Denim industry wastewater treatment by a heterogeneous solar-Fenton process catalyzed by Fe supported on recycled polyethylene terephthalate (PET) by ultrasonic modification.

The textile industry is an important economic sector; however, its wastewater generates a great impact on the environment. A heterogeneous solar Fenton (HSF) process was evaluated for denim wastewater treatment. The catalyst was obtained through ultrasonic modification of recycled polyethylene terephthalate (PET) with Fe nanoparticles (PET/NPs- Fe3O4). The SFH process was optimized using surface response methodology with a face-centered central composite design considering the effects of the hydraulic retention time (10, 25, and 40 min), hydrogen peroxide dosage (500, 1000, and 1500 mg/L), and mass of the packed catalyst (4, 6 and 8 g) on the color, COD, and turbidity removal efficiencies. The operating conditions for maximum COD removal were H2O2 541.7 mg/L, HRT 33.9 min, and PET/NPs- Fe3O4 dose 7.9 g with solar radiation. The removal of 91.2% COD, 86.2% color, 90.4% turbidity, and 81.9% TOC was obtained at 14.2 kJ/L QUva. PET modification yielded 1.6 mg Fe/g PET, and the modification method does not allow Fe leaching. The effluent obtained from the SFH process complies with the maximum permissible limits in Mexican legislation in terms of COD, TOC, turbidity, and color and allows the reuse of PET.

Sustainable removal of nutrients (n and p) in a wastewater treatment plant, with eggshell (biocalcium).

Biological treatments have become insufficient to treat municipal wastewater with greater toxicity and excess nitrogen and phosphate species, thus affecting the organisms that consume the water. In this work, a process was implemented for the removal of nutrients through three stages: stage A, complete aeration (24 h, 43 months); stage B, decreased aeration (12 h, 17 months); and stage C, decreased aeration with biocalcium (12 h, 19 months). The addition of biocalcium from eggshell promoted the formation of flocks, which resulted in the removal of nitrites (61 %), nitrates (84 %), total nitrogen (57 %), total phosphorus (8.3 %), sedimentable solids (50 %), total suspended solids (69 %), BOD5 (76 %), helminth eggs (50 %) and fecal coliforms (54 %). The statistical analyses in the three stages indicated that there is a strong correlation between the concentration of fats and oils and the removal of sedimentable solids and total suspended solids, since these parameters were correlated by 97 and 89 %, respectively. Sedimentable solids were correlated with total suspended solids by 94 %, while nitrates and total nitrogen were correlated 92 %, which favors the removal of nutrients in wastewater. The increase in the concentration of nitrogen in the sludge in stage C generated a C:N ratio of 7.98. This ratio shows that the sludge is feasible for use as a mediator of soils and a biofertilizer because of the high contents of calcium, phosphorus and nitrogen. In addition, biocalcium promoted the precipitation of hydroxyapatite, struvite, calcite and quartz. In general, the three stages of the treatment contributed to the stabilization of the wastewater treatment plant (WWTP) in an efficient, economical, and safe way.

Electro-galvanic alkalization and treatment of rainwater to obtain drinking water.

Rainwater Electro-Galvanic Alkalization (EGA) was performed using copper and magnesium (1:1) electrode. Efficiently removal of pollutants without external energy consumption was carried out, in addition essential ions were dosed for alkalization of rainwater. The optimal system conditions were obtained using response surface methodology (RSM) by considering the following operating variables: flow rate and concentration of the supporting electrolyte (NaCl and CaCl2). Furthermore, the maximum efficiency of nitrate, ammoniacal nitrogen, colour, and turbidity removal was evaluated. The results showed that the response variables were mainly sensitive to the type of supporting electrolyte used and the flow rate. Under experimental conditions of 0.009 M (NaCl) and 20 mL min-1, the removal rate was 74.19%, 72.49%, and 81.43% for nitrates, colour, and turbidity, respectively, and the lowest concentration of ammoniacal nitrogen (0.99mgL-1) was obtained. The kinetic models for nitrate and colour were fitted to zero-order models with k=0.33mgL-1min-1 and k=0.933Pt-Co, respectively. In addition, turbidity was fitted to a first-order model (k=0.1661min-1), and ammoniacal nitrogen was fitted to a second-order model (k=0.0217Lmg-1min-1). The concentration increases of minerals such as Ca and Mg, which rises the rainwater alkalinity after treatment (pH shift from 6.1 to 8.91), was determined by inductively coupled plasma (ICP) analysis.

