Summary of Common Problems And Solutions in Daily Operation of sewage treatment plant System

In the daily operation of the sewage treatment system, we often encounter various abnormal problems, such as: the effluent water quality is not up to standard, the mud cake has high moisture content, and the mechanical and electrical equipment is not working properly. We have summarized the abnormal problems we have encountered in our work. The situation, as well as the corresponding solutions, are for your reference.

l Effluent water quality

1. Excessive organic matter

The main factors that affect the performance of organic matter treatment are:

(1) Nutrients

Generally, nutrients such as nitrogen and phosphorus in sewage can meet the needs of microorganisms, and there is a lot of excess. However, when the proportion of industrial wastewater is large, attention should be paid to whether the ratio of carbon, nitrogen, and phosphorus meets 100:5:1. If the sewage is deficient in nitrogen, ammonium salts can usually be added. If the sewage is deficient in phosphorus, phosphoric acid or phosphate can usually be added.

(2)pH

The pH value of sewage is neutral, generally 6.5 to 7.5. Small decreases in pH may be due to anaerobic fermentation in wastewater delivery pipes. Large pH drops during the rainy season are often caused by urban acid rain, and this situation is particularly prominent in combined systems. Sudden and large changes in pH, whether rising or falling, are usually caused by large discharges of industrial wastewater. To adjust the pH value of sewage, it is usually done by adding sodium hydroxide or sulfuric acid, but this will greatly increase the cost of sewage treatment.

(3)Grease

When the oil content in sewage is high, the aeration efficiency of the aeration equipment will be reduced. If the aeration volume is not increased, the treatment efficiency will be reduced, but increasing the aeration volume will inevitably increase the cost of sewage treatment. In addition, the high grease content in sewage will also reduce the settling performance of activated sludge. In severe cases, it will become the cause of sludge expansion, causing the effluent SS to exceed the standard. For incoming water with a high oil content, it is necessary to add an oil removal device in the pretreatment section.

(4)Temperature

The influence of temperature on the activated sludge process is extensive. First of all, temperature will affect the activity of microorganisms in activated sludge. When the temperature is low in winter, if control measures are not taken, the treatment effect will decrease. Secondly, temperature will affect the separation performance of the secondary sedimentation tank. For example, temperature changes will cause hyperpycnal flow in the sedimentation tank, resulting in short flow; temperature reduction will cause activated sludge to reduce settling performance due to increased viscosity; temperature changes will affect aeration. The efficiency of the system. When the temperature rises in summer, oxygenation will be difficult due to the decrease in the saturation concentration of dissolved oxygen, resulting in a decrease in aeration efficiency and a decrease in air density. To ensure that the air supply volume remains unchanged, it must Increase air supply.

2. Ammonia nitrogen exceeds the standard

The removal of ammonia nitrogen in sewage mainly uses the nitrification process based on the traditional activated sludge process, that is, delayed aeration is used to reduce the system load.

The reasons for excessive ammonia nitrogen in effluent involve many aspects, mainly including:

(1) Sludge load and sludge age

Biological nitrification is a low-load process, and F/M is generally 0.05~0.15kgBOD/kgMLVSS·d. The lower the load, the more complete the nitrification is, and the higher the efficiency of conversion of NH3-N to NO3--N. Corresponding to the low load, the SRT of the biological nitrification system is generally longer, because the generation cycle of nitrifying bacteria is longer. If the sludge residence time of the biological system is too short, that is, the SRT is too short, and the sludge concentration is low, the nitrifying bacteria will be cultured. If you don't get up, you won't get the nitrification effect. How much SRT is controlled depends on factors such as temperature. For biological systems with denitrification as the main purpose, the SRT is usually 11 to 23 days.

(2)Reflow ratio

The backflow ratio of the biological nitrification system is generally larger than that of the traditional activated sludge process. This is mainly because the activated sludge mixture of the biological nitrification system already contains a large amount of nitrate. If the backflow ratio is too small, the activated sludge will stay in the secondary sedimentation tank. The longer the time, the easier it is to produce denitrification, causing the sludge to float. Usually the reflux ratio is controlled at 50 to 100%.

(3)Hydraulic retention time

The hydraulic retention time of the biological nitrification aeration tank is also longer than that of the activated sludge process, which should be at least 8 hours. This is mainly because the nitrification rate is much lower than the removal rate of organic pollutants, thus requiring a longer reaction time.

(4)BOD5/TKN

TKN refers to the sum of organic nitrogen and ammonia nitrogen in water. BOD5/TKN in influent sewage is an important factor affecting the nitrification effect. The larger the BOD5/TKN, the smaller the proportion of nitrifying bacteria in the activated sludge, the smaller the nitrification rate, and the lower the nitrification efficiency under the same operating conditions; conversely, the smaller the BOD5/TKN, the higher the nitrification efficiency. The operation practice of many sewage treatment plants has found that the optimal range of BOD5/TKN value is about 2 to 3.

(5) Nitrification rate

A special process parameter of the biological nitrification system is the nitrification rate, which refers to the amount of ammonia nitrogen converted per unit weight of activated sludge per day. The nitrification rate depends on the proportion of nitrifying bacteria in activated sludge, temperature and many other factors. The typical value is 0.02gNH3-N/gMLVSS×d.

