Mehrab Mehrvar

Integration of advanced oxidation technologies and biological processes: recent developments, trends, and advances.

Abstract The greatest challenge of todays wastewater treatment technology is to optimize the use of biological and chemical wastewater treatment processes. The choice of the process and/or integration of the processes depend strongly on the wastewater characteristics, concentrations, and the desired efficiencies. It has been observed by many investigators that the coupling of a bioreactor and advanced oxidation processes (AOPs) could reduce the final concentrations of the effluent to the desired values. However, optimizing the total cost of the treatment is a challenge, as AOPs are much more expensive than biological processes alone. Therefore, an appropriate design should not only consider the ability of this coupling to reduce the concentration of organic pollutants, but also try to obtain the desired results in a cost effective process. To consider the total cost of the treatment, the residence time in biological and photochemical reactors, the kinetic rates, and the capital and operating costs of the reactors play significant roles. In this study, recent developments and trends (1996–2003) on the integration of photochemical and biological processes for the degradation of problematic pollutants in wastewater have been reviewed. The conditions to get the optimum results from this integration have also been considered. In most of the studies, it has been shown that the integrated processes were more efficient than individual processes. However, slight changes in the configuration of the reactors, temperature, pH, treatment time, concentration of the oxidants, and microorganisms colonies could lead to a great deviation in results. It has also been demonstrated that the treatment cost in both reactors is a function of time, which changes by the flow rate. The minimum cost in the coupling of the processes cannot be achieved unless considering the best treatment time in chemical and biological reactors individually.

Health effects, environmental impacts, and photochemical degradation of selected surfactants in water

Surfactants are depended upon worldwide as cleaning agents. Their usage in such large quantities means that their waste and the potential for pollution are high. Many studies have been done over the last three decades encompassing treatment, alternatives to non-biodegradable surfactants, and the environmental impact. It has been found that although certain surfactants may not be directly toxic, when their concentrations are high in soil, they can act as agents to release toxic pollutants such as polychlorinated biphenyls (PCBs). The focus of this study is to review recent advances in the toxicology, the environmental fate, and the treatment of selected surfactants. In addition, photolytic and photocatalytic degradation of linear alkylbenzene sulfonate in water is presented.

Slaughterhouse wastewater characteristics, treatment, and management in the meat processing industry: A review on trends and advances.

A thorough review of advancement in slaughterhouse wastewater (SWW) characteristics, treatment, and management in the meat processing industry is presented. This study also provides a general review of the environmental impacts, health effects, and regulatory frameworks relevant to the SWW management. A significant progress in high-rate anaerobic treatment, nutrient removal, advanced oxidation processes (AOPs), and the combination of biological treatment and AOPs for SWW treatment is highlighted. The treatment processes are described and few examples of their applications are given. Conversely, few advances are accounted in terms of waste minimization and water use reduction, reuse, and recycle in slaughterhouses, which may offer new alternatives for cost-effective waste management. An overview of the most frequently applied technologies and combined processes for organic and nutrient removal during the last decade is also summarized. Several types of individual and combined processes have been used for the SWW treatment. Nevertheless, the selection of a particular technology depends on the characteristics of the wastewater, the available technology, and the compliance with regulations. This review facilitates a better understanding of current difficulties that can be found during production and management of the SWW, including treatment and characteristics of the final effluent.

Photocatalytic degradation of aqueous organic solvents in the presence of hydroxyl radical scavengers

Tetrahydrofuran (THF) and 1,4-dioxane (DIOX) are two common solvents that are found in contaminated groundwater. Photocatalytic degradation of these two organic solvents in water was studied in the presence of carbonate and bicarbonate, which are hydroxyl radical scavengers. The reactions were performed in an annular slurry photoreactor. It was found that bicarbonate and carbonate ions acted as hydroxyl radical scavengers and slowed down the DIOX degradation rate but did not significantly affect the THF degradation rate. The slight enhancement in the THF degradation rate in the presence of sodium bicarbonate may be due to the increase in pH. In addition, it appears that bicarbonate and carbonate ions were reduced to other organic species during the photocatalytic reaction.

Sonophotolytic degradation of synthetic pharmaceutical wastewater: Statistical experimental design and modeling

The merits of the sonophotolysis as a combination of sonolysis (US) and photolysis (UV/H2O2) are investigated in a pilot-scale external loop airlift sonophotoreactor for the treatment of a synthetic pharmaceutical wastewater (SPWW). In the first part of this study, the multivariate experimental design is carried out using Box-Behnken design (BBD). The effluent is characterized by the total organic carbon (TOC) percent removal as a surrogate parameter. The results indicate that the response of the TOC percent removal is significantly affected by the synergistic effects of the linear term of H2O2 dosage and ultrasound power with the antagonistic effect of quadratic term of H2O2 dosage. The statistical analysis of the results indicates a satisfactory prediction of the system behavior by the developed model. In the second part of this study, a novel rigorous mathematical model for the sonophotolytic process is developed to predict the TOC percent removal as a function of time. The mathematical model is based on extensively accepted sonophotochemical reactions and the rate constants in advanced oxidation processes. A good agreement between the model predictions and experimental data indicates that the proposed model could successfully describe the sonophotolysis of the pharmaceutical wastewater.

