Improved desalination performance of flow-electrode capacitive deionisation by a novel drop-shape channel.

As an emerging desalination technology, flow-electrode capacitive deionisation (FCDI) has the advantages of theoretically infinite adsorption capacity and applicability to high-concentration brine. However, during the operation of FCDI, the flow electrode in the S-shape channel is prone to sedimentation and clogging the channel. This undesirable phenomenon brings low efficiency and security issues. Therefore, a drop-shape channel was designed for FCDI to improve the flow regime of the flow electrode. The flow simulation of the drop-shape channel was performed to select the appropriate geometry to avoid the formation of the vortex and low-velocity region. The simulation results showed that the streamlined design of the drop-shape channel has insignificant velocity gradients. It significantly reduces the low-velocity region and improves the phenomenon of particle sedimentation. The desalination performance with varieties of electrode flow rate, AC content, and voltage was used to investigate the advantage between S-shape and drop-shape channels. It was found that under the conditions of low flow rate, high AC content, and high voltage, the drop-shape channel FCDI system could still obtain better ASRR and CE.

A preliminary attempt at capacitive deionization with PVA/PSS gel coating as an alternative to ion exchange membrane.

PVA/PSS composite gel membrane electrode for membrane capacitive deionization (MCDI) was fabricated and characterised in the present study. The composite electrode with ion exchange surface is prepared by coating glutaraldehyde cross-linked polyvinyl alcohol (PVA) composite hydrogel, with Poly (Sodium 4-Styrenesulfonate) (PSS) added into the network, on the surface of activated carbon (AC) electrode. The feasibility of the gel membrane is analyzed by rheological, swelling rates and ion exchange capacity tests. Then electrochemical test and desalination test are used to study the performance of the MCDI electrode. The results show that coating of composite hydrogel layer improved the hydrophilicity, specific capacitance and lower interfacial electron transfer resistance of the electrode. Finally, we assemble the asymmetrical CDI cell with PVA/PSS composite gel electrode and AC electrode. Compared with the AC electrode, the salt adsorption capacity of PVA6-PSS15 can reach 18.9 mg g-1 and stable charge efficiency at 73.0% at operating voltage of 1.2 V. The decrease in specific capacitance of PVA6-PSS15 after 50 cycles is 1.33%, indicating that the electrode has a good cycling life. The gel membrane coated electrode prepared by PSS provides a new idea for the development of MCDI.

Effect of anion-exchange membrane type for FCDI performance at different concentrations.

Brackish water was an important alternative source of freshwater. Desalination using flow electrode capacitive deionization (FCDI) needs to explore the role of ion exchange membranes (IEM) of FCDI. In this study, brackish water was desalinated using FCDI, and anion exchange membranes with different characteristics were used in the FCDI cell to investigate their influence. The result showed that the membrane polymer matrix was the main influencing factor for ion transport. Ion exchange capacity (IEC) has a huge impact that low IEC made the various ion transport priority. Low IEC not only limits ion transport but also leads to ion leakage in seawater. Resistance had a significant blockage to the effect with weak intensity.

Low-nitrite generation Cu-Co/Ti cathode materials for electrochemical nitrate reduction.

In order to reduce by-product nitrite, a more toxic compound than nitrate, and increase high value-added products ammonia in the electrochemical reduction nitrate process, the novel Cu-Co/Ti cathode material was applied in this process. In this paper, the electrochemical process was carried out in a single compartment electrolytic cell, and with Cu-Co/Ti electrode as cathode, identifying the effects of current density, pH, electrolytes in the nitrate reduction, and the distribution of products. The Cu-Co/Ti cathode exhibited 94.65% NO3--N (nitrate-N) removal, 0.18% NO2--N (nitrite-N) generation, and 40.86% NH4--N (ammonia-N) generation with the assistance of Na2SO4 electrolyte in 6 h at 10 mA cm-2 and pH 6. Compared with the Cu/Ti cathode, the higher nitrate removal ratio and lower nitrite generation ratio were obtained on the Cu-Co/Ti cathode. The excellent performance of Cu-Co/Ti cathode is ascribed to the synergy of Cu and Co, which couples the facilitation of nitrate conversion to nitrite and the acceleration of nitrite reduction on the Cu-Co/Ti cathode. The LSV curves showed that nitrate and nitrite might undergo indirect and direct reduction reactions on Cu-Co/Ti cathode. The possible pathways of nitrate reduction on the Cu-Co/Ti cathodes were proposed. These results highlight the viability of using the Cu-Co/Ti cathode developed at this work for the nitrate removal from contaminated waters. This study achieved low-nitrite generation by Cu-Co/Ti cathode during electrochemical nitrate reduction.

Electrochemical degradation of chloramphenicol using Ti-based SnO2-Sb-Ni electrode.

