Electrochemically Assisted Remediation of Pesticides in Soils and Water: A Review

Environmental impact assessment of the electrokinetic adsorption barriers to remove different herbicides from agricultural soils

In this study, the sustainability of the electrokinetic remediation soil flushing (EKSFs) process integrated without and with adsorption barriers (EKABs) have been evaluated for the treatment of four soils contaminated with Atrazine, Oxyfluorfen, Chlorosulfuron and 2,4-D. To this purpose, the environmental effects of both procedures (EKSFs and EKABs) have been determined through a life cycle assessment (LCA). SimaPro 9.3.0.3 was used as software tool and Ecoinvent 3.3 as data base to carry out the inventory of the equipment of each remediation setup based on experimental measurements. The environmental burden was quantified using the AWARE, USEtox, IPPC, and ReCiPe methods into 3 Endpoint impact categories (and damage to human health, ecosystem and resources) and 7 Midpoints impact categories (water footprint, global warming potential, ozone depletion, human toxicity (cancer and human non-cancer), freshwater ecotoxicity and terrestrial ecotoxicity). In general terms, the energy applied to treatment (using the Spanish energy mix) was the parameter with the greatest influence on the carbon footprint, ozone layer depletion and water footprint accounting for around 70 % of the overall impact contribution. On the other hand, from the point of view of human toxicity and freshwater ecotoxicity of soil treatments with 32 mg kg-1 of the different pesticides, the EKSF treatment is recommended for soils with Chlorosulfuron. In this case, the carbon footprint and water footprint reached values around 0.36 kg of CO2 and 114 L of water per kg of dry soil, respectively. Finally, a sensitivity analysis was performed assuming different scenarios.

Emerging technologies for the removal of pesticides from contaminated soils and their reuse in agriculture

Pesticides are becoming more prevalent in agriculture to protect crops and increase crop yields. However, nearly all pesticides used for this purpose reach non-target crops and remain as residues for extended periods. Contamination of soil by widespread pesticide use, as well as its toxicity to humans and other living organisms, is a global concern. This has prompted us to find solutions and develop alternative remediation technologies for sustainable management. This article reviews recent technological developments for remediating pesticides from contaminated soil, focusing on the following major points: (1) The application of various pesticide types and their properties, the sources of pesticides related to soil pollution, their transport and distribution, their fate, the impact on soil and human health, and the extrinsic and intrinsic factors that affect the remediation process are the main points of focus. (2) Sustainable pesticide degradation mechanisms and various emerging nano- and bioelectrochemical soil remediation technologies. (3) The feasible and long-term sustainable research and development approaches that are required for on-site pesticide removal from soils, as well as prospects for applying them directly in agricultural fields. In this critical analysis, we found that bioremediation technology has the potential for up to 90% pesticide removal from the soil. The complete removal of pesticides through a single biological treatment approach is still a challenging task; however, the combination of electrochemical oxidation and bioelectrochemical system approaches can achieve the complete removal of pesticides from soil. Further research is required to remove pesticides directly from soils in agricultural fields on a large scale.

Resveratrol alleviates inorganic arsenic-induced ferroptosis in chicken brain via activation of the Nrf2 signaling pathway

Inorganic arsenic (iAs) is a well-recognized environmental pollutant that induces severe brain injury in humans and animals. The antioxidant, anti-inflammatory, and anti-ferroptotic effects of resveratrol (Res) were demonstrated in multiple animal experiments. In order to investigate the protective effect of Res on iAs-induced chicken brain injury, the 40 chickens (19-d-old, female) brain injury model was established by oral administration of iAs (30 mg/L NaAsO2) for 6 weeks. All chickens had free access to both food and water during the experiment. The biochemical indices, hematoxylin-eosin staining, and related protein levels of oxidative stress, inflammation and ferroptosis were then determined. Our results indicated that Res (1000 mg/kg) alleviated the iAs-induced brain injury after 6 weeks of oral administration, primarily by reducing the interleukin-1β mRNA expression and nuclear factor kappa B and malondialdehyde level, and increasing the antioxidant enzyme activity and the mRNA expression of nuclear factor erythroid 2-related factor 2 (Nrf2). Taken together, our study demonstrates that Res effectively inhibits iAs-induced oxidative stress and ferroptosis by mediating the Nrf2 signaling pathway, thereby alleviating iAs-induced brain injury in chickens. This is the first time that the amelioration effects of Res on the iAs-induced brain have been investigated from multiple perspectives.

Acetylcholine triggered enzymatic cascade reaction based on Fe7S8 nanoflakes catalysis for organophosphorus pesticides visual detection

BACKGROUND

Organophosphorus pesticides (OPs) play important roles in the natural environment, agricultural fields, and biological prevention. The development of OPs detection has gradually become an effective strategy to avoid the dangers of pesticides abuse and solve the severe environmental and health problems in humans. Although conventional assays for OPs analysis such as the bulky instrument required analytical methods have been well-developed, it still remains the limitation of inconvenient, inefficient and lab-dependence analysis in real samples. Hence, there is an urgent demand to develop efficient detection methods for OPs analysis in real scenarios.

