DEVELOPMENT OF INTEGRATED MEMBRANE BIOREACTOR AND CHEMICAL PROCESSES FOR ADVANCED WASTEWATER TREATMENT

Abstract

The global rise in population and rapid industrialization and urbanization have resulted in a significant increase in wastewater production, putting a strain on existing treatment facilities. This has led to the release of certain pollutants into the aquatic environment, including emerging contaminants such as pharmaceuticals, pesticides, hygiene products, endocrine-disrupting agents, surfactants, and industrial chemicals. These pollutants are found in wastewater, groundwater, rivers and lakes and pose a potential threat to human health and cause various illnesses such as reproductive disorders, cardiovascular disorders, cancer, immune deficiency, nervous system syndrome, brain development delay, and memory disruption. The secondary treatment (biological processes) in a typical treatment plant is the most crucial step as it removes approximately 80-90% of pollutants. However, conventional treatment methods are not effective in completely removing emerging contaminants, and advanced treatment techniques must be utilized. In this work, different types of wastewaters containing emerging pollutants were treated using conventional activated sludge process, membrane filtration, and advanced oxidation processes. The following emerging pollutants were used as targets: caffeine, ibuprofen, metronidazole, naproxen, sulfamethoxazole, bisphenol A, and carbamazepine. The implementation of a sequencing batch reactor (SBR) led to the elimination of a significant amount (78-86%) of total organic carbon (TOC), with only small reductions (11%, 45%, and 6%) observed for naproxen, bisphenol A, and sulfamethoxazole, respectively. The SBR effluents then were treated with membrane filtration and chemical oxidation processes. Track-etch membranes (TEMs) and phase inversion membrane (PIM) were employed. It should be emphasized that TEMs were employed in wastewater treatment for the first time. TOC removal efficiency ranged from 1% to 6% for each of the four membranes evaluated. 10 nm TEM demonstrated almost complete removal of bisphenol A (93%) and insignificant removals for naproxen (11%) and sulfamethoxazole (14%). The elimination mechanism of bisphenol A employing membranes was probably connected to size exclusion and sorption. Ultimately, the effluents from SBR and membrane filtration were treated with sulfate-radical-based advanced oxidation processes (AOPs). Remarkably, full removal of emerging contaminants and TOC were obtained after 30 minutes for the effluents after membrane filtration using 10 mM of K2S2O8 and 25 mg/L of zero-valent iron (ZVI) under UV, demonstrating the great potential of combining membrane filtration and AOPs. Pharmaceuticals commonly found in wastewater, such as caffeine, metronidazole, and ibuprofen, were investigated for removal using a combination of continuous flow-activated sludge process and advanced oxidation processes. The study found that ibuprofen and caffeine were completely degraded, while metronidazole was only partially degraded. However, the presence of ibuprofen and caffeine hindered the nitrification process, while metronidazole suppressed the activity of denitrifying microorganisms. Biological treatment resulted in complete degradation of ibuprofen and caffeine but only 56% degradation of metronidazole. Advanced oxidation processes using hydroxyl and sulfate radicals were then used to eliminate the remaining metronidazole. The study demonstrated the effectiveness of AOPs in treating effluents from biological treatment processes. Moreover, AOPs were used to treat actual slaughterhouse wastewater. TiO2 photocatalysis resulted in a 44% decrease in TOC after 60 min, while UV/98 mM H2O2 led to a 74% reduction in TOC after 150 minutes. Adjusting the pH to 3 and introducing Fe2+ into the system increased TOC removal to 82.5% after 150 minutes. Combining 15 mM K2S2O8 and UV led to a TOC reduction of 85%. Persulfate oxidation was also applied for the first time to treat wastewater from a slaughterhouse. The study shows that UV/K2S2O8 may be used as an additional post-treatment technique after biological treatment for water discharge criteria fulfillment and wastewater reuse. Additional experiments were carried out using sulfate radical-based AOPs. Real municipal wastewater was treated using the UV/K2S2O8/Fe2+ process. Response surface methodology (RSM) was utilized to improve the treatment process by investigating the impacts of four independent parameters on TOC, TC, and TN removal. RSM precisely established the most suitable parameters for complete TOC removal, leading to total TOC mineralization at pH of 7.7, 30 mM K2S2O8, and K2S2O8 to Fe2+ ratio of 7.5 after 106 min. Attempts to use statistical models to determine optimum conditions for complete TC and TN elimination were, however, unproductive. In addition, for the first time, a continuous flow UV/K2S2O8/ZVI system was put into operation for wastewater treatment. The RSM was used to study the impacts of the following process factors on TOC reduction: space time, the concentration of K2S2O8, and the K2S2O8/ZVI molar ratio. Carbamazepine was spiked into both synthetic and actual municipal wastewater to investigate its fate during persulfate oxidation. In the case of synthetic wastewater, 71% TOC reduction and full elimination of carbamazepine were accomplished. In the case of real wastewater, 60% TOC removal and full carbamazepine elimination have been achieved. The complexity of real wastewater and the presence of radical-reducing agents may explain the difference in TOC removal with synthetic wastewater. Finally, the UV/K2S2O8/Goethite process was tested using landfill leachate, a highly contaminated effluent. Sulfamethoxazole was injected into both synthetic (SLL) and real landfill leachate (RLL) and used to evaluate the best treatment parameters for TOC and sulfamethoxazole removal using RSM. After 4.7 h of using the UV/K2S2O8/Goethite system, 87% TOC and 100% sulfamethoxazole were removed from the RLL. In addition, air stripping at pH 11 for 3 hours was utilized to eliminate ammonia from the RLL. For the first time, our studies indicate the efficiency of the UV/K2S2O8/Goethite system in eliminating organic materials from landfill leachate. To summarize, it was discovered that at certain concentrations, emerging pollutants block the activity of microorganisms, hence affecting the effectiveness of the activated sludge process. AOPs based on sulfate radicals are an efficient post-treatment process for the removal of emerging pollutants and TOC following the conventional biological treatment or membrane filtration. Different chemical species such as Fe2+, zero-valent iron, and goethite were used to activate persulfate or hydrogen peroxide under UV. The materials used were characterized using state-of-the-art characterization techniques. Overall, the integrated use of track-etch membrane bioreactor and advanced oxidation processes demonstrated significant efficiency in the elimination of emerging pollutants in wastewater treatment.