| Compared with activated sludge flocs,aerobic granular sludge has better settling ability and a higher substrate removal effiency.Under the exposure of water load,toxic substances and heavy metal,its tolerance ability is stronger,it is widely used at present.Existing research shows that COD loading has influence on the behavior of aerobic granular sludge:higher COD loading will lead to the growth of filamentous bacteria and will disintergrate the sludge particles,lower COD loading is not favorable to the growth of granular sludge.But the mechanism of COD loading influences aerobic granular sludge is unclear. Studies have shown that sewage treatment process of nitrification and denitrification is an important source of nitrous oxide.The global warming potential of nitrous oxide is310times of carbon dioxide,the doubling volume of nitrous oxide in the atmosphere will make the average global temperature to rise0.4℃.So it is very necessary to study the mechanism of release of nitrous oxide.This paper focused on the sequencing batch airlift aerobic granular sludge reactor,studied the effect of different COD loadings on the behavior of aerobic granular sludge and removal effiency of simulated domestic sewage as well as the release regularity of nitrous oxide.Our study’s innovation point was to study the mechanism of nitrification and denitrification process of aerobic granular sludge under the exposure of different COD loadings,combined with the molecular biology technology.It provided theoretical basis for the reduction of release of nitrous oxide.The main research contents and results were as follows:(1)In the process of cultivating aerobic granular sludge,ammonia nitrogen removal rate and COD removal rate of domestic sewage were detected.At15days of cultivation,ammonia nitrogen removal rate was79.32%,the COD removal rate was91.3%; At60days of cultivation,ammonia nitrogen removal rate was99.4%,the COD removal rate was94.2%.Results showed that as the formation of aerobic granular sludge and cultivation,ammonia nitrogen removal rate and the COD removal rate increased.(2)Removal rate of domestic sewage and nitrous oxide emission were determinated,and the effect of COD loading on removal rate and the release of nitrous oxide from the treatment of domestic sewage was studied. Results showed that ammonia nitrogen removal rate and COD removal rate of aerobic granular sludge under the exposure of different COD loadings were similar,they were above90%. The nitrous oxide release of800mg/L was biggest which was0.44pμg·gMLSS-1,the nitrous oxide release of500mg/L was least which was0.225μg·gMLSS-1.(3)To observe the appearance of aerobic granular sludge under the exposure of different COD loadings,scanning electron microscopy was made.Scanning electron microscopy images showed that aerobic granular sludge of300and500mg/L were in different sizes,but they were very tight,their surfaces were consisted of staphylococcus aureus and bacillus.But the aerobic granular sludge of800mg/L wasn’t smooth,its main flora was consisted of a large number of filamentous fungi and its structure was loose.To study the mechanism of COD loading influenced sludge granulation,the experiments studied extracellular polymers(EPS) compostion of aerobic granular sludge under the exposure of different COD loadings.The ratio of protein to polysaccharide was largest when COD loading was500mg/L.EPS and humic acid concentration of800mg/L were biggest,they were respectively14.972mg/gMLSS and2.66mg/gMLSS.(4)The effect of COD loadings on related mechanism of microbiology was studied,using PCR-denaturing gradient gel electrophoresis(DGGE) and real-time PCR technique.The nitrite reductase functional genes of800mg/L were the most which were5.65X105copies/mL.The nitrite reductase functional genes of500mg/L were the most which were1.11×106copies/mL... |
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