Design And Operation Of A New Marine Membrane Bioreactor And Study On Simulation Optimization

The direct discharge of untreated domestic sewage from ships into the ocean will seriously damage the marine ecology and harm human health.The existing commonly used domestic sewage treatment equipment has several disadvantages,like large volume,low level of automation and failure to meet the stricter discharge standards of domestic sewage from ships.To overcome these problems,a new marine membrane bioreactor（MBR）engineering prototype is designed and manufactured in this study,used it to carry out carbon,nitrogen and phosphorus removal experiments and test its biosafety performance,and supplemented by dynamic model to study the technical mechanism of marine domestic sewage.Firstly,a prototype with a volume of 1.792 m³ and a treatment capacity of 30 people /day is designed and the selection of related auxiliary equipment is completed based on the process of ship sewage treatment.The effluent is disinfected by UV dosing,and the exhaust disinfection equipment is used to disinfect the exhaust of the prototype,so as to enhance the biosafety prevention and control ability of the prototype.Several subsystems,like the liquid level subsystem,disinfection subsystem,temperature subsystem and aeration sludge return subsystem are set,and PLC is used as the control center to control the subsystems.The quick start performance of engineering prototype is studied in this paper.The results showed that the effluent COD and TN concentrations of the prototype were lower than the IMO discharge standard within 3 days,which shows that the prototype has the ability of quick start.Secondly,this paper took the actual domestic sewage as the research object to explore the influence of influent HRT changes on the COD and nitrogen removal efficiency of the engineering prototype,and biosafety prevention and control are also investigated in this study.The results show that optimal operational condition occurred at HRT1=7 h,the average effluent concentrations of COD and TN are 64.73 and 6.97 mg/L,respectively.When HRT1 decreased,the biofilm removal efficiency of TN increased gradually,indicating that the "anoxic micro-sludge effect" enhanced the nitrogen removal efficiency under the impact of hydraulic load.High-throughput analysis showed that the synergistic effect of microbialities in different tanks ensured the stable COD and TN removal efficiency of the prototype under different HRT.In this study,the combination of physical and chemical disinfection method is used for the effluent of the prototype,and an optimal disinfection effect is obtained when ClO₂ solution with concentration of 1.2 mg/L was added to the system.In addition,an exhaust gas disinfection equipment is designed to deal with the excessive concentration of bacterial,and the bacterial concentration in the exhaust gas is reduced from 2201 CFU / m³ to 471 CFU/ m³ after treatment,which is lower than the requirements of GB/T 18883-2020（≤ 1500 CFU/ m³）,it also proves that this method has practical significance for COVID-19 prevention and control in closed cabinFinally,a dynamic model was established to simulate the process of sewage treatment by the prototype.The dynamic simulation results show that the average error of effluent COD,TN,and NH₄⁺-N are 7.19%,6.89%,and 7.82%,respectively,indicating that the model can better conform to reality.Three optimization schemes（increasing the DO,increasing the segmented water inlet,and changing the sludge concentration of the aerobic tank）are proposed to solve the unstable nitrogen removal efficiency of the prototype under the impact of hydraulic load.The results show that the denitrification efficiency of engineering prototype can be effectively improved only when the sludge concentration of aerobic tank is increased to more than 5000 mg/L.In conclusion,the combination of control system and simulation can lay a foundation for the realization of software and hardware cooperative control of the prototype in the future.