Influence of pH on short-cut denitrifying phosphorus removal

Through a series of experiments using denitrifying phosphorus-accumulating sludge in sequencing batch reactors （SBRs）, the variations of the intracellular polymers during the anaerobic phosphorus release process at different pH values were compared, the probable reasons for different performances of phosphorus removal were examined, and system operations in a typical cycle were investigated. The results show that the phosphorus removal rate was positively correlated with pH values in a range of 6.5-8.5. When the pH value was 8.0, the anaerobic phosphorus release rate and anoxic phosphorus uptake rate of the activated sludge were 20.95 mg/（g, h） and 23.29 mg/（g, h）, respectively; the mass fraction of poly-13-hydroxybutyrate （PHB） increased to 62.87 mg/g under anaerobic conditions; the mass fraction of polyphosphate was 92.67 mg/g under anoxic conditions; and the effluent concentration of total phosphorus （TP） was 1.47 mg/L. With the increase of pH, the mass fraction of acetic acid and PHB also increased, and the absorption rate of acetic acid was equal to the disintegration rate of polyphosphate. When the pH value was above 8.0, biological phosphorus removal was achieved by chemical phosphorus precipitation, and the phosphorus removal rate decreased.

Effect of carbon source and nitrate concentration on denitrifying phosphorus removal by DPB sludge

Effect of added carbon source and nitrate concentration on the denitrifying phosphorus removal by DPB sludge was systematically studied using batch experiments, at the same time the variation of ORP was investigated. Results showed that the denitrifying and phosphorus uptake rate in anoxic phase increased with the high initial anaerobic carbon source addition. However once the initial COD concentration reached a certain level, which was in excess to the PHB saturation of poly-P bacteria, residual COD carried over to anoxic phase inhibited the subsequent denitrifying phosphorus uptake. Simultaneously, phosphate uptake continued until all nitrate was removed, following a slow endogenous release of phosphate. High nitrate concentration in anoxic phase increased the initial denitrifying phosphorus rate. Once the nitrate was exhausted, phosphate uptake changed to release. Moreover, the time of this turning point occurred later with the higher nitrate addition. On the other hand, through on-line monitoring the variation of the ORP with different initial COD concentration, it was found ORP could be used as a control parameter for phosphorus release, but it is impossible to utilize ORP for controlling the denitrificaion and anoxic phosphorus uptake operations.

Optimization of denitrifying phosphorus removal in a predenitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system:Nitrate recycling,carbon/nitrogen ratio and carbon source type

Because the efficiency of biological nutrient removal is always limited by the deficient carbon source for the low carbon/nitrogen(C/N)ratio in real domestic sewage,the denitrifying phosphorus removal(DNPR)was developed as a simple and efficient method to remove nitrogen and phosphorous.In addition,this method has the advantage of saving aeration energy while reducing the sludge production.In this context,a pre-denitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system,which could also reduce high ammonia effluent concentration in the traditional two-sludge DNPR process,is proposed in this work.The pre-A_(2)NSBR process was mainly composed of a DNPR SBR and a nitrifying SBR,operating as alternating anaerobic/anoxic/post-aeration+nitrification sequence.Herein,the long-term performance of different nitrate recycling ratios(0-300%)and C/N ratios(2.5-8.8),carbon source type,and functional microbial community were studied.The results showed that the removal efficiency of total inorganic nitrogen(TIN,including NH4^(+)-N,NO_(2)^(-)-N,and NO_(3)^(-)-N)gradually increased with the nitrate recycling ratios,and the system reached the highest DNPR efficiency of 94.45% at the nitrate recycling ratio of 300%.The optimum C/N ratio was around 3.9-7.3 with a nitrogen and phosphorus removal efficiency of 80.15%and 93.57%,respectively.The acetate was proved to be a high-quality carbon source for DNPR process.The results of fluorescence in situ hybridization(FISH)analysis indicated that nitrifiers and phosphorus accumulating organisms(PAOs)were accumulated with a proportion of 19.41%and 26.48%,respectively.

