Closed-Loop Electrochemical Recycling of Spent Copper(II) from Etchant Wastewater Using a Carbon Nanotube Modified Graphite Felt Anode

Vitamin B12 and iron-rich sludge-derived biochar enhanced PFOA biodegradation: Importance of direct inter-species electron transfer and functional microbes

Owing to the strong C-F bond in nature and the rigidity of the poly-fluoroalkyl chain, perfluorooctanoic acid (PFOA) is difficult to be eliminated by reactive species and microbes in environments, thus posing a serious threat to ecosystems. Vitamin B12 as a cofactor for enzymes, and biochar as the electron providers and conductors, were integrated to enhance PFOA biodegradation. The raw material of biochar was the sludge after dewatering by adding 50 mg/g DS of Fe(III). After pyrolysis under high temperature (800 °C), biochar (SC800) detected high content of Fe(II) (197.64 mg/g) and abundant oxygen-containing functional groups, thus boosting PFOA biodegradation via donating electrons. 99.9% of PFOA could be removed within 60 d as 0.1 g/L SC800 was presented in the microbial systems containing vitamin B12. Moreover, vitamin B12 facilitated the evolution of Sporomusa which behaved the deflorination. Via providing reactive sites and mediating direct inter-species electron transfer (DIET), SC800 boosted PFOA biodegradation. Corresponding novel results in the present study could guide the development of bioremediation technologies for PFOA-polluted sites.

Degradation of the Three-Phase Boundary Zone of Carbon Fiber Anodes in an Electrochemical System

The electrochemical recycling nanoarchitectonics of graphene oxide from carbon fiber reinforced polymers (CFRPs) is a promising approach due to its economic and environmental benefits. However, the rapid degradation of the CFRP anode during the recycling process reduces its overall efficiency. Although previous studies have investigated the electrochemical oxidation of carbon fibers (CFs) and bonding of CFs to the matrix, few researchers have explicitly studied the electrochemical activity of CFs and the possible fracture caused by strong electrochemical reactions. To address this gap, this study investigates the degradation mechanism of CF anodes by analyzing changes in overall mechanical properties, hardness, elastic modulus, functional groups, and elemental composition of individual fibers. The experimental results demonstrate that the three-phase boundary region experiences the most severe degradation, primarily due to the number of oxygen-containing functional groups, which is the most important factor affecting the degree of degradation. This continuous decrease in the hardness and elastic modulus of individual fibers eventually leads to the fracture of CF anodes.

Blue TiO2 nanotube electrocatalytic membrane electrode for efficient electrochemical degradation of organic pollutants

In this study, a Ti³⁺-doped TiO₂ porous membrane (Blue TiO₂/Ti) was fabricated and employed for electrochemical degradation of organic pollutants in the single-pass flow-through mode. Characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microcopy (SEM) and energy dispersive spectroscopy (EDS) verified that Ti³⁺-doped anatase TiO₂ with nanotube structures was successfully prepared. Electrochemical analysis including linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and electrochemical active surface area (ESA) revealed higher oxygen evolution potential (OEP, 2.23 V vs. Ag/AgCl), larger redox peak current, lower impedance and larger ESA (69 cm²/cm²) of Blue TiO₂/Ti compared to the Ti and TiO₂/Ti membranes. The effects of current density, flow rate and solution environment on the removal of methylene blue (MB) were investigated. The removal rates of various organic pollutants including sulfamethoxazole (SMX), methyl orange (MO), bisphenol A (BPA) and MB could reach 92.2%-99.5%. The quenching experiment proved that hydroxyl radicals (•OH) played the major role in the Blue TiO₂/Ti based electrochemical system. Furthermore, the degradation pathways of two typical pollutants (SMX and MB) were proposed by analyzing the oxidation products with liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), with the assistance of orbital-weighted Fukui index (f_w⁰ and f_w^-) obtained through Density Functional Theory (DFT) calculations. Moreover, toxicity indexes of the oxidation products were obtained and compared to the parent SMX and MB using Toxicity Estimation Software Tool (TEST) software. Finally, the long-term operation performance of the Blue TiO₂/Ti membrane was evaluated.

