Introduces the Shenzhen Luofang Sewage Treatment Plant Phase II project process overview and commissioning process, as well as oxidation ditch flow field and dissolved oxygen field test results. The project's various structures, equipment are able to operate normally, the effluent water quality is comprehensive and stable to meet the national secondary sewage treatment plant level 1 discharge standards, its biological phosphorus removal effect has reached the international advanced level, the unit power consumption at home and abroad in the sewage treatment plant is at the advanced level, the debugging results proved that the project is a success.
1 Project Introduction
1.1 Commissioning Overview
Shenzhen Luofang Wastewater Treatment Plant debugging [1] is to: ensure that the structures, piping systems and electromechanical equipment can be designed to operate normally; to ensure that the operation indexes to meet the design requirements; the establishment of the equipment and the unit operation of the operating procedures; optimization of the operating parameters and treatment results for the future normal operation, laying the foundation for scientific management. Lay the foundation for normal operation and scientific management in the future.
The debugging team first develops the debugging outline according to the design documents, and then puts forward the debugging plan in phases, and specifically engages in the debugging work. Debugging team timely debugging results and problems found in the form of reports to the Shenzhen City Water Supply and Drainage Project Construction Command, and inform the debugging unit.
Commissioning of the relevant units every Monday in Shenzhen Luofang Sewage Treatment Plant held a regular meeting to discuss, coordinate and solve the problems arising from the commissioning. Command from time to time to convene debugging debriefing, study and resolve major problems encountered in the commissioning. Debugging debriefing and make important decisions on the weekly meeting, are formed by the commissioning team minutes of the meeting, notify the commissioning of the relevant units.
The commissioning team first equipment inspection and empty machine debugging (underwater equipment is generally not empty machine debugging, so as not to burn out). Then use the plant a project out of water for oxidation ditch clear water test, and ditch flow field test. When the clean water debugging is trouble-free, the oxidation ditch is then transferred to the sewage debugging and sludge cultivation stage, and determine the dissolved oxygen field, other structures are directly for sewage debugging. Finally, the whole process, a longer period of system commissioning.
1.2 Project Overview
Shenzhen Luofang Sewage Treatment Plant was built in 1990, a project was formally put into operation in 1998, the second phase of the project was started in 1999 to build, has been completed and put into operation.
Shenzhen Luofang Wastewater Treatment Plant Phase II project design scale of 250,000 m3 / d, raw sewage into the plant and the treated effluent water quality indicators (i.e., GB8978-96 "Comprehensive Sewage Discharge Standards" in the first level of the standard) is shown in Table 1, in addition to the table also lists the influent water temperature, effluent water pH and the dewatering of sludge after the moisture content of the requirements.
The main process used in this project is a three-ditch oxidation ditch, see Figure 1. Due to the need for biological phosphorus removal, a separate anaerobic tank is set up before the oxidation ditch. In order to ensure that the anaerobic tank to achieve strict anaerobic state, and in the anaerobic tank before the addition of reflux sludge thickening tank.
The retention time of the reflux sludge thickener is about 0.8 h. The reflux sludge enters into the sludge channel on both sides of the pool, and enters into the pool through the sludge distribution hole. Supernatant and anaerobic tank effluent together directly into the oxidation ditch distribution well, and take away a lot of nitrate. About 50% of the return flow of gravity thickened sludge passes through the sludge discharge pipe and enters the anaerobic tank together with the raw sewage from the sand sedimentation tank.
The anaerobic tank has a hydraulic retention time of 30min, circulating push-flow type, and is equipped with an underwater agitator.
The second phase of the project*** adopts four three-ditch oxidation ditch, each with a design scale of 62,500 m3/d and a design depth of 5.8 m. The rotary brush is installed under the oxidation ditch bridge, and the electric adjustment weir door is set up on both sides of the oxidation ditch side ditch.
Oxidation ditch equipment operation by time control by cycle operation, each cycle is divided into six stages, see Figure 2.
A stage. Running time is 1.5h. Sewage enters the anoxic state of ditch Ⅰ where all submersible mixers are running and all aeration brushes are closed to complete denitrification. Part of the mixed liquid in ditch Ⅰ goes into ditch Ⅱ, and the other part is discharged as return sludge. All rotary brushes and submersible mixers in ditch Ⅱ are running to carry out nitrification. The mixed liquor in ditch Ⅱ in aerobic condition goes into ditch Ⅲ. Ditch Ⅲ is in the state of sedimentation and discharge, all the rotary brushes and submersible mixers in the ditch are shut down, and the discharge water is discharged through the electric adjustment weir door.
