Process modeling and kinetic evaluation of petroleum refinery wastewater treatment in a photocatalytic reactor using TiO2 nanoparticles

A comparison of endosulfan removal by photocatalysis process under UV-A and visible light irradiation: optimization, degradation byproducts and reuse

In this study, the removal efficiency of endosulfan as a persistent organic pollutant and formation of its metabolites were investigated using Ag/TiO2/Fe3O4 photocatalyst under visible and UV-A light. Light intensity, catalyst amount, initial endosulfan concentration, initial pH and time were determined as controllable factors for Taguchi experimental design. The highest removal efficiencies of endosulfan were achieved as 86.14% and 85.46% for visible and UV-A light sources, respectively. According to the greatest best criterion, the level at which the highest S/N ratio was obtained for each parameter was accepted as the optimum value. As a result of the validation experiments, 94.2% and 91.9% efficiency were obtained for visible and UV-A light, respectively. The metabolite formations of endosulfan (endosulfan sulfate, ether, and lactone) remained below 7% in all experiments on a concentration basis. In the reuse experiments of the magnetically recovered photocatalyst, high removal efficiency of around 80% was obtained after four cycles. The removal efficiencies were found to be 86.7% and 84.8%, for real samples taken from the drinking water treatment plant inlet and the spring water network injected with endosulfan under optimal photocatalysis experimental conditions, respectively. It has been shown that nitrate and sulfate anions, which are in significant concentrations in raw water samples, have very little effects on endosulfan removal. The overall results showed that the Ag/TiO2/Fe3O4 photocatalyst was produced successfully, the catalyst was highly effective in the mineralization of endosulfan in synthetic and real water samples under UV and visible light, and effective yields could be obtained even with reuse.

Supplementary information

The online version contains supplementary material available at 10.1007/s40201-023-00864-z.

Z. AL-bonsrulah H. Optimization of oil industry wastewater treatment system and proposing empirical correlations for chemical oxygen demand removal using electrocoagulation and predicting the system's performance by artificial neural network

The alarming pace of environmental degradation necessitates the treatment of wastewater from the oil industry in order to ensure the long-term sustainability of human civilization. Electrocoagulation has emerged as a promising method for optimizing the removal of chemical oxygen demand (COD) from wastewater obtained from oil refineries. Therefore, in this study, electrocoagulation was experimentally investigated, and a single-factorial approach was employed to identify the optimal conditions, taking into account various parameters such as current density, pH, COD concentration, electrode surface area, and NaCl concentration. The experimental findings revealed that the most favorable conditions for COD removal were determined to be 24 mA/cm2 for current density, pH 8, a COD concentration of 500 mg/l, an electrode surface area of 25.26 cm2, and a NaCl concentration of 0.5 g/l. Correlation equations were proposed to describe the relationship between COD removal and the aforementioned parameters, and double-factorial models were examined to analyze the impact of COD removal over time. The most favorable outcomes were observed after a reaction time of 20 min. Furthermore, an artificial neural network model was developed based on the experimental data to predict COD removal from wastewater generated by the oil industry. The model exhibited a mean absolute error (MAE) of 1.12% and a coefficient of determination (R2) of 0.99, indicating its high accuracy. These findings suggest that machine learning-based models have the potential to effectively predict COD removal and may even serve as viable alternatives to traditional experimental and numerical techniques.

Low-Cost Photoreactor to Monitor Wastewater Pollutant Decomposition

Actually, the quality of water is one of the most important indicators of the human environmental impact, the control of which is crucial to avoiding irreversible damage in the future. Nowadays, in parallel to the growth of the chemical industry, new chemical compounds have been developed, such as dyes and medicines. The increasing use of these products has led to the appearance of recalcitrant pollutants in industrial wastewater, and even in the drinking water circuit of our populations. The current work presents a photoreactor prototype that allows the performance of experiments for the decomposition of coloured pollutants using photocatalysis at the laboratory scale. The design of this device included the study of the photometric technique for light emission and the development of a software that allows monitoring the dye degradation process. Open-source hardware platforms, such as Arduino, were used for the monitoring system, which have the advantages of being low-cost platforms. A software application that manages the communication of the reactor with the computer and graphically displays the data read by the sensor was also developed. The results obtained demonstrated that this device can accelerate the photodegradation reaction in addition to monitoring the changes throughout the process.

