Study On The Efficiency Of A~2/O-MBBR Combined Process For Municipal Sewage Treatment

In China’s existing municipal wastewater treatment plants,when the water quantity and water quality of the treated sewage are greatly changed,it is easy to cause the abnormal operation of the process,resulting in the unstable effect of the effluent or not reaching the standard.On the contrary,our country is gradually developing more and more stringent emission standards for pollutants disposed by municipal sewage treatment plants.Under this background,it is urgent to upgrade and reconstruct the existing treatment processes of municipal wastewater treatment plants.This paper aimed at the traditional A~2/O process,and discussed the upgrading and reconstructing of the system without the need for expansion or addition of the volume of the reaction pool,without a large increase in other equipment,convenient operation and easy management and maintenance.The MBBR type A~2/O composite process was formed by adding a new biological carriers with good aerodynamics and fluid mechanics to the A~2/O process.It was used to improve the total amount of microorganism in the biochemical unit and to improve its removal effect on the pollutants of COD,ammonia nitrogen and TN、TP.The research results of physical and chemical properties of biological carriers(including 11 physical and chemical indexes such as specific surface area,specific gravity,accumulation number.)showed that the carriers in this paper was in accordance with the basic requirements of the MBBR reactor for the biological carriers in the surface hydrophilicity,corrosion resistance and service life.The lab-scale experimental results of the MBBR type A~2/O composite process test showed that the optimum carrier filling rate of A type biofilm for the sludge-biofilm symbiotic system was 40%(superior to 20%and 60%).The removal characteristics of pollutants were related to C/N ratio(mass ratio)and DO concentration.In the initial stage of biofilm formation,the change of pH in each unit of MBBR A~2/O composite process was consistent with the biochemical reaction.When the biofilm in the reactor was mature,the COD,ammonia nitrogen,TP,TN of the effluent after the MBBR A~2/O composite process could meet the requirements of the IA standard(GB18918-2002).During the stable operation,the reactor had a certain influence on the operation efficiency of the reactor,and the best sludge recycle ratio was 80%.The results of the sludge characteristics in the reactor showed that the ecological system in the MBBR type A~2/O composite process reactor was complete,the food chain was long,the sludge activity was high,it also had a certain sludge reduction effect,the average sludge yield was only 0.33kgMLSS/kgCOD,which was about half of the traditional A~2/O process.According to the above research conclusins,Aiming at the traditional A~2/O process of Harbin Xinyi sewage treatment plant,A brief analysis is made on the investment cost and comprehensive benefits of the transformation to MBBR type A~2/O composite process.