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    Home > Technical Information

    Technical Summary of Sewage Treatment Plant Operation Site

    Source: Author: Time: 2016-07-25 Views: Times

    The operation management of urban sewage plants, like the operation management of other industries, is a general term for planning, organizing, controlling, and coordinating the whole process of sewage treatment, and it is a variety of management activities of the enterprise. The following editors have collected some technical summaries for you in the hope of helping you.


    1. Organizational structure of sewage treatment plant


    The production and operation functions of the sewage plant are mainly realized by the plant department, the operation department (including the central control room and each work section), the power maintenance department (including the electrician class and the maintenance group), and the laboratory. The operation department guides the operation of each work section. The power and equipment maintenance system of the sewage plant is mainly composed of daily maintenance, regular maintenance, fault maintenance and improvement maintenance. In addition to the operation of the sewage treatment system, the staff of the operation department is also responsible for the daily maintenance of the equipment, including daily inspections and simple routine maintenance, such as adding lubricants, cleaning, replacing filters, and tightening and adjusting equipment for small parts. Mission time is about 0.5 hours). The power maintenance department is mainly responsible for regular maintenance, fault maintenance and improvement maintenance of equipment. The laboratory is directly under the administration of the drainage company, and is actually located in the sewage plant, and works closely with the operation department under the coordination of the plant manager. The dispatch of sewage into the plant is carried out by the plant department with the assistance of the operation department and the drainage and pumping stations.


    2. Water quality monitoring indicators


    Water quality monitoring indicators are implemented in accordance with the levels specified in the Urban Wastewater Treatment Plant Pollutant Discharge Standard GB18918-2002 and the environmental impact assessment report approved when the plant was established. Technical regulations "CJJ60-94 implementation. That is, PH value, SS, BOD5, CODcr, NH3-N, TN, TP once a day, the number of fecal coliforms once a week, and the remaining detection indicators are tested every six months. In order to ensure that the sewage treatment plant can meet the requirements of the Environmental Protection Agency, the general drainage company will appropriately increase the monitoring standards of the sewage treatment plant.


    3. Performance evaluation indicators of wastewater treatment plants for wastewater treatment plants


    The technical assessment index of the wastewater treatment plant for the sewage treatment plant shall include at least the following scope.


    Water quality: effluent water quality compliance rate: CODcr, BOD5, SS, NH3-N, TN, TP Sampling every 2h, taking 24h mixed sample, calculated as daily average. Fecal coliform indicators once a week.


    Effluent water quality compliance rate (%) = (total qualified number of monthly testing indicators-unqualified number) * 100 / total number of monthly testing indicators


    Water volume: overflow rate of untreated sewage (%) = (water delivery volume of the inlet pump station-actual treatment volume of the sewage treatment plant) * 100 / water delivery volume of the pump station


    Laboratory task completion rate: Laboratory task completion rate (%) = (actual test items * 100) / number of items to be tested by item and frequency


    Equipment and Instrument Intactness Rate: Equipment and Instrument Intactness Rate (%) = (Number of Intact Units Inspected * 100) / Total Number of Inspected Units


    Duration of consecutive non-responsibility casualties (days)


    With the improvement of the company's organization and management experience, other indicators can be gradually included in the assessment.


    4. Prerequisites for the first system operation


    Staff training: The initial operation of the system is an important step before the sewage treatment plant is put into normal operation. At this stage, operators should accumulate experience for the normal operation of the system in the future. Job training and safety training for all employees should be completed before the system's initial operation.


    Cleaning, anti-corrosion and equipment fastening in the processing structure of each unit: The sewage treatment plant may not be shut down for a long time after it is put into normal operation. Therefore, all garbage and debris in the structure should be removed before the system runs for the first time. Paint, corrosion and fastening of structures and machinery.


    System single machine commissioning and structure water seepage test: System single machine commissioning and structure water seepage test should be carried out before the system's initial operation, including various process ponds, process equipment, auxiliary equipment, gate valves and weir gates of the water treatment system and mud treatment system. The civil construction subcontractor and equipment supplier and the installation unit shall complete the work separately, and submit the single machine commissioning and water seepage test report of the structure. At the same time, pay attention to the check of the elevation requirements in the process, for example, the elevation of each brush is consistent, and it is coordinated with the elevation of the weir gate. Relevant personnel of the sewage treatment plant shall participate in this work, and carry out inspection and acceptance of single machine commissioning and water seepage testing.


    Inspection of water inlet and outlet conditions: Before the system is initially operated, the sewage collection system should have the ability to collect and enhance sewage, and be able to control the amount of water and the time period through the sewage collection control system. Connected to ensure that the tail water treated by the sewage treatment plant can be discharged into the receiving water body.


