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Sewage treatment plant pump equipment selection, installation and operation and maintenance
**I. Introduction**
Qingdao's sewage treatment plant, with a first phase capacity of 50,000 tons per day, was completed in 2002. The second phase, also with a capacity of 50,000 tons per day, was finished in 2008. A major renovation project was carried out in 2011 to upgrade the facility. In total, there are 85 different types of pumps installed, with a combined power of 1038 kW. This paper analyzes the selection, installation, operation, and maintenance of pump equipment from practical experience, offering valuable insights for similar projects and long-term operational management.
**II. Pump Selection**
In the sewage treatment plant, pumps are primarily used for water lifting, three-stage treatment, sludge return, and residual sludge discharge. Based on the characteristics of the medium, specialized sewage pumps such as submersible pumps and sludge screw pumps are typically employed. When selecting pumps, the following principles should be followed:
1) The pump must meet the required head and flow, and its operating point should lie within the high-efficiency area.
2) For long-term operation, the pump should have a high average efficiency over time, ensuring low operational and maintenance costs.
The operating point of a pump is determined by the intersection of the pipeline characteristic curve (H-Q) and the pump characteristic curve (H-Q). This intersection point represents the optimal flow and head. Additionally, the NPSHa-Q curve and NPSHr-Q curve intersect at the cavitation point, and the pump must operate below this point to avoid cavitation. These curves are usually provided by manufacturers or estimated using empirical formulas like H = K + BQ².
**III. Flow and Head Selection**
For small flow fluctuations, the pump flow can be directly selected based on the system’s needs. However, for inlet pumps with uncertain and periodic flow, it’s important not to select the maximum flow, as this could cause the pump to operate outside the efficient zone, increasing energy consumption and reducing performance. A common practice is to set Q = Qmax / 1.2.
Head selection requires careful consideration. Overestimating the head can lead to excessive power consumption and potential motor overload. It’s recommended that the selected head does not exceed 1.1 times the actual pipeline head. Choosing the right pump model involves matching the performance curve with the system curve, aiming for the highest efficiency point.
**IV. Pump Installation**
Proper installation is crucial for pump performance and longevity. Before installation, technical documents, construction plans, and equipment details should be reviewed. The foundation must be prepared accurately, with proper alignment and elevation checks. Anchor bolts should be properly placed and adjusted to ensure stability. After positioning, the pump’s horizontal and vertical alignment must be verified, and all components tightened symmetrically to prevent misalignment. Motor installation follows a similar process, with attention to shaft alignment and coupling adjustment.
**V. Pump Operation and Management**
Submersible pumps are commonly used in sewage plants and benefit from variable frequency drives (VFDs) to optimize energy use. While VFDs may require higher initial investment, they allow for flexible operation under varying conditions. Regular inspection and maintenance are essential, including checking noise levels, vibration, temperature, and electrical connections. Components like impellers, seals, and bearings should be inspected periodically for wear and replaced when necessary.
Screw pumps, often used for sludge handling, require precise speed control due to their positive displacement nature. They are sensitive to dry running, so temperature sensors and dry-run protection systems are essential. Pre-treatment units, such as grit chambers, help reduce abrasive particles that can damage the pump’s stator and rotor.
**VI. Troubleshooting and Solutions**
Impeller corrosion and wear are common issues in sewage environments due to corrosive substances and abrasive particles. Repair methods include shot peening, thermal spraying, and polymer-based coatings. Another challenge is valve blockage in dosing pumps, which can be resolved by installing a liquid storage device to maintain consistent flow without additional irrigation.
**VII. Conclusion**
Pump management in large-scale sewage treatment plants plays a vital role in overall efficiency and reliability. Through careful selection, accurate installation, and regular maintenance, operators can ensure smooth and cost-effective operations. Continuous learning and improvement are key to maintaining high-performance standards in wastewater treatment facilities.