A critical and recent developments on adsorption technique for removal of heavy metals from wastewater-A review

This review provides a quantitative description of the nano-adsorbent processing and its viability against wastewater detoxification by extracting heavy metal ions. The impact of nano-adsorbent functionalities on specific essential attributes such as the surface area, segregation, and adsorption capacity were comprehensively evaluated. A detailed analysis has been presented on the characteristics of nanomaterials through their limited resistance to adsorb some heavy metal ions. Experimental variables such as the adsorbent dosage, pH, substrate concentration, response duration, temperature, and electrostatic force that influence the uptake of metal ions have been studied. Besides, separate models for the adsorption kinetics and isothermal adsorption have been investigated to understand the mechanism behind adsorption. Here, we reviewed the different adsorbent materials with nano-based techniques for the removal of heavy metals from wastewater and especially highlighted the nano adsorption technique. The influencing factors such as pH, temperature, dosage time, sorbent dosage, adsorption capacities, ion concentration, and mechanisms related to the removal of heavy metals by nano composites are highlighted. Lastly, the application potentials and challenges of nano adsorption for environmental remediation are discussed. This critical review would benefit engineers, chemists, and environmental scientists involved in the utilization of nanomaterials for wastewater treatment.

Recovery of resources from industrial wastewater employing electrochemical technologies: status, advancements and perspectives

In the last two decades, water use has increased at twice the rate of population growth. The freshwater resources are getting polluted by contaminants like heavy metals, pesticides, hydrocarbons, organic waste, pathogens, fertilizers, and emerging pollutants. Globally more than 80% of the wastewater is released into the environment without proper treatment. Rapid industrialization has a dramatic effect on developing countries leading to significant losses to economic and health well-being in terms of toxicological impacts on humans and the environment through air, water, and soil pollution. This article provides an overview of physical, chemical, and biological processes to remove wastewater contaminants. A physical and/or chemical technique alone appears ineffective for recovering useful resources from wastewater containing complex components. There is a requirement for more processes or processes combined with membrane and biological processes to enhance operational efficiency and quality. More processes or those that are combined with biological and membrane-based processes are required to enhance operational efficiencies and quality. This paper intends to provide an exhaustive review of electrochemical technologies including microbial electrochemical technologies. It provides comprehensive information for the recovery of metals, nutrients, sulfur, hydrogen, and heat from industrial effluents. This article aims to give detailed information into the advancements in electrochemical processes to energy use, improve restoration performance, and achieve commercialization. It also covers bottlenecks and perspectives of this research area.

Environmental Risk Assessment of Recycled Products of Spent Coppery Etchant in Jiangsu Province, China

With the vigorous development of the 5G industry, the characteristic hazardous waste, spent coppery etchant, was also produced in large quantities. In recent years, there are many companies that have begun to collect spent coppery etchant for the purpose of producing recycled products, such as copper sulfate, copper oxide, basic copper chloride, and copper powder, which often contain large amounts of heavy metals. However, due to the lack of relevant standards and applicable regulatory measures, some of the recycled products flow to the feed processing industry and even to the food processing industry. This study investigated the pollution status of heavy metals in recycled products of spent coppery etchant and evaluated the impact of recycled products exposure on human health. The results showed that the content of Zn was the highest, which was 21 times higher than the corresponding standard limit. Human health risk assessment indicated that the hazard quotients of As account for 87.5% of the entire HI value, while the average carcinogenic risk values of As for copper sulfate, copper oxide, basic copper chloride, and copper powder are 1.09 × 10⁻⁵, 3.19 × 10⁻⁵, 1.29 × 10⁻⁵, 7.94 × 10⁻⁶, respectively. Meanwhile, suggestions on the supervision of recycled products and the concentration limits of heavy metals in recycled products were put forward.

Electrochemical recovery and high value-added reutilization of heavy metal ions from wastewater: Recent advances and future trends

Wastewater treatment for heavy metals is currently transitioning from pollution remediation towards resource recovery. As a controllable and environment-friendly method, electrochemical technologies have recently gained significant attention. However, there is a lack of systematic and goal oriented summarize of electrochemical metal recovery techniques, which has inhibited the optimized application of these methods. This review aims at recent advances in electrochemical metal recovery techniques, by comparing different electrochemical recovery methods, attempts to target recycling heavy metal resources with minimize energy consumption, boost recovery efficiency and realize the commercial application. In this review, different electrochemical recovery methods (including E-adsorption recovery, E-oxidation recovery, E-reduction recovery, and E-precipitation recovery) for recovering heavy metals are introduced, followed an analysis of their corresponding mechanisms, influencing factors, and recovery efficiencies. In addition, the mass transfer efficiency can be promoted further through optimizing electrodes and reactors, and multiple technologies (photo-electrochemical and sono-electrochemical) could to be used synergistically improve recovery efficiencies. Finally, the most promising directions for electrochemical recovery of heavy metals are discussed along with the challenges and future opportunities of electrochemical technology in recycling heavy metals from wastewater.

