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The continuous aerobic granular sludge (AGS) process is promising for upgrading existing wastewater treatment facilities. However, this approach is still challenging because of its complicated structure and operation. To address this issue, a novel separate aeration self-circulating technology (abbreviated as Zier) was proposed, which is promising for cultivating AGS by its outstanding upflow velocity and circulation multiplier (more than 30 m/h and 200, respectively). This study elaborated on the Zier reactor's feasibility, optimization, and control strategy through computational fluid dynamics simulations, theoretical calculations, and experiments. An appropriate flow regime for efficient removal of pollutant and granulation of sludge was attained at a superficial gas velocity of 1.3 cm/s. Moreover, optimizing the aeration column diameter to half of the reaction column and increasing the height/diameter ratio to 20 dramatically boosted the nitrogen removal capacity over 1.6 kg N/m 3 /d. Utilizing a smaller circulation pipe diameter ensured granulation under a consistent flow regime. By judiciously regulating, multiple CSTRs and PFRs seamlessly integrated within the Zier reactor across a broad spectrum of particle sludge. The validity of these findings was further substantiated through experimental and theoretical validations. Drawing from these findings, a multi-scenario control strategy was proposed as Zier's map. With all the superiorities shown by the Zier reactor, this study could offer new insights into an efficient continuous AGS process., 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.)

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.)

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/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 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.

A modification of the two sludge A 2 /O-BAF system was used to treat low C/N real domestic sewage. In order to improve the utilization of the carbon source, the effects of two step feeds (pre-anoxic zone and anoxic zone) on denitrifying phosphorus and nitrate removal were studied. According to the formula of material balance for COD, the utilization of carbon source was analyzed and evaluated under different ratios of step feed, simultaneously. The results showed that when the ratio of step feed was 7:3 and the influent concentrations of COD, NH 4 + -N, TN, and TP were 174.99, 58.19, 59.10, and 5.15 mg·L -1 , respectively, their effluent concentrations were 29.48, 4.07, 14.10, and 0.40 mg·L -1 , and the removal rates were 82.12%, 92.76%, 75.45%, and 91.20%, respectively. It was found that when the ratio of the denitrifying phosphorus accumulation organisms to the phosphorus accumulation organisms(DPAOs/PAOs) was 98.81%, the efficiencies of denitrifying phosphorus and nitrate removal were optimum. By optimizing step feed, the carbon source was utilized effectively, and the efficiencies of nitrogen and phosphorus removal were improved simultaneously. The theoretical basis has thus been provided for the modification of the two sludge A 2 /O-BAF system to treat low C/N waste water.

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 performance of denitrifying phosphorus removal under nitrification and nitritation was investigated in a lab-scale Modified University of Cape Town (MUCT) process treating real domestic wastewater with low C/N ratio. The experimental results of 180 days showed that nitritation was achieved at short hydraulic retention time (HRT) and low dissolved oxygen (DO) of 0.3-0.5 mg x L(-1), and an average nitrite accumulation rate (NAR) of above 70% was achieved during nitritation stage. The MUCT process showed a good performance of denitrifying phosphorus removal. Under nitritation mode, total and denitrifying phosphorus removal efficiencies were 90% and 91%, respectively; under nitrification mode, total and denitrifying phosphorus removal efficiencies were 60% and 88%, respectively. Although phosphorus removal performance under nitritation was better than that under nitrification, the results of fluorescence in situ hybridization (FISH) indicated that the percentage of phosphorus accumulating organisms (PAOs) in biomass was about 37% under two modes. The effluent COD concentration was below 50 mg x L(-1) during the experimental period. Batch tests of different nitrifying sludges showed that the percentage of denitrifying phosphorus removal bacteria (DPBs) in PAOs using NO2(-)-N as an electron acceptor under nitritation mode was almost the same as that using NO3(-)-N as an electron acceptor under nitrification mode, with an average percentage of 38%. Compared with nitrification mode with conventional phosphorus removal, nitritation mode with denitrifying phosphorus removal has a superior performance treating limited carbon source wastewater.