Simultaneous denitrification and denitrifying phosphorus removal in a full-scale anoxic–oxic process without internal recycle treating low strength wastewater

Performance of a full-scale anoxic-oxic activated sludge treatment plant（4.0×10-5 m-3/day for the first-stage project） was followed during a year.The plant performed well for the removal of carbon,nitrogen and phosphorus in the process of treating domestic wastewater within a temperature range of 10.8℃ to 30.5℃.Mass balance calculations indicated that COD utilization mainly occurred in the anoxic phase,accounting for 88.2% of total COD removal.Ammonia nitrogen removal occurred 13.71% in the anoxic zones and 78.77% in the aerobic zones.The contribution of anoxic zones to total nitrogen（TN） removal was 57.41%.Results indicated that nitrogen elimination in the oxic tanks was mainly contributed by simultaneous nitrification and denitrification（SND）.The reduction of phosphorus mainly took place in the oxic zones,51.45% of the total removal.Denitrifying phosphorus removal was achieved biologically by 11.29%.Practical experience proved that adaptability to gradually changing temperature of the microbial populations was important to maintain the plant overall stability.Sudden changes in temperature did not cause paralysis of the system just lower removal efficiency,which could be explained by functional redundancy of microorganisms that may compensate the adverse effects of temperature changes to a certain degree.Anoxic-oxic process without internal recycling has great potential to treat low strength wastewater（i.e.,TN 〈 35 mg/L） as well as reducing operation costs.

Influence of carbon source and temperature on the denitrifying phosphorus removal process

To supply the valuable operating parameters for the popular usage of the new denitrifying phosphors removal process,it is essential to study the dominant biochemical reactions and the characteristics of denitrifying phosphorus removing bacteria(DPB).Thus,parallel batch experiments using DPB sludge were carried out to assess the effect of substrates(sewage,HAc,and endogenous carbon source)on denitrifying dephosphorus removal efficiency in this study.The results showed that the initial specific phosphorus release rate increased with the high concentration of the short-chain volatile fatty acids ratio in the influent,and sufficient phos-phorus was released by DPB.This improved the subsequent denitrification and phosphorus uptake efficiency.The specific endogenous denitrification mainly relies on the internal carbon source(PHB)stored by poly-P bacteria.Denitrifying phosphorus removing bacteria were very hungry when the internal PHB was consumed.Consequently,the specific endogenous denitrification rate was low and the phosphorus uptake did not happen.On the other hand,in the experiment,the denitrifying phosphorus removal performance under two temperature conditions(8-10°C and 25-26°C)was also investigated and analyzed.It was found that the lower temperature decreased the specific phosphorus release and uptake rate,but did not inhibit the denitrifying phosphorus removal completely.Therefore,the negative influence of the low temperature on the overall phosphorus removal was not significant.

Removal of nitrogen and phosphorus in a combined A^2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.

Effect of Return Sludge Pre-concentration on Biological Phosphorus Removal in a Novel Oxidation Ditch

A pilot-scale,pre-anoxic-anaerobic oxidation ditch was used in this study to treat municipal wastewater with limited carbon source.A novel return activated sludge(RAS) pre-concentration tank was adopted for improv-ing the phosphorus removal efficiency and the effects of RAS pre-concentration ratio were studied.Under the opti-mal operational condition,the suspended total phosphorus(STP) and the total phosphorus(TP) removal efficiencies were around 58.9% and 63.9% respectively and the effluent-P was lower than 0.8 mg·L-1.The reason is that with the optimal RAS pre-concentration ratio,nitrate is completely removed with endogenous carbon source and the secondary phosphorus release is strictly restrained in the pre-anoxic tank.Therefore,the anaerobic phosphorus release and the carbon source uptake by phosphorus accumulation organisms(PAOs) in the sludge,which are ex-tremely important to the phosphorus removal process,can be fully satisfied.Furthermore,the oxidation-reduction potential is proved to be suitable for controlling the RAS pre-concentration ratio due to influent fluctuation and varied conditions.The novel modified system is also beneficial for PAO accumulation.

