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Aerobic granular sludge (AGS) capable of nitrogen and phosphorus removal is mainly limited to the applications in sequencing batch reactors. This study introduced an innovative continuous self-circulating up-flow fluidized bed process (Zier process) using separate aeration. The process was composed of an anoxic column (Zier-A), aeration column (Zier-OO) and aerobic column (Zier-O), and was used to treat actual municipal sewage continuously for 170 days. The process achieved self-circulation of 20-32 times and an up-flow velocity within the reactor of 7-16 m/h which were accurately controlled with only separate aeration. The larger proportion of self-circulating multiple times contributed to particle formation and stability, providing hydraulic shear conditions, and screened the precipitation performance of the granular sludge (GS). Meanwhile, the dissolved oxygen (DO) of Zier-O was controlled at 0.1-0.3 mg/L, and the DO of Zier-A input water was zero. The accurate oxygen supply enhanced simultaneous nitrification and denitrification (SND) as well as short-cut nitrification and denitrification in Zier-O and improved the COD utilization rate and the nitrogen removal rate in Zier-A. The COD treatment capacity reached 2.46 kg-COD/(m³·d). With a hydraulic retention time of 10 h, the process consistently ensured that the average concentrations of ammonia nitrogen and total nitrogen in the effluent were maintained below 5 and 15 mg/L, respectively. Moreover, the process maintained the shape and stability of GS, the median diameter of GS ranged between 300-1210 μm, the percentage of mass with particle size distribution < 200 μm at a height of 150 cm within Zier-A and Zier-O accounted for as low as 0.04%-0.05%, and showed good settling performance. The suspended solids in effluent can be maintained at 50-80 mg/L. Overall, the unique structural setting and control method of the Zier process provide another approach for the application of continuous AGS treatment for municipal sewage., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Adding external carbon sources is an important method for advanced nitrogen removal of secondary effluent in wastewater treatment plants (WWTPs). In order to compare the denitrification performance and economy of different carbon sources sufficiently, as well as the effect of long-term addition of carbon sources on the microbial population structure, four single carbon sources (methanol, ethanol, glucose, and sodium acetate) and four types of composite carbon sources were prepared by mixing sodium acetate and ethanol with a higher reaction rate and cheap glucose. The results showed that the effluent ρ (NO x - -N) concentration of all systems was less than 1.0 mg·L -1 during the experiment. For single-carbon source systems, ethanol had the fastest denitrification rate, followed by sodium acetate and methanol; that of the glucose was the slowest. In the composite carbon source systems, the sodium acetate/glucose (1:1) with COD/ ρ (N) of 9, 10, and 10, respectively. The sodium acetate/glucose (1:1) system had the fastest reaction rate and the best economy. High-throughput sequencing results showed that after more than 70 days of operation, the structure of the microbial community had changed completely. In the glucose-related system, the abundance of Candidatus Saccharibacteria, which is not popular in typical nitrogen removal systems, increased from 1.16% of seed sludge to 47.37%, and ρ correspondingly became the dominant community. This study not only provides a more comprehensive comparison for the selection of carbon sources in WWTPs with ultimate nitrogen removal but also provides basic data for the role of carbon sources in the domestication of microbial communities.Saccharibacteria&#95;genera&#95;incertae&#95;sedis correspondingly became the dominant community. This study not only provides a more comprehensive comparison for the selection of carbon sources in WWTPs with ultimate nitrogen removal but also provides basic data for the role of carbon sources in the domestication of microbial communities.

The effects of low substrate ratio, cooling methods, and pH on nitrogen removal performance were studied in a laboratory-scale anaerobic ammonium oxidation reactor (ASBR) while treating simulated domestic waste water. The results illustrated that the average removal efficiencies of NH 4 + -N and NO 2 - -N increased from 54.4% and 65.3% to 95.8% and 92.5%, respectively, at a temperature of 30℃ and an influent concentration of NO 2 - -N of (30±0.2)mg·L -1 . The substrate ratio (NO 2 -N decreased to 54.6% when the substrate ratio was increased to 1.6, suggesting that the nitrogen removal performance of anaerobic ammonium oxidation was best when the substrate ratio was close to the theoretical value of 1.32.The average removal efficiencies of NH - -N/NH 4 + -N) increased from 0.9 to 1.4.However, the removal efficiency of NH 4 + -N was affected negligibly, and the average removal efficiency of NO 2 -N increased initially and then decreased when the pH was increased gradually from 7.7 to 8.5.The highest nitrogen removal efficiency was achieved when the pH was controlled at 8.3 with a substrate ratio of NO - -N decreased to 54.6% when the substrate ratio was increased to 1.6, suggesting that the nitrogen removal performance of anaerobic ammonium oxidation was best when the substrate ratio was close to the theoretical value of 1.32.The average removal efficiencies of NH 4 + -N and NO 2 - -N decreased from 97.5% and 98.5% to 35.2% and 40.1%, respectively, when the temperature of the reactor dropped from 30℃ to 15℃ at one time. The average removal efficiencies of NH 4 + -N and NO 2 - -N dropped from 97.7% and 98.6% to 52.7% and 62.4%, respectively, when the ladder cooling method(30℃→25℃→20℃→15℃) was used. The average removal efficiencies of NH 4 + -N and NO 2 - -N increased initially and then decreased when the pH was increased gradually from 7.7 to 8.5.The highest nitrogen removal efficiency was achieved when the pH was controlled at 8.3 with a substrate ratio of NO 2 - -N/NH 4 + -N equal to 1.4.

Shortcut nitrification sludge, which was set aside for two months, was recovered using Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ. The aeration rates of Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ were 120, 100, 80, and 60 L·h -1 , respectively, while treating real domestic sewage, and the ratio of aerobic/anoxic was 30 min/30 min at the temperature of 25℃. The influent of ammonia was 50-80 mg·L -1 , and the concentration of effluent ammonia was stable, at below 5 mg·L -1 , after the 12 th , 18 th , 21 st , and 21 st cycles. The removal ratio of ammonia nitrogen was about 95%. The highest concentrations of nitrite for Reactors Ⅰ, Ⅱ, Ⅲ, and Ⅳ were 20.83, 22.81, 21.50, and 20.73 mg·L -1 , respectively, which occurred in the 30 th , 35 th , 38 th , and 42 nd cycles, respectively. The concentrations of effluent nitrate were lower than 0.5 mg·L -1 , and the nitrite accumulation rates were higher than 99%. The activity of ammonia-oxidizing bacteria (AOB) increased gradually and finally stabilized at 100.00%; however, the activity of nitrite-oxidizing bacteria (NOB) was gradually inhibited. The recovery of shortcut nitrification was achieved successfully in the different aeration modes.

