Mehrab Mehrvar - Academia.edu (original) (raw)

Papers by Mehrab Mehrvar

Sustainability

Winery wastewater (WWW) handling strategies often include co-treatment at municipal wastewater tr... more Winery wastewater (WWW) handling strategies often include co-treatment at municipal wastewater treatment plants (WWTPs). Despite this, definitive information regarding oxidation kinetics and process and performance impacts due to co-treatment is lacking. A combined Michaelis–Menten–University of Cape Town kinetic model has been found to best describe the pH-inhibited aerobic biological oxidation of WWW by heterotrophs in activated sludge from four municipal WWTPs. The specific rate of substrate consumption was highest in biomass that had been exposed to WWW (57.3 mg COD/g MLVSS·h) compared to biomass that had not (20.7 mg COD/g MLVSS·h). Bench-scale aerobic co-treatment trials confirm that sorption is a key removal mechanism, with up to 98% chemical oxygen demand and 97% total organic carbon removal after 6 h of reaction time. The WWW solids are quickly incorporated into the biological floc and may improve settleability at loading rates above 75 mg WWW suspended solids/L bioreactor ...

Water, 2021

Despite many wineries being equipped with onsite wastewater treatment, winery wastewater (WWW) co... more Despite many wineries being equipped with onsite wastewater treatment, winery wastewater (WWW) co-treatment at municipal wastewater treatment plants (WWTPs) remains a common practice in wine-making regions. The complex and highly variable nature of WWW can result in negative impacts on WWTP operations, highlighting a need for improved co-treatment methods. In this paper, the feasibility of using the Fenton-like process to pre-treat WWW to enhance co-treatment at municipal WWTPs is assessed. First-stage pre-treatment of the WWW, in the form of dilution and settling or aerobic biological treatment, is used prior to the Fenton-like process. A three-factor BBD experimental design is used to identify optimal reaction time and initial H2O2 and Fe3+ concentrations. Chemical oxygen demand (COD) and total organic carbon (TOC) removal rates are not able to accurately reflect the extent of reaction. Additional trials identified solubilization of particulate COD and TOC, as well as samples hand...

International Conference of Recent Trends in Environmental Science and Engineering, 2021

Various industries rely on water-soluble polymers as additives, therefore, it is imperative to tr... more Various industries rely on water-soluble polymers as additives, therefore, it is imperative to treat them so that they do not enter our environment as persistent pollutants. Though used as a leading method for degradation of organic pollutants, biological treatment can only treat wastewater that is readily degradable by living organisms. If that is not possible, researchers mainly focused on the oxidation of polyvinyl alcohol (PVA) in an Advanced Oxidation Process (AOP) such as UV/H2O2 process as an easy process owing to its relatively developed kinetics, non-selective degradation, low cost, and ease in operation at large-scale [1-3]. In particular, the UV/H2O2 process requires modelling to establish a control system that prevents adverse effects of PVA and residual hydrogen peroxide (H2O2) to the aquatic system and subsequent biological processes by maintaining H2O2 residuals in the treated effluent within a safe level. During this study, the performance of black-box methods was examined in determining the dynamics of polyvinyl alcohol degradation in various UV/H2O2 systems, where process inputs and responses involved hydrogen peroxide concentration and acidity, respectively. The complete data analysis and model fitting is undertaken with MATLAB R2019b software. Models including the linear AutoRegressive with eXogenous Input (ARX), the nonlinear ARX (NARX), and the Hammerstein-Wiener model are compared for their success in providing an accurate representation of statistical dynamics. Comparatively, the sigmoidnetwork-based NARX was better at representing the process dynamics when compared to others. The study also explores the design of PID controllers via ARX and sigmoid-network-based NARX models and analyzes controller performance for set-point tracking and disturbance rejection. The ARX-P, ARX-PI, NARX-P, and NARX-PI controllers were not adequate for a good control design as they exhibit higher offset from set-point, higher overshoot, and longer settling time. The ARX-PID and NARX-PID provide adequate closed-loop responses, while NARX-PID seems better suited for the studied process. However, the ARX-PID has a higher IAE and produces a more robust output response against disturbances as it is adequate for processing disturbances but less useful in tracking process set-points. As a result, to compensate for the complexity in generating models and tuning the parameters with the NARX model, an approximation based on the ARX model is appropriate when its implementation will be followed by another setup for H2O2 elimination. Although feasibility of linear control scheme was presented, it is suggested that similar scenarios should be considered in future designs, validations, and performance evaluations of the entire controlled system, especially for improving controller robustness by implementing multivariate adaptive controls and linear or non-linear predictive controls [4-9].