(6)Dissolved oxygen

Nitrifying bacteria are obligate aerobic bacteria and stop life activities when there is no oxygen. The oxygen uptake rate of nitrifying bacteria is much lower than that of bacteria that decompose organic matter. If sufficient oxygen is not maintained, nitrifying bacteria will not be able to "compete" for the space. oxygen required. Therefore, it is necessary to keep the dissolved oxygen in the aerobic zone of the biological pool above 2 mg/L. Under special circumstances, the dissolved oxygen content needs to be increased.

(7)Temperature

Nitrifying bacteria are also very sensitive to temperature changes. When the sewage temperature is lower than 15°C, the nitrification rate will decrease significantly. When the sewage temperature is lower than 5°C, its physiological activities will stop completely. Therefore, in winter, the phenomenon of excessive ammonia nitrogen in the effluent of sewage treatment plants, especially those in northern regions, is more obvious.

(8)pH

Nitrifying bacteria are very sensitive to pH reaction. Their biological activity is strongest in the pH range of 8 to 9. When the pH is <6.0 or >9.6, the biological activity of nitrifying bacteria will be inhibited and tend to stop. Therefore, the pH of the mixed liquid in the biological nitrification system should be controlled to be greater than 7.0 as much as possible.

3. Total nitrogen exceeds the standard

Wastewater denitrification is based on the biological nitrification process and adds a biological denitrification process. The denitrification process refers to the biochemical reaction process in which nitrates in sewage are reduced to nitrogen by microorganisms under anoxic conditions.

The reasons for excessive total nitrogen in effluent involve many aspects, mainly including:

(1) Sludge load and sludge age

Since biological nitrification is the prerequisite for biological denitrification, only good nitrification can achieve efficient and stable denitrification. Therefore, the denitrification system must also adopt low load or ultra-low load and use high sludge age.

(2) Internal and external reflux ratio

The external backflow of the biological denitrification system is smaller than that of the simple biological nitrification system. This is mainly because most of the nitrogen in the incoming sewage has been removed, and the concentration of NO3--N in the secondary sedimentation tank is not high. Relatively speaking, the risk of sludge floating due to denitrification in the secondary sedimentation tank is very small. On the other hand, the sludge in the denitrification system settles quickly. On the premise of ensuring the required concentration of return sludge, the return ratio can be reduced to extend the residence time of sewage in the aeration tank.

For a well-operated sewage treatment plant, the external return flow ratio can be controlled below 50%. The internal reflux ratio is generally controlled between 300 and 500%.

(3) Denitrification rate

Denitrification rate refers to the amount of nitrate denitrified per unit of activated sludge per day. The denitrification rate is related to factors such as temperature, and the typical value is 0.06~0.07gNO3--N/gMLVSS×d.

(4) Dissolved oxygen in anoxic zone

For denitrification, it is hoped that DO is as low as possible, preferably zero, so that denitrifying bacteria can carry out denitrification with "full force" and improve denitrification efficiency. However, judging from the actual operation of the sewage treatment plant, it is still difficult to control the DO in the anoxic zone below 0.5 mg/L, which affects the biological denitrification process and then affects the total nitrogen index of the effluent.

(5)BOD5/TKN

Because denitrifying bacteria perform denitrification and denitrification in the process of decomposing organic matter, there must be sufficient organic matter in the sewage entering the anoxic zone to ensure the smooth progress of denitrification. Due to the lagging behind in the construction of supporting pipe networks in many sewage treatment plants, the BOD5 entering the plant is lower than the design value, while nitrogen, phosphorus and other indicators are equal to or higher than the design value, making the incoming water carbon source unable to meet the carbon source demand for denitrification. It has also led to the frequent occurrence of total nitrogen in the effluent exceeding the standard.

(6)pH

Denitrifying bacteria are not as sensitive to pH changes as nitrifying bacteria. They can carry out normal physiological metabolism in the pH range of 6 to 9, but the optimal pH range for biological denitrification is 6.5 to 8.0.

(7)Temperature

Although denitrifying bacteria are not as sensitive to temperature changes as nitrifying bacteria, the denitrifying effect will also change with temperature changes. The higher the temperature, the higher the denitrification rate. At 30 to 35°C, the denitrification rate increases to the maximum. When it is lower than 15℃, the denitrification rate will decrease significantly, and when it reaches 5℃, denitrification will tend to stop. Therefore, to ensure the denitrification effect in winter, it is necessary to increase SRT, increase sludge concentration or increase the number of operating tanks.

4. TP exceeds the standard

In biological phosphorus removal, phosphate-accumulating bacteria release phosphorus in an anaerobic state and excessively absorb phosphorus in an aerobic state. After phosphorus removal through the discharge of phosphorus-rich residual sludge, the reasons for excessive TP in the effluent involve many aspects, mainly including:

(1) Temperature

The impact of temperature on the phosphorus removal effect is not as obvious as the impact on the biological denitrification process. Within a certain temperature range, biological phosphorus removal can operate successfully when the temperature change is not very large. Tests have shown that the temperature for biological phosphorus removal should be greater than 10°C, because the growth rate of phosphorus-accumulating bacteria will slow down at low temperatures.

