At this stage, the reactor DO was kept at 0.5mg/L by controlling the aeration rate but ensuring solid-liquid mixing. Fig. 4 shows the relationship between COD and denitrification in R2 to R4 reactors. It shows that complete denitrification has taken place in the reactor from R2 to R4. All nitrates were converted into gaseous nitrogen in the 2h anoxic stage. The actual total nitrogen removal rates of R2 to R4 reactors are 0.42, 0.85 and 0.91mgng-1ssmin-1respectively. These values can be compared with those obtained by conventional biological treatment.
3.5 nitrogen removal with 0.8mg/L DO under stirring.
In order to study the effect of DO on denitrification of microbial particles, the DO concentration in all reactors was increased to 0.8mg/L by increasing aeration rate. Figure 5 shows the relationship between COD and denitrification when the DO concentration in R2-R4 reactors is 0.8 mg/L. The denitrification efficiency of R2-R4 reactors is about 40%, but the nitrate concentration in the effluent of all reactors is still high, and only partial denitrification occurs compared with the result of DO concentration of 0.5mg/L (Figure 4). Figs. 4 and 5 show that the activity of denitrifying bacteria in microbial particles is inhibited by high concentration of DO. Obviously, DO is not an inhibitor of their synthetic substances, but an inhibitor of denitrification reductase activity, and denitrification can be ignored when the dissolved oxygen concentration is greater than1.0 mg/L/L. ..
3.6 Activities of heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria
The respective activities of ammonia nitrogen oxidizer and nitrite oxidizer are described by actual ammonia nitrogen oxygen utilization ratio (SOUR)NH4 and actual nitrogen oxygen utilization ratio (SOUR)NO2, but the activity of heterotrophic bacteria can be quantified according to their actual heterotrophic bacteria oxygen utilization ratio (SOUR) H. Steady-state cultivation of aerobic granular sludge with (SOUR)NH4, (SOUR)NO2 and (SOUR)NO2 at different N/COD ratios is shown in Figure 6. Fig. 7 shows the nitrogen reduction rate (qobs) of (acidic) NH4 and (acidic) NO2. High concentration of DO leads to low denitrification activity. It can be seen from qobs in Figure 7 that aerobic granular denitrifying bacteria seem to be directly proportional to the ratio of N/COD in the culture medium or the number of nitrifying bacteria.
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4 discussion
Fig. 1 shows that microbial particles can be formed when the N/COD ratio of the culture medium ranges from 5/ 100 to 30/ 100. More than 95% of influent COD is removed in the aeration stage, and ammonia is completely converted into nitrate (Figure 2). The sedimentation rate of R4 by aerobic granular sludge cultured in reactor R 1 is greater than 60m/h, and the biological retention of all reactors reaches 9 gvss/L ... The sedimentation rate of conventional activated sludge is less than10m/h.. Compared with conventional bioflocculation, satisfactory settling rate of aerobic granular sludge can ensure that influent biosolids can be easily and effectively separated, and high biological concentration means that compact and small aerobic granular sludge reactors can be developed. Aerobic granular sludge reactor can be well cultivated within 2-4 weeks, while anaerobic granular system (UASB, etc. It takes at least 4 months of careful training to mature. In this study, the aerobic granular sludge reactor has been running stably for more than a year, and the experiment has ended. These results show that the use of aerobic particles can improve the ability of existing sewage treatment plants to simultaneously remove organic matter and nitrogen, which is feasible and beneficial.
As can be seen from Figure 2-6, heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria can exist in different N/COD ratios. In fact, most denitrifying bacteria are special bacteria, widely distributed in various physiological and taxonomic groups. In aerobic exercise
Next, they use oxygen as the ultimate electron acceptor. Figure 3-5 reveals the effects of DO and agitation on the nitrogen removal efficiency of microbial particles. Because the particles cultured by microorganisms are very heavy, if they are not fully stirred, they will all precipitate to the bottom of the reactor. As a result, the contact between particles and dissolved nitrogen is very poor, and as can be seen from fig. 3, denitrification cannot occur effectively. Therefore, in order to achieve effective nitrogen removal efficiency in a particle-based bioreactor, a certain amount of stirring is necessary to ensure good contact between particles and dissolved nitrogen. Under the condition of stirring, as can be seen from Figures 4 and 5, DO less than 0.5mg/L is very beneficial to denitrification, and the denitrification DO concentration of microbial particles of 0.8mg/L is inhibited. In fact, once denitrifying enzyme is synthesized, bacteria will keep it under aerobic conditions, but its function will be inhibited by high concentration of DO. On the other hand, it is widely reported that dissolved oxygen inhibits every step of denitrification to some extent.