Journal of Environmental Chemical Engineering, 2021

In AOP processes, the flow of oxidant must be controlled to minimize the oxidant residuals in a p... more In AOP processes, the flow of oxidant must be controlled to minimize the oxidant residuals in a post biological treatment and to maximize the total organic carbon (TOC) removal and degradation. Designing a controller to regulate the hydrogen peroxide (H2O2) begins with a dynamic model determination of a chemical process. Therefore, a step testing technique is employed to construct a dynamic model of the UV/H2O2 degradation of polyvinyl alcohol (PVA) process based on pH and TOC responses to H2O2 step change. The experimental design consists of three different initial PVA concentrations, of 60.0, 280.0, and 500.0 mg PVA/L. Eight experimental tests were conducted for different hydrogen peroxide mass flowrates ranging from 0.336 to 125 mg H2O2/min. For every test, a transfer function was experimentally determined to describe the dynamics of the UV/H2O2 photochemical reactor for the degradation of PVA. System identification toolbox in Matlab software was used to determine first order plus time delay (FOPTD), second order plus time delay (SOPTD) and ARX polynomial models. The transfer functions and ARX models are a good model representation of the pH response data of a specific step change of H2O2 concentration. For example, the standard deviation of the process gain of test # 1 and its replicate was calculated to be 1.18 and standard deviation of the time constant was calculated to be 1.27. The pH response of the first test was fitted with a FOPTD model with a data fitting score of 88.8%. Test # 2 pH response data was fitted with a SOPTD transfer function with data fitting score of 83.6%. Tests # 6 and 7's pH response was fitted with a FOPTD model with a data fitting score of 94.3 and 87.7 % respectively. The different transfer functions obtained for the low, average, and high PVA concentrations indicate the nonlinearity aspect of polymer systems. All quality models are quite reliable estimations of the pH and TOC response data, since they were developed from experimental tests and parameter estimation techniques based on nonlinear regression approach.

Environmental Science and Pollution Research, 2020

Doping a transition metal into photocatalysts enhances the photocatalytic activity drastically. I... more Doping a transition metal into photocatalysts enhances the photocatalytic activity drastically. In the first part of this study, Taguchi design of experiment is applied to evaluate and optimize the efficiency of the Fe 2 O 3 /TiO 2 photocatalyst synthetized by thermal method assisted by UV radiation. The contribution percentages of Fe:TiO 2 mass ratio, Fe 2 O 3 /TiO 2 dosage, and pH on the total organic carbon (TOC) removal are determined using analysis of variance (ANOVA). In the second part of this study, in order to model the photocatalytic degradation process, the optical properties of the photocatalyst, including the extinction, absorption, and scattering coefficients, are determined. Subsequently, the radiation transfer equation (RTE) is solved numerically based on the surface emission model using the discrete ordinate method. Furthermore, a rigorous model, including chemical reaction rates, radiation transfer, and mass transfer is proposed and validated by a set of experimental data. A satisfactory correlation between the predicted and experimental data with less than 5% error confirms the reliability of the model. The intrinsic kinetic parameters are also determined by comparing predicted values to those of the experimental results by applying non-linear regressions.