Treatment of gaseous streams polluted with H2S: Comparison of electrolytic and electro-Fenton assisted absorption processes.

H2S is a gaseous compound that contributes to air pollution. In this work, the electrochemical oxidation treatment of gaseous streams polluted with H2S is evaluated using a jet mixer and electrochemical cell device, in which the performance of electrolytic and electro-Fenton assisted absorption processes are compared. Results demonstrate the feasibility of both processes to remove H2S, reaching coulombic efficiencies of nearly 100% in the electrolytic assisted absorption, and 70-80% in the electro-Fenton assisted absorption. Aqueous solutions containing phosphate salts as electrolyte were found to be suitable as absorbents for the process. Efficiency in the cathodic production of H2O2 in these solutions using the experimental device was found to be as high as 32.8% (1.184 mgH2O2/min) at 12 °C and atmospheric pressure. Sequential formation of SO2 and SO3 is obtained by the oxidation of H2S contained in the gas. These species are hydrolysed, and a part remained in the absorbent as SO32- and SO42-, while the rest is dragged in the outlet gas. SO3 production is promoted by electrolytic assisted absorption and polysulphides by the electro-Fenton technology. Low concentrations of elemental sulphur are detected in the solid suspensions formed during the process.

Acid mine drainage (AMD) treatment using galvanic electrochemical system Al-Cu.

Acid mine drainage was evaluated using a galvanic (GV) electrochemical system, Al-Cu (anode/cathode), based on a 32 factorial design. The factors analyzed were anodic area/volume ratios (A/V) of 0.037, 0.072, and 0.112 cm2/cm3, and treatment time from 0.25-8 h, and analyses were performed in duplicate with 11 degrees of freedom. The response variables were the total dissolved solids and concentrations of As, Cu, Co, Cr, Pb, Fe, Ni, and SO42-. The pH, electrical conductivity, and temperature were monitored during the process. Significant differences between treatments were determined by analysis of variance with Tukey's test (p < 0.05) using Statgraphics Centurion XVI.I software. The results showed that a greater electrode surface, A/V ratio, and treatment time improved pollutant removal. The spontaneous reactions generated by the galvanic cell, through the current that flows owing to the potential difference between the Al and Cu electrodes, allows the removal of heavy metals, arsenic, and SO42- by coagulation and precipitation mechanisms. The removal efficiencies achieved were Cu (99.1%), As (76.6%), Ni (80.2%), Pb (83.6%), Cr (100%), Fe (93.71%), and 92.9% for sulfates. The X-ray diffraction and Raman analyses of the solid fraction indicated that cuprite was formed with a purity of 96%, and the recovery of Cu by the GV system may be a viable option for mining companies.

SARS-CoV-2 pharmaceutical drugs: a critical review on the environmental impacts, chemical characteristics, and behavior of advanced oxidation processes in water.

This review summarizes research data on the pharmaceutical drugs used to treat the novel SARS-CoV-2 virus, their characteristics, environmental impacts, and the advanced oxidation processes (AOP) applied to remove them. A literature survey was conducted using the electronic databases Science Direct, Scopus, Taylor & Francis, Google Scholar, PubMed, and Springer. This complete research includes and discusses relevant studies that involve the introduction, pharmaceutical drugs used in the SARS-CoV-2 pandemic: chemical characteristics and environmental impact, advanced oxidation process (AOP), future trends and discussion, and conclusions. The results show a full approach in the versatility of AOPs as a promising solution to minimize the environmental impact associated with these compounds by the fact that they offer different ways for hydroxyl radical production. Moreover, this article focuses on introducing the fundamentals of each AOP, the main parameters involved, and the concomitance with other sources and modifications over the years. Photocatalysis, sonochemical technologies, electro-oxidation, photolysis, Fenton reaction, ozone, and sulfate radical AOP have been used to mineralize SARS-CoV-2 pharmaceutical compounds, and the efficiencies are greater than 65%. According to the results, photocatalysis is the main technology currently applied to remove these pharmaceuticals. This process has garnered attention because solar energy can be directly utilized; however, low photocatalytic efficiencies and high costs in large-scale practical applications limit its use. Furthermore, pharmaceuticals in the environment are diverse and complex. Finally, the review also provides ideas for further research needs and major concerns.