RESULTS

Here, by virtue of the highly efficient catalytic performance in Fe7S8 nanoflakes (Fe7S8 NFs), we propose an OPs detection method that rationally integrated Fe7S8 NFs into the acetylcholine (ACh) triggered enzymatic cascade reaction (ATECR) for proceeding better detection performances. In this method, OPs serve as the enzyme inhibitors for inhibiting ATECR among ACh, acetylcholinesterase (AChE), and choline oxidase (CHO), then reduce the generation of H2O2 to suppress the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) that catalyzed by Fe7S8 NFs. Benefiting from the integration of Fe7S8 NFs and ATECR, it enables a sensitive detection for OPs (e.g. dimethoate). The proposed method has presented good linear ranges of OPs detection ranging from 0.1 to 10 μg mL-1. Compared to the other methods, the comparable limits of detection (LOD) of OPs are as low as 0.05 μg mL-1.

SIGNIFICANCE

Furthermore, the proposed method has also achieved a favorable visual detection performance of revealing OPs analysis in real samples. The visual signals of OPs can be transformed into RGB values and gathered by using smartphones, indicating the great potential in simple, sensitive, instrument-free and on-site analysis of pesticide residues in environmental monitoring and biosecurity research.

Trace Amount of Bi-Doped Core-Shell Pd@Pt Mesoporous Nanospheres with Specifically Enhanced Peroxidase-Like Activity Enable Sensitive and Accurate Detection of Acetylcholinesterase and Organophosphorus Nerve Agents

The urgent need for sensitive and accurate assays to monitor acetylcholinesterase (AChE) activity and organophosphorus pesticides (OPs) arises from the imperative to safeguard human health and protect the ecosystem. Due to its cost-effectiveness, ease of operation, and rapid response, nanozyme-based colorimetry has been widely utilized in the determination of AChE activity and OPs. However, the rational design of nanozymes with high activity and specificity remains a great challenge. Herein, trace amount of Bi-doped core-shell Pd@Pt mesoporous nanospheres (Pd@PtBi2) have been successfully synthesized, exhibiting good peroxidase-like activity and specificity. With the incorporation of trace bismuth, there is a more than 4-fold enhancement in the peroxidase-like performance of Pd@PtBi2 compared to that of Pd@Pt. Besides, no significant improvement of oxidase-like and catalase-like activities of Pd@PtBi2 was found, which prevents interference from O2 and undesirable consumption of substrate H2O2. Based on the blocking impact of thiocholine, a colorimetric detection platform utilizing Pd@PtBi2 was constructed to monitor AChE activity with sensitivity and selectivity. Given the inhibition of OPs on AChE activity, a biosensor was further developed by integrating Pd@PtBi2 with AChE to detect OPs, capitalizing on the cascade amplification strategy. The OP biosensor achieved a detection limit as low as 0.06 ng mL-1, exhibiting high sensitivity and anti-interference ability. This work is promising for the construction of nanozymes with high activity and specificity, as well as the development of nanozyme-based colorimetric biosensors.

A comparative study of response surface methodology and artificial neural network based algorithm genetic for modeling and optimization of EP/US/GAC oxidation process in dexamethasone degradation: Application for real wastewater, electrical energy consumption

Dexamethasone (DXM) is a broadly used drug, which is frequently identified in the water environments due to its improper disposal and incomplete removal in wastewater treatment plant. The inability of conventional treatment processes of wastewater causes that researchers pay a great attention to study and develop effective wastewater treatment systems. This work deals with the study of integrated electro-peroxone/granular activated carbon (EP/US/GAC) process in the degradation of dexamethasone (DXM) from a water environment and the remediation of real pharmaceutical wastewater. Two approaches of response surface methodology based on central composite design (RSM-CCD) and artificial neural network based on algorithm genetic (ANN-GA) were employed for modeling and optimization of the process. Both the models presented significant adequacy for modeling and prediction of the process according to statistical linear and nonlinear metrics (R2 = 0.9998 and 0.9996 and RMSE = 0.2128 and 0.1784 for ANN-GA and RSM-CCD, respectively). The optimization study provided the same outcomes for both ANN-GA and RSM-CCD approaches, where approximately complete DEX oxidation was achieved at pH = 9.3, operating time = 10 min, US power = 300 W/L, applied current = 470 mA, and electrolyte concentration = 0.05 M. A synergistic study signified that the EP/US/GAC process made an 82% synergy index as compared to the individual US and EP processes. The calculated energy consumption for the integrated process was achieved to be 2.79 kW h/gCOD. Quenching test by tert-butanol and p-benzoquinone revealed that HO• radical possessed the largest contribution in DEX degradation. The efficiency of EP/US/GAC process in the remediation of real pharmaceutical wastewater showed a significant decline in COD content (92% removal after 180 min), and the ratio of initial BOD/COD ratio of 0.27 was elevated up to 0.7 after 100 min treatment time. The performance stability of EP/US/GAC system showed no remarkable drop in removal efficiency, and leakage of lead ions from the anode surface was negligible and below WHO guideline for drinking water. Generally, this research work manifested that the integrated EP/US/GAC system elevated the degradation efficiency and can be proposed as a pretreatment step before biological treatment processes for the remediation of recalcitrant wastewaters.

