Short-range deep biological denitrification method for urban landfill leachate
The invention relates to a method for removing biochemical organic matters and high ammonia nitrogen in high ammonia nitrogen organic wastewater through stable and efficient short-cut nitrification and denitrification, belongs to the technical field of biological treatment of sewage by a biochemical method, and is suitable for treating urban domestic garbage leachate and other high ammonia nitrogen organic industrial wastewater such as sludge anaerobic digestion liquid and aquaculture wastewater.
The annual total amount of garbage in China currently reaches 2.4 hundred million tons, and the annual growth rate of urban domestic garbage in recent years is more than 8-10%. At present, about 90% of garbage in China is treated by a landfill method, and a large amount of garbage percolate is generated by landfill. The landfill leachate is high ammonia nitrogen organic wastewater with complex components, the pollution discharge amount of the national leachate accounts for about 1.6 per mill of the total annual discharge amount, and the pollution discharge amount accounts for 5.27 percent calculated by chemical oxygen consumption. The leachate treatment is the last link of the sanitary landfill, and the immeasurable pollution and harm are brought to the surrounding environment by improper treatment, and the leachate treatment threatens the human health, and simultaneously causes the sanitary landfill to lose the original significance.
Because the quality and the change rule of the percolate are not well known, the treatment process and the design parameters of the urban sewage are blindly moved to the percolate treatment process, the treatment cost is high, and the effluent can not reach the standard at all. At present, the general view is that the leachate with high ammonia nitrogen can inhibit the activity of microorganisms, so before the biochemical treatment, the pretreatment needs to be carried out by adopting a physical and chemical technology such as stripping. Our experiments prove that the view does not conform to the water quality characteristics and the change rule of the percolate, and the application of the view to practice inevitably causes design errors and waste of construction funds. The economic and efficient percolate treatment technology is abandoned, and the extremely high-cost reverse osmosis treatment technology is simply and blindly used, so that the treatment of the percolate is difficult to continue due to high cost, and therefore, the removal of nitrogen is a difficult point and a key point of sewage advanced treatment, and the difficult point can be thoroughly solved only by utilizing the biological denitrification technology.
In the biological denitrification process, ammonia nitrogen is converted into nitrate nitrogen through nitrification, and the nitrate nitrogen is converted into nitrogen through denitrification and escapes from water. In the nitrification stage, the conversion of ammonia nitrogen into nitrate is performed by two different reactions performed by two independent bacteria, namely, firstly, the ammonia nitrogen is converted into Nitrite (NO) by nitrosobacteria (Nitrosomonas)2
N), then by nitrifying bacteria (Ni)trobacter) to convert nitrite to Nitrate (NO)3
-N). The final product of nitrification in the conventional biological denitrification process is nitrate, and NO is used for denitrification3
-N is an electron acceptor. For denitrifying bacteria, both nitrite and nitrate can be used as final acceptor, so the whole biological denitrification process can be carried out
The way is completed, namely the shortcut nitrification and denitrification biological denitrification process. The partial nitrification and denitrification are reduced by two steps compared with the full nitrification and denitrification: the oxygen supply is saved by 25 percent; saving 40% of carbon source required by denitrification; the sludge generation amount is reduced; reduction of nitreAlkali feeding amount in the chemical process; the reaction time is shortened, and the volume of the reactor is correspondingly reduced by 30 to 40 percent.
Compared with the full-process nitrification denitrification, the short-process nitrification can further reduce the denitrification cost of the landfill leachate with high ammonia nitrogen, and fundamentally solve the denitrification problem. But due to influence on NO2The control factors for the accumulation of-N are complex and nitrobacteria can rapidly convert NO2Conversion of-N to NO3N, thus causing the short-cut nitrification denitrification process which is realized to be restored to the whole nitrification process. Therefore, the shortcut biological denitrification of the high ammonia nitrogen percolate does not make a breakthrough in theory and practice so far.
