Ammonia oxidation by in-situ chloride electrolysis in etching wastewater of semiconductor manufacturing using RuSnOx/Ti electrode: Effect of plating mode and metal ratio.

The indirect chloride-mediated ammonia oxidation encounters challenges in maintaining the effectiveness of metal oxide anodes when treating wastewaters with complex compositions. This study aims to develop a highly stable anode with RuO2-SnO2 coatings for treating an etching effluent from semiconductor manufacturing, which majorly contains NH3 and organic compounds. The RuSnOx/Ti electrode was synthesized using wet impregnation and calcination processes. The metal oxide configuration on Ti plate substrate was tuned by varying the step-dipping process in RuCl3 and SnCl4 baths. A 10-day continuous-flow electrolysis was conducted for studying the ammonia removal and chlorine yield under variable conditions, including detention, pH, current density, and initial ammonia and chloride concentrations. In the RuSnOx coatings, the configuration comprising RuO2 nanorods as the surface layer and an intermediate layer of SnO2 crystallites (by plating Ru3+ for three times to cover one Sn4+ layer, denoted as the Ru3Sn/Ti electrode) exhibited the best durability for acid washing, along with relatively high Faradaic efficiency and low energy consumption. To further improve the treatability of real wastewater (NH3-N = 634 mg L-1, chemical oxygen demand (COD) = 6700 mg L-1, Cl- = 2000 mg L-1, pH 11), the duel-cell electrolyzers were constructed in series under a current density of 30 mA cm-2 and 45 min detention. Ultimately, removals of NH3 and COD reached 95.8% and 76.3%, respectively, with successful limitation of chloramine formation.

Optimizing the Micro/Mesoporous Structure of Hierarchical Porous Carbon Synthesized from Petroleum Pitch Using the Solvent-Free Method for Ultra-Fast Capacitive Deionization.

In this work, a solvent-free ZnO-template method is used to synthesize hierarchical porous carbons (denoted as HPC-X; X = 1, 1.5, 2, and 4 g of ZnO) via the pyrolysis of petroleum industrial-residual pitch with ZnO. The proposed method allows precise control of the micro/meso/macroporous structure of the HPC by adjusting the amount of ZnO. The results show that the average pore size of HPCs prominently increases from 2.4 to 3.7 nm with the increase in the ZnO/pitch ratio. In addition, it is shown that HPCs have a high surface area between 1141 and 1469 m2 g-1, a wide-range pore size distribution (micro-, meso-, and macropores), and a tap density ranging from 0.2 to 0.57 g cm-3. The capacitive deionization performances of HPCs for sodium and chloride ions are investigated. The results show that HPC-2 exhibits the highest electrosorption capacity of 9.94 mg g-1 within 10.0 min and a maximum electrosorption capacity of 10.62 mg g-1 at 1.2 V in a 5.0 mM NaCl solution. Hence, HPC-2 is a highly promising candidate as an electrode material for rapid deionization.

Membrane capacitive deionization for low-salinity desalination in the reclamation of domestic wastewater effluents.

This study aims to investigate the feasibility of desalinating secondary effluent from a domestic wastewater treatment plant (DWTP) using membrane capacitive deionization (MCDI) for reclamation purposes. The desalination performance of a MCDI stack with 10 pairs of 20 cm × 20 cm activated carbon electrodes was evaluated in single-pass mode. As evidenced, the MCDI stack outperformed the capacitive deionization stack. The water quality characteristics of the inflows and product water were also analyzed. Our results revealed that MCDI can effectively remove undesired ions such as calcium and nitrate from the DWTP effluent for water reclamation. In particular, the solution conductivity of the product water was observed to be as low as 1.27 µS/cm. Removal of the ions was easily performed by the electrostatic field-assisted deionization process. The use of MCDI for low-salinity wastewater reclamation demonstrated favorable energy performance with a low volumetric energy input and a molar energy input of 0.12 kWh/m3 and 0.03 kWh/mole, respectively; and the energy efficiency of this system is expected to be further improved by energy recovery or incorporation of energy-producing processes. These results are indicative of the benefits of using MCDI as part of the treatment processes for the reclamation of wastewater with low salinity.

