogen peroxide (H₂O₂) is frequently used in combination with ultraviolet (UV) light to treat trace organic contaminants in advanced oxidation processes (AOPs). In small-scale applications, such as wellhead and point-of-entry water treatment systems, the need to maintain a stock solution of concentrated H₂O₂ increases the operational cost and complicates the operation of AOPs. To avoid the need for replenishing a stock solution of H₂O₂, a gas diffusion electrode was used to generate low concentrations of H₂O₂ directly in the water prior to its exposure to UV light. Following the AOP, the solution was passed through an anodic chamber to lower the solution pH and remove the residual H₂O₂. The effectiveness of the technology was evaluated using a suite of trace contaminants that spanned a range of reactivity with UV light and hydroxyl radical (HO^•) in three different types of source waters (i.e., simulated groundwater, simulated surface water, and municipal wastewater effluent) as well as a sodium chloride solution. Irrespective of the source water, the system produced enough H₂O₂ to treat up to 120 L water d^–1. The extent of transformation of trace organic contaminants was affected by the current density and the concentrations of HO^• scavengers in the source water. The electrical energy per order (<i>E</i>_EO) ranged from 1 to 3 kWh m^–3, with the UV lamp accounting for most of the energy consumption. The gas diffusion electrode exhibited high efficiency for H₂O₂ production over extended periods and did not show a diminution in performance in any of the matrices

Concomitant Leaching and Electrochemical Extraction of Rare Earth Elements from Monazite

Rare earth elements (REEs) have become increasingly important in modern day technologies. Unfortunately, their recycling is currently limited, and the conventional technologies for their extraction and purification are exceedingly energy and chemical intensive. New sustainable technologies for REE extraction from both primary and secondary resources would be extremely beneficial. This research investigated a two-stage recovery strategy focused on the recovery of neodymium (Nd) and lanthanum (La) from monazite ore that combines microbially based leaching (using citric acid and spent fungal supernatant) with electrochemical extraction. Pretreating the phosphate-based monazite rock (via roasting) dramatically increased the microbial REE leaching efficiency. Batch experiments demonstrated the effective and continued leaching of REEs by recycled citric acid, with up to 392 mg of Nd L^–1 and 281 mg of La L^–1 leached during seven consecutive 24 h cycles. Neodymium was further extracted in the catholyte of a three-compartment electrochemical system, with up to 880 mg of Nd L^–1 achieved within 4 days (at 40 A m^–2). Meanwhile, the radioactive element thorium and counterions phosphate and citrate were separated effectively from the REEs in the anolyte, favoring REE extraction and allowing sustainable reuse of the leaching agent. This study shows a promising technology that is suitable for primary ores and can further be optimized for secondary resources

Transmission electron microscopy (TEM) images of thin sections of the five different bacterial species, loaded with platinum particles.

<p>The precipitation of platinum was induced by the presence of hydrogen gas. No Pt particles were observed during the recovery of cisplatin by <i>Bacillus toyonensis</i> and <i>Pseudomonas stutzeri</i>, while <i>Geobacter metallireducens</i> was not studied for this complex.</p

An overview of the platinum recovery efficiencies (%) at pH 2 is given; the Pt recovery was investigated with and without (sorption control) the addition of H₂-gas.

<p>The platinum recovery was studied using five different bacterial species and five Pt-complexes (n = 1). All recoveries were measured after 48 h, except for: * 68 h, ** 107 h and *** 168 h, and **** 320 h. The chemical reduction was studied for all Pt-species using H₂-gas.</p

The effect of the addition of Pt(II)Cl42- on the membrane integrity of different bacterial cells during platinum recovery as a function of time.

<p>Four different bacterial cultures were studied; <i>Shewanella oneidensis</i> MR-1, <i>Cupriavidus metallidurans</i> CH34, <i>Bacillus toyonensis</i> and <i>Pseudomonas stutzeri</i>. The recovery experiment was started at t₀ by the addition of 100 mg L^-1 Pt and H₂-gas as electron donor. The pH was initially set at pH 2.0.</p

X-ray absorption near edge spectroscopy (XANES) spectra of biomass pellet samples after Pt(II)Cl42- recovery (100 mg L^-1 Pt; 50 mg L^-1 Pt in case of anaerobic <i>S</i>. <i>oneidensis</i>), by three bacterial species: <i>Geobacter metallireducens</i>, <i>Cupriavidus metallidurans</i> CH34 and <i>Shewanella oneidensis</i> MR-1.