As and [Formula: see text] cooccurrence in drinking water: critical review of the international scenario, physicochemical behavior, removal technologies, health effects, and future trends.

Drinking water contaminated with As and [Formula: see text] is increasingly prevalent worldwide. Their coexistence can have negative effects due to antagonistic or synergistic mechanisms, ranging from cosmetic problems, such as skin lesions and teeth staining, to more severe abnormalities, such as cancer and neurotoxicity. Available technologies for concurrent removal include electrocoagulation ~ adsorption > membranes > chemical coagulation > , and among others, all of which have limitations despite their advantages. Nevertheless, the existence of competing ions such as silicon > phosphate > calcium ~ magnesium > sulfate > and nitrate affects the elimination efficiency. Mexico is one of the countries that is affected by As and [Formula: see text] contamination. Because only 10 of the 32 states have adequate removal technologies, more than 65% of the country is impacted by co-presence problems. Numerous reviews have been published concerning the elimination of As or [Formula: see text]. However, only a few studies have focused on the simultaneous removal. This critical review analyzes the new sources of contamination, simultaneous physicochemical behaviors, available technologies for the elimination of both species, and future trends. This highlights the need to implement technologies that work with actual contaminated water instead of aqueous solutions (55% of the works reviewed correspond to aqueous solutions). Similarly, it is necessary to migrate to the creation of pilot, pre-pilot, or prototype scale projects, because 77% of the existing studies correspond to lab-scale research.

Photo-electrooxidation treatment of Acetaminophen in aqueous solution using BDD-Fe and BDD-Cu systems.

In this study, acetaminophen (ACT) in aqueous solution was treated with electrooxidation and photo-electrooxidation processes (PEO). An electrochemical cell was used for the treatment of different concentrations of ACT (10, 50 and 80 mg L-1). A 23 factorial design was proposed, and the variables studied were current intensity 0.5 A (45.45 mA cm-2) and 1.0 A (90.91 mA cm-2), electrode configuration (anode:BDD, cathode:Fe or Cu) and presence/absence of UV light; NaCl 0.043 M (2.5 g L-1) was used as supporting electrolyte, the initial pH was 5.5, and the treatment time was 3 h. The aqueous solutions were characterized before and after the treatment using infrared spectroscopy (FT-IR), Ultraviolet-visible spectroscopy (UV-Vis), chemical oxygen demand (COD), total organic carbon (TOC), total carbon (TC), and fluorescence spectroscopy. The optimal operating conditions using an initial ACT concentration of 80 mg L-1 were 1.0 A, BDD-Fe configuration and UV light (254 nm). The removal efficiencies were 100% of ACT and 82.75% of TOC after 15 min of treatment. At concentrations of 50 and 10 mg L-1, 77.16% and 50.29% of TOC were removed after 10 and 5 min of treatment, respectively. Finally, the kinetic study showed an increase in the rate constants when the UV light was applied.

Defluoridation of drinking water by magnesium and aluminum electrocoagulation in continuous flow-rate: a response surface design.