The prior percolate device is shown in figure 1 and mainly comprises a water tank I, a UASB II, an A/O reactor IV, a secondary sedimentation tank V, other accessory equipment and pipelines. The water tank is connected with a water inlet 17 at the bottom of the UASB II through a water inlet pump 9; the UASB II top is equipped with outlet pipe 29 and is connected with the anoxic reaction zone of A/O reactor IV, and A/O reactor IV divide into anoxic reaction zone and aerobic reaction zone. The aerobic reaction zone is connected with the bottom of the secondary sedimentation tank V through a sludge reflux pump 63, and the upper part of the secondary sedimentation tank V is provided with a water outlet valve 84.
The working process is as follows: pumping the original percolate from a water tank I into a water inlet 17 at the bottom of a UASB II by using a water inlet pump 9, carrying out a methanogenesis reaction in the UASB II from bottom to top, enabling the supernatant to enter an anoxic reaction zone of the A/O reactor IV through a water outlet pipe 29 arranged at the top of the UASB II, carrying out denitrification with the backflow mixed liquor, enabling the supernatant to enter an aerobic reaction zone for nitration reaction after the anoxic reaction is finished, enabling the mixed liquor to flow back to the anoxic zone through an internal circulating pump 92 after the nitration reaction is finished, enabling part of the mixed liquor to enter a secondary sedimentation tank V for mud-water separation, discharging the separated supernatant out of a system through a water outlet valve, and enabling sludge at the bottom to enter the aerobic reaction zone of the A/O reactor IV through a sludge reflux.
The existing process is a combination of anaerobic reaction and aerobic reaction, and denitrification is carried out after the anaerobic reaction, so that the anaerobic degradation of organic matters and biological denitrification of the process form an incompatible contradiction: if the anaerobic condition is sufficient, the efficiency of the subsequent anoxic denitrification is low because of lack of organic carbon sources, and physicochemical processes such as a membrane process and the like are added for further denitrification; if the anaerobic treatment effect is poor, the organic load of the aerobic reactor is too high, so that a large amount of heterotrophic bacteria grow and reproduce, the growth and reproduction of autotrophic nitrifying bacteria are inhibited, sufficient nitrification cannot be completed, and the denitrification of the system fails. The inhibition effect of high ammonia nitrogen on microorganisms, particularly aerobic microorganisms, makes the prior art need to add physicochemical pretreatment to degrade the ammonia nitrogen to a lower level and then carry out biological treatment. The prior art is difficult to realize the high-efficiency removal of ammonia nitrogen and further cannot realize stable short-cut nitrification and denitrification.
The existing biological denitrification technologies of the landfill leachate are full-process nitrification and denitrification, stable and efficient short-process nitrification cannot be realized, and the full-process nitrification has large aerobic aeration amount and requires a reactor with larger effective volume, and the complete denitrification of the garbage leachate requires biochemical COD/TKN (total Kjeldahl nitrogen)>4.0. Thus, the COD/TKN of leachate from some landfills, especially late landfill leachate, is much less than 4.0, resulting in inefficient denitrification by total nitrification. The stable short-cut nitrification COD/TKN is more than 2.4, so that the high-efficiency denitrification can be realized, the short-cut nitrification deep denitrification adapts to the quality of the percolate, and the construction and operation cost can be saved. The complete nitrification of the high ammonia nitrogen landfill leachate is a difficult problem of sewage treatment, and the stable and efficient short-range biological denitrification of the landfill leachate is a great breakthrough of the treatment of the landfill leachate, and the existing domestic and foreign documents are not reported.