Salt effect on MUCT system performance of nitrogen and phosphorus removal

The effect of salinity on biological nitrogen and denitrifying phosphorus removal was investigated in a Modified University of Cape Town(MUCT)system.Removal rates of COD,NH_(4)^(+)-N,NO_(3)^(-)-N,NO_(2)^(-)-N,phosphorus and the sludge characteristics at salt concentrations(0.0,3.2,6.4,11.2 and 16.0 g L^(-1))were analyzed.With the salt concentration increasing,all the COD,NH_(4)^(+)-N,TN and TP removal rates exhibited a trend of decline,and exhibited an initial reduction and subsequent increase at every stage of salt concentration.NH_(4)^(+)-N,TN and TP removal rates were 92.7%,51.5%and 67.2%in 16 g L^(-1) salt concentration,respectively.And they were outperformed the literature reported and acceptable in practical applications.When the salinity of wastewater changed from 0.0 to 16.0 g L^(-1),the biomass yield coefficients increased from 0.0794 to 0.126 g VSS/g COD.Increased salinity had a detrimental effect on phosphorus-accumulating organisms(PAOs)and denitrifying PAOs(DPAOs)(especially DPAOs).Therefore,phosphorus removal gradually depended on PAO.The simultaneous nitrification and denitrification(SND)rate and nitrogen removal rate(including nitrification rate,denitrification rate,and total nitrogen removal rate)gradually decreased with the increased salinity.

Identification and Metabolic Mechanism of Non-fermentative Short-cut Denitrifying Phosphorus-removing Bacteria

To investigate the characteristics and metabolic mechanism of short-cut denitrifying phospho- rus-removing bacteria （SDPB） that are capable of enhanced biological phosphorus removal （EBPR） using nitrite as an electron acceptor, an aerobic/anoxic sequencing batch reactor was operated under three phases. An SDPB-strain YC was screened after the sludge enrichment and was identified by morphological, physiological, biochemical properties and 16S rDNA gene sequence analysis. Denitrifying phosphorus-removing experiments were conducted to study anaerobic and anoxic metabolic mechanisms by analyzing the changes of chemical oxygen demand （COD）, phosphate, nitrite, poly-fl-hydroxybutyrate （PHB）, and glycogen. The results show that strain YC is a non-fermentative SDPB similar to Paracoccus denitrificans. As a kind of non-fermentative bacteria, the energy of strain YC was mainly generated from phosphorus release （96.2%） under anaerobic conditions with 0.32 mg P per mg synthesized PHB. Under anoxic conditions, strain YC accumulated 0.45 mg P per mg degraded PHB, which produced most of energy for phosphate accumulation （91.3%） and a little for glycogen synthesis （8.7%）. This metabolic mechanism of strain YC is different from that of traditional phosphorus-accumulating organisms （PAOs）. It is also found that PHB, a kind of intracellular polymer, plays a very important role in denitrifying and accumulating phosphorus by supplying sufficient energy for phosphorous accumulation and carbon sources for denitrification. Therefore, monitoring AP/APHB and ANO2 -N/APHB is more necessary than monitoring AP/ACOD, ANO2 -N/ACOD, or AP / ANO2 -N.