Journal of Chemical Technology & Biotechnology, 2020

In this study, the photochemical degradations of three commonly used artificial sweeteners, namel... more In this study, the photochemical degradations of three commonly used artificial sweeteners, namely aspartame (ASP), acesulfame K (ACE), and sucralose (SUC) were investigated in multicomponent aqueous systems through UV/H2O2. A recirculating batch photochemical reactor setup was utilized for experimental work. The treatability of the multicomponent system was monitored in the form of total organic carbon (TOC) reduction. A two-level fractional factorial design of experiments (DOE) was adopted. The individual and multifactor interaction effects of the concentration of the three sweeteners, the applied hydrogen peroxide dosage and the operating temperature on TOC reduction were investigated. The biodegradability characteristics of the sweeteners were investigated for both single and multicomponent systems through respirometry. Their degradations were compared to those of the UV/H2O2 system. It was determined that the UV/H2O2 process is suitable treatment technique, achieving TOC removal efficiencies over 90% with a UV exposure of 45 min. The operating temperature and the applied H2O2 dosing on the final TOC removal were found to be significant. An interaction between ASP and SUC resulted in a temporary improvement in TOC removal midway through the treatment process. Respirometric studies confirmed that ACE and SUC are non-biodegradable. The biodegradation characteristics of ASP was found to be acceptable with a 6-day biochemical to theoretical oxygen demand (BOD6/ThOD) ratio of 0.63±0.02. I would also like to thank engineering specialists Mr. Ali Hemmati and Mr. Daniel Boothe of Ryerson University's Department of Chemical Engineering for providing their support and assistance throughout my work. I would also like to thank the members of my research team, Melody Johnson, Yi Ping Lin, Ciro Bustillo-Lecompte and Mohsen Nasirian for their help and guidance. I would also like to thank my dear friends

The Canadian Journal of Chemical Engineering, 2019

The winemaking process produces a large volume of wastewater with highly variable characteristics... more The winemaking process produces a large volume of wastewater with highly variable characteristics. Methods in place to manage winery wastewater (WWW) vary, with some wineries treating their WWW on‐site, while others direct the WWW to municipal wastewater treatment plants (WWTPs). Despite the significant presence and growth of the wine industry in the Niagara Region of Ontario, Canada, few data are available regarding the characteristics and treatment of WWW in this geographic region. This work presents a comprehensive review of full‐scale treatment methods currently in place to manage and treat WWW at 53 wineries in the Niagara Region. The most common type of on‐site treatment is the constructed wetland process, providing overall removal rates of >98% for chemical oxygen demand (COD) and >98% for total suspended solids (TSS) for the combined treatment of WWW and site‐generated sanitary sewage. Subsurface effluent discharge is the most widely used disposal strategy, while large...

DESALINATION AND WATER TREATMENT, 2018

Methyl orange, a well-known detrimental azo dye, is treated by N-doped TiO 2 photocatalyst synthe... more Methyl orange, a well-known detrimental azo dye, is treated by N-doped TiO 2 photocatalyst synthesized by the simple and effective annealing method. In this study, the effects of light intensity in terms of irradiance by the number of lamps, photon energy and radiation sources, the initial concentration of total organic carbon (TOC), and pH on the degradation efficiency of methyl orange are investigated. A four-factor Box-Behnken design along with response surface methodology is used to maximize the removal of TOC and color. Statistical models are developed to predict both color and TOC removals as response variables. In all cases, the light intensity and TOC concentration cross-factor interaction with the light wavelength is intensified when the latter is at the lowest range value while pH does not require adjustments. Maximum TOC and color removals of 96.11% and 98.18%, respectively, were achieved at the optimum operating conditions of light intensity in terms of five lamps, light wavelength of 418 nm (visible light range), initial TOC concentration of 10.54 mg/L, and pH of 6.66. The model was validated by an additional experiment at the optimal operating conditions. The agreement between experimental values and model predictions demonstrate the proposed models could effectively describe the degradation of azo dyes by photocatalysis using the N-doped TiO 2 composite under visible light.

Catalysts, 2018

Titanium dioxide (TiO2) photocatalysis is one of the most commonly studied advanced oxidation pro... more Titanium dioxide (TiO2) photocatalysis is one of the most commonly studied advanced oxidation processes (AOPs) for the mineralization of deleterious and recalcitrant compounds present in wastewater as it is stable, inexpensive, and effective. Out of all, doping with metal and non-metals, and the heterojunction with another semiconductor were proven to be efficient methods in enhancing the degradation of organic pollutants under ultraviolet (UV) and visible light. However, complex degradation processes in the treatment of an actual wastewater are difficult to model and optimize. In the present study, the application of a modified photocatalyst, Ag/TiO2/Fe2O3, for the degradation of an actual confectionery wastewater was investigated. Factorial studies and statistical design of experiments using the Box-Behnken method along with response surface methodology (RSM) were employed to identify the individual and cross-factor effects of independent parameters, including light wavelength (nm...

