Study On The Performance Mechanism Of EGSB Reactor At Different Temperatures

Expended granular sludge blanket (EGSB) reactor is one kind of the new high effect anaerobic bio-reactor which developed in the last 10 years. EGSB reactor possesses the technologic advantages of lower operating costs and higher treatment efficiency, and so on, and has been characterized to be one of the most promising biological technologies to remove organic pollutants from wastewater.Similar to other anaerobic bio-reactors, the performance of the EGSB reactor is highly dependent upon operational temperature and it has been evidenced that controlling suitable temperature, maintaining sufficient biomass and fully mixing between the anaerobic granular sludge and wastewater in the reactor are of great importance to ensure that the treating system runs at a high efficiency stably. It hasn't been seen the numerical modeling of operating characteristics and biochemical reaction dynamics of EGSB reactor In this paper, the incorporate EGSB reactor had been designed that set height/diameter as 19:1, and intensively investigated the performance mechanism and the microorganism characteristics of the biofilm on the wall of EGSB reactor by regulating the three operating situations at high temperature (55℃), medium temperature (35℃) and low temperature (15℃), in addition, modeled and analyzed the gray system modeling-GM model of the biochemical reaction process.The results demonstrated that in medium temperature situations, changing three-stage operational mode (i. e. high influent flux and low influent concentration, low influent flux and low ascend velocity of flow, high influent flux and high ascend velocity of flow) could rapidly startup the EGSB system during a lag time as short as 46d, achieving a good characteristics of granule sludge. EGSB reactor could increase the organic load quickly after succeeded the startup process, and the ability to restrict shock loading is strong. Moreover, EGSB reactor was capable of stable eliminating COD from domestic wastewater with a removal rate of 85% above on average at a high organic load of 42 kg/(m3·d). In the same situations, the results of second startup of the EGSB reactor with granular sludge leakage show, the time needed for incubation was observed as long as 61d, likely due to lack of initial incubated sludge (3.5g/L) that limits the effectiveness of three-stage operation as mentioned above. Therefore, the high influent concentration of source granule sludge is necessary for rapid startup.When the temperature was increased to the high temperature situations, the EGSB reactor that was stably operated after startup for 22d showed a stable COD removal rate of 85% above. Though the COD load decreased to 36.57 kg/(m3·d), the characteristics of hydraulic retention time (HRT) of 3.3 h and short operation time showed, the treatment efficiency was satisfying at high temperature. In low temperature situations, the EGSB reactor performed well to decompose COD with mean removal rate of 85% at HRT of 3.3 h and volumetric loading rate of 17.5 kg/(m3·d). At the same time, at medium, high and low temperatures, the EGSB reactor holds the well capability of resisting pH impulsion and degradation VFA when influent pH is 5.4~7.3.For the first time, this paper researched the microorganism characteristics of the biofilm on the wall of EGSB reactor. When the biofilm thickness was at the level of 5mm, it has the assistant effect on the forming of granular sludge and removal rate of COD, and effectively enlarge the capability of impulsion load. In medium temperature situations, the removal rate of COD increased at 10%~26.58%, in high temperature situations, the removal rate of COD increased at 27.78%~30.54%, and in low temperature situations, the biofilm on the wall has a minimum contribute to the removal of COD in EGSB reactor, at a level of 5%~10%. In this view, the effect of biofilm on the wall in reactor is a significant factor.According to the study of Monod equation, the dynamics model of organic materials removal rate has been setup. It's found that the maximum degradation velocity has relation with a special bacterium and temperature;νmax increases with the increasing of temperature, the amount of sludge and background concentration have little effect on it. The metabolize ability of granular sludge in the cultivating phase is weaker than the mature phase. On the base of operation data in medium, high and low temperature situations, for the first time, the grey theory is adopted with the aim function that is known solving method to solveθ and 1/Y0 in medium, high and low temperature situations and obtain the dynamic variety equation of contamination concentration and the increasing relation of microbes.The results of paper research are very significant on the theory and practice to guide the cultivation of granule sludge in EGSB reactor and the application of EGSB reactor in projects.