Nitrogen removal by a newly discovered Pseudomons sp. strain, DK1, isolated from activated sludge was investigated. Using glucose as a carbon source and a n (C)/ n (N) ratio of five, batch experiments showed that the aerobic denitrification removal rate was 4.09 mg·(L·h) -1 and 4.43 mg·(L·h) -1 with NaNO 3 or NaNO 2 , respectively. Completely nitrogen removal was achieved when using these two nitrogen sources. DK1 was also found to heterotrophically remove NH 4 + -N at a rate of 2.32 mg·(L·h) -1 and to carry out anoxic denitrification of a range of concentrations of NO 2 - -N (from about 100 to 300 mg·L -1 ) within a maximum of 36 hours of inoculation. In the presence of both NO 3 -N. Simultaneous nitrification and denitrification (SND) capacity of the DK1 strain was observed when using ammonium and nitrate or ammonium and nitrite and the corresponding nitrogen removal rates reached as high as 95.06% and 94.69% within 30 hours of inoculation, respectively. Ammonium with both nitrate and nitrite resulted in a 100% nitrogen removal within the same time frame. The ability to achieve SND and to denitrify both NO - -N and NO 2 - -N, DK1 was found to preferentially denitrify NO 3 - -N. Simultaneous nitrification and denitrification (SND) capacity of the DK1 strain was observed when using ammonium and nitrate or ammonium and nitrite and the corresponding nitrogen removal rates reached as high as 95.06% and 94.69% within 30 hours of inoculation, respectively. Ammonium with both nitrate and nitrite resulted in a 100% nitrogen removal within the same time frame. The ability to achieve SND and to denitrify both NO 3 - -N and NO 2 - -N makes the DK1 strain potentially useful for future application in nitrogenous wastewater treatment.

A cost-effective process, consisting of a denitrifying upflow anaerobic sludge blanket (UASB), an oxygen-limited anoxic/aerobic (A/O) process for short-cut nitrification, and an anaerobic reactor (ANR) for anaerobic ammonia oxidation (anammox), followed by an electrochemical oxidation process with a Ti-based SnO2-Sb2O5 anode, was developed to remove organics and nitrogen in a sewage diluted leachate. The final chemical oxygen demand (COD), ammonia nitrogen (NH4(+)-N) and total nitrogen (TN) of 70, 11.3 and 39 (all in mg/L), respectively, were obtained. TN removal in UASB, A/O and ANR were 24.6%, 49.6% and 16.1%, respectively. According to the water quality and molecular biology analysis, a high degree of anammox besides short-cut nitrification and denitrification occurred in A/O. Counting for 16.1% of TN removal in ANR, at least 43.2-49% of TN was removed via anammox. The anammox bacteria in A/O and ANR, were in respective titers of (2.5-5.9)×10(9) and 2.01×10(10)copy numbers/(gSS)., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The long-term stability of nitrogen removal from municipal landfill with high ammonia nitrogen (NH(4+)-N) content was investigated by using a biological system consisting of a first-stage up-flow anaerobic sludge bed (UASB) and sequencing batch reactor (SBR) under normal and low temperature conditions. The 623 days experimental results clearly showed: the efficient denitrification and methanogenesis were conducted in a same UASB reactor, and almost 100% of denitrification was obtained, when feed COD concentration ranged from 1,000 mg x L(-1) to 13 800 mg x L(-1), effluent COD concentration was between 150 mg x L(-1) and 1,234 mg x L(-1), and when the influent ammonia nitrogen (NH(4+)-N) changed from 574 mg x L(-1) to 2,360 mg-L(-1), the effluent NH:-N was below 10 mg x L(-1), the removal efficiency reached 90% and 98%, respectively. Especially, above 99.2% removal efficiency of TN was obtained, and effluent TN concentration was below 30 mg L(-1)), advanced and efficient nitrogen and organic removal were achieved in the biological system. Furthermore, stable nitrification and denitrification were achieved during the entire experiment period, especially, were maintained successfully for 171 days at the temperature below 15 degrees C and the lowest temperature of 10. 2 degrees C during two winters.

In order to test the start-up and maintain method for short-cut advanced nitrogen removal process at low temperature, this study used a pilot-scale SBR process with a working volume of 7.0 m3 to treat domestic wastewater. Real-time control strategy based on blower frequency (BF) and pH was applied to control the pilot-scale SBR process. Results showed that short-cut nitrification process achieved within 50 days at low temperature (11-16 degrees C), and the nitrite accumulation rate (NAR) of SBR process increased from 19.8% to 90%. Short-cut nitrification process in pilot-scale SBR was maintained for as long as 550 days in the temperature range of 9-28 degrees C, and NAR was maintained above 95%. Meanwhile, the total nitrogen (TN) in effluent was 3 mg x L(-1) and the TN removal efficiency was above 95%. Therefore, it is feasible to start-up and maintain the short-cut advanced nitrogen removal process under low temperature condition in the SBR process.

A pilot-scale modified UCT step feed process was proposed to treat the municipal wastewater with lower COD/N in a large-scale wastewater treatment plant. Effects of influent distribution ratios and nutrients ratios (COD/N, COD/P and TN/P) on nutrients removal capabilities were importantly investigated. The removal mechanisms of organics and nutrients and sludge characteristics were ultimately discussed. According to the continuous experiments, the stable and high process performance was obtained. The average COD removal efficiencies and effluent concentration of (83.8 +/- 3.86)% and (43.7 +/- 8.35) mg/L were achieved in the influent COD loading of 0.79-0.93 kg/(m3 x d). The COD removal in anaerobic and anoxic zones accounted for 60.2% - 76.2%. With the influent distribution ratio of 40%: 30%: 30%, as much as 88.2% of TN removal efficiency was observed. It should be considered the removal of 32.8% through simultaneous nitrification and denitrification process. The average effluent NH(4+)-N and TN were (0.21 +/- 0.20) mg/L and (7.90 +/- 1.27) mg/L, respectively. It was extremely important that as much as 32.6% - 39.5% of the denitrifying phosphorus accumulation organisms contributed to the high phosphorus removal efficiency of 97.2%. A linear positive relationship was observed between nitrogen removal efficiency and COD/N in the range of 4.64 and 7.41 (R2 = 0.96). Phosphorus removal efficiency was found to be a function of the influent COD/P and TN/P, varying from 35.0 to 92.5 and from 6.24 to 12.5, respectively (R2 = 0.87 and R2 = 0.89). In addition, the great sludge settleability was obtained with the mean SVI of (82.6 +/- 4.99) mL/g.

The behaviors of biological phosphorus (P) and nitrogen (N) removal in a lab-scaled anaerobic/anoxic/oxic-biological aerated filter (A2/O-BAF) combined system were investigated during the treatment of real domestic wastewater with the temperature at 15 degrees C, the C/N ratio of 4.9 and internal recycle ratio of 100%, 200%, 300% and 400%. Experimental results clearly showed that COD, N and P can be simultaneously deeply removed in this combined system. When the total HRT was 8.0 h, SRT was 15 d,sludge recycle ratio was 100% and MLSS was 4.0 mg x L(-1), the concentrations of COD, total phosphorus (TP) and ammonia nitrogen could be reached to less than 50.0, 0.5 and 1.0 mg x L(-1) in the effluent, respectively. The concentrations of total nitrogen (TN) could be reduced from 70.9, 72.1, 70.6 and 73.3 mg x L(-1) in the raw wastewater to that of 24.8, 16.5, 9.6 and 8.7 mg x L(-1) in the effluent, respectively. The removal efficiencies of TN were 65.0%, 77.1%, 86.4% and 88.1%, respectively. There was no distinct relationship between the internal recycle ratio and the removal efficiencies of COD, TP and ammonia nitrogen. However, the removal efficiencies of TN increased with the increasing of the internal recycle ratio, the rising rate was descending. Both the capacity of denitrifying and phosphorus removal in anoxic zone increased simultaneously with the increasing of the internal recycle ratio. Batch tests indicated that the population of denitrifying polyphosphate-accumulating organisms (DPAOs) was up to 40.5% of the total phosphate-accumulating organisms (PAOs).