    Checking the process water flow capacity at the design load: Checking the process water flow capacity at the design load refers to checking whether the water flow capacity of the process flow from the inlet lift pump to the water outlet can reach the design load. Since it has been commissioned by a single machine, sewage can be checked into the plant to save water. If there is any problem, the contractor shall be notified to carry out the modification until the design load is reached.


    System linkage: The system linkage of the new sewage treatment plant shall be completed by the general contractor. The purpose of the system linkage test is to check the equipment operation, process parameter monitoring and control capabilities, and to check the coordination of equipment operation. During the system linkage process, it is important to debug the operation of the automatic control and on-site control systems.


    5.Inoculation sludge selection


    The inoculum sludge should use the remaining sludge of the municipal sewage treatment plant in the nearby city. To reduce the transportation pressure, the dehydrated sludge should be taken. Generally, it is first cultured in one group of oxidation ditches. After the cultivation is successful, the second group of oxidation ditches is driven into the second group of oxidation ditches by the back flow sludge pump to continue to cultivate the activated sludge.


    6. Activated sludge domestication (take oxidation ditch as an example)


    The first stage


    Feed water to the oxidation ditch reaction tank and start the underwater thruster. When the water is continuously fed until the water level in the oxidation ditch reaches 1/3 of the designed effective water depth, the inoculated sludge is evenly poured into the oxidation ditch reaction tank, and the aeration is started by aeration system, and the water is continuously fed to the oxidation ditch. The water level in the pond reaches the designed operating level (using a rotary brush or rotary dish aeration system, and aeration is started at this time). During the continuous water intake process after the sludge inoculation is completed, the aeration amount is gradually increased to the maximum. After the water level of the oxidation ditch reaches the designed operating level, water will continue to flow into the secondary sink. When the secondary sedimentation tank enters the water for 2 hours, the sedimentation tank scraper and the sludge return pump are started, so that the activated sludge settled in the secondary sedimentation tank can be quickly collected in the initial stage of sludge domestication and returned to the biological treatment tank. . The sludge reflux rate should be adjusted by observing the status of the sludge reflux. Generally, the sludge reflux ratio should be controlled between 50 and 100%. When the secondary sedimentation tank reaches the normal operating water level, the status of the activated sludge should be observed and the water inflow should be controlled until fuzzy flocs appear. At this time, the water can be appropriately fed in and the water can be replaced to supplement nutrients. The amount of water can be controlled to be oxidized. Repeat the above operation for 25% of the tank capacity. When the secondary settling pond begins to overflow, subsequent sewage treatment processes, such as disinfection processes, are initiated. After the water level of the biological treatment tank reaches the normal operating level, the dissolved oxygen (DO) concentration value in the oxidation ditch should be monitored at any time (through the dissolved oxygen analyzer) to determine whether the aeration is sufficient and make corresponding adjustments. In the activated sludge acclimation process, the dissolved oxygen concentration should be able to meet the following three situations that may occur.


    a) The dissolved oxygen concentration in the inflow and return sludge is low; more oxygenation is needed;


    b) Insufficient oxygen in the inlet water, which needs sufficient dissolved oxygen to quickly change it into an oxygenated environment;


    c) When the sewage is rich in nutrients, a large amount of dissolved oxygen is required to meet the growth of microorganisms.


    During the sludge acclimation process, the minimum dissolved oxygen concentration should ensure that the dissolved oxygen concentration at the outlet of the oxidation ditch is not less than 1.0 mg / L. In the first stage of acclimation of activated sludge, due to the low concentration of activated sludge, a large amount of foam may be generated during aeration. In actual operation, corresponding treatment measures are taken, such as spraying water droplets. Measures to remove foam.


    second stage


    After entering the second stage of sludge acclimation work, while monitoring dissolved oxygen, the 30-minute sedimentation ratio (SV) and nutrient parameters of activated sludge should be monitored. In the process of monitoring the activated sludge sedimentation ratio, it can be found that the color of the mud-water mixture in the first few days of this stage is almost the same as the color of the inlet water. As the aeration time increases, the particles of the mud-water mixture become larger and the sedimentation performance becomes OK, and the color gradually becomes dark brown. At this stage, the activated sludge sedimentation ratio can reach 20%. The purpose of detecting nutrients is to provide conditions for the growth of microorganisms. During the process of domestication of activated sludge, the parameters of nutrient substances BOD: N: P should be controlled at about 100: 5: 1. If this parameter cannot be reached, nutrients should be added. Make adjustments.


    The third stage


    After the activated sludge acclimation work entered the third stage, the activated sludge acclimation work was basically completed. At this stage, the key parameters of the mud-water mixture should be monitored, analyzed and controlled strictly in accordance with the analysis plan listed in Sample Table 3-1, and relevant data should be saved for reference of the normal operation of the system. When the activated sludge concentration value reaches the specified range and is relatively stable, it can be considered that the domestication of activated sludge is basically completed. After the biochemical and sedimentation treatment of the sewage, the effluent SS should meet the standard. During this stage, the remaining sludge should be discharged according to the actual operating conditions.