A Novel Rotary Dryer Filled with Alumina Ceramic Beads for the Treatment of Industrial Wastewaters: Numerical Simulation and Experimental Study

In this study, a new type of rotary dryer filled with inert alumina ceramic bead (ACB) fillers was introduced to treat the industrial wastewater, e.g., the high-salt wastewater and landfill leachate. Numerical simulations based on the Discrete Element Method (DEM) on the motion trajectory of ACB fillers in the rotary dryer were conducted, and the parameters of flight structure, rotational speed, and filling degree on the dynamic behavior of ACB fillers were optimized. Under various rotational speeds and filling degrees, the experimental results fit the numerical-simulated results very well. The optimized flight configuration was the straight flights with a length of 65 mm, and the optimized rotational speed and filling degree were 35 rpm and 15%, respectively. Under the optimized condition, both the response variables, the mass of particles in the airborne phase (MAP) and the percentage of occupied area in the airborne region (OAR), have the optimal values, in which the dryer will have a better drying performance. Besides, the lower-right area of the drum is empty which is convenient for the installation of the inlet pipe. The drying experiments of industrial wastewaters were also studied using this ACB filled rotary drum dryer under the optimized conditions. Under the optimal operational conditions, the evaporation capacities of the high-salt wastewater and landfill leachate could reach as high as 49.7 kg/h and 90 kg/h, respectively. This study highlights the integration of evaporation and drying processes of this novel ACB filled rotary dryer and provides an efficient and zero-liquid-emission strategy for the thermal treatment of industrial wastewater.

Overview of recent developments of resource recovery from wastewater via electrochemistry-based technologies

As the rapid increase of the worldwide population, recovering valuable resources from wastewater have attracted more and more attention by governments and academia. Electrochemical technologies have been extensively investigated over the past three decades to purify wastewater. However, the application of these technologies for resource recovery from wastewater has just attracted limited attention. In this review, the recent (2010-2020) electrochemical technologies for resource recovery from wastewater are summarized and discussed for the first time. Fundamentals of typical electrochemical technologies are firstly summarized and analyzed, followed by the specific examples of electrochemical resource recovery technologies for different purposes. Based on the fundamentals of electrochemical reactions and without the addition of chemical agents, metallic ions, nutrients, sulfur, hydrogen and chemical compounds can be effectively recovered by means of electrochemical reduction, electrochemical induced precipitation, electrochemical stripping, electrochemical oxidation and membrane-based electrochemical processes, etc. Pros and cons of each electrochemical technology in practical applications are discussed and analyzed. Single-step electrochemical process seems ineffectively to recover valuable resources from the wastewater with complicated constituents. Multiple-step processes or integrated with biological and membrane-based technologies are essential to improve the performance and purity of products. Consequently, this review attempts to offer in-depth insights into the developments of next-generation of electrochemical technologies to minimize energy consumption, boost recovery efficiency and realize the commercial application.

Graphite Felt Modified by Atomic Layer Deposition with TiO2 Nanocoating Exhibits Super-Hydrophilicity, Low Charge-Transform Resistance, and High Electrochemical Activity

Graphite felt (GF) is a multi-functional material and is widely used as electrodes of electrochemical devices for energy and environmental applications. However, due to the inherent hydrophobicity of graphite felt, it must be hydrophilically pretreated to obtain good electrochemical activity. Metal oxides coating is one of the feasible methods to modify the surface of GF, and in order to ensure that the metal oxides have a better conductivity for obtaining higher electrochemical activity, a subsequent H₂ heat-treatment process is usually adopted. In this study, atomic layer deposition (ALD) is used to deposit TiO₂ nanocoating on graphite felt (GF) for surface modification without any H₂ thermal post-treatment. The results show that the ALD-TiO₂-modified GF (ALD-TiO₂/GF) owns excellent hydrophilicity. Moreover, the ALD-TiO₂/GF exhibits excellent electrochemical properties of low equivalent series resistance (R_s), low charge-transfer resistance (R_ct), and high electrochemical activity. It demonstrates that ALD is an applicable technique for modifying the GF surface. In addition, it can be reasonably imagined that not only TiO₂ film can effectively modify the GF surface, but also other metal oxides grown by ALD with nanoscale-thickness can also obtain the same benefits. We anticipate this work to be a starting point for modifying GF surface by using ALD with metal oxides nanocoating.

