Research On Microbial Community Constructure In Activated Sludge With The Variation Of PH

pH is an important environmental factor, directly affects the growth metabolism,species and surface characteristics of activated sludge microorganisms. The purpose of the study lay in exploring the sludge mixed liquor characteristics, removal efficiency of COD, NH4+-N, TN and the law of activated sludge microbial community structure by running the SBR to control the pH 5.0-10.0 respectively.The study showed that the supernatant was cloudy and sludge bulking phenomenon was obvious in low pH system, but sludge mixture character was good,the SVI value kept at 67-85 mL/g and supernatant fluid was clear, when the system pH was 7.0-10.0. The higher pH system had better COD removal rate, but the difference wasn't obvious and the removal rate of COD was always above 85%.System denitrification effect was strongly influenced by pH. With the increase of pH,the removal rate of ammonia nitrogen trended to rise obviously. The ammonia nitrogen removal rate was only 30% to 40% at pH of 5.0, but when the pH was 8.0,ammonia nitrogen removal rate could achieve above 80%. When the pH raised further,ammonia nitrogen removal rate would further increase. The total nitrogen removal rate was different from the removal of ammonia nitrogen slightly, with the increase of pH, total nitrogen removal rate first increased and then decreased. The best removal rate was 74% at the pH of 8.0 and the removal rate was only 10%-20% at the low pH condition. The total nitrogen removal was disappointing because denitrification was inhibited by inappropriate pH environment and a amount of residual ammonia nitrogen owing to the low removal rate at the low pH. The decrease of total nitrogen removal rate at the high pH conditions was caused mainly by the inappropriate pH environment inhibiting the function of denitrifying bacteria.Microbial community structure showed some differences along with the change of pH. The diversity of total bacteria was rich, and under the condition of higher or lower pH, the activated sludge had more specific microorganisms, but lower number of each microorganism. The stripe number of denitrifier especially ammonia oxidizing bacteria and denitrifying bacteria was relatively single and the abundance was strikingly low. By calculation, diversity index of the total bacteria and various kinds of denitrifier generally trended to first increase and then decrease. The similarityindex between any two sluge samples was generally low both the total bacteria and denitrifier, it showed that the total bacteria and denitrifier were sensitive to the change of pH and the dominant bacteria changed frequently. Cluster analysis results showed that the division generally follow change rule of the pH, but the similarity of ethnic groups was on the low side. The results of cloning and sequencing showed that the total bacterium mostly belonged to Uncultured bacterium. Chloroflexi and Rhodocyclaceae were the dominant species during the whole operation process.Rhodanobacter was only found under the neutral and alkaline conditions.Xanthomonas was only found in low pH conditions. In additon, other bacteria had been found including Zoogloea sp., TM7 and Proteobacterium.