N2O Emission and Hydroxylamine Oxidase (HAO) Activity in a Nitrogen Removal Process Based on Activated Sludge with Three COD/NH4+ Ratios.

This study dealt with nitrous oxide (N2O) emission and hydroxylamine oxidase (HAO) activity of waste sludge in a nitrification and denitrification process employing three carbon nitrogen (C/N) ratios in a sequencing batch reactor (SBR). The experimental results indicated that N2O emission increased dramatically after the C/N ratio in the sludge increased from 6.5 to 9.3, which was greater than the N2O emission at two other C/N ratios (3.5, 6.5). The HAO activity in the anoxic period was higher with all three C/N ratios than in the aerobic period. The results suggest that N2O was produced primarily in the aerobic period and the main source of the N2O emission resulted from denitrification by nitrifying bacteria and aerobic hydroxylamine oxidation. When a relatively deficient carbon source existed, the N2O emission under anoxic conditions was affected by the HAO activity and vice versa. When the HAO activity was relatively high, it was found that more N2O was released.

Condition optimization of iron-air fuel cell to treat phosphate-containing wastewater regarding sustainable development.

Increasing use of phosphorus products and excessive exploitation of phosphorus resources become two major problems in perspective of phosphorus sustainable development. Phosphorus recovery is the shortcut to solve this dilemma. Combining electrochemistry, an iron-air fuel cell was adopted to recover phosphate and electricity from phosphate-containing wastewater in our previous studies. The present study focused on investigating the effects of catholyte/anolyte conductivity, external resistance, and anolyte pH on the performance of iron-air fuel cell, and obtaining the optimized conditions. Furthermore, the electrochemical methods of phosphate recovery were compared and assessed, and it is concluded that iron-air fuel cell has great potential for energy recovery. The phosphate removal efficiencies and vivianite yield roughly positively correlated with the catholyte conductivity and the anolyte pH, but negatively correlated with the external resistance and the anolyte conductivity. The electricity generation roughly positively correlated with the catholyte conductivity and anolyte conductivity, but showed limitations in the test range of anolyte pH and external resistance. To pursue high phosphate removal efficiencies and vivianite yield, the catholyte conductivity, external resistance, anolyte pH and anolyte conductivity were suggested to be 35 g-NaCl/L, 10 Ω, 8 and 0 g-NaCl/L. While if electricity generation was the primary goal, these parameters should be 35 g-NaCl/L, 220 Ω, 5 and 70 g-NaCl/L. The optimized conditions will help to improve the phosphate removal efficiency, vivianite yield and electricity generation, and to promote the development of iron-air fuel cell technology.

Applying sheet iron to enhance the treatment efficiency of digested effluent with continuous flow and the corresponding mechanism.

Because of the unstable wastewater quantity and quality, the biological treatment efficiency of digested effluent was not as expected. A convenient and effective way was eagerly required to improve the efficiency of biological treatment. By sheet iron addition (R1), the COD and TN removal efficiencies under continuous flow condition increased by 59% and 37% respectively. The bulk pH maintained at around 7.5 which benefited most bacteria, while in the control (R0, without sheet iron addition) the pH decreased to 5.0. Both chemical and bio-removal of COD existed in R1, but the chemical removal dominated (63.71%). The enhanced COD removal efficiency came from the chemical oxidation by Fe3+ (47.43%) and Fe0 (10.86%). For the TN removal, the enhancement mainly came from the improvement of anammox activity by Fe3+ (14.87%), the bio-oxidation of ammonium with Fe3+ as electron acceptor (8.78%), and the bio-reduction of nitrate/nitrite with Fe2+ and H2 as electron donor (35.76%). By the first-order kinetic fitting analysis, the COD and TN removal rate in R1 was higher than that in R0. Thus, for a quick and high COD and TN removal from digested effluent, the addition of Fe0/Fe2+/Fe3+ was suggested, and the best form should be Fe0 (e.g., sheet iron). The addition of sheet iron reduces the cost of nitrogen removal and improves the efficiency of COD and TN removal. Comparing with the combined processes, this novel approach has potential advantages with simple operation and high efficiency. It endows the biological process much broader application in digested effluent treatment.