Research progress on remediation of organochlorine pesticide contamination in soil

Deteriorated soil pollution has grown into a worldwide environmental concern over the years. Organochlorine pesticide (OCP) residues, featured with ubiquity, persistence and refractoriness, are one of the main pollution sources, causing soil degradation, fertility decline and nutritional imbalance, and severely impacting soil ecology. Furthermore, residual OCPs in soil may enter the human body along with food chain accumulation and pose a serious health threat. To date, many remediation technologies including physicochemical and biological ways for organochlorine pollution have been developed at home and abroad, but none of them is a panacea suitable for all occasions. Rational selection and scientific decision-making are grounded in in-depth knowledge of various restoration techniques. However, soil pollution treatment often encounters the interference of multiple factors (climate, soil properties, cost, restoration efficiency, etc.) in complex environments, and there is still a lack of systematic summary and comparative analysis of different soil OCP removal methods. Thus, to better guide the remediation of contaminated soil, this review summarized the most commonly used strategies for OCP removal, evaluated their merits and limitations and discussed the application scenarios of different methods. It will facilitate the development of efficient, inexpensive and environmentally friendly soil remediation strategies for sustainable agricultural and ecological development.

Microbial electrochemical system: an emerging technology for remediation of polycyclic aromatic hydrocarbons from soil and sediments

Worldwide industrialization and other human activities have led to a frightening stage of release of hazardous, highly persistent, toxic, insoluble, strongly adsorbed to the soil and high molecular weight ubiquitous polycyclic aromatic hydrocarbons (PAHs) in soils and sediments. The various conventional remediation methods are being used to remediate PAHs with certain drawbacks. Time taking process, high expenditure, excessive quantities of sludge generation, and various chemical requirements do not only make these methods outdated but produce yet much resistant and toxic intermediate metabolites. These disadvantages may be overcome by using a microbial electrochemical system (MES), a booming technology in the field of bioremediation. MES is a green remediation approach that is regulated by electrochemically active microorganisms at the electrode in the system. The key advantage of the system over the conventional methods is it does not involve any additional chemicals, takes less time, and generates minimal sludge or waste during the remediation of PAHs in soils. However, a comprehensive review of the MES towards bioremediation of PAHs adsorbed in soil and sediment is still lacking. Therefore, the present review intended to summarize the recent information on PAHs bioremediation, application, risks, benefits, and challenges based on sediment microbial fuel cell and microbial fuel cell to remediate mount-up industrial sludge, soil, and sediment rich in PAHs. Additionally, bio-electrochemically active microbes, mechanisms, and future perspectives of MES have been discussed.

Cork barriers for the remediation of soils polluted with lindane

The in-situ removal of lindane from spiked soil was studied using cork barriers combined with electrokinetic and ohmic heating soil remediation processes. Both vertical and horizontal cork barriers have been evaluated to retain pollutants mobilized by electro-osmotic flow or volatilized by ohmic heating. Moreover, the addition of surfactant solutions in electrolyte wells has been evaluated to promote the dragging of lindane by electrokinetic fluxes. Results indicated that the drag of lindane by liquid flows is not as important as expected, opposite to what happened with the dragging by gaseous flows. The retention of gaseous lindane was also confirmed in adsorption tests carried out in a column packed with cork granules. The addition of surfactant had a very limited effect on the mobility of lindane, and dragging of this species to the electrode wells or to a permeable reactive barrier. On the contrary, the reactivity of lindane during the electrochemical treatments is relevant due to the electrokinetic basic front promoting the in-situ conversion of lindane into less chlorinated pollutants.

An overview of bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils

The global problem of petroleum contamination in soils seriously threatens environmental safety and human health. Current studies have successfully demonstrated the feasibility of bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils due to their easy implementation, environmental benignity, and enhanced removal efficiency compared to bioremediation. This paper reviewed recent progress and development associated with bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils. The working principles, removal efficiencies, affecting factors, and constraints of the two technologies were thoroughly summarized and discussed. The potentials, challenges, and future perspectives were also deliberated to shed light on how to overcome the barriers and realize widespread implementation on large scales of these two technologies.

The study of the removal of penconazole fungicide from surface water using carboxymethyl tragacanth-based hydrogel grafted with poly (acrylic acid-co-acrylamide)

In this study, a polymeric adsorbent based on carboxymethyl tragacanth (CMT) grafted by poly acrylic acid-co-acrylamide (AAc-co-AAm) synthesized by radical polymerization for the first time was used to remove the fungicide penconazole (PEN) or Topas 20% from surface water. The parameters of solution pH, adsorption isotherm, and adsorption kinetics of PEN were studied by the synthetic adsorbent. The surface morphology and functional groups of CMT-g-poly (AAc-co-AAm) were confirmed by XRD, SEM and FT-IR techniques. Adsorption of PEN on CMT-g-poly (AAc-co-AAm) follows the Freundlich and pseudo-second-order models. The significant maximum adsorption capacity of the synthesized polymer was found to be 196.08 mg/g. The synthetic adsorbent had good reproducibility in PEN removal for up to 5 cycles. CMT-g-poly (AAc-co-AAm) is a cost-effective and non-toxic adsorbent for the decontamination of surface water from pesticides.