Disclosure of Invention
The invention aims to realize about 99 percent of high ammonia nitrogen removal through stable and efficient short-range biological nitrification and denitrification without any physicochemical pretreatment, and the total nitrogen TN removal rate of the early percolate can reach 96 percent. Treatment of COD/NH4 +And (3) when the-N-is 2-3, in the late landfill leachate, no carbon source is added, and the total nitrogen TN removal rate is 70-80%. Aiming at the technical defects and the recognition bias of the existing landfill leachate treatment, the short-range deep biological denitrification method for the municipal landfill leachate is provided. Before anaerobic denitrification, organic matters in inlet water are firstly consumed as a carbon source for denitrification, and anaerobic methanogenesis reaction can be thoroughly carried out, so that proper environmental conditions are created for subsequent short-cut nitrification reaction. Because the effluent reflows and dilutes the ammonia nitrogen concentration of the influent, no physicochemical pretreatment process is needed, and the concentration of free ammonia FA only inhibits Ammonia Oxidizing Bacteria (AOB) but not Nitrite Oxidizing Bacteria (NOB), thereby realizing stable and efficient shortcut nitrification and denitrification. The invention not only solves the contradiction of the prior art, but also has the characteristics of simple process flow, adaptation to the fluctuation of the water quality and the water quantity of the percolate, flexible operation and simple operation. The method can be applied to actual application, greatly reduce construction and operation cost and has no secondary pollution.
The technical principle is as follows:
the COD of the landfill leachate reaches 30000mg/L (the COD concentration of the municipal sewage is 200-500mg/L), and the organic matters are greatly degraded by denitrification and anaerobic methanogenesis reaction by adopting two stages of UASB. Most organic matters of leachate enter the aerobic reactor and are degraded, which creates a suitable condition for the autotrophic nitrifying bacteria to oxidize ammonia nitrogen, and the ammonia nitrogen in the aerobic reactor is thoroughly nitrified, so that the ammonia nitrogen concentration of inlet water is greatly diluted when outlet water flows back, the inhibition effect on microorganisms in a system is greatly weakened, and the thorough shortcut nitrification and high-efficiency denitrification of the ammonia nitrogen become possible. The denitrification in the primary UASB can fully utilize the raw water carbon source to complete denitrification, simultaneously recover the alkalinity to provide an inorganic carbon source for the subsequent nitrification reaction of the aerobic tank, and simultaneously maintain the higher pH (more than 8.2) of the system so as to maintain the higher FA concentration.
By adjusting the effluent reflux ratio and the sludge reflux ratio, the concentration of free ammonia FA of the aerobic reactor is gradually reduced from the water inlet end to the water outlet end within the range of 70-1mg/L, so that only NOB is inhibited, but AOB is not inhibited, and 90-99% of NH is contained4 +Oxidation of-N by nitrosobacteria to nitrite nitrogen NO2 --N, 1-10% NH4 +Conversion of-N to NO3 --N. Meanwhile, a large amount of alkalinity consumed by the nitration reaction is recovered through thorough denitrification, higher pH value is maintained, and short-cut nitration is promoted and maintained. Again, the lowest pH through the "valley" (A/O reactor pH curve)Point) effectively and accurately controls the aeration time to maintain stable short-cut nitrification and prevent the conversion into full-process nitrification. Then the denitrification is finished by respectively treating the water reflux and the secondary sedimentation tank sludge reflux, namely the denitrifying bacteria use the organic carbon source as an electron donor, NOx -And the N is reduced into nitrogen as an electron acceptor and escapes from the leachate to complete the short-range biological denitrification.