Photocatalytic degradation of aqueous tetrahydrofuran, 1,4-dioxane, and their mixture with TiO 2

Photocatalytic degradation of tetrahydrofuran, 1,4-dioxane, and their mixture in a slurry pho- toreactor was studied. Using both GC/MS and ion chromatography (IC) methods, possible intermediates were detected and the reaction mechanism pathways for both compounds were proposed. Kinetic models were developed and the kinetic parameters were estimated using a statistical method of non-linear parameter es- timation in which all experimental data were utilized. It was shown that tetrahydrofuran was disappeared via direct oxidation as well as hydroxyl radical attack. A modified Langmuir-Hinshelwood described the degrada- tion behavior of tetrahydrofuran and the binary system. 1,4-Dioxane obeyed a simple Langmuir-Hinshelwood kinetic form in the single compound system.

Preliminary analysis of a tellerette packed-bed photocatalytic reactor

Abstract A novel tellerette packed bed photoreactor (TPBP), in which titanium dioxide was immobilized on stainless steel tellerette packings, was developed to provide a combination of good light and mass transfer. The experiments revealed that mass transfer limitations in this packed bed photoreactor were insignificant, such that the reaction appeared to be kinetically controlled even in regions closest to the illumination sources. A combination of measurements and simple modelling suggests that the TPBP may have potential use due to the effective mass transfer and UV light penetration characteristics.

Combined anaerobic-aerobic and UV/H2O2 processes for the treatment of synthetic slaughterhouse wastewater

The biological treatment of a synthetic slaughterhouse wastewater (SSWW) is studied using an anaerobic baffled bioreactor (ABR) and an aerobic activated sludge (AS) at a laboratory scale in continuous mode. The total organic carbon (TOC) loading rate, the total nitrogen (TN) loading rate, and the flow rate are 0.03–1.01 g/(L.day), 0.01–0.19 g/(L.day), and 2.93–11.70 mL/min, respectively. The results reveal that combined anaerobic-aerobic processes had higher efficiency to treat SSWW than a single process. Up to 96.36% TOC, 80.53% TN, and 99.38% 5-day carbonaceous biochemical oxygen demand (CBOD5) removal from an influent concentration of 1,009 mgTOC/L, 420 mgTN/L, and 640 mgCBOD5/L at the hydraulic retention time (HRT) of 6.24 days and a flow rate of 3.75 mL/min are achieved. The UV/H2O2 process is studied to treat a secondary effluent of SSWW with TOC loadings of 65–350 mg/L. Up to 75.22% TOC and 84.38% CBOD5 removal are obtained at the HRT of 3 h with H2O2 concentration of 900 mg/L. Optimum molar ratios of 13.87 mgH2O2/mgTOCin and 4.62 mgH2O2/mgTOCin.h are also obtained. Combined anaerobic-aerobic and UV/H2O2 processes enhanced the biodegradability of the TOC, TN, and CBOD5 present in the SSWW. Up to 99.98% TOC, 82.84% TN, and 99.69% CBOD5 overall removals are obtained for an influent concentration of 1,005 mgTOC/L, 200 mgTN/L, and 640 mgCBOD5/L at the HRT of 4 days and a flow-rate of 5.90 mL/min.

Treatment of an actual slaughterhouse wastewater by integration of biological and advanced oxidation processes: Modeling, optimization, and cost-effectiveness analysis

Biological and advanced oxidation processes are combined to treat an actual slaughterhouse wastewater (SWW) by a sequence of an anaerobic baffled reactor, an aerobic activated sludge reactor, and a UV/H2O2 photoreactor with recycle in continuous mode at laboratory scale. In the first part of this study, quadratic modeling along with response surface methodology are used for the statistical analysis and optimization of the combined process. The effects of the influent total organic carbon (TOC) concentration, the flow rate, the pH, the inlet H2O2 concentration, and their interaction on the overall treatment efficiency, CH4 yield, and H2O2 residual in the effluent of the photoreactor are investigated. The models are validated at different operating conditions using experimental data. Maximum TOC and total nitrogen (TN) removals of 91.29 and 86.05%, respectively, maximum CH4 yield of 55.72%, and minimum H2O2 residual of 1.45% in the photoreactor effluent were found at optimal operating conditions. In the second part of this study, continuous distribution kinetics is applied to establish a mathematical model for the degradation of SWW as a function of time. The agreement between model predictions and experimental values indicates that the proposed model could describe the performance of the combined anaerobic-aerobic-UV/H2O2 processes for the treatment of SWW. In the final part of the study, the optimized combined anaerobic-aerobic-UV/H2O2 processes with recycle were evaluated using a cost-effectiveness analysis to minimize the retention time, the electrical energy consumption, and the overall incurred treatment costs required for the efficient treatment of slaughterhouse wastewater effluents.

Comparison of the photoactivities of two commercial titanium dioxide powders in the degradation of 1,4-dioxane

Two different commercial photocatalysts, Degussa P25 and Hombikat UV 100, were used to de- grade 1,4-dioxane photocatalytically in an annular slurry photoreactor. The optimum photocatalyst loading for Degussa P25 was found to be 1.5 g L −1 while for Hombikat UV 100 was between 3.0-4.0 g L −1 . The pho- toactivity of Degussa P25 is higher than that of Hombikat at lower photocatalyst loadings whereas it is lower at higher photocatalyst loadings. This was found both experimentally and also by mathematical modeling of the radiation within the photoreactor zone. The photoactivity of UV 100 titanium dioxide was found to be twice that of Degussa P25 at optimum loadings.