85AbstractThe biochemical characteristics of short time retention in anaerobic zone and sequence reversing of anaerobic and anoxic zones on phosphorus release and up take were studied in bench scale experiments The results showed that:(1) the effective phosphorus release, fully or not, is not the sufficient and necessary condition deciding the ability of excess Pup take To a certain extent, a relatively longer HRT and a more sufficient anaerobic environment produce a stronger potential of excess Pup take in the following aerobic condition(2) a much better effect of N-P removal can be obtained in biological nutrient removal process by reversing the position of anaerobic and anoxic zones and turning in tore versed A2/O process Its phosphorus and nitrogen removal rates are markedly higher than that of conventional A2/O process, whereas the COD removal rates are about equalKeywords: wastewater; treatment; nitrogen removal; phosphorus removal; reversed A2/O processPrinciple and Characteristics of Reversed A2/O ProcessConventional biological nitrogen and phosphorus removal process is anaerobic (A1) / hypoxia (A2) / aerobic (O) layout. The layout of the theory based on an understanding that : Poly effective microbial phosphorus levels of phosphorus release, fully or not, to improve the phosphorus removal capacity is of the utmost importance, anaerobic zone so that the former can microbial polymer and carbon priority full phosphorus release. However, the existence of inner loop, Conventional technology systems emit residual sludge actually only a small part of a complete experience phosphorus release, the uptake process, the rest were basically anaerobic state without direct access from anoxic and aerobic zone, which is detrimental to the phosphorusBecause of the lack of oxygen is located in the central system, denitrification carbon allocation in an unfavorable position, It will affect the nitrogen removal system; As anaerobic residents, Sludge back to the anaerobic zone nitrate have a negative impact on In order to avoid the impact of the development of some new technology (such as Application of UCT Well, etc.) tends to complicate; actual operating experience shows that According to anaerobic-aerobic two denitrification process design system is also often a good phosphorus removal capacity. Therefore, the conventional biological nitrogen and phosphorus removal process (A1/A2/O) layout reasonable worth further exploration1 Materials and Methods Activated Sludge from sewage biological nitrogen and phosphorus removal small-scale test system, the sewage from the actual city sewage. The table of Sewage sludge and the nature Table 1 sewage sludge and the natureSewage SludgeCOD (mg/L) 400-800 MLSS (g/L) 3.0-4.0BOD5 (mg/L) 50-450 VSS/SS 0.60-0.64TN (mg/L) 45-65 N (mgN/gVSS) 110-130TP (mg/L) 2.5-10.0 P (mgN/gVSS) 48-60VFA (mg/L) 25-173 SVI 180-2302 Test results and discussion 852.1Short-termanaerobicenvironment and its phosphate accumulating bacteria to the impact Short-term anaerobic environment in the biological nitrogen and phosphorus removal system plays a key role The purpose of testing is to investigate the short-term anaerobic environment and biochemical characteristics of phosphate accumulating bacteria explained that the uptake behavior.1）A trial of two identical plexiglass column, 30 were effective size L (see figure 1). - With a central axis together with the rotation of three-dimensional elastic filler, not two-packing, mixing impeller. Motor speed for 15-20 min, the column are provided to cover.  Column for a link membrane operation, HRT=20~30 h, the temperature of 24 ~ 29 ℃. To separate study of urban sewage in short-term anaerobic environment sewage VFA changes, The introduction of small pilot did not test the activated sludge system. Column exclusively for anaerobic microbial environment from sewage natural growth up vaccination or facultative anaerobic bacteria. Clearly, anaerobic than general nitrogen and phosphorus removal system more fully anaerobic zone. Column 2 as a contrast, the absence of any treatment. A formal test of the two-instantaneous left empty, and fresh sewage, then start the motor, sampling every 2 hours, Analysis of sewage VFA with the changes of time, In the experimental conditions, short-term anaerobic environment and not increase the sewage capacity VFA, Anaerobic placed in the district will fill the area VFA increased consumption.Under anaerobic digestion theory, Sewage of organic macromolecules into VFA requires hydrolysis and acid (hydrogen production) 2 process. While earlier studies have considered in this process and bacteria belonging to dominant species, But on the life of sewage sludge digestion of that fact, the opposite is true. the anaerobic bacteria and bacteria than over 100 times. Generally