Analyzing the mechanism of nitrous oxide production in aerobic phase of anoxic/aerobic sequential batch reactor from the perspective of key enzymes.

How the vast majority of nitrous oxide (N2O) in the aerobic zone of nitrogen bio-removal process is produced is still a controversial issue. To solve this issue, this study measured the activities of two key denitrifying enzymes (nitric oxide reductase (Nor) and nitrous oxide reductase (N2OR)) in an A/O SBR with different chemical nitrogen demand (COD)/total nitrogen (TN) ratios. By analyzing the Spearman's correlations between the N2O production, the enzyme activities, and the factors, the main N2O production process was identified. By comparing the activities of these enzymes, this study analyzed the reasons for the N2O production. Results show that Nor activities had a linear relationship with total N2O concentrations (y = 0.34749 + 31.31365x, R2 = 0.83362) and were not affected by COD (r = 0.299, N = 15, P = 0.279 > 0.05), which showed that most of the N2O released and produced came from the autotrophic denitrification. N2OR activities had a positive correlation with COD (r = 0.692, N = 15, P = 0.004 < 0.01), which showed that heterotrophic denitrification played a role as an N2O consumer. Nor activities were much higher than N2OR activities and the gap between them increased when the total N2O concentration increased, showing that the heterotrophic denitrification was difficult to consume all the N2O produced by the autotrophic denitrification. Reducing autotrophic denitrification is the best way to reduce N2O production in aerobic phase.

An iron-air fuel cell system towards concurrent phosphorus removal and resource recovery in the form of vivianite and energy generation in wastewater treatment: A sustainable technology regarding phosphorus.

Phosphorous (P) recovery from industrial wastewaters solves both P deficiency and P pollution problems. A sequencing batch iron-air fuel cell was set up to recover P from synthetic wastewater containing 0.6 g-P/L Na2HPO4. In the cell, ferrous iron goes into the liquor from iron-anode to precipitate soluble P and form vivianite. Electrons travel from iron-anode to air-cathode through external circuit thus to generate energy. During 3 months' continuous operation, the P removal efficiency stably achieved at around 97.6%, and the average output voltage of cell was 404 mV. After long time operation, performance degradation of iron-air fuel cell was observed due to the electrode passivation caused by the accumulation of P precipitate on the iron-anode surface. The precipitate layer on the iron-anode impeded, but it did not block the mass transfer of ferrous iron to the anode liquor. The cell still worked with 25% decrease of output voltage, 86% decrease of current density, 87% decrease of power density and 9 times increase of internal resistance. Further analyses by XRD, FITR and Mössbauer illustrated that vivianite was the main component in both precipitates on the iron-anode surface and at the bottom of anode chamber with respective content of 66% and 30%. Vivianite on the iron-anode surface was a preferable choice due to higher content for P recovery. The iron-air fuel cell system could be a feasible option for achieving the multiple goals of P pollution control, resource recovery as vivianite, and energy generation, thereby contributing to the sustainable development of wastewater treatment.

[Operational Performance and Microbiological Characteristics of an Iron-Salt Denitrification Reactor in Co-substrate Mode].

When iron salt is used as an autotrophic denitrification electron donor, the high iron yield generated by oxidation is easy to precipitate, resulting in "iron encrustation" on the surface of denitrifying microorganisms, which inhibits their activity and even leads to their death. In order to solve the degradation of the efficiency of the autotrophic ferric denitrification reactor caused by the "iron encrustation" coating, this paper adopted the co-substrate mode to cultivate the ferric denitrification reactor; that is, a small amount of sodium acetate was added into the water of the reactor as an organic electron donor, to realize the efficient and stable operation of the ferric denitrification reactor. The results showed that adding an appropriate amount of organic matter could make the iron salt denitrification reactor run efficiently and stably, with an efficiency of up to 0.51 kg·(m3·d)-1, for more than 30 days. Heterotrophic bacteria could always be detected during the operation of the reactor in the co-substrate mode. Combined with the transmission electron microscopy (TEM) test results of the sludge, it was found that during the stable operation of the iron-salt denitrification reactor, heterotrophic bacteria were the main cause of iron-salt denitrification, and their unique iron-salt metabolism mode could effectively avoid the formation of iron encrustation. This study effectively solved the problem of microbial "iron encrustation" coating in the process of iron-salt denitrification, and will contribute to the development and application of autotrophic denitrification technology.

