What is a Venturi-Aerator?
The Venturi-Aerator is used in conjunction with a self-priming pump. The pump draws water from the source and pumps it into the venturi-aerator. Within the venturi-aerator, there is an “accelerating zone”, where the pumped fluid is accelerated, creating a low pressure area within the “aspirating zone”. Here it draws in atmospheric air at the rate of 2.2 times the rate of the fluid being pumped.
The air and water then passes into the “mixing and oxidation zone” where the wastewater and air are mixed under pressure. The turbulent mixing facilitates the removal of substances with weak Henry’s constants such as CO2 and VOC’s. It also oxidises sulphur containing molecules such as hydrogen sulphide and mercaptans for effective odour and corrosion control, as well as reducing the size of organic solids.
The fluid, saturated with dissolved oxygen is then pumped back into the source.
Because of the nature of the system [using a self-priming pump], mixing and destratification is controlled by the positioning of the suction and discharge of the pump. Water can therefore be drawn from anywhere and at any depth of the tank or lagoon, and can be discharges anywhere and at any depth.
Where to use them?
Venturi-Aerators can be used by many industries for various reasons. Some of these include, but not limited to:-
- Biological treatment and odour control at industrial wastewater treatment plants.
- Odour control, corrosion control and BOD reduction at Sewage Pumping Stations •
- Odour control and pH improvement at Food Process Plants
- Sludge separation to enhance settling and performance of the primary clarifier at WWTP’s
- Septage Receiving – for odour control, BOD reduction, degassing H2S and “shearing” organic materials
- Mixing and Equalization
- Supernatant aeration from digesters
- Landfill leachate aeration prior to head-works further treatment
- Oil & Grease Recovery
- Effluent aeration to streams or wetlands
- Stripping PCE, TCE, etc. from industrial waste streams and groundwater
- Lagoon aeration with two zones
- Stripping CO2 to raise pH, allowing for nitrification (pH >6.8) to begin
- Destratification of lakes, dams etc
Why use a Venturi-Aerator?
Venturi-Aerators are mounted on the bank of the lagoon, pond, or tank they are treating. Other forms of aeration involve the equipment being in or on the water to be treated.
This means that installing a Venturi-Aerator is simpler and involves less risk to personnel. Installation costs will therefore be lower, there will be no need for expensive floating walkways, tethering systems or overhead cranes for retrieval.
On-going monitoring and maintenance is also much easier, simpler and safer with a Venturi-Aerator. All mechanical equipment will need some kind of maintenance or repair. The easier it is to access will almost certainly determine whether it gets routine maintenance and monitoring. Floating type or submersible type systems will not get much attention [unless they break down], because of the difficulty in accessing them. This lack of attention will shorten intervals between major repairs and shorten overall asset life.
In contrast, a Venturi-Aerator and its driver [a Gorman-Rupp self-priming pump] are easily accessed for monitoring and routine maintenance. This allows operators to keep equipment at peak operating efficiency and make minor repairs before they become major problems. They are also able to perform these maintenance tasks in relative safety on lagoon banks.
Not only are Venturi-Aerators safer and easier to maintain that other forms of aeration, they are also very efficient if used with the right pump. Standard Oxygen Transfer Rates [SOTR] as high or higher than 1.86kgO2 per kW per hour can be achieved when pump efficiencies are high and pumps have a flooded suction.
Systems are easily accessed. Pump clearances can be adjusted in minutes. Suction and discharge positioned to suit.
How to Apply Venturi-Aerators?
Venturi-Aeration Chemical Engineers can work out the size and type of system required if given the right information. The types of information needed is as follows:-
- The size of the tank or lagoon [Length x Width x Depth]
- The amount of inflow into the tank or lagoon
- The type of operation needing the treatment [Sewage Treatment Plant, Food Process plant etc]
- The goal of the treatment [increase dissolved oxygen, reduce BOD or COD, increase pH levels, destratification, oxidation of the fluid, odour reduction etc]
- The target of the treatment
What are the limitations of Venturi-Aerators?
Venturi-Aerators are limited to approximately 37kg of oxygen transfer per hour by a single [six inch] unit. To deliver more oxygen [by atmospheric aspiration], multiple units must be used. Alternatively, if oxygen demands have peaks [for example, the “Vintage” period at wineries], pure oxygen can be aspirated from a stationary source [like a liquid oxygen plant or liquid oxygen tanker]. This can increase oxygen transfer by 2-3 times per unit.
Two Venturi-Aeration systems aspiration Oxygen into a wet well.