Capacitive deionization of arsenic-contaminated groundwater in a single-pass mode.

A single-pass-mode capacitive deionization (CDI) reactor was used to remove arsenic from groundwater in the presence of multiple ions. The CDI reactor involved an applied voltage of 1.2 V and six cell pairs of activated carbon electrodes, each of which was 20 × 30 cm2. The results indicate that this method achieved an effluent arsenic concentration of 0.03 mg L-1, which is lower than the arsenic concentration standard for drinking water and irrigation sources in Taiwan, during the charging stage. Additionally, the ability of the CDI to remove other coexisting ions was studied. The presence of other ions has a significant influence on the removal of arsenic from groundwater. From the analysis of the electrosorption selectivity, the preference for anion removal could be ordered as follows: NO3- > SO42- > F- > Cl- >As. The electrosorption selectivity for cations could be ordered as follows: Ca2+ > Mg2+ > Na+ âˆ¼ K+. Moreover, monovalent cations can be replaced by divalent cations at the electrode surface in the later period of the electrosorption stage. Consequently, activated carbon-based capacitive deionization is demonstrated to be a high-potential technology for remediation of arsenic-contaminated groundwater.

Electro-removal of arsenic(III) and arsenic(V) from aqueous solutions by capacitive deionization.

The feasibility of the electro-removal of arsenate (As(V)) and arsenite (As(III)) from aqueous solutions via capacitive deionization was investigated. The effects of applied voltage (0.0-1.2V) and initial concentration (0.1-200mgL(-1)) on arsenic removal were examined. As evidenced, an enhancement of arsenic removal can be achieved by capacitive deionization. The capacity to remove As(V) at an initial concentration of 0.2mgL(-1) on the activated carbon electrode at 1.2V was determined to be 2.47×10(-2)mgg(-1), which is 1.8-fold higher than that of As(III) (1.37×10(-2)mgg(-1)). Notably, the possible transformation of arsenic species was further characterized. The higher effectiveness of As(V) removal via electrosorption at 1.2V was attributed to the formation of an electrical double layer at the electrode/solution interface. The removal of As(III) could be achieved by the oxidation of As(III) to As(V) and subsequent electrosorption of the As(V) onto the electrode surface of the anode. The presence of sodium chloride or natural organic matter was found to considerably decrease arsenic removal. Single-pass electrosorption-desorption experiments conducted at 1.2V further demonstrated that capacitive deionization is a potential means of effectively removing arsenic from aqueous solutions.

Electro-enhanced removal of copper ions from aqueous solutions by capacitive deionization.

This study was performed to determine the feasibility of electrosorptive removal of copper ions from aqueous solutions using a capacitive deionization process. The electrosorptive potential of copper ions was determined using cyclic voltammetry measurements, and copper electrodeposition could be suppressed at a voltage less than 0.8 V. Importantly, the experimental results demonstrated a significant enhancement of electrosorption capability of copper ions using the activated carbon electrodes under electro-assistance, associated with electrical double-layer charging. At 0.8 V, the equilibrium electrosorption capacity was enhanced to 24.57 mg/g based on the Langmuir model, and the electrosorption constant rate was increased to 0.038 min(-1) simulated by a first-order kinetics model. Moreover, the activated carbon electrode showed great regeneration performance for the removal of low level copper ions. Additional experiments regarding electrosorption selectivity were performed in the presence of sodium chloride, natural organic matter, or dissolved silica. Copper ions that were preferentially electroadsorbed on the electrode surface can be effectively removed in a competitive environment. Therefore, the electrosorption process using activated carbon electrodes can be recommended to treat copper solutions at low concentrations for wastewater treatment and water purification.