Multi-Class Weed Recognition Using Hybrid CNN-SVM Classifier

The Convolutional Neural Network (CNN) is one of the widely used deep learning models that offers the chance to boost farming productivity through autonomous inference of field conditions. In this paper, CNN is connected to a Support Vector Machine (SVM) to form a new model CNN-SVM; the CNN models chosen are ResNet-50 and VGG16 and the CNN-SVM models formed are ResNet-50-SVM and VGG16-SVM. The method consists of two parts: ResNet-50 and VGG16 for feature extraction and SVM for classification. This paper uses the public multi-class weeds dataset DeepWeeds for training and testing. The proposed ResNet-50-SVM and VGG16-SVM approaches achieved 97.6% and 95.9% recognition accuracies on the DeepWeeds dataset, respectively. The state-of-the-art networks (VGG16, ResNet-50, GoogLeNet, Densenet-121, and PSO-CNN) with the same dataset are accurate at 93.2%, 96.1%, 93.6%, 94.3%, and 96.9%, respectively. In comparison, the accuracy of the proposed methods has been improved by 1.5% and 2.7%, respectively. The proposed ResNet-50-SVM and the VGG16-SVM weed classification approaches are effective and can achieve high recognition accuracy.

A real-time smart sensing system for automatic localization and recognition of vegetable plants for weed control

Tomato is a globally grown vegetable crop with high economic and nutritional values. Tomato production is being threatened by weeds. This effect is more pronounced in the early stages of tomato plant growth. Thus weed management in the early stages of tomato plant growth is very critical. The increasing labor cost of manual weeding and the negative impact on human health and the environment caused by the overuse of herbicides are driving the development of smart weeders. The core task that needs to be addressed in developing a smart weeder is to accurately distinguish vegetable crops from weeds in real time. In this study, a new approach is proposed to locate tomato and pakchoi plants in real time based on an integrated sensing system consisting of camera and color mark sensors. The selection scheme of reference, color, area, and category of plant labels for sensor identification was examined. The impact of the number of sensors and the size of the signal tolerance region on the system recognition accuracy was also evaluated. The experimental results demonstrated that the color mark sensor using the main stem of tomato as the reference exhibited higher performance than that of pakchoi in identifying the plant labels. The scheme of applying white topical markers on the lower main stem of the tomato plant is optimal. The effectiveness of the six sensors used by the system to detect plant labels was demonstrated. The computer vision algorithm proposed in this study was specially developed for the sensing system, yielding the highest overall accuracy of 95.19% for tomato and pakchoi localization. The proposed sensor-based system is highly accurate and reliable for automatic localization of vegetable plants for weed control in real time.

Application of a Zero-Valent Iron/Cork as Permeable Reactive Barrier for In Situ Remediation of Phenanthrene in Soil

This paper proposes an eco-efficient treatment technology for removing phenanthrene (PHE) from kaolinite soil, incorporating a permeable reactive barrier (PRB) in an electrokinetic (EK) remediation system, which was made by modifying the granulated cork (GC) with Fe@Fe2O3, identified as EK/Fe@Fe2O3/GC. The novel product Fe@Fe2O3/GC was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and element mapping. EK tests were conducted to investigate the performance of the EK/Fe@Fe2O3/GC for removal of PHE from soil. The results showed that PHE was driven by the electro-osmotic flow toward the cathode and reacted with the EK/Fe@Fe2O3/GC. Further, the removal efficiency of PHE in the soil was higher in the presence of H2O2 due to the additional reactions achieved. The results were discussed in light of the existing literature.

Sustainability prioritization of technologies for cleaning up soils polluted with oil and petroleum products: A decision support system under complex spherical fuzzy environment

The transition towards a sustainable land management (SLM) needs for utilizing appropriate technologies for controlling soil pollution, and ensures the development of environmental, economic, technical, and social dimensions in region. Using these technologies for cleaning up soils polluted with oil and petroleum products in Behbahan city (in the southwest of Iran) is considered. The soil pollution control technologies (SPCTs) can assist local authorities, governments, investors, and developers to reduce climate change, mitigate soil, water, and air pollution and construct the sustainable communities. With the aim of balance between the issues in the context of sustainability policy, criteria (principles) including environmental, economic, technical, and social aspects are considered. The research takes into consideration the applicability of a novel multi-criteria decision-making approach namely complex spherical fuzzy set-based CODAS (Combinative distance-based assessment). The approach can be used to choose the suitable technology in a sustainable mode, considering the principles related to sustainability pillars. It comprises various technologies for soil pollution control and prioritizes technologies from the most to least as: Biorestoration technology, Excavation technology, Soil venting technology, Soil flushing, and Hydraulic barriers technology.

Removal of ofloxacin from wastewater by chloride electrolyte electro-oxidation: Analysis of the role of active chlorine and operating costs

Electro-oxidation (EO) has received increasing attention as an efficient and green method for removing pollutants from wastewater. Chloride anions (Cl^-), which commonly exist in wastewater, can act as an electrolyte for the EO process. However, the role of reactive chlorine species (RCS) generated near electrodes is often underestimated. In this study, we generated hydroxyl radicals (OH) and RCS in a boron-doped diamond (BDD) electrode system and investigated its degradation mechanism for ofloxacin (OFX) removal. The findings suggested that OFX degradation was dominated by OH existing near the anode in solution, with RCS playing a supporting role. Based on the produced intermediates, we proposed an OFX decomposition pathway. The biological toxicities of the intermediates were evaluated through the ECOSAR and T.E.S.T. procedure. Nearly half of the intermediates are less toxic than the parent compound. After optimizing the operating parameters by the response surface methodology, 20 mg/L OFX was almost completely degraded after 10 min of reaction in 1.45 g/L NaCl with a current density (j) of 18 mA/cm², and the total organic carbon was decreased by 30.55 %. The energy consumption and current efficiency were 0.648 kW·h/g_TOC and 8.65 %, respectively. Comparing the operating costs of the proposed and other EO methods, our method emerged as a viable new treatment scheme for similar polluted wastewaters. This study aims to comprehensively understand the potential application value of BDD electrodes in the treatment of Cl^- containing organic wastewater.