The granulation of activated sludge was investigated using two parallel sequencing batch reactors (SBRs) operated in biological nitrogen and phosphorus removal conditions though the reactor configuration and operating parameters did not favor the granulation. Granules were not observed when the SBR was operated in biological nitrogen removal period for 30d. However, aerobic granules were formed naturally without the increase of aeration intensity when enhanced biological phosphorus removal (EBPR) was achieved. It can be detected that plenty of positive charged particles were formed with the release of phosphorus during the anaerobic period of EBPR. The size of the particles was about 5-20 μm and their highest positive ζ potential was about 73 mV. These positive charged particles can stimulate the granulation. Based on the experimental results, a hypothesis was proposed to interpret the granulation process of activated sludge in the EBPR process in SBR. Dense and compact subgranules were formed stimulated by the positive charged particles. The subgranules grew gradually by collision, adhesion and attached growth of bacteria. Finally, the extrusion and shear of hydrodynamic shear force would help the maturation of granules. Aerobic granular SBR showed excellent biological phosphorus removal ability. The average phosphorus removal efficiency was over 95% and the phosphorus in the effluent was below 0.50 mg L(-1) during the operation., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Limited filamentous bulking under low dissolved oxygen (DO) is a new technology for energy saving and high quality effluent. In order to investigate the feasibility of this technology, four sequence batch reactors (SBRs) were occupied to operate at different regimes to stimulate different processes under low DO (0.5 mg/L). Sludge settleability, floc structure, pollutant removal and aerated energy consumption were investigated. The results showed that limited filamentous bulking under low DO was hard to realize in the single-stage aerobic reactors for they were prone to bulking severely, while it could be achieved stably in the pre-denitrification reactors when the feed length was between 60 and 90 minutes. Compared with normal sludge at the same DO, limited filamentous bulking sludge acquired by low DO displayed its high energy-saving effect. In addition, the specific ammonia consumption rate of limited filamentous bulking sludge was about 2 times higher than the one of normal sludge. On the contrary, the total nitrogen removal efficiency was lower. Further analysis indicated that stable limited sludge bulking could be achieved in a good alternative anoxic/anaerobic/aerobic condition without too high organic loading.

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.

A lab-scale anaerobic-anoxic-aerobic (A(2)O) process was operated to investigate denitrifying phosphorus removal and nitritation-denitritation from domestic wastewater, especially regarding the impact of nitrite accumulation caused by nitritation on phosphorus removal. The results showed that mean total nitrogen (TN) removal was only about 47% and phosphorus removal was almost zero without the pre-anoxic zone and additional carbon source. Contrastively, with configuration of pre-anoxic zone, TN and phosphorus removal was increased to 75% and 98%, respectively, as well as denitrifying phosphorus removal of 66-91% occurred in the anoxic zone. Nitritation-denitritation was achieved through a combination of short aerobic actual hydraulic retention time and low dissolved oxygen levels (0.3-0.5 mg/L); however, phosphorus removal deteriorated with increase of nitrite accumulation rates. The free nitrous acid (FNA) concentration of 0.002-0.003 mg HNO(2)-N/L in the aerobic zone inhibited phosphorus uptake, which was major cause of phosphorus removal deterioration. Through supplying the carbon sources to enhance denitrification and anaerobic phosphorus release, nitrite and FNA concentrations in the aerobic zone were reduced, and phosphorus removal was improved. Compared with nitrification-denitrification, nitritation-denitritation reduced the carbon requirement by 30% and performed biological nutrients removal well with mean TN and phosphorus removal of 85% and 96%, respectively., (Copyright © 2010 Elsevier Inc. All rights reserved.)

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.

At normal temperature, short-cut nitrification and denitrification was achieved in a lab-scale A2O process treating low C/N ratio domestic wastewater by controlling DO concentration of 0.3-0.5 mg/L and increasing the internal reflux ratio to decrease the actual aerobic HRT. However, the phosphorus removal in A2O process was deteriorated with the increasing of the nitrite concentration in the effluent. The factors causing phosphorus removal deterioration, such as the influent COD concentrations, temperature, pH and free nitrous acid (FNA) were systematically analyzed. Experimental results showed that the nitrite accumulation resulting from short-cut nitrification affected anaerobic P release and aerobic P uptake. Especially, the higher FNA concentration (HNO2-N 0.002-0.003 mg/L) in the aerobic zone significantly inhibited the aerobic P uptake, which was the major reason causing P removal deterioration. Through adding the carbon sources in influent to enhance anaerobic P release and denitrification, the nitrite and FNA concentrations in the aerobic zone were decreased, and the P removal was recovered. More than 96% of PO4(3-) -P could be removed in A2O process.