Fig. 6 shows that with the increase of N/COD ratio of culture medium, the activities of ammonia nitrogen and nitrite oxidizing bacteria are greatly improved, but the activities of heterotrophic bacteria in aerobic granular sludge are rapidly reduced. The results showed that when the N/COD ratio of the culture medium increased, the number of a few nitrifying bacteria would gradually exceed the number of heterotrophic bacteria, and the dominant position of heterotrophic bacteria would become smaller and smaller. Similar phenomena have been reported in biofilm reactors.
Fig. 7 shows the influence of culture medium DO and N/COD ratio on the quantitative activity of denitrifying bacteria in the whole microbial particle. Early discussions showed that denitrifying bacteria were very sensitive to the DO concentration in the bioreactor. The activity of denitrifying bacteria is much higher at 0.5 mg/L dissolved oxygen than at 0.8 mg/L dissolved oxygen. When the DO concentration is 0.5mg/L, the actual total nitrogen removal rates of microbial particles cultured in R2 to R4 reactors are 0.42, 0.85 and 0.91mgn/(GSS min), which can be compared with the activity data obtained by conventional denitrification treatment. We know that qobs increases with the increase of N/COD ratio of culture medium. Fig. 6 shows that increasing the N/COD ratio of the culture medium leads to an increase in the number of denitrifying bacteria in aerobic granular sludge, and fig. 2 shows the nitrate concentration in the reactor.
It has also increased. Batchlor( 1982) proposed a formula to describe the effects of DO and nitrate concentration on denitrifying bacteria:
( 1)
Where: qNO3 represents the actual nitrogen reduction rate (mgng-1ssmin-1);
QNO3。 MAX represents the maximum actual nitrogen reduction rate;
SNO3 stands for NO3-N concentration, mg/l;
Se stands for the semi-reaction rate constant of organic medium, mg/l;
KO stands for oxygen half reaction rate constant, mg/l;
According to this model, increasing nitrate concentration will lead to an increase in the actual nitrate reduction rate, but increasing DO will reduce the actual nitrate reduction rate. This experimental data is consistent with the expected effect of the model. Therefore, heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria can exist in microbial particle phase, and it is expected to obtain a new type of efficient particle-based bioreactor.
Microbial particles cultured in SBRS medium with different N/COD ratio can remove organic matter and nitrogen at the same time. It is known that heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria can exist in granules, and the change of microbial quantity in granules has a great relationship with the ratio of N/COD in culture medium. Cultivation of microbial particles in a medium with high N/COD ratio can improve nitrification and denitrification activities, while the activity of heterotrophic bacteria in the particles tends to decrease. This is also the reason why microbial particles have more advantages than traditional activated sludge. Different strains can exist in the same microbial model, which provides a platform for bacterial cooperation. In this case, a more compact bioreactor for removing organic carbon and nitrogen can be realized. DO concentration and stirring affect the nitrogen removal efficiency of microbial particles. When the concentration of DO is 0.5mg/L, complete denitrification can be achieved, and stirring is a necessary condition to ensure the full contact between particles and dissolved nitrogen. Otherwise, the denitrification of microbial particles is very slow. This paper opens up a new, compact and efficient granular biological treatment process for environmental engineers to remove organic matter and nitrogen from sewage.
The relationship between the actual growth rate and proportion of the two strains in the system.
