11
2026
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03
Common Problems and Solutions for Dissolved Air Flotation (DAF) Units
Author：
1. Sludge fails to float, thin scum, turbid effluent
Causes
- Improper dosing (insufficient or excessive PAC/PAM)
- Insufficient dissolved air, low pressure in the dissolved air tank
- Too low reflux ratio
- Unsuitable wastewater pH
- Suspended solids too light or too heavy to attach to bubbles
Solutions
- Adjust PAC and PAM dosage; find optimal dosage via jar tests on site
- Control dissolved air pressure at 0.35–0.45 MPa
- Increase reflux ratio (normally 20%–30%)
- Adjust pH to 7.5–8.5
- Enhance flocculation to form large, dense flocs
2. Scum cannot be scraped off, sticks to the surface
Causes
- Scum too thin and fragmented
- Excessive PAM causing viscosity
- Scraper speed too fast
- Incorrect liquid level in DAF
Solutions
- Reduce PAM, increase PAC appropriately
- Lower scraper speed
- Adjust water level so scum is just picked up by the scraper
- Extend retention time properly to compact scum
3. Low dissolved air water, few bubbles, poor performance
Causes
- Clogged releasers
- Insufficient air intake to the dissolved air tank
- Worn reflux pump, unable to build up pressure
- Air leakage in pipelines
Solutions
- Clean/unclog releasers
- Check air intake valve and check valve
- Repair reflux pump to ensure stable pressure
- Inspect pipeline seals and eliminate leakage
4. Effluent with excessive micro-bubbles, milky white
Causes
- Excessively high dissolved air pressure
- Excessive release rate
- Scum broken up
- Effluent weir height too high or too low
Solutions
- Reduce dissolved air pressure moderately
- Partially close reflux valve
- Adjust effluent weir height to avoid disturbing scum
- Extend stabilization time in the outlet zone
5. Scraper not moving, abnormal noise, overload
Causes
- Excessively thick scum, high resistance
- Lack of lubricant in gear reducer
- Chain/guide rail jammed
- Motor malfunction
Solutions
- Increase scraping frequency to avoid thick accumulation
- Lubricate the gear reducer
- Remove foreign matter from guide rails and chains
- Check motor and limit switches
6. Unstable dissolved air tank pressure (fluctuates up and down)
Causes
- Unstable air intake
- Leaking check valve
- Flow fluctuation of reflux pump
- Abnormal water level inside the tank
Solutions
- Adjust air intake needle valve for stable air supply
- Repair check valve and drain valve
- Ensure stable operation of influent pump and reflux pump
- Maintain normal water level in dissolved air tank
7. High power consumption, frequent pump tripping
Causes
- Clogged releasers/pipelines
- Worn pump impeller
- Motor overload
- Improper valve opening
Solutions
- Fully unclog releasers and pipelines
- Repair or replace pumps
- Check electrical circuits and thermal relays
- Adjust valves properly to avoid overpressure
8. Poor treatment performance for oil and emulsified liquid
Causes
- No demulsification
- Wrong dosing sequence
- Overly low temperature
- Excessive DAF loading
Solutions
- Perform demulsification first (adjust pH, add demulsifier)
- Sequence: demulsification → PAC → PAM
- Heat moderately if necessary
- Reduce influent flow and extend reaction time
On-site Quick Rules (easy to remember)
- Scum not floating → insufficient chemicals/air → adjust dosage and pressure
- Sticky scum → too much PAM → reduce dosage and speed
- Insufficient bubbles → clogging/leakage → clean releasers and check for air leaks
- Turbid effluent → poor flocculation/insufficient air → strengthen flocculation and adjust reflux
- Scraper stuck → thick scum/jammed → scrape more often and clean tracks
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