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Research On High-efficient Partial Nitrification And Anammox Enrichment

Posted on:2011-02-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:A H HuFull Text:PDF
GTID:1101330332975941Subject:Environmental Engineering
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The nitrogenous pollutants discharged into water body are increasing along with the rapid development of agriculture and industry as well as improvement of human's living standard, which brought seriously deleterious effects on human health and ecological safety. For nitrogen pollution control, it is necessary to develop efficient and economical processes for nitrogen removal from wastewater. Partial nitrification-anammox process is one of the novel biological processes for nitrogen removal and has become one of the research hotspots in the field due to its advantages of high volumetric loading rate, samll energy consumption, low operation cost. Both aerobic and anaerobic ammonia oxidizers are chemolithoautotrophic microorganisms, they are sensitive to environmental conditions, which limits the wide use of this novel process in full-scale. The microorganisms are the core of biotechnology for nitrogen removal from wastewater. So some important influence factors on partial nitrification and anammox enrichment were investigated to lay a theoretical foundation for the break-through of this process. Major research results are as follows:(1) The effect of anoxic stress on short-cut nitrification sludge and its mechanism:①Anoxic stress could decrease nitrification activity of nitrifying activated sludge. The longer the duration of anoxic stress, the lower the nitrification activity. The inhibition of ammonia oxidation activity was more serious than that of nitrite oxidation activity. After anoxic stress for 12h and 24h, the average specific ammonia oxidation rate decreased from 0.894 mgN(?)(g MLSS)-1(?)h-1 to 0.453 mgN(?)(g MLSS)-1(?)h-1 and 0.387 mgN(?)(g MLSS)-1(?)h-1, respectively; meanwhile, average specific nitrite oxidation rate decreased from 0.761 mgN(?)(g MLSS)-1(?)h-1 to 0.485 mgN(?)(g MLSS)-1(?)h-1,0.459 mgN(?)(g MLSS)-1(?)h-1, respectively.②Anoxic stress could reduce the anti-oxidative enzyme activity. The longer the nitrifying activated sludge exposed to anoxic environment, the lower the anti-oxidative enzyme activity. After anoxic stress for 12h and 24h, Catalase (CAT) activities decreased from 100% to 83% and 79%, respectively; Peroxidase (POD) activities decreased from 100% to 90% and 76%, respectively.③Anoxic stress could weaken the toxicity resistance to reactive oxygen, resulting in the decrease of nitrification rate. After anoxic stress for 12h and 24h, the specific ammonia oxidation activities treated with H2O2 were 0.257 mgN(?)(g MLSS)-1(?)h-1,0.227 mgN(?)(g MLSS)-1(?)h-1 and 0.136 mgN(?)(g MLSS)-1(?)h-1.(2) The long-term effect of organic matter on short-cut nitrification sludges:①The long-term presence of organic matter in ammonia-contaning wastewater resulted in decrease of spefic ammonia oxidation rate and increase of affinity for ammonia.②The long-term presence of organic matter in ammonia-contaning wastewater resulted in decrease or even disappearance of nitrite oxidation rate. The nitrite oxidation rate of inoculated nitrifying sludge (S1), autotrophic nitrifying sludge (S2) and mixotrophic nitrifying sludge (S3) was in the following order:S2>S1>S3. Both S1 and S2 had high nitrite affinity and could oxidize nitrite to under detectable limit. However, the tolerance to nitrite of S1 was not as good as that of S2. When nitrite-N concentration was 200 mg(?)L-1, the nitrite oxidation activity of S1 was inhibited, while that of S2 was not inhibited.③The long-term presence of organic matter in ammonia-contaning wastewater resulted in a weak tolerance to nitrite. The inhibition of nitrite to ammonia oxidation was 37.5% and 82.6% when 200 mgN(?)L-1 and 800 mgN(?)L-1 nitrite were added, respectively. The inhibitory effect of nitrite was not obsereved for S2 even if nitrite of 800 mgN(?)L-1 was used.③The long-term presence of organic matter in ammonia-contaning wastewater resulted in a stable and efficient nitrite accumulation of 92.17%±2.67% which was higher than that of S2 (63.58%±4.19%).⑤The long-term presence of organic matter in ammonia-contaning wastewater resulted in different predominant ammonia-oxidizing bacteria. There were two kinds of predominant ammonia-oxidizing bacteria in S1 that had been identified as Nitrosomonas, but there was only one in S2 or S3.(3) The effect of organic matter on the activity and gowth of anammox enrichment:①Adding organic matters at low concentration promoted ammonia and nitrite conversion rate. The ammonia and nitrite conversion rate were enhanced by 33.2%-98.8% and 17.6%-56.8%, respectivey, when organic matters were added. The stimulation of anammox activities by citrate and succinate was the most obvious, increasing ammonia conversion rate by 98.8% and 60.5%, and nitrite conversion rate by 55.0% and 40.6%, respectively.②Addtion of succinate, citrate or glucose could optimize the performance of anammox bioreactor and shorten doubling time of anammox bacteria. The maximum substrate concentrations and volumeric TN removal rates were higher than those in control bioreactor. With addition of succinate, citrate or glucose, the doubling times of anammox bacteria were 25.67d,27.39d and 32.23d, respectively, which were all shorter than that in control reactor.③The microbial community was changed by the addtion of succinate, citrate or glucose. Some anammox bacteria similar to Planctomycetes sp. were enriched. (4) The effect of hydroxylamine on the activity and gowth of anammox enrichment:①Anammox enrichment was shown able to convert hydroxylamine to hydrazine, as well as hydrazine to ammonia, with the average conversion rates of 0.207 and 0.031 mmol(?)gVSS-1(?)h-1.②It could convert hydroxylamine and nitrite simultaneously, with ammonia as an intermediate product. The maximum conversion rates of hydroxylamine and nitrite were 0.535 and 0.145 mmol(?)gVSS-1(?)h-1, respectively. Their conversion rates were enhanced by 26.7% and 120.7%, respectively, by raising the ratio of hydroxylamine to nitrite from 1:1 to 2:1. The characteristics of nitrogenous substrate conversion by anammox enrichment could be explained using the speculative anammox pathway based on van de Graaf model.③The volumetric TN removal rate went up to 14.224 kgN(?)m-3(?)d-1, with increment of 90% in two months, when fed with ammonia and nitrite as the normal substrates. The output of biomass ascended with substrate concentration increment. When ammonia concentration in influent was 23 mmol(?)L-1, the average sludge growth in one day was 595 mgVSS(?)L-1.④Hydroxylamine was toxic chronically to anammox bacteria. After 6d-supply of hydroxylamine, ammonia and nitrite conversion activity decreased; and after 11 d-supply of hydroxylamine, hydroxylamine conversion activity decreased either. The anammox activity could not be recovered by reducing ammonia and nitrite at low concentration. Continuous supply of hydroxylamine led to dark red granular sludge, EPS decrease and cell hydrolysis.⑤In initial phase, intermittent supply of hydroxylamine could enhance growth.of anammox bacteria by 5.6 to 1.2-fold. Sludge growth gradually decreased as addition of hydroxylamine increased. Intermittent supply of hydroxylamine resulted in a noticeable increase of putative iron particles in anammoxosome.
Keywords/Search Tags:biological nitrogen removal, short-cut nitrification, anaerobic ammonia oxidation (Anammox), enrichment, anoxic stress, organic matter, hydroxylamine
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