3.3 Denitrification requires no stirring and DO.
Fig. 3 shows the relationship between COD and denitrification in R2 to R4 reactors under anaerobic conditions. It can be seen that a small amount of denitrification reaction occurred in the reactor. The total nitrogen removal rates of R2 to R4 reactors are 2 1, 24% and 26% respectively, but the COD removal rate is very low under this operating condition. Because the actual specific gravity of aerobic particles is higher than that of control water, they will precipitate to the bottom of the reactor without sufficient stirring. This will lead to insufficient contact between the particles and the culture medium solution, and as a result, mass transfer is limited due to the lack of stirring substances, which is the reason for the observed low denitrification efficiency (Figure 3).
3.4 Nitrogen removal with 0.5mg/L DO under stirring.
At this stage, the reactor DO was kept at 0.5mg/L by controlling the aeration rate but ensuring solid-liquid mixing. Fig. 4 shows the relationship between COD and denitrification in R2 to R4 reactors. It shows that complete denitrification has taken place in the reactor from R2 to R4. All nitrates were converted into gaseous nitrogen in the 2h anoxic stage. The actual total nitrogen removal rates of R2 to R4 reactors are 0.42, 0.85 and 0.91mgng-1ssmin-1respectively. These values can be compared with those obtained by conventional biological treatment.
3.5 nitrogen removal with 0.8mg/L DO under stirring.
In order to study the effect of DO on denitrification of microbial particles, the DO concentration in all reactors was increased to 0.8mg/L by increasing aeration rate. Figure 5 shows the relationship between COD and denitrification when the DO concentration in R2-R4 reactors is 0.8 mg/L. The denitrification efficiency of R2-R4 reactors is about 40%, but the nitrate concentration in the effluent of all reactors is still high, and only partial denitrification occurs compared with the result of DO concentration of 0.5mg/L (Figure 4). Figs. 4 and 5 show that the activity of denitrifying bacteria in microbial particles is inhibited by high concentration of DO. Obviously, DO is not an inhibitor of their synthetic substances, but an inhibitor of denitrification reductase activity, and denitrification can be ignored when the dissolved oxygen concentration is greater than1.0 mg/L/L. ..
3.6 Activities of heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria
The respective activities of ammonia-nitrogen oxidant and nitrite oxidant are described by actual ammonia-nitrogen oxygen utilization ratio (SOUR)NH4 and actual nitrogen-oxygen utilization ratio (SOUR)NO2, but the activity of heterotrophic bacteria can be quantified according to its actual oxygen utilization ratio (SOUR) H. (SOUR)NH4, (SOUR)NO2 and (SOUR)NO2 of aerobic granular sludge under different N/COD ratios are shown in Figure 6. Fig. 7 shows the nitrogen reduction rate (qobs) of (acidic) NH4 and (acidic) NO2. High concentration of DO leads to low denitrification activity. It can be seen from qobs in Figure 7 that aerobic granular denitrifying bacteria seem to be directly proportional to the ratio of N/COD in the culture medium or the number of nitrifying bacteria.
[Next Page]
4 discussion
Fig. 1 shows that microbial particles can be formed when the N/COD ratio of the culture medium ranges from 5/ 100 to 30/ 100. More than 95% of influent COD is removed in the aeration stage, and ammonia is completely converted into nitrate (Figure 2). The sedimentation rate of R4 by aerobic granular sludge cultured in reactor R 1 is greater than 60m/h, and the biological retention of all reactors reaches 9 gvss/L ... The sedimentation rate of conventional activated sludge is less than10m/h.. Compared with conventional bioflocculation, satisfactory settling rate of aerobic granular sludge can ensure that influent biosolids can be easily and effectively separated, and high biological concentration means that compact and small aerobic granular sludge reactors can be developed. Aerobic granular sludge reactor can be well cultivated within 2-4 weeks, while anaerobic granular system (UASB, etc. It takes at least 4 months of careful training to mature. In this study, the aerobic granular sludge reactor has been running stably for more than a year, and the experiment has ended. These results show that the use of aerobic particles can improve the ability of existing sewage treatment plants to simultaneously remove organic matter and nitrogen, which is feasible and beneficial.