Treatment of electroplating industry wastewater: a review on the various techniques

Water pollution by recalcitrant compounds is an increasingly important problem due to the continuous introduction of new chemicals into the environment. Choosing appropriate measures and developing successful strategies for eliminating hazardous wastewater contaminants from industrial processes is currently a primary goal. Electroplating industry wastewater involves highly toxic cyanide (CN), heavy metal ions, oils and greases, organic solvents, and the complicated composition of effluents and may also contain biological oxygen demand (BOD), chemical oxygen demand (COD), SS, DS, TS, and turbidity. The availability of these metal ions in electroplating industry wastewater makes the water so toxic and corrosive. Because these heavy metals are harmful to living things, they must be removed to prevent them from being absorbed by plants, animals, and humans. As a result, exposure to electroplating wastewater can induce necrosis and nephritis in humans and lung cancer, digestive system cancer, anemia, hepatitis, and maxillary sinus cancer with prolonged exposure. For the safe discharge of electroplating industry effluents, appropriate wastewater treatment has to be provided. This article examines and assesses new approaches such as coagulation and flocculation, chemical precipitation, ion exchange, membrane filtration, adsorption, electrochemical treatment, and advanced oxidation process (AOP) for treating the electroplating industry wastewater. On the other hand, these physicochemical approaches have significant drawbacks, including a high initial investment and operating cost due to costly chemical reagents, the production of metal complexes sludge that needs additional treatment, and a long recovery process. At the same time, advanced techniques such as electrochemical treatment can remove various kinds of organic and inorganic contaminants such as BOD, COD, and heavy metals. The electrochemical treatment process has several advantages over traditional technologies, including complete removal of persistent organic pollutants, environmental friendliness, ease of integration with other conventional technologies, less sludge production, high separation, and shorter residence time. The effectiveness of the electrochemical treatment process depends on various parameters, including pH, electrode material, operation time, electrode gap, and current density. This review mainly emphasizes the removal of heavy metals and another pollutant such as CN from electroplating discharge. This paper will be helpful in the selection of efficient techniques for treatment based on the quantity and characteristics of the effluent produced.

The Combined Effect of Bubble and Photo Catalysis Technology in BTEX Removal from Produced Water

Among the several ways used in wastewater treatment, the photocatalysis process is a more novel and alternative process that is increasingly employed in recent years. This work aims to improve the performance of the photocatalyst process by using air bubbles in removing the BTEX from produced water as an indicator of process efficiency. The study also shows the effect of influencing factors (pH and residence time) on the photocatalysis process. The study was done in a rectangular column with dimensions of 200 mm width, 30 mm depth, and 1500 mm height. Commercial titanium oxide (TiO2) coated on a plate by the varnish was used as a source of the photocatalyst. The experiment was carried out under different values of gas flow rate (0-3 L/min) to evaluate its effect on the photocatalyst process, the effect of other variables of pH (3-11), and irradiation time (30-120) min was also studied. A new method of the coating was adopted by using an alumina plate with varnish as an adhesive. The characteristics results show that the coated plate has hydrophilic properties and that there is no significant change in the crystal structure of the TiO2 nanoparticles and the varnish before and after 60 h of the photocatalytic process, indicating that the plate is still effective after 60 h usage under different conditions. The results also show that the introduction of air bubbles enhances the removal efficiency of BTEX significantly and the best removal effectiveness of BTEX was 93% when pH = 5 after 90 min and 90% when pH = 3 after 120 min. The removal rate also reached 86% when pH = 7 after 120 min all at a flow rate of 3 L/min. The percentage of removal decreased at pH = 9 and 11, reaching 64% and 50%, respectively after 120 min and a flow rate of 3 L/min. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Nanomaterials and Technology Applications for Hydraulic Fracturing of Unconventional Oil and Gas Reservoirs: A State-of-the-Art Review of Recent Advances and Perspectives