Electrochemical oxidation of fipronil pesticide is effective under environmental relevant concentrations

Pesticide overuse has posed a threat to agricultural community as well as for the environment. In order to treat this pollution at its source, decentralized and selective technologies such as electrochemical processes appear especially relevant to avoid the possible generation of toxic degradation products. Electrochemical oxidation (ECO) is a promising electrochemically-driven process, but most studies evaluate performance under pollutant concentrations that are orders of magnitude higher than environmental relevant conditions. This work explores ECO treatment of fipronil using boron-doped diamond (BDD) as anode and titanium plate as cathode at small concentrations found in agricultural run-off. The effect of applied current density and initial contaminant concentrations were also studied. For a current density of 20 mA cm^-2 the decrease of COD and fipronil were about 97% and 100% after 360 min of electrolysis, respectively. Engineering figures of merit were evaluated to assess competitiveness of ECO decentralized propositions. Results suggest effective and feasible treatment of fipronil by ECO.

Electrocatalytic oxidation of antidiabetic drug metformin adsorbed on intercalated MXene

Two-dimensional (2D) Ti₃C₂T_x transition metal carbide (MXene) nanosheets intercalated with sodium ions (SI-Ti₃C₂T_x MXene) were used in the adsorption and electrochemical regeneration process for removal of the antidiabetic drug metformin (MF) as a model emerging pollutant. After MF adsorption, SI-Ti₃C₂T_x MXene oxidized the MF on its surface through its electrocatalytic activity at very low current density and cell potential. For complete oxidation the optimum parameters were 0.525 C g^-1, 0.005 mA cm^-2, and pH 6 in absence of NaCl or 26.25 C g^-1 and 0.5 mA cm^-2 in the presence of 2.5 w/v% NaCl. The overall regeneration of SI-Ti₃C₂T_x is governed by a combined mechanism, i.e., desorption followed by degradation. The degradation mechanism, such as direct electron transfer or indirect oxidation, depends on the applied operating conditions. Thus, the investigation suggests that these 2D sheets are good nanoadsorbents as well as good electrocatalysts and proves their usefulness in practical water-treatment applications.

Application of electro-Fenton and photoelectro-Fenton processes for the degradation of contaminants in landfill leachate

Worldwide, most solid waste ends its life in landfill sites, which have a significant environmental impact in several respects. In particular, rainfall over landfill sites results in the production of an aqueous leachate containing compounds having low biodegradability, high toxicity, and a high organic load. For this reason, this study aims to investigate the applicability of electro-Fenton (EF) and photoelectro-Fenton (PEF) processes as alternative for treating a local landfill effluent with high organic content (chemical oxygen demand (COD) = 2684.7 mg-O₂ L ^-1) in a continuous-flow reactor (using, for first time, this kind of system with higher electrodes area of 35 cm²) using boron-doped diamond anode (Nb/BDD) and a carbon felt cathode (FC) electrodes. The effects of current density j (30, 60 and 90 mA cm^-2) and UV radiation wavelength (UVA and UVC) were studied to evaluate the treatment efficiency as well as the energy consumption. Results clearly showed that, the best efficiencies removing organic matter, in terms of COD, were about 66%, 68% and 89% with an energy consumption of only 19.41, 17.61 and 17.59 kWh kg COD^-1 for EF, PEF-UVA and PEF-UVC respectively, at 90 mA cm^-2 after 4 h of operation. The treatment of this kind of effluent produced organic and inorganic by-products, the acetic and formic acids as well as NO₂^-, NO₃^-, and NH₄⁺, being assessed their concentrations.

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Combining Soil Vapor Extraction and Electrokinetics for the Removal of Hexachlorocyclohexanes from Soil

This paper focuses on the evaluation of the mobility of four hexachlorocyclohexane (HCH) isomers by soil vapor extraction (SVE) coupled with direct electrokinetic (EK) treatment without adding flushing fluids. SVE was found to be very efficient and remove nearly 70 % of the four HCH in the 15-days of the tests. The application of electrokinetics produced the transport of HCH to the cathode by different electrochemical processes, which were satisfactorily modelled with a 1-D transport equation. The increase in the electric field led to an increase in the transport of pollutants, although 15 days was found to be a very short time for an efficient transportation of the pollutants to the nearness of the cathode. Loss of water content in the vicinity of the cathode warns about the necessity of using electrokinetic flushing technologies instead of simple direct electrokinetics. Thus, results point out that direct electrokinetic treatment without adding flushing fluids produced low current intensities and ohmic heating that contributes negatively to the performance of the SVE process. No relevant differences were found among the removal of the four isomers, neither in SVE nor in EK processes.