As can be seen from Figure 2-6, heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria can exist in different N/COD ratios. In fact, most denitrifying bacteria are special bacteria, widely distributed in various physiological and taxonomic groups. In aerobic exercise
Next, they use oxygen as the ultimate electron acceptor. Figure 3-5 reveals the effects of DO and agitation on the nitrogen removal efficiency of microbial particles. Because the particles cultured by microorganisms are very heavy, if they are not fully stirred, they will all precipitate to the bottom of the reactor. As a result, the contact between particles and dissolved nitrogen is very poor, and as can be seen from fig. 3, denitrification cannot occur effectively. Therefore, in order to achieve effective nitrogen removal efficiency in a particle-based bioreactor, a certain amount of stirring is necessary to ensure good contact between particles and dissolved nitrogen. Under the condition of stirring, as can be seen from Figures 4 and 5, DO less than 0.5mg/L is very beneficial to denitrification, and the denitrification DO concentration of microbial particles of 0.8mg/L is inhibited. In fact, once denitrifying enzyme is synthesized, bacteria will keep it under aerobic conditions, but its function will be inhibited by high concentration of DO. On the other hand, it is widely reported that dissolved oxygen inhibits every step of denitrification to some extent.
Fig. 6 shows that with the increase of N/COD ratio of culture medium, the activities of ammonia nitrogen and nitrite oxidizing bacteria are greatly improved, but the activities of heterotrophic bacteria in aerobic granular sludge are rapidly reduced. The results showed that when the N/COD ratio of the culture medium increased, the number of a few nitrifying bacteria would gradually exceed the number of heterotrophic bacteria, and the dominant position of heterotrophic bacteria would become smaller and smaller. Similar phenomena have been reported in biofilm reactors.
Fig. 7 shows the influence of culture medium DO and N/COD ratio on the quantitative activity of denitrifying bacteria in the whole microbial particle. Early discussions showed that denitrifying bacteria were very sensitive to the DO concentration in the bioreactor. The activity of denitrifying bacteria is much higher at 0.5 mg/L dissolved oxygen than at 0.8 mg/L dissolved oxygen. When the DO concentration is 0.5mg/L, the actual total nitrogen removal rates of microbial particles cultured in R2 to R4 reactors are 0.42, 0.85 and 0.91mgn/(GSS min), which can be compared with the activity data obtained by conventional denitrification treatment. We know that qobs increases with the increase of N/COD ratio of culture medium. Fig. 6 shows that increasing the N/COD ratio of the culture medium leads to an increase in the number of denitrifying bacteria in aerobic granular sludge, and fig. 2 shows the nitrate concentration in the reactor.
It has also increased. Batchlor( 1982) proposed a formula to describe the effects of DO and nitrate concentration on denitrifying bacteria:
( 1)
Where: qNO3 represents the actual nitrogen reduction rate (mgng-1ssmin-1);
QNO3。 MAX represents the maximum actual nitrogen reduction rate;
SNO3 stands for NO3-N concentration, mg/l;
Se stands for the semi-reaction rate constant of organic medium, mg/l;
KO stands for oxygen half reaction rate constant, mg/l;
According to this model, increasing nitrate concentration will lead to an increase in the actual nitrate reduction rate, but increasing DO will reduce the actual nitrate reduction rate. This experimental data is consistent with the expected effect of the model. Therefore, from this theme, we can know that heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria can exist in microbial particle phase, and it is expected to use new and efficient particle-based bioreactor.
Abstract: In sequencing batch reactor, microorganisms are cultured with different N/COD ratios. The results show that heterotrophic bacteria, nitrifying bacteria and denitrifying bacteria can be neutralized in microbial particles. However, increasing the ratio of N/COD in the culture medium will lead to significant changes in the number of three strains in the granules. Domestication in the medium with high N/COD ratio improved the activities of nitrifying bacteria and denitrifying bacteria in granular sludge, but the number of heterotrophic bacteria in granular sludge decreased with the increase of N/COD ratio. It is found that dissolved oxygen concentration has a significant effect on denitrification efficiency of microbial particles. At the same time, the research results also show that providing reliable hybrid power ensures a large number of liquid and particle migration during denitrification. It can be proved that a single particle based on SBR can remove all organic matter and nitrogen efficiently and stably. The first study shows that microbial particles have the ability to simultaneously remove organic carbon and nitrogen from wastewater.