Adopt city landfill leachate short distance degree of depth biological denitrification device, its characterized in that: the device mainly comprises an integrated water tank I, a primary UASB II, a secondary UASB III, an A/O reactor IV and a secondary sedimentation tank V;
the integrated water tank I is divided into an original leachate water tank 1 and a treated water tank 6, and the original leachate water tank 1 is connected with a water inlet 17 at the bottom of a primary UASB II through a water inlet pump 9; a water discharge valve 11 is arranged at the upper part of the treated water tank 6, the middle part of the treated water tank 6 is connected with a secondary sedimentation tank V through a pipe 90, and the bottom of the treated water tank 6 is connected with a pressure pipe 10 of a water inlet pump 9 through a treated water circulating pump 1;
the primary UASB II is internally provided with a three-phase separator 22 and an air duct 23, the air duct 23 is connected with an alkali liquor bottle 26, the alkali liquor bottle 26 is connected with a wet gas flowmeter 28, the top of the primary UASB II is provided with a water outlet pipe 29 connected with a water inlet 38 at the bottom of the secondary UASBIII, the upper part of the water outlet pipe 29 is provided with an internal circulation water outlet valve 18 connected with an internal circulation pump 20, and the internal circulation pump 20 is connected with a water inlet 17 at the bottom of the primary UASB II through a pipeline;
the secondary UASBIII is internally provided with a three-phase separator 35 and an air duct 36, the air duct 36is connected with an alkali liquor bottle 39, the alkali liquor bottle 39 is connected with a wet gas flowmeter 41, the top of the secondary UASB is provided with a water outlet pipe 50 connected with an A/O reactor IV, the upper part of the water outlet pipe 50 is provided with an internal circulation water outlet valve 39 connected with an internal circulation pump 41, and the internal circulation pump 41 is connected with a water inlet 38 at the bottom of the secondary UASB through a pipeline;
the A/O reactor IV is divided into an anoxic reaction zone and an aerobic reaction zone, a stirrer 62 is arranged in the anoxic reaction zone, the aerobic reaction zone is connected with an air pump 59, and the aerobic reaction zone is connected with the bottom of the secondary sedimentation tank V through a sludge reflux pump 63;
the upper part of the secondary sedimentation tank V is provided with a water outlet valve 84, and the water outlet valve 84 is connected with the treated water tank 6 through a return pipe 90.
The invention provides a treatment process for realizing short-range biological denitrification of landfill leachate by using the device, which comprises the following steps:
1. the aerobic nitrification sludge is added into an A/O reactor IV and a secondary sedimentation tank V, and the inoculation amount enables the sludge concentration MLSS to be 3000-4000 mg/L; adding 10-6 times diluted percolate into the original water tank 1, starting the water inlet pump 9, pumping the diluted percolate into the A/O reactor IV through the surpassing pipe 97, improving the water inlet load, and enabling the water inlet COD of the A/O reactor IV to be less than 2500mg/L and NH4 +-N<300mg/L, a/O reactor IV anoxic zone free ammonia FA ═ 30-70mg/L, the lowest point of pH change occurs at the end of a/O reactor IV;
2. when the A/O reactor IV is treating water NH4 +-N<15mg/L, and NO2 --N accumulation>90%, completing the start-up of the shortcut nitrification of the a/O reactor IV;
3. adding denitrifying sludge to a first-level UASB II, adding anaerobic granular sludge to a second-level UASBIII, starting a water inlet pump 9 and a treated water reflux pump 15 to mix original leachate and system treated water into the first-level UASB II according to a flow ratio of 1: 3-1: 4, starting an internal circulation pump 20, and enabling the water inlet and reflux treated water load to enable NO of first-level UASB II effluent to be NO2 -N is less than 10mg/L, namely short-range denitrification is completed, NO2 -Conversion of-N to N2A discharge system;
4. the effluent of the first-level UASB II enters a second-level UASBIII, when the liquid is full of the second-level UASBIII, an internal circulating pump 41 is started to carry out methanogenesis reaction, and the inflow load and the treated water reflux ratio are adjusted to ensure that the COD of the effluent of the second-level UASBIII is 2500-3500 mg/L;
5. the effluent of the second-level UASBIII enters an anoxic zone of the A/O reactor IV, a stirrer 62 is started to carry out denitrification of the return sludge, and biochemical COD/TKN is more than 3.0 by controlling the water inlet load of the A/O reactor IV, so that denitrification of the anoxic zone is finished; then the mixed liquid enters an aerobic reaction zone, an air pump 59 is started for aeration, high nitrogen is removed through short-cut nitrification, and NH in the treated water4 +-N＜15mg/L，NO2 -the-N accumulation rate is 90-99%, and the high-efficiency short-cut nitrification and denitrification are finished;
6. after the short-distance nitration is finished, the mixed liquor enters a secondary sedimentation tank V for mud-water separation, after the mud-water separation is finished, a sludge reflux pump 63 is started to reflux the activated sludge to an anoxic zone of an A/O reactor IV, and the sludge reflux ratio is 50-100%; and (4) returning the effluent of the secondary sedimentation tank V to the treated water tank 6, and performing effluent return or overflow effluent.