[Effect of Organic Characteristics on Sludge Settleability in an AAO System].

The effects of different mixed organic matter ratios on sludge settleability were examined from the succession patterns of microbial community structure, and changes of microbial intracellular and extracellular polymers in the activated sludge. The experimental results showed that when organic matter was dissolved in the influent, the sludge settleability was optimal (SVI=70 mL·g-1), which was better than that for influent water with partially dissolved organic matter (SVI=120 mL·g-1) and particulate organic matter (SVI=280 mL·g-1). According to the analysis of microbial community structure, Thiothrix, Chryseolinea, and Trichococcus were important in influencing the sludge settleability. Of these, particulate organic matter promoted the growth of Trichococcus, and dissolved organic matter promoted the growth of Thiothrix and Chryseolinea. In addition, changes in the bacterial community also had an important influence on the changes of intracellular and extracellular polymers, which either enhanced or impeded settleability. The higher the content of dissolved organic matter in the influent, the higher the storage of intracellular polymeric substances and, therefore, the better the sludge settleability. The sludge settleability was significantly negatively correlated with polysaccharides, proteins, and the Zeta potential in the LB-EPS.

[Effect of an Aerobic Unit and a Sedimentation Unit on Sludge and Nitrogen Removal in an Anoxic Unit in a Continuous-flow System].

Using an A2/O process with three dissolved oxygen (DO) levels[3.0-3.5 mg·L-1(Ⅰ stage), 2.0-2.5 mg·L-1(Ⅱ stage), 1.5-2.0 mg·L-1(Ⅲ stage)], the sludge and denitrification characteristics of its aerobic unit and sedimentation unit were investigated and compared with that of an anoxic-aerobic (A/O) process with a DO content of 1.5-2.0 mg·L-1. The results showed that denitrification in the sedimentation unit was accomplished with both internal and external carbon sources, but sludge's denitrification was more efficient with the use of external carbon sources. Nitrate reductase activity and denitrification activity in the sludge in sedimentation unit were highest when DO content was 1.5-2.0 mg·L-1 under aerobic conditions, and the denitrification efficiency of the A2/O process was greatest under anoxic conditions. The residual PHB in the aerobic A/O process was higher than that in the A2/O process with experimental sludge loading. The denitrification activity of the sludge in the A/O process was higher, and the nitrate reductase activity was 1.08 times higher than that in the A/O process. After returnning of the sludge, denitrification in the anoxic A/O process was poor, although the removal of nitrate nitrogen was sufficient. In comparison, denitrification in the anoxic unit of the A2/O process was better. Denitrification of the sludge in the sedimentation unit was directly related to denitrification in the anoxic unit. Therefore, to ensure that denitrification in sedimentation unit does not seriously affect the separation of sludge and water, appropriate control of the aerobic operation and the maintenance of denitrification in the sedimentation unit will contribute more to the denitrification efficiency of the system rather than simply controlling the level of anoxia.

[Effect of Microbial Community Structure and Metabolites on Sludge Settling Ability Under Three Different Switching Condition Processes].

