Pure Oxygen-driven Advanced Membrane Aerated Bioreactor For Biological Treatment Of Wastewater

The treatment of wastewater is a critical challenge facing the world,with increasing population growth,industrialization,and urbanization leading to an ever-growing demand for efficient and sustainable treatment solutions.Biological treatment methods have been extensively used in wastewater treatment plants（WWTPs）,relying on microbial activity to degrade organic matter.Aeration is a critical parameter that directly affects the dissolved oxygen（DO）concentration,fouling,mixing of solids,and operational costs of the treatment process.Although air-based aeration is efficient with most types of wastewater,pure oxygen has been found to provide a more economical and efficient DO supply,especially for high-strength wastewater.As a result,pure oxygen-based aeration has emerged as a promising technology in the wastewater industry.An overview of the integration of pure oxygen in wastewater treatment systems,including its impact,challenges,and advantages,as well as its effect on microbial community structure and multifaceted assessment is presented in the introduction of this thesis.Furthermore,an investigation of a fully sustainable pure oxygen-driven WWTP combined with renewable energy applications and green gas production is also presented.Moreover,the use of biofilm-based reactors has become increasingly popular in the treatment of high-strength wastewater due to their ability to retain microbial cells in the form of biofilm,providing high active biomass concentration and automatic liquid and solid separation.An overview of microbial biofilm-based reactors developed over the last half-century is also presented.Based on the many challenges that face the WWT industry,the studies implemented in this thesis presented a comprehensive investigation utilizing the recently attractive membrane aerated biofilm reactor（MABR）technology to overcome these challenges.In addition,novel developed combinations of MABR-based technology with other technologies are proposed and investigated to enhance the system performance.The recently attractive MABR technology has been evaluated as a highly cost-effective biofilm-based wastewater treatment technology.It implements a gas-permeable hollow fiber membrane aerated with low-pressurized air（oxygen supplier）to achieve direct oxygen diffusion to the attached biofilm.This study assesses the use of green energy-produced pure oxygen gas to drive MABR for wastewater treatment,aiming to provide insight into the cost-effectiveness,efficiency,and ability to face the treatment challenges of this approach.This study compared the conventional air-based MABR（A-MABR）with a pure oxygen-based MABR（PO-MABR）under different operation conditions of flow rate,hydraulic retention time（HRT）,gas pressure,C/N ratio,and temperature.Besides,as the varied climatic conditions,in particular,temperature variation affects the treatment efficiency and effluent quality of WWTPs with conventional processes,by influencing the growth rate,metabolism,and activity of bacteria,it presents another challenge.Therefore,the PO-MABR system was utilized to test the system performance in cold temperatures presenting a cost-effective technology as a potential solution for cold climate areas.Furthermore,the study optimized and investigated an advanced nano technology-based PO-MABR system,named Z-PO-MABR,for the treatment of high-strength wastewater.The system combines pure oxygen feeding and nano zeolite in a MABR system to enhance the removal of WW pollutants and demonstrates superior performance compared to conventional systems.Finally,an attractive combination of the pure oxygen-driven MABR and the hydrogen-driven MABR system,which is conventionally used in ground water treatment,to propose a high performance against WW pollutants achieving a full removal of total nitrogen（TN）is investigated.Both systems implement a gas-permeable hollow fiber membrane fed with low-pressurized gases（pure oxygen and hydrogen）,which is produced from a solar-powered water electrolysis cell,to achieve direct diffusion to the attached biofilms.The experimental work of the thesis and the main findings are summarized briefly as follows:Chapter 2,a MABR system driven by pure oxygen gas was assessed for wastewater treatment at different conditions and compared with the air-ventilated MABR.An automatic electrical control system was fabricated at a bench-scale experimental