Recently, the sv30 of our biochemical tank is between 60 and 80, and the sludge concentration is only 5,000, how to reduce the SV30, O(∩_∩)O thank you!

Higher SV30 indicates that the sludge settling performance decreases, and it is very likely that sludge expansion occurs, there are many reasons for sludge expansion, here is a piece of information you can refer to, and I hope that it will help you:

Control of activated sludge expansion

Abstract: Starting from the intrinsic factors of the production of sludge expansion, we analyze the causes of filamentous bacterial overpopulation, and put forward solutions and ideas for several common activated sludge process to propose solutions and ideas.

Keywords: filamentous bacteria, sludge expansion, selection tank, activated sludge process

Sludge expansion is a difficult problem that has been accompanied by activated sludge since its inception and often occurs. Its main features are: sludge structure is loose, the quality becomes light, the sedimentation compression performance is poor; SV value increases, sometimes up to 90%, SVI reaches more than 300; a large number of sludge loss, turbidity of the effluent; the secondary sedimentation is difficult to solid-liquid separation, the concentration of return sludge is low, sometimes accompanied by a large number of foam production, unable to maintain the normal work of biochemical treatment. Sludge expansion is one of the more serious anomalies in the biochemical treatment system, which directly affects the quality of the effluent, and jeopardizes the operation of the entire biochemical system.

The incidence of sludge expansion is quite high, in Europe nearly 50% of the municipal sewage plants will have different degrees of sludge expansion each year, in our country the incidence is also very high. Basically, all types of activated sludge processes are currently subject to sludge expansion. Sludge expansion is not only high and common, but also difficult to control once it occurs and usually takes a long time to adjust. There are many theories on sludge expansion, but they are not completely consistent and even contradictory, which causes a lot of trouble for water treatment workers. In this paper, we will start from the intrinsic factors of sludge expansion, organize a few more mature and generally meaningful views, and summarize the general method of sludge expansion control.

1, the causes of sludge expansion sludge expansion is divided into filamentous bacteria expansion and non-filamentous bacteria expansion. Non-filamentous bacteria expansion mainly occurs in the wastewater water temperature is low and the sludge load is too high, when the bacteria adsorbed a large amount of organic matter, it is too late to metabolize the extracellular storage of a large number of highly viscous polysaccharide material, making a large increase in the surface adhesion, it is difficult to precipitate compression. And when there is a serious lack of nitrogen, there can also produce expansion phenomenon. Because if the lack of nitrogen, microorganisms to facilitate the work can not make full use of the carbon source synthesis of cellular material, excess carbon source will be turned to polysaccharide extracellular storage, this storage is highly hydrophilic compounds, easy to form the combination of water, thus affecting the sludge settling performance, resulting in a highly viscous sludge expansion. Non-filamentous bacteria sludge expansion occurs when its biochemical treatment efficiency is still high, the effluent is also relatively clear, sludge microscopy can not see filamentous bacteria. Non-filamentous bacteria expansion occurs less often, and the harm is not very serious, here will not focus on research.

Filamentous bacterial expansion is more common in daily practice, the causes are also very complex. There are many factors affecting the filamentous bacteria sludge expansion, but we should first realize that the activated sludge is a mixed culture system, in which there are at least 30 kinds of filamentous bacteria that may cause sludge expansion. And filamentous bacteria are an indispensable and important class of microorganisms in the relationship with the activated colloid system **** born. Its presence plays a good role in purifying sewage. It is important to maintain the floc structure of sludge, maintain the purification efficiency of biochemical treatment, and in the precipitation of suspended matter in the filtering role. Facts have also proved that in the filamentous bacteria and bacterial colloid bacteria balance is not produce sludge expansion, only when the growth of filamentous bacteria more than bacterial colloid bacteria, there will be sludge expansion phenomenon.