Compared with the prior art, the method for treating the landfill leachate by the two-stage UASB + A/O process has the following advantages:
1) the reflux treated water can not only complete denitrification, realize denitrification and simultaneously recover alkalinity and improve system pH, but also dilute the high ammonia nitrogen concentration of the inlet water, so that the FA concentration only inhibits NOB, but not AOB, thereby maintaining short-cut nitrification;
2) most organic matters in the effluent of the primary UASB are removed by the secondary UASB through a methanogenesis reaction, and meanwhile, part of organic carbon is converted into inorganic carbon due to higher pH, so that the alkalinity is greatly improved after the anaerobic reaction. The large-scale degradation and alkalinity generation of the organic matters create proper matrix and environment conditions for the subsequent shortcut nitrification of high ammonia nitrogen of the aerobic reactor;
3) the residual organic matters in the anaerobic effluent are firstly used as NO in the returned sludge2 -N denitrified as a carbon source and degraded in the absence of oxygen. Therefore, most of the biochemical organic matters in the process are removed under anaerobic and anoxic conditions without the need of using a special anaerobic reactorOnly the aeration cost is saved, part of the waste water is used as a denitrification carbon source, and the other part of the waste water is converted into methane or alkalinity;
4) after entering the aerobic zone, the residual organic matters are thoroughly degraded and the high ammonia nitrogen is nitrified. The alkalinity in anaerobic effluent is utilized through short-cut nitrification, high ammonia nitrogen is thoroughly removed, not only is 25% of aeration quantity saved, but also 40% of carbon source required by denitrification is saved, and the method is important for denitrification of landfill leachate lacking in carbon source;
5) in the nitration process, the pH value is used as a control parameter, and the lowest point of the pH value is used as a control point, so that the end point of the ammonia oxidation can be accurately and effectively indicated. Therefore, when the lowest point of the pH value appears, the aeration is stopped, so that not only can the aeration amount be saved, the over-aeration is prevented, the aeration cost is saved, but also the stable short-cut nitrification and denitrification can be maintained.
FIG. 1 is a schematic view of a conventional leachate treatment system;
FIG. 2 is a schematic view of a short-cut deep biological denitrification method for municipal landfill leachate according to the present invention;
I-an integrated water tank, II-a first-stage UASB, III-a second-stage UASB, an IV-A/O reactor and a V-secondary sedimentation tank;
i-integrated water tank: 1-an original leachate water tank, 6-a treated water tank, 7-a water suction pipe, 8-a water inlet valve, 9-a water inlet pump, 10-a pressure pipe of the pump 9, 11-a water outlet valve, 12-a treated water return valve, 13-a treated water inlet valve, 14-a treated water inlet pipe, 15-a treated water inlet pump and 16-a pressure pipe of the pump 15;
II-first order UASB: 17-a first-stage UASB water inlet, 18-a first-stage UASB internal circulation valve, 19-a first-stage UASB internal circulation water inlet pipe, 20-a first-stage UASB internal circulation pump, 21-a first-stage UASB internal circulation water outlet pipe, 22-a three-phase separator, 23-a gas guide pipe, 24-a gas circuit clear-and-pass valve, 25-a biogas discharge pipe, 26-an alkali liquor bottle, 27-an alkali liquor bottle and flowmeter connecting pipe, 28-a wet gas flowmeter, 29-a first-stage UASB water outlet pipe and 30-37-a first-stage UASB sampling valve;
