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

Efficient adsorption of hexavalent chromium in water by torrefaction biochar from lignin-rich kiwifruit branches: The combination of experiment, 2D-COS and DFT calculation

A biochar (KBC) enriched with O functional groups was prepared by torrefaction using lignin-rich kiwifruit branches (KBM) as a raw material, which was characterized, and then KBC was used to adsorb hexavalent chromium (Cr6+) from water. The results showed that KBC contained more functional groups compared to KBM. The maximum adsorption of Cr6+ by KBC could reach 143.64 mg·g-1 and also had better adsorption performance than other adsorbents reported in some other reports. Cr6+ absorption by KBC was mainly a mechanism of electrostatic interaction and adsorption-reduction coupling. FTIR and XPS revealed that -OH, -COOH, CO and CC on KBC participated in Cr6+ adsorption and new groups (C=O) were generated during the process of adsorption, which implied that a redox reaction occurred. 2D-COS and DFT calculations showed that the order of functional groups on KBC interacting with Cr6+ was -OCH3 > -COOH > -OH > phenolic hydroxyl, and the binding tightness of the different functional groups to Cr6+ was -OCH3 (the shortest displacement of both groups after the adsorption) > -COOH > -OH > phenolic hydroxyl. KBC has good regeneration performance, and it is a good adsorbent for Cr6+.

Electrocoagulation in treatment of municipal wastewater- life cycle impact assessment

The purpose of this study is investigation of electrocoagulation (EC) as a treatment of municipal wastewater, integrating life cycle impact assessment (LCIA) for assessing its environmental performance of investigated treatment. The study evaluated the effectiveness of EC in removing physico-chemical and microbial parameters using aluminum (Al) and iron (Fe) electrodes in monopolar and bipolar modes. Bipolar arrangement of Al(-)/Al/Al/Al(+) electrodes achieved the highest removals: 70% COD, 72% BOD5 followed by complete elimination of total phosphorous, turbidity and microbial parameters. This treatment was subject to investigation of the influence of reaction time (t = 10-60 min) on removals at higher current density (CD = 3.33 mA/cm2). In order to reduce energy consumption, the same reaction time range was used with a reduced CD = 2.33 mA/cm2. Following removal efficiencies obtained: 47-72% COD (higher CD) and 53-78% (lower CD); 69-75% BOD5 (higher CD) and 55-74% CD (lower CD); 12-21% NH4- (higher CD) and 7-22% NH4- (lower CD). Total P, NO3- and NO2- compounds showed the same removals regardless the CD. Decrease in current density did not influence removals of total suspended matter, turbidity, salinity as well as microbial parameters. The bipolar arrangement of Al(-)/Al/Al/Al(+) electrodes, assuming a lower CD = 2.33 mA/cm2 and t = 30 min, was assessed with the Recipe 2016Midpoint (H) and USEtox v.2 LCIA methods to explore the environmental justification of using EC for wastewater treatment. The LCIA results revealed that the EC process significantly reduces water eutrophication and toxicity for freshwater and marine ecosystems, but has higher impacts in global warming, fossil fuel consumption, human toxicity, acidification, and terrestrial ecotoxicity due to high energy consumption. This can be mainly explained by the assumption in the study that the EC precipitate is dispersed to agricultural soil without any pre-treatment and material recovery, along with relatively high energy consumption during the process.

Conversion of locally available materials to biochar and activated carbon for drinking water treatment

For environmental sustainability and to achieve sustainable development goals (SDGs), drinking water treatment must be done at a reasonable cost with minimal environmental impact. Therefore, treating contaminated drinking water requires materials and approaches that are inexpensive, produced locally, and effortlessly. Hence, locally available materials and their derivatives, such as biochar (BC) and activated carbon (AC) were investigated thoroughly. Several researchers and their findings show that the application of locally accessible materials and their derivatives are capable of the adsorptive removal of organic and inorganic contaminants from drinking water. The application of locally available materials such as lignocellulosic materials/waste and its thermo-chemically derived products, including BC and AC were found effective in the treatment of contaminated drinking water. Thus, this review aims to thoroughly examine the latest developments in the use of locally accessible feedstocks for tailoring BC and AC, as well as their features and applications in the treatment of drinking water. We attempted to explain facts related to the potential mechanisms of BC and AC, such as complexation, co-precipitation, electrostatic interaction, and ion exchange to treat water, thereby achieving a risk-free remediation approach to polluted water. Additionally, this research offers guidance on creating efficient household treatment units based on the health risks associated with customized adsorbents and cost-benefit analyses. Lastly, this review work discusses the current obstacles for using locally accessible materials and their thermo-chemically produced by-products to purify drinking water, as well as the necessity for technological interventions.