    Fourth stage


    The purpose of this stage is to record the operating parameters, that is, the key control parameters of activated sludge 30-minute sedimentation ratio (SV), biological microscopy, sludge reflux ratio, and remaining sludge discharge. Provide a reference for the normal operation of the system. When the influent concentration is low and sludge growth is poor, the sludge reflux ratio should be increased, and sludge reflux ratio should be reduced when conditions such as sludge expansion occur. At this stage of sludge domestication and during the normal operation of the system afterwards, the sludge reflux ratio should be strictly controlled. If the sludge reflux ratio is not guaranteed, the following phenomenon may occur: insufficient activated sludge to treat the pollutants. This situation usually occurs one to two weeks before the start of the system; if the sludge backflow is relatively small, causing the sludge to stay in the sedimentation tank for a long time, and the anaerobic reaction of the sludge in the secondary sedimentation tank may occur Floating and odor; thick sludge layer formed in the secondary sedimentation tank, which may lead to a higher concentration of suspended solids in the effluent; when there is sufficient dissolved oxygen concentration, the activated sludge will produce nitrification in the biological treatment tank The reaction may lead to denitrification in the sedimentation tank and increase the amount of sludge. After the fourth stage of sludge acclimatization is completed and after sludge acclimation is completed, the operating parameters of activated sludge should be within the design control range and be relatively stable.


    7, temperature requirements


    Temperature is one of the environmental factors for domestication of shadow sludge. Various microorganisms grow in a specific range of temperature. The temperature range for domestication of sludge is 10 ~ 40 ℃, and the optimal temperature is 20 ~ 30 ℃. Therefore, it is recommended not to put the system in the winter for the first time.


    8.pH requirements


    pH is also one of the influencing factors. During sludge domestication and subsequent normal operation, the pH of the system's inlet water should be controlled between 6 and 9.


    9, nutritional requirements


    Good nutritional conditions are a prerequisite for bacterial flora metabolism and growth. In the process of sludge domestication, the parameters of nutrient substances should be controlled at BOD: N: P of about 100: 5: 1 to provide good growth conditions for sludge domestication.


    10.Dissolved oxygen (DO) requirements


    DO is the main control index in the sludge acclimation process. During the sludge acclimation process, the range of DO should be controlled to 0.5 ~ 2.0mg / L. (The measurement point of the dissolved oxygen concentration is 4.5 meters downstream of the water of the rotary disc aerator). DO can be detected by a dissolved oxygen analyzer or manually to understand the change rule of DO in the pool.


    11. MLSS requirements


    Biological is the active part of sludge and the main body of organic matter metabolism. It plays a major role in biological treatment process, and the value of MLSS of mixed liquid sludge concentration can relatively indicate the biological part. The concentration of activated sludge should be controlled at 2 ~ 4g / L.


    12, biological phase microscopy requirements of sludge


    Activated sludge is in different growth stages, and various types of microorganisms also show different proportions. Bacteria are responsible for the basic and basic metabolic functions of decomposing organic matter, while protozoa (including metazoans) eat free bacteria. Normally activated activated sludge contains bellworms, rotifers, ciliates, and gelatin pellets. When the mycelium pellets are large. Bellworms are active and numerous. When rotifers and nematodes appear, the sludge is mature and of good quality.


    13.Requirement of sedimentation ratio (SV) for 30 minutes


    During normal operation of activated sludge, the sedimentation ratio of sludge within 30 minutes should be controlled between 15% and 30%.


    14.Adjustment of sludge age


    Its main basis is the sludge concentration in the oxidation ditch, the suspended solids concentration (SS) and the sludge sedimentation performance index (SVI) in the oxidation ditch. The main control means is to adjust the remaining sludge discharge. Residual sludge discharge is the most important operation in the activated sludge process control. It controls the concentration of the mixed liquid, controls the sludge age, changes the species and growth rate of microorganisms in the activated sludge, changes the aeration tank oxygen demand and changes Settling performance of sludge.