（2）pH value

When the pH is between 6.5 and 8.0, the phosphorus content and phosphorus uptake rate of phosphorus-accumulating microorganisms remain stable. When the pH value is lower than 6.5, the phosphorus uptake rate drops sharply. When the pH suddenly drops, the concentration of phosphorus rises sharply in both the aerobic and anaerobic zones. The greater the pH drop, the greater the release. This shows that the phosphorus release caused by the drop in pH is not a result of the pH change caused by the phosphorus-accumulating bacteria themselves. It is a physiological and biochemical reaction, but a purely chemical "acid dissolution" effect, and the greater the anaerobic release caused by the drop in pH, the lower the aerobic phosphorus uptake capacity, which shows that the release caused by the drop in pH is destructive. Invalid. As the pH increases, slight absorption of phosphorus occurs.

(3)Dissolved oxygen

Each milligram of molecular oxygen can consume 1.14 mg of easily biodegradable COD, causing the growth of phosphorus-accumulating organisms to be inhibited and making it difficult to achieve the expected phosphorus removal effect. The anaerobic zone should maintain a lower dissolved oxygen value to facilitate the fermentation of anaerobic bacteria to produce acid, thereby allowing the phosphorus-accumulating bacteria to better release phosphorus. In addition, less dissolved oxygen is more conducive to reducing the consumption of easily degradable organic matter. In turn, the phosphorus-accumulating bacteria synthesize more PHB.

In the aerobic zone, more dissolved oxygen is needed, which is more conducive for the phosphorus-accumulating bacteria to decompose the stored PHB substances and obtain energy to absorb the dissolved phosphate in the sewage to synthesize cellular phosphorus. The DO in the anaerobic zone should be controlled below 0.3 mg/l, and the DO in the aerobic zone should be controlled above 2 mg/l to ensure the smooth progress of anaerobic phosphorus release and aerobic phosphorus absorption.

(4) Anaerobic tank nitrate nitrogen

The presence of nitrate nitrogen in the anaerobic zone consumes the organic matrix and inhibits the release of phosphorus from PAO, thereby affecting the absorption of phosphorus by phosphate-accumulating bacteria under aerobic conditions. On the other hand, the presence of nitrate nitrogen will be used by Aeromonas as an electron acceptor for denitrification, thereby affecting its use of fermentation intermediates as electron acceptors to produce acid during fermentation, thus inhibiting the phosphorus release and phosphorus uptake of PAO. Ability and PHB synthesis ability. Each milligram of nitrate nitrogen can consume 2.86 mg of COD that is easily biodegradable, causing the anaerobic phosphorus release to be inhibited, and is generally controlled below 1.5 mg/l.

(5) Mud age

Since the biological phosphorus removal system mainly removes phosphorus by discharging the remaining sludge, the amount of remaining sludge determines the phosphorus removal effect of the system, and the age of the sludge has a direct impact on the discharge of remaining sludge and the uptake of phosphorus by the sludge. Impact. The younger the sludge age, the better the phosphorus removal effect. This is because reducing the sludge age can increase the discharge of remaining sludge and the amount of phosphorus removal in the system, thereby reducing the phosphorus content in the effluent of the secondary sedimentation tank. However, for biological treatment processes that simultaneously remove phosphorus and denitrification, in order to meet the growth requirements of nitrifying and denitrifying bacteria, the sludge age is often controlled to be larger, which is why the phosphorus removal effect is unsatisfactory. Generally, the mud age of biological treatment systems for the purpose of phosphorus removal is controlled to be 3.5 to 7 days.

(6)COD/TP

In the wastewater biological phosphorus removal process, the type and content of the organic substrate in the anaerobic stage and the ratio of nutrients required by microorganisms to the phosphorus in the wastewater are important factors that affect the phosphorus removal effect. When different organic matter is used as the substrate, the anaerobic release and aerobic uptake effects of phosphorus are different. Easily degradable organic matter with small molecular weight (such as volatile fatty acids, etc.) is easily utilized by phosphorus-accumulating bacteria to decompose the polyphosphate stored in the body to release phosphorus, and has a strong ability to induce phosphorus release, while high-molecular refractory organic matter induces Phosphate-accumulating bacteria have poor phosphorus-releasing ability. The more complete the release of phosphorus during the anaerobic phase, the greater the uptake of phosphorus during the aerobic phase. In addition, the energy produced by phosphorus-accumulating bacteria during the anaerobic stage is mainly used to absorb low-molecular organic substrates as the basis for survival under anaerobic conditions. Therefore, whether the incoming water contains enough organic matter is an important factor related to whether phosphorus-accumulating bacteria can successfully survive under anaerobic conditions. It is generally believed that the COD/TP in the influent water must be greater than 15 to ensure that there is sufficient substrate for phosphorus-accumulating bacteria to achieve the ideal phosphorus removal effect.

(7)RBCOD (easily degradable COD)

Studies have shown that when easily degradable carbon sources such as acetic acid, propionic acid and formic acid are used as phosphorus release substrates, the release rate of phosphorus is larger. The release rate has nothing to do with the concentration of the substrate, but is only related to the concentration of activated sludge and the composition of microorganisms. , the release of phosphorus caused by this type of matrix can be expressed by a zero-order reaction equation. In order for other types of organic matter to be utilized by phosphate-accumulating bacteria, they must be converted into such small-molecule, easily degradable carbon sources, so that phosphate-accumulating bacteria can utilize their metabolism.