III-second order UASB: 38-a second-stage UASB water inlet, 39-a second-stage UASB internal circulation valve, 40-an internal circulation water inlet pipe, 41-a second-stage UASB internal circulation pump, 42-an internal circulation water outlet pipe, 43-a three-phase separator, 44-an air guide pipe, 45-an air path clear valve and 46-a biogas discharge pipe; 47-alkali liquor bottle, 48-alkali liquor bottle and flowmeter connecting pipes, 49-wet gas flowmeter, 50-secondary UASB water outlet pipe and 51-58-secondary UASB sampling valve;
IV-A/O reactor: 59-an air pump, 60-an aerator pipe, 61-an air flowmeter, 62-a stirrer, 63-a sludge reflux pump, 64-a sludge reflux pipe, 65-73-an air regulating valve, 74-82-an aerator and 83-an aeration tank water outlet pipe;
v-secondary sedimentation tank: 84-secondary sedimentation tank water outlet valve, 85-87-sampling valve, 88-central pipe, 89-sludge reflux pump sludge inlet pipe, 90-water outlet reflux pipe, 91-internal circulation water inlet pipe, 92-internal circulation pump, 93-internal circulation water outlet pipe, 94-water inlet valve, 95-override valve and 96-secondary UASB water outlet valve.
Detailed description of the preferred embodiment 1 (treatment of landfill leachate in early stages)
With reference to the examples, as shown in fig. 2, the process of the present invention operates as follows:
the experimental water is taken from a regulating reservoir of a certain refuse landfill in Beijing, and the percolate is dark black, viscous and has malodor, and the quality of the percolate is as follows: COD 7000-25000 mg/l; 53500-14000 mg/l of BOD; NH4+ -N1250-2450 mg/l; SS 2000-4000 mg/l; the alkalinity is 8000-11000 mg/l; TP 9-15 mg/l; the pH value is 7.2-7.9. Sampling and analyzing once every two days, and the analysis methods adopted in the test are all standard methods released by the national environmental protection agency. The leachate is typical urban domestic garbage leachate, and has high concentration of organic matters and ammonia nitrogen, but relatively low content of heavy metals. The test system is shown in FIG. 1 and consists of two stages of UASB and A/O pools. UASB1 has an inner diameter of 5cm, a height of 210cm, and an effective volume of 4.25L. The UASB2 has an inner diameter of 8cm, a height of 200cm, and an effective volume of 8.25L. The effective volume of the A/O pool is 15L, and the A/O pool is divided into ten cells on average, wherein the first cell is an anoxic zone.
The specific process is as follows:
firstly, the aerobic nitrification sludge is added into an A/O reactor IV, and the inoculation amount is up to 3000-4000mg/L of sludge concentration MLSS. According to the water quality condition of the original percolate, the raw water is diluted by 10 times and then added into an original water tank 1. The valves 94 and 96 are closed, the valves 95, 65 to 73 and 89 are opened, and the water inlet pump 9, the air pump 59, the stirrer 54 and the return sludge pump 63 are started. The water inflow rate is gradually increased according to the gradients of 3L/d, 4L/d and 5L/d, and the sludge reflux rate is 50-100% of the water inflow rate. The COD of the inlet water is ensured to be less than 2500mg/L, NH4 +-N<300 mg/L. While ensuring that the anoxic zone of the a/O reactor IV contains 30-70mg/L of free ammonia FA and that the "trough" (lowest point of the pH curve) appears at the end of the a/O reactor IV. Operating under the above conditions when the A/O reactor IV is discharging NH water4 +-N<15mg/L, and NO2 --N accumulation rate (NO)2 --N/NO2 --N+NO3 --N)>90%, marking the end of the start of the short-cut nitrification of the system and then carrying out the combined start of the system.