Keywords: microbial particle N/COD organic matter removal nitrification reaction denitrification reaction
1, Introduction
With the implementation of more and more strict environmental protection laws and regulations, advanced, economical and effective wastewater denitrification technology has become more and more important. Many improvements and methods for removing nitrogen from wastewater have been developed and implemented. Basically, those processes of nitrogen removal can be divided into suspended sludge and fixed membrane culture. Sludge bulking exists in those suspended sludge systems. The disadvantage of large volume is that it is very sensitive to load impact, but the fixed membrane system has problems such as biofilm-related blockage and shedding. At the same time, because nitrifying bacteria are sensitive to the environment and have low growth rate, it is difficult to obtain and maintain sufficient nitrifying biomass in conventional suspended and fixed culture wastewater treatment systems. But nitrification is the first step of denitrification, which is to convert nitrite and nitrate into nitrogen.
Aerobic particles in sewage treatment are a recently described phenomenon and a potential biological synonym in active research. Compared with the traditional sewage treatment system, the granular system has several advantages. Such as great density and stronger microbial structure, good sedimentation capacity, high biomas retention time and resistance to high organic loading rate. Aerobic granular technology seems to be a potential challenge to the removal of ammonia nitrogen from wastewater. Therefore, it is very desirable that mixed aerobic particles can remove organic carbon and nitrogen at the same time, because organic matter and nitrogen often exist in wastewater. Complete denitrification includes nitrification and denitrification. Nitrite and nitrate formed by nitrification need denitrification to generate nitrogen. As we all know, denitrification is an anaerobic process, which is affected by dissolved oxygen [DO]. Up to now, there is little information about simultaneous removal of organic matter and nitrogen by microbial particles. Therefore, this paper mainly studies the development of aerobic granular sludge under different substrate N/COD ratios, the feasibility of simultaneous removal of organic matter and nitrogen by single granular bioreactor, and the effects of [DO] and mixing degree on the nitrogen removal efficiency of microbial granular sludge.
2 materials and methods
2. 1 establishment and operation of the reactor
Four cylinders (8 cm in height and 6 cm in diameter) with an effective volume of 2.4L were used as sequencing batch reactors (SBR), and each cylinder had the same geometric structure. The reactor has been in operation for more than a year. 340 days ago, the reactor 1-4 (r 1 to R4) was supplied with an air velocity of 2.4L/min, which was equivalent to a surface rising air velocity of 2.4cm/min. During this period, the DO concentration in the reactor exceeded 2.0 mg/L. All reactors were operated in sequence for 4 hours: water inflow for 4 minutes, aeration for 230 minutes, sedimentation for 2 minutes and drainage for 4 minutes. The drain is located in the middle of the cylindrical reactor. After 340 days, in order to observe the denitrification performance of microbial particles cultured under different substrate N/COD ratios, the circulation time of SBR was increased to 6 hours, that is, water inflow for 4 minutes, aeration for 230 minutes, anaerobic or anoxic stage for 2 hours, precipitation for 2 minutes and drainage for 4 minutes. The following three experiments were carried out: (1) After 342 days, the DO concentration in all reactors decreased to 0.8mg/L, and the air flow rate decreased to1.0l/min; ⑵ After 350 days, the DO of the reactor further decreased to 0.5 mg/L, and the aeration rate decreased to 0.5 L/min. ⑶ After 355 days, all reactors stopped aeration to create an anaerobic environment. In the anaerobic or anoxic stage, ethanol is added to the reactor as an additional carbon source in the denitrification stage, and its concentration is 600 mg/L.