The application of hydraulic fracturing stimulation technology to improve the productivity of unconventional oil and gas reservoirs is a well-established practice. With the increasing exploration and development of unconventional oil and gas resources, the associated geological conditions and physical properties are gradually becoming more and more complex. Therefore, it is necessary to develop technologies that can improve the development benefits to meet these challenges. In recent years, improving the effect of hydraulic fracturing stimulation in unconventional oil and gas reservoirs through the use of nanomaterials and technologies has attracted increasing attention. In this paper, we review the current status and research progress of the application of nanomaterials and technologies in various aspects of hydraulic fracturing in unconventional oil and gas reservoirs, expound the mechanism and advantages of these nanomaterials and technologies in detail, and provide future research directions. The reviewed literature indicates that nanomaterials and technologies show exciting potential applications in the hydraulic fracturing of unconventional reservoirs; for example, the sand-carrying and rheological properties of fracturing fluids can be significantly enhanced through the addition of nanomaterials. The use of nanomaterials to modify proppants can improve their compressive strength, thus meeting the needs of different reservoir conditions. The fracturing flowback fluid treatment efficiency and purification effect can be improved through the use of nanophotocatalysis and nanomembrane technologies, while degradable fracturing completion tools developed based on nanomaterials can effectively improve the efficiency of fracturing operations. Nanorobots and magnetic nanoparticles can be used to more efficiently monitor hydraulic fracturing and to accurately map the hydraulic fracture morphology. However, due to the complex preparation process and high cost of nanomaterials, more work is needed to fully investigate the application mechanisms of nanomaterials and technologies, as well as to evaluate the economic feasibility of these exciting technologies. The main research objective of this review is to comprehensively summarize the application and research progress of nanomaterials and technologies in various aspects of hydraulic fracturing in unconventional oil and gas reservoirs, analyze the existing problems and challenges, and propose some targeted forward-looking recommendations, which may be helpful for future research and applications.

Application of Nanocatalysts in Advanced Oxidation Processes for Wastewater Purification: Challenges and Future Prospects

The increase in population demands for industrialization and urbanization which led to the introduction of novel hazardous chemicals in our environment. The most significant parts of these harmful substances found in water bodies remain in the background, causing a health risk to humans and animals. It is critical to remove these toxic chemicals from the wastewater to keep a cleaner and greener environment. Hence, wastewater treatment is a challenging area these days to manage liquid wastes effectively. Therefore, scientists are in search of novel technologies to treat and recycle wastewater, and nanotechnology is one of them, thanks to the potential of nanoparticles to effectively clean wastewater while also being ecologically benign. However, there is relatively little information about nanocatalysts’ applicability, efficacy, and challenges for future applications in wastewater purification. This review paper is designed to summarize the recent studies on applying various types of nanocatalysts for wastewater purification. This review paper highlights innovative work utilizing nanocatalysts for wastewater applications and identifies issues and challenges to overcome for the practical implementation of nanocatalysts for wastewater treatment.

The Perspective and Challenge of Nanomaterials in Oil and Gas Wastewater Treatment

Oil and gas wastewater refers to the waste stream produced in special production activities such as drilling and fracturing. This kind of wastewater has the following characteristics: high salinity, high chromaticity, toxic and harmful substances, poor biodegradability, and a difficulty to treat. Interestingly, nanomaterials show great potential in water treatment technology because of their small size, large surface area, and high surface energy. When nanotechnology is combined with membrane treatment materials, nanofiber membranes with a controllable pore size and high porosity can be prepared, which provides more possibilities for oil–water separation. In this review, the important applications of nanomaterials in wastewater treatment, including membrane separation technology and photocatalysis technology, are summarized. Membrane separation technology is mainly manifested in ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). It also focuses on the application of semiconductor photocatalysis technology induced by TiO₂ in the degradation of oil and gas wastewater. Finally, the development trends of nanomaterials in oil and gas wastewater treatment are prospected.