(8)Glycogen

Glycogen is a branched macromolecular polysaccharide composed of multiple glucoses. It is the storage form of intracellular sugar. As shown in the figure above, glycogen in phosphorus-accumulating bacteria is formed in an aerobic environment. The stored energy is metabolized in an anaerobic environment to form NADH, the raw material for the synthesis of PHAs, and provides energy for the metabolism of phosphorus-accumulating bacteria. Therefore, in the case of delayed aeration or peroxidation, the phosphorus removal effect will be very poor, because excessive aeration will consume part of the glycogen in the phosphate-accumulating bacteria in an aerobic environment, resulting in a shortage of NADH, the raw material for forming PHAs in anaerobic conditions. .

(9)HRT

For a well-operated urban sewage biological nitrogen and phosphorus removal system, it generally takes 1.5 to 2.5 hours to release phosphorus and 2.0 to 3.0 hours to absorb phosphorus. Overall, it seems that the phosphorus release process is more important. Therefore, we are more concerned about the residence time of sewage in the anaerobic section. If the HRT of the anaerobic section is too short, the effective release of phosphorus will not be guaranteed, and the sewage content in the sludge will not be guaranteed. Facultative acidifying bacteria cannot fully decompose macromolecular organic matter in sewage into low-grade fatty acids that can be absorbed by phosphorus-accumulating bacteria, which will also affect the release of phosphorus; HRT is too long and unnecessary, which not only increases infrastructure investment and operating costs, but also Some side effects may occur. In short, phosphorus release and phosphorus absorption are two interrelated processes. Phosphorus-accumulating bacteria can better absorb phosphorus in the aerobic section only after sufficient anaerobic phosphorus release, and only phosphorus-accumulating bacteria with good phosphorus absorption can absorb phosphorus in the anaerobic section. The oxygen section releases excessive amounts of phosphorus, and proper regulation will form a virtuous cycle. The data obtained by our factory during actual operation is: the HRT of the anaerobic section is 1 hour and 15 minutes to 1 hour and 45 minutes, and the HRT of the aerobic section is 2 hours to 3 hours and 10 minutes.

(10)Reflow ratio (R)

An extremely important point in the A/O process to ensure the phosphorus removal effect is to make the system sludge "carry" enough dissolved oxygen in the aeration tank into the secondary sedimentation tank. The purpose is to prevent the sludge from being anaerobic in the secondary sedimentation tank. Oxygen releases phosphorus, but if the sludge cannot be discharged quickly, the mud layer in the secondary sedimentation tank is too thick, and no matter how high the DO is, it cannot guarantee that the sludge will not release phosphorus anaerobically. Therefore, the return ratio of the A/O system should not be too low and should be maintained Sufficient reflux ratio to discharge the sludge in the secondary sedimentation tank as soon as possible. However, an excessively high return flow ratio will increase the energy consumption of the return flow system and aeration system, shorten the actual residence time of sludge in the aeration tank, and affect the removal effect of BOD5 and P. How to reduce the reflux ratio as much as possible while ensuring rapid mud discharge requires repeated exploration in actual operation. It is generally believed that R is within the range of 50~70%.

5. Suspended matter exceeds the standard

Whether the suspended solids index in the effluent reaches the standard mainly depends on whether the quality of the biological system sludge is good, the sedimentation effect of the secondary sedimentation tank and whether the process control of the sewage treatment plant is appropriate.

The reasons for the excessive suspended solids in the effluent of the secondary sedimentation tank include the following aspects:

(1) Selection of process parameters for secondary sedimentation tank

Whether the design parameters of the secondary sedimentation tank are appropriately selected is an important factor in whether the suspended solids index of the effluent will exceed the standard. At the beginning of the design of many sewage treatment plants, in order to save construction costs, the hydraulic retention time was greatly shortened and the hydraulic surface load was increased as much as possible. As a result, the secondary sedimentation tank often turned over during operation, causing the suspended solids in the effluent to exceed the standard. In addition, when some sewage treatment plants need to control the sludge concentration of the biological pool at a higher level due to actual process adjustment needs, it will also cause the solid surface load of the secondary sedimentation tank to be too large, affecting the effluent water quality. Therefore, it is generally believed that there should be more room for setting these process parameters in the secondary sedimentation tank to facilitate the control and adjustment of the sewage treatment plant process.

Generally speaking, the main process parameters that affect the sedimentation effect of the sedimentation tank are hydraulic retention time, hydraulic surface load and sludge flux.

Ø Secondary sedimentation tank hydraulic retention time

The hydraulic residence time of sewage in the secondary sedimentation tank is an important parameter for the operation of the secondary sedimentation tank. Only with sufficient residence time can good flocculation effect be ensured and high sedimentation efficiency be obtained. Therefore, it is recommended that the hydraulic retention time of the secondary sedimentation tank be set at about 3 to 4 hours.

Ø Hydraulic surface load of secondary sedimentation tank

For a sedimentation tank, when the amount of water input is constant, the size of particles it can remove is also certain. Among the particles that can be removed, the settling velocity of the smallest particle is exactly equal to the hydraulic surface load of the sedimentation tank. Therefore, the smaller the hydraulic surface load, the more particles can be removed, the higher the sedimentation efficiency, and the lower the index of suspended solids in the effluent. The secondary sedimentation tank is designed with a smaller hydraulic surface load, which is conducive to the effective sedimentation of suspended solids such as sludge. It is generally recommended that the hydraulic surface load of the secondary sedimentation tank be controlled at 0.6~1.2m3/m2×h.