speaking, the most important hydrolysis and fermentation reactions are through the anaerobic bacteria. Moreover, due to the anaerobic bacteria biochemical inefficient, the process takes longer hydraulic retention time. Andrews and Pearson (1965) have made use of soluble organic and inorganic synthesis sewage on the anaerobic VFA fermentation process dynamics have been studied, the results indicate that When HRT 2.5 d reactor at the highest concentration of VFA. The test used by the HRT =2~3 h (with anaerobic biological phosphorus removal process similar to the HRT). only 500mg/L COD sewage around. In such conditions, column is in fact very difficult to create a similar kind of sludge digestion anaerobic environment and cultivating a large tertiary anaerobes, Microbial biofilm on the main consumption remains the VFA and bacteria, and had one of the VFA-volume did not increase, Instead consumption soon. Column 2 exclusively for sewage and its small number of microorganisms, their VFA in a very long time remained essentially constant. Only after a certain period of time, with the proliferation of microorganisms, VFA decline only noticeable decline. This test shows that urban sewage of general terms, short-term anaerobic sewage district will not increase the amount of VFA.2）Of a column, column 2 left empty, and small test system from the end of aerobic District 3 L mixture, 3 L with a mixture of sewage into two separately to a packed column, column 2, then start the motor; Anaerobic two-run 2-3 h after removal fillers and impellers. Aeration and at the same time into the state every 30 h sampling analysis two-phosphorus release. Up take characteristics at different times using the actual sewage four group repeatability test. As the actual changes in sewage water, the sewage concentration of the VFA were dropped.Show : under anaerobic conditions influent VFA higher, column 1, column 2 of the greater amount of phosphorus release, and the understanding of the past is the same. - A biofilm existence and nature, a result of anaerobic environment-two more than the full. When the VFA more, the ORP low-level prompted a phosphate accumulating bacteria at a faster rate to absorb VFA PHB, Meanwhile release phosphate. The figure shows that an early-phosphorus release rate was significantly greater than 2 column. Figure 3 (d) influent VFA minimum, a column phosphorus release curve has been in the top-two until the end of the anaerobic, Post-2 and P-curve before an intersection. But a facultative - biofilm while consumption VFA, when the reactor VFA insufficient, facultative biofilm and phosphate accumulating bacteria to VFA competition on the surface, make-a rapid rate of phosphate release attenuation. Column 2 is basically non-existent competition, Therefore phosphate accumulating bacteria can long maintain a higher rate of phosphorus and eventually release the total amount of phosphorus over a column. In addition Figure 3 (d), adding a column filler total phosphorus than-two small, VFA and the higher the influent more obvious difference, see Figure 3 (a, b). In the follow-up aerobic conditions, a poly-phosphate uptake from excessive capacity than-2, When anaerobic lasted 3 hours reduced by two hours of this difference increases markedly,The phenomenon is worthy of special attention, and it shows phosphate accumulating bacteria anaerobic effective phosphorus release, fully or not, is not to determine their aerobic capacity excessive uptake of necessary and sufficient conditions. This popular phosphate accumulating bacteria on the anaerobic effective phosphorus release, the higher their excessive uptake of the more awareness is basically contradictory. From the above analysis of the phenomenon to promote aerobic bacteria Poly excessive phosphorus uptake more dynamic 85nature can be drawn from the judgment, to a certain extent, phosphate accumulating bacteria in the anaerobic environment lasted longer and the environment ORP lower promote aerobic uptake greater impetus. And the effects of phosphorus, phosphorus release may not belong to a fully equipped in the face of necessity. Aerobic uptake of energy from the cells can be stored carbon (PHB), can be obtained from other sources. When this difference by anaerobic lasted 3 hours reduced to 2 hours become particularly evident show anaerobic environment for excessive microbial up take of utmost importance.2.2 Anaerobic, anoxic environment inversion of phosphate accumulating bacteria impact Using two identical geometry plexiglass column experiments, in the effective volume was 30 L, I have the bottom sampling. Its anaerobic, anoxic mode uses a figure (column 2) shown in the removable mixing impeller, Motor speed of 2.0 ning. Aerobic state by aeration aerated first began testing, test systems from small aerobic area from the end of the mixture of 3 L, 3 L with a mixture of sewage, a land divided into two columns were inserted into two. - A moment of the initial KNO3 add another appropriate solution, then start the motor respectively to the lack of oxygen, anaerobic state of agitation. After stirring for 2 h and then joined the two-KNO3 solution. 