1, sludge loading on sludge expansion

It is generally believed that the growth of microorganisms in activated sludge are in line with the Monod equation:

where X ---- organism concentration, mg/L;

S ---- growth-limiting substrate concentration, mg/L;

μ ---- growth-limiting substrate concentration, mg/L;

μ ---- growth-limiting substrate concentration, mg/L;

μ ---- growth-limiting substrate concentration, mg/L;

μ ---- growth-limiting substrate concentration, mg/L.

KS----- saturation constant whose value is the substrate concentration at μ=μmax/2, mg/L;

μmax----- maximum specific growth rate of microorganisms in saturating concentration, d-1

It was demonstrated that most of the filamentous bacteria have a lower value of KS and μmax than that of the bacterial gelatin clusters, so, according to the above Monond's equation, filamentous bacteria with low KS and μmax values have high growth rates at low substrate concentrations, whereas bacteriophages with higher KS and μmax values dominate at high substrate concentrations. The same theory that suggests that low loading is favorable for the growth of filamentous bacteria is the surface area/volume ratio (A/V) hypothesis. Surface area and volume, in this case, refers to the surface area and volume of microorganisms in the activated sludge. This hypothesis suggests that the specific surface area (A/V) of filamentous bacteria that extend outside the flocculent greatly exceeds the specific surface area of bacteriophage bacteria. When the microorganisms are in a substrate-restricted and controlled state, the filamentous bacteria with a large surface area are more favorable than the bacteriophage in obtaining substrate, and as a result, the filamentous bacteria become dominant in the aeration tank.

Low load easily lead to sludge expansion of this point of view both in the actual operation and in the theory have a more mature explanation. However, in our country, usually the load design of biochemical reaction is higher, a large number of sludge expansion is in the high load conditions, which caused people to the theory of doubt. In fact, sludge expansion under high load conditions is often caused by insufficient oxygen supply and lower DO concentration in the aeration tank. We will address the effect of dissolved oxygen DO on sludge expansion below.

2, the effect of dissolved oxygen concentration on sludge expansion microbial degradation of organic matter is essentially the process of oxygen utilization. Dissolved oxygen is an important control parameter in the operation of activated sludge method, and the level of DO concentration in the aeration tank directly affects the removal efficiency of organic matter and the growth of activated sludge. Low DO concentration has been recognized as one of the main factors causing filamentous bacteria sludge expansion. Filamentous bacteria proliferate faster than flocculent bacteria at low DO concentration due to their larger specific surface area and lower oxygen saturation constant, which leads to filamentous sludge expansion. According to various research responses, the critical value of DO for sludge expansion is not certain, the requirement of DO concentration is closely related to the sludge load, the higher the load, the corresponding critical value will be larger. The determination of this value is closely related to the process selection, pool type and influent type, and must be based on the actual situation combined with the experiment can be derived.

3, other aspects of the impact on sludge expansion

1) Type of sewage The type of sewage has a significant impact on sludge expansion. Generally speaking, those sewage containing easily biodegradable and soluble organic components, especially low molecular weight hydrocarbons, sugars and organic acids and other types of substrates are prone to cause sludge expansion, such as brewing, dairy, petrochemical and paper wastewater.

2) Imbalance of nutrients When the sewage N, P is insufficient, easy to cause the occurrence of sludge expansion. Overnight that the appropriate ratio of N, P for BOD5: N: P = 100: 5: 1. Many studies have shown that many filamentous bacteria have a strong affinity for nutrients N, P, which may be the lack of nutrients leading to sludge expansion.

3) pH and temperature It is generally believed that low pH is easy to cause filamentous bacteria to multiply. And the effect of temperature on filamentous bacteria is also very common. For example, in winter Microthix parvicella dominates in the filamentous flora, while Nocardia form, type 0041 or Nostocoida limnicda are more likely to proliferate in the warm season. Also organic acids and hydrogen sulfide produced by early anaerobic digestion of sewage before entering the water treatment system may contribute to the occurrence of sludge swelling. Thiobacillus bakeri and Thiobacillus filamentosus of Thiobacillus are able to derive energy from the oxidation of hydrogen sulfide. And so the bacteria proliferate in a very long filamentous nature, sometimes up to 1 cm long, which leads to the occurrence of sludge expansion.

