english To ensure effective dissolved air water preparation for sewage treatment air flotation, several key conditions must be strictly controlled, as dissolved air water quality directly determines bubble generation efficiency and pollutant separation performance.
Raw Water Pretreatment
Suspended solids and emulsified oil in sewage can clog dissolved air releasers and disrupt bubble formation. Thus, pretreatment steps like coarse filtration or coagulation—achieved by adding polyaluminum chloride—are necessary to reduce suspended solids content to below 50 mg/L and break down oil droplets.
Without this step, impurities may adhere to releaser pores or interfere with air-water mixing, undermining subsequent dissolved air water production.
Pressure Regulation
In Dissolved Air Flotation (DAF), the dissolved air tank typically operates at a pressure range of 0.3–0.5 MPa. This range balances air solubility and bubble stability.
Lower pressure leads to insufficient air dissolution, resulting in too few micro-bubbles, while excessive pressure causes large bubbles exceeding 100 μm that rise too fast and fail to attach to lightweight pollutants.
A pressure relief valve must be used to maintain stable pressure, avoiding fluctuations that disrupt consistent dissolved air water quality.
Temperature and Air Quality
Water temperature affects air solubility—higher temperatures above 35°C reduce the amount of air that can dissolve in water, so cooling systems may be needed for high-temperature sewage.
Additionally, the air used for dissolution should be oil-free and dust-free; compressed air with oil residues can contaminate dissolved air water, forming an oil film on bubble surfaces that weakens their ability to adhere to pollutants.
Gas-Water Contact Efficiency
The dissolved air tank should have a reasonable volume to ensure a 2–5 minute residence time, allowing full mixing between air and water.
Internal structures like packed beds or baffles can further enhance contact, ensuring air dissolves uniformly rather than forming large, ineffective bubbles.
Critical Control Parameters
- Maintain suspended solids below 50 mg/L through pretreatment
- Control pressure in the 0.3-0.5 MPa range for optimal bubble formation
- Keep water temperature below 35°C to preserve air solubility
- Use oil-free and dust-free compressed air supply
- Ensure 2-5 minute residence time in dissolved air tank
- Implement proper pressure relief mechanisms for stability
These conditions work synergistically: neglecting any one factor—such as poor pressure control or inadequate pretreatment—will significantly lower dissolved air water quality and weaken the overall air flotation effect.
