Study On Partial Nitrification In The Immobilization Biological Reactor

The problems caused by ammonia in municipal, agricultural and industrial wastewater have become a significant concern throughout the world. Usually found as ion (NH4+-N) in aqueous environments, ammonia could decrease dissolved oxygen, cause toxicity problems to the aquatic life, and also lead to eutrophication of lakes, rivers or even drinking water reservoirs.Among the various biological methods to solve the problem, partial nitrification is considered as the most cost effective one. Sequencing processes such as SHARON and CANON, which take advantage of partial nitrification, could reduce 25% of the oxygen consumption in nitrification and 40% of the organic carbon requirement in denitrification process. Construction investment as well as operation cost can also be saved.By removing the ammonia nitrogen in the synthetic wastewater with immobilized activated sludge, the strategy in obtaining partical nitrification and the influencial operation parameters are discussed in the present research. Meanwhile, to explain the achieved partial nitrification from the view of microbiology thoroughly, the immobilized nitrifiers'appereance as well as their community structures are investigated by SEM and PCR-DGGE, respectively. As a sequencing process, ANAMMOX process was also operated in the present research.The main research contents are as following:(1) Discussion of the possibility to achieve partial nitrification in aerobic fluidized bed reactor with immobilized nitrifiers by quickly increasing the influent ammonia concentration;(2) Obsevation of the influences of operation parameters on partial nitrification, such as free ammonia, temperature, dissolved oxygen as well as organics. And the optional operation parameters of the partial nitrification reactor;(3) Comparison of the difference in acclimation time, ammonia oxidation rate and activated energy between immobilized nitrifiers and other nitrification processes in other studies;(4) Flexbile operation of a partial-complete nitrification reactor;(5) The explaination of the partial nitrification from the microbiology perspective. The appearance of the microorganisms and their community structures are studied with SEM and PCR-DGGE, respectively. The differences between the partial nitrification and complete nitrification microorganisms are also discussed.Based on the analysises above, the following conclusions can be made: (1) Compared to the immobilized pellets without PAC addition, the pellets with PAC addition have higher ammonia oxidation rate and pellet removing efficiency. The ammonia oxidation rate in average is 34.66 mg-N/L·h and the maxiam pellet removing efficiency is 698.2 mg/(L-pellet·h). Meanwhile the PAC added pellets have a relatively low activated energy than those in other reported studies.(2) A stable and long-lasting partial nitrification can be obtained by quickly increasing the ammonia concentration in influent. Operation parameters, such as temperature, dissolved oxygen do not have serve effect on the obtained partial nitrification. A desired partial nitrification can be achieved at pH of 7.8-8.5, dissolved oxygen of 3-5 mg/L and temperature of 24-29℃. Organics have an obvious influence on partial nitrification, however, a nitrification reaction can be obtained even when TOC concentration is up to 800mg/L. Nitrite accumulation obove 90% can be regained even after a long time of placement.(3) The partial-complete nitrification system can achieve a maximum pellet removing efficency of 680 mg/(L-pellet-h), when ammonia concentration in influent is 300 mg/L. The ammonia concentration in effluent can be reduced to 30 mg/L in 8 hours. Flexible operation can be obtained by changing the HRT of the two reactors.(4) The SEM images of the microorganisms in the partial nitrification system show the microorganisms in present study are ellipsoidal and coarse with a length of 0.5μm.With a gradient of 20%-50% denaturant,the DGGE profile of the partial nitrification pellets showed that the band pattern of AOB community structure were almost uniform, which reveals the influencing factors such as ammonia concentration, temperature and DO had little impact on the stability of AOB community and the stability can be maintained after a period of placement. Generated phylogenetie trees of AOB showed the sequences are related to Nitrosomonas group.With a gradient of 20%-50% denaturant, the DGGE profile of pellets in both the partial and complete nitrification systems showed that the band pattern for NOB in partial nitrification reactor was more complex than that in the complete nitrification reactor, this reveals the complexity of microorganisms can be attributed to the complexity difference of feed component. By comparing the phylogenetic distance of sequences, a band, which appeares only in complete nitrification reactor and is absent in the partial nitrification reactor, is found closely relate to Nitrobacter Sp.219 and Nitrobacter Sp.263.