Using sodium acetate as the carbon source, sludge settling ability (settleability) was investigated under three processes:AAO nitrogen and phosphorus removal(process Ⅰ), AO nitrification-denitrification (process Ⅱ), and aerobic carbon removal (process Ⅲ). The succession of microbial community structures in sludge was traced, the content and composition of microbial metabolites were monitored, and the effects of operational mode on sludge settleability were analyzed. The results showed that the settleability of process Ⅰ was the best, followed by process Ⅲ and Ⅱ. Under the different operating conditions, the dominant bacteria and microbial community structure of the system changed significantly. The relative amount of Thiothrix was the dominant bacteria affecting the sludge settleability. The abundances of Thiothrix were only 0.08% and 1.51% with fresh sludge and in process Ⅰ; this abundance increased to 9.41% in process Ⅱ and decreased to 4.29% in process Ⅲ. The anaerobic zone of process I had an inhibitory effect on the growth of the bacterium, while the anoxic zone of process Ⅱ stimulated its dominant growth. At the same time, comparison showed that the microbial population diversity was highest in process Ⅰ. followed by processes Ⅱ and Ⅲ. The introduction of anoxic and anaerobic zones led to the increase of system function and environmental complexity, and increased microbial community diversity. Analyses of extracellular polymeric substances (EPS) and fluorescence characteristics showed that the changes in microbial community structure had a significant effect on the composition and content of EPS, which aggravated the process of improving or deteriorating settleability. The sludge settleability was found to be positively correlated with the ratio of protein and polysaccharide in loosely bound EPS.

[Function of Polyphosphate Kinase Gene in Biological Phosphate Removal During the Wastewater Treatment Process].

This study aimed to identify the function of polyphosphate kinase gene (ppk) in phosphorus removal. With the Red system, the target DNA with the homologous short arms was amplified in the plasmid pKD4. Then the target DNA was transformed into E. coli ATCC25922 which already had the suicide plasmid pKD46 by electroporation. The plasmid pCP20 was transformed into the recombinant strains to delete the kanamycin resistance gene. With the screening by negative resistance, together with verification using positive and negative primers, the construction of ppk gene deletion strain E. coli/ppk- Kan- was confirmed. The growth characteristics of both the wild-type strain and the mutant strain were determined, and the phosphate accumulating characteristics were compared when cultured in the phosphate luxuriant medium after induced in the phosphate lacking medium. Also the phosphate accumulating characteristics of the two strains were compared after cultured in the anaerobic and aerobic alternating conditions for 5 times. The results showed that the ppk deletion strain E. coli/ppk- Kan- was successfully constructed. There was no growth difference between the mutant strain and the wild-type strain. But in the first 4 hours of log phase, the mutant strain grew faster than the wild-type strain. And 8h later, when both strains were in stationary phase, the mutant strain grew slower than the wild type, indicating that ppk affected the growth of the bacteria. Cultured in the phosphate lacking medium and the phosphate luxuriant medium, the mutant strain's ability of phosphate accumulating didn't decrease in spite of having no ppk gene. After 5 times induction, the amounts of phosphorus in both strains were about 1%-2%. The phosphate amounts in the cells did not increase with increasing inducing times. Polyphosphate or PHB was detected neither at anaerobic phase nor at the aerobic phase. It indicated that the deletion of ppk did not affect the phosphorus removal in wastewater treatment process, and the ppk gene did not show the function of phosphorus removal.

[Application of FCM-qPCR to Quantify the Common Water Pathogens].

In the past, fecal E. coli was always regarded as the indicator organism for estimation of pathogens in water. However, a weak relation between fecal E. coli and water viruses or bacterial pathogens has been demonstrated by previous studies. Therefore, for water pathogen study, it is essential to select and quantify typical pathogens. In this study, a combination of quantitative PCR ( qPCR) with flow cytometry (FCM) was established to detect the concentrations of viruses, bacteria and several typical pathogens (e.g., E. coli, Legionnella, HAdV, Giardia, Cryptosporidium) in water. The method was applied to measure the pathogen concentrations in the influent and effluent of a wastewater treatment plant (WWTP), as well as its receiving river. The results revealed that the WWTP treated the pathogens with high removal efficiency ( > 93%); the effluent of WWTP did not show a negative effect on pathogen concentration of the receiving river. The study provides a technical support for the evaluation of WWTP treatment effect and the ecological impact of WWTP effluent on receiving river.