A Review on the Treatment of Petroleum Refinery Wastewater Using Advanced Oxidation Processes

The petroleum industry is one of the most rapidly developing industries and is projected to grow faster in the coming years. The recent environmental activities and global requirements for cleaner methods are pushing the petroleum refining industries for the use of green techniques and industrial wastewater treatment. Petroleum industry wastewater contains a broad diversity of contaminants such as petroleum hydrocarbons, oil and grease, phenol, ammonia, sulfides, and other organic composites, etc. All of these compounds within discharged water from the petroleum industry exist in an extremely complicated form, which is unsafe for the environment. Conventional treatment systems treating refinery wastewater have shown major drawbacks including low efficiency, high capital and operating cost, and sensitivity to low biodegradability and toxicity. The advanced oxidation process (AOP) method is one of the methods applied for petroleum refinery wastewater treatment. The objective of this work is to review the current application of AOP technologies in the treatment of petroleum industry wastewater. The petroleum wastewater treatment using AOP methods includes Fenton and photo-Fenton, H2O2/UV, photocatalysis, ozonation, and biological processes. This review reports that the treatment efficiencies strongly depend on the chosen AOP type, the physical and chemical properties of target contaminants, and the operating conditions. It is reported that other mechanisms, as well as hydroxyl radical oxidation, might occur throughout the AOP treatment and donate to the decrease in target contaminants. Mainly, the recent advances in the AOP treatment of petroleum wastewater are discussed. Moreover, the review identifies scientific literature on knowledge gaps, and future research ways are provided to assess the effects of these technologies in the treatment of petroleum wastewater.

Photoelectrocatalytic reactor improvement towards oil-in-water emulsion degradation

Oil-in-water (O/W) emulsion is critical wastewater that is challenging to eliminate and requires a long treatment process, and it is necessary to develop highly effective removal methods before releasing it into natural water sources. This research has selected the photoelectrocatalytic (PEC) technique to solve this problem by developing a PEC reactor for high efficiency in O/W degradation and understanding the essential factors related to the PEC reactor's efficiency improvement. The PEC reactor has been designed on a large scale with suitable positioning of an electrode that is, designing a light source near the anode electrode to enhance light irradiation efficiency and including a circulating pump to provide continuous flow to the solution through the electrode surface. We studied the main factors of supporting the electrolyte, electrode characteristics, and catalytic process. We investigated the O/W-degradation efficiency using a UV/Vis spectrophotometer, chemical oxygen demand (COD) measurement, and GC-MS analysis. We optimized the PEC reactor using the developed BiVO₄ photoanodes and placed them parallel with the zinc plates. Then, we controlled the applied potential at 1.0 V in 0.1 M Na₂SO₄ supporting an electrolyte under visible light irradiation. The developed PEC reactor can be degraded in the O/W emulsion up to 76% and decreased the COD value up to 78% for 7h. This PEC cell can be completely decomposed of many functional groups, such as carbonyl, ester, nitrile, amine, phosphate, chloro group, and nitro group, that were contained in the O/W substance. The highlight of this research is the designed light source and circulating pump inside of the PEC reactor to enhance the light irradiation, refresh the anode electrode, and understand the critical factor for the improvement of O/W-degradation efficiency. This PEC reactor presents a high-efficiency O/W degradation with practical use and a fast process suitable for further application in high turbidity of wastewater treatment from the oil industry.