Kinetic Modeling for Environmental Systems [Working Title], 2019

Synthetic water-soluble polymers, well-known refractory pollutants, are abundant in wastewater ef... more Synthetic water-soluble polymers, well-known refractory pollutants, are abundant in wastewater effluents since they are extensively used in industry in a wide range of applications. These polymers can be effectively degraded by advanced oxidation processes (AOPs). This entry thoroughly covers the development of the photochemical kinetic model of the polyvinyl alcohol (PVA) degradation in UV/ H 2 O 2 advanced oxidation batch process that describes the disintegration of the polymer chains in which the statistical moment approach is considered. The reaction mechanism used to describe the photo-degradation of polymers comprises photolysis, polymer chain scission, and mineralization reactions. The impact of operating conditions on the process performance is evaluated. Characterization of the polymer average molecular weights, total organic carbon, and hydrogen peroxide concentrations as essential factors in developing a reliable photochemical model of the UV/H 2 O 2 process is discussed. The statistical moment approach is applied to model the molar population balance of live and dead polymer chains taking into account the probabilistic chain scissions of the polymer. The photochemical kinetic model provides a comprehensive understanding of the impact of the design and operational variables.

DESALINATION AND WATER TREATMENT, 2019

The aim of this study is to develop a novel photocatalyst doped by a noble metal onto two semicon... more The aim of this study is to develop a novel photocatalyst doped by a noble metal onto two semiconductor oxides for the applications of photocatalytic wastewater treatment. An alternative preparation method of UV-assisted thermal synthesis is used to synthesize this photocatalyst. The two photocatalysts, Fe 2 O 3 and TiO 2 , were combined with different mass ratios of Fe:TiO 2 followed by doping the synthesized Fe 2 O 3 /TiO 2 with a silver ion with different mass ratios of Ag:TiO 2 to produce the novel photocatalyst Ag/TiO 2 /Fe 2 O 3. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy is employed to evaluate the formation, the morphology, and the elemental analysis of the composite photocatalyst. The phase and the crystal structure of the new composites are investigated by X-ray diffraction. The specific surface area of all photocatalysts is analyzed based on the Brunauer-Emmett-Teller method by adsorption of nitrogen gas at 77 K. Removal of methyl orange is used to examine the photocatalytic degradation efficiency of the photocatalysts. Results indicate that the specific surface area of the Ag/TiO 2 /Fe 2 O 3 photocatalyst was significantly increased and the photocatalytic activity of the new photocatalyst was enhanced for the degradation of aqueous methyl orange. The new composite has the potential to absorb light at a higher wavelength in the visible region where the redshift occurs. By applying the Ag/TiO 2 /Fe 2 O 3 photocatalyst with a mass ratio of 0.01 Ag:TiO 2 and 0.01 Fe:TiO 2 , the maximum degradation of methyl orange reaches to 89.5% and 95.5% under UV-A radiation and natural sunlight, respectively. Diffractograms confirm that the substitutions occur in the crystal lattice of the main photocatalyst.