In order to characterize the dense and regular level of aerobic granular sludge (AGS) which was cultivated by different carbon sources, the SEM images of mature AGS were used in the study. The calculation process using Photoshop and Fips2 on fractal characteristics of these granules was built. The lowest box-counting dimension was bulking aerobic granular sludge cultivated by glucose (No. 1), which was 1.794 +/- 0.011; the box-counting dimension of AGS cultivated by peptone (No. 3) and domestic sewage (No. 5) were reached up to 1.866 +/- 0.018 and 1.880 +/- 0.015. The boundary box-counting dimension of the AGS was also calculated and the average value was 1.14. The AGS cultivated by beer (No. 6) was more regular in shape and the boundary box-counting dimension was 1.115 +/- 0.003. The AGS cultivated by landfill leachate (No. 7) was the most irregular in shape. This study indicates that fractal dimension provides an approach for quantification of dense and regular level of AGS, furthermore, it could be used to characterize the status of AGS, such as bulking.

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.

Nitrite and nitrate have been generally recognized to have an inhibitory effect on metabolism of denitrifiers. The nitrite inhibition on nitrate reduction under various pH conditions and the cross effect of the both electron acceptors on each other were investigated through a series of batch tests by using a biological nutrient removal (BNR) sludge. The results showed that the nitrate reduction activity had a much stronger relationship with the free nitrous acid (FNA) than that of nitrite concentration, suggesting that FNA, rather than nitrite is likely the actual inhibitor on nitrate reduction. Sixty percent inhibition of nitrate reduction was observed at an FNA concentration of 0.01-0.025 mg x L(-1), while total inhibition occurred when the FNA concentration was greater than 0.2 mg x L(-1). Furthermore, nitrite reduction by the BNR sludge was also found to be inhibited by HNO2. The reduction rate decreased by approximately 80% when the FNA concentration was increased from 0.01 mg x L(-1) to 0.2 mg x L(-1). The inhibitory effect of nitrate on nitrite reduction was found to be insignificant, with the most recovery rates under different nitrate concentrations larger than 90%. However, the nitrate reduction rate was observed to recover only 3.04%-72.54%. The recovery rate from inhibition was independent of the duration of the inhibition and the feeding mode of inhibitor, but strongly dependent on the concentration of inhibitor the biomass was exposed to during the inhibition period.

The secondary effluent of three WWTPs was treated by ozonation to investigate organic biodegradability enhancement. The bulk experimental method was used. Ozone adding dosage was controlled to be 2, 4, 6, 8, 10 mg/L by adjusting the adding time. Results showed, UV254 and SUVA(UV254/DOC)decreased with the increasing of the ozone dosage. When ozone adding dosage was 6 mg/L, UV254 and SUVA decreased about 54.4% and 56.6% respectively; while BOD5/COD, BDOC and BDOC/DOC were improved above 30%, 360% and 360% respectively. It could be concluded that suitable ozonation could improve the biodegradation of the organic substances in the secondary effluent. The organic substance was analyzed by the excitation-emission matrix (EEM) to investigate the variation regularity of organic matter changes of the ozoned and non-ozoned secondary effluent. The main organic substances of the secondary effluent in the plant were aromatic protein like substances and humic substances, ozone could significantly remove these types of organic substance.

Aerobic sludge granules with compact structure, wide diverse microbial species and excellent settling capabilities have drawn interest of researchers engaging in work in the area of biological wastewater treatment. This review provides recent advances on aerobic biogranulation technology and application. Granulation mechanism, characteristics and its microbial phase, influence of different environmental factors, granulation model and its application in treating the municipal and toxic industrial wastewater were discussed. Then a prospect concerned for future research is also put forward.