Photocatalytic Decolorization and Biocidal Applications of Nonmetal Doped TiO2: Isotherm, Kinetic Modeling and In Silico Molecular Docking Studies

Textile dyes and microbial contamination of surface water bodies have been recognized as emerging quality concerns around the globe. The simultaneous resolve of such impurities can pave the route for an amicable technological solution. This study reports the photocatalytic performance and the biocidal potential of nitrogen-doped TiO₂ against reactive black 5 (RB5), a double azo dye and E. coli. Molecular docking was performed to identify and quantify the interactions of the TiO₂ with β-lactamase enzyme and to predict the biocidal mechanism. The sol-gel technique was employed for the synthesis of different mol% nitrogen-doped TiO₂. The synthesized photocatalysts were characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and diffuse reflectance spectroscopy (DRS). The effects of different synthesis and reaction parameters were studied. RB5 dye degradation was monitored by tracking shifts in the absorption spectrum and percent chemical oxygen demand (COD) removal. The best nanomaterial depicted 5.57 nm crystallite size, 49.54 m² g⁻¹ specific surface area, 11–40 nm particle size with spherical morphologies, and uniform distribution. The RB5 decolorization data fits well with the pseudo-first-order kinetic model, and the maximum monolayer coverage capacity for the Langmuir adsorption model was found to be 40 mg g⁻¹ with K_ads of 0.113 mg⁻¹. The LH model yielded a higher coefficient K_C (1.15 mg L⁻¹ h⁻¹) compared to the adsorption constant K_LH (0.3084 L mg⁻¹). 90% COD removal was achieved in 60 min of irradiation, confirmed by the disappearance of spectral peaks. The best-optimized photocatalysts showed a noticeable biocidal potential against human pathogenic strain E. coli in 150 min. The biocidal mechanism of best-optimized photocatalyst was predicted by molecular docking simulation against E. coli β-lactamase enzyme. The docking score (−7.6 kcal mol⁻¹) and the binding interaction with the active site residues (Lys315, Thr316, and Glu272) of β-lactamase further confirmed that inhibition of β-lactamase could be a most probable mechanism of biocidal activity.

Bioremediation of hydrocarbon containing wastewater in anoxic-aerobic sequential reactors

Anoxic-aerobic sequential moving-bed reactors were operated for the degradation of synthetic petroleum refinery wastewater containing phenol (750 mg/L), hydrocarbons (1250 mg/L), S^2- (750 mg/L), NH₄ ⁺-N (350 mg/L), NO₃ ^-N (1000 mg/L) and surfactant as nonylphenol-monoethoxylate (0.2 mmol/L). Kerosene, heavy oil and their mixture were used as hydrocarbon source. Anoxic reactor was a disc-bed reactor and aerobic reactor was moving-bed reactor operated at hydraulic retention times (HRT) of 48 and 16 h respectively at 27 ± 3°C. In anoxic reactor, removals of S^2- and NO₃ ^-N were more than 99% along with 50-60% removal of hydrocarbons and phenol. Removal of organics deteriorated in anoxic reactor with heavy oil in feed having higher density and viscosity. Residual organics and NH₄ ⁺-N were removed in aerobic reactor with more than 99% efficiency. Biomass activity decreased in anoxic reactor and increased in aerobic reactor with an increase in density and viscosity of hydrocarbon in feed. Abiotic study confirmed most of the removals were due to biodegradation.

Inactivation and change of tetracycline-resistant Escherichia coli in secondary effluent by visible light-driven photocatalytic process using Ag/AgBr/g-C3N4

Control of antibiotic-resistant bacteria (ARB) and their related genes in secondary effluents has become a serious issue because of increased awareness of their health risks. A considerable number of techniques have been developed in recent years, particularly in relation to advanced oxidation. However, limited information is known about cellular behavior and resistance characteristic change during photocatalytic treatment. In this study, the inactivation of tetracycline (TC)-resistant Escherichia coli (TC-E. coli), removal of TC-resistant genes (TC-RGs), and antibiotic susceptibility were evaluated by employing photocatalytic treatment using Ag/AgBr/g-C₃N₄ with visible light irradiation. The effects of light intensity, photocatalyst dosage, and reaction ambient temperature on photocatalysis were modelled and investigated. The rate of TC-E. coli removal was also optimized. Results demonstrated that the optimal conditions for TC-E. coli removal included light intensity of 96.0 mW/cm², photocatalyst dosage of 211.0 mg/L, and reaction ambient temperature of 23.7 °C. Under such conditions, the ARB removal rate was 6.1 log after 90 min and the related TC-RG removal rates were 49%, 86%, 69%, and 86% for tetA, tetM, tetQ, and intl1, respectively. The minimum inhibitory concentration test after photocatalysis shows that the antibiotic resistance of TC-E. coli was enhanced, which may be mainly due to the changes in the membrane potential and resulted in difficulty in destroying the bacteria through antibiotic contact. Hence, photocatalytic treatment could be an ideal method for ARB and antibiotic-resistant gene (ARG) control in wastewater, but the health risks of the remaining ARB and ARG should be investigated further.

