Venturi Aeration, Inc.

Venturi Aeration Oxygenator Unit As Pre-aeration for Constructed Wetlands and Reed Beds

Constructed wetlands are a type of wastewater and sludge treatment system that uses phyto- (plant) and rhizo- (roots) remediation to achieve the biological reduction of organic and inorganic compounds in a wastestream. Reeds are the plants most commonly used and they are selected by species based on the specific location of the constructed wetlands or reed bed.

While Constructed Wetlands are most commonly stand-alone units, there are certain applications where the influent wastewater flow from the process plant has certain characteristics that could require additional or enhanced pretreatment in order to reduce the footprint of the constructed wetland. In those cases, a Venturi Aeration Oxygenator unit is used for pre-aeration to achieve reductions designed to reduce the toxicity and biological loadings of wastewater going into the Constructed Wetland. This reduces the overall capital cost of the total project, and increases performance of the combined system.

Pre-aeration of the influent wastewater in a separate aeration tank using a Venturi Aeration Oxygenator unit has many benefits for Constructed Wetland systems:

1. Dissolved Oxygen: The liquid being processed through the venturi aerator unit is saturated with dissolved oxygen (DO). The discharged liquid is highly oxygenated with DO levels ranging between 5.0 mg/l and 7.5 mg/l.

2. Mixing and Equalization: The discharge from the venturi aerator unit mixes and equalizes the influent liquids with the contents of the preaeration tank. Any solids are kept in suspension by circulating the tank contents at 2 fps.

3. Odor Control: Imbedded malodorous and corrosive hydrogen sulfide from organic material is readily oxidized into soluble SO4, a non-odorous form of sulfur.

4. BOD Reduction: Pre-aeration induces large amount of dissolved oxygen into the aeration tank to effect BOD5 reduction from nascent bacteria in the sanitary wastestream to levels at which the Constructed Wetland can be effective; this is usually < 800 mg/L.

5. Nitrification: With excess amounts of dissolved oxygen in the aeration tank, nitrification at pH levels >6.8 begin in the aeration tank enhancing the Constructed Wetland’s performance. The constructed wetland has both aerobic and anaerobic areas in the reeds to both nitrify and denitrify.

6. Floatation of FOG: Conditioning with the Venturi Aeration Oxygenator causes imbedded fats, oils and grease (FOG) to separate and float to prevent their migration into the Constructed Wetland system.

7. Temperature: The Venturi Aeration Oxygenator has the ability to reduce the temperature of the influent wastewater. In field tests on the Venturi Aeration Oxygenator device with septage, temperature reductions have been documented to range between 2° and 6° C in summer months in New England. Reducing elevated temperatures of the process liquid increases the solubility of dissolved oxygen, thus allowing for greater amounts of DO to achieve targeted biological reductions.

8. Non-chemical pH Control: As the nascent bacteria become active aerobically they produce carbon dioxide as a digestive byproduct. The increase in carbon dioxide lowers the pH. This acidity may stress micro-organism performance and reed viability. Since carbon dioxide is readily strippable with the venturi aerator device, a steady state pH can be maintained on the liquids being decanted into the Constructed Wetland.

9. Hydraulic Shear: Solids that migrate from the primary settling tank are conditioned in the venturi aeration device to increase their surface to enhance digestion.

10. Strips VOCs: The venturi aeration device protects the biomass and reed beds in the Constructed Wetland by stripping certain weak Henry’s Constant VOCs that may be present in cleaning chemicals or detergents that could cause degrade performance of the reed beds or even kill them.

There are many applications for Constructed Wetlands or Reed Beds, not all of them require pre-aeration. However in those cases where pre-aeration is required a computer model has been developed to calculate the desired amount of dissolved oxygen that would be needed in pre-aeration to achieve targeted reductions in BOD5 for the influent wastewater. The computer model can assist the consulting engineer in the proper sizing of the aeration tank and venturi aeration oxygenator device to ensure desired reductions are achieved for liquids decanted to the reed beds

Summary: The addition of a Venturi Aeration Oxygenator unit in a pre-aeration and equalization tank can greatly enhance the performance of the Constructed Wetland system allowing it to treat larger quantities of wastewater than could otherwise be achieved without adding additional expensive pretreatment equipment to treat the influent flow. This reduces overall project costs and increases efficiencies. Because of the many specific benefits listed above from pre-aeration, the Venturi Aeration Oxygenator should be utilized for preconditioning difficult wastestreams.