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.

Nitrite accumulation during the denitration process with SBR treating pre-treated by anoxic/anaerobic up-flow anaerobic sludge bed (UASB) was observed at low temperatures. The effects of types of carbon sources on nitrite accumulation were investigated for comprehensive understanding the mechanism of nitrite accumulation. Experimental results clearly showed that nitrite accumulated obviously when five carbon sources (methanol, ethanol, sodium acetate, sodium propinoate and glucose), except for glucose, were used as electron donor. Additionally, nitrite accumulations were observed at four different initial nitrate concentrations and lower temperatures. The maximum concentrations of nitrite accumulation were 37.8, 21.5, 25.2 and 18.8 mg/L, respectively, and the corresponding nitrite accumulation rates (N/VSS x t) were 0.117, 0.136, 0.235 and 0.068 g/(g x d) during the nitrite accumulation period. Two break points of "nitrate knee" and "nitrite knee" on oxidation reduction potential (ORP) profile indicated that the reduction reactions of nitrate and nitrite were completed, respectively.

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.

SBR reactor was performed to incubate polyphosphate accumulating organism (PAO), and it was checked out of the system by fluorescence in situ hybridization. As PAO is a kind of ordinary heterotrophic bacteria, it was excluded the ability of phosphate release and uptake and it was considered only the capacity of denitrification of the target biomass. The results indicated that acetate and PHB can be the electron donors of PAO to denitrify. When fed with acetate, the denitrifying rate and PHB producing rate were independent of initial nitrate concentration. However, served as more nitrate in the reactor, it would be less PHB produced and fewer nitrate reducing when using same amount of acetate. In view of PHB stored as an internal carbon and energy source, it presented as a reaction of zero-order to the substrate by PAO to denitrify, such as nitrate, besides, the specific denitrifying rate was 0.9733 mg/(g x h) and the specific PHB consuming rate was 2.4626 mg/(g x h).

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.

A SBR was used in this study for investigating the influence of carbon source on EBPR metabolism and microorganism communities when feeding with acetate and propionate. The SBR was operated with a cycle time of 8 h and each cycle consisted of 4 min feeding, 2 h anaerobic period, 5 h aerobic period, 35 min setting, 15 min decanting and 6 min waiting. The COD of influent was kept at 300 mg/L during the experiment. Acetate and propionate were used as the sole carbon source for operation of 60 days, respectively. The phosphorus release/ COD consumption in the end of anaerobic phase were 0.35 and 0.27 when acetate and propionate were used as the carbon source, respectively. The PHA composition was different when different carbon source was dosed. PHB accounted for 92.6% in the end of anaerobic phase but the value for PHV was only 7.4% when acetate was selected as the carbon source. No PH2MV was detected during this process. The compositions of PHA were PHB (10.2%), PHV (35.8%) and PH2MV (54.0%) in the end of anaerobic cycle when propionate was used as the sole carbon source. There was variation of microorganism communities during this process for the results of DGGE combined with SEM micrographs and PHA staining. Coccus morphotype PAOs were accumulated in acetate-fed phase and rod morphotype PAOs were accumulated in propionate-fed stage. Different PAOs were accumulated and the metabolic pathways were different when different carbon sources were used, but good EBPR could be achieved during all these conditions.

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.

The affecting factors and controlling methods of how realizing and maintaining half-nitrosofication of dewatering liquid of digested sludge were investigated in an A/O process. The experimental results showed that the nitritation was obtained in 29 d under bulk liquid temperature of 9-20 degrees C, average DO of 5.4 mg/L, SRT of about 30 d and influent ammonia loading rate of 0.64 kg/(m3 x d). The nitritation with 70% nitrite accumulation efficiency was maintained during 65 d when average FA concentration in A/O reactor was more than 4 mg/L. Furthermore, the half-nitrosofication with effluent ammonia and nitrite ratio of 1:1.32 was obtained. When the ammonia loading rate reduced to 0.19 kg/(m3 x d) (FA < 1 mg/L), the nitritation disappeared, and the high FA as a main factor of maintaining half-nitrosofication was proved again with FISH under the condition of different FA. TN removal concentration was about 91 mg/L under influent COD of 282 mg/L and raw C/N ratio of 0.85 in the A/O system, which due to nitritation saving much carbon sources. The study showed that the half-nitrosofication of the dewatering liquid was obtained and stably maintained when FA was more than 4 mg/L in the A/O reactor by dynamic controlling influent ammonia loading rate and pH value in the system under middle or low temperature, high DO, long SRT.