setup to evaluate the performance of the PO-MABR under various conditions.The results revealed that the tested PO-MABR system had achieved tremendous superiority over the A-MABR system in terms of the Chemical Oxygen Demand（COD）removal rate,recording 97%removal of COD for the PO-MABR.Thicker biofilm and different microbial structures were detected in the pure oxygen-driven MABR leading to better nitrification and denitrification processes,which achieved higher TN removal by about 19%over the A-MABR system.In addition,the PO-MABR system presented a high resistance to the impact of low temperature,and the ability to treat high and low-strength wastewater was also proved.Chapter 3,a laboratory-scale PO-MABR system was constructed to investigate the performance of the system at different temperatures and compared it with the conventional A-MABR system.The results indicated that the PO-MABR system outperformed the A-MABR system in terms of COD removal efficiency,achieving 97.9%COD removal at high temperatures and 86.5%at very low temperatures.In contrast,the A-MABR system did not provide any removal rate at 5℃.The deeper oxygen penetration through the biofilm（850μm）and higher oxygen profile（up to 50 mg/L）observed in the PO-MABR system enhanced the activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria,resulting in higher COD,NH₄⁺-N,and TN removal rates,which were 28.7%,19.1%,and 18.8%,respectively higher than the A-MABR.Besides,PO-MABR enhanced the production of extracellular polymeric substances（EPS）which achieved higher protection for the bacterial cells against low temperatures,in addition to facilitating nutrient and gas exchange within the biofilm.Furthermore,the PO-MABR system exhibited a shorter startup time（22 days at 35℃）,40%faster than the A-MABR system,in addition to a longer steady state period.Chapter 4,a combination of the advantages of both pure oxygen and nano zeolite has been applied in a nano zeolite-amended pure oxygen-based MABR system（Z-PO-MABR）.A bench-scale experimental setup of the novel system was fabricated and first investigated under different critical operation conditions to be optimized,then it was tested in a long-term operation at the optimal conditions in terms of carbon and nitrogen removals.Optimization of key parameters resulted in high removal rates of COD（98%）and TN（96.9%）from high-strength wastewater（COD=2027 mg/l and NH₄⁺-N=208 mg/L）at 72 g/Lr of nano zeolite and 9 hours of HRT.The system showed promising potential for efficient treatment of high-strength wastewater,with higher removal rates compared to conventional MABR and PO-MABR systems in continuous and batch flow modes.The Z-PO-MABR system offers a sustainable and cost-effective solution for enhanced wastewater treatment.Chapter 5,a combined pure oxygen-hydrogen-based MABR system（PO-H-MABR）was investigated under various operational conditions and the energy consumption is assessed.A solar power-based water electrolysis cell was used to generate the required pure oxygen and hydrogen for the bench-scale experimental setup of the PO-H-MABR system.The system provided a significant removal of TN from the low C/N ratio（C/N=8）wastewater,due to a highly efficient denitrification in the H-MABR stage.The obtained results revealed that up to 98.75%of TN and 89%of COD were removed at the optimal conditions of 0.04 MPa O₂ and H₂ gas pressures,3 hours of HRT through each phase,and 0.1 L/h of influent flow rate.While the energy consumption was estimated at 6 KWh/m³ of wastewater.The simultaneous nitrification-denitrification processes were proved to occur in the system.Furthermore,a higher hydrogen pressure of 0.09 MPa,comparing with 0.04 MPa,could be applied to allow the system consume all the produced hydrogen gas from the water electrolysis cell（without H₂ gas losses）with the same energy consumption,leading to a higher TN removal rate of 99.2%.Therefore,the current study highly nominates the pure oxygen-based MABR,whereby the pure oxygen could be a by-product of clean hydrogen energy production via water electrolysis,to be a promising wastewater treatment system for efficient COD and nitrogen removal,which shows excellent performance even under low temperature probably due to the thicker biofilm generated under pure oxygen condition.The incorporation with zeolite powder leads to highly efficient TN nitrogen removal of high strength wastewater.For the low C/N wastewater,a high TN removal was also achieved by PO-H-MABR system.