Effects Of Feeding Pattern And Nutrients On The Microbial Community Structure, Morphology And Growth Characteristics Of The Anaerobic Sludge

Anaerobic biological treatment is the most widely used technology in treating high concentrated organic wastewater and municipal wastewater because of its energy efficiency, resource recovery(methane), less excess sludge production and loading shock resistence. Sludge granulation is the key factor for the successful operation of an anaerobic system. Understanding the anaerobic sludge granulation, the microbial community and growth characteristics are very important for the performance improvement of anaerobic treatment systems. However, most of the relevant researches focused on the Upflow Anaerobic Sludge Blanket(UASB) reactors. Compared to UASB reactors, Anaerobic Sequencing Batch Reactor(ASBR) and Continuous Stirred Tank Reactor(CSTR) are of process simplicity, operation flexibility and treatment stability, especially suitable for dealing with the organic wastewater with high content of suspended solid. Therefore, in-depth invstigation of the sludge granulation, microbial community structure, morphology and growth chracteristics in two typical reactors are of significant meaning for the reactor design, operation and management.The research focuses mainly on the effects of feeding pattern and nutruents on the microbial community structure, morphology and growth chracteristics of anaerobic sludge formed in ASBR and CSTR reactors. Firstly, Hydrogen Utilization Rate(HUR) for regulating and evaluating of the the anaerobic biological treatment systems was investigated. Secondly, diagnosis of the acidification and recovery of ASBR reactors were carried out. Then, effects of feeding patterns on determining the sludge granulation, morphology and the microbial community by use of Fluorescence in situ Hybridization(FISH) methods was implimented; representation of the microbial growth based on ammonia nitrogen utilization; establishment of the dynamic model between sludge growth and the substrate utilization by determing the sludge yield coefficient and the decay rate; the effects of nutrients on the microbial storage performance of the CSTR and UASB reactors. The main results and conclusion are made as follows:1. HUR was highly influenced by sludge concentrations because of the limitation on H2 gas transfer, and the critical value of sludge concentration should not be higher than 1 g-VSS/L for the determination of the maximum HUR. Field survey of five different anaerobic reactors showed that HUR can be used as a key indicator for evaluating and monitoring of the anaerobic reactor performance. A relatively high HUR would guarantee a low hydrogen partial pressure, which could result in higher degradation rates of propionate and butyrate, and thus improve the reactor performance.2. In ASBR reactor, acidification occurred after BES addition, which resulted in the effluent COD and VFAs increased and the biogas production, methane content and p H value decreased, all of which can be used to estimate the acidification of the reactor. A three-step strategy, sludge elutriation, p H regulation and increasing the substrate concentration gradually, was applied to recover the reactor. The results showed that the acidified reactor could be restored in 50 days.3. Stirring mode and intensity played a key role in the anaerobic sludge granulation. The axial-flow stirring could produce a milder shear force and an excellent liquid circulation, which provide a well hydraulic condition for the sludge granulation. After approximately 45 and 60 days cultivation, the sludge in ASBR and CSTR reactors were almost granulation, respectively. With the sludge granulation, hydrogen partial pressure in two reactors decreased significantly and the specific methanogenic activities of sludge increased gradually. Microbial Structure observation showed that EPS and filamentous bacteria play an important role in the sludge granulation. Filamentous bacteria waved each other to wrap other bacteria together and made the granules compact. There existe two forms of EPS in the granules, “needle-shaped” and “sheath-shaped”. The former was fund merely in ASBR reactor, and the latter in both reactors.The microbial community structure of the granules formed in two reactors was fund to be completely different. A layered structure, in which acidogenesis bacteria distributed in the outer layer and methanogens in the centre, was observed for the anaerobic granules in CSTR. The dominate aceticlastic methanogens were filamentous. Whereas, a clustered structure, anaerobic granules had under the intermittent flow condition, in which the syntrophic consortia of acidogens and methanogens were evenly throughout the interior of the granule, was observed for the anaerobic granules in ASBR. The clustered structure would keep maintaining the hydrogen partial pressure in a low level. Aceticlastic methanogens exsited mainly in morphology of monomer cocci under this condition.4. The effects of NH4+-N on the microbial growth in ASBR were greater than that in CSTR. For the same reactor, the specific growth rate of the acidogens was greater than that of the methanogens. Based on the sludge yield coefficient and decay rate, a dynamic model between sludge growth and substrate utilization was established.The content and molecular weight(MW) distribution of the intracellular protein were different under the two different feeding patterns. The protein content in ASBR sludge was 482 mg/g VSS and that in CSTR reactor 650 mg/g VSS. Compared with CSTR reactor, a broader spectrum of molecular weight of intracellular protein in ASBR was observed, which resulted in the slower sludge decay rate and higher sludge production rate.5. The anaerobic microbial storage was proved to be a universal phenomenon in continuous reactors, such as CSTR and UASB, by the batch tests. The storage could be traggied as nutrients were limited. The glycogen storage was the largest with nitrogen deficiency and smallest with nitrogen and phosphorus simultaneous deficiency. The microbial glycogen storage under any nutrients deficiency condition was greater than that in the nutrient balance condition. The microorganisms were able to maintain its cellular structure and metabolic activity by storing glycogen excessively under nutrient deficiency condition.