1. Overview
A sewage treatment plant was officially put into operation in October 1992. It uses secondary biochemical treatment, traditional activated sludge process, and blast aeration. During its 14 years of operation, the plant has always been committed to strengthening process control to ensure that the effluent meets discharge standards, and has made due contributions to water pollution control. At the same time, a series of problems were discovered during operation. During the practice, through the efforts of technical personnel, corresponding improvements were made to ensure that the old factory can play its due role.
2. Existing problems and countermeasures
2.1 Problems and solutions to the grille decontamination machine The grille is a key process in the pretreatment process. Its function is to intercept and remove large particles. of solid matter, and at the same time protects the sewage pump in the subsequent process, reduces floating matter in the sedimentation tank, and prevents blockage of the process pipeline. The factory's original design had only one grille with a 25mm gap, which was a medium-thick grille type. There are four shortcomings:
(1) The drainage facility in the service area is a combined rainwater and sewage system. There is a large amount of screen slag in the rainy season. Coupled with the large amount of water, cloth strips, soft plastic products and other debris are washed away in the water. Passing through the fence and entering subsequent structures will have a greater impact on water pumps, especially submersible pumps.
(2) The plant does not have fine grates, and the amount of scum formed by floating objects in the sedimentation tank is very large. The operator who removes the scum has a heavy workload, plus a long period of skimming. The slag operation causes a large amount of sewage to return to the grate well and must be lifted again, which increases the energy consumption of the sewage pump.
(3) Only one grille is a design defect. If the grille fails, water inflow must be stopped. Therefore, the grille is required to have reliable sludge removal performance. The factory's original grille decontamination machine was a high-chain grille decontamination machine. Due to the material problem of the tooth scraping arm, it was easy to deform, which affected the accuracy of the teeth entering the slot. The slag removal effect was poor, which affected production.
(4) The factory once installed a fine grid with a grid pitch of 6 mm at the outlet of the grit chamber. However, due to site restrictions, it was unable to install an accident crossing device. Water often leaked out, affecting production. Forced to demolish. Therefore, fine grilles cannot be added.
In order to solve the above problems, the factory updated the original high-chain grid decontamination machine and installed a rotary grid with model number XGS1702-4800 and a grid pitch of 10mm produced by Qingyuan Environmental Protection Machinery Factory. The screen decontamination machine greatly increases the amount of screen slag removed, creates good conditions for the operation of the submersible pump, ensures production requirements, and solves the problem of no fine screen in the plant and the problem of too much floating matter in a sedimentation tank. Moreover, the machine has a good electrical control system and can operate in various operating modes including automatic continuous cleaning, timed interval cleaning and manual cleaning. The operation mode can be changed in different seasons to achieve energy saving effects.
Through actual operation, it was found that the new grille decontamination machine also has certain defects: (1) The tooth chain of this machine is made of nylon. Because it is an outdoor environment, the temperature changes greatly in winter and summer, and coupled with sunlight, the teeth The chain is prone to aging and breaking. It is very troublesome to replace. The author believes that equipment reliability is very important since it operates in an outdoor environment and has no backup grille. Therefore, it is more reliable to use stainless steel as the tooth scraper material. (2) Due to the long continuous operation time of this machine, its function is to fish out grate slag, and the weight changes greatly, and the force of the tooth grate chain changes greatly. The check pads on both sides that have a fixed function are easy to fall off, but this part is a non-standard product. , spare parts are difficult. (3) Due to site restrictions and financial issues, there is no supporting equipment for automatic transmission and pressing of screen slag, which makes the labor intensity high for workers, and it is impossible to keep the screen slag from falling to the ground. The above defects need to be solved when the old factory is renovated.
2.2 Problems with dehydrators and solutions The factory originally had two dehydrators, model DY2000 belt filter press, and the equipment is the first generation model of the Municipal Environmental Protection Machinery Factory. There are many problems during operation: (1) The filter belt washing device cannot meet the actual requirements, and the filter belt washing effect is poor. Filter belt cleaning is the most critical process of the belt filter press. If the effect is not good, the water passing capacity of the filter belt cannot be restored, and the dehydration process cannot be continued continuously.
