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Germany, Austria, Switzerland


Horizand® horizontal filtration

The patented Passavant® horizontal filtration Horizand® technology is the (flow) direction of the future. In contrast to upflow or downflow reactors, it offers considerable advantages.

Unique Features

  • Lesser volume: small footprint and simple structural design
  • No stagnant water over the filter medium, less uncontrolled oxygen entry (relevant for denitrification) & no algae growth when exposed to sunlight
  • Continuous filtration operation
  • Less space required due to an external backwashing unit 
  • Less air flow for backwashing
  • Additional filtration capacity when converting existing filter tanks
  • Defined filter layer thicknesses
  • Flexible Arrangements
  • Easy operation and handling


Distinctive features compared to other technologies

Significant smaller footprint with the same filtration area compared to continuously operated upstream flow slide bed filters, at least in part due to the external washing unit, avoiding additional space usage within the reactor due to expansion/backwashing.

In contrast to classic (discontinuous) vertical filtration, no space is wasted for expansion/backwashing. This means the footprint is significantly smaller and the civil engineering costs for new systems are considerably lower.


The Passavant® horizontal filtration Horizand® enables adsorption filtration with granular activated carbon
(GAC filtration) or other adsorber matrices to remove trace substances from water and wastewater.

Other versions of this patented technology include a simple sand filtration for suspended solids removal or usage as a denitrification filter. Since water and air (or emitted nitrogen gas) stream in crossflow in denitrification filters, they may be independently controlled. All variants are available in steel or concrete silos.


Denitrification filters

Denitrification filters are typically employed downstream of the aeration tank to reduce nitrogen content in wastewater treatment. Due to the long retention time, a biofilm forms on the filter medium, which favors nitrogen-reducing bacteria. As with GAC filtration, the flow is parallel in horizontal direction. This means that the throughput capacity is not hindered due to ensuing gas bubbles, as wastewater and gas stream in crossflow, increasing efficiency and requiring less nutrient input (carbon source).


Sand filters

When used as sand filters for the separation of suspended solids and other fine particles, the water to be treated can either be fed into the sand bed through the inner distributor cylinder and flow horizontally and radially outwards, or stream from the periphery flowing radially to the core.