Removal of COD and SO42− from Oil Refinery Wastewater Using a Photo-Catalytic System—Comparing TiO2 and Zeolite Efficiencies

Advanced oxidation processes (AOPs) have many prospects in water and wastewater treatment. In recent years, AOPs are gaining attention as having potentials for the removal of different ranges of contaminants from industrial wastewater towards water reclamation. In this study, the treatability efficiencies of two photo-catalysts (TiO2 and zeolite) were compared on the basis of the removal of chemical oxygen demand (COD) and SO42− from oil refinery wastewater (ORW) using photo-catalytic system. The effects of three operating parameters: catalyst dosage (0.5–1.5 g/L), reaction time (15–45 min), mixing rate (30–90 rpm) and their interactive effects on the removal of the aforementioned contaminants were studied using the Box–Behnken design (BBD) of response surface methodology (RSM). Statistical models were developed and used to optimize the operating conditions. An 18 W UV light was incident on the system to excite the catalysts to trigger a reaction that led to the degradation and subsequent removal of contaminants. The results obtained showed that for almost the same desirability (92% for zeolite and 91% for TiO2), TiO2 exhibited more efficiency in terms of mixing rate and reaction time requirements. At the 95% confidence level, the model’s predicted results were in good agreement with experimental data obtained.

Photocatalytic treatment of petroleum industry wastewater using recirculating annular reactor: comparison of experimental and modeling

In this study, the treatment of petroleum wastewater has been investigated by applying heterogeneous photocatalytic process using a recirculating annual reactor. An attempt has been made to study the effect of operating parameters such as TiO₂ load, initial concentration of the pollutant, emitted photonic flux, and pH of the solution. The degradation efficiency of toluene and benzene, as target molecules, was studied. In fact, result showed that the toluene is better degraded alone than when it is in a mixture. The rate of elimination of toluene separately was 89.5%, while it was 76.19 and 79.55% in the binary (toluene/benzene) and the ternary mixtures (toluene/benzene/xylene), respectively. Moreover, the mineralization of the solution decreased more rapidly when toluene was pure with a rate of 83.13% compared to binary and ternary mixtures. A mathematical model is proposed taking into account the parameters influencing the process performances. The mass transfer step, the degradation, and the mineralization kinetics of the pollutants were defined as model parameters. To build the model, mass balances are written in bulk region and catalyst phase (solid phase). The degradation mechanism on solid phase is divided in two stages. Firstly, the removal of toluene gives an equivalent intermediate (EI). Secondly, EI is oxidized into carbon dioxide (CO₂). This approach gives a good agreement between modeling and empirical data in terms of degradation and mineralization. It also allows for the simulation of toluene kinetics without knowing the plausible chemical pathway. A satisfactory fit with experimental data was obtained for the degradation and mineralization of toluene.

