ASTRASAND® is a continuous sand filter, in which the filter bed is continuously cleaned during the filtration operation. It can be applied for different purposes: for physical-chemical treatment (solids removal) and/or biological treatment (phosphate and nitrogen removal).

ASTRASAND® is already applied in more than 350 projects worldwide, on different types of water, such as process, waste, surface, cooling and ground water.

Applications of continuous filtration by ASTRASAND®

  • Biological nitrification/denitrification
  • Polishing of municipal and industrial wastewater
  • Re-use of water in combination with membrane filtration and disinfection
  • Direct filtration of surface water with in-line flocculation
  • (Biological) side stream filtration of cooling water
Typical influent and effluent characteristics
Characteristic Influent Effluent
Biological denitrification (in mg NOx-N/l) 10 - 50 0 - 5
  5 - 10 0 - 1
Phosphate removal (in PO4-P/l) 5 - 10 1 - 2
  1 - 2 0.1 - 0.2
Suspended solids (in mg TSS/l) 40 - 200 10 - 50
  10 - 40 1 - 10
Biological nitrification (in mg NH4+-N/l) 5 - 30 0.2 - 2

Advantages of ASTRASAND®

  • Robust, continuous, self-cleansing system
  • Capable of coping with fluctuations
  • Suitable for physical-chemical as well as biological treatment (or a combination)
  • No moving parts, thus high up-time and low maintenance
  • Compact installation with small footprint
  • Constant effluent output
  • Low operational costs
  • Modular design
  • Proven over 20 years

Working principle

The polluted water is transported into the filter by means of the feed pipeline (1). Water enters the filter bed (4) through the supply pipe (2) and the distributors (3). This water is purified as it flows upward through the filter. The filtrate is discharged from the upper part of the filter (5). The filter bed moves downward as the water flows up. Dirty sand (6) is continuously extracted from the sand bed and washed, after which it is released back on top of the sand bed (7).

The sand circulation is based on the airlift principle, forcing a mixture of dirty sand and water upward through a central pipeline (8). Intensive scouring movements separate the impurities from the sand particles. At the top of the pipeline the air is released, and the dirty water is discharged (9). The sand then settles in the washer (10) at the top of the filtration tank where the sand is washed with a small amount of filtrate. This removes the final traces of pollutant from the sand. Flow is achieved through a difference in level between the filtrate (11) and the rinse water (9).

The plant can be equipped with a system to monitor the uniformity of sand circulation, and the process can be fully optimised for specific applications by applying an advanced control system.