[Microbial Diversity of Filamentous Sludge Bulking at Low Temperature].

To investigate the characteristics of microbial diversity during filamentous bulking at low temperature, the induction of sludge bulking was successfully carried out using a low-temperature sequencing batch reactor(SBR). With the help of Illumina MiSeq high-throughput sequencing technology, the overall changes in the microbial community structure of activated sludge, the characteristics of each specific microbial community, and the specific genera were all investigated under different sludge sedimentation performances. The results showed that filamentous bulking can be successfully induced after the system operating temperature drops to (14±1)℃, and the COD and TN removal rates can still be maintained at approximately 90% and 86%, respectively, with the sludge volume index deteriorating to 663.99 mL·g-1. The occurrence of sludge bulking at low temperature will not only reduce the overall diversity and uniformity of microorganisms in the system and increase the abundance of filamentous bacteria from 0.49% to 26.04% but also cause the abundance of denitrifying bacteria to reduce from 21.04% to 13.99% and that of dephosphorization bacteria to reduce from 4.25% to 1.93%. Of the five filamentous genera founded, the abundances of three filamentous bacteria represented by Thiothrix increased, whereas only that of the Haliscomenobacter decreased. Of the 19 denitrifier genera founded, the abundances of five species represented by Nitrosomonas increased, whereas those of seven species represented by Nitrospira decreased. Moreover, the abundances of Pseudomonas and Tetrasphaera increased out of the eight phosphorus-removing bacteria genera, whereas the abundances of the five bacteria genera represented by Candidatus_Competibacter decreased. Although sludge bulking has a significant impact on the structure of the microbial community, the 477 operational taxonomic units and 227 bacterial species that are always present in the different sludge samples indicate that the main microorganisms in the reactor are still relatively stable during the bulking process.

[Effect of Step Feed on Denitrifying Phosphorus and Nitrate Removal in a Modification of the Two Sludge A2/O-BAF System].

A modification of the two sludge A2/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, NH4+-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 A2/O-BAF system to treat low C/N waste water.

[Denitrifying phosphorus removal in a Modified University of Cape Town (MUCT) process treating domestic wastewater under nitrification and nitritation].

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.

Understanding the granulation process of activated sludge in a biological phosphorus removal sequencing batch reactor.

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.

Denitrifying phosphorus removal and impact of nitrite accumulation on phosphorus removal in a continuous anaerobic-anoxic-aerobic (A2O) process treating domestic wastewater.

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.

[Optimization of a modified UCT step feed process treating municipal wastewater].

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.

[Effect of internal recycle ratio on nitrogen and phosphorus removal characteristics in A2/O-BAF process].

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).

[Effect of nitrite accumulation on enhanced biological phosphorus removal (EBPR) in A2O process treating domestic wastewater].

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.

[Formation and reaction mechanism of simultaneous nitrogen and phosphorus removal by aerobic granular sludge].

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.

Enhanced biological phosphorus removal by granular sludge: from macro- to micro-scale.

In this study, phosphorus accumulating microbial granules were successfully cultivated in a sequencing batch reactor (SBR) using synthetic wastewater. The average diameter of the granules was 0.74 mm and the diameter distribution fitted well with normal distribution with a correlation coefficient of 0.989. Good performance of biological phosphorus removal (BPR) was obtained in the granular system. The average phosphorus removal efficiency was over 94.3% and the level of phosphorus in the effluent was below 0.50mg/L during 300 days of operation. Particle analysis showed that positive charged particles were formed with the release of phosphorus in the anaerobic stage. These particles served as the cores of granules and stimulate the granulation. The maturated granules had a well-formed micro-pore structure with an average pore width between 291.5 nm and 446.5 nm. The spatial distribution of phosphorus decreased gradually from the surface to the center of the granules. Smaller granules had a higher specific area, pore width and phosphorus removal activity than bigger granules.

[Effects of COD/TN and HRT(s) on nutrients removal by an alternating anoxic/oxic CAST].

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.

[Autotrophic nitrogen removal and enhanced biological phosphorus removal from municipal wastewater in a three-sludge system].

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.

[Optimization effect of nitrogen and phosphorus removal in unifed SBR process for domestic wastewater].

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.

[Modified step-feed A/O biological nitrogen removal process for enhanced phosphorus removal].

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.

[Influence of carbon source on EBPR metabolism and microorganism communities].

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.

[Salt effects on treatment performance and microbial community structure in MUCT].

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.

[Influence of carbon source on biological nutrient removal in A2O process].

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.

[Inhibitory effect kinetics of nitrite acting as electron acceptor on anoxic phosphorus uptake and denitrification].

Nitrite has been found in previous research an inhibitor on anoxic phosphorus uptake in enhanced biological phosphorus removal systems (EBPR). However, the inhibiting nitrite concentration reported varied in a large range and no kinetics study concerned on anoxic phosphorus uptake. This study investigates the nitrite inhibition on anoxic phosphorus uptake with sequencing batch reactor (SBR) in different concentrations of NO2- and under different pH gradient. The activated sludge was cultured with A2/O Oxidation Ditch pilot-scale reactor performing EBPR. The progress of SBR is as follows: the activated sludge was taken out an aerobic zone of the A2/O Oxidation Ditch to SBR, then phosphorus was released with acetate fed in anaerobic phase, subsequently phosphorus uptake proceeded with NO2- added in anoxic phase. It is pointed that not only NO2- but pH inhibited anoxic phosphorus uptake. The result indicated that (1) specific denitrification rate and specific phosphorus uptake rate correlated the original nitrite accord with Andrews's inhibition model under the constant pH. (2) If pH was in the range of 6.5 to 8.0, nitrite inhibited DPR much stronger when pH was less, vice versa. (3) Kinetics parameter was as follows: the max specific denitrification rate was 4.55 mg/(g x h), the half saturation constant of the denitrification process was 2.14 mg/L; and the max specific phosphorus uptake rate was 3.06 mg/(g x h), the half saturation constant of the phosphorus uptake process was 2.64 mg/L.

[Cultivation and characteristic of aerobic granular sludge enriched by phosphorus accumulating organisms].

This research focused on the enrichment of phosphorus accumulating organisms (PAO) and the formation of granular sludge simultaneously. After fed with flocculent sludge the SBR was run for two months for the cultivation of PAO. Then the granular sludge enriched by PAO was found. After that acetate was used instead of propionate to inhibit the glycogen accumulating organisms(GAO). The experiment testified that acetate was beneficial to the growth of the PAO granules. The system could release and take up more phosphorus when it was fed by acetate. Moreover, when the size of the granules became bigger, the performance indexes of the granules, for example the settling velocity, OUR, density, aquiferous rate and integral rate were also improved. On the other hand, the amount of PAO was found to become more and more in this process by the system performance evaluation and FISH analysis. As a result, the ratio of PAO could reach 70% of the total bacteria. The aerobic granular sludge enriched by PAO showed very good capability of COD and phosphorus removal. The COD removal efficiency could reach about 95% and phosphorus removal efficiency could reach almost 100%.

[Characteristics and affecting factors of denitrifying phosphorus removal in two-sludge sequencing batch reactor].

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.