The goal of this research is to apply an electrocoagulation process in continuous flow for the defluoridation of drinking water. Two sampling sites were studied, Temascalcingo (T), Mexico state and Jerecuaro (J), Guanajuato, with fluoride (F-) concentrations above the norms (2.3 mg L-1 and 4.5 mg L-1, respectively). In addition, a second Temascalcingo sample was enriched (TE) to 9.2 mg L-1 F- to study the effect of the F- concentration. A response surface design was proposed through a Box-Behnken model, and the variables studied were electrode system, flow-rate and current intensity. 51 experiments were performed with T-site to determine the best operating conditions for the system. These conditions were applied to the J-site. The experiments for T, Al/Al system achieves an F- concentration within permissible limits (0.72 mg L-1 F-) at 10 min of treatment, 0.2 A (Current density j 48.78 A m-2) and 10 mL min-1 with a removal efficiency of 68.69%, and after 160 min, the removal increased to 99.56%. AlMg/AlMg needs 10 min to achieve a concentration of 0.75 mg L-1 F- at 0.2 A (j 25 A m-2), 16 mL min-1 with a removal efficiency of 67.39%, and after 100 min, the removal is increased to 92.17%. An important and novel advantage is the use of AlMg allows an acceptable removal of F- (<1.5 mg L-1) at high and low concentrations in short periods of time; this also allows save energy costs and the effluent is free of residual aluminum, avoiding side effects.

The impact of coronavirus SARS-CoV-2 (COVID-19) in water: potential risks.

This review summarizes research data on SARS-CoV-2 in water environments. A literature survey was conducted using the electronic databases Science Direct, Scopus, and Springer. This complete research included and discussed relevant studies that involve the (1) introduction, (2) definition and features of coronavirus, (2.1) structure and classification, (3) effects on public health, (4) transmission, (5) detection methods, (6) impact of COVID-19 on the water sector (drinking water, cycle water, surface water, wastewater), (6.5) wastewater treatment, and (7) future trends. The results show contamination of clean water sources, and community drinking water is vulnerable. Additionally, there is evidence that sputum, feces, and urine contain SARS-CoV-2, which can maintain its viability in sewage and the urban-rural water cycle to move towards seawater or freshwater; thus, the risk associated with contracting COVID-19 from contact with untreated water or inadequately treated wastewater is high. Moreover, viral loads have been detected in surface water, although the risk is lower for countries that efficiently treat their wastewater. Further investigation is immediately required to determine the persistence and mobility of SARS-CoV-2 in polluted water and sewage as well as the possible potential of disease transmission via drinking water. Conventional wastewater treatment systems have been shown to be effective in removing the virus, which plays an important role in pandemic control. Monitoring of this virus in water is extremely important as it can provide information on the prevalence and distribution of the COVID-19 pandemic in different communities as well as possible infection dynamics to prevent future outbreaks.

Evaluation and comparison of advanced oxidation processes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D): a review.

Organochlorine pesticides have generated public concern worldwide because of their toxicity to human health and the environment, even at low concentrations, and their persistence, being mostly nonbiodegradable. The use of 2,4-dichlorophenoxyacetic acid (2,4-D) has increased in recent decades, causing severe water contamination. Several treatments have been developed to degrade 2,4-D. This manuscript presents an overview of the physicochemical characteristics, uses, regulations, environmental and human health impacts of 2,4-D, and different advanced oxidation processes (AOPs) to degrade this organic compound, evaluating and comparing operation conditions, efficiencies, and intermediaries. Based on this review, 2,4-D degradation is highly efficient in ozonation (system O3/plasma, 99.8% in 30 min). Photocatalytic, photo-Fenton, and electrochemical processes have the optimal efficiencies of degradation and mineralization: 97%/79.67% (blue TiO2 nanotube arrays//UV), 100%/98% (Fe2+/H2O2/UV), and 100%/84.3% (MI-meso SnO2), respectively. The ozonation and electrochemical processes show high degradation efficiencies, but energy costs are also high, and photocatalysis is more expensive with a separation treatment used to recover the catalyst in the solution. The Fenton process is a viable economic-environmental option, but degradation efficiencies are often low (50-70%); however, they are increased when solar UV radiation is used (90-100%). AOPs are promising technologies for the degradation of organic pollutants in real wastewater, so evaluating their strengths and weaknesses is expected to help select viable operational conditions and obtain optimal efficiencies.