Operation of three parallel AN/AO processes to enrich denitrifying phosphorus removing bacteria for low strength wastewater treatment

Three parallel anaerobic-anoxic/anaerobic-aerobic （AN/AO） processes were developed to enrich denitrifying phosphorus removal bacteria （DPB） for low strength wastewater treatment. The main body of the parallel AN/AO process consists of an AN （anaerobic-anoxic） process and an AO （anaerobic-aerobic） process. In the AO process, the common phosphorus accumulating organisms （PAOs） was dominate, while in the AN process, DPB was dominate, The volume of anaerobic zone（Vana）：anoxie zone（Vano） ： aerobic zone （Vaer） for the parallel AN/AO process is 1：1：1 in contrast with a Vana：Vaer and Vano：Vaer of 1：2 and 1：4 for a traditional biological nutrient removal process （BNR）. Process 3 excels in the 3 processes on the basis of COD, TN and TP removal. For 4 month operation, the effluent COD concentration of process 3 did not exceed 60 mg/L; the effluent TN concentration of process 3 was lower than 15 mg/L; and the effluent TP concentration of process 3 was lower than 1 mg/L.

Characteristics of anoxic phosphors removal in sequence batch reactor

The characteristics of anaerobic phosphorus release and anoxic phosphorus uptake were investigated in sequencing batch reactors using denitrifying phosphorus removing bacteria （DPB） sludge. The lab-scale experiments were accomplished under conditions of various nitrite concentrations （5.5, 9.5, and 15 mg/L） and mixed liquor suspended solids （MLSS） （1844, 3231, and 6730 mg/L）. The results obtained confirmed that nitrite, MLSS, and pH were key factors, which had a significant impact on anaerobic phosphorus release and anoxic phosphorus uptake in the biological phosphorous removal process. The nitrites were able to successfully act as electron acceptors for phosphorous uptake at a limited concentration between 5.5 and 9.5 mg/L. The denitrification and dephosphorous were inhibited when the nitrite concentration reached 15 mg/L. This observation indicated that the nitrite would not inhibit phosphorus uptake before it exceeded a threshold concentration. It was assumed that an increase of MLSS concentration from 1844 mg/L to 6730 mg/L led to the increase of denitrification and anoxic P-uptake rate. On the contrary, the average P-uptake/N denitrifying reduced from 2.10 to 1.57 mg PO4^3--P/mg NO3^--N. Therefore, it could be concluded that increasing MLSS of the DEPHANOX system might shorten the reaction time of phosphorus release and anoxic phosphorus uptake. However, excessive MLSS might reduce the specific denitrifying rate. Meanwhile, a rapid pH increase occurred at the beginning of the anoxic conditions as a result of denitrification and anoxic phosphate uptake. Anaerobic P release rate increased with an increase in pH. Moreover, when pH exceeded a relatively high value of 8.0, the dissolved P concentration decreased in the liquid phase, because of chemical precipitation. This observation suggested that pH should be strictly controlled below 8.0 to avoid chemical precipitation if the biological denitrifying phosphorus removal capability is to be studied accurately.

Anoxic Biological Phosphorus Uptake in A^2O Process

A lab-scale anaerobic-anoxic-oxic (A2O) process used to treat a synthetic brewage wastewater was investigated. The objectives of the study were to identify the existence of denitrifying phosphorus removing bacteria (DPB), evaluate the contribution of DPB to biological nutrient removal and enhance the denitrifying phosphorus removal in A2O bioreactors. Sludge analysis confirmed that the average anoxic P uptake accounted for approximately 70% the total amount of P uptake, and the ratio of anoxic P uptake rate to aerobic P uptake rate was 69%. In addition, nitrate concentration in the anoxic phase and different organic substrate introduced into the anaerobic phase had significant effect on the anoxic P uptake. Compared with conventional A2O processes, good removal efficiencies of COD, phosphorus, ammonia and total nitrogen (92.3%, 95.5%, 96% and 79.5%, respectively) could be achieved in the anoxic P uptake system, and aeration energy consumption was saved 25%. By controlling the nitrate recirculation flow in the anoxic zone, anoxic P uptake could be enhanced, which solved the competition for organic substrates among poly-P organisms and denitrifiers successfully under the COD limiting conditions. Therefore, in wastewater treatment plants the control system should be applied according to the practical situation to optimize the operation.

