| In the biological nitrogen removal process, if the conversion of NO2-to NO3-bynitrite oxidizing bacteria (NOB) was inhibited in the nitrification process, and thenitrogen removal via NO2-as the terminal electron acceptor for denitrification, theshort-cut SND process could be achieved..The shortcut nitrification denitrificationvia NO2-has several advantages, such as reduce25%oxygen consumption and save40%organic carbon. However, nitrite accumulation might result in large amount ofN2O emission in the biological nitrogen removal process. N2O is an importantgreenhouse gas, having a global warning potential of310times relative to that ofcarbon dioxide (CO2). Moreover, the reaction of N2O with atomic oxygen contributesto depletion of in stratosphere ozone, and N2O can cause e the formation of acid rain.Therefore, the study of N2O emission characteristic and reduction of N2O emission inthe short-cut SND process has important practical significance.In the study, the short-cut SND process was set up in a lab-scale sequencingbatch airlift reactor (SABR), and polymerase chain reaction (PCR) and denaturinggradient gel electrophoresis (DGGE) technology was using to study the succession ofmicrobial community which provided fundamental data for the regulation and controlof N2O release in the way of microbial population structure. Besides, the effect ofcarbon source (such as different carbon species, C/N and carbon feeding method) onthe nitrogen removal and N2O emission characteristics of the short-cut SND processwere investigated.Primarily, based on the completed SND process, the system could be switched tothe short-cut SND process as increasing the free ammonia (FA) inhibition for nitriteoxidation bacteria(NOB) by adjusting the influent pH from7.0~7.3to8.0~8.3. Usingthe completed SND process as a reference, the N2O emission characteristic and thecommunity succession of the shortcut SND process were also observed. The resultssuggested that, in shortcut SND process, the total nitrogen removal and SNDefficiency was13.2and11.5percents higher than those in completed SND process,respectively. However, the N2O accumulated emission amount was approximately4 times as much as that in the complete SND process.The community structure was significantly changed when the system wasswitched from the completed SND process to short-cut SND, which showed that somestrains of nitrite-oxidizing bacteria were washed out and some ammonia-oxidizingbacteria and filamentous bacteria were enriched. Uncultured Simplicispira sp.,Candidatus Microthrix parvicella, Pseudomonas fluorescens and Nitrosomonaseuropaea were enriched based on targeted sequence of16S rDNA. Nitrosomonas-likeAOB was the dominated bacterium containing amoA functional gene, which may playa leading role in contributing to the dramatically variant of N2O emission. The band innosZ DGGE profiles was abundant, and Paracoccus denitrification, Rhizobiummelitoli, Azospirillun, Achuromobacter and Bradyrhizobium were the dominantspecies.The effect of different carbon sources, carbon to nitrogen (C/N) ratios and carbonfeeing methods on the nitrogen removal and N2O emission characteristics of theshortcut SND process were studied. The obtained result suggested that carbon specieshad great impact on the nitrogen removal and N2O emission during the shortcut SNDprocess. Among glucose, acetate and starch, the reactor achieved the maximumnitrogen removal efficiency and the minimum N2O conversion rate when glucose wasused as carbon source, while the maximum N2O conversion rate in the system withadditional carbon source of acetate. The N2O conversion rate of the reactor withadditional carbon source of acetate was25percent higher than those of glucose andstarch.In the system of with additional carbon source of glucose,20percent of totalnitrogen removal and19percent of SND efficiency were improved, and N2Oconversion rate was reduced from63.2to29.8percent of by increasing C/N from3:1to7:1. However, the ammonia nitrogen removal rate and total nitrogen removal ratebegan to fall when the C/N ratio ascended to9:1. Considering the stability of reactoroperation and carbon source minimization,7:1was the optimized C/N in the short-cutSND process.In the short-cut SND process with additional carbon source of glucose and C/N ratio of7:1, reduction N2O emission could be achieved under the carbon step-feeingcondition. The total nitrogen removal was8and17percent higher than those ofthrowaway-feeding and continuity-feeing, respectively, and7and16percent of SNDefficiency was also higher than those. Besides, the amount of N2O emission was49.5mg·cycle-1, and11and33percent of N2O conversation rate was less than those ofthrowaway-feeing and continuity-feeing, respectively.These obtained results suggested that the short-cut SND process had a highefficiency biological nitrogen removal process, while a considerable amount of N2Oemission was also accompanied. The effective nitrogen removal and limited N2Oemission can be achieved through the optimization of operation conditions. |
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