The raw water tank 1 is filled with raw percolate, and the treated water tank 6 is filled with system treated water. And (3) opening valves 8 and 13, starting a water inlet pump 9 and a treated water reflux pump 15, wherein the flow rate of the water inlet pump is 5.5L/d, the flow rate of the treated water reflux pump is 4 times of the flow rate of the raw water, namely 22.0L/d, the flow rate of the primary UASB water inlet mixed liquid is 27.5L/d, simultaneously, opening a valve 18, and starting an internal circulating pump 20 to perform primary UASB internal circulation, wherein the circulating flow rate is 24L/d.
The influent mixed liquor of the primary UASB passes through the reactor from bottom to top and carries out biochemical reaction with the microorganisms in the column body. The water inlet mixed liquid firstly generates short-range denitrification in the reactor, and the denitrifying bacteria utilize the original osmosisThe organic carbon source rich in the filtrate is used for refluxing the treated water NO2 -N is converted to nitrogen. After denitrification is finished, the methanogen in the primary UASB converts part of the residual organic organisms into methane. The generated nitrogen and methane flow from bottom to top, are separated by the three-phase separator 22, enter the alkali liquor bottle 26 through the gas guide pipe 23, and CO in the biogas in the alkali liquor bottle 262Is absorbed by alkali liquorAnd the nitrogen and methane are discharged after being measured by a wet gas flow meter 28. The sampling valve 30-37 is used for sampling and analyzing the height of the reactor, so that the change rule of the pollutants in the reactor is researched, and the change rule of the microorganisms is researched. Then separated by a three-phase separator, and the supernatant enters a secondary UASB through a water outlet pipe 29 of the primary UASB.
After primary UASB treatment, the effluent NO2 -N is almost completely converted to nitrogen. The organic matters in the original leachate are partially degraded through denitrification and methanogenesis reactions.
And opening the valve 39, starting the internal circulation pump 41, and enabling the mixed liquid of the primary UASB effluent and the internal circulation supernatant to enter the bottom water inlet of the secondary UASB. The flow rate of the internal circulation pump 41 is 100L/d, the inflow mixed liquid flows from bottom to top, and simultaneously contacts with anaerobic bacteria in the reactor, most organic matters in the inflow are degraded and converted into methane through a methane-producing reaction. The generated methane flows from bottom to top, is separated by the three-phase separator 43, enters the alkali liquor bottle 47 through the gas guide pipe 44, and CO in the biogas in the alkali liquor bottle 472Absorbed by the lye and the methane is metered by the wet gas flow meter 49 and discharged. The change rule in the reactor can be obtained by sampling and analyzing the sampling valves 51-58. The secondary UASB effluent flows gravitationally into the a/O reactor IV through outlet pipe 50.
And starting the stirrer 62 to stir the mixed liquid to complete denitrification of the return sludge. And starting a sludge reflux pump 63 to reflux the sludge in the secondary sedimentation tank to the water inlet end of the A/O reactor IV. By denitrification of the agitated anoxic zone (1 cell), NO of the sludge is returnedx -N is converted to nitrogen. And opening air regulating valves 65-73, regulating the flow of the gas flow meter to 400L/h, starting an air pump 59, and aerating the mixed liquid in the aeration tank through an air pipe 60 and aeration heads 74-82. Complete the complete short-cut nitrification of the oxygen combination high ammonia nitrogen of the residual organic matters in the aeration zone (2-10 chambers). The mixed liquid of the A/O reactor enters a central pipe 88 of a secondary sedimentation tank V through a water outlet pipe 83, water is uniformly distributed in the secondary sedimentation tank, and then mud-water separation is carried out. After the sludge and water are separated, the water outlet valve 84 is opened, and the supernatant enters the treated water tank 6 through the water outlet return pipe 90. Is openedValve 11, and final effluent overflow system.