On the Dynamics of the Carbon-Bromine Bond Dissociation in the 1-Bromo-2-Methylnaphthalene Radical Anion

This paper studies the mechanism of electrochemically induced carbon-bromine dissociation in 1-Br-2-methylnaphalene in the reduction regime. In particular, the bond dissociation of the relevant radical anion is disassembled at a molecular level, exploiting quantum mechanical calculations including steady-state, equilibrium and dissociation dynamics via dynamic reaction coordinate (DRC) calculations. DRC is a molecular-dynamic-based calculation relying on an ab initio potential surface. This is to achieve a detailed picture of the dissociation process in an elementary molecular detail. From a thermodynamic point of view, all the reaction paths examined are energetically feasible. The obtained results suggest that the carbon halogen bond dissociates following the first electron uptake follow a stepwise mechanism. Indeed, the formation of the bromide anion and an organic radical occurs. The latter reacts to form a binaphthalene intrinsically chiral dimer. This paper is respectfully dedicated to Professors Anny Jutand and Christian Amatore for their outstanding contribution in the field of electrochemical catalysis and electrosynthesis.

Research on Field Soybean Weed Identification Based on an Improved UNet Model Combined With a Channel Attention Mechanism

Aiming at the problem that it is difficult to identify two types of weeds, grass weeds and broadleaf weeds, in complex field environments, this paper proposes a semantic segmentation method with an improved UNet structure and an embedded channel attention mechanism SE module. First, to eliminate the semantic gap between low-dimensional semantic features and high-dimensional semantic features, the UNet model structure is modified according to the characteristics of different types of weeds, and the feature maps after the first five down sampling tasks are restored to the same original image through the deconvolution layer. Hence, the final feature map used for prediction is obtained by the fusion of the upsampling feature map and the feature maps containing more low-dimensional semantic information in the first five layers. In addition, ResNet34 is used as the backbone network, and the channel attention mechanism SE module is embedded to improve useful features. The channel weight is determined, noise is suppressed, soybean and grass weeds are identified, and broadleaf weeds are extracted through digital image morphological processing, and segmented images of soybean plants, grass weeds and broadleaf weeds are generated. Moreover, compared with the standard semantic segmentation models, FCN, UNet, and SegNet, the experimental results show that the overall performance of the model in this paper is the best. The average intersection ratio and average pixel recognition rate in a complex field environment are 0.9282 and 96.11%, respectively. On the basis of weed classification, the identified weeds are further refined into two types of weeds to provide technical support for intelligent precision variable weed spraying.

Enhancing soil vapor extraction with EKSF for the removal of HCHs

This paper evaluates the combination of electrokinetic soil flushing (EKSF) with soil vapor extraction (SVE) for the removal of four hexachlorocyclohexane (HCH) isomers contained in a real matrix. Results demonstrate that the combination of EKSF and SVE can be positive, but it is required the application of high electric fields (3 V cm^-1) in order to promote a higher temperature in the system, which improves the volatilization of the HCH contained in the system. Electrokinetic transport is also enhanced with the application of higher electric gradients, but these transport processes are slower than the volatilization processes, which are the primary in this system. Hence collection of species in the electrolyte wells is negligible as compared to the compound dragged with air by the SVE but the temperature increase demonstrates a good performance. Combination of EKSF with SVE can efficiently exhaust the four HCH isomers reaching a removal of more than 90% after 15 days of treatment (20% more than values attained by SVE) but it is required the application of high electric fields to promote a higher temperature in the system (to improve the volatilization) and EK transport (to improve the dragging). 1-D transport model can be easily used to estimate the average pore water velocity and the effective diffusion of each compound under the different experimental conditions tested.

Removal of lindane using electrokinetic soil flushing coupled with air stripping

This paper evaluates the remediation of soil spiked with lindane using a combined treatment consisting of electrokinetic soil flushing (EKSF) with air stripping to elucidate the main processes occurring in the soil when electric fields of 0.75 V cm−1 and 1.50 V cm−1 are applied. The results demonstrate that lindane is efficiently transported to the anodic and cathodic wells using flushing fluids containing sodium dodecyl sulfate (SDS). Additionally, an important amount is volatilized and stripped with the injected air. In the cathodic well, lindane is rapidly transformed into other species because of the strongly alkaline media. These other species are also found in the portions of soil next to this well, confirming the efficient transport of chlorinated organics with SDS. After 14 days of operation, nearly 50% of the spiked lindane can be removed from the soil. Operation with large electric fields does not improve the performance of the treatment technology and results in lower current intensities and electro-osmotic fluxes and in higher evaporated water, despite the water content in the soil matrix, indicating the coexistence of multiple inputs in these processes.

Graphical abstract

Forward-Looking Roadmaps for Long-Term Continuous Water Quality Monitoring: Bottlenecks, Innovations, and Prospects in a Critical Review

Long-term continuous monitoring (LTCM) of water quality can bring far-reaching influences on water ecosystems by providing spatiotemporal data sets of diverse parameters and enabling operation of water and wastewater treatment processes in an energy-saving and cost-effective manner. However, current water monitoring technologies are deficient for long-term accuracy in data collection and processing capability. Inadequate LTCM data impedes water quality assessment and hinders the stakeholders and decision makers from foreseeing emerging problems and executing efficient control methodologies. To tackle this challenge, this review provides a forward-looking roadmap highlighting vital innovations toward LTCM, and elaborates on the impacts of LTCM through a three-hierarchy perspective: data, parameters, and systems. First, we demonstrate the critical needs and challenges of LTCM in natural resource water, drinking water, and wastewater systems, and differentiate LTCM from existing short-term and discrete monitoring techniques. We then elucidate three steps to achieve LTCM in water systems, consisting of data acquisition (water sensors), data processing (machine learning algorithms), and data application (with modeling and process control as two examples). Finally, we explore future opportunities of LTCM in four key domains, water, energy, sensing, and data, and underscore strategies to transfer scientific discoveries to general end-users.

