| Shortcut nitrification is a new and efficient biological wastewater treatment technology.Compared with the traditional full-time nitrification,shortcut nitrification has the unparalleled superiority,such as reducing aeration time and sludge production.However,harsh environment and high loss rate of the ammonia oxidizing bacteria increased the difficulty of the fast start-up of shortcut nitrification.The membrane bioreactor has efficient interception,which is beneficial to enriching slow-growing microorganisms.Based on this,the continuous stirred tank reactor and the membrane bioreactor were selected in this study for a comparative study about the differences of the start-up characteristic of shortcut nitrification.And the carbon source and the sludge source,conducive to the fast start-up of shortcut nitrification in the membrane bioreactor,were further investigated.Throughout the research process,a combination of conventional water quality analysis and microbiological analysis was used to provide a more comprehensive theoretical basis for the fast start-up of shortcut nitrification.The research results of this paper are as follows:?1?In order to achieve the bioreactor for the fast start-up of shortcut nitrification,the continuous stirred tank reactor?CSTR?and the membrane bioreactor?MBR?were selected to inspect the feature differences of the fast start-up of shortcut nitrification.The results showed that the start-up of shortcut nitrification could be successfully achieved in the CSTR and MBR after 56 and 44 days'operation respectively with temperature around 30?±1?,pH of 7.5-8.0 and dissolve oxygen?DO?of 0.6-1.0mg·L-1,as well as combining anoxic/aerobic ratio 1:3?15min:45min?with shortening hydraulic retention time?HRT?.The start-up period of MBR was shorter.On the 14th,28th and 56th day,average nitrite accumulation efficiency in the CSTR and MBR was51%,66%,89%and 50%,71%,93%,and nitrate formation rate of the two reactors was successively 7.4,4.0,1.7 and 7.6,3.5,1.0 mg·?g·h?-1?NO3--N/MLVSS?.A higher nitrite accumulation efficiency and a lower nitrate formation rate were detected in the MBR on the 28th and 56th day,which could be beneficial to the fast start-up of shortcut nitrification.During the whole operation period,the shortcut nitrification sludge in the two reactors was both yellow,the sludge volume index?SVI?was between 55 and 110 m L·g-1,and the mixed liquor volatile suspended solids?MLVSS?/mixed liquor suspended solids?MLSS?was around 0.6-0.8.The good sludge performance created favorable conditions for the fast start-up of shortcut nitrification in the CSTR and MBR.After the successful start-up of shortcut nitrification,the microbial abundance and diversity in the CSTR and MBR decreased significantly,and the microbial quantity and diversity of the MBR were higher than that of the CSTR.Proteobacteria was the dominant phylum in the CSTR and MBR shortcut nitrification reactors,accounting for 42.1%and 44.2%respectively.Meanwhile,it could be detected from the genus level that the ammonia oxidizing bacteria in the CSTR and MBR was Nitrosomonas,and the percentages were 10.4%and 12.8%respectively.?2?In order to identify the appropriate carbon source for the fast start-up of shortcut nitrification in the MBR,the influent water containing organic carbon source and only inorganic carbon source were adopted to inspect the feature differences of the fast start-up of shortcut nitrification.The results showed that the start-up of shortcut nitrification could be successfully achieved in the autotrophic MBR reactor after 52 days'operation,whose start-up period was longer compared with 44 days of the heterotrophic MBR reactor with the same influent water quality and operating condition.During the stable operation,the nitrate formation rate of the heterotrophic and autotrophic MBR reactors was 1.0 and 2.0 mg·?g·h?-1?NO3--N/MLVSS?respectively,and the average nitrite accumulation efficiency was 93%and 86%.The shortcut nitrification was both achieved in the two reactors,and the more stable nitrosification could be obtained in the heterotrophic MBR reactor.During the whole operation,the SVI value of the autotrophic and heterotrophic MBR reactors was stable at 55-85 mL·g-11 and 55-110 mL·g-11 respectively,and the MLVSS/MLSS was fluctuated within the range of 0.6-0.85,which ensured the fast start-up of shortcut nitrification.Compared with inoculated sludge,the microbial abundance and diversity of the sludge samples running 56 d in the heterotrophic and autotrophic MBR reactors showed a decreasing trend,and the autotrophic MBR reactors had a larger decline.After the successful start-up of shortcut nitrification,Bataproteobacteria was the dominant communities on the Proteobacteria in the heterotrophic and autotrophic MBR reactors at a class level,accounting for 59.6%and 55.1%respectively.Nitrosomonas was the dominant genus in the two reactors,which could be up to12.8%in the heterotrophic MBR reactor,higher than 12.1%in the autotrophic MBR reactor.Only a small proportion of Nitrospira and Terrimonas were detected in the autotrophic MBR reactor,which were 1.1%and 4.6%respectively.?3?In order to explore the best sludge source for the fast start-up of shortcut nitrification in the MBR,the anaerobic nitrification sludge?R1?and 1:1 mixed inoculated sludge?anaerobic nitrification sludge:denitrification sludge??R2?were inoculated to inspect the feature differences of the fast start-up of shortcut nitrification.The results showed that the start-up of shortcut nitrification could be successfully achieved in the R1 and R2 reactors after 8 and 30 days'operation respectively with the same influent water quality and operating condition.Compared with inoculation of the common sludge,the start-up period of the two reactors was shorter,and 1:1mixed inoculated sludge?R2?was more feasible.During the stable shortcut nitrification of the reactors,average nitrite accumulation efficiency in the R1 and R2reactors was 92%and 94%,and nitrate formation rate of the two reactors was 1.0 and0.7 mg·?g·h?-1?NO3--N/MLVSS?respectively.The shortcut nitrification in the R2reactor was more stable.After 56 days'operation,the R2 reactor had the better sludge settling performance,the SVI was between 70 and 95 mL·g-1,and the MLVSS/MLSS was around 0.65-0.85.From the ACE,Chao,Shannon and Simpson indices,after the start-up of shortcut nitrification,the abundance and diversity of microorganisms in the R1 reactor decreased significantly,while the abundance of microorganisms in the R2reactor reduced,and the diversity did not change lightly.After 56 days of operation,the main phylum in the R1 and R2 reactors was Proteobacteria,Bacteroidetes and Chloroflexi,among which Proteobacteria was predominant,accounting for 48%and54.7%respectively;the dominant genus was Nitrosomonas,20.2%and 19.7%respectively.In addition,the dominant genus was Thauera and Paracoccus in the inoculated sludge from the R1 and R2 reactors,and the abundance values of the two successful shortcut nitrification reactors reduced significantly. |
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