2.2 vehicles
Reactor 1-4 was inoculated with 650 ml of fresh activated sludge (equivalent to 3000 mg/L suspended solids) from the local municipal sewage treatment plant. The initial biomass concentration of the reactor is 2000 mg dry weight per liter. Artificial substrates are mainly ethanol, ammonium chloride, sodium bicarbonate and other essential elements as a single carbon source. The chemical oxygen demand of ethanol is fixed at 500mg/L, while the concentration of ammonia nitrogen varies from 25 to 150mg/L in R 1 R4, and the N/COD ratio of each substrate is 5/ 100-30/ 100, respectively. In order to meet the growth requirements of nitrifying bacteria, the ratio of bicarbonate to ammonia nitrogen in all reactors is kept constant at 8.0mg/mg. Trace elements in artificial wastewater can be found elsewhere. The pH of the reactor is lowered to the range of 8.2-7.5. The test temperature is controlled at 25℃.
2.3 Analysis method
2.3. 1 concentration of ammonia nitrogen and nitrogen.
The concentrations of ammonia, nitrite and nitrate are measured by flow injection analyzer (), while the concentration of COD is measured by standard method.
2.3.2 Oxygen utilization rate of biological species
The biological species oxygen utilization rate (SOUR)h of heterotrophic bacteria and the biological species oxygen utilization rates of ammonia nitrogen and nitrite ((SOUR)NH4 and (SOUR)NO2) of ammonia nitrogen-oxidizing bacteria and nitrite-oxidizing bacteria can be measured by standard methods (APHA, 1998). ). A certain number of particle samples are carefully washed with tap water and then put into clean BOD bottles. Then, the BOD bottle is filled with the pre-inflated nutrient and culture medium solution, and the probe with oxygen sensor placed in the stirrer is immediately inserted into the BOD bottle. Record the decline of DO at intervals of 15S. According to the record of DO concentration in the whole process, the oxygen utilization rate of the born species can be calculated. The concentrations of biomass, COD, NH4-N and NO2-N kept constant at 500 mg/L, 400 mg/L, 20 mg/L and 20mg/L respectively. Acid) H, ((acid) NH4) and (acid) NO2 were determined in ethanol, NH4Cl and NaNO2. Acidity test was conducted at 25℃.
2.3.3 Physical characteristics of particles
Use a laser particle size analysis system (Malvern Mastersizer series 2600) or an image analyzer (Quantimner 500 image analyzer, Lecia Cambridge Instruments). Suspended solids (SS) and volatile suspended solids (VSS) were measured by standard methods (APHA, 1998).
Three results
3. Aerobic granular sludge with different N/COD ratios in1culture medium
The average floc size of inoculated sludge is 90 μm m. After 20 days of operation, aerobic particles were formed in four reactors. Aerobic particle size gradually stabilized. After 40 days, the average diameters of R 1, R2, R3 and r 4 are 1.9 mm, 1.5 mm, 0.5 mm and 0.4 mm respectively. In the steady state, the biomass concentration in the reactor increased by more than10 GSS/L. When the N/COD ratio of the culture medium increased from 5/ 100 to 30/ 100, the VSS/SS ratio decreased from 0.94 to 0.79. Microbial observation showed that the aerobic granular sludge in the four reactors was compact in structure, and its shape was obviously spherical compared with inoculated sludge.
3.2 Relationship between COD and nitrification under aerobic conditions
Fig. 2 shows the relationship between COD and nitrification when the reactor R 1 runs for 4 hours. The data jump is as follows: (1) Almost all influent COD is removed in the first 30 minutes; ⑵ When the ratio of N/COD in the culture medium is 5/ 100, nitrite and nitrate are not produced in the reactor R 1, but it can be observed when the ratios of N/COD in each culture medium are 10, 20/ 100 and 30/ 100. (3) After removing COD, the reactors from R2 to R4 are completely nitrated; (4) The removal of ammonia nitrogen 30 minutes before the circulating time is the requirement of microbial growth, and nitrogen source replaces the nitration reaction, because neither nitrite nor nitrate is produced at this stage; 5] As far as nitrite formation is concerned, no slow nitrate product can be seen; In fact, nitrification reaction is mainly completed by two kinds of bacteria, ammonia-nitrogen oxidizing bacteria are responsible for the formation of nitrite, and nitrite oxidizing bacteria convert nitrite into nitrate. Under normal culture conditions, there are at least two factors that affect the efficiency of nitrification reaction, namely ammonia-nitrogen oxidizing bacteria and nitrite oxidizing bacteria in microbial population.