Using a three-sludge system consisted of anaerobic/oxic (A/O) process, partial nitritation and anaerobic ammonium oxidation (ANAMMOX) reactors, cost-effective removal of nitrogen and phosphate from municipal wastewater was achieved. The experimental results showed that effluent total phosphorus (TP) of the A/O system was less than 0.5 mg/L under hydraulic retention time (HRT) of 3.6 h. Partial nitritation with nitrite accumulation efficiency of 75% -96% was realized in the partial nitritation system under room temperature, DO < 0.2 mg/L and HRT of 4.6 h. Under temperature of 27-30 degrees C and HRT of 1.4 h, effluent total nitrogen (TN) and TN removal rate of ANAMMOX reactor were less than 8 mg/L with the minimum value of 1.6 mg/L and 0.57 kg/(m3 x d), respectively. In the three-sludge system, phosphate accumulating organisms, ammonia-oxidizing bacteria and Anammox bacteria existed under suitably environmental condition to optimize the microbial community structure and improve treatment efficiency of various units. Autotrophic nitrogen removal can reduce 62.5% of the oxygen supply, save 100% of denitrification carbon sources theoretically, lower the sludge production, and greatly decrease carbon dioxide emission. As compared to traditional biological nutrient removal process, the three-sludge system has great advantages and potential in energy saving and carbon dioxide emission reduction to realize sustainable development of water resources.

The effects of different COD/TN and HRT(s) (hydraulic retention time of select) on nutrients removal were investigated by using an alternating anoxic/oxic CAST (cyclic activated sludge technology) fed with municipal wastewater. The results showed that various COD/TN and HRT(s) had a bigger influence on the nitrogen removal efficiency rather than the COD removal efficiency. As the influent C/N ratios were about 2.6 and 3.5, ammonia was removed by 98% and TN removal efficiency was increased from 62.9% to 76.2% and 72.1% to 84.6%, respectively, by increasing the HRT(s) from 1.8 h to 5 h. When the COD/TN ratio was increased to about 4.4, TN removal efficiency was decreased from 86.3% to 58.2% by enlarging the HRT(s), which was due to the incomplete nitrification of ammonia. It was also observed that both of increasing the COD/TN and HRT(s) could improve the phosphorus removal performance of the system. Furthermore, effluent of CAST reached the demanded A of integrated wastewater discharge standards (GB 18918-2002) when the COD/TN and HRT(s) were 4.4 and 1.8 h, respectively.

Aerobic granular sludge (AGS) for simultaneous nitrogen and phosphorus removal (SNPR) was cultivated and studied in two lab-scale sequencing batch reactors (named as A & B) treating real domestic wastewater, additional carbon (sodium propionate and sodium acetate for A, glucose for B) was added to make the ratio of COD:N:P as 360:60:6, good SNPR was achieved at normal (18-27 degrees C) and low temperature (9-13 degrees C). The microbial community composition and distribution, distribution of cells and extracellular polymeric substances (EPS) and morphologies of the AGS were investigated using fluorescence in situ hybridization (FISH), in situ fluorescent staining and scanning electron microscope (SEM), respectively. FISH results showed that ammonium-oxidizing bacteria comprised 12% of all the bacteria and were mainly located at the outer parts of the granules; phosphates accumulating organisms comprised 40% of all the bacteria and were mainly located in the inner parts of the granules. Nitrification was the rate controlling step; denitrifying phosphate accumulating organisms inside the granular sludge might be responsible for denitrification in the aerobic phase, which enabled effective SNPR. Live/dead fluorescent staining results showed that dead cells were distributed throughout the granules and live cells were principally distribution of polysaccharide (including alpha-mannopyranosyl, alpha-glucopyranosyl sugars and beta-D-glucopyranose polysaccharides) of EPS in AGS were influenced by different carbon sources, but the contents and distributions of protein and lipids were not, the contents of protein was the largest. Polysaccharide was responsible for the formation and maintenance of aerobic granular sludge. SEM results showed that bacilli and cocci were the main bacteria in the granules of A and B, respectively. Carbon sources affected the bacteria type and the SNPR efficiency, sodium propionate and sodium acetate were better than glucose.

The treatment of real leachate from municipal landfill with high ammonia nitrogen (NH4(+) -N) content was investigated by using lab-scale first-stage up-flow anaerobic sludge bed (UASB)-SBR biological system. The denitritation kinetics characteristics of microbial population in the SBR reactor was also studied. Experimental results clearly showed that the average organic loading rate of UASB reactor reached 6.5 kg/(m x d), the average organic removal rate was 5.3 kg/(m3 x d). High concentrations of COD and nitrogen contained in landfill leachate were removed efficiently, average COD and NH4(+) -N of influent could be reduced from 6 537 mg x L(-1) and 2 021 mg x L(-1) to 354 mg x L(-1) and 2.8 mg x L(-1), respectively, the removal efficiencies reached 94.6% and 99.8%, respectively. Especially, above 99.2% removal efficiency of TN was obtained, and effluent TN concentration below 20 mg x L(-1), so advanced nitrogen removal was achieved in the biological system. Ammonia nitrogen was removed by high effective partial nitrification with above 90% nitrite accumulation ratio, and the denitritation kinetics characteristics of the microbial population was fit well for Monod Equation.

In order to improve the nitrogen removal efficiency and to achieve the sludge reduction in traditional wastewater treatment plants, a combined hydrolysis-anoxic-oxic (H-A-O) pilot-scaled reactor was used in this study to investigate the possibility and validity of using excess activated sludge (EAS) fermentation liquids to enhance the nitrogen removal. The results clearly showed that sludge acidification rate in fermentation reactor can reach to 43.2%. The percentages of acetic acid, propionic acid and butyric acid in the fermentation liquids were 68.4, 25.3 and 6.3%, respectively, while those in domestic wastewater were 73.0, 12.2 and 13.8%, respectively. Bioavailability of soluble chemical oxygen demand (SCOD) from fermentation liquids and domestic wastewater were investigated in batch reactors with nitrate as the electron accepter as well. The corresponding specific denitrification rates were 0.15 g NO₃⁻-N/g VSS d⁻¹ and 0.09 g NO₃⁻-N/g VSS d⁻¹. When the substances were enough, the denitrification reaction appeared to follow the zero-order kinetics. The results also showed that, when the H-A-O pilot-scaled reactor was operated continuously and sludge fermentation liquids were applied as additional carbon source in the A-O reactor, the removal efficiencies of SCOD, NH₄+-N and total nitrogen (TN) were higher than 90, 95 and 79%, respectively. EAS reduction rate in this system was able to reach 40.4%, and the sludge VSS/SS ratio decreased from 0.82 to 0.59 after hydrolysis step.

SBR reactors were used to investigate the N2O emission in shortcut nitrification and simultaneous nitrification and denitrification (SND). Shortcut nitrification with nitrosation rate above 90% was realized by real-time control strategy. The N2O emission and variation of nitrosation rate were investigated under 4 DO levels (0.5, 1.0, 1.5, 2.0 mg/L). The results turned out that the optimal DO to maintain high nitrosation rate and minimum N2O emission was 1.5 mg/L and the N4O emission was 0.06 g per ammonium removed. The SBR filled with carbon fiber performed under low DO and pulse feeding. The SND rate was over 79% during the experiment. The N2O emission was studied under DO 0.2, 0.4, 1.0 and 1.5 mg/L. It turned out that the optimal DO was 1.0 mg/L and the N2O emission was 0.021 g per ammonium removed. Compared to the shortcut nitrification, the N2O emission of SND was 1/3 of the short-cut nitrification under optimal DO.