[Achievement of Sulfate-Reducing Anaerobic Ammonium Oxidation Reactor Started with Nitrate-Reducting Anaerobic Ammonium Oxidation].

The transformation of nitrite-reducing anaerobic ammonium oxidation to sulfate-reducing anaerobic ammonium oxidation in an UASB was performed and the changes in microbial community were studied. The result showed that the sulfate reducing anaerobic ammonium oxidation process was successfully accomplished after 177 days' operation. The removal rate of ammonium nitrogen and sulfate were up to 58. 9% and 15. 7%, the removing load of ammonium nitrogen and sulfate were 74. 3 mg.(L.d)-1 and 77. 5 mg.(L.d)-1 while concentration of ammonium nitrogen and sulfate of influent were 130 mg.(L.d)-1 and 500 mg.(L.d)-1, respectively. The lost nitrogen and sulphur was around 2 in molar ratio. The pH value of the effluent was lower than that of the influent. Instead of Candidatus brocadia in nitrite reducing anaerobic ammonium oxidation granular sludge, Bacillus benzoevorans became the dominant species in sulfate reducing anaerobic ammonium oxidation sludge. The dominant bacterium in the two kinds of anaerobic ammonium oxidation process is different. Our results imply that the two anaerobic ammonium oxidation processes are carried out by different kind of bacterium.

[Application of FISH-NanoSIMS technique in environmental microbial ecology study].

With the development of microbial ecology techniques, it is possible to analyze the distribution and function of microorganisms simultaneously in complex ecosystems. To explore the application of FISH-NanoSIMS in environmental microbial ecology study, our study used the stable isotope labeled compounds 13C-C6H12O6, and 15N-NH4Cl as C and N sources for cultivating the pure culture (manganese oxidizing bacteria, Pseudomonas sp. QJX-1) and environmental samples (the shallow soil and anaerobic sludge). FISH-NanoSIMS was used to detect the distribution of microorganisms and relatively quantify secondary ions (12C-, 13C-, 12C(14)N-, 12C15N-) in cultivated samples, in order to explore the utilization of C and N isotopes sources by the pure culture and microorganisms in environment samples. The results showed that the contents of 13C and 5N in the area of bacteria were significantly greater than the natural abundance in all samples. It indicated that Pseudomonas sp. QJX-1 and some specific bacteria in environmental samples could metabolize 13C-C6H12O6 and 15N-NH4C1. Furthermore, this study revealed that for Pseudomonas sp. QJX-1, the manganese oxidation only occurred when the carbon and nitrogen were consumed to a low level. For environmental samples, the bacterial nitrification and denitrification were both observed in the shallow soil and anaerobic sludge. In a word, our study demonstrated that the combination of FISH and NanoSIMS could simultaneously examine microbial distribution and microbial metabolic activity in environmental samples, which will help us to obtain the eco-physiology information of microbial community.

Phosphorus metabolism and population dynamics in a biological phosphate-removal system with simultaneous anaerobic phosphate stripping.

In this study, the metabolism of phosphorus and changes in population dynamics were investigated via simultaneous chemical stripping in sidestream in an acetate-fed sequencing batch reactor. The synthesized intracellular polyphosphate (poly-P) by polyphosphate-accumulating organisms (PAOs) gradually decreased when the biomass was subjected to 83 d of P stripping. Initially, the P removal efficiency of the system improved from 94.3% to 96.9%. Thereafter, a relatively high level of P in effluent was observed, during which time the stoichiometric ratios of Prelease/HAcuptake decreased, Glycogendegraded/HAcuptake and poly-ß-hydroxyvalerate/PHA increased. The results revealed that a metabolic shift from polyphosphate-accumulating metabolism to glycogen-accumulating metabolism. Correspondingly, PAOs declined to less than 1% of the population, glycogen-accumulating organisms proliferated to almost 20% instead. The results of PCR­DGGE also indicated that the microbial community structure considerably changed in response to the gradually decreasing poly-P content. These findings imply that intracellular poly-P level is important for the stable of P removal system. Furthermore, it suggests that it is not a stable and effective way for P recycling from anaerobic stage of the biological P removal system in sidestream.