Short-term effects of excessive anaerobic reaction time on anaerobic metabolism of denitrifying polyphosphate- accumulating organisms linked to phosphorus removal and N20 production

The short-term effect of anaerobic reaction time （AnRT） （i.e., 90, 120 and 150 min） on the denitrifying phosphorus （P） removal performance and N20 production was examined using a denitrifying enhanced biologic phosphorus removal （EBPR） sludge acclimatized with mixed acetate （HAc） and propionate （Pro） （in the molar ratio 3 ： 1） as carbon sources. The results showed that when the AnRT was prolonged from 90 to 150 rain, the anaerobic polyhydroxyalkanoate （PHA） synthesis was decreased by 15.3%. Moreover, the ineffective PHA consumption occurred in anaerobic phases and contributed to an increased NO2-N accumulation and higher flee nitrous acid （FNA） concentrations （〉t0.001-0.0011 mg HNO2-N/L） in the subsequent anoxic phases, causing a severe inhibition on anoxic P-uptake and denitrification. Accordingly, the total nitrogen （TN） and total phosphorus （TP） removal efficiencies dropped by approximately 6.3% and 85.5%, respectively; and the ratio of anoxic NzO-N production to TN removal increased by approximately 3.8%. The fluorescence in situ hybridization （FISH） analysis revealed that the sludge was mainly dominated by Accumulibacter （62.0% （SEmean = 1.5%））. In conclu- sion, the short-term excessive anaerobic reaction time negatively impacted denitrifying P removal performance and stimulated more NzQ production, and its effect on P removal was more obvious than that on nitrogen removal.

Advanced nitrogen and phosphorus removal in A^(2)O-BAF system treating low carbon-to-nitrogen ratio domestic wastewater

A laboratory-scale anaerobic-anoxic-aerobic process(A^(2)O)with a small aerobic zone and a bigger anoxic zone and biologic aerated filter(A^(2)O-BAF)system was operated to treat low carbon-to-nitrogen ratio domestic wastewater.The A^(2)O process was employed mainly for organic matter and phosphorus removal,and for denitrification.The BAF was only used for nitrification which coupled with a settling tank Compared with a conventional A^(2)O process,the suspended activated sludge in this A^(2)OBAF process contained small quantities of nitrifier,but nitrification overwhelmingly conducted in BAF.So the system successfully avoided the contradiction in sludge retention time(SRT)between nitrifying bacteria and phosphorus accumulating organisms(PAOs).Denitrifying phosphorus accumulating organisms(DPAOs)played an important role in removing up to 91%of phosphorus along with nitrogen,which indicated that the suspended activated sludge process presented a good denitrifying phosphorus removal performance.The average removal efficiency of chemical oxygen demand(COD),total nitrogen(TN),total phosphorus(TP),and NH_(4)^(+)-N were 85.56%,92.07%,81.24%and 98.7%respectively.The effluent quality consistently satisfied the national first level A effluent discharge standard of China.The average sludge volume index(SVI)was 85.4 mL·g^(-1)additionally,the volume ratio of anaerobic,anoxic and aerobic zone in A^(2)O process was also investigated,and the results demonstrated that the optimum value was 1:6:2.

Denitrification and Dephosphatation by Anaerobic/Anoxic Sequencing Batch Reactor

Removal of denitrifying phosphorus was verified in a laboratory anaerobic/anoxic sequencing batch reactor (A/A SBR). The results obtained demonstrated that the anaerobic/anoxic strategy can enrich the growth of denitrifying phosphorus removing bacteria (DPB) and take up phosphate under anoxic condition by using nitrate as the electron acceptor. The phosphorus removal efficiency was higher than 90% and the effluent phosphate concentration was lower than 1 mg·L-1 after the A/A SBR was operated in a steady-state. When the chemical oxygen demand(COD) of influent was lower than 180mg· L-1, the more COD in the influent was, the higher efficiency of phosphorus removal could be attained under anoxic condition. However, simultaneous presence of carbon and nitrate would be detrimental to denitrifying phosphorus removal. Result of influence of sludge retention time (SRT) on denitrifying phosphorus removal suggested that the decrease of SRT caused a washout of DPB and consequently the enhanced biological phosphorus removal decreased with 8 days SRT. When the SRT was restored to 16 days, however, the efficiency of phosphorus removal was higher than 90%.

