**Guidelines for Selection and Application of Aeration Fans in Sewage Treatment Plants**
The aeration system of the sewage treatment plant is the core link of the activated sludge process, which directly affects the COD/BOD removal rate, nitrogen and phosphorus removal efficiency, and energy consumption cost. As a key equipment, the aeration fan needs to meet requirements such as stable oxygen supply, energy saving, and corrosion resistance. The following are the selection principles, mainstream equipment comparison, operation optimization, and maintenance points for aeration fans in sewage treatment plants.
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**1、 Function and performance requirements of aeration fan**
**1. Core functions**
-Oxygen Supply: Provides oxygen for microbial degradation of organic matter (BOD) (DO needs to be maintained at 2-4mg/L).
-Mixing: To prevent sludge sedimentation and maintain the suspension state of the mixture.
-Denitrification and Phosphorus Removal: Nitrification/Denitrification (A2O process) is achieved by controlling the aeration rate.
**2. Performance requirements**
|* * Indicator * * | * * Requirement * * | * * Explanation * *|
|----------------|--------------------------|-----------------------------|
|* * Airflow stability * * | Fluctuations<5 | Avoid DO fluctuations affecting microbial activity|
|* * Pressure range * * | 49~78 kPa (5~8 meters water depth) | Need to overcome water depth+pipeline resistance|
|* * Energy Efficiency Ratio * * | ≥ 4.5m3/min · kW | Low efficiency fans will significantly increase power consumption|
|* * Corrosion resistance * * | Shell anti-corrosion (such as epoxy spraying) | Sewage containing HS and humid corrosive gases|
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**2、 Comparison of mainstream aeration fans in sewage treatment plants**
**1. Roots blower**
-* * Features * *:
-Constant air volume and strong adaptability to pressure (especially suitable for factories with large changes in water depth).
-Simple structure and low maintenance cost.
-* * Disadvantages * *:
-The single-stage efficiency is relatively low (60-70), and the noise is loud (requiring the addition of a muffler).
-* * Applicable scenarios * *: Small and medium-sized sewage treatment plants (air volume<50m3/min), SBR process.
**2. Multi stage centrifugal fan**
-* * Features * *:
-High efficiency (75-85), suitable quantity (50-300m3/min).
-Low noise, adjustable by frequency conversion.
-* * Disadvantages * *:
-The efficiency decreases significantly under high-pressure conditions (>80kPa).
-* * Applicable scenarios * *: Large sewage treatment plants (such as AAO process) that require continuous and stable aeration.
**3. Magnetic levitation/air suspension fan**
-* * Features * *:
-No mechanical friction, efficiency>90, energy saving 30-50.
-Noise level<75dB, lubrication free maintenance.
-* * Disadvantages * *:
-The initial investment is high (3-5 times that of Roots blower).
-* * Applicable scenarios * *: High standard sewage treatment plants (such as A upgrading), areas with high electricity bills.
**Comparison Table of Fan Types**
|* * Type * * | * * Airflow Range (m3/min) * * | * * Pressure (kPa) * * | * * Efficiency * * | * * Applicable Scale * *|
|----------------|----------------------|---------------|----------|--------------------|
|Roots blower * * | 1~100 | 9.8~98 | 60~70 | Small and medium-sized plants (≤ 50000 tons/day)|
|Multi stage centrifugation | 50~300 | 30~80 | 75~85 | Large scale plants (≥ 50000 tons/day)|
|Maglev * * | 20~200 | 40~90 |>90 | High standard/energy-saving renovation project|
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**3、 Key parameters for selecting aeration fans**
**1. Airflow calculation**
-* * Formula * *:
\[
Q=\ frac {0.001 \ times BOD_5 \ times Q_ {sewage} \ times S} {E \ times 24}
\]
-(Q): Required air volume (m3/min)
-BOD_5: influent BOD concentration (mg/L)
-(Q_ {Sewage} \): Sewage flow rate (m3/d)
-(S): Oxygen transfer coefficient (usually 1.5~2.0)
-(E): Aeration efficiency (15-30 for microporous aeration)
>Example: Processing capacity of 10000 tons per day, BOD=200mg/L， If E=20, the required air volume is approximately * * 42m3/min * *.
