Flotation

DESCRIPTION OF THE PROCESS

This system allows about the total removal from the refluent waters of the solid matters in suspension and partially of the organic carbon.

The process acts through the treatment phases that will be more fully described later in the relation, therefore it is better to underline that the liquid goes previously under a treatment that separates mechanically the coarse solid matters before going under chemical-physical flotation treatment, that allows to remove from the water even the solid matters in suspension and even the fats.

The muds remained from the flotation treatment can reach a concentration of 8/10 % of dry matter, to be sent to a further anaerobic digestion for the production of biogas.

The benefits reached with this process are:

• High clarification performance
• Minimum occupied surface
• Reduced energetic and working costs
• Reduced mainteinance
• Easy conduct

MECHANICAL SEPARATION PHASES

The mechanic separation phase is necessary for the removal of the coarse and solid parts from the liquid and it also avoids the possible clogging of the pipes necessaries for the following floating pre-treatment.

EQUALIZATION AND BALANCING PHASES

This phase is necessary to obtain a liquid matter with constant characteristics of concentration and mainteinance of the peaks of maximum flow.
During this stage, the liquid matter coming from the mechanical separator is conveyed, by fall, in a tank with appropriate dimensions, in order to contain the peaks of maximum flow.
In this tank the mixers operates at low speed in order to avoid the sedimentation of the suspended solid parts and to
grant an ideal homogenizing of the liquid matter.

The liquid matter is taken with a centrifugal pump from a pit with constant level connected with the tank, and it is then conveyed to the next flotation stage.

CHEMICAL-PHYSICAL FLOTATION STAGE

During this stage, the liquid matter is istantaneously subjected to several abatements: reduction of the organic carbon (60-70%), of the phosfates (80/90%) and of the metals copper and zinc (80/90%).
Another advantage of this phase is the re cycling of muds to convey directly to any anaerobic digestor, with a high concentration of dry matter.
Moreover, it is evident the opportunity to highly reduce the dimensions of any next stage of biological oxidation.
The flotation process starts from the centrifugal pump placed in the pit next to the equalization tank, on which delivery pipe is inserted an aspirator which, with the pressure of the same hot water that it treats, takes in a controller air quantity, and mixes it with water in the form of little bubbles

A reactive for the coagulation of the sospended solid matters is injected in the same pipe.
The coagulates formed in it, embody one or more air bubbles, avoiding their rupture once they emerge on the surface.
Then, in the same pipe, an agglomeration reactive is injected to help the increase of the mud coagulates, making them more voluminous with the same weight, and so more light by comparison with the water transferred.
When the matter with this addiction is introduced in the flotation tank, the fat and mud part is quite instantaneously separated from the liquid part.

The mud that has reached the surface is then removed by a scraper with multiple blades, while the clarified water is transferred in any next treatment stage.