(2) The design of the flocculation reactor needs to be improved. The inlet of the sludge mixture is above the reactor, and a stepped drop mixing is used inside. The reaction is violent. The conditioning reaction between the flocculant PAM and the sludge is rapid, fragile, and irreversible. Therefore, The reaction flocculation is easily broken into pieces. In the gravity dewatering section, the size of the flocculation is insufficient and the material is easy to run away. Therefore, the requirements for the molecular weight of the flocculant are too high, and PAM with high molecular weight is more expensive. On the other hand, the mud cake output is low due to material running. (3) Due to technical problems with the weaving of the filter screen at that time, the filter belt interface of the machine was a metal spiral pin ring interface. During operation, the scraper was severely worn and the mud cake peeled off, which made it more difficult to clean the filter belt and had a short service life. . (4) The original design of the vacuum roller has a small hole diameter, slow shearing, dehydration and water filtration, poor effect, and easy material leakage. Moreover, the filtrate in the roller is not completely discharged and deposited, causing the vacuum roller to lose its function and affecting the mud cake output.
In order to solve practical problems in operation, attention was paid to overcoming the shortcomings of old equipment when selecting new equipment. The updated dehydrator is the DYQ2000 dehydrator. The features of this machine are: (1) In terms of filter belt cleaning, the nozzle in the cleaning water tank is a new product. The naturally formed pressure is greater than that of the old nozzle, and it is easy to disassemble. During the installation of the equipment, a pipeline booster pump was added, model ISG50-200A, with a flow rate of 11.7m3/h and a head of 0.45MPa. The flushing water was increased from the original 6m3/h to 9m3/h, and the flushing pressure was increased from the original machine. The 0.4Mpa was increased to 0.7MPa, the flushing effect was good, and the mud cake output was significantly increased. (2) The number of hollow rollers in the pressing section is changed from one to two, and the diameter of the first roller is increased from the original ф40cm to ф80cm, and the diameter of the water passing hole is enlarged, which makes it easier to realize the pre-pressing process and make a large amount of sludge floc The free water on the surface quickly squeezes the filter belt, which reduces the moisture content of the sludge in the pressing section, reduces the material loss during the extrusion process, and significantly increases the sludge cake output. (3) The structure of the flocculation reactor is more reasonable. The mud mixture enters from the bottom of the reactor and is equipped with a flocculation stirring device. The generated floc overflows from the upper mouth of the reactor and enters the gravity dewatering section. The intensity of the entire reaction process is reduced. The floc is not easy to break. Actual operation shows that the floc formation is good. Compared with the old dewatering machine, the requirements for the molecular weight of the flocculant PAM are slightly lower. (4) The filter belt of this machine is interface-less and has a long service life.
After a period of use, this machine has basically overcome the shortcomings of the old dewatering machine, but there are still certain problems: (1) The design diameter of the mud inlet pipe is small and prone to blockage. (2) The pipelines of the dissolving tank and storage tank of the ancillary equipment are easily blocked, and the dosage of the dosing pump is too small due to its shape. The above issues need to be gradually improved and improved together with the manufacturers.
2.3 Equipment energy-saving measures
After the plant was put into use in 1992, there were problems with aging equipment and high energy consumption during actual operation. During the 14 years of operation and management, the plant has always regarded energy saving and consumption reduction as an important issue in management and equipment transformation. Energy-saving transformation of sewage pumps and aeration systems is the focus of the work.
2.3.1 Problems with sewage pumps and their solutions and effects. The sewage pumps of this plant were originally designed as four 250WDL vertical water pumps, each with a power of 70kw and a water supply of 1290m3/h (actual measurement). There are problems. There are: (1) The pump manufacturer has stopped production and cannot provide spare parts. (2) The water pump packing is easy to wear, water leakage is serious, sewage splashes everywhere, the pump room has poor sanitary spare parts, replacement of packing is labor-intensive, frequent replacement, and heavy maintenance. (3) High energy consumption and low efficiency.
In order to solve the above problems, the factory replaced the 4# sewage pump with a Flygt pump CP3300LT620 model in 1999, a 44kw submersible pump. The measured water supply was 1330m3/h, which can meet the actual requirements and has good operating results. . The energy saving of water pumps was actually measured, and the average measured results were: the Flygt pump consumes 760 kWh/d per day, while the old pump consumes 1,400 kWh/d per day, and can save 640 kWh/d per day. According to current Calculated at a stage electricity cost of 0.53 yuan/kWh, one pump can save 339.2 yuan per day and 124,300 yuan a year. The energy saving and consumption reduction effect is obvious, and the equipment maintenance is simple, the failure rate is low, and a lot of maintenance costs can be saved.
