Injectors...

Injectors all mix air and water together under a high localised pressure. This form of aeration is often very efficient, and as such the processes can be used for injecting oxygen into the water. However when the process is used with air, gas supersaturation with nitrogen gas can occur leading to possible gas bubble trauma or sublethal toxicological problems. If an injection process is used for adding air to water it is important to also measure the total gas pressure of the water and the partial pressure of nitrogen gas. Total gas meters are detailed in this catalogue which will allow you to monitor these parameters. Injectors produce a jet of water containing the air bubbles, this jet of water creates good horizontal movement of the water as indicated in the diagram below. The systems are, however, generally poor at vertically mixing the water column and at bringing oxygen enriched water to the sediment in the pond. Under these conditions it is likely that the sediment will be prone to becoming anaerobic.

Mechanic agitators and injectors all exert kinetic energy in physically moving the water in order to dissolve the gases into solution. Because of this one factor and other considerations detailed in this site, fine bubble diffused aeration can be up to 5 times more energy efficient than surface agitators. Under conditions of 2 mg / L dissolved oxygen in a 5,000 cubic metre tank we measure an oxygen transfer efficiency of 6.8 kg of oxygen per kw of energy expended. The surface agitators only gave a transfer of 2.5 kg of oxygen per kw expended.

Oxygen Generators...

Oxygen generators produce an oxygen enriched gas with a purity of 90 % to 95 %. The equipment provides for a convenient cost effective means of producing oxygen on-site for water treatment and aquaculture applications.  Oxygen generators operate by removing the nitrogen from the atmosphere using molecular sieves contained in two pressure vessels. Air is applied to the generator at a pressure of 90 psi,  a selection of air compressors matched to the oxygen generators are available from this web site. The table below gives the range of oxygen generators available, air flowrate require and the amount of oxygen produced. The first four units are complot systems inclusive of air compressors.

Air flow required (N m3 / min)	Discharge pressure (psi)	Capacity (L / minute)	Capacity (g / minute) *	Capacity (L / hour)	Capacity (g / hour) *
Compressor included	5	7	10	420	600
Compressor included	35	5	7	300	428
Compressor included	35	11	15.7	660	942
Compressor included	35	16	22.9	960	1,371
Compressor included	35	22	31.4	1,320	1,885
0.14	-	9	13	540	771
0.29	-	20	20.6	1,200	1,714
0.47	-	35	50	2,100	3,000
0.81	-	70	100	4,200	6,000
1.23	-	110	157	6,600	9,428
2.18	-	190	271	11,400	16,285
* The weight of oxygen can be up to 10 % lower than the figures in the table above

Energy Requirement for Mixing...

Aeration tanks may be square or rectangular and may contain one or more aerators. The depth and width of the aeration tanks for mechanical surface aerators are dependent on aerator size. For example, the effective mixing depth and width of 7.5 kW-aerator are about 2.5 and 10 m, respectively. Typical power requirements for maintaining a completely mixed flow regime with mechanical aerators vary form 20 to 40 W/m³, depending on the design of the aerator and the geometry of the tank.