**2. Pressure determination**
-Total pressure=water depth pressure+pipeline loss+aerator resistance**
-Water depth pressure: An increase of 9.8kPa per meter of water depth.
-Aerator resistance: Micro porous discs have a resistance of about 4-6kPa, while nanotubes have a resistance of about 2-4kPa.
**3. Energy saving optimization**
-Variable frequency control: Adjust the speed based on DO feedback (DO set to 2-4mg/L).
-Aerator: The oxygen utilization rate of nanotubes is greater than 30, saving 15% of electricity compared to traditional disc type aerators.
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**4、 Key points for installation and maintenance**
**1. Installation requirements**
-* * Basic shock absorption * *: concrete foundation+shock pad, vibration speed ≤ 4.5mm/s.
-Pipeline layout:
-The wind speed of the main pipeline is ≤ 15m/s, and the branch pipeline is ≤ 10m/s (to reduce resistance).
-Avoid right angled bends and use a 45 ° diagonal joint.
**2. Daily maintenance**
|* * Project * * | * * Cycle * * | * * Operation * *|
|------------------|--------------|-----------------------------------|
|* * Air filter * * | Weekly | Clean the filter cotton or replace the filter element|
|Lubricating oil * * | Every 3 months | ISO VG220 for Roots blower and synthetic oil for centrifuge|
|* * Bearing temperature * * | Real time monitoring | If it exceeds 85 ℃, the machine needs to be stopped for inspection|
|* * Coupling alignment * * | Every 6 months | Laser calibration deviation<0.05mm|
**3. Common fault handling**
-Insufficient air volume: Check for clogged filter cartridges, leaking pipes, or worn impellers.
-Abnormal vibration: Check for loose anchor bolts, damaged bearings, or rotor scaling.
-Motor overload: Adjust the parameters of the frequency converter or clean the blockage of the aeration head.
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**5、 Economic analysis (taking a 10000 ton/day sewage plant as an example)**
|* * Wind turbine type * * | * * Initial investment * * | * Annual electricity fee (0.6 yuan/kWh) * * | * * 10-year total cost * *|
|----------------|-------------|-------------------------|----------------|
|Roots blower * * | ¥ 200000 | ¥ 360000 (75kW × 24h × 365 days) | ¥ 560000|
|* * Multi stage centrifugation * * | ¥ 500000 | ¥ 280000 (58kW) | ¥ 780000|
|Maglev * * | ¥ 1.2 million | ¥ 180000 (37kW) | ¥ 1.38 million|
>* * Note * *: Although maglev has a high investment, the cost can be recovered through electricity bills within 5-7 years.
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**6、 Selection suggestions**
1. * * Small and medium-sized factories (≤ 20000 tons/day) * *:
-Optimal selection of Roots blower and frequency converter, balancing cost and adjustment flexibility.
2. * * Large scale factories (≥ 50000 tons/day) * *:
-Choose a multi-stage centrifugal fan for better air volume stability.
3. * * High standard/energy-saving renovation * *:
-Recommended magnetic levitation fan, with significant long-term energy-saving benefits.
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**Summary**
The selection of aeration fans for sewage treatment plants needs to be comprehensively considered in terms of treatment scale, process requirements, and energy consumption budget
-Roots blower is suitable for small and medium-sized factories with limited budgets.
-Multi stage centrifugation is suitable for stable operation in large factories.
-Magnetic levitation is suitable for projects with high electricity bills or carbon neutrality goals.
**Key optimization points * *:
-Match aerators (such as nanotubes).
-Adopting frequency conversion control+DO linkage.
-Regular maintenance ensures the efficiency of the fan.
