CLOTH MEDIA FILTER ISO DISC

Working principles:
The Alfa Laval AS-H Iso-Disc Cloth Media Filter operates continuously in an outside-in flow pattern. The cloth media is mounted on the outsides of a hollow filter element which allows the water to pass through the cloth into the centre of the hollow element by gravity. As water passes through the cloth media, the particulate solids are captured on the outer surface of the cloth. The filtered water exits the element at a high level discharge port which directs the water into a collection trough.

Vacuum cleaning of the cloth media (Backwashing):
With time, the captured solids progressively build up on the outside of the cloth media and slowly generate resistance to the water flow, causing the water level to rise in the tank. A sensor monitors the water level, and at a preset high level, a backwash is instigated to clean the cloth media and remove the captured solids.
Unlike other fine solids filtration systems, Iso-Disc uses fixed elements with static filtration media and achieves backwashing by moving a horizontal, bi-directional backwash suction manifold up and down each element. A centrifugal pump generates vacuum at the backwash suction manifold/cloth media surface, which gently relieves the cloth of its solids load via the backwash manifold. As a result, the resistance to water flow is removed, and water level falls in the tank as filtration continues.

When the water level within the tank reaches a predetermined high water level, a simple PLC control system will intiate a backwash event. Actuated valves between the backwash manifolds and the backwash pump open and close in a programmed sequence to facilitate backwashing of the individual filter elements, one at a time. The manifold is driven up and down the
elements using a single electric motor drive and four corner mounted gearboxes. This ensures complete vacuum cleaning of the filter cloth while minimizing the rate at which backwash water is returned to the treatment facility. The efficient cleaning system ensures the minimal number of backwashes per hour.
At the end of each backwashing cycle, the pump, valves and manifolds are parked until the next backwash is required at high water level. After an operator selected number of operation hours or a set number of backwash events, a sludge withdrawal valve will open and remove sediment from the bottom of the tank.
The Iso-Disc operation is self-managing; as flow and load increases or decreases, the backwashing frequency naturally compensates to maintain steady state filtration conditions. At times of high flow and load, the backwash frequency will increase. Reduced flow and load will result in longer periods between backwashing. In all cases, the cloth media polishing filter remains in operation during backwashing.