Anoxic phosphorus removal in a pilot scale anaerobic-anoxic oxidation ditch process

The anaerobic-anoxic oxidation ditch(A^(2)/O OD)process is popularly used to eliminate nutrients from domestic wastewater.In order to identify the existence of denitrifying phosphorus removing bacteria(DPB),evaluate the contribution of DPB to biological nutrient removal,and enhance the denitrifying phosphorus removal in the A^(2)/O OD process,a pilot-scale A^(2)/O OD plant(375 L)was conducted.At the same time batch tests using sequence batch reactors(12 L and 4 L)were operated to reveal the significance of anoxic phosphorus removal.The results indicated that:The average removal efficiency of COD,NH^(+)_(4),PO^(3–)_(4),and TN were 88.2%,92.6%,87.8%,and 73.1%,respectively,when the steady state of the pilotscale A^(2)/O OD plant was reached during 31–73 d,demonstrating a good denitrifying phosphorus removal performance.Phosphorus uptake took place in the anoxic zone by poly-phosphorus accumulating organisms NO^(-)_(2) could be used as electron receptors in denitrifying phosphorus removal,and the phosphorus uptake rate with NO^(-)_(2) as the electron receptor was higher than that with NO^(–)_(3) when the initial concentration of either NO^(-)_(2) or NO^(–)_(3) was 40 mg/L.

Combined effects of volume ratio and nitrate recycling ratio on nutrient removal,sludge characteristic and microbial evolution for DPR optimization

The optimization of volume ratio(V_(An)/V_(A)/V_(0))and nitrate recycling ratio(R)in a two-sludge denitrifying phosphorus removal(DPR)process of Anaerobic Anoxic Oxic-Moving Bed Biofilm Reactor(A^(2)/O-MBBR)was investigated.The results showed that prolonged anaerobic retention time(HRT An:1.25→3.75 hr)exerted favorable effect on chemical oxygen demand(COD)removal(57.26%→73.54%),poly-β-hydroxyalkanoates(PHA)synthesis(105.70→138.12 mg COD/L)and PO_(4)^(3-)release(22.3→38.9 mg/L).However,anoxic retention time(HRT A)and R exhibited positive correlation with PHA utilization(43.87%-81.34%)and denitrifying phosphorus removal(DPR)potential(NO_(3)-/PO^(3-)_(4):0.57-1.34 mg/mg),leading to dramatical TN removal variations from 68.86%to 81.28%.Under the V An/V A/V O ratio of 2:6:0,sludge loss deteriorated nutrient removals but the sludge bioactivity quickly recovered when the oxic zone was recovered.The sludge characteristic and microstructure gradually transformed under the dissolved oxygen(DO)control(1.0-1.5→1.5-2.0 mg/L),in terms of sludge volume index(SVI:194→57 m L/g VSS),median-particle-size(D 50:99.6→300.5μm),extracellular polymeric substances(EPS)(105.62→226.18 mg/g VSS)and proteins/polysaccharides(PN/PS)ratio(1.52→3.46).Fluorescence in situ hybridization(FISH)results showed that phosphorus accumulation organisms(PAOs)(mainly Cluster I of Accumulibacter,contribution ratio:91.79%-94.10%)dominated the superior DPR performance,while glycogen accumulating organisms(GAOs)(mainly Competibacter,contribution ratio:82.61%-86.89%)was responsible for deteriorative TN and PO_(4)^(3-)removals.The optimal HRT A and R assembled around 5-6.5 hr and 300%-400%based on the PHA utilization and DRP performance,and the oxic zones also contributed to PO_(4)^(3-)removal although it showed low dependence on DO concentration and oxic retention time(HRT_(0)).