Phosphate removal from food industry wastewater by chemical precipitation treatment with biocalcium eggshell.

The physicochemical treatment (PT) of food industry wastewater was investigated. In the first stage, calcium magnesium acetate (CaMgAc4) was synthesized using eggshell (biocalcium), magnesium oxide and acetic acid in a 1:1:1 stoichiometric ratio. In the synthesis process, the thermodynamic parameters (ΔH, ΔS and ΔG) indicated that the reaction was endothermic and spontaneous. The samples were characterized by infrared spectroscopy (IR), scanning electronic microscopy (SEM), X-ray diffraction (XRD) and electron X-ray dispersive spectroscopy (EDS). CaMgAc4 was used to precipitate the phosphate matter. IR analysis revealed that the main functional groups were representative of the acetate compounds and the presence of OH- groups and carbonates. In the physicochemical treatment, a response surface design was used to determine the variables that influence the process (pH, t, and concentration), and the response variable was phosphorus removal. The treatments were carried out in the wastewater industry with an initial concentration of 658 mg/L TP. The optimal conditions of the precipitation treatment were pH 12, time 12 min, and a CaMgAc4 concentration of 13.18 mg/L. These conditions allowed the total elimination (100%) of total phosphorus and phosphates, 81.43% BOD5 and 81.0% COD, 98.9% turbidity, 95.01% color, and 92% nitrogen matter.

Industrial wastewater treatment using magnesium electrocoagulation in batch and continuous mode.

In the present study, the electrocoagulation (EC) performance of a Mg-Mg system was applied for the industrial wastewater treatment, from an industrial park that covers different activities such as: food, automotive, pharmaceutical, chemistry and cosmetics, after primary clarification. The effects of major operating parameters such as pH, reaction time, and current density were investigated for chemical oxygen demand (COD), color, and turbidity removal efficiency. The batch system was found convenient, achieving 63.52% COD, 96% color, and 99.32% turbidity removal at optimized operating conditions of pH 7.12, reaction time of 75 min, and current density of 201.5 A/m2. On the other hand, for continuous EC, the process removed approximately 46.58%, 95.96%, and 87.19% of the COD, color, and turbidity respectively, at 90 min of retention time, current density 440 A/m2, and a rate of 20 mL/min. Additionally, concerning nutrient removal (N and P), the EC system with Mg electrodes was highly efficient; batch treatment removed 97% of total phosphorus and 67% of ammoniacal nitrogen, whereas the continuous treatment removed 98.5% of total phosphorus and 83% of ammoniacal nitrogen. The sludge characterization before and after EC treatment was made by SEM, EDS, Fluorescence spectroscopy, IR spectroscopy. Minerals such as chlorite, crossite, richterite, pyroaurite, langbeinite as weel as aliphatic and polysubstituted aromatics compounds, sulfates and phosphates inorganic ions, and organic phosphorus were reduced. The energy cost in the batch EC is US$0.05/m3. A numerical CFD model was used to estimate the velocity fields and guarantee the presence of turbulent kinetic energy within a continuous flow reactor.

Assessing the viability of electro-absorption and photoelectro-absorption for the treatment of gaseous perchloroethylene.

This work focuses on the development of electro-absorption and photoelectro-absorption technologies to treat gases produced by a synthetic waste containing the highly volatile perchloroethylene (PCE). To do this, a packed absorption column coupled with a UV lamp and an undivided electrooxidation cell was used. Firstly, it was confirmed that the absorption in a packed column is a viable method to achieve retention of PCE into an absorbent-electrolyte liquid. It was observed that PCE does not only absorb but it was also transformed into phosgene and other by-products. Later, it was confirmed that the electro-absorption process influenced the PCE degradation, favoring the transformation of phosgene into final products. Opposite to what is expected, carbon dioxide is not the main product obtained, but carbon tetrachloride and trichloroacetic acid. Both species are also hazardous but their higher solubility in water opens possibilities for a successful and more environmental-friendly removal. The coupling with UV-irradiation has a negative impact on the degradation of phosgene. Finally, a reaction mechanism was proposed for the degradation of PCE based on the experimental observations. Results were not as expected during the planning of the experimental work but it is important to take in mind that PCE decomposition occurs in wet conditions, regardless of the applied technology, and this work is a first approach to try to solve the treatment problems associated to PCE gaseous waste flows in a realistic way.