Hybrid electrochemical/membrane couplings processes for enhancing seawater pretreatment and desalination

This research focuses on boosting seawater pretreatment and desalination through electrocoagulation (EC)/ultrafiltration (UF) and electrocoagulation (EC)/nanofiltration (NF) processes. We first optimized the key parameters of the EC process using aluminum (Al) and iron (Fe) electrodes. Experimental results show EC process is efficient under optimal conditions. Second, membrane filtration using UF (ES10B), NF(UTC60) and NF(200) as post-processing steps to the EC process were experimented with. EC(Al)/NF(UTC60) combination resulted in the highest removal rate of organic matter (COD 98%, TOC 95%, fluorescence [humic and fulvic acids] 68%), optical density (OD600nm 75%, turbidity 70%, conductivity 64%). In terms of major ions removal, up to 55% was achieved as NF decreases conductivity, salinity, and hardness. EC(Al)/NF(UTC60) seawater permeate demonstrated the best results in terms of lowest flux decline (J/Jo  = 0.9) and fouling, which was realized by resistance in series and recovery factor rate (%). Additionally, NF(UTC60) fouling reversibility led to a longer lifetime and higher recovery factor (93%). PRACTITIONER POINTS: Pretreatment by hybrid processes was experimented with to enhance the saline water treatment. Organic matter (COD 98%, TOC 95%, fluorescence [humic and fulvic acids] 68%) and turbidity were successfully removed. Salinity and hardness (conductivity 64%) were highly reduced by NF. Flux decline, retention rate, and membrane fouling were studied.

A review on recent environmental electrochemistry approaches for the consolidation of a circular economy model

Availability of raw materials in the chemical industry is related to the selection of the chemical processes in which they are used as well as to the efficiency, cost, and eventual evolution to more competitive dynamics of transformation technologies. In general terms however, any chemically transforming technology starts with the extraction, purification, design, manufacture, use, and disposal of materials. It is important to create a new paradigm towards green chemistry, sustainability, and circular economy in the chemical sciences that help to better employ, reuse, and recycle the materials used in every aspect of modern life. Electrochemistry is a growing field of knowledge that can help with these issues to reduce solid waste and the impact of chemical processes on the environment. Several electrochemical studies in the last decades have benefited the recovery of important chemical compounds and elements through electrodeposition, electrowinning, electrocoagulation, electrodialysis, and other processes. The use of living organisms and microorganisms using an electrochemical perspective (known as bioelectrochemistry), is also calling attention to "mining", through plants and microorganisms, essential chemical elements. New process design or the optimization of the current technologies is a major necessity to enhance production and minimize the use of raw materials along with less generation of wastes and secondary by-products. In this context, this contribution aims to show an up-to-date scenario of both environmental electrochemical and bioelectrochemical processes for the extraction, use, recovery and recycling of materials in a circular economy model.

Electrochemical treatment of wastewater containing urea-formaldehyde and melamine-formaldehyde