Ø Solid surface load of secondary sedimentation tank

The size of the solid surface load of the secondary sedimentation tank is also an important factor affecting the sedimentation effect of the secondary sedimentation tank. The smaller the solid surface load of the secondary sedimentation tank, the better the sludge concentration effect in the secondary sedimentation tank. On the contrary, the concentration effect of sludge in the secondary sedimentation tank will be worse. Excessive solid surface load will cause the mud level in the secondary sedimentation tank to be too high. Many sludge flocs will flow out with the sewage before settling, affecting the effluent suspended solids index. Generally, the maximum solid surface load of the secondary sedimentation tank should not exceed 150kgMLSS/m2×d.

(2) Activated sludge quality

The quality of activated sludge is an important factor affecting whether the suspended solids in the effluent exceed the standard. High-quality activated sludge is mainly reflected in four aspects: good adsorption performance, high biological activity, good settling performance and good concentration performance.

Colloidal pollutants must first be adsorbed onto activated sludge flocs and further adsorbed near the surface of bacteria before they can be catabolized. Therefore, activated sludge with poor adsorption performance also has poor ability to remove colloidal pollutants. The biological activity of activated sludge refers to the ability of microorganisms in the sludge floc to decompose organic pollutants. Activated sludge with poor biological activity must remove organic pollutants slowly. Only activated sludge with good settling performance can effectively separate mud and water in the secondary sedimentation tank. On the contrary, if the sludge settling performance deteriorates, the separation effect will inevitably decrease, resulting in turbid water from the secondary sedimentation tank and excessive SS. In severe cases, it may also lead to a large loss of activated sludge, resulting in insufficient biomass in the system, which in turn affects the removal of organic pollutants. catabolic effects. Only when activated sludge has good concentration performance can a higher sludge concentration be obtained in the secondary sedimentation tank. On the contrary, if the concentration performance is poor and the sludge concentration decreases, it is necessary to ensure sufficient return sludge volume and increase the return ratio. However, increasing the return flow ratio will shorten the actual residence time of sewage in the aeration tank, resulting in insufficient aeration time and affecting the treatment effect.

(3) Water inlet SS/BOD5

The proportion of MLVSS in the activated sludge of the biological system has a great relationship with the incoming water SS/BOD5. When the incoming water SS/BOD5 is high, the proportion of MLVSS in the activated sludge of the biological system is low, and vice versa. According to operating experience, when SS/BOD is below 1, the MLVSS ratio can be maintained above 50%. When SS/BOD5 is above 5, the VSS ratio will drop to 20-30%. When the proportion of MLVSS in activated sludge is low, in order to ensure the nitrification effect, the system must maintain a higher sludge age. The sludge aging is more obvious, resulting in the effluent SS exceeding the standard.

(4) Toxic substances

Influent sewage containing toxic substances such as strong acid, strong alkali or heavy metals will poison the activated sludge and lose its treatment effect. In severe cases, the sludge may even disintegrate, causing the sludge to fail to settle and the suspended solids in the effluent to exceed the standard. The fundamental solution to the problem of activated sludge poisoning is to strengthen the management of upstream pollution sources.

(5)Temperature

The influence of temperature on the activated sludge process is extensive. First of all, temperature will affect the activity of microorganisms in activated sludge. When the temperature is low in winter, if control measures are not taken, the treatment effect will decrease. Secondly, temperature will affect the separation function of the secondary sedimentation tank. For example, changes in temperature will cause hyperpycnal flow in the secondary sedimentation tank, leading to short flow phenomena; when the temperature decreases, the activated sludge will increase in viscosity and reduce its settling performance.

l Moisture content of mud cake

In my country, the activated sludge method is generally used for sewage treatment that has been put into use or is under construction. The activated sludge has a short sludge age design, and there are basically no sludge concentration and sludge digestion facilities in the design, making The amount of remaining sludge is large, and there are many organic components in the sludge, making it difficult to dehydrate. Therefore, if you want to control the moisture content of the mud cake below 80%, you need to increase the dosage of PAM, which will increase the cost of sewage treatment.

In order to ensure the sludge concentration and dehydration effect, in the preparation of sludge dewatering flocculant, the concentration of the flocculation agent should be controlled within the range of 0.1% to 0.5%. If the concentration is too low, the amount of solution will be large and the frequency of dispensing will increase. If the concentration is too high, the viscosity of the medicine will be too high, which may lead to uneven mixing. The resistance of the screw pump will increase when transporting the medicine, which will easily accelerate equipment loss and pipeline blockage. In addition, the specific gravity of different batches and different types of flocculants varies greatly. The preparation concentration of the agent needs to be calibrated regularly or irregularly according to the actual situation, and the dosage of the agent should be adjusted in a timely manner to ensure the sludge dehydration effect and reduce the waste of agents. At the same time, pay attention to moisture-proof and invalidation of dry powder pharmaceuticals during storage and use.

l Electromechanical equipment

To ensure the normal and stable operation of the sewage and sludge treatment system, it is also very important to ensure the operating status of the electromechanical equipment supporting the process. At the same time, the stable and efficient operation of electromechanical equipment has a great impact on energy conservation and consumption reduction in sewage treatment plants.

