Use:

clarification and recycling of waste water in paper industry,
clarification of municipal waste water,
clarification of waste water in food and petrochemical processing plants
treatment of potable water,
The system has proved extremely efficient especially when the sludge is recycled to the production and when the quality of waste water varies.
Features and advantages

extremely short cleaning procedure, approximately 3 minutes,
simple operation, high output and high clarifying capacity
space saving design
low construction and maintenance cost,
low cost of operation - the operation of the device is completely automated, which includes the automatic self-cleaning during the working process
smaller devices can be constructed in portable or pilot version.
Technology and operation

The continuous flotation clarifying plant uses flotation (by air bubbles) and settling (precipitation of solid particles to the bottom of the tank) techniques to eliminate solid particles. The insoluble solid particles are thus removed from water. By the use of suitable auxiliary chemicals some in water dissolved substances can be removed as well. This is particularly useful for the treatment of potable water. The modern flotation plants are constructed so as to guarantee the best contact of waste water with air bubbles. The most commonly used procedure is the saturating in side current. In this procedure a portion of the clarified water is conveyed under pressure into a special tank – the saturator – into which air is injected. The air pressure must be a little higher than the pressure of the water in the saturator. Air is injected into water through plastic membranes with large surfaces to achieve quick mixing of air and water. At high pressure more air is dissolved in water than at atmospheric pressure. The raw water is mixed under pressure with aerated water before it is conveyed into the flotation tank. When the mixture reaches the flotation tank the pressure drops to the atmospheric pressure and the suspended particles in the water start to attach to air bubbles and to float to the surface. The speed of separation is approx 0,25m/min, which is ten times faster than in the classical gravitation precipitator. The mixture of raw water and aerated water is introduced into the flotation tank through a centrally positioned rotating distributor. The velocity of the water flow equals the velocity of the movable distributor that travels in the opposite direction.

The result is zero velocity. The quiescent state of water in the tank enables the air bubbles to attach the suspended particles making them specifically lighter and enabling them to float to the surface. The clarified water collects in the lower part of the flotation tank, passes into the central clean part of the tank and from there it is drained out. The solid particles that settle on the bottom of the tank are swept by the rotating distributor into the sattled sludge sump and cyclically removed. After the flotation process has been completed the thick layer of floated sludge is scooped from the surface of the water. A special scoop attached to the rotating distributor removes this sludge and discharges it out of the tank. The immediate removal of the floating sludge prevents the sludge to sink again and contaminate the already clarified water. The floated sludge contains 3-4% of dry substance. Such sludge is suitable for immediate recycling. When further thickening is required, the costs of condensation are considerably lower.

 

It represents an integration of the modern flotation and filtration plants in a single processing unit that enables additional cleaning of waste water.

Use:

The Continued Flotation/Filtration Clarifying Plant is useful where the supply of huge quantities of highly clarified water is to be guaranteed. The possible fields of use are:

for clarification of water in closed circuits for reduction of organic pollution and removal of suspended substances
for additional cleaning of municipal and industrial wastewater after the biological cleaning (elimination of phosphorus),
for treating of potable water from springs that occasionally give slightly turbid water,
for elimination of scarcely decomposed organic pollutants when treating drinking water from sources that are rich in substances resulting from decomposition of organic materials that are of natural origin but give the water a bitter taste.
Technology and Operation In the upper part of the flotation tank a rotating device or distributor introduces the mixture of raw and aerated water into the tank and with a spiral scoop removes the floated sludge from the surface. The lower part of the tank is divided in filter bed segments or cells with layers of filter media for supplementary clarifying of water. After the flotation process has been completed the clarified water is drained through the filters at the bottom of the tank . One-layer sand filter or two-layer filter composed of the hydro- anthracite and filter sand are used for this purpose. Depending on the application, a wide variety of filtering media may be used including special filtering materials that bind certain substances. After a certain time of use the filters get clogged and have to be cleaned. The segments are routinely taken off-line for backwashing. The backwashing of filters occurs automaticly and includes the following phases:

preliminary braking up of the filtrating layer with water,
breaking up of the filtrating layer with air,
backwashing of filters with water at different flow speeds.
For these purposes a portion of the clarified water is used and subsequently removed. The cleaned filter segment is put back on line , while the filtrate that is not perfectly clear returns into the cleaning process. . Thus purified water is collected in the tank for clarified water that is usually positioned under the flotation filter.

Results of some tests in industrial plants: After the tertiary cleaning of municipal wastewaters to which approximately 20mg/L of aluminium sulphate and 0,5mg of cationic polyelectrolyte have been added, the value of the residual KPK dropped from 17,5 to 7,5 mg/l, i.e. for 40%. The concentration of phosphorus in the effluent dropped from the average concentration of 9mg/l to 4,3 mg/l, i.e. for approx 50%. It is possible to lower the concentration of the residual phosphorus to less than 1mg/l by using special chemical auxiliary substances The efficiency of removal of solid particles exceeds 98%. The percentage of the floated sludge amounts to 1,5 - 2,5% of the treated water. It contains 3-6g/l of dry substance, mostly composed of parts of cellulose, micro organisms and phosphates.