Stage B. Running time is 1.5h. Wastewater enters the aerobic state of ditch Ⅱ where all rotary brushes and submersible mixers are running. All rotary brushes and submersible mixers in Ⅰ ditch are also fully operated. The mixed liquor in ditch Ⅱ enters ditch Ⅲ and ditch Ⅰ. Ditch III is in a settling and effluent condition.
C stage. Running time is 1h. Wastewater enters ditch Ⅱ in aerobic condition with all rotary brushes and submersible mixers running, and part of the mixed liquid in ditch Ⅱ enters ditch Ⅲ, and the other part is discharged as return sludge. All rotary brushes and underwater mixers in Ⅰ ditch are turned off in pre-sedimentation state. The remaining activated sludge is discharged from ditch Ⅰ. Ditch Ⅲ is in the state of sedimentation and water discharge.
D, E, F stage. The operation state is basically the same as that of A, B and C stages respectively, only that Ⅰ ditch and Ⅲ ditch are interchanged.
2 commissioning process
2.1 unit commissioning
November 19, 2001, the commissioning team began the equipment inspection and empty machine commissioning preparatory work. December 3, began to oxidation ditch equipment inspection and empty machine commissioning. December 4, began to lift the pump room commissioning preparations, pre-commissioning inspections and empty machine operation test.
December 25, 2001, began to 1?# oxidation ditch and 2?# oxidation ditch injection of the first phase of the project's secondary sedimentation tank water. In the process of water injection, found that the expansion joints of the oxidation ditch outlet catchment tank leakage, water injection suspended. 28 December, after the construction unit rectification, oxidation ditch outlet tank leakage problem solved, oxidation ditch began to introduce the first phase of the project of the second sinking tank water. Then, the commissioning team carried out the oxidation ditch equipment clear water operation commissioning, and check the anaerobic tank equipment.
On January 10, 2002, the Phase II thickener and anaerobic tank were pumped from the oxidation ditch into the Phase I secondary sedimentation tank effluent, and the equipment clean water operation commissioning began.
During the above equipment inspection and clear water commissioning process, the commissioning team has never found any serious problems, but has identified many minor problems that have been submitted in batches to the design, supervision, construction, installation and manufacturers. So far, all problems directly affecting operation have been rectified, and there are still some remaining problems in the process of rectification.
January 15, 2002, the second phase of the project began to enter the sewage, with load sewage commissioning and sludge culture preparation.
On January 21, 2002, according to the characteristics of the two phases of the plant, the activated sludge of the first phase of the plant, through the thickening tank of the sludge dewatering system, overflowed into the influent system of the second phase of the project, and sludge cultivation formally began. on January 25, the two oxidation ditches reached 1.6g/L and 0.9g/L of MLSS, respectively; and on January 29, 1.6mg/L and 1.1mg/L. The MLSS of the two oxidation ditches reached 1.6mg/L and 1.1mg/L respectively. 1.1mg/L. On February 28, the MLSS of the middle ditch and side ditch of 1?# oxidation ditch reached 4.1g/L and 4.4g/L respectively, and that of 2?# oxidation ditch reached 3g/L and 2.9g/L, which have met and exceeded the design requirements, marking the end of the sludge cultivation phase of the plant. Oxidation ditch effluent is clear.
2.2 System Commissioning
After the unit commissioning is successfully completed, the wastewater treatment plant system is put into a longer period of trial operation to carry out further system commissioning work, in order to confirm the system's processing performance, to find out and promptly correct the irregularities that may occur, to optimize the operating parameters, to ensure that the whole system achieves the best operating condition and processing effect.
System commissioning will be through a number of PDCA cycle, find problems, solve problems, and constantly optimize the process parameters, improve the system treatment effect, until the system fully meet the design requirements.
March 9, 2002, the second phase of the system commissioning began to carry out. Due to the unit debugging work is carried out very fully, so the system debugging work is very smooth, the water quality will soon stabilize to meet the design requirements.
In June 2002, the system commissioning work was successfully completed.
3 treatment effect
3.1 the main pollutants in the water
March 2002, the commissioning team of Shenzhen Luofang Sewage Treatment Plant Phase II project of the incoming and outgoing water quality and process parameters of a comprehensive laboratory analysis.