Catalytic degradation of O-cresol using H2 O2 onto Algerian Clay-Na

Clay material is used as a catalyst to degrade an organic pollutant. This study focused on the O-cresol oxidative degradation in aqueous solution by adding H₂ O₂ and Mont-Na. The catalytic tests showed a high catalytic activity of Mont-Na, which made it possible to achieve more than 84.6% conversion after 90 min of reaction time at 55°C in 23.2 mM H₂ O₂ . The pH value was found to be negatively correlated with the degradation rate of O-cresol. UV-Vis spectrophotometry revealed that the increase of degradation rate at low pH is related to the formation of 2-methylbenzoquinone as intermediate product. In addition, the content of iron in Mont-Na decreased after the catalytic test, bringing further evidence about the O-cresol catalytic oxidation. The mineralization of O-cresol is also confirmed by the different methods of characterization of Mont-Na after the catalytic oxidation test. The effect of the O-cresol oxidation catalyzed by natural clay is significant. PRACTITIONER POINTS: Algerian Montmorillonite-Na is used as a catalyst to degrade an organic pollutant: O-cresol. It shows a great potential for catalyst properties in the presence of the oxidizing reagent H₂ O₂ . It proved to be an effective means for the degradation of O-cresol contained in wastewaters.

Treatment of petroleum refinery effluent using ultrasonic irradiation

Ultrasonic irradiation is one of the advanced oxidation methods used in wastewater treatment. In this study, ultrasonic treatment of petroleum refinery effluent was examined. An ultrasonic homogenizator with a 20 kHz frequency and an ultrasonic bath with a 42 kHz frequency were used as a source for ultrasound. The effects of parameters such as ZnO amount, ozone saturation time, and type of ultrasound source on the degradation of petroleum refinery effluent were investigated. The degradation of petroleum refinery effluent was measured as a change in initial chemical oxygen demand (COD) and with time. According to the results, degradation increased with the addition of ZnO in an ultrasonic probe. There was also a positive effect of ozone saturation before sonication then applying ultrasound on the degradation for an ultrasonic probe. It was observed that there was no positive effect of ZnO addition and ozone saturation on degradation for an ultrasonic bath.

Promoting sun light-induced photocatalytic degradation of toxic phenols by efficient and stable double metal cyanide nanocubes

Aromatic substituted phenols and their by-products discharged from numerous industries are of environmental concern due to their toxic, carcinogenic, recalcitrant, and bioaccumulating properties. Therefore, their complete removal from waters by low-cost, efficient, environmentally friendly nanomaterial-based treatment techniques is desirable. Double metal cyanide complexes (DMCC) are the extremely useful heterogeneous and recoverable catalyst. Hence, green route has been developed for several DMCC and their photocatalytic efficiency was evaluated for degradation of toxic phenols. Herein, nanocubes for hexacyanocobaltate of iron (FeHCC ~ 200 nm), nickel (NiHCC < 10 nm), and zinc (ZnHCC ~ 500 nm) were synthesized after employing Aegle marmelos. Subsequently, at neutral pH and sunlight irradiation, 15 mg of catalysts were able to degrade the maximum extent of phenols (1 × 10^-4 M) in the order: 3-aminophenol (96% ZnHCC > 94% FeHCC > 93% NiHCC) > phenol (94% ZnHCC > 92% FeHCC > 91% NiHCC) > 2,4-DNP (92% ZnHCC > 91% FeHCC > 90% NiHCC). This is attributed to highest basicity of 3-aminophenol containing excess of free electrons. Highest catalytic potential of ZnHCC (X_m = 0.54-0.43 mg/g) is because of its highest surface area and negative zeta potential along with sharp morphology and crystallinity. Adsorption of phenols over catalyst was statistically significant with Langmuir isotherms (R² ≥ 0.96; p value ≤ 0.05). Small and non-toxic by-products like oxalic acid, benzoquinone, (Z)-hex-3-enedioic acid, (Z)-but-2-enal, and (Z)-4-oxobut-2-enoic acid were identified in GC-MS. Degradation modes involving hydroxylation, oxidative skeletal rearrangement, and ring opening clearly supported enhanced oxidation of phenols by ^•OH. Overall, due to greater active sites, high surface activity, low band gap, and semiconducting nature, DMCC revealed promising potential for solar photocatalytic remediation of wastewater.