A pilot-scale step-feed A/O system was used to treat low C/N municipal wastewater. To obtain high quality simultaneous nitrogen and phosphorus removal, a modified step-feed A/O system was developed and the nitrogen and phosphorus removal efficiency was evaluated between the original and modified system. The result showed that TN removal efficiency was 66.52% and TP removal efficiency was only 29.24% before the modified configuration was applied. When the modified system was adopted, the satisfied simultaneous nitrogen and phosphorus removal was achieved. TP removal efficiency increased to 89.81% and TN removal efficiency was 73.61% when the optimal feeding ratio (0.45:0.35:0.20) was applied. Compared to the original configuration, TN removal efficiency increased about 7.09% due to the enhanced denitrifying phosphorus removal, which saved the carbon source for denitrification. To evaluate the selection and dominance of polyphosphate-accumulating organisms (PAOs) and denitrifying polyphosphate-accumulating organisms (DNPAOs), batch test was explored to examine the anaerobic phosphorus release, aerobic and anoxic phosphorus uptake. The result showed that both PAOs and DNPAOs were accumulated gradually when the modified system was applied. The maximal aerobic P uptake rate [P/(MLSS x t)] was increased from 2.34 mg/(g x h) to 10.67 mg/(g x h) and the anoxic P uptake rate was increased from 0.33 mg/(g x h) to 2.81 mg/(g x h) when the modified system was operated.

Appropriate change of the traditional operation modes was investigated in a UniFed SBR lab-scale apparatus treating actual domestic wastewater with low C/N and C/P. Results showed that when the feed/decant time was extended from 2 h to 3 h and 4 h, the phosphorous removal efficiency increased from 59.93% to 88.45% without any external carbon source. In the mode of anoxic-aerobic condition, TIN of the effluent reduced obviously, the removal efficiency increased from 49.54% to 60.75% for utilizing limited substrate in influents with low C/N = 2.57, adequately. In the mode of alternation of anoxic-aerobic condition, the nitrogen and phosphorous removal efficiency increased clearly. The carbon source in the influent can be used adequately and it occurred denitrifying dephosphatation in anoxic segment 2. This mode was optimal for the treatment of actual domestic wastewater with low C/N and C/P.

In order to realize the combination of "low oxygen limited filamentous sludge bulking" and short cut nitrification,the startup method of short cut nitrification and the maintenance strategies of sludge settleability were investigated under limited filamentous sludge bulking condition by using sequencing batch reactor (SBR). The effects of environmental factors like water quality, pH, DO,temperature and operation methods like mixture flow pattern, aeration mode, influent pattern on sludge settleability were analyzed. The results show that, when pH is between 7.2 and 8.0 and temperature is between 20 degrees C and 25 degrees C, short cut nitrification can be gradually realized through maintaining low DO and controlling the aeration time accurately. Nitrite accumulating ratio can increase from 28% to 80% after operating 160 cycles. Sludge settleability can be maintained effectively by changing the influent volume exchanging ratio (VER) assisted by aeration rate .The sludge volume index (SVI) can be maintained around 150 mL/g by adjusting the VER from 0.25 to 0.33 under limited sludge bulking. At the end of the aerobic phase, dissolved total nitrogen concentration increase slightly.

The experiment investigated the nitrous oxide production under different C/N ratios during denitrification, taking nitrate and nitrite as electron acceptor respectively. Ethanol was selected as carbon source. The C/N ratios were 0, 1.2, 2.4, 3.5, 5.0 and 20 when nitrate was taken as electron acceptor and C/N ratios 0, 1.8, 2.4, 3.0, 4.3, 5.2, 6.6, 20.6 when electron acceptor was nitrite. The results indicated that: the optimum C/N ratio was 3.0 taking nitrite as electron acceptor and the N2O production was 0.044 mg x L(-1); the optimum C/N ratio was 5.0 taking nitrate as electron acceptor and the N2O production was 0.135 mg x L(-1) which was 3 times higher than that of nitrite as electron acceptor. Though the electron acceptor changed, the trend of N2O production was similar: when carbon source was badly insufficient, the production of N2O and denitrification rate were both quite small; the N2O production increased with the increasing of the quantity of carbon source; when the carbon source was excessive, the N2O production sharply raised. Consequently, compared to complete nitrification and denitrification, short-cut nitrification and denitrification could save 40% carbon source. Moreover, controlling C/N = 3 could reduce the production of N2O in short-cut nitrification.

Under the well-controlled experimental conditions, the biological treatability of real municipal landfill leachate with high strength nitrogen and high chemical oxygen demand (COD) concentration using anoxic/anaerobic upflow anaerobic sludge bed (UASB) -sequencing batch reactor (SBR) combined process was conducted in laboratory. The results indicated: stable anoxic/anaerobic UASB-SBR process performance was developed during running continuously for five phase (116 d) when feed COD concentration was range from 1 237.2 mg/L to 12596.8 mg/L, effluent COD concentration was between 108.4 mg/L and 528.26 mg/L, and when the influent ammonia nitrogen (NH4(+) -N) was changed from 155.8 mg/L to 1298.0 mg/L, the effluent NH4(+) -N was varied from 0.12 mg/L to 4.1 mg/L, it achieved high COD and NH4(+) -N removal efficiency. In this present study, it is noted that the anoxic UASB1 has two significant effects: firstly, denitrification reaction of high efficiency was conducted for SBR nitrified effluent recirculated by using the abundant organic matters in the raw leachate as carbon source. Secondly, its removal COD was highly effected by anaerobic biodegradation. The effluent COD of anoxic UASB1 was biodegraded further in the anaerobic UASB2 and aerobic SBR, the maximum organic loading rates (OLR) (as COD) were 13.0, 2.09, 2.14 kg/(m3 x d), respectively. In addition, the correlation between OLR with OLRrem and COD removal efficiency of three reactors was studied, relation between nitrogen loading rate (NLR) with NH4(+) -N removal efficiency of SBR was tested by linear regression analysis, it was found that the OLR of anoxic UASB1, anaerobic UASB2 and aerobic SBR increased linearly with OLRrem. As to SBR, the correlation was significant between NLR (as N) with NLRrem. In addition, the OLR of three reactors shows second order exponential correlation with COD removal efficiency. At last, when the water temperature of SBR ranged from 20.7 degrees C to 10.3 degrees C, and dissolved oxygen was controlled below 1.0 mg/L, the efficiencies of nitrification and denitrification were above 98.5% and 97.7% during the whole experimental running period, it achieved advanced nitrogen removal.

The experimental system consisted of anoxic filter and aerobic suspended carrier biofilm reactor. The partial nitrification was achieved and maintained stably in the aerobic reactor under normal temperature (15-29 degrees C) and high DO (6-9 mg/L). The nitritation with 70%-80% nitrite accumulation efficiency was obtained when FA concentration was in the range of 1.0-10.3 mg/L by controlling influent ammonia loading rate (ALR), ratio of alkalinity and ammonia and HRT in the aerobic reactor. The effluent nitrite/ammonia ratio was about 1.25 when the average influent ammonia, influent ALR and influent ratio of alkalinity and ammonia were 315.80 mg/L, 0.43 kg/(m3 x d) and 5.25, respectively. So the effluent of partial nitrification process provided the influent substrate demand for the following ANAMMOX process. The integrative analysis indicated that the proper FA concentration was the main factor achieving the partial nitrification. The study developed a novel partial nitrification technology adapt to water characteristics of digested sludge liquor.