At normal temperature of 19 degrees C +/- 1 degree C and seed sludge from the system of conventional nitrogen removal via nitrate composed of both ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB), the competition and optimization of AOB and NOB was investigated in a lab-scale SBR treating domestic wastewater. The reactor was operated under the aeration rate of 40 L/h with the average DO concentration below 1.0 mg/L, and combined with the control of aeration time, i.e., aeration was stopped before the pH "ammonia valley" was detected. After AOB became pre-dominant nitrifying bacteria (nitrite accumulation rate NO2(-)-N/NOx(-)-N reached 50%), the aerobic durations were gradually prolonged from 3 h to 4 h and 5 h to improve the ammonia removal efficiencies and enhance AOB dominant. By the above operational pattern, nitrogen removal via nitrite was successfully achieved with NO2(-)-N/NOx(-)-N over 95%. Fluorescence in-situ hybridization (FISH) analysis showed that AOB was accounted for 9.97% of total biomass. The on-line control of aerobic duration was an effective method to maintain the partial nitrification and the NH4(+)-N removal efficiency was above 97%. The research results also proved that at normal temperatures, for the seed sludge from the conventional nitrogen removal via nitrate, AOB would not become dominant nitrifying bacteria only by the aeration time control without the DO restriction.

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.

In order to treat the digested sludge dewatering liquor bypass and reduce influent ALR of wastewater treatment plant, the startup and maintenance of nitritation was investigated in an A/O reactor. NOB activity was inhibited and nitritation was stated up successfully by increasing the influent ALR (in N, the same below) step by step from 0.23 kg/(m3 x d) to 0.78 kg/(m3 x d), in spite of normal temperature, long SRT and high DO concentration. Due to the deficiency of alkalinity in influent, nitritation could be maintained steadily by the associated inhibition of free ammonia (FA) and free nitrous acid (FNA). The nitrite accumulation ratio always kept at above 90% during the period of maintaining nitritation for 30 days, and correspondingly the average concentration of DO was higher than 2 mg/L. The nitrite accumulation ratio did not decline even if the average DO concentration increased to 4.8 mg/L, which demonstrated that high DO could not destroy the nitritation built by the associated inhibition of FA and FNA. The concentration of FNA at the last chambers was increased by reducing the influent ALR in order to enhance the inhibition of FNA. The nitritation was still maintained for two months although the inhibition of FA was weakened. But the nitritation was destroyed completely in 3 days after the inhibition of FNA was eliminated, which showed the inhibition of FNA to NOB was very critical to maintain steadily nitritation.

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.

It is essential for a full-scale treatment plant processing saline wastewater to understand the effects of salt on an activated sludge system and the performance of pollutant removal. For this purpose, a bench-scale modified university of cape town (MUCT) process was tested to treat real saline sewage with salt concentrations of 5, 8, 10 and 15 g/L. The experimental results indicated that salt in sewage significantly affected nutrient removal compared with organic removal. Total phosphorous removal efficiency in MUCT deceased from 92% when treating freshwater to 72% when treating 8 g/L saline wastewater, while total nitrogen removal efficiency decreased from 75% to 62%. Vital number of aerobic heterotrophic bacteria shrunk when salt concentration in wastewater was over 15 g/L, resulting in decreased organic removal efficiency. Obvious nitrite accumulation in the aerobic tank and denitrifying nitrite by polyphosphate accumulating organisms (PAOs) in the anoxic tank occurred in the MUCT treating saline sewage containing over 8 g/L NaCl. Elevated salt level enhanced the carbon requirement for phosphorus release. Population shift in biological community (aerobic-heterotrophic, nitrifying, and denitrifying organisms) in treatment system was observed in response to salinity inhibition, which contributed to an insight into the nature and the magnitude of the salt effects.

