передовые технологии подготовки и очистки воды в промышленности и энергетике
 

Settlers

Settlers - The settler is a technological equipment for the treatment of the sewage with the elimination of the suspended solids and oil products.

The settlers can be of primary type, for the use before the industrial or biological treatment facilities and also they can be of secondary type used to extract the activated sludge.

The settlers can be vertical, horizontal and radial depending on the movement direction of the liquid flow.

The settlers also include the clarifiers where simultaneously with the settling the sewage filtration is carried out through the layer of the suspended deposits and also the deposit consolidators where simultaneously with the water treatment the consolidation of the formed deposits is carried out.

To increase the efficiency of the deposit formation the different flocculants are added into the sewage water that helps to increase the speed of precipitation of the suspended solids.
Horizontal settler:
1 - water supply tray;
2 - drive of the scraping mechanism;
3 - scraping mechanism;
4 - water discharge tray;
5 - discharge of deposits.


The radial settlers are used in case of the sewage consumption of more than 20 000 m3/day. In comparison with the horizontal settlers the radial settlers have some advantages: the simplicity and safety of use, efficiency, the possibility of construction of the structures of higher capacity. The disadvantage is the moving frame with the scrapers.

The primary radial settlers are equipped with the sludge scrapers moving the formed deposits into the pit located in the center. The deposits are eliminated from the pit with the help of the pump or under the hydrostatical pressure. The secondary radial settlers are equipped with the rotating sludge suckers which eliminate the activated sludge directly from the deposits layer without moving it into the pit. The rotation frequency of the sludge scrapers and suckers is 0,8-3 h"1.

In the settlers with the peripheral water inlet you can obtain 1,2-1,3 times more treatment efficiency and 1,3-1,6 times more capacity than in the traditional radial settlers with the same time of settling. The settler with the peripheral inlet has the distributive device which is a peripheral ring tray with the ridged water discharge device or slot bottom holes and semi-immersed partition plate which create with the side guide of the settler the ring area where the quick energy blow-out of the incoming jets, separation and trapping of the floating substances take place. The water enters the working area of the settler through the ring space created by the lower rim of the partition and bottom. During the water movement from the periphery to the center the precipitated substances are ped out from it. The clarified water is discharged through the discharge devices. The calculated duration of the water presence in the settler is taken equal to not less than 1 h.

The settlers with the rotating joined distributive devices are used for the treatment of the domestic and production water containing up to 600 mg/l of the suspended solids. The settling of the water in the settler is carried out nearly in the static conditions although the conveying capacity is nearly 40% higher than of the traditional radial settlers.

The settler has the rotating spout with the width of 0,5-1,5 m divided by the partition into two parts. The sewage water is delivered into one part of the spout from the centrally located water supply pipe and discharged into the settler through the vertical slots. The treated water is delivered into another part of the spout through the discharge rim and is taken from the settler.


The radial settler with the central drive in two versions:
1 - tank;
2 - discharge spout;
3 - charging funnel;
4 - discharging cone;
5 - central shaft;
6 - rakes;
7 - frame;
8 - drive;
9 - mechanism for lifting of the shaft with rakes;
10 - indicator of thickener overloading.


The settlers can be of the diameter of 18, 24 and 30 m. The effectiveness of the clarification is taken equal to 65%, with the coefficient equal to 0,85. The most popular settlers are settlers with the water inlet through the central pipe with the flared end. The speed of the water movement in the pipe is taken equal to 30 mm/sec.
The distance between the baffle plate and pipe flared end must ensure the speed of the water inflow into the settling area of not more than 20 mm/sec. We recommend to take the diameter and height of the pipe flared end equal to 1,35 of the central pipe diameter, and the diameter of the baffle equal to 1,3 of the diameter of the pipe flared end. The vertical settlers with the downward and upward flow and with the peripheral water inlet vary only with the structure of the intake and discharge devices. But they have 1,3-1,5 times more capacity than the settlers with the central pipe. The treated water is discharged through the tray located on perimeter of the settler.

The thin-layer settlers. The thin-layer settlers are used to increase the effectiveness of the settling process. They can be vertical, radial or horizontal. They have the water distributive, water collecting and settling zones. The settling zone of such settlers is divided by the tube or sheet-like elements to obtain the series of layers of the small depth (up to 150 mm). With small depth the settling is carried out quickly that allows to decrease the dimensions of the settlers.

The thin-layer settlers are classified according to the following characteristics: the structure of the inclining units - tubular and shelf-type; the working mode Ц periodic (cyclic) and continuous operation; the mutual movement of the clarified water and forced out deposits Ц with the straight-flow, counter-flow and combined movement.

The cross profile of the tubular sections can be square-angled, square, hexangular or round. The shelf-type sections are assembled using the flat or ridged sheets and have the square-angled cross profile. The components of the settler are made of steel, aluminum and plastic (polypropylene, polyethylene, fiber-glass plastics).

The inclination tilt of the units in the settlers of the periodic (cyclic) action is rather small. The accumulated deposits are eliminated with the help of the reversed current washing of the clarified water. The inclination tilt of the elements in the settlers of the continuous action is 45-60∞. The effectiveness of the tubular and shelf-type settlers is nearly equal.

The deposit spouts of the settlers with the depth of 1,2-1,5 m and with the inclination tilt of 50∞ have the bottom slots with the width of 0,15 m through which the deposits enter the septic chamber. The calculations for the deposit spouts are made the same way as for the horizontal settlers. The water speed is taken equal to 5-10 mm/sec. The treatment efficiency is 40-50%. The volume of the septic chamber is determined according to the average sewage temperature during the winter period. In case of the fermentation of the activated sludge the volume of the chamber should be increased by 30-70%.

The settlers-clarifiers are used in case of the increased content of the hardly precipitated substances in the sewage water. As a result of the combination of the precipitation, flocculation and filtration processes of the sewage water through the layer of the suspended deposits the efficiency of the treatment reaches 70%.

There are clarifier structures both with the preliminary water coagulation and aggregation and without them, with the combination of these processes in one device. The settler-flocculator is widely used. There is a flocculation chamber inside the settler into which the sewage water is delivered through the central pipe. The air ejection, partial oxidation of organic substances, flocculation and sorption of the impurities take place in the flocculation chamber. In the settling area the water passes through the layer of the suspended deposits where the finely dispersed impurities are trapped. The precipitated deposits are eliminated under the hydrostatic pressure force.


The settler-flocculator
1 - body;
2 - spout;
3 - holes for the discharge of the clarified water;
4 - air separator;
5 - central pipe;
6 - distributive pipes.