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The dissolved air means mixture of air and water at a higher pressure. At higher pressures the air can get dissolved and can remain in same state till the pressure is maintained. The air gets released after the pressure is reduced. To dissolve the air, to maintain the dissolved state and to use for separation process requires separate scheme. NIRMAL have specialized process in for this purpose.


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The treated effluent is used for dissolving air. The treated effluent is pumped by means of multistage high pressure pump into high pressure motive stream side of water jet ejector. The specially computer designed convergent nozzle forces the high pressure water into the high velocity jet which creates the relative pressure drop and so low pressure zone on the suction side. Due to low pressure on the suction side, the compressed air gets sucked and gets dissolved in the mixing zone of the water jet ejector. Since the specific gravity of the air too smaller than water, more air gets sucked. The dissolution of air will be only upto extent of saturation level. The extra air will remain undissolved. The mixture of air and water along with excess additional air enters in the pressure vessel. The mixture of air and water will have air as dissolved and so will have properties of water. This water is hence forth called as dissolved air, will move vertically downwards. The excess air will move upwards which will get sucked automatically by the water jet ejector. Thus air water ratio in the dissolved air will be maintained. In the pressure vessel due to the retention time the size of the dissolved air is homogenized and uniform size air bubbles are available for flotation.

The dissolved air will be inserted in the flotation clarifier through the throttled dissolved air valves. The entry of the dissolved air will be from the bottom, so that entire portion of the flotation clarifier will be stripped by the dissolved air and fine impurities will be made to float. The throttled dissolved air valves will create the pressure drop as the flotation clarifier being open is at atmospheric pressure. The throttled dissolved air will generate billions of microscopic ultra-fine air bubbles which will adhere to the fats, oils, grease, fibres and suspended solids and make it to float upwards in the form of compact sludge. The dissolved air will rise slowly maintaining the laminar state in the flotation clarifier and will not disturb the flocculated state.

Overall the dissolved air bubbles will perform following.

The treated effluent will then pass through parallel plate coalescer to remove the air bubbles from outgoing effluent. Such removal will polish the waste water not only for air bubbles but also for fine impurities. This Mechanical Desludging, Hydraulic Desludging and Combined Desludging.

The multistage high pressure pump capacity may not be same as actual dissolved air inserted in the clarifier. It is normal convention to use higher capacity pump so that adequate dissolved air is ready for achieving the desired results. For tuning the pump capacity and the actual dissolved air discharge, there are two methods employed. It is also important to maintain constant pressure. Only NIRMAL scheme uses following controls to maintain so as to pressure variation less than 0.01 kg/cm2. The control circuit will be designed to have the operations automatic with additional safety measures. Optionally alarm anunciators will indicate the measures to be taken to avoid worst conditions.

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Last modified: March 13, 2004

Nirmal Engineers
17 Nav Sarvodaya Society, Vartak Road, Vile Parle (East)
Mumbai 400057, Maharashtra INDIA
Phone / Fax: 91 22 26145623 E-mail:

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