High Rate Downflow Industrial-Grade Filters

Veolia’s High Rate Downflow (HRD™) multimedia filtration produces an extremely high quality effluent thanks to unmatched performance.


With one of the longest operating cycles, HRD™ provides greater economy and efficiency in challenging applications to remove solids larger than 5 microns. The innovative HRD™ distribution system controls velocity and hydraulic balance, protecting the media during high flow rates of up to 7 gallons per minute per square foot of filter area.


HRD™ systems are pre-engineered to comply with stringent specifications and are delivered assembled in a packaged skid mounted with piping, valves, and controls. With capacities ranging from 60 to 3,500 gpm, HRD™ can combine multiple media options such as silica sand, garnet and anthracite coal for achieving unparalleled filtration efficiency that produces effluent quality with solids content below 1 mg/l in a wide spectrum of low-solids applications.


  • Greater operational cycle time by forcing the solids deep into the media.
  • Outstanding filtration performance enhanced by a consistent, continuous flow uniformly distributed across the filter bed thanks to a robust internal design of integrated stainless steel headers with wedge wire wound laterals.
  • High-quality filtration media with a high uniformity coefficient for exceptional particulate removal.
  • Four superposed layers of filtration media for increased solids holding capacity.
  • Integrated cleaning system enhanced with air scouring for optimal air distribution and media bed agitation and expansion.

Available in vertical or horizontal configurations, HRD™ systems are designed for effective removal of oil and suspended solids from sea water, cooling water and oil field brine. HRD™ technology is also ideal for treating industrial water streams in the mining, refining and petrochemical sectors and sewage effluents after tertiary treatment where conventional sand filters are not effective.



Two filtration mechanisms are at work in a media filter: entrapment and adhesion. Entrapment is related to the interception of particles within the media void areas and flow channels determined by the media effective size and uniformity coefficient. Adhesion consists of mutual absorption, chemical bonds, and electrostatic forces between the media bed and solids particles that are attracted to each other through the use of charge-reversing chemical additives such as polyelectrolyte.

The combination of both mechanisms, entrapment and adhesion, effectively remove particles from the liquid. To intercept a wide range of solids and protect the filter bed from plugging, different layers of high-uniformity coefficient material (i.e. anthracite, sand, garnet) are superposed to remove increasingly smaller particles as the liquid flows down and reaches the bottom of the filter bed.

Once the removal mechanisms have progressed and the filter bed reaches solids saturation, the filter needs to be cleaned. HRD™ uses enhanced air scouring to scrub the media with the right flow of air that increase the agitation without over-expanding the media bed.

After less than 10 minutes, the backwash cycle is complete by flushing the solid contaminants out of the filter media.