Capacitive Deionization of Saline Water by Using MoS2-Graphene Hybrid Electrodes with High Volumetric Adsorption Capacity

Capacitive deionization (CDI) has received wide attention as an emerging water treatment technology because of its low energy consumption, low cost, and high efficiency. However, the conventional carbon electrode materials for CDI have low densities, which occupy large volumes and are disadvantageous for use in limited space (e.g., in household or on offshore platforms). In order to miniaturize the CDI device, it is quite urgent to develop high volumetric adsorption capacity (VAC) electrode materials. To overcome this issue, we rationally designed and originally developed high VAC MoS₂-graphene hybrid electrodes for CDI. It is interesting that MoS₂-graphene hybrid electrode has a much higher NaCl VAC of 14.3 mg/cm³ with a gravimetric adsorption capacity of 19.4 mg/g. It has been demonstrated that the adsorption capacity is significantly enhanced because of the rapid ion transport of MoS₂ and high electrical conductivity of graphene. In situ Raman spectra and high-angle annular dark-field scanning transmission electron microscopy tests demonstrated a favorable Faradaic reaction, which was crucial to enhancing the NaCl VAC of the MoS₂-graphene hybrid electrode. This work opens a new avenue for miniaturizing future CDI devices.

Highly effective removal of Cu(II) in aqueous solution by using mesoporous TiO2

Mesoporous TiO₂ has been prepared by a brief and simple sol-gel processing and applied for the removal of Cu(II) from aqueous solution. The adsorption behavior of mesoporous TiO₂ for Cu(II) was investigated using batch experiments. Results showed that the pseudo-second-order model and Langmuir isotherm were more accurate to describe the kinetics process and adsorption isotherm. Mesoporous TiO₂ adsorbent displayed excellent Cu(II) adsorption efficiency (195.52mg g^-1). The thermodynamic parameters showed that the adsorption was spontaneous and endothermic. It was also found that mesoporous TiO₂ could be used at least seven times without obvious loss of its original adsorption efficiency. Therefore, the obtained mesoporous TiO₂ could be employed as an effective and low-cost adsorbent for removal of Cu(II) from contaminated effluents.

Preparation of a SnO2–Sb electrode on a novel TiO2 network structure with long service lifetime for degradation of dye wastewater

Developing effective electrodes with long service lifetime for electrochemical degradation of dyes is of paramount importance for their practical industrial applications. We constructed a novel SnO₂–Sb electrode (Ti/TiO₂-NW/SnO₂–Sb electrode) based on a uniform TiO₂ network structure decorated Ti plate (Ti/TiO₂-NW) for a long-term electrocatalytic performance. The SnO₂–Sb coating layer on this electrode was grown on the Ti/TiO₂-NW by pulse electrodeposition. The introduction of the three-dimensional TiO₂-NW enhances the bonding strength between the Ti substrate and the SnO₂–Sb surface coating. An accelerated life test shows that the service life of Ti/TiO₂-NW/SnO₂–Sb electrode is 11.15 times longer than that of the traditional Ti/SnO₂–Sb electrode. The physicochemical properties of the electrodes were characterized through SEM, EDS, XRD and HRTEM. In addition, through LSV, EIS, CV and voltammetric charge analysis, it is found that compared with the traditional electrode, the Ti/TiO₂-NW/SnO₂–Sb electrode possesses a higher oxygen evolution potential, a lower charge transfer resistance and a larger electrochemical active surface area. Besides, this novel electrode also exhibits an outstanding electrocatalytic oxidation ability for degradation of acid red 73 in simulated sewage. After a 5 hours' test, the removal efficiency of acid red 73 and the COD reached 98.6% and 71.8%, respectively, which were superior to those of Ti/SnO₂–Sb electrode (89.1% and 58.8%). This study highlights the excellent stability of the Ti/TiO₂-NW/SnO₂–Sb electrode and provides an energy-efficient strategy for dye degradation.

A novel TiO₂ network structure modified SnO₂–Sb electrode has been prepared by electrodeposition with long service lifetime and low energy consumption.