A mini review on bio-electrochemical systems for the treatment of azo dye wastewater: State-of-the-art and future prospects

Azo dyes are typical toxic and refractory organic pollutants widely used in the textile industry. Bio-electrochemical systems (BESs) have great potential for the treatment of azo dyes with the help of microorganisms as biocatalysts and have advanced significantly in recent years. However, the latest and significant advancement and achievements of BESs treating azo dyes have not been reviewed since 8 years ago. This review thus focuses on the recent investigations of BESs treating azo dyes from the year of 2013-2020 in order to broaden the knowledge and deepen the understanding in this field. In this review, azo dyes degradation mechanisms of BESs are first elaborated, followed by the introduction of BES configurations with the emphasis on the novelties. The azo dye degradation performance of BESs is then presented to demonstrate their effectiveness in azo dye removal. Effects of various operating parameters on the overall performance of BESs are comprehensively elucidated, including electrode materials, external resistances and applied potentials, initial concentrations of azo dyes, and co-substrates. Predominant microorganisms responsible for degradation of azo dyes in BESs are highlighted in details. Furthermore, the combination of BESs with other processes to further improve the azo dye removal are discussed. Finally, an outlook on the future research directions and challenges is provided from the viewpoint of realistic applications of the technology.

Skeletal Ni electrode-catalyzed C-O cleavage of diaryl ethers entails direct elimination via benzyne intermediates

Diaryl ethers undergo electrocatalytic hydrogenolysis (ECH) over skeletal Ni cathodes in a mild, aqueous process that achieves direct C-O cleavage without initial benzene ring saturation. Mechanistic studies find that aryl phenyl ethers with a single para or meta functional group (methyl, methoxy, or hydroxy) are selectively cleaved to the substituted benzene and phenol, in contrast to recently reported homogeneous catalytic cleavage processes. Ortho positioning of substituents reverses this C-O bond selectivity, except for the 2-phenoxyphenol case. Together with isotope labeling and co-solvent studies, these results point to two distinct cleavage mechanisms: (a) dual-ring coordination and C-H activation, leading to vicinal elimination to form phenol and a surface-bound aryne intermediate which is then hydrogenated and released as the arene; and (b) surface binding in keto form by the phenolic ring of the hydroxy-substituted substrates, followed by direct displacement of the departing phenol. Notably, acetone inhibits the well-known reduction of phenol to cyclohexanol, affording control of product ring saturation. A byproduct of this work is the discovery that the ECH treatment completely defluorinates substrates bearing aromatic C-F and C-CF₃ groupings.

Biomass conversion holds promise as a more sustainable source of platform chemicals, but limitations in the ways in which lignin can be broken down is a current bottleneck. Here the authors report an electrocatalytic hydrogenolysis over skeletal Ni that cleaves diaryl ethers, chemically resistant moieties in both renewable carbon sources and persistent organic pollutants.

Electrochemical Oxidation of Methyl Orange in an Active Carbon Packed Electrode Reactor (ACPER): Degradation Performance and Kinetic Simulation

The efficient removal and kinetic modelling of methyl orange (MO) degradation using an electrocatalytic oxidation method in an activated carbon (AC) packed electrode reactor (ACPER) were conducted. A significantly high (81.2%) chemical oxygen demand (COD) and 100.0% MO decolorization efficiency were observed under the experimental conditions of current density of 3.0 mA·cm⁻², flow velocity of 0.3 L·h⁻¹, and treatment duration of 1.68 h using a β-PbO₂/Ti anode. The high removal efficiency is ascribed to the anode expansion effect after AC packing. The anode expansion coefficient (λ) of the ACPER was calculated to be 0.63 from the cyclic voltammetry (CV) measurement, which means the further current utilization for MO oxidation. Based on the current utilization efficiency on anodic and particle electrode surfaces, a phase-reaction kinetics model was proposed for the simulation of MO COD removal efficiency. Our simulation results showed that the newly established average current efficiency (ACE) and energy consumption (E_sp) model well matched the MO experimental degradation data. Our work broadens the scope of the application of ACPER in the treatment industry wastewater containing organics and provides a new strategy for the energy utilization evaluation during the removal of organic matter by electrocatalytic oxidation.

A hybrid CNN-SVM classifier for weed recognition in winter rape field

BACKGROUND

Weed recognition is key for automatic weeding, which is a challenging problem. Weed recognition is mainly based on different features of crop images. The extracted image features mainly include color, texture, shape, etc. The designed features depend on manual work, which is blind to some extent. Meanwhile these features have poor generalization performance on a sample set. The final discrimination results tend to have a greater difference. The current study proposed a deep convolutional neural network (CNN) with support vector machine (SVM) classifier which aims to improve the classification accuracy of winter rape seeding and weeds in fields.

RESULTS

The VGG network model was adopted, which received a true color image (224 × 224 pixels) of rape/weed as the input. The proposed VGG-SVM model was able to identify rape/weeds with average accuracies of 99.2% in the training procedures and 92.1% in the test procedures, respectively. A comparative experiment was conducted using the proposed VGG-SVM model and five other methods. The proposed VGG-SVM model obtained a higher classification accuracy, greater robustness and real time.

