How Biological Treatment Works

Biological growth

Biological growth, similar to that found in percolating filters, grows on the discs' surfaces. An aerobic, freely circulating bio-mass is found in the rotor basins, which contributes to the biological treatment of the wastewater.
Bio-degradable organic wastes are therefore being treated by both the intermittently submerged bio-mass growing on the discs, and the suspended bio-mass present in the basin.

The rotating motion of the rotor discs create turbulence in the basin, keeping the free biomass aerated and in constant suspension until it eventually leaves with the treated effluent for secondary settling in the Clarifier (Humus Settling Tank). 

Oxidation, Generation and De-generation of Biological Growth

The oxygen required for the oxidation process is absorbed through the wet upper surfaces of the bio-mass growing on the discs while it is passing through the atmosphere.
Full oxygen absorption is immediately achieved due to the large contact area of the disc surfaces and the oxygen freely available in the atmosphere above the plant. 

The continuous absorption of oxygen by the bio-mass allows the oxygen to penetrate effectively to the deepest parts of the bio-mass, mainly by diffusion. The immediate submersion of the rotating, oxygen saturated bio-mass causes part of the absorbed oxygen to be transferred to the suspended bio-mass in the basin. Therefore, the absorption of oxygen into the process is not through direct absorption of air by the wastewater, but rather almost exclusively through the absorption of oxygen on the wet surfaces of the bio-mass growing on the disc.

The oxygen absorption is so effective that despite the fact the oxygen is absorbed by both the disc bio-mass growth and by those suspended in the basin, over 2mg/L of oxygen is still present in the liquid leaving the Rotating Disc stage. 

Since the waste substances present in the liquid are constantly converted into harmless substances, all bio-mass within the rotor unit is continually increasing. The excess bio-mass is automatically removed from the Rotating Disc stage by the flow of the wastewater through the plant. 

Sludge thus produced is removed from the treated effluent by further settling in the Clarifier, which directly follows the Rotating Disc stage.

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