During the commissioning period, the SS of the two oxidation ditch effluent of the second phase of the project is 18mg/L at most, 5mg/L at least, 12mg/L on average, which is much lower than that of the design requirement of ≤20mg/L.
During the commissioning period, the BOD of the oxidation ditch effluent is 10mg/L at most, 1-2mg/L at least, 5-6mg/L on average, all of which is much better than that of the design requirement of ≤20mg/L.
The water quality and process parameters of the Luofang Wastewater Treatment Plant in Shenzhen have been comprehensively analyzed by the commissioning team.
During the commissioning period, the COD of the oxidation ditch effluent is 49-58mg/L at maximum, 11-12mg/L at minimum, and 30mg/L on average, which is much lower than that of the design requirement of ≤60mg/L.
During the commissioning period, the pH of the oxidation ditch effluent is in the range of 7.23-8.17, which meets the design requirement of 6.5-9.
The water from Phase II of the project has the following characteristics To summarize, the main pollutant indicators of Phase II project effluent have reached and are much better than the design requirements.
3.2 Nutrients in and out of the water
The ammonia nitrogen in the effluent of the second phase of the project is designed to be ≤15mg/L, and the actual ammonia nitrogen in the effluent of the two ditches is only 5.34mg/L at most, and the average is between 0.22-0.67mg/L, which is greatly better than the design requirements.
During the commissioning period, total phosphorus in the effluent of the two ditches averaged between 0.26 and 0.27mg/L, less than 0.5mg/L.
3.3 Oxidation ditch sludge indicators
During the commissioning period, the second phase of the project oxidation ditch ditch in the suspended solids concentration in the mixture of between 1752 and 5448mg/L, an average of 3456 to 3478mg/L, in line with the design requirements of 3.4g/L.
Because there is no primary sedimentation tank in the second phase of the project, the activated sludge has more mud and sand, and the organic matter is relatively less, and the concentration of volatile suspended solids in the mixed liquor of the middle ditch of the oxidation ditch is low, which accounts for only 43% of the MLSS.
During the commissioning period, the sludge volume index (SVI) of the middle ditch of the oxidation ditch of the second phase project was 78-96mL/g, which was below 100mL/g, indicating that the performance of sludge settling was good.2?# The SVI of the side ditch of the oxidation ditch was 95.96mL/g, and the performance of sludge settling was not as good as that of the middle ditch.
3.4 Sludge dewatering effect
Shenzhen Luofang Wastewater Treatment Plant Phase II Project added 3 sets of centrifugal thickening and dewatering machines in the dewatering room of the original Phase I Project, which enlarged the sludge dewatering capacity.
The residual sludge of Phase II project is thickened and dewatered directly in the centrifuges, while the sludge dewatering of Phase I project needs to be thickened in the belt filter press thickeners and then dewatered in the belt filter press dewaterers. Compared with the two, the workflow of the Phase II project is shorter and easier to operate.
During the commissioning period, the average water content of sludge after centrifuge dewatering in the second phase of the project was between 69% and 71%, which was much better than the design requirement of 80%. Compared with the average 82% water content of sludge after dewatering in the Phase I project, the dewatering effect of the Phase II project is significantly improved.
3.5 Production operation
According to the "Statement of Production Operation of Shenzhen Sewage Treatment Plant" compiled by Shenzhen Luofang Sewage Treatment Plant, the production operation since March 2002 when it entered into the commissioning of the trial operation system is shown in Table 2.
Table 2 Production Operation of the Phase II Project in 2002 Monthly Wastewater Volume (10,000m3) Inlet Volume
(10,000m3/d) unit power consumption
(kW-h/m3) dry sludge (t) unit of sludge production
(t/ 10,000m3) Phase I Phase II I,II Phase II converted 3241.9214.17.140.23194.9391.520.434258.0225.07.500.22218.57101.820 .455276.0289.39.330.22258.82132.450.466247.0280.79.360.24518.00275.540.98 average 255.7252.38.330.23297.58150.330.58 As seen in Table 2, during the period of March to June 2002, the The water intake of the second phase of the project ranged from 7.14 to 93.6 thousand m3/d, with an average of 83.3 thousand m3/d, which is only 67% of the designed water intake of 125 thousand m3/d, and is still insufficient.
The unit power consumption of the second phase project is between 0.22 and 0.24kW-h/m3, with an average of 0.23kW-h/m3, which is undoubtedly at an advanced level in domestic and international sewage treatment plants.
