| Conventional A2/O process is arranged in the order of anaerobic/anoxic/aerobic zones. The nitrifying liquid from the aerobic zone is returned to the anoxic zone to perform denitrification, most sludge from the secondary clarifiers is returned to the anaerobic zone and little of them leave the system in the form of excessive sludge. The reversed A2/O process, which exchanges the anaerobic and anoxic zones of conventional A2/O process, is arranged in the order of anoxic/anaerobic/aerobic. Such a configuration allows the nitrification liquid backflow to be canceled and guarantee the nitrogen removal efficiency by increasing the sludge reflux ratio properly. Reversed A2/O process has been proved by plentiful practice to be able to remove phosphorus and nitrogen efficiently. Compared to wastewater treatment plants (WWTPs) employed conventional A2/O process, many WWTPs designed according to the reversed A2/O process conception can either save investment during construction or economize running cost during daily operation.To reveal how the change of "anaerobic/anoxic" zones affect the system on denitrification and phosphorus removal performance and carbon source metabolism, the paper focused on carbon source load and carbon source type with a parallel comparative study on the reversed A2/O process and the conventional A2/O process on the basis of the existing research results. By parallel comparative study on the pilot scale experiment, the different nitrogen and phosphorus removal mechanism and the microbes’ activity under aerobic conditions, the paper revealed the carbon source utilization efficiency, nitrogen phosphorus removal performance and the regularity link between microbial metabolic activity of the inverted A2/O process and conventional A2/O process. The theory basis of high efficiency and energy saving of the reversed A2/O process was founded, which may provide theoretical guidance to further optimization of the reversed A2/O process.The main results are as follows:1. During the pilot scale experiment, organic removal performance and ammonia nitrogen removal performance and phosphorus removal performance, reversed A2/O process system was superior to conventional A2/O process system in both two kinds of different carbon source under the condition of load and type. And under poor conditions of carbon source, the reversed A2/O process system showed significant advantages. Reversed A2/O process system showed wider applicability in terms of carbon source and carbon source load types.As far as the organic and ammonium removal performance is concerned, the reversed A2/O process always performed better than the conventional A2/O process under the two carbon load conditions and two carbon type conditions; as far as the denitrification efficiency is concerned, the reversed A2/O process always showed better efficiency than the conventional A2/O process under the two carbon load conditions and the gap is more apparent when lower carbon load conditions is adopted, the reversed A2/O process always showed little better efficiency than the conventional A2/O process under the two carbon type conditions; when it comes to the phosphorus removal, the reversed A2/O process always did better than the conventional A2/O process under the two carbon load conditions and carbon type conditions and the advantage of reversed A2/O process is more notable when the carbon sources are less favorable. So, the reversed A2/O process system showed wider applicability of nitrogen and phosphorus removal performance in terms of carbon source and carbon source load types, and under poor conditions of carbon source, the reversed A2/O process system showed significant advantages.2. Denitrification mechanism study shows that reversed A2/O process system was superior to conventional A2/O process system in denitrification performance and denitrification reaction of carbon source utilization efficiency under different carbon source type and carbon source load. Under poor conditions of carbon source, the reversed A2/O process system showed significant advantages in denitrification performance.As far as nitrification performance is concerned, comparison research of the nitrification performance under the conditions of different carbon source type and carbon source load revealed that the average specific nitrification rate of the reversed A2/O process was significantly higher than that of conventional A2/O process during the main stage of the ammonia nitrogen nitrification. It is indicated that, the nitrification ability of the reversed A2/O process system was superior to conventional A2/O process system; As far asdenitrifying denitrification performance is concerned, reversed A2/O process system was similar denitrification efficiency to conventional A2/O process system when sufficient VFAs are provided. When the carbon source is insufficient, the reversed A2/O process showed similar performance to the conventional A2/O process when relatively insufficient carbon sources are provided, but great better performance when absolutely insufficient carbon sources are provided; As far as carbon sources use efficiency is concerned, to achieve the same denitrification efficiency, conventional A2/O process system needed more carbon sources or more high-quality carbon source types. Therefore, under the two different conditions of carbon source type and carbon source load, the reversed A2/O process system showed higher carbon sources use efficiency. The more unfavorable circumstances of carbon source quantity or carbon source type is provided, the superior denitrification performance reversed A2/O process system showed than conventional A2/O process system.3. Phosphorus removal mechanism study shows that:Reversed A2/0process system was superior to conventional A2/O process system in phosphorus removal performance under the condition of two different carbon source load and carbon source type. Under poor conditions of carbon source, the reversed A2/O process system showed significant advantages in phosphorus removal performance.During the anaerobic and anoxic stages, although conventional A2/O process system consumes carbon source to synthesize intracellular substances in anoxic zone and reaches a higher level of phosphorus release, but the intracellular substances was mostly consumed by low phosphorus absorb reaction in anaerobic zone especially in poor condition of VFA. Because of that itsmicrobial intracellular substances and phosphorus release level was lower than reversed A2/O process system. This fully shows that conventional A2/O process system exist inefficient use of carbon source or waste problems in anaerobic and anoxic stages. During rapidly phosphorus absorption in the aerobic stages, whether microbial intracellular substances of conventional A2/O process system is higher or lower than reversed A2/O process system, its phosphorus uptake rate of microorganism using intracellular substances is lower than reversed A2/O process system.4. Reversed A2/O process system microorganisms had higher carbon source utilization efficiency and metabolic capability than conventional A2/O process system microorganisms under two different carbon source type and carbon source load conditions, with the same condition of organic matter and nitrogen removal or phosphorus removal load, the reversed A2/O process system needed shorter aerobic time or consumed less energy, and showed a better energy-saving performance.The comparison study on the microbes’dehydrogenase activity, electron transport system activity and specific oxygen uptake rate during aerobic stage shows that:compared to the conventional A2/O process system, the reversed A2/O process system had significantly higher levels of biochemical reactivity under two different carbon source type and carbon source load conditions. The comparison study on carbon source metabolic activity of microorganisms’taken from the two process systems by using Biolog method shows that: under two different conditions of carbon source type and carbon source load conditions, activated sludge microorganisms in the reversed A2/O process was superior to conventional A2/O process on the degradation of the common carbon sources such as sugars and amino acids, as well as the average utilization rate. The microbes in reversed A2/O process system had higher activity in terms of carbon metabolism. |
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