To achieve stable advanced nitrogen removal via nitrite in SBR, factors influencing pH variation in treating real domestic wastewater were investigated. The characteristic points were found to be appeared obviously on pH profile at both ends of ammonia oxidization and denitrification by analyzing the mechanism of biological nitrogen removal and the balance of carbonic acid. Using pH as control parameter in SBR for treating domestic or municipal wastewater with low organic concentration and suitable alkalinity could achieve advanced nitrogen removal with effluent TN below 1 mg/L. Moreover, it could prevent the decrease of nitrite accumulation rate causing by excessive aeration, which plays an important role on the stability of advanced nitrogen removal via nitrite. Based on theoretical analysis and experimental study, the real-time control strategy of advanced nitrogen removal via nitrite was established. To accommodate the different water quality and retain the accuracy of control strategy, 18 adjustable variables were set up in control strategy. The control strategy established a foundation for developing control software and control system of advanced nitrogen removal via nitrite.

The experiment investigated the production and conversion rate of N2O during nitrification using saline sewage and municipal wastewater. Different kinds of sludge were used, domesticated by saline sewage influent (salinity 7.5 g/L) and municipal wastewater (salinity 0.1 g/L), respectively. The results showed that the production of N2O using saline sewage was 2.85 times higher than that using municipal wastewater. The production and conversion rate of N2O during nitrification under different salinities were also investigated. The results showed that the production of N2O was almost the same when salinity decreased from 7.5 g/L to 5.0 g/L, even 2.5 g/L. However, specific ammonia oxidation rate was increased with the decrease of salinity. The sudden increase of salinity, from 7.5 g/L to 10 g/L, resulted in the increase of N2O production and conversion rate but decrease of specific ammonia oxidation rate. Consequently, It is important to avoid the severe fluctuation of salinity resulted in the increase of N2O production and conversion rate.

A 52.5 L pilot-scale biosystem, based on A2O configaration, was employed to investigate the effect of carbon source on biological nutrient removal and its metabolism process. Acetic acid and propionic acid were selected as the sole carbon source in different step. The COD was about 250 mg/L and NH4(+) -N was about 52 mg/L in the influent. The results showed that the removal efficiency of TN was about 65% and without any relationship to the carbon source. The TP viariation along the reactor, PHA formation and content were determined by different carbon source. When acetic acid was the sole carbon source, more phosphate was released in the anaerobic phase compared to propionic acid as the carbon source and the content of PHA was mainly PHB and PHV. The amount of PHB and PHV was almost equal. PHB was depleted in the following anoxic and aerobic phase for phosphorus removal but PHV was almost constant along the reactor. When propionic acid was the sole carbon source, less phosphate was released in the anaerobic phase and the content of PHA was mainly PHV. Almost no PHB and PH2MV were formed. PHV was depleted in the following anoxic and aerobic phase for phosphate uptake. Besides, the glycogen formation, variation and amount were different when different carbon source was dosed. More glycogen was depleted and formed in anaerobic and anoxic/aerobic phase when acetic acid was used as carbon source. Compared to acetic acid, propionic acid was more suitable for biological nutrient removal in wastewater treatment systems.

To obtain high quality drainage, external carbon source (ethanol) was used to enhance denitrification when low COD/N sewage was fed to a pilot-scale step-feed A/O system. To use carbon source sufficiently, five different external carbon addition control strategieswere proposed based on different control parameters, ORP and on-line nitrate, and dosing positions, D3 and D4. Control strategies were evaluated on investment, treatment efficiency and operation cost basis. The results showed that for the short hydraulic retention time in anoxic zone, the control parameter could not reach the set-point when control strategy I and II were applied. As a result, excessive feeding of external carbon source was occurred and the average COD concentrations in D4 were 192.8 mg/L and 158.9 mg/L for the insufficient usage of carbon. In this condition, effluent TN concentrations were 17.42 mg/L and 19.04 mg/L and the external carbon dosage rates were 92 mL/(m3 x d) and 84 mL/(m3 x d), respectively. Control strategies III, IV and V controlled the external carbon dosage in D3 and D4 simultaneously. The results indicated that the strategies had strong resistance to peak loadings and reduced the effluent TN concentration effectively. The average effluent TN concentrations, 7.30 mg/L, 8.2 mg/L and 7.49 mg/L and the external carbon dosage rates, 29 mL/(m3 x d), 45 mL(m3 x d) and 27 mL/(m3 x d), were achieved respectively. Finally, based on the amount of on-line sensors, reliability of treatment efficiency and cost of operation, the control strategies proposed in this paper were evaluated together. Compared to the other control strategies, the suggested external carbon addition strategy III was testified to be an optimal control strategy, which was characterized by good dynamic qualities, strong resistance to peak loadings, quick responding to loadings, and the lower external carbon addition amount.

In order to optimize the utilization of influent carbon source, a feeding pattern so-called "coefficient of influent flow rate" was adopted in a pilot-scale step-feed A/O process treating domestic wastewater. The effects of influent flow distribution ratio on nitrogen removal efficiency were investigated when the reactor was operated at different loading rates and COD/TKN ratio of 3, 5, 7, 9, 11, 13, respectively. The experiment results indicated that the wasting of nitrification capacity occurred when high loading rate and low C/N ratio (COD/TKN <5) were applied, while ammonia removal efficiency was decreased obviously at the same time. When the system was operated at high loading rate and high C/N ratios, the insufficient nitrification occurred in first stage, which resulted in the absence of electron accepter in the downstream anoxic zone. Consequently, the total nitrogen (TN) removal efficiency was decreased even though the COD/TKN was higher than 9. However, due to the unlimited nitrification, the increased C/N ratio led to an enhancement of TN removal efficiency when the system was operated at low influent loading rate. When the influent COD/TKN was kept at 13 around, relatively low effluent TN concentration less than 2 mg/L, and a highest TN removal efficiency of 97.6% were achieved, respectively. For the feeding pattern selected for the study, the conclusions obtained from the experiment results showed that the influent flow coefficient method could use carbon source sufficiently and decrease the influent flow rate of last stage when the wastewater with higher C/N(C/N > alpha) was fed. However, a completely nitrification should be promised in each stage during this period. When the wastewater with low C/N ratio (C/N < alpha), due to the limited carbon source, C/N is the key parameter for TN removal efficiency. From the point view to favor the growth of nitrifiers and satisfy the ammonia effluent standard, the balanced loading of nitrifiers in each stage strategy maybe substitute the feeding pattern proposed in this study as an optimal choice.

To investigate the responding behavior of denitrifying bacteria to different carbon source (i.e., methanol, ethanol, sodium acetate, sodiumpropionate, glucose, domestic wastewater and endogenous carbon source), several batch experiments using the sludge from the Carrousel oxidation ditch were carried out at 15.4 degrees C +/- 0.8 degrees C. The results from sodium acetate feeding experiment show the highest maximum specific denitrification rate (MSDR), which is 6.51 mg/(g x h). However, the denitrificaion yield, which is 0.48, is at lowest level and an obvious accumulating of nitrite is observed. Compared to the other sole carbon source, a lower MSDR, 0.91 mg/(g x h) is shown when methanol is used as carbon source, which also suggests that the sufficient adaptation time should be promised for denitrifying bacteria. When the reactor is operated without exogenous carbon source, denitrifying bacteria can use the endogenous carbon source as electron donor for denitrification, but the specific denitrification rate is at lowest level accordingly. The MSDR value of 3.63 mg/(g x h) is obtained with fermented domestic wastewater feeding, which is equivalent to the MSDR attained from the test using VFAs as carbon source. Though the MSDR decreases a lot at low temperature, external carbon source addition improves the denitrification performance to some extent definitely.