Journal of Environmental Sciences, 2017

A nitrogen-doped titanium dioxide composite photocatalyst (N-TiO 2) with heterojunction structure... more A nitrogen-doped titanium dioxide composite photocatalyst (N-TiO 2) with heterojunction structures is synthesized by three different approaches: a novel UV-assisted thermal synthesis, annealing, and microwave technique. Photocatalytic activities of synthesized photocatalysts are evaluated by the degradation of Methyl Orange under ultraviolet light types A (UV-A), B (UV-B), and C (UV-C), visible light, and direct sunlight irradiation. Results show that by using N-TiO 2 photocatalyst prepared by the UV-assisted thermal synthesis and annealing, the degradation increases by 16.5% and 20.4%, respectively, compared to that by bare TiO 2. The best results are obtained at a nitrogen to TiO 2 mass ratio of 0.15 (N: TiO 2). The enhancement of the photocatalytic activity observed in the visible range is mainly attributed to the increasing separation rate of photogenerated charge carriers. The novel UV-assisted thermal synthesis has produced encouraging results as a preparation method for the nitrogen-doped TiO 2 photocatalyst; thus, further studies are recommended for process optimization, immobilization, and scale-up to evaluate its applicability in wastewater treatment.

Physico-Chemical Wastewater Treatment and Resource Recovery, 2017

The meat processing industry is one of the largest consumers of total freshwater used in the agri... more The meat processing industry is one of the largest consumers of total freshwater used in the agricultural and livestock industry worldwide. Meat processing plants (MPPs) produce large amounts of slaughterhouse wastewater (SWW) because of the slaughtering process and cleaning of facilities. SWWs need significant treatment for a sustainable and safe discharge to the environment due to the high content of organics and nutrients. Therefore, the treatment and final disposal of SWW are a public health necessity. In this chapter, the regulatory frameworks relevant to the SWW management, environmental impacts, health effects, and treatment methods are discussed. Although physical, chemical, and biological treatment can be used for SWW degradation, each treatment process has different advantages and drawbacks depending on the SWW characteristics, best available technology, jurisdictions, and regulations. SWWs are typically assessed using bulk parameters because of the various pollutant loads derived from the type and the number of animals slaughtered that fluctuate amid the meat industry. Thus, an on-site treatment using combined processes would be the best option to treat and disinfect the slaughterhouse effluents to be safely discharged into receiving waters.

Journal of Environmental Science and Health, Part B, 2017

In this study, a three-factor, three-level Box-Behnken design with response surface methodology a... more In this study, a three-factor, three-level Box-Behnken design with response surface methodology and quadratic programming were used to maximize the total organic carbon (TOC) removal and minimize the H2O2 residual in the effluent of the combined UV-C/H2O2/VUV system for the treatment of actual slaughterhouse wastewater. The initial TOC concentration (TOCo), the initial concentration of H2O2, and the irradiation time were the three independent variables studied in the design of experiments. The multiple response approach was used to obtain desirability response surfaces at the optimum factor settings. Thus, the optimum conditions to achieve a maximum TOC removal of 46.19% and a minimum H2O2 residual of 1.05% were TOCo of 213 mg/L, H2O2,o of 450 mg/L, and irradiation time of 9 min. The obtained optimal operating conditions were validated with an additional test. Consequently, maximum TOC removal of 45.68% and minimum H2O2 residual of 1.03% were obtained experimentally, confirming the reliability of the statistical model.

Journal of Geoscience and Environment Protection, 2016

The characteristics of the slaughterhouse effluents and current wastewater treatment practices in... more The characteristics of the slaughterhouse effluents and current wastewater treatment practices in the province of Ontario, Canada are analyzed. Meat processing plants are found to produce large amounts of wastewater due to the slaughtering process and cleaning of their facilities. Furthermore, the composition of the wastewater varies according to the type and number of animals slaughtered and the water requirements of the process. However, the slaughterhouse wastewater usually contains high levels of organics and nutrients. Several slaughterhouses in Ontario discharge their wastewater into the municipal sewer system after primary pretreatment at the meat processing plant. Therefore, due to the high-strength characteristics of the slaughterhouse effluents, an extensive treatment for a safe discharge into the environment is required. Thus, the combination of biological processes and advanced oxidation technologies for slaughterhouse wastewater treatment is evaluated in this study. Results show that the application of combined biological and advanced oxidation processes is recommended for on-site slaughterhouse wastewater treatment.