In order to maintain stable short-cut nitrification, the pH value of the aerobic zone of the A/O reactor IV is periodically detected in the running process, a pH change curve is drawn, and the position of the 'ammonia valley' and the end point of the short-cut nitrification of the ammonia nitrogen are determined. If the "valley" occurs earlier (e.g., in cell 6), the flow rate to the feed pump 9 is increased accordingly, increasing the system processing load. Or reducing the air supply amount of the air pump 59,reducing the DO concentration of the aerobic zone, and delaying the 'ammonia valley' until the 9 th to 10 th cells appear, thereby inhibiting the growth of Nitrite Oxidizing Bacteria (NOB) and preventing the short-cut nitrification from being damaged. If the short-cut nitrification is not finished in the aerobic zone, the flow of the water inlet pump 9 can be reduced, or the air supply quantity of the air pump 59 can be increased. The flow of the water outlet reflux pump 15 can be increased, the reflux ratio is increased, the free ammonia FA concentration of the system is reduced, and the total nitrogen removal rate is further improved.
The continuous test results show that: the maximum COD removal rates in UAS B1 and UASB2 were 12.5 and 8.5Kg COD/m, respectively3D, NO in UASB1x -Maximum removal rate of-N of 3.0KgNOx --N/m3D. The COD of the effluent of the two-stage UASB is 2000-3000mg/l, wherein about 50 percent of COD is difficult to biochemically generate, which creates favorable conditions for the nitrification of high ammonia nitrogen in the A/O reactor. The COD removal rate of the system is 80-92 percent, and the COD of the effluent is 800-1500 mg/l. NH of original leachate4 +The maximum NH of the A/O cell at an N concentration of 1100-4 +N removal rate of 0.68Kg NH4 +-N/m3D, NH at 17-30 ℃4 +The removal rate of-N is about 99 percent, and NO is2 -the-N accumulation rate is 90-99%. Outlet water NH4 +-N concentration lower than 15 mg/l. NO in return effluent and return sludge in secondary sedimentation tankx -And N, realizing almost complete denitrification in the anoxic sections of the UASB1 and the A/O pool respectively, so that the removal rate of inorganic nitrogen TIN in the system is 80-92%.
Thorough denitrificationprovides sufficient alkalinity for nitrification, so that the pH value of the A/O pool is more than 8.5, and necessary conditions are created for realizing stable short-cut nitrification. The sludge of each reactor in the system is independent, and respective dominant flora is formed to respectively complete denitrification, methane production and nitrification reactions. Compared with physicochemical processes such as ammonia stripping, reverse osmosis and the like and the traditional whole-course biological denitrification process, the system is economic and efficient, has no secondary pollution, provides practical technical parameters for short-range nitrification removal of high ammonia nitrogen in the percolate, and reduces the construction and operation cost of percolate treatment to a greater extent.
Detailed description of the preferred embodiment 2 (treatment of landfill leachate in late stage)
Treating typical advanced municipal domestic waste leachate by a two-stage UASB + A/O system, performing reflux treatment water denitrification in a first-stage UASB, performing methanogenesis reaction in a second-stage UASB, and performing NH in an A/O reactor4 +-N short-cut nitration. The removal rate of organic matters in the system is 50-70%, and the COD of the effluent of the system is 1000-1500 mg.L-1. When the operation temperature is 17-29 ℃, stable NO is realized2 -Short-cut nitrification with an accumulation rate of-N of 90-99%. NH during the test4 +-N load (ALR) 0.28-0.60 kgNH4 +-N·m-3·d-1，NH4 +The N nitration rate is 90-100%. When ALR is less than 0.45kgNH4 +-N·m-3·d-1Nitration rate>98%, effluent NH4 +-N＜15mg·L-1. In the influent COD/NH4 +And when the-N is 2-3, the removal rate of the inorganic nitrogen TIN is 70-80%. The activated sludge is detected by adopting Fluorescence In Situ Hybridization (FISH), and the result shows that NH in the activated sludge of the A/O process4 +About 4% of total bacteria by-oxidizing bacteria (AOB), NO2 -The number of oxidizing bacteria N (NOB) is less than 0.2% of the total bacteria.