2, the general solution of sludge expansion

The first category: emergency measures for temporary emergency, the main method is to add drugs to enhance the performance of sludge settling or directly kill the filamentous bacteria. Adding coagulants such as iron salt and aluminum salt can directly improve the compaction of sludge to ensure the precipitation of water. In addition, the addition of some chemicals, such as chlorine, added to the reflux sludge can also be achieved to eliminate the phenomenon of sludge expansion. The addition of hydrogen peroxide and ozone can also play a role in destroying the effect of filamentous bacteria. This method generally can reduce the SVI value faster, but these methods do not fundamentally control the propagation of filamentous bacteria, once the dosage is stopped, the sludge expansion phenomenon can come back again. And dosing may destroy the microbial growth environment of the biochemical system, resulting in a reduction in the treatment effect, so this approach can only be used as a temporary emergency.

The second type: improve the biochemical environment of the sewage plant sludge expansion occurs, generally can not be from the process, pool type and aeration to solve the problem, can only be in the process of running on the basis of changing the microbial growth environment in the biochemical pool to inhibit or eliminate the excessive propagation of filamentous bacteria. In the case of different processes and water quality, it is difficult to have a one-size-fits-all solution. But the biochemical process is often met with several should pay attention to the problem must be noted.

1) control of the nature of the sewage First of all, we should check and adjust the pH value, when the pH value is below 5 or less, not only on the sludge expansion will be favorable, but also on the normal biochemical reaction will have some harm, so when the pH value is low should be adjusted in time. In addition, in the northern cold areas must pay attention to the water temperature in winter, if the water temperature is low, should be heated, because the low temperature will also lead to the occurrence of sludge expansion. The use of blast aeration can be effective in winter higher water temperature.

When the sewage nutrient deficiency or imbalance, should be supplemented with N, P content should be controlled in BOD: N: P = 100: 5: 1 or so. If the sewage treatment biochemical system before the occurrence of digestive phenomena, the production of low molecular organic acids will be conducive to the growth of filamentous bacteria, which can be improved by pre-aeration of wastewater in the conditioning tank. General use of air diffuser to 3-5 meters of effective water depth adjustment pool aeration, gas supply can be controlled at 0.5-1.0m3/waste water meters 3? hours. It can make the adjusting pool of wastewater to keep fresh, and effectively prevent the odor due to anaerobic will bring.

2) Maintaining sufficient dissolved oxygen in the tank is particularly important for high load biochemical system, generally should control at least DO>2 mg/L.

4) Sludge in the sedimentation tank should be discharged or refluxed in a timely manner, to prevent it from anaerobic phenomenon. If anaerobic phenomenon occurs, all kinds of gases adsorbed on the sludge will make the sludge float and the settling performance deteriorate. Moreover, the return of anaerobic sludge will lead to the proliferation of filamentous bacteria. In this case, in addition to the sludge and remove the dead space in the sedimentation tank, and shorten the residence time of sludge in the tank, should also increase the aeration tank DO value 1ff8 /span>12) so that the water in and out of the sedimentation tank to maintain a more dissolved oxygen, or in the sludge reflux into the biochemical tank before aeration regeneration

After the solution of the above problems, if the phenomenon of sludge expansion can not be controlled, according to the actual situation to be analyzed. The actual situation is analyzed, the following for a few common processes put forward some guidance for sewage workers reference.

A. High-load activated sludge process

At present, the design of activated sludge process in China usually adopts the medium load (0.3KgBOD5/(kgMLSS?d)), and in practice, people always adopt the higher load from the economic point of view, so the sludge expansion under the high load is more widely significant in China. In the case of high load, the most common is DO insufficiency, so first take to improve the gas-water ratio, strengthen the aeration, in the first end of the push-flow aeration tank using jet aeration and so on, observe for a period of time, to find out where the problem lies.