Removal of inorganic chemical species and organic matter from slaughterhouse wastewater via calcium acetate synthesized from eggshell.

The physicochemical treatment (PT) of slaughterhouse wastewater (SWW) was investigated. In the first stage, calcium acetate (Ca(Ac)2) was synthesized in five different ways: (1) acetic acid (HAc) and chicken eggshell (CaAc1), (2) lime (CaAc2), (3) a 1:1 eggshell and lime mixture (CaAc3), (4) a 1:2 eggshell and lime mixture (CaAc4), and (5) calcium oxide via the calcination of eggshell (CaAc5). The synthesized Ca(Ac)2 samples were characterized by IR, SEM, XRD, and EDS. Subsequently, the samples were used to precipitate oxyanions and organic matter. The experiments were carried out at pH 4 and 12. For the treatment with CaAc1 at pH 4, an acid (HCl, H2SO4, or HAc) was also added. The best results for CaAc1 in acid media were attained with HCl, where removal efficiencies of 82.23% total suspended solids, 76% turbidity, 81.43% color, 53.86% Fe, 69.74% Cu, and 14.64% Na were observed. This treatment also removed ∼99% fecal and total coliforms, 26.49% COD, and 78.39% TOC. The experiments were also performed at pH 12 using CaAc1. These afforded removal efficiencies of 92.7% turbidity, 84.7% color, 40.5% phosphates (PO43-), and 64.7% sulfates (SO42-). In addition, this method removed metals, 35.37% COD and 99% fecal and total coliforms.

Pre-treatment of soft drink wastewater with a calcium-modified zeolite to improve electrooxidation of organic matter.

Wastewater from soft drink manufacturing, having a high organic load (chemical oxygen demand (COD) = 4,500 mg L-1) and high alkalinity (2,653.7 mg L-1 CaCO3; pH 12), was pretreated with a calcium-modified zeolite to reduce the alkalinity and improve the electrooxidation of organic matter. The natural zeolite clinoptilolite was modified in various ways with Ca(OH)2 and CaCl2. The CaCl2-modified zeolite (ZSACaCl-72h) was more effective for the treatment of soft drink wastewater than the congener modified with Ca(OH)2, where the former reduced the alkalinity by 86% after 8 h. Electrooxidation of soft drink wastewater without zeolite pre-treatment was carried out with boron-doped diamond (BDD) electrodes under the optimal conditions (current intensity: 3 A; sample pH: 12), with 98% and 94.05% reduction of the COD and total organic carbon (TOC), respectively, after 14 h of treatment. Soft drink wastewater pretreated with calcium-modified clinoptilolite was also electrooxidized using the BDD system. The results showed that the pre-treatment was extremely convenient, reducing the treatment time to 6 h compared to the electrooxidation of wastewater. At a current intensity of 3 A, the treatment time was 8 h, with 100% reduction of colour and COD and 97.5% reduction of TOC.

Soft drink wastewater treatment by electrocoagulation-electrooxidation processes.

The aim of this work was to implement a coupled system, a monopolar Electrocoagulation (EC)-Electrooxidation (EO) processes, for the treatment of soft drink wastewater. For the EC test, Cu-Cu, anode-cathode were used at current densities of 17, 51 and 68 mA cm-2. Only 37.67% of chemical oxygen demand (COD) and 27% of total organic carbon (TOC) were removed at 20 min with an optimum pH of 8, this low efficiency can be associated with the high concentration of inorganic ions which inhibit the oxidation of organic matter due to their complexation with copper ions. Later EO treatment was performed with boron-doped diamond-Cu electrodes and a current density of 30 Am-2. The coupled EC-EO system was efficient to reduce organic pollutants from initial values of 1875 mg L-1 TOC and 4300 mg L-1 COD, the removal efficiencies were 75% and 85%, respectively. Electric energy consumption to degrade a kilogram of a pollutant in the soft drink wastewater using EC was 3.19 kWh kg-1 TOC and 6.66 kWh kg-1 COD. It was concluded that the coupled system EC-EO was effective for the soft drink wastewater treatment, reducing operating costs and residence time, and allowing its reuse in indirect contact with humans, thus contributing to the sustainable reuse as an effluent of industrial wastewater.