Nitrogen removal through the nitrite pathway has been successfully achieved using on-line aeration length control. However, it takes a long time period to get steady performance when using on-line control as the sole strategy. On the other hand, salt inhibition has also been used to achieve the nitrite pathway, with potentially adverse effects on the overall microbial community at high salt concentrations. The objective of this study is to develop a control strategy based on the combination of low salt inhibition levels and on-line control to accelerate the achievement of nitrite pathway in a sequencing batch reactor (SBR) treating domestic wastewater. Salt concentrations and on-line control parameters were chosen in batch tests. The recovery of the nitrite-oxidizing bacteria (NOB) activity was examined after stopping on-line control and salt dosing. The findings clearly show that combining salt inhibition at low salinity (5 g/L) with on-line pH control is an efficient strategy to achieve nitrogen removal via nitrite quickly and steadily.

A system consisting of a two-stage UASB and anoxic-oxic reactor was used to study the influence of FA on short-cut nitrification of the actual municipal landfill leachate with high ammonia concentration. In the UASB1, denitrification and methanogenesis took place simultaneously. The effluent COD of UASB1 was further removed in the UASB2. Then the denitrification of nitrite and nitrate in the returned sludge by using the residual COD and nitrification was finished in the A/O reactor. The experiment experienced three stages during 79 d. The stable short-cut nitrification was achieved in the first stage (40 d). The short-cut nitrification was damaged in the second stage (19 d), and the short-cut nitrification was recovered in the last stage (20 d). The results of 79 d showed that when the FA concentration was about 40-70 mg x L(-1), the stable short-cut nitrification could be achieved. For example, the nitrite accumulation was 97% in the system during the first stage, and the ammonia removal efficiency was 99%. But when the FA concentration was about 160 mg x L(-1), the nitrification would be inhibited. In the third stage, raw leachate was diluted by tap water in order to decrease the FA concentration. And then the short-cut nitrification was recovered soon. In a word, the FA concentration is an important factor to achieve the short-cut nitrification of the municipal landfill leachate.

Aeration control is the important control variable for the biological nitrogen removal process, which determines the system removal performance and operational cost. Some typical control strategies of aeration for aerobic-anoxic biological nitrogen removal process were studied using Benchmark-BSM1 platform model. It was demonstrated that the best control strategy of aeration was feedforward-feedback control, following by feedback control, constant DO control and constant aeration flow rate control. Compared with constant DO control, the effluent ammonia concentration, the maximum effluent ammonia concentration and aeration cost were reduced by 24%, 18%, and 9%, respectively, with the feedforward-feedback control. The aeration control ideas and control strategies at different conditions were determined. In order to achieve nitrification optimal control, the aeration flow and aeration volume should be both controlled.

The characteristics of denitrifying phosphorus removal in a lab-scale two-sludge anaerobic-anoxic/nitrification SBR (A2 NSBR) system were studied fed with domestic wastewater. The influence of some key operation parameters, like C/P, C/N, and HRT, were examined using parallel tests, pH, dissolved oxygen (DO) and redox potential (ORP) were monitored on line to validate whether they could be used as the control parameters for this denitrifying phosphorus removal process. Results indicated that P removal efficiency showed an increased trend on the whole with the increase of the C/P. When the influent C/P was greater than 19.39, good phosphorus removal efficiency was achieved. However, the phosphorus removal efficiency deteriorated once the influent C/P decreased less than 15.36. On the other hand, relatively good phosphorus removal efficiency could be maintained in the A2 NSBR system even at a low C/N ratio, though the denitrification efficiency decrease instead. It is also found that increasing the influent C/N increased the PHB amount stored by polyphosphate accumulating organisms (PAO) and therefore the ultimate denitrification and phosphorus removal efficiency were both improved. For an excessively high C/N, the incompletely reacted COD will be residual to anoxic stage. Thus, the pure denitrification reaction, which preferentially supports OHOs, becomes the dominant reaction. This decreases the amount of available electron acceptors for denitrifying polyphosphate accumulating organisms (DNPAOs) at the anoxic stage which eventually impacts the anoxic phosphorus removal capacity. In addition, since A2 NSBR has two completely independent SBR systems, it benefits to establish a process control system in terms of the parameters DO, ORP, and pH.

The effects of 7 groups of different influent C/N ratio (2.75, 4.28, 5.7, 6.5, 6.97, 8.08, 11.19) on the removal efficiencies of total nitrogen, phosphorus and COD as well as the sludge settling performance were investigated in a UniFed SBR lab-scale apparatus treating actual domestic wastewater. The results showed that when the C/N ratio was lower than 5.7, TN removal efficiency increased sharply as C/N ratio increased, from 43.6% of 2.75 to 80.84% of 5.7. Afterwards, TN removal efficiency increased very slowly as C/N ratio increased, because only TN removal efficiency caused by SND during aeration period could be enhanced. P removal efficiency increased as C/N ratio increased, because PAOs could get more organic carbon source from the influent to produce PHB and release PO4(3-), avoiding the adverse influence of NO(x)- on PO4(3-) release. The higher the C/N ratio, the more the quantities of P release and uptake, the quicker P uptake rate, the better P removal performance was. Regardless of the C/N ratio, excellent COD (average 93.15%) removal efficiencies were maintained throughout the experiment. When Influent C/N ratio was bigger than 6.97 and organic load exceeded 0.38 kg/(kg x d), SVI rose quickly as C/N ratio increased. Non-silk bacteria sludge bulge appeared because of low DO and high organic load.

In order to reduce nitrous oxide (N2O) production from real wastewater and optimize the DO concentration and the aeration mode, nitrification efficiency and N2O production from nitrification treating domestic wastewater under difference DO concentrations were investigated using lab-scale SBR. The obtained results show energy consumption was saved at DO concentration of 0.4 mg L(-1), whereas, ammonia oxidation rate was very low. Ammonia oxidation rate was increased with DO increasing. N2O was produced during the nitrification for treating domestic wastewater with low ammonium concentration. N2O production at the DO concentration of 0.4 mg L(-1) and 0.9 mg L(-1) were 1.5 mg L(-1) and 1.6 mg L(-1), respectively. While N2O production at the DO concentration of 1.5 mg L(-1) and 2.0 mg L(-1) were 0.5 mg L 1)and 0.4 mg L-'(-1)respectively. When DO concentration increased above 1.5 mg L-'(-1)the ammonia oxidation rate increased slightly with N2 0O production sharply decreasing. Therefore, from the aspects of enhancing the efficiency of nitrogen removal with lower energy consumption and reducing N2 Oproduction, the optimal controlled DO concentration was 1.5 mg L-. -1)

Study was conducted by use of the mixed organism of activated sludge and suspended biofilm coexisting in a hybrid biological reactor (HBR) system for simultaneous nitrogen and phosphorous removal. The experimental results showed that, DO and COD/TN were the main factors affected the effluent. The maximum phosphorous releasing rate (the rate of PO4(3-)-P concentration at releasing end to the initial PO4(3-)-P concentration) was 249%, TN removal efficiency was 80.0%, and PO4(3-)-P removal efficiency was 92.2% by controlling the aeration rate (Qair) at 0.07 m3/h. TN and PO4(3-)-P removal efficiency will be decreased, whenever aeration rate increasing or decreasing. With the increasing of COD/TN, the TN and PO4(3-)-P removal efficiency was increased. TN removal efficiency was increased from 70.3% to 84.9%, and PO4(3- -P removal efficiency was increased from 82.2% to 96.0%, when COD/TN was increased from 3.2 to 10.5. The SVI of the activated sludge was less than 90 mL/g during the experiments. It was found during the research process that high phosphorus and nitrogen removal efficiency can be simultaneous achieved without anaerobic and anoxic phase, which was conventionally considered as a key phase for phosphorus and nitrogen removal.