Antibiotic residues may be very harmful in aquatic environments, because of limited treatment efficiency of traditional treatment methods. An electrochemical system with a Ti-based SnO2-Sb-Ni anode was developed to degrade a typical antibiotic chloramphenicol (CAP) in water. The electrode was prepared using a sol-gel method. The performance of electrode materials, impact factors and dynamic characteristics were evaluated. The Ti-based SnO2-Sb-Ni electrode was compact and uniform as shown by characterization using SEM and XRD. The electrocatalytic oxidation of CAP was carried out in a single-chamber reactor by using a Ti-based SnO2-Sb-Ni electrode. For 100 mg L-1 CAP, the CAP removal ratio of 100% and the TOC removal ratio of 60% were obtained at the current density of 20 mA cm-2 and in a neutral electrolyte at 300 min. Kinetic investigation has shown that the electro-oxidation of CAP on a Ti-based SnO2-Sb-Ni electrode displayed a pseudo-first-order kinetic model. Free radical quenching experiments presented that the oxidation of CAP on Ti-based SnO2-Sb-Ni electrode resulted from the synergistic effect of direct oxidation and indirect oxidation (·OH and ·SO4-). Doping Ni on the Ti/SnO2-Sb electrode for CAP degradation was presented in this paper, showing its great application potential in the area of antibiotic and halogenated organic pollutant degradation.

Treatment performance and microbial community under ammonium sulphate wastewater in a sulphate reducing ammonium oxidation process.

A laboratory testing of simultaneous removal of ammonium and sulphate was studied from the sulphate reducing ammonium oxidation (SRAO) process in a circulating flow completely anaerobic bioreactor. Three different stages of starting SRAO process were studied, and final batch tests analysis of SRAO process was conducted. During the SRAO process, the influent concentrations of NH4+-N and SO42- were controlled to be 80-180 and 300-969 mg L-1 respectively. The highest removal efficiencies of NH4+-N and SO42--S were up to 94.80% and 52.57%. N/S [n(NH4+-N)/n(SO42--S)] conversion rates during the experiment had not been unified, which may be caused by the experiment's complex process. In order to further validate the biochemical interaction between ammonium and sulphate, batch tests were carried out. The extra electron acceptor, such as bicarbonate, was thought to react with ammonium by bacteria. The increase of NO3- production and HCO3- removal in the effluent indicated the occurrence of the new interaction between N-C. NH4+ was converted to NO2- and NO3-. Planctomycetes, Proteobacteria, Chloroflexi and Acidobacteria were detected in the anaerobic cycle growth reactor. The conversion of SRAO was mainly caused by the high performance of Planctomycetes. These results showed that nitrogen was converted by the partial nitrifying process, the denitrification process, and the traditional anammox process simultaneously with the SRAO process.

Effect of nitrite and nitrate on sulfate reducing ammonium oxidation.

The effects of nitrite and nitrate on the integration of ammonium oxidization and sulfate reduction were investigated in a self-designed reactor with an effective volume of 5 L. An experimental study indicated that the ammonium oxidization and sulfate reduction efficiencies were increased in the presence of nitrite and nitrate. Studies showed that a decreasing proportion of N/S in the presence of NO2 - at 30 mg·L-1 would lead to high removal efficiencies of NH4 +-N and SO4 2--S of up to 78.13% and 46.72%, respectively. On the other hand, NO3 - was produced at approximately 26.89 mg·L-1. Proteobacteria, Chloroflexi, Bacteroidetes, Chlorobi, Acidobacteria, Planctomycetes and Nitrospirae were detected in the anaerobic cycle growth reactor. Proteobacteria was identified as the dominant functional bacteria removing nitrogen in the reactor. The nitritation reaction could promote the sulfate-reducing ammonium oxidation (SRAO) process. NH4 + was converted to NO2 and other intermediates, for which the electron acceptor was SO4 2-. These results showed that nitrogen was converted by the nitrification process, the denitrification process, and the traditional anammox process simultaneously with the SRAO process. The sulfur-based autotrophic denitration and denitrification in the reactor were caused by the influent nitrite and nitrate.

Double dielectric barrier discharge cells for promoting the catalytic degradation of volatile organic compound released by industrial processes.

In this study, the recycling of gas flow was added to oxidize mixture (toluene and xylene) in the post-plasma catalysis (PPC) system, and the MnOx catalysts using impregnation method were used to further oxidize the VOC mixture. The circulation and catalysts were of enhancement for the plasma degradation on both toluene and xylene. The improvement of CO2 selectivity and the reduction of NO, NO2, and O3 were 64.4%, 92.0%, 62.2%, and 51.9%, respectively. The fresh and used catalysts were characterized for the ozone decomposition and mixture degradation in the NTP-REC-CATAL system with the 15 wt% loading amount of catalysts. The results showed that OH groups, lattice oxygen, and manganese sites were potential and significant for the catalytic ability for O3 and mixture conversion. Aldehyde was detected from FT-IR characterization after treating, which indicates that it is the main intermediate NTP-REC-CATAL process. The air plasma was employed to reactive catalytic activity.

Study of sulfate-reducing ammonium oxidation process and its microbial community composition.