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.

Preliminary studies had been conducted to determine the correctness of the theory and technique of energy saving achieved by limited filamentous bulking under low DO using a lab-scale A/O reactor with real domestic wastewater as the influent. The results showed that SVI could be maintained 150-230 mL/g and sludge settleability would not become very poor under the condition of low DO. During the period of limited filamentous bulking, COD and total nitrogen removal efficiencies were improved, and distinct simultaneous nitrification and denitrification (SND) was achieved, while ammonia removal efficiency would slightly decline with decreasing of DO, compared with the period of good settleability sludge under high DO. COD, ammonia and total nitrogen removal efficiencies were 86%, 70% and 63%, respectively. It was found that about 10%-25% nitrogen would be removed by SND based on the mass balance of nitrogen. Besides, SS in the effluent was almost negligible and the effluent turbidity was lower than 3 NTU. Significantly, aeration consumptions would be decreased by 17% under the condition with DO of 0.5 mg/L compared with 2.0 mg/L according to theoretical calculation of air requirements to keep different DO levels, which was about 57% in lab-scale reactor correspondingly.

How to prevent and control filamentous bulking sludge has being a research focus and attracted much attention. To date despite the extensive research that has been done on bulking sludge, filamentous bulking still occurs world-wide and a comprehensive solution does not seem to be available. Particularly, there are few studies about making use of the characteristics of filamentous bacteria and achieving energy saving by filamentous bulking. Limited filamentous bulking, a novel method for energy saving while equal or better treatment performance by allowing slight and controlled filamentous bulking sludge at low dissolved oxygen (DO), was proposed based on full-scale field observations. The practical operation showed that limited filamentous bulking resulted from a decline in DO concentration. COD, SS and TP removal could be enhanced and energy saving could be achieved by limited filamentous bulking at low DO. The derivation of limited filamentous bulking is introduced firstly, and then the theoretical fundamentals of the technique of limited filamentous bulking are presented and analyzed, including the occurrence of limited filamentous bulking caused by low DO, the enhanced effect of filamentous bacteria on pollutants removal and the energy saving mechanism by using limited filamentous bulking. Besides, the paper provides some new perspectives about the application and research direction of limited filamentous bulking in future.

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.

To discuss the characteristics of effluent organic matter (EfOM) from biologically treated sewage effluent, the impact of pH value on SBR was originally evaluated with an artificial wastewater. The results revealed that dissolved organic matter (DOM) from SBR was greatly influenced by pH value. When pH value of the SBR with original pH of 6.5 was decreased to 6.0, DOC of its effluent gradually increased from its original 4.0 mg x L(-1). Further increasing pH can alleviate this increase. For the SBR with original pH of 8.0, DOC of effluent decreased rapidly from its original 4.0 mg x L(-1) to 2 mg x L(-1), while further decreasing pH to 6.5 did not affected this. Tannin and soluble microbial products (SMPs) including protein, carbohydrate and DNA consist to the main part of DOM in the sewage effluent. The pH value had a long-term impact on the formation of SMPs. Decreasing pH will result in its gradual increase. The impact of pH value on anaerobic process dominated the DOM degradation during the operation period. Higher pH value was helpful for the degradation of DOM.

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 improve A/O process denitrification efficiency, five integrated control strategies of nitrate recirculation flow and external carbon dosage for denitrification were proposed and evaluated using the COST/IWA simulation Benchmark. Results show that control strategy No.1 is the best integrated control strategies from both external carbon consumption, effluent quality, and the stability of controller. It comprises two feedback control loops: one is to determine the flow rate of external carbon source, keeping the nitrate concentration at the end of anoxic zone at a pre-specified level 2 mg/L, and the other is to adjust the flow rates of the nitrate recirculation to keep the nitrate concentration at the end of the aerobic zone at a pre-specified level based on the effluent quality (usually 8-12 mg/L). This strategy can guarantee highly effective use of anoxic denitrification capacity in the low-load condition, and meet effluent discharge standards through carbon dosage in the high-load condition.

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)

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.