If the above measures are taken after a period of time is still no better, you can consider adding a soft filler in the head of the aeration tank. This part of the organic acid removal rate is very high, thus removing the growth of filamentous bacteria to promote factors to help flocculent bacteria growth. This method is more effective, but the cost is high and inconvenient for future maintenance and management. Alternatively, a selector with a hydraulic retention time of about 15 min in front of the aeration tank can generally inhibit the growth of filamentous bacteria very effectively. For the SBR process with intermittent feed, the reactor itself is completely mixed, and there is a concentration gradient of its pollutant substrate in time, so there is no need for another selector. The usual reason for sludge expansion in intermittent SBR processes is that the sludge concentration is too high, while the influent organic matter concentration is low or the water volume is low resulting in low sludge loading. In this case, lowering the discharge ratio, increasing the initial concentration of substrate, and forcing the SBR to discharge sludge will generally provide effective control of the sludge expansion phenomenon. For continuous-feed SBRs such as ICEAS and CASS, if sludge expansion occurs, it is necessary to set up a pre-reaction zone or bioreactor at the influent end.

B. Low-load activated sludge process

Low-load activated sludge process has a low substrate concentration in the aeration tank, and the filamentous bacteria are easy to get high growth efficiency, so it is the most likely to produce sludge expansion. In addition to the water quality and aeration on the way out, the most fundamental and effective is the aeration tank is divided into multiple compartments and to push the flow mode of operation, or the addition of a compartmentalized set of small pre-aeration tank as a bio-selector, in this selector using high sludge load, adsorption of some organic matter and elimination of organic acids. This approach not only helps to inhibit sludge expansion, and can effectively improve the biochemical treatment. In the aeration tank to increase the packing method is also the same in the low load complete mixing process 1138 View tirades / span> For A/O and A2 / O process can be set up in the aerobic section before the anoxic section and anaerobic section, as well as the sludge reflux system, so that the mixed bacterial colony alternately in anoxic and aerobic state, and make the organic concentration of cyclic changes, which not only controls the sludge expansion and improves the sludge sedimentation performance. This not only controls sludge expansion but also improves sludge settling performance. The alternating oxidation ditch and UNITANK process and other continuous water intake system because of its own time and space on the actual "selector", so the sludge expansion has a strong control ability. If these two processes occur sludge expansion, can be adjusted through the aeration to control the amount of dissolved oxygen and control the amount of reflux sludge to regulate the sludge load and DO, through a period of time to improve, generally be able to control the phenomenon of sludge expansion.

3, summary

In general, the sludge expansion due to a variety of filamentous bacteria, and the growth of suitable environments are not the same. In the case of different processes and different water quality, the microbial growth environment is very subtle, which requires the occurrence of sludge expansion, water treatment workers need to make a lot of practical experiments and analysis based on the actual situation, bold practice, in order to solve the problem of sludge expansion. Here is a summary of the views in this paper.

Filamentous bacteria is an indispensable part of the growth of microorganisms. Sludge expansion phenomenon lies in the excessive growth of filamentous bacteria, to eliminate sludge expansion is fundamental to make filamentous bacteria and activated sludge bacterial colloid balanced growth; complete mixing more than the push-flow type of sludge expansion, low sludge load than the high sludge load is easy to easily produce sludge expansion; influent water in the water temperature, pH, nutrient composition and whether there is a pre-treatment digestive reaction, etc., is the treatment of sludge expansion should be the first problem to be examined; The sludge expansion under high load generally lies in the lack of dissolved oxygen; low load sludge expansion using biological selector is a proven method. Due to the diversity of filamentous bacteria, there are still many inconsistencies in the theoretical explanation and practical report on sludge expansion, bold practice and constantly summarize and widely communicate with peers in order to find effective solutions faster.