Study Of The Complete Autotrophic Nitrite-nitrification And Electrochemical Bio-denitrification Combined Process And Its Microbial Community Structure

The influence of influent pH, NH4+-N, free ammonia (FA) and other parameters on the low carbon to nitrogen ratio ammonia wastewater treatment efficiency of combined processs, which was the complete autotrophic nitrite-nitrification and electrochemical bio-denitrification combined process(CANNED), was studied in this research. The bacterial morphology and community of the nitrite-nitrification part and electrochemical bio-denitrification part of CANNED, which was operated at different influent concentrations of free ammonia (FA), was also analyzed by the Scanning electron microscope(SEM) and fluorescence in situ hybridization (FISH).. The research conclusions was as follows.1.The study results of the CANNED was as follow:(1)The low DO(0.2-0.6mg/L)and the rapidly increasing of the influent ammonia concentration could accelerate the start-up of the nitrite-nitrification, and could also acclimate the sludge of the MBR reactor.(2)The operating conditions of the electrochemical bio-denitrification part was as follow, the current was not more than 2.5A, the current density was not higher than 0.11mA/cm2, and the concentration of influent ammonia was not higher than 300mg/L.(3)When the DO concentration was in low dissolved conditions, i.e.0.2-0.6mg/L, the pH and the concentration of FA would effect the nitrite-nitrification in MBR significantly. The nitrite-nitrification could not occur when the concentration of FA was lower than 2mg/L,but it could take place quickly when the concentration of FA was2-5 mg/L.(4)The optimum operation conditions of the CANNED equipment was as follow, the DO was 0.2-0.6mg/L, the pH was of 8.2 to 8.4, the suitable temperature was 17～30℃,the influent concentration of the ammonia nitrogen was not higher than 600mg/L, ammonia nitrogen load was no more than 0.73kg/(m3-d), and the HRT was not less than 20h. Under the above mentioned optimum operation conditions, the CANNED equipment could operate steadily, i.e., the removal of the influent ammonia nitrogen of MBR, and the nitrite production rate was about 50%, the total nitrogen removal efficiency was above 80%; and the effluent concentration of sulfate was not more then 800mg/L.It was feasible to reduce the concentration of sulfate by increasing the HRT appropriately or the current.(5)When the concentration of the influent ammonia nitrogen was not more than 600mg/L, the effluent concentration of the ammonia nitrogen and pH would meet the different reuse purpose standard which was demanded by the《water reuse standards》(CJ25.1-89).2.The Microbiology and Molecular Biology way was used to analyze the bacterial morphology and community of CANNED, the research results was showed as that:(1)The dominant species was thiobacillus denitrificans in nitrite-nitrification MBR when the concentration of FA was 0.5mg/L. The AOB and NOB number was account for 0.92% and 2.8%. The dominate species was nitrite bacteria in MBR when the concentration of FA was 12.4-48.6mg/L. The AOB and NOB number was account for 33.6%-47.4% and 1.0%-2.95% of the total bacterial number. This above mentioned phenomenon indicated that the growth of the AOB would be accelerated and was benefit of the nitrosification with the concentration of FA increase.(2)When the concentration of FA was about 0.5-12.4mg/L, the number of thiobacillus denitrificans, anammox bacteria and eubacteria was account for 7.2%-15.3%, 7.2%-10.3% and 9.1%-14.3% of the total bacteria numberrespectively, only a small amount of short bacilli, cocci and filamentous bacteria were shown on the electron microscope photographs.When the concentration of FA was increased to 48.6mg/L, the above three kinds of bacteria were 34.5%,44.2% and 60.8% of total bacteria respectively, which was in accordance with the SEM results indicating that the growth of the bacteria would be accelerated with the FA increase.