(1) Grille machine

The grid decontamination machine is the first step in the sewage treatment process, and it is also one of the most prone to failure equipment in the sewage treatment plant. Once a failure occurs, the sewage treatment plant will not be able to receive water normally.

common problem:

Ø Screen machine jamming: Regardless of continuous operation or intermittent operation, because the screen machine is in contact with sewage for a long time, it is easy to cause bearing wear and jamming during operation, causing the chain or rake teeth to pull off or other mechanical failures. For this reason, it is necessary to strengthen the lubrication and maintenance of the relevant mechanical parts of the grille machine, and daily inspections must be in place in a timely manner.

Ø The grate machine is clogged: Sewage often contains some long fibers, plastic bags and other easily entangled debris, which can easily cause clogging of grates and rake teeth. On the one hand, this will reduce the cross-section of the grid, causing the flow rate of the grid to be too large and the pollution interception efficiency to decrease. On the other hand, it will also cause problems such as slow water flow in the canal, sedimentation of gravel, and overflow of the canal. Generally, it can only be solved through technical transformation and improvement or frequent maintenance, and manual cleaning is used.

(2) Lift water pump

Most domestic sewage treatment plants currently use submersible pumps to lift sewage. It was found from actual operation that during the use of the submersible pump, due to the large amount of various impurities and scum in the sewage, these impurities are easily entangled in the gap between the impeller and the sealing ring of the water pump, causing the mechanical sealing effect and water pump efficiency to decrease, causing the Sewage enters the sealing chamber and causes failure. In severe cases, it will cause overflow damage to the water pump motor. To address this problem, we mainly need to enhance the slag collecting effect of the grating machine, regularly check the insulation and sealing of the submersible pump, calculate and improve the pump efficiency, and rotate it regularly.

Because the water inflow to the sewage treatment plant changes 24 hours a day, and the completeness of the supporting sewage collection system is different, the water inflow to the sewage treatment plant may change greatly in different periods, especially in the combined drainage system, where the water inlet changes seasonally. The characteristics are very obvious. Therefore, there should be a large adjustment space in the selection and configuration of submersible pumps. Usually, the drainage volume of multiple water pumps can be sampled in a gradient configuration, combined with a fixed-speed pump and a speed-regulating pump control method. The fixed-speed pump is selected according to the average flow rate to meet the basic flow demand. The speed-regulating pump operates at variable speeds to adapt to changes in flow rate. When the flow rate fluctuates greatly, the number of operating units is increased or decreased to supplement it.

(3) Blower

The blower is the key equipment in the sewage treatment process and consumes the largest amount of energy. Air volume, wind pressure, power consumption, noise, etc. are the basic technical parameters for selecting a blower. During use, it is necessary to combine the characteristics of the process operation and pay attention to its applicable range and adjustment capabilities.

The microporous aeration system of the biological reaction tank in the sewage treatment plant generally uses a centrifugal blower. Centrifugal fans have the advantages of high efficiency, long service life, no need for lubrication in the casing, and the gas will not be contaminated by oil. Especially in terms of air supply volume, applicable range of wind pressure, noise control, and stable operation, they are better than Roots blowers. superior. Roots blowers are generally suitable for situations where the pool depth is shallow and the required air volume and wind pressure are small.

In terms of energy consumption control, variable frequency adjustment control can be used. In terms of equipment configuration, the air volume of multiple blowers can also be configured in gradients for different working conditions to enhance the flexibility of process operation adjustment and reduce power consumption.

The oil cooler and oil filter must be cleaned regularly to ensure oil quality, and must be replaced and inspected regularly to prevent emulsification. There are two ways of oil cooler: air cooling and water cooling: when using air cooling, pay attention to regularly cleaning the heat sink of the air cooler to prevent clogging and accumulation of dirt; when using water cooling, you need to regularly clean and maintain the cooling tower and corresponding pipelines, and pay attention to ensure circulating cooling. For water quality, corrosion and scale inhibitors can be added regularly to prevent bacterial growth, scaling of coolers and pipelines, and galvanic battery reaction corrosion of copper components, which will affect the cooling effect and even pollute the oil quality.

The filter should be cleaned or replaced regularly to ensure that the inlet negative pressure is within the specified range and to reduce the occurrence of blower surge failure caused by excessive negative pressure.

(4) Aeration head

At present, most aeration methods use microporous membrane aeration, including disc type, spherical cap type, plate type, tube type and other types of rubber membrane microporous aerators. After the aerator is used for a period of time, the oxygenation efficiency will decrease due to clogging of micropores, increased resistance, aging of rubber, and deterioration of elasticity. In order to avoid clogging of the aerator or excessive increase in resistance, the aerator should be cleaned regularly. Formic acid cleaning or atmospheric high-pressure air cleaning can be used. When using formic acid cleaning, you must carefully control the concentration of formic acid, the frequency of cleaning, and pay attention to operational safety; when using large-volume air cleaning, you must carefully control the size, intensity, and frequency of cleaning. In addition, be sure to regularly open the drainage valve of the aeration system to drain the condensed water. Seriously blocked or damaged aeration heads should be replaced in time to ensure the uniformity of aeration in the biological pool and prevent dead corners and sludge accumulation.

(5) Mud discharge equipment

Due to differences in processes, some sewage treatment processes do not have secondary sedimentation tanks, such as SBR, UNITANK, etc., and the bottom of the tank is flat, which can easily form a mud layer funnel during mud discharge. The concentration of the mixed liquid discharged in the later period decreased and insufficient sludge was not discharged, resulting in a decrease in the concentration of remaining sludge and an increase in energy and chemical consumption for sludge treatment.

