Coupling UV irradiation and electrocoagulation for reclamation of urban wastewater

Distillery industrial wastewater(DIW) treatment by the combination of sono(US), photo(UV) and electrocoagulation(EC) process

The color and Chemical Oxygen Demand (COD) reduction in distillery industrial effluent (DIW) was investigated utilizing photo (UV), sono (US), electrocoagulation (EC), UV + US, UV + EC, US + EC, and US + UV + EC technologies. The empirical study demonstrated that the UV + US + EC process removed almost 100% of color and 95.63% of COD from DIW while consuming around 6.97 kWh m^-3 of electrical energy at the current density of 0.175 A dm^-2, COD of 3600 mg L^-1, UV power of 32 W, US power of 100 W, electrode pairings of Fe/Fe, inter-electrode distance of 0.75 cm, pH of 7, and reaction time of 4 h, respectively. The values found were much greater than those produced using UV, US, EC, UV + US, UV + EC, and US + EC methods. The influence of various control variables such as treatment time (1-5 h), current density (0.075-2.0 A dm^-2), COD (1800-6000 mg L^-1), inter-electrode distance (0.75-3.0 cm), electrode pairings (Fe/Fe, Fe/Al, Al/Fe, Al/Al), UV (8-32 W), and US (20-100 W) on the color and COD reduction were investigated to determine the optimum operating conditions. It was observed that, an increase in treatment time, current density, UV and US power, decrease in the COD, and inter-electrode distance with Fe/Fe electrode combination improved the COD removal efficiency. The UV and US + EC processes' synergy index was investigated and reported. The results showed that, the US + UV + EC treatment combination was effective in treating industrial effluent and wastewater.

A Review of Hybrid Process Development Based on Electrochemical and Advanced Oxidation Processes for the Treatment of Industrial Wastewater

Nowadays, increased human activity, industrialization, and urbanization result in the production of enormous quantities of wastewater. Generally, physicochemical and biological methods are employed to treat industrial effluent and wastewater and have demonstrated high efficacy in removing pollutants. However, some industrial effluent and wastewater contain contaminants that are extremely difficult to remove using standard physicochemical and biological processes. Previously, electrochemical and hybrid advanced oxidation processes (AOP) were considered a viable and promising alternative for achieving an adequate effluent treatment strategy in such instances. These processes rely on the production of hydroxyl radicals, which are highly reactive oxidants that efficiently break down contaminants found in wastewater and industrial effluent. This review focuses on the removal of contaminants from industrial effluents and wastewater through the integration of electrochemical and advanced oxidation techniques. These processes include electrooxidation, electrocoagulation/electroflocculation, electroflotation, photo-Fenton, ozone-photo-Fenton, sono-photo-Fenton, photo-electro-Fenton, ozone/electrocoagulation, sono-electrocoagulation, and peroxi/photo/electrocoagulation. The data acquired from over 150 published articles, most of which were laboratory experiments, demonstrated that the hybrid process is more effective in removing contaminants from industrial effluent and wastewater than standalone processes.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Removal of phenol from steel wastewater by combined electrocoagulation with photo-Fenton

Phenol and its derivatives are available in various industries such as refineries, coking plants, steel mills, drugs, pesticides, paints, plastics, explosives and herbicides industries. This substance is carcinogenic and highly toxic to humans. The purpose of the study was to investigate the removal of phenol from wastewater of the steel industry using the electrocoagulation-photo-Fenton (EC-PF) process. Phenol and chemical oxygen demand (COD) removal efficiency were investigated using the parameters pH, Fe²⁺/H₂O₂, reaction time and current density. The highest removal efficiency rates of phenol and COD were 100 and 98%, respectively, for real wastewater under optimal conditions of pH = 4, current density = 1.5 mA/cm², Fe²⁺/H₂O₂ = 1.5 and reaction time of 25 min. Combination of the two effective methods for the removal of phenol and COD, photocatalytic electrocoagulation photo-Fenton process is a suitable alternative for the removal of organic pollutants in industry wastewater because of the low consumption of chemicals, absence of sludge and other side products, and its high efficiency.

Oxidation of municipal wastewater by free radicals mechanism. A UV/Vis spectroscopy study

This study investigates the oxidation of municipal wastewater (WW) by complexation with natural polyphenols having radical scavenging activity, such as (3,4,5 tri-hydroxy-benzoic acid) gallic acid (GA) in alkaline pH (>7), under ambient O₂ and temperature. Physicochemical and structural characteristics of GA-WW complex-forming are evaluated by UV/Vis spectroscopy. The comparative analysis among UV/Vis spectra of GA monomer, GA-GA polymer, WW compounds, and GA-WW complex reveals significant differences within 350-450 and 500-900 nm. According to attenuated total reflectance (ATR) spectroscopy and thermogravimetric analysis (TGA), these spectra differences correspond to distinct complexes formed. This study suggests a novel role of natural polyphenols on the degradation and humification of wastes.

Electrolytic and electro-irradiated processes with diamond anodes for the oxidation of persistent pollutants and disinfection of urban treated wastewater

This paper analyzes the advantages and drawbacks of the combination of UV irradiation with electrolysis with the aim to give insight about the feasibility of the application of this technology for the reclaiming of conventionally-treated wastewater. The oxidation of synthetic solutions containing five selected model complex pollutants has been compared, showing that UV irradiation improves the results of electrolysis for progesterone, metoprolol and caffeine and deteriorates the performance for the degradation of sulfamethoxazole and dimethyl-phthalate. Differences observed becomes lower when mineralization is compared showing that the effects of UV irradiation are diluted when a mixture of species is oxidized. Results suggest that high ThOD/TOC (Theoretical Oxygen Demand/Total Organic Carbon) ratios improve the synergistic coupling of technologies while low values lead to a clear antagonistic effect. Because during oxidation progress this ratio is decreased, the observed effect on mineralization is much lower than in the oxidation of the raw molecule. Opposite to this low effect on the oxidation of organics, the improvement in the performance of the disinfection by coupling UV to electrolysis is much clearer. In addition, UV irradiation modifies significantly the chlorine speciation and helps to prevent the formation of hazardous species such as chlorate and perchlorate during the electrochemical processes.

Reduction of nutrients, microbes, and personal care products in domestic wastewater by a benchtop electrocoagulation unit

To preserve environmental and human health, improved treatment processes are needed to reduce nutrients, microbes, and emerging chemical contaminants from domestic wastewater prior to discharge into the environment. Electrocoagulation (EC) treatment is increasingly used to treat industrial wastewater; however, this technology has not yet been thoroughly assessed for its potential to reduce concentrations of nutrients, a variety of microbial surrogates, and personal care products found in domestic wastewater. This investigation's objective was to determine the efficiency of a benchtop EC unit with aluminum sacrificial electrodes to reduce concentrations of the aforementioned biological and chemical pollutants from raw and tertiary-treated domestic wastewater. EC treatment resulted in significant reductions (p < 0.05, α = 0.05) in phosphate, all microbial surrogates, and several personal care products from raw and tertiary-treated domestic wastewater. When wastewater was augmented with microbial surrogates representing bacterial, viral, and protozoan pathogens to measure the extent of reduction, EC treatment resulted in up to 7-log10 reduction of microbial surrogates. Future pilot and full-scale investigations are needed to optimize EC treatment for the following: reducing nitrogen species, personal care products, and energy consumption; elucidating the mechanisms behind microbial reductions; and performing life cycle analyses to determine the appropriateness of implementation.