In this study, the simultaneous removal of ammonium and sulfate was detected in a self-designed circulating flow reactor, in which ammonium oxidization was combined with sulfate reduction. The highest removal efficiencies of NH4 +-N and SO4 2-S were 92% and 59.2%. NO2 - and NO3 - appeared in the effluent, and experimental studies showed that increasing the proportion of N/S in the influent would increase the NO2 - concentration in the effluent. However, N/S [n(NH4 +-N)/n(SO4 2-S)] conversion rates during the experiment were between 2.1 and 12.9, which may have been caused by the experiment's complex process. The microbial community in the sludge reactor included Proteobacteria, Chloroflexi, Bacteroidetes, Chlorobi, Acidobacteria and Planctomycetes after 187 days of operation. Proteobacteria bacteria had a more versatile metabolism. The sulfate-reducing ammonium oxidation (SRAO) was mainly due to the high performance of Proteobacteria. Nitrospirae has been identified as the dominant functional bacteria in several anammox reactors used for nitrogen removal. Approximately 12.4% of denitrifying bacteria were found in the sludge. These results show that a portion of the nitrogen was converted by nitrification-denitrification, and that traditional anammox proceeds simultaneously with SRAO.

Preparation of a novel Cu-Sn-Bi cathode and performance on nitrate electroreduction.

Cu-Sn-Bi layer coated on Ti substrate was prepared using electrodeposition method and applied as cathode material for electrochemical reduction of nitrate in this research. Linear sweep voltammetry (LSV), chronoamperometry (CA), scanning electron microscope (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) were used to scrutinize the electrochemical performance and the cathode materials. LSV results illustrated that Cu-Sn-Bi cathode possessed the ability for nitrate reduction. Preparation conditions including deposition time, current density, temperature and the content of Bi were optimized based on NO3 -N removal and byproducts selectivity. Results showed that the cathode with Bi content of 3.18 at.%, and electrodepositing at current density of 6 mA cm-2, 35 °C for 30 min achieved the best performance during the experiment. The increase of Bi content could improve the electrocatalytic activity and stability of the cathode. Compared with other common researched cathodes (Cu and Fe), Cu-Sn-Bi (3.18 at.%) exhibited better performance, i.e. the highest NO3 -N removal of 88.43% and the selectivity of harmless N2 was 77.80%. The kinetic studies showed that the reduction of nitrate on Cu-Sn-Bi followed pseudo-first-order kinetics.

Removal of Pb(II) from aqueous solutions by adsorption on magnetic bentonite.

Bentonite is a porous clay material that shows good performance for adsorbing heavy metals and other pollutants for wastewater remediation. In our previous study, magnetic bentonite (M-B) was prepared to solve the separation problem and improve the operability. In this study, we investigated the influence of various parameters on the Pb(II) adsorption of M-B, and it showed effective performance. About 98.9% adsorption removal rate was achieved within 90 min at adsorbent dose of 10 g/L for initial Pb(II) concentration of 200 mg/L at 40 °C and pH 5. The adsorption kinetic fit well by the pseudo-second-order model, and also followed the intra-particle diffusion model up to 90 min. Moreover, adsorption data were successfully reproduced by the Langmuir isotherm; the maximum adsorption capacity was calculated as 80.40 mg/g. The mechanism of interaction between Pb(II) ions and M-B was ionic exchange, surface complexation, and electro-static interactions. Thermodynamics study indicated that the reaction of Pb(II) adsorption on M-B was endothermic and spontaneous; increasing the temperature promoted adsorption. This study was expected to provide a reference and theoretical basis for the treatment of Pb-containing wastewater using bentonite materials.

Adsorption behavior of magnetic bentonite for removing Hg(ii) from aqueous solutions.

Bentonite is a porous clay material that shows good performance for adsorbing heavy metals and other pollutants for wastewater remediation. However, it is very difficult to separate the bentonite from water after adsorption as it forms a stable suspension. In this paper, we prepared magnetic bentonite (M-B) by loading Fe3O4 particles onto aluminum-pillared bentonite (Al-B) in order to facilitate its removal from water. The functional groups, skeleton structure, surface morphology and electrical changes of the prepared material were investigated by FT-IR, XRD, BET, SEM, VSM and zeta potential measurements. It was used as an adsorbent for Hg(ii) removal from aqueous solutions and the influence of various parameters on the adsorption performance was investigated. The adsorption kinetics were best fitted by the pseudo-second-order model, and also followed the intra-particle diffusion model up to 18 min. Moreover, adsorption data were successfully reproduced by the Langmuir isotherm, and the Hg(ii) adsorption saturation capacity was determined as 26.18 mg g-1. The average adsorption free energy change calculated by the D-R adsorption isotherm model was 11.89 kJ mol-1, which indicated the occurrence of ionic exchange. The adsorption thermodynamic parameter ΔH was calculated as 42.92 kJ mol-1, which indicated chemical adsorption. Overall, the thermodynamic parameters implied that Hg(ii) adsorption was endothermic and spontaneous.