<p>X-ray absorption near edge spectroscopy (XANES) spectra of biomass pellet samples after Pt(II)Cl42- recovery (100 mg L^-1 Pt; 50 mg L^-1 Pt in case of anaerobic <i>S</i>. <i>oneidensis</i>), by three bacterial species: <i>Geobacter metallireducens</i>, <i>Cupriavidus metallidurans</i> CH34 and <i>Shewanella oneidensis</i> MR-1.</p

X-ray absorption near edge spectroscopy (XANES) spectra of biomass pellet samples after Pt(IV)Cl62- recovery (100 mg L^-1 Pt; 50 mg L^-1 Pt in case of anaerobic <i>Shewanella</i>), by two bacterial species: <i>Geobacter metallireducens</i> and <i>Shewanella oneidensis</i> MR-1.

<p>X-ray absorption near edge spectroscopy (XANES) spectra of biomass pellet samples after Pt(IV)Cl62- recovery (100 mg L^-1 Pt; 50 mg L^-1 Pt in case of anaerobic <i>Shewanella</i>), by two bacterial species: <i>Geobacter metallireducens</i> and <i>Shewanella oneidensis</i> MR-1.</p

Biogenic Nanopalladium Based Remediation of Chlorinated Hydrocarbons in Marine Environments

Biogenic catalysts have been studied over the last 10 years in freshwater and soil environments, but neither their formation nor their application has been explored in marine ecosystems. The objective of this study was to develop a biogenic nanopalladium-based remediation method for reducing chlorinated hydrocarbons from marine environments by employing indigenous marine bacteria. Thirty facultative aerobic marine strains were isolated from two contaminated sites, the Lagoon of Mar Chica, Morocco, and Priolo Gargallo Syracuse, Italy. Eight strains showed concurrent palladium precipitation and biohydrogen production. X-ray diffraction and thin section transmission electron microscopy analysis indicated the presence of metallic Pd nanoparticles of various sizes (5–20 nm) formed either in the cytoplasm, in the periplasmic space, or extracellularly. These biogenic catalysts were used to dechlorinate trichloroethylene in simulated marine environments. Complete dehalogenation of 20 mg L^–1 trichloroethylene was achieved within 1 h using 50 mg L^–1 biogenic nanopalladium. These biogenic nanoparticles are promising developments for future marine bioremediation applications

Electrolytic Membrane Extraction Enables Production of Fine Chemicals from Biorefinery Sidestreams

Short-chain carboxylates such as acetate are easily produced through mixed culture fermentation of many biological waste streams, although routinely digested to biogas and combusted rather than harvested. We developed a pipeline to extract and upgrade short-chain carboxylates to esters via membrane electrolysis and biphasic esterification. Carboxylate-rich broths are electrolyzed in a cathodic chamber from which anions flux across an anion exchange membrane into an anodic chamber, resulting in a clean acid concentrate with neither solids nor biomass. Next, the aqueous carboxylic acid concentrate reacts with added alcohol in a water-excluding phase to generate volatile esters. In a batch extraction, 96 ± 1.6% of the total acetate was extracted in 48 h from biorefinery thin stillage (5 g L^–1 acetate) at 379 g m^–2 d^–1 (36% Coulombic efficiency). With continuously regenerated thin stillage, the anolyte was concentrated to 14 g/L acetic acid, and converted at 2.64 g (acetate) L^–1 h^–1 in the first hour to ethyl acetate by the addition of excess ethanol and heating to 70 °C, with a final total conversion of 58 ± 3%. This processing pipeline enables direct production of fine chemicals following undefined mixed culture fermentation, embedding carbon in industrial chemicals rather than returning them to the atmosphere as carbon dioxide