A comparative study of an up-flow aerobic/anoxic sludge fixed film bioreactor and sequencing batch reactor with intermittent aeration in simultaneous nutrients (N, P) removal from synthetic wastewater

The performance of two bench scale activated sludge reactors with two feeding regimes, continuous fed (an up-flow aerobic/anoxic sludge fixed film (UAASFF) bioreactor) and batch fed (sequencing batch reactor (SBR)) with intermittent aeration, were evaluated for simultaneous nutrients (N, P) removal. Three significant variables (retention/reaction time, chemical oxygen demand (COD): N (nitrogen): P (phosphorus) ratio and aeration time) were selected for modeling, analyzing, and optimizing the process. At high retention time (≥6 h), two bioreactors showed comparable removal efficiencies, but at lower hydraulic retention time, the UAASFF bioreactor showed a better performance with higher nutrient removal efficiency than the SBR. The experimental results indicated that the total Kjeldahl nitrogen removal efficiency in the UAASFF increased from 70.84% to 79.2% when compared to SBR. It was also found that the COD removal efficiencies of both processes were over 87%, and total nitrogen and total phosphorus removal efficiencies were 79.2% and 72.98% in UAASFF, and 71.2% and 68.9% in SBR, respectively.

Mutagenicity and cytotoxicity evaluation of photo-catalytically treated petroleum refinery wastewater using an array of bioassays

Degradation and detoxification of petroleum refinery wastewater (PRW) was carried out by advanced oxidation processes (UV/TiO₂/H₂O₂ and gamma radiation/H₂O₂). Response surface methodology (RSM) was used to optimize the independent variables. The cytotoxicity was evaluated using Allium cepa, brime shrimp and haemolytic assays; whereas mutagenicity was tested by Ames tests (TA98 and TA100 strains). Maximum reductions in COD and BOD were recorded as 78% and 87% for UV/TiO₂/H₂O₂ and 77% and 86% for gamma ray/H₂O₂, respectively. Treatments with both methods at optimized conditions reduced the cytotoxicity and mutagenicity of PRW, however, UV/TiO₂/H₂O₂ system was found slightly efficient as compared to gamma ray/H₂O₂. From the results, it can be concluded that AOP's can successfully be utilized for the degradation of toxic pollutants in petroleum refinery wastewater. Moreover, the bioassays used in this study offered a good reliability for checking the detoxification of treated and un-treated PRW wastewater.

Evaluating photo-degradation of COD and TOC in petroleum refinery wastewater by using TiO2/ZnO photo-catalyst

The aim of this study is to investigate the performance of combined solar photo-catalyst of titanium oxide/zinc oxide (TiO₂/ZnO) with aeration processes to treat petroleum wastewater. Central composite design with response surface methodology was used to evaluate the relationships between operating variables for TiO₂ dosage, ZnO dosage, air flow, pH, and reaction time to identify the optimum operating conditions. Quadratic models for chemical oxygen demand (COD) and total organic carbon (TOC) removals prove to be significant with low probabilities (<0.0001). The obtained optimum conditions included a reaction time of 170 min, TiO₂ dosage (0.5 g/L), ZnO dosage (0.54 g/L), air flow (4.3 L/min), and pH 6.8 COD and TOC removal rates of 99% and 74%, respectively. The TOC and COD removal rates correspond well with the predicted models. The maximum removal rate for TOC and COD was 99.3% and 76%, respectively at optimum operational conditions of TiO₂ dosage (0.5 g/L), ZnO dosage (0.54 g/L), air flow (4.3 L/min), reaction time (170 min) and pH (6.8). The new treatment process achieved higher degradation efficiencies for TOC and COD and reduced the treatment time comparing with other related processes.

Novel nanorose-like Ce(iii)-doped and undoped Cu(ii)–biphenyl-4,4-dicarboxylic acid (Cu(ii)–BPDCA) MOSs as visible light photocatalysts: synthesis, characterization, photodegradation of toxic dyes and optimization

A novel nanorose-like metal organic system (MOS) based on Cu(ii) and biphenyl-4,4-dicarboxylic acid (Cu–BPDCA) doped by Ce(iii) was hydrothermally synthesized and characterized via EDS, FE-SEM, XRD, DRS and FT-IR analysis.