Tricklingfilter systems

These systems make a good alternative for treating residential and industrial waste water in contexts which are not suitable for activated sludge plants.

Organic matter degradation is performed by microorganisms that build up on plastic elements scattered throughout an adequately sized chamber.

Process description

Stages are the same as in activated sludge plants, the only difference is that biomass builds up instead of remaining suspended.

PRIMARY DECANTATION in an Imhoff tank, to retain floating material and any settleable solids and obtain a partially clarified effluent with pollutant load cut by approx. 30%. Suds waste is pretreated in a grease condensation tank.

BIOLOGICAL OXIDATION ON BIOMASS BUILD-UP Waste water flows along pierced channels and is distributed onto the plastic fills. The microorganisms cling to the latter and start degrading organic matter. Pollutant load reduction, which is strictly bound to organic load and to retention time, can reach 90% in this stage.

FINAL DECANTATION The water and sludge matter is pumped into the hopper decantation chamber, where sludge descends towards the bottom of the tank and purified water flows into the sampling well to then merge with the receiving water body. Settled sludge is recovered and recycled in the upper part of the trickling filter.

Industrial waste water must be specifically pretreated before undergoing treatment.

Running and maintenance

The plants do not require special maintenance and adequately sized galvanized manholes, positioned right above the equipment, make running operations easier. However, it is recommendable to periodically monitor biological film evolution and the degree of treatment efficiency.

The following operations must be carried out following start-up:

  1. periodical check of biological film concentration thickness and of the purifying process
  2. periodical check of the timer clock controlling pumps operation
  3. periodical cleaning of the pretreatment chambers, removal of detached film build-up if needed and leak channel cleaning

The plant exploits microorganisms, therefore users must absolutely avoid harmful substances able to hamper the evolution of the same.

Also high temperature and substantial variation in organic load can affect microorganism evolution, and hence the degree of efficiency of the treatment.

Products and technical features

Trickling filter plants for small loads are made up of a single item divided into sections. Waste water flows along a pierced channel into the largest chamber, which contains the receiving plastic elements. Such chamber is adjoining to one of the two smaller ones, which holds a pump directing the waste into the second space, namely the secondary sedimentation chamber.

The film is kept moist thanks to recirculation controlled by a pump that directs the waste water from the secondary sedimentation chamber upstream the Imhoff pretreatment tank. Preliminary grease sedimentation and separation is essential to prevent the plastic fills from clogging. Plants designed for larger loads are fitted with a separate filtration and decantation chamber.


The plastic fills used in this system are spheres with diameter approx. 9 cm, usable surface corresponding to 135 m²/m³ and 96% clear volume, against respectively 50-100 m²/m³ surface and 40% hollow found in stone.

The high hollow ratio guarantees better waste water recirculation and lowers the risk the bottom of the tank is clogged due to excessive film growth. In addition, the special shape and plastic composition of the material ensure adequate waste water retention time.