Water Quality Research Journal, 2011

Correlative reaction kinetics based on nonlinear least square regression were obtained to predict... more Correlative reaction kinetics based on nonlinear least square regression were obtained to predict the degradation of p-aminophenol (PAP), C.I. Reactive Yellow 84 (RY84), C.I. Reactive Blue 19 (RB19), and C.I. Direct Red 23 (DR23) in combined ultrasonolysis and ozonation. Effects of ultrasonolysis and ozonation as individual processes, as well as the synergetic effect for the degradation of azo dyes, were studied by linear and nonlinear regression methods. An initial dye concentration correlation index (φ) for each compound was developed to study the effects of initial concentrations of organics on their reaction rate constants. Reaction rate constants for the azo dyes’ degradation in ozonation and ultrasonolysis alone and their combination were obtained for different operating conditions. Results showed that ultrasonolysis alone was almost ineffective for decolorization and mineralization of azo dyes, but the combination of ozonation and ultrasonolysis had a significant effect on th...

Chemical Engineering Journal, 2014

The treatment ability and efficiency of sonophotolytic process, aerobic activated sludge (AS) pro... more The treatment ability and efficiency of sonophotolytic process, aerobic activated sludge (AS) process, and their combination in reduction of total organic carbon (TOC), total nitrogen (TN), chemical oxygen demand (COD), and biological oxygen demand (BOD) from a synthetic pharmaceutical wastewater (SPWW) were studied. Batch mode experiments were performed to obtain optimal experimental operating conditions for sonophotolysis process. Ultrasonic power of 140 W, initial pH solution of 2, and air flow rate of 3 L/min were found as optimum. The initial optimum molar ratio of H2O2/TOC was found to be 13.77 for sonophotolysis process alone in batch mode. In continuous mode, sonophotolysis was able to reduce TOC by 90% after 180 min retention time. Aerobic AS process alone after 48 h retention time reduced TOC by 67%. Combined sonophotolysis and aerobic AS processes improved the biodegradability of the SPWW and resulted in 98% TOC and 99% COD removal while decreasing the retention time in sonophotoreactor and aerobic AS reactor to 120 min and 24 h, respectively. Additionally, the consumption of H2O2 was reduced significantly in the combined processes. iv ACKNOWLEDGMENTS I would like to express my sincere thanks to my primary supervisor, Dr. Mehrab Mehrvar, and my co-supervisor, Dr. Ramdhane Dhib, for offering me the opportunity to study and work in their research group. Their continuous guidance and financial support during my graduate studies are highly appreciated. I am very thankful to the Engineering Specialists of the Chemical Engineering Department, Ali Hemmati, Daniel Boothe, and Tondar Tajrobehkar, for providing invaluable assistance during the experimental set up. I would also like to express my gratitude to my parents (Dariush and Giti) and my brothers (Arash, Ashkan, and Omid) for their love and support earlier and during my studies in Canada. I would like to name