The wastewater containing urea-formaldehyde (UF) and melamine-formaldehyde (MF) from the medium-density fiberboard (MDF) lamination factory disposed into the waterbodies adversely affects human health and aquatic life. Therefore, its treatment before discharge is necessary. Researchers have used various techniques to treat this type of wastewater in the past, but none have tried electrochemical (EC). However, EC can potentially remove pollutants such as chemical oxygen demand (COD), total organic carbon (TOC), formaldehyde (FA), total nitrogen (TN), nitrogen nitrate (NO3-N), and other hydrocarbons. Hence, this study uses the EC technique to treat wastewater containing UF and MF with aluminium electrodes. The experiments were run in batch mode with a 250 mL working volume in a 500 mL Pyrex glass beaker using a variable DC power supply (0-30 V and 0-5 A). The impacts of various parameters, including reaction time (RT) 30-240 min, current density (CD) 8.66-51.94 mA/cm2, inter-electrode distance (IED) 1-2 cm, and mixing speed in the range of 60-120 rpm were examined to achieve the best pollutant removals. The best removal percentage was reached at the optimized conditions of 150 min RT, 43.28 mA/cm2 CD, 1.5 cm IED, and 80 rpm: 81.1% TOC, 61.5% COD, 76.7% TN, 28.3% NO3-N, and 55.2% FA. During the EC process, electrodes and energy consumption were estimated at around 2.367 (g/L) and 0.18 (kWh/L), respectively. A kinetic analysis was also carried out to determine the pollutant's removal trend. This study concluded that the pseudo-first-order kinetic model was the best fit for removing TOC and FA with regression coefficients of 0.96 and 0.83, respectively.

Integrating of electrocoagulation process with submerged membrane bioreactor for wastewater treatment under low voltage gradients

Treating and reusing wastewater has become an essential aspect of water management worldwide. However, the increase in emerging pollutants such as polycyclic aromatic hydrocarbons (PAHs), which are presented in wastewater from various sources like industry, roads, and household waste, makes their removal difficult due to their low concentration, stability, and ability to combine with other organic substances. Therefore, treating a low load of wastewater is an attractive option. The study aimed to address membrane fouling in the submerged membrane bioreactor (SMBR) used for wastewater treatment. An aluminum electrocoagulation (EC) device was combined with SMBR as a pre-treatment to reduce fouling. The EC-SMBR process was compared with a conventional SMBR without EC, fed with real grey water. To prevent impeding biological growth, low voltage gradients were utilized in the EC deviceThe comparison was conducted over 60 days with constant transmembrane pressure and infinite solid retention time (SRT). In phase I, when the EC device was operated at a low voltage gradient (0.64 V/cm), no significant improvement in the pollutants removal was observed in terms of color, turbidity, and chemical oxygen demand (COD). Nevertheless, during phase II, a voltage gradient of 1.26 V/cm achieved up to 100%, 99.7%, 92%, 94.1%, and 96.5% removals in the EC-SMBR process in comparison with 95.1%, 95.4%, 85%, 91.7% and 74.2% removals in the SMBR process for turbidity, color, COD, ammonia nitrogen (NH3-N), total phosphorus (TP), respectively. SMBR showed better anionic surfactant (AS) removal than EC-SMBR. A voltage gradient of 0.64 V/cm in the EC unit significantly reduced fouling by 23.7%, while 1.26 V/cm showed inconsistent results. Accumulation of Al ions negatively affected membrane performance. Low voltage gradients in EC can control SMBR fouling if Al concentration is controlled. Future research should investigate EC-SMBR with constant membrane flux for large-scale applications, considering energy consumption and operating costs.

Efficacious degradation of ethylene glycol by ultraviolet activated persulphate: reaction kinetics, transformation mechanisms, energy demand, and toxicity assessment

Ethylene glycol or 1,2-ethanediol (EG) is a persistent and toxic substance in the environment and extensively applied in petrochemical, surfactants, antifreeze, asphalt emulsion paints, cosmetics, plastics, and polyester fiber industries. Degradation of EG by using ultraviolet (UV) activated hydrogen peroxide (H2O2) and persulfate (PS) or persulfate anion (S2O82-) based advanced oxidation processes (AOPs) were explored. The result obtained demonstrate that UV/PS (85.7 ± 2.5%) has exhibited improved degradation efficiency of EG as compared to UV/H2O2 (40.4 ± 3.2%) at optimal operating conditions of 24 mM of EG concentration, 5 mM of H2O2, 5 mM of PS, 1.02 mW cm-2 of UV fluence, and pH of 7.0. Impacts of operating factors, including initial EG concentration, oxidant dosage, reaction duration, and the impact of different water quality parameters, were also explored in this present investigation. The degradation of EG in Milli-Q® water followed pseudo - first order reaction kinetics in both methods having a rate constant of about 0.070 min-1 and 0.243 min-1 for UV/H2O2 and UV/PS, respectively, at optimum operating conditions. Additionally, an economic assessment was also conducted under optimal experimental conditions, and the electrical energy per order and total operational cost for treating per m3 of EG-laden wastewater was observed to be about 0.042 kWh m-3 order-1 and 0.221 $ m-3 order-1, respectively, for UV/PS, which was slightly lower than UV/H2O2 (0.146 kWh m-3 order-1; 0.233 $ m-3 order-1). The potential degradation mechanisms were proposed based on intermediate by-products detected by Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS). Moreover, real petrochemical effluent containing EG was also treated by UV/PS, demonstrating 74.7 ± 3.8% of EG and 40.7 ± 2.6% of total organic carbon removal at 5 mM of PS and 1.02 mW cm-2 of UV fluence. A toxicity tests on Escherichia coli (E. coli) and Vigna radiata (green gram) confirmed non-toxic nature of UV/PS treated water.