[Characterization of manganese oxidation by Pseudomonas sp. QJX-1].

A manganese-oxidizing bacteria (QJX-1) was isolated from the soil of a manganese mine. It was identified as Pseudomonas sp. QJX-1 by 16S rDNA sequencing. Experimental results showed that the Pseudomonas sp. QJX-1 has a multi-copper oxidase gene CumA, which is an essential component for manganese oxidation by Pseudomonas sp. Under the condition of low initial inoculum level (D600, 0.020), 5.05 mg x L(-1 Mn2+ could be oxidized by QJX-1 within 48 h with a conversion rate of as high as 99.4%. In comparison with the eutrophic conditions, the oligotrophic condition dramatically increased the biological manganese oxidation rate. Biofilm formation by employing the quartz sand could further improve the oxidation rate of Mn2+. Based on these results, it is speculated that biological manganese oxidation in underground water treatment is comparatively high.

[Influence of buffer solutions on the performance of microbial fuel cell electricity generation].

Microbial fuel cell (MFC) is a potential green technology due to its application in wastewater treatment and renewable energy generation. Phosphate buffer solution (PBS) has been commonly used in MFC studies to maintain a suitable pH for electricity generating bacteria and/or to increase the solution conductivity. However, it has some drawbacks using PBS in MFC: One is that the addition of a high concentration of phosphate buffer in MFCs is expensive, especially for the application in wastewater treatment; the other is that phosphates can contribute to the eutrophication conditions of water bodies if the effluents are discharged without the removal of phosphates. By adding PBS buffer as the comparison, the study investigated the effect of borax buffer and in the absence of buffer on the performance of electrical power, coulomb efficiency and effluent pH. 200 mmol/L PBS was the best, conductivity was 1.973 mS/cm,the maximum power density was 36.4 mW/m2 and the maximum coulomb efficiency was 2.92%, effluent pH was almost at (7.00 +/- 0.05). 100 mmol/L borax buffer solution, conductivity was 1.553 mS/cm; the maximum power density was 26.2 mW/m2 coulomb efficiency of 6.26%, which was 2.14 times to PBS and greatly increased the electron recovery efficiency with the effluent pH was (7.35 +/- 0.05). While free buffer solution conductivity was 0.314 mS/cm, maximum power density was 27.64 mW/m2; coulomb efficiency was 2.82% and the effluent pH of approximately 7.43. The electrolyte which in absence of buffer solution conductivity was 1/6 of adding PBS buffer, 1/5 of borax buffer, while its power density lower 8.76 mW/mr2 than adding PBS and higher 1.24 mW/m2 than borax buffer. The results showed that adding the suitable concentration of borax buffer may improve the electron recovery efficiency and under batch conditions, MFC run successfully without adding buffer solution to MFC.

[Enhanced biological phosphorus removal in single aerobic process].

When SBR with sodium acetate as the sole carbon source and operated under alternative anaerobic and aerobic condition had achieved a good performance in phosphate removal, it was shifted to completely aerobic treatment system, and found that a good phosphorus removal with removal efficiency of the highest of 73.9%, the lowest of 40% and an average of about 50% was still achieved. The phosphate removal could last 80 cycles before regeneration. Phosphate content of sludge in the SBR increased from 1.43% to 6.56%. PHB and glycogen in the sludge were 27 mg/g and 26 mg/g, respectively. Both of them in the sludge during the whole cycle were of slight variation. Based on analysis of carbon consumption and phosphate absorption as well as their relationship, it is considered that this enhanced biological phosphorus removal in single aerobic process is due to that, the sludge in the system can use ATP released from aerobic oxidation of sodium acetate after acclimation to condition of sodium acetate as the sole carbon to synthesize poly-P granule in cell to a certain content.

