GROUNDWATER AND LEACHATE: EX-SITU CHEMICAL/PHYSICAL TREATMENT
Air Stripping of Water contaminated by VOCs
Typical Air Stripping System
Volatile organics are partitioned from the extracted ground water by increasing the surface area of the contaminated water exposed to air....
Process
Note:
Uses:
Advantages/Disadvantages:
Process
- A spray nozzle at the top of the tower distributes contaminated water over the packing/shells.
- Water percolates very slowly through column of polymeric shells (maximum shell surface area for maximum air-water contact & minimum space required.
- Air inlet at base of column – air rises, causing air stripping. Volatile contaminants are released from water to air, thus rising to top air outlet.
- A sump at the bottom of the tower is to collect clean, decontaminated water.
Note:
- Typically conducted in a packed tower, an aeration tank or increasingly, tray aeration towers.
- Units are often permanently installed on concrete pads.
- May be enhanced by an air heater or a fan forcing air against the water flow. This increases effectiveness of treatment, while a much smaller volume tower would be required.
- Can be operated in batch or continuous modes. In batch mode, the air stripper is intermittently fed from a collection tank - greater energy efficiency as mixing in the storage tanks eliminates inconsistencies in feed water composition.
- After process old aggregate (shells) are mixed with some new aggregate to maintain effectiveness.
Uses:
- Used to separate VOCs from water - effective only for VOC/Semi-VOC concentrations with a Henry's constant >0.01. [If < 0.01 - has v. low volatility & would require pre-heating].
- Inorganic contaminant certainly require pre-treatment.
- Often used to separate BTEX, chloroethane, TCE, DCE, and PCE from water.
Advantages/Disadvantages:
- Rapid, good quality cleanup.
- Requires large column/tower ( 5 to 12 meters ).
- Process energy costs are high.
- Total cost is influenced by rate of inflow, volatility of contaminant & off-gas treatment required.
- Off-gases may require treatment.