Effects of supporting electrolytes in treatment of arsenate-containing wastewater with power generation by aluminumair fuel cell electrocoagulation

Control strategies for microplastic pollution in groundwater

Groundwater is the primary source of water that occurs below the earth's surface. However, the advancement in technology and the increasing population, which lead to the discharge of contaminants such as microplastics (MPs), have an adverse impact on the quality of groundwater. MPs are ubiquitous pollutants that are widely found throughout the world. The maximum abundance of MPs is 4 items/L and 15.2 items/L in groundwater at the specific location of China and USA. Various factors can affect the migration of MPs from soil to groundwater. The occurrence of MPs in water causes serious health issues. Therefore, taking appropriate strategies to control MP contamination in groundwater is urgent and important. This review summarizes the current literature on the migration process of MPs from soil to groundwater along with possible methods for the remediation of MP-polluted groundwater. The main objective of the review is to summarize the technical parameters, process, mechanism, and characteristics of various remediation methods and to analyze strategies for controlling MP pollution in groundwater, providing a reference for future research. Possible control strategies for MP pollution in groundwater include two aspects: i) prevention of MPs from entering groundwater; ii) remediation of polluted groundwater with MPs (ectopic remediation and in-situ remediation). Formulating legislative measures, strengthening public awareness and producing more environment-friendly alternatives can be helpful to reduce the production of MPs from the source. Manage plastic waste reasonably is also a good strategy and the most important part of the management is recycling. The shortcomings of the current study and the direction of future research are also highlighted in the review.

Removal of nutrients and other emerging inorganic contaminants from water and wastewater by electrocoagulation process

The continual discharge of emerging inorganic pollutants into natural aquatic systems and their negative effects on the environment have motivated the researchers to explore and develop clean and efficient water treatment strategies. Electrocoagulation (EC) is a rapid and promising pollutant removal approach that does not require any chemical additives or complicated process management. Therefore, inorganic pollutant treatment via the EC process is considered one of the most feasible processes. The potential developments of EC process may make the process a wise choice for water treatment in the future. Thus, the present study mainly focuses on the use of EC technology to remove nutrients and other emerging inorganic pollutants from water medium. The operating factors that influence EC process efficiency are explained. The major advancement of the EC technique as well as field-implemented units are also discussed. Overall, this study mainly focuses on emerging issues, present advancements, and techno-economic considerations in EC process.

Optimum parameters for humic acid removal and power production by Al-air fuel cell electrocoagulation in synthetic wastewater

Although humic acid (HA) is a complex natural organic matter, it can potentially harm the environment and human health. In this study, aluminum-air fuel cell electrocoagulation (AAFCEC) was used to remove HAs from water while generating electricity. Initial pH, electrolyte concentration, HA concentration electrode distance and external resistance were investigated to determine the power generation and removal efficiency. The results showed that the better performance of power generation has been acquired in the alkaline solution and larger electrolyte concentration and short electrode distance. Further, Al-Ferron complexation timed spectrophotometry was used to determine the Al speciation distribution in the solution under different parameters. The power density of the cell reached 313.47 mW/cm² for the following conditions: 1 g/L NaCl concentration, 3 cm electrode distance, 20 Ω external resistor, and pH 9. After about an hour of electrolysis, the optimum removal rate of HA was above 99%. The results demonstrated that the AAFCEC is an efficient and eco-friendly water treatment process, and it could be further developed and disseminated in the rural areas and households.

Electrochemical Mini-Platform with Thread based Electrodes for Interference Free Arsenic Detection

