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2026
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03
Common Problems and Solutions for Dissolved Air Flotation (DAF) Machine
Author：
1. Scum cannot float up, 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 pH of wastewater
- Suspended solids too light or too heavy to adhere to bubbles
Solutions
- Adjust the dosage of PAC and PAM; find the optimal dosage through on-site jar tests
- Control dissolved air pressure at 0.35–0.45 MPa
- Increase the reflux ratio (generally 20%–30%)
- Adjust pH to 7.5–8.5
- Strengthen flocculation to form large and dense flocs
2. Scum cannot be scraped away and sticks to the water surface
Causes
- Scum too thin and fragmented
- Excessive PAM leading to high viscosity
- Scraper speed too fast
- Incorrect liquid level in DAF
Solutions
- Reduce PAM and increase PAC appropriately
- Reduce the scraper speed
- Adjust the water level so that scum is just picked up by the scraper
- Extend the retention time properly to compact the scum
3. Low dissolved air water flow, few bubbles, poor treatment effect
Causes
- Clogged releaser
- Insufficient air intake into the dissolved air tank
- Worn reflux pump, unable to build up pressure
- Air leakage in pipelines
Solutions
- Clean or unclog the releaser
- Check the air intake valve and check valve
- Repair the reflux pump to ensure stable pressure
- Check pipeline seals and eliminate air leakage
4. Effluent contains a lot of micro-bubbles and appears milky white
Causes
- Excessively high dissolved air pressure
- Excessive release amount
- Scum broken up
- Effluent weir too high or too low
Solutions
- Reduce dissolved air pressure appropriately
- Partially close the reflux valve
- Adjust the effluent weir height to avoid disturbing scum
- Extend the stabilization time in the outlet zone
5. Scraper does not move, abnormal noise, overload
Causes
- Excessively thick scum, high resistance
- Lack of oil in the gear reducer
- Chain or guide rail jammed
- Motor failure
Solutions
- Increase scraping frequency to avoid thick scum accumulation
- Lubricate the gear reducer
- Remove foreign matter from guide rails and chains
- Check the motor and limit switches
6. Unstable pressure in dissolved air tank (fluctuates up and down)
Causes
- Unstable air intake
- Leaking check valve
- Flow fluctuation of the reflux pump
- Abnormal water level inside the tank
Solutions
- Adjust the air intake needle valve to maintain stable air supply
- Repair the check valve and drain valve
- Ensure stable operation of influent pump and reflux pump
- Maintain normal water level in the dissolved air tank
7. High power consumption, frequent pump tripping
Causes
- Clogged releaser or pipelines
- Worn pump impeller
- Motor overload
- Improper valve opening
Solutions
- Fully unclog releasers and pipelines
- Repair or replace the water pump
- Check the electrical circuit and thermal relay
- Adjust valves properly to avoid overpressure
8. Poor treatment effect on 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 Troubleshooting Tips (easy to memorize)
- Scum not floating → insufficient chemicals / air → adjust dosage and increase pressure
- Sticky scum → too much PAM → reduce dosage and speed
- Insufficient bubbles → clogging / leakage → clean releaser and check for air leaks
- Turbid effluent → poor flocculation / insufficient air → strengthen flocculation and adjust reflux
- Scraper not moving → thick scum / jamming → scrape more frequently and clean the tracks
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