Recent advances in carbon-based nanomaterials for the treatment of toxic inorganic pollutants in wastewater

Wastewater contains inorganic pollutants, generated by industrial and domestic sources, such as heavy metals, antibiotics, and chemical pesticides, and these pollutants cause many environmental problems.

Nutrients and Environmental Factors Cross Wavelet Analysis of River Yi in East China: A Multi-Scale Approach

The accumulation of nutrients in rivers is a major cause of eutrophication, and the change in nutrient content is affected by a variety of factors. Taking the River Yi as an example, this study used wavelet analysis tools to examine the periodic changes in nutrients and environmental factors, as well as the relationship between nutrients and environmental factors. The results revealed that total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen (NH4+-N) exhibit multiscale oscillation features, with the dominating periods of 16-17, 26, and 57-60 months. The continuous wavelet transform revealed periodic fluctuation laws on multiple scales between nutrients and several environmental factors. Wavelet transform coherence (WTC) was performed on nutrients and environmental factors, and the results showed that temperature and dissolved oxygen (DO) have a strong influence on nutrient concentration fluctuation. The WTC revealed a weak correlation between pH and TP. On a longer period, however, pH was positively correlated with TN. The flow was found to be positively correct with N and P, while N and P were found to be negatively correct with DO and electrical conductance (EC) at different scales. In most cases, TP was negatively correlated with 5-day biochemical oxygen demand (BOD₅) and permanganate index (COD_Mn). The correlation between TN and COD_Mn and BOD₅ was limited, and no clear dominant phase emerged. In a nutshell, wavelet analysis revealed that water temperature, pH, DO, flow, EC, COD_Mn, and BOD₅ had a pronounced influence on nutrient concentration in the River Yi at different time scales. In the case of the combination of environmental factors, pH and DO play the largest role in determining nutrient concentration.

Water Treatment Using Natural Coagulant and Electrocoagulation Process: A Comparison Study

Water treatment is the primary consideration before utilizing water for different purposes. Surface water is highly vulnerable to pollution, either due to natural or anthropogenic processes. The main targets of this study were to investigate surface water treatment using Moringa Oleifera (MO), the electrocoagulation process (EC), and the Moringa Oleifera assisted electrocoagulation process (MOAEC). The Moringa Oleifera, EC process, and Moringa Oleifera-assisted EC process are effective mechanisms for the removal of COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand), TDS (Total Dissolved Solids), phosphate, TSS (Total Suspended Solids), and color from surface water. Different operating parameters such as pH (5–11), the dosage of coagulant (0.2–0.5 g), contact time or reaction time (20–50 minutes), current (0.2–0.5 A), and settling time (5–20 minutes) were considered. The maximum removal efficiency using Moringa Oleifera and the EC process was COD (85.48%), BOD (78.50%), TDS (84.5%), phosphate (95.70%), TSS (93.90%), color (94.50%), and COD (90.50%), BOD (87%), TDS (97.50%), phosphate (89.10%), TSS (95.80%), and color (96.15%), respectively. Similarly, with the application of MOAEC, 91.47%, 89.35%, 97.0%, 90.20%, 9.10%, and 95.70% of COD, BOD, TDS, phosphate, TSS, and color were removed, respectively. The EC process and MOAEC were more effective in the removal of COD, BOD, TDS, TSS, and color than using MO. More phosphate was removed using MO than the EC process and MOAEC. Additionally, the effects of different operating parameters were studied on the removal efficiency.