The unit sludge production of the second phase of the project is between 0.43 and 0.98t dry sludge/ 10,000m3 of sewage, with an average of 0.58t dry sludge/ 10,000m3 of sewage, which is also relatively low in similar sewage treatment plants at home and abroad.
4 Oxidation ditch flow field and dissolved oxygen field
4.1 Oxidation ditch flow field
In March-April 2002, the commissioning team carried out the oxidation ditch flow field measurement, *** arranged 28 measurement points, each point measuring the flow rate of 7 different depths, the location of the flow rate measurement point is shown in Figure 9, the results of flow rate measurements are shown in Tables 3 and 4.
Because the two side ditches are the
As the working conditions of two side ditches are exactly the same, so the flow field must be exactly the same, so only one of the side ditch flow field can be measured. Whether it is a side ditch or a middle ditch, its internal conditions are centrosymmetric, so its flow field must also be centrosymmetric, so only half of the flow field can be measured. For the convenience of measurement, the measurement point is arranged near the working bridge.
Beyond the following and side ditch section 11, all the measured flow velocity is greater than 0.3m/s, to meet the design requirements.
However, the flow velocities of side ditch section 1 and side ditch section 11 are special. As can be seen from Figure 9, both are located in the oxidation ditch water flow turn after the return area, so the longitudinal flow velocity is smaller. However, since the measurement results fail to reflect the lateral flow rate and vertical flow rate that should be present in the return area, the actual flow rate in both areas should be greater, and the turbulence in the return area is strong, so it is impossible to have the bad phenomenon of activated sludge deposition in both areas.
Summary of the above, the flow field of oxidation ditch is basically good, and there is no activated sludge deposition at any location.
4.2 Dissolved oxygen field of oxidation ditch
In March 2002, the commissioning team carried out the measurement of dissolved oxygen field of oxidation ditch. *** arranged 10 measurement points, dissolved oxygen measurement point location is shown in Figure 10. dissolved oxygen measurement results are shown.
Because of the limitations of the cable length of the dissolved oxygen probe, each point can only measure the dissolved oxygen at a depth of 1.5m underwater, however, the oxidation ditch is well-mixed, and the dissolved oxygen at this point can basically represent the situation of the whole section.
See from Figure 11, in the rotating brush is not open, the underwater propeller is fully open conditions, the oxidation ditch side ditch in anoxic state, this time the average dissolved oxygen in the range of 0.1 ~ 0.9mg / L, all the data averaged 0.36mg / L, to meet the process requirements.
Obviously, because the oxidation ditch just from the aerobic stage into the anoxic stage when the dissolved oxygen will be higher, and then gradually reduced, so the measured side ditch dissolved oxygen data have a certain range is reasonable.
See from Figure 12, in the rotating brush and underwater thruster full open conditions, oxidation ditch in the ditch is in aerobic state, at this time the average dissolved oxygen in the range of 4.12 ~ 7.37mg / L, all the data averaged 5.22mg / L, to meet the process requirements.
Also due to the oxidation ditch just from the anoxic stage into the aerobic stage of dissolved oxygen will be lower, and then gradually improve, so the measured dissolved oxygen data in the ditch there is a certain range, is also reasonable.
It is worth noting that, it is generally believed that the oxidation ditch dissolved oxygen can only reach the level of 3mg / L or so, and Luofang Wastewater Treatment Plant oxidation ditch aerobic state of the ditch on March 17, 2002, measured point 2 of the highest measured dissolved oxygen reached 7.54mg / L, the day in the ditch of the average of all measurement points of the dissolved oxygen as high as 7.37mg / L, much higher than the literature contained in the other oxidation ditch, which should be the plant's excellent treatment results. should be one of the reasons for the excellent treatment effect of the plant. This phenomenon indicates that the plant has an excellent design, good aeration and mixing equipment, and a high level of management. Of course, the process does not require such high dissolved oxygen, in actual operation can be appropriate to reduce the number of open aeration rotary brush to reduce energy consumption.
5 Conclusion
Shenzhen Luofang Sewage Treatment Plant Phase II project of the various structures, equipment can operate normally, the effluent quality of water to meet the standards of comprehensive and stable, debugging results to prove that the project is a success.
The effect of biological phosphorus removal in the second phase of the project has undoubtedly reached the international advanced level, and it is worthwhile to summarize the experience in design, construction, commissioning and management.
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