Adsorption-regeneration by heterogeneous Fenton process using modified carbon and clay materials for removal of indigo blue.

Indigo blue dye is mainly used in dyeing of denim clothes and its presence in water bodies could have adverse effects on the aquatic system; for this reason, the objective of this study was to promote the removal of indigo blue dye from aqueous solutions by iron and copper electrochemically modified clay and activated carbon and the saturated materials were regenerated by a Fenton-like process. Montmorillonite clay was modified at pH 2 and 7; activated carbon at pH 2 and pH of the system. The elemental X-ray dispersive spectroscopy analysis showed that the optimum pH for modification of montmorillonite with iron and copper was 7 and for activated carbon was 2. The dye used in this work was characterized by infrared. Unmodified and modified clay samples showed the highest removal efficiencies of the dye (90-100%) in the pH interval from 2 to 10 whereas the removal efficiencies decrease as pH increases for samples modified at pH 2. Unmodified clay and copper-modified activated carbon at pH 2 were the most efficient activated materials for the removal of the dye. The adsorption kinetics data of all materials were best adjusted to the pseudo-second-order model, indicating a chemisorption mechanism and the adsorption isotherms data showed that the materials have a heterogeneous surface. The iron-modified clay could be regenerated by a photo-Fenton-like process through four adsorption-regeneration cycles, with 90% removal efficiency.

A combined electrocoagulation-electrooxidation treatment for industrial wastewater.

This study addresses the elimination of persistent organic compounds in industrial wastewater using a synergistic combination of electrocoagulation and electrooxidation. Electrocoagulation is a relatively quick process (30 min), which is very effective in removing colloidal and suspended particles, as seen in changes in coliforms, turbidity, and color and in the general absorbance by UV-vis spectroscopy. However, it is relatively ineffective in eliminating stable persistent organic compounds--in this work, only half of the COD was eliminated from wastewater and an oxidation peak in the cyclic voltammetry scan remained. Electrooxidation is very effective in breaking down organic compounds through oxidation as reflected in the elimination of COD, BOD(5), and oxidative peak in cyclic voltammetry, but requires so much time (21 h) that it has very limited practicality, especially when colloidal and suspended particles are present. Electrooxidative mineralization of electrocoagulated wastewater, in which most of the colloids and charged species have been removed, takes less than 2h. In the coupled technique, electrocoagulation quickly coagulates and removes the colloidal and suspended particles, as well as many charged species, then electrooxidation oxidizes the remaining organics. The coupled process eliminates COD, BOD(5), color, turbidity, and coliforms in a practical amount of time (2h).

A combined electrocoagulation-sorption process applied to mixed industrial wastewater.

The removal of organic pollutants from a highly complex industrial wastewater by a aluminium electrocoagulation process coupled with biosorption was evaluated. Under optimal conditions of pH 8 and 45.45 Am(-2) current density, the electrochemical method yields a very effective reduction of all organic pollutants, this reduction was enhanced when the biosorption treatment was applied as a polishing step. Treatment reduced chemical oxygen demand (COD) by 84%, biochemical oxygen demand (BOD(5)) by 78%, color by 97%, turbidity by 98% and fecal coliforms by 99%. The chemical species formed in aqueous solution were determined. The initial and final pollutant levels in the wastewater were monitored using UV-vis spectrometry and cyclic voltammetry. Finally, the morphology and elemental composition of the biosorbent was characterized with scanning electron microscopy (SEM) and energy dispersion spectra (EDS).