For the operation of these processes, it is appropriate to adopt intermittent sludge discharge methods or transform into a multi-point sludge discharge system.

In addition, in the biological treatment system with a secondary sedimentation tank, regular maintenance of the mud scraper and suction machine in the secondary sedimentation tank is required to ensure smooth mud discharge and prevent mud accumulation from affecting the outlet SS and other indicators.

(6) Dehydrator

The mechanical dehydration methods currently used in China mainly include centrifugal dehydrators and belt filter press dehydrators.

1. Centrifugal dehydrator

During operation, the required range of solid content of concentrated sludge entering the centrifugal dewatering machine, feed volume (installed capacity), maximum output, centrifuge differential speed, rotation speed, different types of polyacrylamide (PAM) filling rates and inputs should be studied. The effect of added concentration on the solid content of sludge after dehydration in the centrifuge, the SS value of separated water and the recovery rate.

If you want to achieve the ideal separation effect for the sludge dehydration treatment of the centrifugal dewatering machine, you can consider two aspects:

Ø The greater the speed difference, the shorter the residence time of sludge in the centrifuge, the higher the moisture content of the mud cake, and the greater the solid content of the separated water. On the contrary, the smaller the speed difference, the longer the sludge stays in the centrifuge and the more complete the solid-liquid separation. However, sludge clogging must be prevented. Adjustments can be made automatically using speed differences to compensate for changing solids content in the feed.

Ø When the sludge properties have been determined, the feed dosing rate can be changed and the dosing amount can be reduced to improve solid-liquid separation; increasing the flocculant filling rate can accelerate the solid-liquid separation speed and improve the separation effect.

common problem:

Ø Start-up alarm or vibration alarm

When the centrifugal dehydrator is turned on, a low differential speed alarm causes the main motor to shut down or the vibration is large or the sound is abnormal, causing the alarm to shut down. The above situation is caused by incomplete flushing before the last shutdown, that is, incomplete flushing will lead to two situations: First, there is too much mud accumulated at the mud discharge end of the centrifuge, causing the speed difference between the drum and the screw conveyor to be too large when it is turned on again. The second is that there are irregular residual solids on the inner wall of the drum, causing the drum to rotate unbalanced and causing a vibration alarm.

Ø Alarm when shaft temperature is too high

This is mainly due to insufficient lubrication due to blockage of the grease oil pipe and excessive shaft temperature. Since the grease dosing device of the centrifugal dehydrator is a semi-automatic device, the oil pipe is slender compared to the manual dosing system, and the interval is long. Adding grease once is prone to blockage of the oil pipe. Once it occurs, it needs to be cleaned manually in time. The main principle is to refuel more frequently to ensure the effective smooth flow of the slender oil pipe. Of course, you cannot add too much grease, otherwise it will also cause the bearing temperature to rise.

When the centrifugal dehydrator is turned on, a low differential speed alarm causes the main motor to shut down or the vibration is large or the sound is abnormal, causing the alarm to shut down. The above situation is caused by incomplete flushing before the last shutdown , that is, incomplete flushing will lead to two situations: First, there is too much mud accumulated at the mud discharge end of the centrifuge, causing the speed difference between the drum and the screw conveyor to be too large when it is turned on again . The second is that there are irregular residual solids on the inner wall of the drum, causing the drum to rotate unbalanced and causing a vibration alarm.

Ø The host alarms and shuts down

When the centrifugal dehydrator is turned on or the dehydrator speed is adjusted during operation, the main motor frequency converter is adjusted too large or too fast, which can easily cause acceleration (deceleration) speed overvoltage and cause the main motor to alarm. During operation, it was found that it is generally safer to adjust the frequency conversion at around 2Hz. When the centrifugal dehydrator is in the flushing state, especially when flushing at high speed, it is easy to cause acceleration (deceleration) overvoltage. Therefore, there should be operator supervision next to the centrifugal dehydrator during high-speed flushing.

Ø The centrifugal dehydrator does not produce mud

When the centrifugal dewatering machine is operating normally, the related equipment is operating normally, but there is no muddy phenomenon, the filtrate is relatively turbid, the differential speed and torque are also high, there is no abnormal sound, no vibration, and the torque changes left and right during high-speed and low-speed flushing. It's not big, but there have been cases where the torque suddenly goes up and down, and it's difficult to start again, and there's no differential speed.

This situation mostly occurs in the rainy season. Due to the large amount of incoming water, the impact on the sludge load in the biological pool is large, resulting in loose remaining sludge and small sludge particles. The smaller the sludge particles and the larger the specific surface area (exponentially increasing), the higher the hydration strength and greater resistance to dehydration and filtration. The sludge has poor flocculation effect and is not easy to dewater. At this time, if the process is not adjusted in time, the centrifugal dehydrator may have insufficient torque (too high), and the differential speed will be tracked in the constant torque control mode. Once the speed difference is too large, it will easily lead to a short residence time of the sludge in the dehydrator and a thin solid ring layer; on the other hand, the greater the speed difference, the greater the relative movement between the drum and the spiral, which will affect the liquid ring layer. The degree of disturbance will inevitably increase, and part of the separated sludge in the solid ring layer will return to the liquid ring layer and may be lost with the separation liquid. In this case, the dewatering machine will not produce mud.