In order to increase the efficiency of nitrogen removal by endogenous denitrification, and to realize the excess activated sludge reduction in the traditional wastewater treatment process, this investigation proposes a hydrolysis/anoxic/oxic (H/A/O) process utilizing nitrogen removal with excess activated sludge reduction. The experimental equipment for continuous treatment of domestic wastewater was set up and the pilot experiment was conducted. The results showed that, without adding external carbon sources and alkalinity, the removal efficiency of COD, NH4+-N and TN were higher than 90%, 95% and 75%, respectively, under the condition that the hydraulic retention time was 10 h and the backflow ratio of nitrification liquor was 300%, the COD of influent between 220-410 mg/L, the NH4+-N of influent between 36-58 mg/L. When the carbon source was not the limiting condition of the denitrification, with the increasing of the return nitrification liquor, the nitrogen removal efficiency increased. On the contrary, with the increasing of the return nitrification liquor, the nitrogen removal efficiency decreased. It has been tested that the reduction rate of excess activated sludge in the system reached 56.2%. The nitrogen removal efficiency was improved greatly by the wastewater and excess activated sludge hydrolysis. It's proved that using hydrolysis as pre-treatment of wastewater and excess activated sludge is feasible, thas it not only improved the biodegaradability of wastewater and the nutrient removal efficiency, but also enhanced the stability for the operation of the wastewater treatment system, and then the wastewater and excess activated sludge were treatment simultaneously.

An UASB+Anoxic/Oxic (A/O) system was introduced to treat a mature landfill leachate with low carbon-to-nitrogen ratio and high ammonia concentration. To make the best use of the biodegradable COD in the leachate, the denitrification of NOx- -N in the recirculation effluent from the clarifier was carried out in the UASB. The results showed that most biodegradable organic matters were removed by the denitrification in the UASB. The NH4+ -N loading rate (ALR) of A/O reactor and operational temperature was 0.28-0.60 kg NH4+ -N/(m3 x d) and 17-29 degrees C during experimental period, respectively. The short-cut nitrification with nitrite accumulation efficiency of 90%-99% was stabilized during the whole experiment. The NH4+ -N removal efficiency varied between 90% and 100%. When ALR was less than 0.45 kg NH4+ -N/(m3 x d), the NH4+ -N removal efficiency was more than 98%. With the influent NH4+ -N of 1200-1800 mg/L, the effluent NH4+ -N was less than 15 mg/L. The shortcut nitrification and denitrification can save 40% carbon source, with a highly efficient denitrification taking place in the UASB. When the ratio of the feed COD to feed NH4+ -N was only 2-3, the total inorganic nitrogen (TIN) removal efficiency attained 67%-80%. Besides, the sludge samples from A/O reactor were analyzed using FISH. The FISH analysis revealed that ammonia oxidation bacteria (AOB) accounted for 4% of the total eubacterial population, whereas nitrite oxidation bacteria (NOB) accounted only for 0.2% of the total eubacterial population.

The simultaneous nitrification and denitrification in step-feeding biological nitrogen removal process were investigated under different influent substrate concentrations and aeration flow rates. Biological occurrence of simultaneous nitrification and denitrification was verified in the aspect of nitrogen mass balance and alkalinity. The experimental results also showed that there was a distinct linear relationship between simultaneous nitrification and denitrification and DO concentration under the conditions of low and high aeration flow rate. In each experimental run the floc sizes of activated sludge were also measured and the results showed that simultaneous nitrification and denitrification could occur with very small size of floc.

It was realized nitrite accumulation in a pilot-scale pre-denitrification process at normal temperature. The influence factors, temperature, pH, FA and DO, for nitrite accumulation were analyzed. The nitrite was accumulated in the beginning time with the DO kept at 0.5 mg/L, however the phenomenon of nitrite accumulation was vanished when the DO increased to 1.5 mg/L. At last the nitrite accumulation was resumed when DO reduced to 0.5 mg/L. So it could be obtained that DO was the main factor to realize nitrite accumulation in the study. It was found that it was possible to keep stable and high nitrite accumulation effectively control DO at 0.5 mg/L.

It is realized short-cut nitrification and denitrification in an A/O pilot-scale plant treating actual domestic wastewater controlling DO concentration (0.5 mg/L) in low level at normal temperature, the average nitrite accumulation rate reached 85 % or above. Three operational modes: low DO short-cut nitrification and denitrification (Mode 1), low DO complete nitrification and denitrification (Mode 2) and high DO complete nitrification and denitrification (Mode 3) were briefly compared, based on the nitrogen removal, operating cost, sludge characteristics and operational mechanism. Experimental results showed that the Model is the best modes of biological nitrogen removal, in terms of improving nitrogen removal and reducing operating cost. The net pH change in aerobic zones and anoxic zones is high for Mode 1, but the net pH change in anoxic zones is very small for Mode 3. The nitrification rate is the smallest for Mode 2, and the nitrification rate for Mode 3 is little higher than that of Mode 1; the denitrification rate for Model is larger than that of Mode 3 about 15 %. It is feasible using DO and pH on-line sensors to control the nitrification process.

A pilot-scale Orbal oxidation ditch was operated for 17 months to optimize nitrogen removal from domestic wastewater of average COD to total nitrogen ratio of 2.7, with particular concern about the roles of dissolved oxygen (DO), mixed liquor suspended solids (MLSS) and return activated sludge (RAS) recycle ratio. Remarkable simultaneous nitrification and denitrification (SND) was observed and mean total nitrogen (TN) removal efficiency up to 72.1% was steadily achieved, at DO concentration in the out, middle and inner channel of 0.1, 0.4 and 0.7 mg/L, respectively, with an average MLSS of 5.5 g/L and RAS recycle ratio of 150%. Although the out channel took the major role in TN removal, the role of middle channel should never be ignored. The denitrification potential could be fully developed under low DO, high MLSS with adequate RAS ratio. The sludge settleability was amazingly improved under low DO operation mode, and some explanations were tried. In addition, a series of simplified batch tests were done to determine whether novel microorganisms could make substantial contribution to the performance of nitrogen removal. The results indicated that the SND observed in this Orbal oxidation ditch was more likely a physical phenomenon.