Herein, a fully integrated thread/textile-based electrochemical sensing device has been demonstrated. A hydrophilic conductive carbon thread, chemically modified with gold nanoparticles through an electrodeposition process, was used as a working electrode (WE). The hydrophilic thread coated with Ag/AgCl and an unmodified bare hydrophilic thread were used as reference electrode (RE) and counter electrode (CE) respectively. The device was fabricated with hydrophilic conductive carbon threads supported by capillary tubes and these integrated electrodes were placed in a 2 mL glass vial. The physico-chemical characterization of the working electrode was carried out using SEM (scanning electron microscopy) and X-ray photoelectron spectroscopy (XPS). Furthermore, the fabricated sensing platform, was tested for electrochemical sensing of arsenic. The electrocatalytic oxidation activity of arsenic in the designed platform was investigated via cyclic voltammetry (CV) and square wave Voltammetry (SWV). An oxidation peak at -0.4 V corresponding to the oxidation of arsenic was obtained. Scan rate effect was performed using CV analysis and the diffusion coefficient was found to be 2.478×10-10 with a regression coefficient of R2 = 0.9647. Further, concentration effect was accomplished in the linear range 0.4 μM to 60 μM. The limit of detection was obtained as 0.416 μM. For the practical application, effect of interference from other chemicals and real sample analysis from the tap water and blood serum sample was carried out which gave remarkable recovery values.

Arsenic and fluoride removal by electrocoagulation process: A general review

The environmental sector has expressed a growing interest in using electrocoagulation (EC) to treat groundwater/wastewater for drinking/recycling purposes. In the EC process, the electro-dissolution of sacrificial metallic anodes through direct application of current/cell potential dissolves the metals, which precipitate as oxides and hydroxides depending on the electrolyte pH. These particles have large surface areas and can remove pollutants by coagulation. The EC process has been considered an alternative technology due to its versatility, efficiency, low cost, and environmental compatibility. Unfortunately, the lack of knowledge about scaling-up this process has limited its implementation at the industrial scale. The aim of this study is to provide a review of the EC process used for removing arsenic and fluoride from groundwater and wastewater. Approximately 80 published studies were reviewed for this paper. The fundamentals of the EC process and importance of its operating conditions, i.e., electrode material, current density, supporting electrolyte, and pH, are reported in this paper. Additionally, overview of floc characterization and energy consumption are also presented. Finally, this paper also discusses the future perspectives.

Combined metal/air fuel cell and electrocoagulation process: Energy generation, flocs production and pollutant removal

Electrocoagulation (EC) which is characterized by in-situ generation of highly absorbable hydroxide flocs, is an environmentally friendly process for treating heavy metal ions and toxic organic wastewater. In order to decrease EC's energy consumption, a combined metal/air FC-EC process which contains two successive parts: metal/air fuel cell (FC) and electrocoagulation (EC) was studied with the consideration of hydroxide flocs production, pollutant removal and energy generation analysis. For the combined iron/air FC-EC process, the porous nickel cathode which has a good performance in high polarization zone was selected as the ideal air cathode. It was found that iron/air FC-EC with acid electrolyte condition has a high energy generation (as high as 20% EC energy consumption). The energy generation increases with iron/air FC time. Also energy generation increases with wastewater's conductivity. Beside the energy generation, the iron/air fuel cell generate extra coagulants Fe²⁺ for the subsequent EC process. The coagulants generated from iron/air FC and EC process together have further spontaneous hydrolysis reactions with the OH^- to form hydroxide flocs, which are beneficial for a rapid adsorption and pollutant trapping. Compared with EC process, iron/air (or Al/air) FC-EC process shows lower energy consumption and high removal efficiency for treating acid wastewater.

Nanomaterials-based treatment options for chromium in aqueous environments

Sustainable development and the restoration of ecosystems are the important goals for civilization. Currently, heavy metal contamination of aquatic environments has become a serious issue. Chromium (Cr) is simultaneously an essential metallic element and one of 20 chemicals posing a maximum threat to living beings. To mitigate that threat, various treatment methods have been developed, including adsorption, electrocoagulation, photoelectrocatalysis, fuel cells, bioremediation, chemical precipitation, ultrafiltration, ion exchange, and co-precipitation. However, selection of the most energy- and cost-efficient wastewater treatment option has proven challenging, as each approach is subject to shortcomings involving energy consumption, treatment capacity, and efficiency. This review describes the potential role of diverse functional nanomaterials (e.g., iron/iron oxide nanoparticles, carbon nanostructures, metal organic frameworks, and their commercial counterparts) in treatment of Cr in aqueous environments with respect to key figure of merits, such as, adsorption capacity, removal efficiency, and partition coefficient. In addition, their performance was compared with the most common treatment options. The results of this study will help determine the most effective and economical options for control of Cr in aquatic environments.