Granulation Process And Characteristics Of Nitrogen And Phosphorus Removal In Aerobic Granular Sludge Reactors

Aerobic granular sludge has good settling capability with low SVI, it has a good performance of muddy water separation, high sludge concentration and metabolic activity, as the result, it can remove COD, nitrogen and phosphorus effectively. Therefore cultivation of aerobic granular sludge has good prospect for further application, and in recent years, it is becoming a hot research topic in aera of wastewater treatment. In this study, the control of alternation loading was used as the key strategy to cultivate aerobic granular sludge in sequencing batch reactor (SBR). The properties of aerobic granular sludge and the efficiency of nitrogen and phosphorus removal were analyzed, and optimizated the conditions of EPS extraction. Also, Fluorescence in Situ Hybridization (FISH—a molecular mocrobiology method—was used to investigate distribution characterstics of functional microorganisms relating to nitrogen and phosphorus removal and the relationship between functional mocroorganisms and efficiencies of nitrogen and phosphorus removal. The main experimental results were summarized as follows:By using laboratory simulation wastewater, adding the mixed carbon sources, decreasing of dissolved oxygen, and three stage improved method, during 120 days continuous operation, aerobic granular sludge was successfully cultivated in SBR, whose particle size is approximately 1.0mm. The mature aerobic granular sludge had a color of golden yellow, and the shape of aerobic granular sludge was sphere or spheroidicity with sharp edge and dense structure. The SVI30 of aerobic granular sludge was about 23 mL/g, the sludge concentration was about 12.0g/L and ZETA potential at about-12mV. In the aerobic granular sludge stabilization stage, after 60 days of culture, the particle size increased to 1.52.5mm, also the morphology and the structure remains stable.The experiment use three stage—the initial operation stage,the operation load regulation stage and the stable stage—control mode successful cultivated aerobic granular sludge. The initial operation stage:the removal efficiency of COD, ammonia nitrogen, total phosphorus were 60%,80%, and 40%; the operation load regulation stage:feeding COD load alternating changed among 400mg/L,700mg/L,1000mg/L,in order to formating strong selection pressure and promoting the formation of aerobic granular sludge;the stable stage:in SBR reactor for nitrogen and phosphorus removal effect is improved obviously, the removal rate of COD, ammonia nitrogen and total phosphorus kept above 94%,95%and90%, respectively.The experiment based on EPS extraction method was optimized, and determing the optimum extraction conditions and methods for protein and polysaccharide. Analysis results show that:the heating extraction for the final extraction method in this experiment, the optimum temperature is 80℃, extraction time is 40 min.Fluorescence in situ hybridization (FISH) was used in this study to analyze functional bacteria relating to the removal of nitrogen and phosphorus. Results had been got as follows: the density of bacteria in aerobic granular sludge was very high, and the distribution was uniform. During the cultivation of aerobic granular sludge, the diameter of particles was growing bigger and bigger. When it reached to a certain extent, fluorescent signal of aerobic granular sludge’s inner space becomed weakened, and the amount of bacteria had reduced at the same time when the anaerobic zone and anoxic zone had formed. This inhibited the growth of bacteria. Sometimes the limitation of mass transfer also could cause the reduction of bacteria number when the diameter of particles grew to a certain extent.Aerobic granular sludge’s ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) existed in external surface and mesectoderm. And this extented the practical retention time of NOB in the reactor, and NOB—the bacteria with lower growth rate—enriched in SBR. And also due to nitrite, which was produced by AOB and was demanded for the growth of NOB, NOB grew in the mesectoderm and external surface adhering to AOB.