Online Storage Technology of the Separate Sewage System: Demonstration Study in a Typical Plain River Network City
Abstract
:1. Introduction
2. Methodology
2.1. Site Description
2.2. I/I Quantification
2.3. SWMM-Based Analysis of Storage Capacity
- (1)
- Base Model-Hydraulic Module
- (2)
- Infiltration Module
- (3)
- Inflow module
- (4)
- Storage capacity evaluation
2.4. Rule-Based Control Strategy for Online Storage Scheduling
- The pumping stations are classified according to their importance of the service area and ground elevation. Commercial, residential areas, and areas with low ground elevation (prone to flooding) are listed as critical protection areas; industrial areas away from the city center, logistics areas, and areas with high ground elevation are listed as general areas.
- When there is an increase in the I/I induced by rainfall, priority is given to ensuring the normal operation of pumping stations in critical areas, increasing the conveying amount of water and avoiding sewage overflow in these areas. For general areas, reduce the conveying amount of water from pumping stations, alleviating the pressure of their water load on pumping stations in downstream critical areas.
- The pre-emptying rule before rainfall. Suppose the weather forecast indicates that a rainfall event will occur. In that case, the sewage plant and the pumping station intake can be increased in advance for pre-emptying of the pipe network to cope with the upcoming rainfall event.
- Water-level balancing rules of lateral pumping stations under rainfall. Under rainfall, a pumping station (called “pumping station A”) exceeds its critical water level, in addition to flow restriction upstream, the water-level balance of lateral pumping stations (other pumping stations that converge to the same downstream pumping station) can also be carried out. Suppose the water level of the lateral pumping station B is below the critical level. In that case, the flow of pumping station B can be reduced (using the storage room of the pipeline system when the critical level has not been reached). In contrast, the flow of pumping station A can be increased to ensure that the total flow is relatively stable to better achieve the level balance between pumping stations A and B, making full use of the storage room of different pumping stations.
- Limit water-level protection rules. Set the limit levels (including the minimum and maximum values) for each pumping station. When the level is lower than the minimum value, all pumps must be forced off; a pump (or multiple pumps) must be forced on when the level is higher than the maximum value.
- Flow restoration rules after rainfall. After rainfall, if all other downstream pumping stations and the front pond of the sewage plant have returned to their normal level range, the pumping station can be released from the rain flow restriction and return to dry-season level control mode. Executing judgment on individual pumping stations allows all pumping stations to gradually return to the dry-season control mode. However, it should be noted that in order to avoid unstable pumping station operation, when cutting back to dry-season control mode, instead of starting multiple pumps (not including those previously switched on), only one pump should be switched on for a certain period of time, followed by the next pump.
- In accordance with the above principles, changes in water levels at the pumping stations and complaints of sewage overflow in their service areas are monitored during rainfall, and the operation of pumping stations is scheduled based on manual experiences and storage capacities evaluated from Section 2.3.
- (1)
- If the rising rate and duration of water level at the Xiangmen pumping station exceed a specific value, indicating the flow amount of influent is large. According to particular rules, the pump-control water level is increased up to the maximum limit to maximize online storage capacity at this level.
- (2)
- At the same time, calculate and assess the storage capacities of the two upstream pumping stations of Xuanqiao and Pingzhi and their corresponding pipes in their service areas. Prioritize the reduction of water conveyance from the Xuanqiao pumping station in accordance with its importance and storage capacity to reduce the pressure of rising water levels at the downstream Xiangmen pumping station.
- (3)
- If the water level of the Xiangmen pumping station is still rising, reduce the amount of water conveyed from the Pingzhi pumping station. Conversely, when the peak flow has passed and the water level at Xiangmen pumping station tends to be normal, the pumping stations will gradually return to their original operating state in order.
3. Results and Discussion
3.1. I/I Quantification
3.2. SWMM Model and Storage Capacity Evaluation
3.3. Effects of Rule-Based Control Strategy
- The peak-time water level and duration are significantly reduced. Compared with 2020, the average duration of peak hours during daytime is reduced by 3 h, and the highest water level is reduced by 56 cm. The average duration of peak hours at night is reduced by 1 h, and the highest level is reduced by 55 cm. The design cooperative control mode reduces the duration of peak hours and the highest level and fully guarantees the safety of the pipe network operation.
- The storage capacity of the pipe network has increased significantly. After implementation, the storage capacity was increased by 198 and 293% during the day and night, separately.
- The number of pump starts and stops was reduced by 96%. The number of frequent starts and stops before commissioning was 15.8 times/day; after commissioning, the number of frequent starts and stops was 0.6 times/day, an overall decrease of 96% compared to the same period in the previous year. The number of frequent starts and stops of the sewage pumping station has been significantly reduced, which has a positive effect on the pump-life extension and the reduction of energy consumption of the pumping station.
- In terms of energy consumption per unit in the pumping stations, the average unit consumption before was 0.037 kWh/m3 and after was 0.032 kWh/m3, a 12.2% overall decrease compared to the same period in 2020.
- Inflow fluctuations of the sewage plant were reduced by 30%. Through pre-drainage during the usual period, staggered conveyance and discharge during the peak period utilizing full use of the sewage network storage room make the influent flow to plants water relatively balanced, ensuring a stable sewage plant operation and effluent quality.
4. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Indicator | Statistical Type | Source of Sewage | Upstream Mixed Sewage | Downstream Mixed Sewage | Infiltration | |||||
---|---|---|---|---|---|---|---|---|---|---|
Residents | Productive Service | S1 | S2 | S3 | S5 | S6 | S7 | Groundwater | ||
TN | Range | 51.9~109.0 | 17.9~31.6 | 4.9~28.0 | 15.7~51.3 | 35.8~99.6 | 8.0~44.0 | 22.4~59.2 | 27.5~58.1 | 1.1~3.5 |
Average | 69.3 | 23.9 | 13.3 | 27.4 | 60.7 | 17.6 | 37.4 | 43.3 | 2.5 | |
Standard deviation | 17.0 | 6.0 | 8.2 | 11.6 | 19.4 | 11.6 | 10.2 | 9.9 | 0.8 | |
Coefficient of variation | 0.25 | 0.25 | 0.62 | 0.42 | 0.32 | 0.66 | 0.27 | 0.23 | 0.31 | |
Electric conductivity | Range | 756~1743 | 998~1274 | 670~793 | 752~1172 | 790~1229 | 632~1040 | 624~995 | 908~1233 | 690~739 |
Average | 1156 | 1110 | 728 | 889 | 955 | 778 | 761 | 1012 | 714 | |
Standard deviation | 242 | 126 | 41 | 132 | 119 | 129 | 122 | 101 | 21 | |
Coefficient of variation | 0.21 | 0.11 | 0.06 | 0.15 | 0.12 | 0.17 | 0.16 | 0.1 | 0.03 | |
18O | Range | −3.55~−3.44 | −3.57~−3.33 | −4.57~−3.74 | −4.05~−3.49 | −4.02~−2.83 | −5.17~−4.20 | −4.74~−4.44 | −4.27~−3.82 | −6.23~−5.31 |
Average | −3.50 | −3.48 | −4.09 | −3.83 | −3.64 | −4.74 | −4.59 | −4.00 | −5.72 | |
Standard deviation | 0.04 | 0.12 | 0.25 | 0.17 | 0.32 | 0.31 | 0.09 | 0.13 | 0.38 | |
Coefficient of variation | 0.01 | 0.03 | 0.06 | 0.04 | 0.09 | 0.06 | 0.02 | 0.03 | 0.07 | |
2H | Range | −27.55~−27.05 | −28.02~−26.74 | −33.25~−27.31 | −30.00~−26.67 | −29.44~−20.69 | −38.56~−31.06 | −32.26~−30.50 | −31.79~−29.44 | −40.29~−30.71 |
Average | −27.29 | −27.47 | −30.31 | −28.56 | −26.40 | −35.55 | −31.14 | −30.51 | −36.05 | |
Standard deviation | 0.14 | 0.57 | 1.64 | 1.30 | 2.59 | 2.50 | 0.58 | 0.67 | 4.25 | |
Coefficient of variation | 0.01 | 0.02 | 0.05 | 0.05 | 0.10 | 0.07 | 0.02 | 0.02 | 0.12 |
Spatial Hierarchy | Typical Plots | Service Area of Pumping Station | Service Area of WWTP | |||
---|---|---|---|---|---|---|
Monitoring points | S1 | S2 | S3 | S5 | S6 | S7 |
Hourly average infiltration rate (%) | 27 | 15 | 8 | 55 | 48 | 22 |
Hourly average infiltration flow (L/s) | 0.63 | 0.65 | 0.20 | 22.14 | 188.55 | 415.31 |
Maximum hourly infiltration rate and flow | 2.61 | 2.05 | 2.52 | 1.36 | 1.13 | 1.59 |
Area Names | Xinzhuang | Sanyuan | Chengxi | Chengnan | Jiaoyuyuan | Fuxing |
---|---|---|---|---|---|---|
Parameter a | 0.0663 | 0.0700 | 0.0463 | 0.0997 | 0.0302 | 0.3948 |
Parameter b | 0.5490 | 0.5266 | 0.6885 | 0.4722 | 0.5197 | 0.4824 |
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Dai, X.; Xu, G.; Ding, Y.; Zeng, S.; You, L.; Jiang, J.; Zhang, H. Online Storage Technology of the Separate Sewage System: Demonstration Study in a Typical Plain River Network City. Water 2022, 14, 3194. https://doi.org/10.3390/w14203194
Dai X, Xu G, Ding Y, Zeng S, You L, Jiang J, Zhang H. Online Storage Technology of the Separate Sewage System: Demonstration Study in a Typical Plain River Network City. Water. 2022; 14(20):3194. https://doi.org/10.3390/w14203194
Chicago/Turabian StyleDai, Xiaohu, Guozhong Xu, Yongwei Ding, Siyu Zeng, Lan You, Jianjun Jiang, and Hao Zhang. 2022. "Online Storage Technology of the Separate Sewage System: Demonstration Study in a Typical Plain River Network City" Water 14, no. 20: 3194. https://doi.org/10.3390/w14203194
APA StyleDai, X., Xu, G., Ding, Y., Zeng, S., You, L., Jiang, J., & Zhang, H. (2022). Online Storage Technology of the Separate Sewage System: Demonstration Study in a Typical Plain River Network City. Water, 14(20), 3194. https://doi.org/10.3390/w14203194