The aim of this work is operational optimization of an A/O process in the lab plant with synthetic wastewater for improving nitrogen removal efficiency. Ammonia control aims at maintaining the required concentration of ammonia in the effluent by manipulating the dissolved oxygen (DO) set point and aeration volumes. Nitrate control aims at the optimal use of the denitrification potential at any moment by continuously adjusting the internal recirculation flow or (and) external carbon addition flow in order to maintain a desired nitrate set point in the anoxic zone. The control strategies have been based on a hierarchical structure where a high level or supervisory control selects the set point of the low level or conventional controllers. Results indicated that it was possible to increase nitrogen removal efficiency, improve the effluent water quality, save energy, and reduce operating costs.

The control strategy and simulation of external carbon addition were specially studied in an anoxic-oxic (A/O) process with low carbon: nitrogen (C/N) domestic wastewater. The control strategy aimed to adjust the flow rate of external carbon dosage to the anoxic zone, thus the concentration of nitrate plus nitrite (NOx(-) -N) in the anoxic zone was kept closed to the set point. The relationship was studied between the NOx(-) -N concentration in the anoxic zone (S(NO)) and the dosage of external carbon, and the results showed that the removal efficiency of the total nitrogen (TN) could not be largely improved by double dosage of carbon source when S(NO) reached about 2 mg/L. Through keeping S(NO) at the level of about 2 mg/L, the demand of effluent quality could be met and the carbon dosage could be optimized. Based on the Activated Sludge Model No. 1 (ASM No. 1), a simplified mathematical model of external carbon dosage was developed. Simulation results showed that PI controller and feed-forward PI controller both had good dynamic response and steady precision. And feed-forward PI controller had better control effects due to its consideration of influent disturbances.

A bench-scale reactor(72 L) red with domestic sewage, was operated more than 3 months with three operation modes: traditional mode, modified mode and real-time control mode, so as to evaluate effects of the operation mode on the system performance and to develop a feasible control strategy. Results obtained from fixed-time control study indicate that the variations of the pH and oxidation-reduction potential(ORP) profiles can represent dynamic characteristics of system and the cycle sequences can be controlled and optimized by the control points on the pH and ORP profiles. A control strategy was, therefore, developed and applied to real-time control mode. Compared with traditional mode, the total nitrogen(TN) removal can be increased by approximately 16% in modified mode and a mean TN removal of 92% was achieved in real-time control mode. Moreover, approximately 12.5% aeration energy was saved in real-time control mode. The result of this study shows that the performance of nitrogen removal was enhanced in modified operation mode. Moreover, the real-time control made it possible to optimize process operation and save aeration energy.

Control of sludge age and mixed liquid suspended solids concentration in the activated sludge process is critical for ensuring effective wastewater treatment. A nonlinear dynamic model for a step-feed activated sludge process was developed in this study. The system is based on the control of the sludge age and mixed liquor suspended solids in the aerator of last stage by adjusting the sludge recycle and wastage flow rates respectively. The simulation results showed that the sludge age remained nearly constant at a value of 16 d in the variation of the influent characteristics. The mixed liquor suspended solids in the aerator of last stage were also maintained to a desired value of 2500 g/m3 by adjusting wastage flow rates.

The principal aim of this paper is to develop an approach to realize stable biological nitrogen removal via nitrite under normal conditions. Validation of the new method was established on laboratory-scale experiments applying the sequencing batch reactor (SBR) activated sludge process to domestic wastewater with low C/N ratio. The addition of sodium chloride (NaCl) to influent was established to achieve nitrite build-up. The high nitrite accumulation, depending on the salinity in influent and the application duration of salt, was obtained in SBRs treating saline wastewater. The maintenance results indicated that the real-time SBRs can maintain stable nitrite accumulation, but conversion from shorter nitrification-denitrification to full nitrification-denitrification was observed after some operation cycles in the other SBR with fixed-time control. The presented method is valuable to offer a solution to realize and to maintain nitrogen removal via nitrite under normal conditions.

The effect of nutrient (N and P) deficiency on activated sludge settleability and characteristics of activated sludge flocs in Sequencing Batch Reactor (SBR) fed with brewery wastewater were investigated. The results showed that the activated sludge had good settling properties at influent BOD5/N/P was 100/5/1,100/5/0.8 and 100/4/0.8 respectively. When BOD5/N/P was 100/0.94/0.31,100/2/0.4,100/3/0.6 respectively, the sludge settleability became worse due to excessive growth of filamentous. When BOD5/N/P was 100/0.94/1,100/5/0.31,100/5/0.4,100/5/0.6 respectively, non-filamentous activated sludge bulking occurred. Adding sufficient nutrient to the influent, the sludge bulking was controlled effectively and the low SVI was recovered. When increasing COD loading rate, the duration of recovery could be diminished. When nitrogen and phosphorus were insufficient synchronously, aerobic granular sludge was formed which was averagely 2mm-6mm in diameter.

With domestic wastewater of low ratio of carbon and nitrogen (C/N), the control of external carbon dosage was studied for the predenitrification process with continuous flow. The objective is to keep the external carbon usage as low as possible while nitrate plus nitrite concentrations (NOx(-)-N) of outflow under demand. The experimental results show that nitrogen removal efficiency couldn't be improved by increasing total recirculating rate with total recirculating rate more than 2 for lack of carbon source and removal efficiency of TN couldn't be largely improved by double dosage of carbon source with constant recirculating rate when NOx(-)-N concentration reaches about 2 mg/L. Based on the analysis of the relationship between the external carbon addition and total recirculating rate, a control method was proposed. The external carbon dosage is controlled by keeping NOx(-)-N concentration of anoxic zone at the level of 2 mg/L, and the total recirculating rate is determined by stated effluent NOx(-)-N concentration. The control method not only can determine the reference point of carbon dosage, but also can optimize the usage of carbon addition. It is easy to be carried out in wastewater treatment plants.

In order to improve nitrogen removal in anoxic/oxic(A/O) process effectively for treating domestic wastewaters, the influence factors, DO(dissolved oxygen), nitrate recirculation, sludge recycle, SRT(solids residence time), influent COD/TN and HRT(hydraulic retention time) were studied. Results indicated that it was possible to increase nitrogen removal by using corresponding control strategies, such as, adjusting the DO set point according to effluent ammonia concentration; manipulating nitrate recirculation flow according to nitrate concentration at the end of anoxic zone. Based on the experiments results, a knowledge-based approach for supervision of the nitrogen removal problems was considered, and decision trees for diagnosing nitrification and denitrification problems were built and successfully applied to A/O process.

The Anaerobic-Anoxic/Nitrification (A2N) system is a continuous-flow, two-sludge process in which Poly-p bacteria are capable of taking up phosphate under anoxic conditions using nitrate as an electron acceptor. The process is very efficient because it maximizes the utilization of organic substrate for phosphorus and nitrogen removal. Further, the process solves the competition for organic substrate among Poly-p organisms and denitrifies as well as the problem of overgrowing of slow nitrifiers by fast organotrophs. An experimental lab-scale A2N system fed with domestic sewage was tested over a period of 260 days. The purpose of the experiment was to examine phosphorus removal capacity of a modified A2N two-sludge system. Factors affecting phosphorus and nitrogen removal by the A2N system were investigated. These factors were the influent COD TN ratio. Sludge Retention Time (SRT), Bypass Sludgy Flow rate (BSF), and Return Sludge Flow rate (RSF). Results indicated that optimum conditions for phosphorus and nitrogen removal were the influent COD/TN ratio around 6.49, the SRT of 14 days, and the BSF and RSF were fixed about 26%-33% of inffuent flow rate.