Study On Performance Of Partial Nitrification Granular Sludge In CSTR And Its Controlling Influence

Granular sludge can not only improve the settling performance,but also enrich nitrifying bacteria with low growth rate.Compared to the flocculent sludge,granular sludge with compacted biological structure and high density bacteria can cope with the fluctuation of external environment obviously."Nitrosation technology" is referred to as NH₄⁺-N is oxidized to NO₂^--N,and the NO2--N is directly reduced to N₂ as NH₄⁺-N electronic donor.However,it is difficult for the current nitrosation process?e.g.,short-cut nitrification and denitrification,short-cut nitrification and anaerobic ammonium oxidation?to sustain long-term stable operation,thus the stability of the nitrosation has become the key restricted link in the whole process of denitrification.At present,most of the granular sludge are mainly cultured and maintained in the sequencing batch reactor?SBR?which has high ratio of height to diameter.But there are a lot of restricts in the practical engineering application,and continuous flow process is prior to be chosen by environmental engineers.Granular sludge was inoculated to the continuous flow reactor and the performance of nitrosation was rapidly improved.It is valuable for the technology to be applied in practical engineerings.This thesis systematically studied the CSTR process of granular sludge and the key influence factors?nitrogen volume load and C/N ratio?on the nitrification of granular sludge.And the control strategy to improve the stability of nitrosation granular sludge with long-term operation was also evaluated.The main research contents and results of this paper include the following three aspects:?1?In order to investigate the effect of different reactor types on the short-cut nitrification granular sludge,we inoculated mature heterotrophic aerobic granular sludge in CSTR.Results indicated that granular sludge in continuous flow reactors gradually was disintegrated into tiny flocs and the settling performance of sludge was deteriorated significantly during the initial period of operation.However,fine sludge particles were formed after 53 days.The particles that less than 0.3mm diameter were increased rapidly and become the predominant sludge,while the particle that larger than 0.8mm of diameter were decreased gradually.Finally,the particles with0.3⁰.8mm of diameter become dominate in CSTR.The removal rates of ammonia nitrogen and nitrite accumulation rate were more than 95% and 80% respectively,which remain steady.Low dissolved oxygen?DO?(0.3⁰.5mg·L^-1)is an important condition for the nitrification.?2?To maintain the long-term stability of nitrosation by regulating the running conditions of the process.We divided the whole operation into four stages?a total of 181d?.The results show that increasing nitrogen volume load?NLR?could be the effective strategy to get long-term stable nitrosation process.The shape of the particles become more regular and the structure of those was more compact in the following operation.The sludge with good performance had good ability to deal with the impact of the high DO in a short time,and nitrite oxidizing bacteria?NOB?activity was effectively suppressed.Sludge removal load and reach 0.24kgN·?kg·d?^-1.Further improving nitrogen load resulted in the decrease of ammonia nitrogen removal rate,while the accumulation rate of nitrite nitrogen maintain more than 80%.Through the determination of activity of functional bacteria,we found that the sludge particles had high activity.The ammonia nitrogen removal rate [q?NH₄⁺-N?],the nitrate accumulation rate[q?NO₂^--N?] and the oxidation rate of ammonia oxidizing bacteria?SOUR-A?reached 90±5mg·?g·h?^-1,80±5mg·?g·h?^-1,86±5mg·?g·h?^-1,separately.In addition,in the particle dominated by autotrophic bacteria,the concentration of protein increased gradually while that of EPS maintained stable at around 26³4mg·g^-1.?3?To explore the short-term impact of biodegradable organic matter on the activities of different functional microbes in autotrophic partial nitrification granular sludge?PNG?,the variations of both nitrogen transformation performance and DO uptake of PNG were investigated in this study,by carrying out successive batch tests with and without the organics stressing.Results showed that the higher C/N ratio was used,the lower specific nitrite accumulation rate of q?NO₂^--N?was observed.Meanwhile,the increase of heterotrophic bacteria?HeB?activities caused the fast DO uptake by PNG,which could suppress NOB with the low oxygen affinity,effectively.When inorganic substrate culture was employed in the following phase,both HeB and NOB showed the low activities,with the significant increase in q?NO₂^--N?.In short,the adverse effects of biodegradable organic matter on the performance of PNG system was partial reversible,which could benefit to enhance the advantage of AOB and improve the stability of partial nitrification reaction.