Experimental And Mathematical Simulation Study On Simultaneous Nitrogen And Phosphorus Removal Of Aerobic Granular

The problem of eutrophication is serious and in our country.The process of nitrogen and phosphorus removal has always been a research hotspot.There are some problems in simultaneous nitrogen and phosphorus removal in sewage treatment in China,such as insufficient carbon source,high energy consumption of aeration and so on.Several technologies have been proposed to remove nitrogen(N)and phosphorus(P)from wastewater.The majority of these technologies rely on an external source of soluble organic carbon to facilitate P recovery.Simultaneous nitrification,denitrification and phosphorus removal(SNDPR)is an elegant process that can uptake influent carbon and effectively remove both nitrogen(N)and P from wastewater.Therefore,in this study,a synthetic influent that replicated the nutrient and carbon concentrations of municipal wastewater was used to explore the culture conditions of aerobic granular sludge with simultaneous nitrogen and phosphorus removal capacity and the effects of carbon-nitrogen ratio,anaerobic aerobic time distribution,dissolved oxygen and precipitation time on simultaneous nitrification and denitrification phosphorus removal.Based on the results the following can be concluded:(1)In the SBR reactor,the granulation of aerobic granular sludge is related to a series of operation parameters,such as inoculation sludge,matrix composition,organic load,aeration(hydraulic shear force),exchange ratio,reaction cycle and precipitation time.Granular sludge can be cultivated rapidly by increasing COD concentration and aeration rate.By shortening precipitation time,flocculent sludge with poor settling performance can be washed out to maintain the concentration and stability of granular sludge.(2)The sludge index of the granular sludge with good nitrogen and phosphorus removal ability is as low as 17.46,the granular sludge is yellowish and has a certain luster.The surface is smooth and the particles are dense.The particle sizes of more than 75%are distributed between 900 and 1300 ?m.The largest particles have formed round particles visible to the naked eye.A large number of different bacteria are distributed on the surface and inside the particles,including denitrifying phosphorus accumulating bacteria and nitrifying denitrifying bacteria,forming a stable ecosystem.(3)Finally,the COD removal rate of the cultivated aerobic granular sludge is about 95%,the ammonia nitrogen treatment efficiency is between 95%and 100%,almost completely removed and the removal rate of total nitrogen is about 90%,realizing the complete absorption of phosphorus.It indicates that the aerobic granular sludge has an efficient ability of nitrogen and phosphorus removal.(4)The operational cycle included a 40 min anaerobic period with 10 min of feeding(synthetic medium),115 min of aerobic period,5 min settling and 10 min decanting.The total reaction period is 3 hours and the aeration rate is 5 L/min.In this mode,at the end of the anaerobic phase of the reactor cycle,the PO43--P concentration reached 25.62 mg/L,and the removal rate of phosphorus in the effluent reached more than 90%at the end of the reaction.In low-carbon wastewater.The use of COD to create such a high concentrated stream of P did not hinder effective removal of NOx-N.Simultaneous nitrogen and phosphorus removal can be realized,and the energy consumption is low,and the operation cost is reduced.(5)The occurrence of SND is due to the microenvironment of anoxic and aerobic conditions in activated sludge flocs or particles.High concentration of DO will destroy the balance between anoxic microenvironment and aerobic microenvironment.At low DO concentration,nitrite and nitrate were denitrified in granular sludge,and only a small amount of nitrite and nitrate were produced.At the same time,phosphorus accumulating bacteria,phosphorus release and phosphorus uptake were not affected,and there was no large accumulation of nitrate nitrogen in the whole process.(6)PAOs appear to have a higher affinity towards oxygen than nitrifiers,and an early completion of P uptake and a similar rate of nitrification and denitrification appear to be important to achieve good nutrient removal.(7)The optimal conditions of simultaneous nitrification and denitrification for phosphorus removal were analyzed through experiments,and the corresponding mathematical model was established.The experimental data were fitted with the model prediction data by using MATLAB software,and the expected results were obtained.The use of mathematical model simulation is helpful to reduce the consumption of experimental costs,verify the correctness of experimental results,and provide a reliable basis for the design and optimization of granular sludge.