Backflush filter / Backflushing

A liquid filter serves to optimize water quality by reducing or removing particles such as turbidity, microorganisms, or unwanted water-soluble substances.

There are two main types of filters:

• Physical filters that operate mechanically through screening, including gravel, stone, plastic, metal, sand, or fabric filters, as well as ultra- and microfiltration. These primarily separate particulate substances that are too large to pass through the filter medium or membrane.
• Chemical-physical filters that remove dissolved substances through processes such as adsorption on activated carbon or ion exchange.

A backflush filter is specifically designed to automatically flush itself when clogged. This prevents blockages or deposits (filter cake) and ensures consistent filter performance. Such a filter must be backflushable and possibly equipped with a mechanism that allows the filter elements to be cleaned by flushing with liquid or air in the opposite direction. This process removes accumulated dirt particles or a filter cake and flushes them out.

The quality and quantity of the filtrate from the backflush process determines whether renewal, post-cleaning, or possible disinfection is necessary. In the case of particularly stubborn contamination, it may be necessary to remove the filter or membrane for separate cleaning or replacement.

An innovation in backflush filter technology is active filter elements. In normal operation, they function like standard filter surfaces, but during backflushing, they expand to facilitate the detachment of filtered solids. These filters are designed for fine filtration of particles in the range of 1000 µm to 50 µm.

Especially in the mechanical filtration of challenging liquids such as wastewater or industrial water, the degree of contamination affects the lifespan and quality of the filter. For longer service life and better results, backflushable filters or membranes are recommended. The backflushing medium can vary as needed, often using compressed air, chemicals, or the filtrate itself.