Effect Of Flow Pattern On The Nitrification Rate And Community Composition Of Nitrifying Bacteria In Activated Sludge

As the functional bacteria, nitrifying bacteria have a decisive influence on the denitrification. During the nitration reaction, the flow state would determine the substrate concentration distribution in the reactor of the space and time. Which would emerge crucial influence on the community structure of nitrifying bacteria and the rate of nitration reaction in the activated sludge, and the nitrification effect of the system.In the study, SBR reactor is used to simulated as plug-glow flow system, while, CSTR reactor as completely hybrid one. During the experimental process, the operating conditions of these two reactors are the same. Temperature is20±1℃COD loading is1.06kg/(m3·d), and N loading is0.15kg/(m3·d). Two reactors have operated continuously100days. Researches about the influence of flow patterns on the reactor performance and nitrifying bacteria community structure in activated sludge, according to the continuous monitoring of the water quality and measuring the nitrifying bacteria in activated sludge. According to the test data and phenomena, the main conclusions are drawn as follows:(1) The flow pattern has a significant impact on the nitrification rate of activated sludge in different reactors. In the plug-flow reactor (SBR), the max ammonia oxidation rate is16.55±2.05mg N/(gVss·h), and the max nitrited oxidation rate is15.33±2.02mg N/(gVss·h). In the completely hybrid reactor (CSTR), the max ammonia oxidation rate is10.13±0.73mg N/(gVss·h), and the max nitrited rate is9.34±2.56mg N/(gVss·h).(2) The flow pattern has a significant impact on community structure of nitrifying bacteria. The content of Ammonia oxidizing bacteria is4.3%(±0.8%) in the plug-flow system, while the dominant ammonia oxidizing bacteria is Nitrosomonas europaea/Nitrosococcus mobilies lineage. The content of Nitrite-oxidizing bacteria is5.4%(±1.2%) in plug-flow activated sludge, whose dominant nitrite-oxidizing bacteria is Nitrobacter. And the content of Ammonia oxidizing bacteria is4.1%(±0.9%) in completely hybrid system, in which the dominant ammonia oxidizing bacteria belongs to Nitrosospira spp.. The Nitrite-oxidizing bacteria content is6.8%(±1.1%) in the completely hybrid system, and the dominant nitrite-oxidizing bacteria is Nitrospira spp..(3) The flow pattern impacts the distribution characteristics of substrate concentration in the reactor, leading to the nitrifying bacteria dynamic parameters quite different. The ammonia-oxidizing bacteria matrix half-saturation constant is3.01±0.97mgNH4+-N/L, and the nitrite matrix half-saturation constant is4.22±0.18mg NO2--N/L in plug-flow system, while the ammonia-oxidizing bacteria matrix half-saturation constant is0.43±0.19mg NH4+-N/L, and the nitrite matrix half-saturation constant is2.15±0.64mg NO2--N/L in the plug-flow system completely hybrid system.(4) It is more suitable for r-strategists(nitrosospira, nitrospira) to grow in a plug-flow system, whose Ks value is great and less appetency to the substrate. While K-strategists(nitrosospira, nitrospira) prefer to living in completely system, whose Ks value is more little and more appetency to the substrate.