When the incoming mud concentration is low and the sludge is loose, operating with high speed, low differential speed and low mud inflow can effectively solve the problem of no mud discharge, and the operation effect is also good. The purpose of high speed is to increase the separation factor. Generally speaking, the smaller the sludge particles, the lower the density, and the higher the separation factor is required. On the contrary, a lower separation factor is required; using a low differential speed can extend the residence time of the sludge in the dehydrator. When the sludge flocculation effect is enhanced, the time for centrifugal separation in the drum will be extended. At the same time, due to the reduced relative movement between the drum and the spiral, the disturbance to the liquid ring layer will also be reduced. Therefore, the solid recovery rate and the solid content of the mud cake will be reduced. The rate will be increased; low mud input volume will also increase the solid recovery rate and mud cake solid content rate.

2. Belt filter press dehydrator

The belt filter press dehydrator is made up of two tensioned upper and lower filter belts that carry the sludge layer and pass through a series of regularly arranged roller cylinders in an S-shape. The tension of the filter belt itself forms the squeezing and shearing of the sludge layer. Force, the capillary water in the sludge layer is squeezed out, and a mud cake with a larger solid content is obtained.

In order to maintain the normal operation of the belt filter press dewatering machine, the following operation and maintenance matters need to be paid attention to:

(1) For those with pre-dewatering area (concentration area), ensure that the mud is evenly distributed; (2) The filter belt scraper is made of soft material to reduce wear on the filter belt and the filter belt interface; (3) Ensure that the filter belt is flushed with water Pressure, the filter belt washing system should try to use stainless steel self-purifying nozzles, which can flush out the dirt blocked in the nozzles by itself, ensuring the porosity of the filter belt and the sludge dehydration effect; (4) Regular maintenance of the automatic belt deviation prevention device and pressure increase and decrease device , Reduce filter belt edge wear; (5) Ensure that the automatic control system is equipped with a chain protection device to prevent damage to the entire machine caused by malfunction.

common problem:

Ø Filter belt slipping

This is mainly due to overload of mud inlet, the amount of mud inlet should be reduced; the tension of the filter belt is too small, the tension should be increased; the roller cylinder is damaged, and should be repaired or replaced in time.

Ø Filter belt deviation

This is mainly due to uneven mud feeding and uneven spreading on the filter belt. The mud inlet should be adjusted or the mud smoothing device should be replaced. The roller rollers are partially damaged or excessively worn and should be inspected and replaced. The relative positions of the roller rollers are not consistent. The balance should be checked and adjusted; the correction device is not sensitive. Repairs should be checked.

Ø The filter belt is seriously clogged

This is mainly due to incomplete flushing each time, and the flushing time or flushing water pressure should be increased; the tension of the filter belt is too large, and the tension should be appropriately reduced; excessive dosing, that is, excessive PAM dosing, the viscosity increases, and the filter cloth is often blocked. In addition, the filter belt is not Fully dissolved PAM can also easily block the filter belt; too much sand in the incoming mud can also easily block the filter cloth. The operation control of the sewage pretreatment system should be strengthened.

Ø The solid content of the mud cake decreases

This is mainly due to insufficient dosing amount, inappropriate dosing concentration or unreasonable dosing point location, which cannot achieve the best flocculation effect; the belt speed is too high, the mud cake becomes thinner, resulting in a decrease in solid content, and the belt speed should be reduced in a timely manner. speed, generally the thickness of the mud cake should be 5 to 10 mm; the tension of the filter belt is too small to ensure sufficient pressing force and shearing force, which will reduce the solid content. The tension should be appropriately increased; the filter belt is clogged and cannot filter out water, which reduces the solid content. The operation should be stopped and the filter belt flushed.

3.Monitoring instruments

Because there are many impurities in the sewage monitored by the instruments and the environment is poor, it is often easy to cause large errors in online instrument measurements or high damage rates, which greatly affects the intensity of online monitoring and the level of automated control of sewage treatment plants.

Since the concentration of pollutants in the incoming water of the sewage treatment plant is high and there are many suspended solids, it is easy to form fouling in the sampling pipes and the sampling pipes of the analytical instruments. Therefore, it is necessary to configure a water sample pretreatment unit and select an analysis that matches the water quality concentration. Instrument range. When selecting equipment, the automatic control system configured for some large-scale equipment with its own control system must be consistent with the selection of the main control system in the factory. Otherwise, it will not be easy for the equipment to establish communication with the entire automatic control system in the factory, or a large cost will be invested in establishing communication. . In addition, a set of detailed maintenance and operation procedures should be established during operation. For example, maintenance work must be planned in advance and corresponding spare parts prepared; analytical instruments should be calibrated and calibrated regularly, pipelines and pretreatment units should be cleaned, and consumption should be replaced. parts and wearing parts; strengthen the daily management of the online monitoring system, etc.

Due to the special structure design of sewage treatment plants and the large amount of sewage they process, lightning strikes in sewage treatment plants are generally serious, posing a greater threat to the safe operation of outdoor equipment. Second- and third-level lightning protection for field equipment and instruments to prevent damage to field equipment and instruments caused by lightning strikes. If these facilities are lacking in order to control project costs, greater costs will be paid in future operation and management work.