Applied Computational Fluid Dynamics, 2012

Advanced oxidation processes (AOPs) play an important role in the degradation or the production o... more Advanced oxidation processes (AOPs) play an important role in the degradation or the production of a wide range of organic materials. Many organic compounds such as pharmaceuticals, dyes, herbicides, and pesticides have been subjected to degradation and remediation purposes in water and wastewater treatment systems using AOPs. Some of the organic compounds such as drugs, vitamins, or fragrances could be also produced by oxidation processes. As the standard of living increases, many chemicals such as pharmaceuticals, pesticides, herbicides, and dyes are extensively consumed. Each of these products may cause health issues by their accumulation in aquatic environment. Pharmaceuticals such as antibiotics are partially metabolized and excreted by humans and animals. Improper disposal, dumping, and accidental discharge of drugs lead to the increase of the concentration of compounds such as analgesics, antibiotics, steroids, and hormones in aquatic environment, which cause environmental and health problems. Residual pesticides and herbicides originate from the direct pollutant in production plant, disposal of empty containers, equipment washing, and surface runoff. High levels of these compounds are toxic, mutagenic, carcinogenic, and tumorigenic. Some other wastes such as landfill leachate are subjected to advanced treatment methods. Old landfill leachates (>10 years) are nonbiodegradable in nature due to the existence of organic compounds with high molecular weights. Although the composition of landfill leachates varies widely with respect to the age of the landfill, type of wastes, and climate conditions, they can be categorized into four groups of dissolved organic matter, inorganic macro components, heavy materials, and xenobiotic organic substances. Another type of toxic chemicals which cannot be removed using conventional treatment methods is endocrine disrupting compounds (EDCs). EDCs, especially the steroidal hormones, are well recognized exogenous agents that interfere with the synthesis, action, and/or elimination of natural hormones in the body. Conventional processes are not effective in destruction of these types of organic compounds; therefore, powerful advanced treatment processes are required in order to mineralize them. There are several options for choosing an oxidation process: wet air oxidation, supercritical water oxidation, incineration, and AOPs. AOPs have been promising in the treatment of contaminated soils and waters. The AOPs could be employed to fully or partially oxidize organic pollutants usually using a combination of different oxidants. In contrary to the conventional physical and chemical treatment processes, AOPs do not transfer pollutants from one phase to another, i.e., organic www.intechopen.com Applied Computational Fluid Dynamics 156 pollutants are completely destroyed. Most AOPs are able to generate hydroxyl radicals. These hydroxyl radicals are active and powerful, capable of reacting with almost all types of organics, including non-biodegradable and recalcitrant compounds. These oxidizing hydroxyl radicals are initiated by photolysis, photocatalysis, sonolysis, radiolysis, and other AOPs alone or in combination in the presence of some reagents such as hydrogen peroxide (H 2 O 2), ozone, and homogeneous or heterogeneous catalysts. Hydroxyl radicals are extremely powerful, short-lived oxidizing agent, and non-selective in nature and could react with a wide range of organic chemicals with reaction constant of several orders of magnitude higher than the reaction with molecular ozone under the same conditions. AOPs are used to convert toxic, non-biodegradable, inhibitory, and recalcitrant pollutants into simpler and less harmful intermediates, so they could be treated subsequently in biological processes. Due to the high operating and capital costs of AOPs, the complete mineralization of organic compounds using AOPs is practically impossible; therefore they are mainly combined with other processes such as biological systems to be cost-effective. With sufficient contact time and proper operating conditions and design, the mineralization efficiency of the AOPs is maximized by optimization of the processes in such a way that the total costs of the processes are minimized while the removal rates of organic pollutants are maximized. Since conducting experiments is time-consuming and expensive or sometimes impossible to do, the modeling of the photoreactors is necessary. Computational fluid dynamics (CFD) is one of the numerical methods to solve and analyze the transport equations. CFD has been used recently in order to find the velocity, radiation intensity, pollutant concentration distribution inside the photoreacotrs (

Chemical Engineering Research and Design, 2012

The combination of sonolysis and photolysis in the presence of hydrogen peroxide (H 2 O 2) in a 7... more The combination of sonolysis and photolysis in the presence of hydrogen peroxide (H 2 O 2) in a 7-L external-loop airlift sonophotoreactor was used to treat the aqueous solution of p-aminophenol. The central composite design (CCD) and response surface methodology (RSM) were employed to evaluate the interaction effects of the initial H 2 O 2 concentration (x 1 = 100-900 mg/L), the ultrasonic power (x 2 = 25-65 W), the air flow rate (x 3 = 1-5 L/min), and the initial concentration of p-aminophenol (x 4 = 10-50 mg/L) on the p-aminophenol degradation and total organic carbon (TOC) reduction efficiencies as well as to optimize operating conditions. The coefficients of determination (R 2) and adjusted-R 2 obtained from the analysis of variance (ANOVA) were 0.9900 and 0.9812 for the p-aminophenol degradation; and 0.9742 and 0.9516 for the TOC removal, respectively, ensuring a satisfactory adjustment of the quadratic regression model with experimental results. The linear, square, and interaction effects of x 1 , x 2 , x 3 , and x 4 were also calculated. Genetic algorithm optimization was employed to maximize the mineralization efficiency. 79% TOC reduction efficiency after 90 min and 86.5% p-aminophenol removal efficiency after 30 min were achieved under recirculating batch mode at operating conditions of x 1 = 740 mg/L, x 2 = 65 W, x 3 = 5 L/min, and x 4 = 24 mg/L.