    15. Calculation of sludge age


    QS = (MLSS * Va) / (Q * SSi)


    In the above formula:


    QS: sludge age (d)


    MLSS: concentration of suspended solids in the mixed solution (mg / L)


    Q: inlet water flow (m3 / d)


    SSi: suspended solids concentration in water (mg / L)


    16.Calculation formula of average cell residence time


    MCRT = (MLSS * Va) / (Qw * SSr + Q * SSe)


    In the above formula:


    MLSS: concentration of suspended solids in the mixed solution (mg / L)


    Va: volume of oxidation ditch (m3)


    Qw: daily sludge discharge (m3 / d)


    SSr: reflux sludge concentration (mg / L)


    SSe: concentration of suspended solids in effluent (mg / L)


    QS of activated sludge is about 15 days, MCRT should generally be slightly lower than QS, and gradually lowered during the operation. The reflux sludge concentration SSr is mainly controlled by the reflux ratio. When the reflux ratio increases, the sludge concentration decreases, and when the reflux ratio decreases, the sludge concentration increases. The sludge concentration is used to calculate F / M.


    17.Adjusting the amount of dissolved oxygen


    The main basis is the dissolved oxygen (DO) concentration in the oxidation ditch, the main means is the control of aeration intensity; in the oxidation ditch, the sewage mixed liquid circulates in the oxidation ditch, and it is propelled and oxygenated by a rotating brush, a disc or a meter. In the downstream of the aeration device, the dissolved oxygen concentration changes from high to low, and the aerobic section gradually transitions to the anoxic section. The dissolved oxygen concentration DO in the aerobic section should be controlled between 1 mg / L and 3 mg / L, and the DO in the anoxic section should Control 0.2 ~ 0.5mg / L. Rotary brush (rotary disc) exposure can adjust the height of the weir, so that the rotary brush (rotary disc) can change the submergence buoyancy and change the aeration amount. Turn on or reduce the number of brushes (disc) to adjust the aeration. If the amount of aeration is reduced and the flow velocity of water in the pool is affected (should be controlled above 0.25m / s), an underwater thruster should be added to ensure the flow velocity in the pool and not to cause sedimentation.


    18.Adjustment of the amount of returning sludge


    Its main basis is the sludge sedimentation index and the thickness of the secondary sedimentation tank, and the main control method is the reflux ratio. In the oxidation ditch process, all the sludge from the secondary sedimentation tank after the reasonable discharge of the remaining sludge must be returned to the oxidation ditch to ensure the sludge concentration in the aeration tank, thereby ensuring its processing capacity, and the control of the amount of returned sludge is Based on this requirement, the methods are: control according to the mud level of the secondary sedimentation tank, that is, the mud level determined according to the design requirements, or control the thickness of the mud layer between 0.3 and 0.9 m, and make the thickness of the mud layer less than the depth of the water above the mud level 1/3. If the actual mud level exceeds the set mud level, the backflow should be increased. If the mud level is lower than the set value, the backflow should be reduced to gradually control the mud level to the set value, but the adjustment amount should not exceed 10%. Check the change of mud level during the next inspection, and then give appropriate adjustments. When the mud level of the second settling tank is stable, at a value, it means that all the sludge has returned to the aeration tank and reached the process requirements. The flow is directly related to the amount of water inflow. The amount of water inflow increases (or decreases). The amount of sludge brought out of the aeration tank increases (or decreases) proportionally. The return flow should also increase (or decrease) proportionally. Therefore, it is customary to use the reflux ratio (R), that is, the ratio of the amount of sludge returned to the water.


    19. Rectification of running status


    The unsatisfactory running status is usually caused by the above three adjustments. Improper hydraulic load (F / M) may also be one of the reasons, or it may be mechanical or hydraulic faults and sudden changes in the quality of the incoming water (such as unplanned industries Impact load of sewage). The timely adjustment must be summarized after the long-term trend analysis of seasonal water quality (water temperature) water volume during operation. The adjustment of operating parameters has a lag effect, so it should be adjusted carefully (single adjustment amount should be less than 10%) and patiently observe. For common operation fault characterization and countermeasures, please refer to Appendix IV, System Fault Diagnosis Guide. Each plant can be added or deleted according to its own situation. In the process of correcting the running state, the key process control parameter is F / M, which is the BOD5 sludge load. The F / M calculation formula is as follows:


    F / M = (Q * BOD5) / (MLVSS * Va)


    MLVSS = f • MLSS


    In the above formula:


    Q: Water inflow (m3 / d)


    BOD5: five-day biochemical oxygen demand (mg / L)


    f: constant, generally 0.75 for municipal sewage


    MLVSS: Concentration of volatile suspended solids in the mixed solution (mg / L)


    Va: effective volume of oxidation ditch (m3)


    Since it takes five days for BOD5 to obtain results, the COD is also used to push BOD5. The F / M value of the oxidation ditch should be controlled between 0.05 and 0.15.


    20.Fault scheduling


    Emergency status of sewage plants include:


    a) power failure or power failure;


    b) major faults in the plant;


    c) pipeline pump station failure;


    d) Storm and flood.


    The dispatch of sewage entering the factory during a heavy rain is coordinated with the drainage management office and the lifting pump station with the assistance of the central control room.

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