Plate and Tube Settlers

PLATE AND TUBE SETTLERS

Plate and Tube Settlers have been developed as an alternative to shallow basins and are used in conjunction with both existing and specially designed sedimentation basins. Plate and Tube Settlers are shallow settling devices consisting of stacked offset trays or bundles of small plastic tubes of various geometries. They are used to enhance the settling characteristics of sedimentation basins.

The shape, hydraulic radii, angle of inclination, and length of the plate and tube settlers will vary according to the particular installation. Normal practice is to Insert the plate or tube settlers in sedimentation basins (either rectangular or circdar) of sufficient depth. The flow within the basin passes upward through the plate or tube modules and exits from the basin above the modules. The solids that settle out within the plates or tubes move by means of gravity counter currently downward and out of the tube modules to the basin bottom.

To be self-cleaning, plate or tube settlers are usually set at an angle between 45° and 60° above the horizontal. When the angle of inclination of plate or tube is more than 60° the efficiency of the settling basin decreases. If the plates and tubes are Inclined at angles less than 45°, settler will tend to accumulate solids, which must be flushed out periodically (usually with high pressure hose). The need for flushing poses a problem with the use of plate and tube settlers where the characteristics of the solids to be removed vary from day to day.

Tube settlers are a light weight structure composed of closely spaced tubes on an incline (usually between 45° and 60°). Clarifier up flow is passed through these tubes. Settling within these tubes and contact clarification of fine floc results in a build-up of particles on the tube surfaces. Particles combine to form agglomerates which become heavy enough to slough against the upward flow and slide down the tube slope to join the sludge blanket below.

Tubes are supplied in module form - each being 1 meter wide by 1 meter long by 0.67 meters high. The modules are arranged on a supporting framework to form a layer within the clarifter. The tube settlers are suspended at a height 700mm below the top water level.

The above figure shows the supporting framework, module installation and settler positioning at Inlet clarifter in waste water treatment.

The framework is held up bv a number of 'hooks' over the top rim of the ciarifier tank. This was done to minimize the installation time. The entire installation may be completed in three days in an existing Water Treatment Plant, the clear water storage was filled to capacity prior to installation of the tube settlers to allow for the three days the plant was off line.

Advantages of tube settlers are:

• Solids removal efficiency will be higher leading to clarified water turbidity as less than 10 NTU

• Hence the load on the filter will be less.

• Treatment plant capacity of the existing Water treatment Plant could be increased by 50 to 60%

Advantages of Plate settlers are:

• Compact design: Space saving; Cost saving;

• No moving parts: Low maintenance; No spare parts;

• Simple installation: Saves money; Immediate start-up at full capacity

• Ease of access: Individual removal of each lamella plate; Easily available for inspection;

• Sludge handling benefits: High underflow sludge concentration; Low cost for sludge withdrawal;

• Flexible system: Retrofitting of existing tank; Custom design;

Disadvantages of Take settlers/plate settlers are

• Algae growth in tubes and platen may cause maintenance and odor problems.

• Easy to clean in Lamella but not in Tubular Module.

• Careful attention is necessary far, the design of inlet and outlet stucture to I avoid turbulence and uneven flow.

• Sometimes high pressure hose water is injected to flush out the solids.