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Sand polishing filters

Tertiary treatment systems

What are sand polishing filters?

Sand polishing filters are generally placed after a wastewater treatment plant and can also be placed after a septic tank, they are designed to treat or polish the effluent to a higher standard before releasing into the ground.

In Ireland Sand polishing filters, such as the Tricel Sandcel, must be designed according to the EPA Code of Practice.

How do sand polishing filters work?

Sand polishing filters are placed over a 300mm layer of pea gravel which sits on top of a layer of free draining subsoil. The area of the gravel layer is determined by the following formula:

Area = Population Equivalent (PE) x Percolation Test (PT) value x 0.125

Installation of GRP panels for a Tricel Sandcel sand polishing filter

With the Tricel Sandcel sand polishing filter, GRP panels are placed around the area to create the outside frame.

Layers of certified sand and pea gravel for Sand polishing filter

Layers of certified sand and pea gravel then get added to the inside of the area created by the secured panels.

Sand polishing filter pipework

The pipework to disperse the effluent is then placed towards the top of the sand polishing filter, ensuring the liquid gets spread evenly throughout.

A layer of topsoil then gets added to the surface of the sand polishing filter.

The images below are of Tricel Sandcel sand polishing filter taken during the yearly maintenance of a Tricel Novo wastewater treatment plant. This sand polishing filter got planted with a lawn which allows it to blend with its surroundings.

Tricel Sandcel sand polishing filter
Sandcel sand polishing filter by Tricel

What are the benefits of sand polishing filters?

  • The primary benefit is an excellent treatment of effluent. Indeed, sample testing of some sites where the placing of a Sandcel sand polishing filter is employed after a Tricel Novo has shown a final effluent quality of <1 mg/ltr BOD5.
  • Ideal for small and compact sites, eliminating the need for large percolation areas.
  • Aesthetic finish: the filter can be covered with topsoil and planted with a lawn to blend into your garden.

What to look for in sand polishing filters?

The quality of the materials used to build sand polishing filters will have an impact on its longevity, efficiency and cost.

  • Glass Reinforced Plastic (GRP) panels are strong and durable and will not rot or decay. Whereas wood panels might be cheaper, they will not last as long as GRP ones.
  • Certified sands and gravel get used in the filter to ensure that the filter-bed will not break down over time. Sand grain and gravel size, as well as their uniformity, is paramount to provide a good rate of treatment and filtration.
  • Accessibility of the pipework is essential to future-proof your system. Tricel installs service pods to ensure that the pipework is accessible.

Domestic and commercial usage possible

Sand polishing filters are suitable for both domestic and commercial use, with large and bespoke sizes available on request. Read about our case study of a Sandcel sand polishing filter installation with a Tricel Novo wastewater treatment plant.

Contact us if you have any questions or would like to receive a quote for a sand polishing filter.

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