At present, the update work of the plant's #1 sewage pump and two return pumps has been completed, and the operating results are very good.
2.3.2 Aeration system energy-saving issues and effect of measures The plant’s aeration tank was originally designed to use a perforated tube aeration device. Due to long use, it was severely corroded, seriously blocked, and had low aeration efficiency. The energy consumption of the aeration tank accounts for a large proportion of the energy consumption of the entire sewage plant, which is the focus of energy saving and consumption reduction. In October 2002, the factory transformed the perforated pipes in the three west corridors of the second group of aeration tanks into silicone rubber tube aeration pipes, and conducted a comparative experiment from November 1 to 30, 2002. Under the experimental conditions Under the same circumstances, the same blower and the same air inlet pipe, but the aerators are different. The east side is a perforated pipe and the west side is a modified aerator. When measured using a portable dissolved oxygen monitor, the dissolved oxygen in the west side is on average higher than The dissolved oxygen in the east has doubled, proving that the oxygen utilization rate is twice as high as before the transformation, and the effect is good.
The factory also measured the actual effect of the blower, and the results showed that the current blower consumes more power to produce the same volume of air than similar blowers on the current environmental protection equipment market. In the renovation of the old factory that will be carried out in the near future, the factory will choose frequency modulated magnetic levitation centrifugal fans with lower energy consumption to achieve energy saving effects.
2.4 Foam problem A large amount of foam often appears in the aeration tank of this plant in winter, especially when the pressure is low in cloudy weather in winter. The foam floats on the pool surface, overflows the aisles, and is sometimes blown by the wind and flies everywhere, affecting hygiene. Sometimes it is even impossible to take samples for testing. In severe cases, it brings activated sludge particles and affects normal operations.
After special research on the foam problem, *** found out 5 reasons for the foam problem, and took targeted measures to control the foam problem in winter. (1) Reasons related to temperature. Due to the low temperature, the bubbles generated in the aeration tank are not easy to break and are easy to accumulate. At this time, the process should be adjusted to appropriately reduce dissolved oxygen, etc., to destroy the foam accumulation conditions. (2) When the content of surfactant substances in the incoming water is high, it is easy to produce a large amount of foam through blasting. Coupled with the temperature conditions, foam accumulation is very easy to occur. Therefore, the source of pollution should be identified and measures should be taken to make the incoming water free of surfactants. Foaming material, the foam will disappear naturally. (3) Since the aerators used in the two aeration tanks in the east and west of the plant are different, they are medium bubble type and micro bubble type. The dissolved oxygen in the west is always higher than that in the east. The bubbles generated by microporous aeration are small and not easy to break. , easy to accumulate, so the foam in the west side of the plant's aeration tank is more serious. The plant took measures to completely clear the perforated pipes on the east side and improve the air supply efficiency of the perforated pipes, so that the dissolved oxygen in the aeration tanks on the east side and the aeration tank on the west side was close. After proper regulation, the foam was controlled. (4) In the renovation of the old plant that will be carried out soon, the aerator of the aeration tank on the east side will be modified so that the two groups of aeration tanks in the east and west will use the same tubular aerator to facilitate the adjustment of dissolved oxygen. Improve oxygen utilization. (5) When the MLSS of the aeration tank is too low, it is easier to generate foam. Therefore, strictly control the MLSS above 1.5g/l in winter, and the effect of controlling foam accumulation is obvious.
3. Conclusion
The above is a brief analysis of several problems and solutions encountered by the author in the operation and management of the plant. It is a little experience of the technical transformation work. I hope everyone can correct me. Since most of the structures and equipment of the plant are seriously aging and have entered a period of renovation and renovation, in the future we will continue to take energy conservation and consumption reduction as the premise, deeply tap the energy-saving potential in technical transformation and operation management, and resolutely implement the economic operation approved by Tangshan Drainage Company indicators, and gradually solve the problems in actual operation and design defects through technical reforms, so that the old factory can be rejuvenated.