[Improvement of denitrifying dephosphatation in an anaerobic/anoxic sequencing batch reactor and its stability].

An anaerobic/anoxic sequencing batch reactor (A/A SBR) was conducted to investigate the conditions for screening and enrichment of denitrifying phosphorus removing bacteria (DPB). The results showed that, when the concentration of COD in influential of anaerobic stage, the concentration of NO3 -N in influent of anoxic stage and pH value were 300 mg/L, 50 mg/L and 7.0 respectively, DPB could become dominant populations quickly in the system in two-time feeding mode, and the reactor performed well for denitrifying phosphorus removal. The A/A SBR still performed well by shifting the system to one-time feeding mode. With the same concentration of phosphate of 20 mg x L(-1) in the influent, the phosphorus removal with adding the phosphate just before the beginning of anoxic stage proved to be better than that of directly increasing the phosphate concentration in the influent.

[Relationship between phosphorus content in activated sludge and sludge bulking in biological nutrient removal SBR systems].

In order to investigate the relationship among phosphorus content of sludge, filamentous bacteria and sludge settleability, two sets of Sequencing Batch Reactor (SBR) inoculated activated sludge that had different dominant filamentous bacteria and fed with synthetic wastewater were operated in A2/O process. Phosphorus concentration in influent was increased from 10 mg/L to 30 mg/L. Result showed that with increase of phosphorus in influent from 10 mg/L to 20 mg/L and 30 mg/L, phosphorus content of the sludge in reactor No. 1 was raised from 2.5% at early stage of inoculation to 8.17% and 9.23% correspondingly. SVI increased rapidly from 110 mL/g to 300 mL/g around and were about 135-150 mL/g subsequently. It is considered that improvement of settlement of sludge in the reactor No.1 was contributed to certain extent to the increase of phosphorus content in the sludge to 8% above. While in reactor No. 2 phosphorus content in its sludge was only raised from 1.89% to 6.77% and 6.95% correspondingly with increase of phosphorus in influent from 10 mg/L to 20 mg/L and 30 mg/L. SVI of the sludge increased from 138 mL/g to 190-320 mL/g, and finally kept at 280 mL/g to 300 mL/g. Settlement of sludge in the reactor No.2 wasn t improved by increase of the phosphorus content in sludge. The different performance of sludge in settlement between the two reactors is considered to due to existence of S. natans in the reactor No. 1 that was stimulated to conduct biological phosphorus removal resulting in an increase of dense of the sludge. In contrast, it was not so in the reactor No. 2. Whether or not sludge bulking can be controlled by increase of phosphorus content in activated sludge depends on the succession of predominant filamentous bacteria.

Promoting nitrification by using functional gel as immobilizing medium under different temperature stimulation patterns.

Nitrification with nitrifiers immobilized by temperature stimuli-responsive N-isopropylacrylamide-Chlorophyll (NIPA-CH) gel was investigated under several patterns of temperature stimulation, compared with that at constant temperature. The results show that in response to a cyclic temperature stimulus of 32-36 degrees C or 32-34 degrees C with a period of 4 or 2 h, respectively, the gel swelled and shrank reversibly and promoted biological nitrification. But in the case of a cyclic temperature change of 32-36 degrees C with a stimulation cycle of 2 h, nitrite oxidization declined. The results suggested that adequate stimulus facilitated substrate transfer into gels that promoted nitrification in the reactor, but quite frequent swelling and shrinking of the gel squeezed nitrifier out of the gel resulting in washing nitrifier out and declining nitrification. When gels that undergone cyclic temperature stimuli began to swell at 32 degrees C, oxygen consumption of nitrifiers in the gels was more than that of nitrifiers in the gels at constant temperature of 32 degrees C all the time, but when gels of two reactors shrank at 36 degrees C, their oxygen consumption reduced and there was almost no difference between them regardless of their undergone temperature stimuli once or not. Practical application of nitrifier immobilized by NIPA-CH gel in wastewater treatment was also discussed.