Effect of temperature on anoxic metabolism of nitrites to nitrous oxide by polyphosphate accumulating organisms

Temperature is an important physical factor, which strongly influences biomass and metabolic activity. In this study, the effects of temperature on the anoxic metabolism of nitrite （NO2） to nitrous oxide （N2O） by polyphosphate accumulating organisms, and the process of the accumulation of N2O （during nitrite reduction）, which acts as an electron acceptor, were investigated using 91% ：e 4% Candidatus Accumulibacterphosphatis sludge. The results showed that N2O is accumulated when Accumulibacter first utilize nitrite instead of oxygen as the sole electron acceptor during the denitrifying phosphorus removal process. Properties such as nitrite reduction rate, phosphorus uptake rate, N2O reduction rate, and polyhydroxyalkanoate degradation rate were all influenced by temperature variation （over the range from 10 to 30℃ reaching maximum values at 25℃）. The reduction rate of N2O by N2O reductase was more sensitive to temperature when N2O was utilized as the sole electron acceptor instead of NO2, and the N2O reduction rates, ranging from 0.48 to 3.53 N2O-N/（hr.g VSS）, increased to 1.45 to 8.60 mg N2O-N/（hr·g VSS）. The kinetics processes for temperature variation of 10 to 30℃ were （01 = 1.140-1.216 and θ2 = 1.139-1.167）. In the range of 10℃ to 30℃, almost all of the anoxic stoichiometry was sensitive to temperature changes. In addition, a rise in N2O reduction activity leading to a decrease in N2O accumulation in long term operations at the optimal temperature （27℃ calculated by the Arrhenius model）.

Effects of nitrite on phosphate uptake in anaerobic-oxic process

An anaerobic-oxic(A/O)biological phosphorus removal reactor was operated to study the effect of nitrite on phosphate uptake.The phosphorus uptake profile was determined under different operating conditions.The results indicated that in addition to oxygen and nitrate(DPB_(Na),nitrate denitrifying phosphorus removal),to some extent,nitrite could also serve as an electron acceptor to achieve nitrite denitrifying phosphorus removal(DPB_(Ni)).The quantity and rate of phosphorus uptake of DPBNi,however,were evidently lower than that of DPBNa.The experiment results revealed that nitrite would bring toxic action to phosphate-accumulating organisms(PAOs)when NO_(2)^(−)-Ni93.7 mg/L.The nitrite existing in the anoxic reactor made no difference to the quantity and rate of denitrifying phosphorus removal,but it could reduce the consumption of nitrate.Moreover,the data showed that the aerobic phosphate uptake of DPBNi was lower than that of anaerobic phosphorus-released sludge in a traditional A/O process.However,there was not much difference between these two kinds of sludge in terms of the total phosphorus uptake quantity and the effluent quality.

Effect of different carbon sources on performance of an A2N- MBR process and its microbial community structure

Effect of different carbon sources on purification performance and change of microbial community structure in a novel AzN-MBR process were investigated, The results showed that when fed with acetate, propionate or acetate and propionate mixed （ 1 ： 1 ） as carbon sources, the effluent COD, NH4＋- N, TN and TP were lower than 30, 5, 15 and 0.5 mg-L-1, respectively. However taken glucose as carbon source, the TP concentration of effluent reached 2.6 1 mg.L-1. Process analysis found that the amount of anaerobic phosphorus release would be the key factor to determine the above effectiveness. The acetate was beneficial to the growth of Candidatus Accumulibacter associated with biological phosphorus removal, which was the main cause of high efficiency phosphorus removal in this system. In addition, it could eliminate the Candidatus Competibacter associated with glycogen-accumulating organisms and guarantee high efficiency phosphorus uptake of phosphorus accumulating organisms in the system with acetate as carbon source.