Removal of humic acid by fixed-bed electrocoagulation reactor: Studies on modelling, adsorption kinetics and HPSEC analyses

Development and application of novel high throughput metal waste chips and foam electrodes for electrocoagulation treatment of graywater

In this study, novel high throughput metal waste chips and foam electrodes were developed for the electrocoagulation of graywater for the first time. The developed electrodes were then compared with traditional metal plate electrodes, which showed higher efficiency of developed electrodes. The effective parameters of pH, electrode distance, applied voltage, and reaction time on COD removal were optimized using RSM as a multivariate optimization technique, and the data were analyzed by ANOVA, normal plot, residual distribution, and 3D plots. The optimal conditions for electrocoagulation of graywater using metal (Al) plate electrode were determined as a pH of 6.86, electrode distance of 5 mm, and applied voltage of 5 V for a reaction time of 10 min, resulting in 89.1% COD removal and 74% turbidity removal. Finally, the performance of aluminum plate electrodes, foam electrodes, and electrodes made from metal waste chips was compared using COD removal efficiency as the index, revealing 84%, 93%, and 87% COD removal, respectively. These results demonstrated that the newly developed electrodes are suitable for graywater treatment with excellent COD removal efficiency, metal chip waste recycling, and cost-saving.

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.

Electrocoagulation technology for water purification: An update review on reactor design and some newly concerned pollutants removal

Water shortage and quality deterioration are plaguing people all over the world. Providing sustainable and affordable treatment solutions to these problems is a need of the hour. Electrocoagulation (EC) technology is a burgeoning alternative for effective water treatment, which offers the virtues such as compact equipment, easy operation, and low sludge production. Compared to other water purification technologies, EC shows excellent removal efficacy for a wide range of contaminants in water and has great potential for addressing limitations of conventional water purification technologies. This review summarizes the latest development of principle, characteristics, and reactor design of EC. The design of key parameters including reactor shape, power supply type, current density, as well as electrode configuration is further elaborated. In particular, typical water treatment systems powered by renewable energy (solar photovoltaic and wind turbine systems) are proposed. Further, this review provides an overview on expanded application of EC in the removal of some newly concerned pollutants in recent years, including arsenite, perfluorinated compounds, pharmaceuticals, oil, bacteria, and viruses. The removal efficiency and mechanisms of these pollutants are also discussed. Finally, future research trend and focus are further recommended. This review can bridge the large knowledge gap for the EC application that is beneficial for environmental researchers and engineers.

Arsenite removal from groundwater by aerated electrocoagulation reactor with Al ball electrodes: Human health risk assessment

The application of conventional electrocoagulation (EC) process for removal of As(III) from groundwater suffers from the need of external oxidation agent for oxidation of As(III) to As(V). To tackle this limitation, an aerated EC reactor for the removal of As(III) from groundwater was evaluated in this study. The effect of initial pH_i, air flow rate, applied current, and electrode height in the EC reactor was examined. The experimental results showed that removal of arsenic mostly dependent on the applied current, electrode height in EC reactor, and air flow rate. The As(III) removal efficiency (99.2%) was maximum at pH_i of 7.5, air flow rate of 6 L min^-1, applied current of 0.30 A, and electrode height in EC reactor of 5 cm, with an total operating cost of 0.583 $ m^-3. Furthermore, the carcinogenic risk (CR) and non-carcinogenic risk of arsenic (As) was in the range of tolerable limits at all operating conditions except applied current of 0.075 A at the end of the aerated EC process to remove As from groundwater. The present EC reactor process is able to remove As(III) from groundwater to below 10 μg L^-1, which is maximum contaminant level of arsenic in drinking water according to the World Health Organization (WHO).

Optimization of membrane modification using SiO2 for robust anti-fouling performance with calcium-humic acid feed in membrane distillation

The goal of this study was to prepare a robust anti-wetting and anti-fouling polyethersulfone (PES) membrane for the rejection of a highly saline (NaCl and CaCl₂·2H₂O) feed solution containing humic acid (HA) in direct contact membrane distillation (DCMD). Response surface methodology (RSM) was used to determine the optimum formulation of the used materials. The variable factors selected were polydimethyl siloxane (PDMS) and silica (SiO₂); liquid entry pressure (LEP) and contact angle (CA) were selected as responses. Scanning electron microscopy (SEM) analysis confirmed the SiO₂ deposition and Fourier-transform infrared spectroscopy (FTIR) test evidenced the new functional groups i.e., Si-OH, siloxane, and C-F bond vibrations at 3446, 1099 cm^-1, and 1150-1240 cm^-1 respectively on the membrane surface. The average roughness (Ra) was increased four times for the coated membranes (0.202-0.242 µm) as compared to that for pristine PES membrane (0.053 µm). The optimum PES-13 membrane exhibited consistent flux of 12 LMH and salt rejection (> 99%) with anti-fouling characteristic in DCMD using the feed solution of 3.5 wt% NaCl + 10 mM CaCl₂·2H₂O + 10 mg L^-1 HA. The PES-13 membrane may therefore be a key membrane for application in DCMD against CaCl₂·2H₂O-containing salty solutions with HA.

Electrochemical Removal of Humic Acids from Water Using Aluminum Anode: Influence of Chloride Ion and Current Parameters

The removal by electrochemical treatment in batch of humic acids (HA) extracted from leonardite has been analyzed using aluminum electrodes at 25°C and neutral pH, under galvanostatic conditions. HA removal, inferred from UV-Vis spectra and total organic carbon determination, occurred within few minutes of treatment under the experimental conditions tested, and no electrode passivation was observed. The removal rate increased with NaCl concentration and electric current density. Our data indicate that energy consumption per unit weight of HA removed can be significantly reduced by operating at low current density under galvanostatic conditions and/or high salt concentration, thus confirming electrochemical treatment as a powerful technology for wastewater treatment.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.