Study On The Process Of Simultaneous Nitrification And Denitrification In A Semi-suspended Bio-carrier Biofilm Reactor

At present,the domestic wastewater treatment plants mainly use suspended and fixed type carriers,in order to make up for their shortcomings,this study developed a new type of carrier,semi-suspended bio-carrier,combined with the advantages of suspended and fixed type carrier.A reactor suitable for the carrier was designed,and then a dissolved oxygen(DO)microelectrode dynamic measure chamber was designed to realize the solution matrix outside the biofilm same to the solution in the reactor.Experiment investigations processing capacity of synthetic domestic wastewater in different C/N in the reactor.The mechanism of simultaneous nitrification and denitrification(SND)under different C/N conditions was also investigated in terms of biofilm mass transport,biofilm characteristics and molecular biology.The experiment also attempts to find the best C/N for semi-Suspended bio-carrierbioreactor.The start-up of the reactor is divided into two parts.The first part is the unstable stage of biofilm which does not open the bottom aeration.The time is 3 days.The second part is that the biofilm can adhere stably to the biofilm and open the aeration device at the bottom of the carrier so that the bio-carrier presents a semi suspension state and operates for 11 days.On the last day of the reactor,the water quality of the bio-carrier and dissolved oxygen in the biofilm were analyzed by time period,and the biofilm on the bio-carrier was used to analyze the biofilm characteristics and molecular biology.The main results are as follows:The water treatment capacity of semi-suspended bio-carrier reactor is: when C/N=20,ammonia nitrogen removal rate is 100%,total nitrogen removal rate is about 99%,COD removal rate is 100%,COD consumption rate is 49.26 mg/h,TN consumption rate is2.4mg/h.In the research process of SND: the higher C/N the more can improve the transfer rate of ammonia and COD in biofilm,the ammonia consumption time was higher than the COD time consumption is the main reason can not achieve complete SND.When in the Low C/N,because of the thin biofilm lacking anoxic layer,the denitrification is restricted,and when COD is not consumed the denitrification is stop in the biofilm;in the meantime in the low C/N TB-EPS is the lowest,which makes the removal rate of TN suddenly dropped andSND efficiency declined in the biofilm when the reactor open the bottom aeration.The higher C/N,the higher the pore density of the biofilm,the higher the mass transfer resistance,and the longer the time is for aerobic,anoxic and anaerobic layers of the biofilm.At the higher C/N,due to the high concentration of COD,the proportion of nitrifying bacteria in the biofilm decreased,so that the consumption time of ammonia nitrogen increased,so that simultaneous nitrification and denitrification could not be carried out completely.In summary,mass transfer and microbial factors have a combined effect on SND efficiency.Biofilm biomass,biofilm structure,thickness,and EPS play an important role in the SND process.The use of semi-suspended bio-carrier significantly improved the biological diversity in the biofilm reactor,which could achieve removal of total nitrogen under a C/N ratio of 20 h after8 h.From the three aspects of biofilm characteristics,mass transfer and molecular biology,it can provide a reliable scientific basis for the popularization and stable use of novel carrier.