CONCLUSIONS

The VGG-SVM weed classification model proposed in this study is effective. The model can be further applied to the recognition of multi-sample mixed crop images in fields.

Can the green energies improve the sustainability of electrochemically-assisted soil remediation processes?

The green powering of electrochemically-assisted soil remediation processes had been strongly discouraged. Low remediation efficiencies have been reported as a consequence of the reversibility of the transport processes when no power is applied to the electrodes, due to the intermittent powering of renewable sources. However, it has been missed a deeper evaluation from the environmental point of view. This work goes further and seeks to quantify, using life cycle assessment tools, the environmental impacts related to the electro-kinetic treatments powered by different sources: grid (Spanish energy mix), photovoltaic and wind sources. The global warming potential and the ozone depletion showed higher environmental impacts in case of using green energies, associated with the manufacturing of the energy production devices. In contrast to that, results pointed out the lowest water consumption for the treatment powered with solar panels. The huge water requirements to produce energy, considering a Spanish energy mix, drop the sustainability of this powering strategy in terms of water footprint. Regarding toxicities, the pollutant toxicity was highly got rid of after 15 days of treatment, regardless the powering source used. Nevertheless, the manufacturing of energy and green energy production devices has a huge impact into the toxicity of the remediation treatments, increasing massively the total toxicity of the process, being this effect less prominent by the electro-kinetic treatment solar powered. In view of the overall environmental impact assessed, according to mid and endpoint impact categories, it can be claimed that, despite the high energy requirements and affectation to the global warming potential, the use of solar power is a more sustainable alternative to remediate polluted soils by electrochemical techniques.

Electrochemical oxidation of sulfamethoxazole by nitrogen-doped carbon nanosheets composite PbO2 electrode: Kinetics and mechanism

In this study, nitrogen-doped carbon nanosheets (NCNSs) were prepared and successfully combined into the PbO₂ electrode by the composite electrodeposition technology, thereby NCNS-PbO₂ electrode was obtained. The electrochemical degradation of sulfamethoxazole (SMX) in aqueous solution by NCNS-PbO₂ electrode was studied. The main influence factors on the degradation of SMX, such as the initial concentration of SMX, current density, electrolyte concentration and initial pH value, were analyzed in detail. Under the optimal process conditions, after 120 min of treatment, the removal ratio of SMX and chemical oxygen demand (COD) reached 99.8 % and 60.7 %, respectively. The results showed that the electrochemical degradation of SMX fitted pseudo-first-order reaction kinetics. The electrochemical performance of NCNS-PbO₂ electrode was better than that of PbO₂ electrode by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, as well as the use of cyclic voltammetry and electrochemical impedance spectroscopy for electrochemical performance testing. This was because the doping of nitrogen atoms improved the properties of carbon nanosheets. After the composite, the active sites on the surface of PbO₂ were improved, the particle size of PbO₂ was reduced, and the electrical conductivity and electrocatalytic activity of the electrode were improved. In addition, the intermediate products were determined by GC-MS method, and the possible degradation pathways of SMX were proposed.

Reusable smartphone-facilitated mobile fluorescence biosensor for rapid and sensitive on-site quantitative detection of trace pollutants

Increasing exposure to toxic pollutants highlights the need for their sensitive detection technologies that can be rapidly adapted and deployed in various settings. Optical biosensors are an excellent solution due to their outstanding features. However, the sophisticated and expensive optical design limits their scalability and actual application. Herein, an innovative reusable smartphone-facilitated mobile fluorescence biosensor (s-MFB) was built through integrating miniaturized all-fiber optical system and microfluidic system with smartphone. An asymmetric Y-shaped fiber optic coupler (Y-FOC) is constructed for simultaneous transmission of excitation light and the collected fluorescence. In particular, the incidence rays are introduced into the fiber bio-probe at a specific angle through the single-mode fiber of the Y-FOC, which enhances the evanescent wave field and the number of total internal reflections. The s-MBF showed a LOD for free Cy5.5 of 0.1 nM. Combining indirect competitive immunoassay with the s-MFB, this new assay, which achieve quantitative detection of bisphenol A and norfloxacin in 15 min with high sensitivity and reusability, substantially reduces the complexity and improves the scalability of trace pollutants detection. The adjunctive smartphone application allows on-site real-time quantitative detection, automated interpretation of reporting results, and early-warning of pollution accidents.

A review on disinfection technologies for controlling the antibiotic resistance spread

The occurrence of antibiotic-resistant bacteria (ARB) in water bodies poses a sanitary and environmental risk. These ARB and other mobile genetic elements can be easily spread from hospital facilities, the point in which, for sure, they are more concentrated. For this reason, novel clean and efficient technologies are being developed for allowing to remove these ARB and other mobile genetic elements before their uncontrolled spread. In this paper, a review on the recent knowledge about the state of the art of the main disinfection technologies to control the antibiotic resistance spread from natural water, wastewater, and hospital wastewater (including urine matrices) is reported. These technologies involve not only conventional processes, but also the recent advances on advanced oxidation processes (AOPs), including electrochemical advanced oxidation processes (EAOPs). This review summarizes the state of the art on the applicability of these technologies and also focuses on the description of the disinfection mechanisms by each technology, highlighting the promising impact of EAOPs on the remediation of this important environmental and health problem.