4 h after the end of the two-the same time, stirring impeller removed, and transferred to the state of aeration. Therefore, the column is based on an actual running A2/A1/O, column 2 A1/A2/O according to the conventional manner. Every 30 min sampling, analysis and comparison of two-and NO3 -- N PO43--P changes in the law Results Figure 4. By Figure 4, we can see that a column from time to zero nitrate, the previous two hours, in fact, in a hypoxic state, denitrification, phosphorus release simultaneously. But compared to column 2, a column before the phosphorus release rate is low; To 30 min, phosphorus release almost completely stopped, 60 minutes after With the depletion of basic nitrate, phosphorus release rate increased rapidly; to 240 min, concentration-65 mg. A map of nitrate point rise was due to misoperation of interesting, a column of phosphorus release curves have emerged point A 'corresponding changes. Column 2 in 120 minutes to join nitrate, its former two hours for anaerobic and after 2 h of hypoxia basic. Column 22 h before the phosphorus release rate soon, to 120 min PO43--P as high as 7.3 mg. 120 min after the addition of nitrate due to gather phosphorus uptake from the beginning. However, the lack of oxygen under microbial ATP lower yields, thus, the stage of uptake rate is not high. To 180 min nitrate depleted, the uptake has basically stopped. After entering the aeration state, although the two-uptake restart, but ahead of the existence of hypoxia, causing its uptake rate is much lower than one column. Aeration began, a column of PO43--P concentrations as high as 6.5 mg, column 2 is only 5.3 mg. But to 480 minutes, a column of PO43--P concentration of 0.1 mg. and the two-PO43--P is 1.05 mg, a difference of 10 times. From the angle of nitrogen, both of the columns with all the denitrification of nitrate. However, a column of more than denitrification rate of 4.12 mgN/(h·gVSS) Column 280 mgN/(h·gVSS), a faster-in column 2.From the above discussion it can be seen that conventional biological nitrogen and phosphorus removal process of anaerobic, anoxic environment right. significantly improve the system of nitrogen and phosphorus removal effect. A2/A1/O in the inversion mode, the carbon problem still exists. And phosphate accumulating bacteria causing the phosphorus levels significantly lower than conventional A1/A2/O way. But in this way, because in front of nitrate hypoxic zone has been depleted, its anaerobic environment more fully, anaerobic microbial phosphorus directly into the biochemical more efficient aerobic environment. Anaerobic conditions in the gully formed under the impetus of phosphorus has been used more efficiently. Conventional nitrogen and phosphorus removal process, the sludge back often than 0.5% Circulation within 2.0-3.0 than in between. All domestic and foreign participation in the cycle of sludge that typically only less than half the total return of sludge experienced a complete release of phosphorus, uptake process, and in fact most of the sludge anaerobic stage without directly access to hypoxic and aerobic environment. Accordingly, the remaining discharges of sewage sludge rich in phosphorus content of the sludge is in fact only a very small proportion, It will affect the phosphorus removal system. Unlike this, A2/A1/O way to allow the participation of all the sludge back all experienced complete phosphorus release, the uptake process, Therefore, the remainder of its emissions higher phosphorus sludge, the effect of phosphorus are better with a "group" effect advantages. The way of A2/A1/O, lack of oxygen to be of priority carbon, nitrogen and therefore its capabilities. In the experimental conditions, denitrification rate and manner A1/A2/O more than 50%. From an engineering perspective, A2/A1/O will not only have better nitrogen and phosphorus removal capacity possibly more traditional nitrogen and phosphorus removal process more simple. Projects take certain measures to bring the sludge back and the inner loop back into a system it is entirely possible, for the development of this simple, efficient biological nitrogen and phosphorus removal process is very beneficial. 2.3 Inversion of the characteristics A2/OUsing two parallel systems were tested and a system to A2/O inversion running, System A2/O two conventional manner. The two systems are effective volume of 77.2 L, the proportion 85of all A2 (A1) : A1 (A2) : O=1 : 1:2, 2 residence time of water for 21h among the non-aeration impeller mixing.Initially, from the sewage plant production aeration activated sludge from the introduction of small pilot system, after a month of trial run, filter resistance to 2-3 L, COD dropped to below 50 mg, began an official trial. The test parameters and operating results are shown in table 2. Because reversed A2/O process with the abolition of the cycle, so their return only one system, total return than the conventional A2/O than a 20% reduction process. Test a small flow control more difficult and therefore a system of the actual water level in the system is slightly larger 2 This leads to the actual HRT slightly short in Table 2 of 8 h, corresponding to filter resistance than the 2 High. As a comparison test, the difference for a system slightly negative. From Table 2 we can see that the two systems is the ability to remove COD, and is as high as 90%, and COD is the highest water in the following 50 mg, form a system of COD System 2 is slightly higher than the actual water level caused by excessive. It can be said that the inversion process in A2/O COD removal capacity with conventional A2/O process quite satisfactory. It is noteworthy that the two systems function of removing nitrogen and phosphorus significantly different. System 1 (inverted A2/O Process) of the effluent TN is 8.9mg/L, the removal of 84.7%; System 2 (conventional A2/O Process) of the effluent TN is 14.9 mg, the removal rate of 74.4%. System TN removal of a system than two full 10% higher. It was also observed that the water system a mere 0.67 mg TP, TP than their removal system was up nearly 9% 2.2 effluent water system which shows significant differences in the inverted A2/O nitrogen and phosphorus removal process is better than conventional functional A2/O Technology Table 2 inverted with the conventional process operating parameters A2/OThe effect of operating conditionsInverted A2/O Process (1system) Inverted A2/O Process (2system)Temperature (℃) 29.6 29.6HRT (h) 8 8DO (mg/L) 1.8 2.0Sludge back 2.0 0.71Inner Loop 0 1.80Reflux RatioTotal 2.0 2.51MLVSS (mg/L) 2117 1960SRT (d) 12 12Intake 446 446Effluent 39.9 38.7COD (mg/L)Removal (%) 91.1 91.3Intake 58.1 58.1Effluent 8.9 14.9TN (mg/L)Removal (%) 84.7 74.4Intake 9.6 9.6Effluent 0.67 1.51TP (mg/L)Removal (%) 93.0 84.33 Conclusions 1）General urban sewage, short anaerobic (HRT =2~3 h) did not increase the sewage capacity VFA, in the anaerobic zone set up to fill the area marked intensification of VFA consumption.2）Poly phosphorus anaerobic bacteria effective phosphorus release, fully or not, is not determined in follow-up under the condition of excessive aeration uptake capacity of the necessary and sufficient conditions. And the effects of phosphorus, phosphorus release may not belong to a fully equipped in the face of necessity. Aerobic uptake of energy from the cells can be stored carbon (PHB), may also from the oxidation of other extracellular matrix was3）By promote excessive phosphorus uptake from the nature of power and anaerobic zone HRT and anaerobic environment anaerobic degree. In a certain range, anaerobic environment 85HRT longer, the more fully anaerobic, phosphate accumulating bacteria uptake of the more dynamic. 4）Conventional nitrogen and phosphorus removal of anaerobic, anoxic environment turned upside down, could be better nitrogen and phosphorus removal. Its features is : a hypoxic zone in anaerobic zone, nitrate here depleted, anaerobic zone ORP lower to establish stronger microbial uptake motivation; b anaerobic microbial phosphorus discharged directly into the biochemical more efficient aerobic environment. In its form under anaerobic conditions uptake dynamics can be more fully utilized, c of the lack of oxygen at the end of the first. Allow denitrification carbon priority to further strengthen the capacity of nitrogen.5） Inverted A2/O process with the conventional system of the small Parallel experiments show that Inverted A2/O nitrogen and phosphorus removal process function better than conventional A2/O process, COD removal capacity with conventional about equal. 6） Due to the abolition of the inner circle, reversed A2/O process in a more simple process. Meanwhile, in the return of all sludge have undergone a complete anaerobic-aerobic process. Phosphorus in connection with a "group" effect, which is very favorable.References [1]Sewage apex with the biological phosphorus removal for protecting environment studies, 1994,7 (5) : 1-6 [2] Liu Jia Shi high aeration tanks MLSS concentration of production research for protecting water supply and drainage, 1993,19 (8)[3]Maekawa T,Chun-Min L， Xing-Dong FN itrogen and phosphorus removal for swine wastewater using intermittent aeration batch reactor followed by ammonium crystalliztion process［J］Water Research,1995，29(12) ：2643