Wastewater Treatment


Sand polishing filters from Tricel (Sandcel) are secondary or tertiary treatment systems that comply with the Environmental Protection Agency’s (EPA) Code of Practice.

Wastewater treatment

Guide to Tricel Sandcel sand polishing filters


Tricel Sandcel panels are made from a composite material known as Sheet Moulding Compound, or SMC, a type of glass-reinforced plastic.

They are strong, durable, chemical-resistant, and impact-resistant, and the material will not rot or deteriorate over time.

Tricel Maxus underground buffer tank and overground treatment unit

Where should a sand polishing filter be used?

A sand polishing filter is used after a septic tank or wastewater treatment unit to treat further the effluent (based on ground requirements).

  • Sand polishing filter as a secondary treatment system 

If placed after a septic tank (primary treatment), a Tricel Sandcel is described as a secondary treatment system. 

  • Tertiary treatment system

If it is placed after a wastewater treatment plant (secondary treatment), the Sandcel is then described as a tertiary system.

How does a Sandcel sand polishing filter work?

Sandcel is a pipework system designed to direct wastewater to stratified layers of certified sands according to current EPA guidelines for effluent treatment.

A service pod is used to access all of the pipework in these filters, whether installed above or below ground.

Sandcel Sand Polishing Filter installation

Drawing of Sandcel as a tertiary treatment (following a Tricel Novo)

Pipe network on Sandcel

Close up to a Sandcel pipe network completed before final gravel layer is laid.

Service pod on Sandcel

Sandcel filters all come with a service pod allowing access to the entire pipe network. To maintain pressure within the network, the laterals terminate in the pod and are capped and sealed. As a result, service and rodding are possible through the pipe system.

What are the benefits of using a sand polishing filter, and why should you use it or recommend it?

Sandcel’s sand polishing filter is suitable for homeowners, site assessors, and engineers alike because it meets a wide range of requirements.


  • Ideal for smaller sites (only 16 m2 for an application with six people, reducing the need for a large percolation area).
  • The Sandcel sand polishing filter blends into any garden design, as it can be buried, covered with soil, and planted with grass.
  • Suitable for sensitive sites with a high level of treatment.
  • Low maintenance requirements, maintenance contract available.


Site Assessors and Engineers

  • Reduces the size of the percolation area, which is ideal for tight sites.
  • Reduces the soil depth in your rock bed (free-draining soil); 900 mm is usually required.
  • Constructed from high-quality materials (GRP panels, certified sand, gravel).
  • Designed for high effluent treatment (using a sand polishing filter bed to ensure an even distribution of effluent around the entire bed).
  • Ideal for sensitive areas (e.g., near a river or in a conservation area) thanks to a high quality of effluent treatment, which helps preserve the environment. Sandcel reduces nutrients discharged into the environment.
Sandcel, sand polishing filter case study

How to build a sand filter?

Sand polishing filters made by Tricel are constructed as follows:

  • GRP panels
  • Certified sands
  • 10mm pea gravel
  • Servicing pods
  • Pipes
  • Geotextile cover (as a top layer to block the soil from clogging the pipework)

Sand polishing filters are installed after a packaged wastewater treatment system or septic tank.

GRP panels

GRP panels

Layers of pea gravel and sands

Layers of pea gravel and sands

Network of pipes and servicing pod

Network of pipes and servicing pod

How deep does a Sandcel sand polishing filter go?

Depending on how much soil exists on-site, the Sandcel sand polishing filter can be installed above or below ground.
We recommend leaving 100mm between the top of the panels and the ground level to ensure enough soil to cover the pipes and promote grass growth.

Can a sand polishing filter be buried?

Sandcel sand polishing filters can be buried, but they must be placed 400mm above the bedrock or water table, whichever is higher. This prevents contamination of groundwater.

Sandcel Sand Polishing Filter being installed

Sandcel Sand Polishing Filter being installed

Sandcel Sand Polishing Filter installed

Sandcel Sand Polishing Filter installed

How large is the base?

EPA Code of Practice tertiary distribution area formula determines the base size.


0.125 x PE x T = Area in m2

Standard sizes and dimensions of Tricel’s Sandcel Sand Polishing Filters

DetailsSandcel 900 Sandcel 1200 Sandcel 1500
Capacity (litres per day) 90012001500
Length (mm)400040006350
Width (mm)385050004000
Depth (mm)100010001000
Footprint (m2)15.4 (165.77 sq/ft)20 (215.28 sq/ft) 25.4 (269.10 sq/ft)

Gravel calculator for Tricel’s Sandcel. How to calculate how much gravel is required?

Use the illustration below (Sandcel stratified layers) as a reference for the calculator.

Sandcel Sand Polishing Filter

Note: these calculations only apply to Tertiary systems, so they are not appropriate when Sandcel is used as a secondary treatment system.


Step 1: Area calculator

A gravel distribution bed is required to disperse the treated effluent from the Sandcel. A 300mm layer of 10mm gravel should be used as the distribution bed.

For calculating the area, you must have available:

  • the population equivalent (PE) value 
  • and the surface/subsurface value

For subsoil with a Subsurface/surface the distribution area is calculated using the below table from EPA Code of Practice 2021.

EPA CoP Table 10.1

For example with a 6PE with a subsurface/surface value of 3-20

For a range of 3 < PV < 20, looking at the column “tertiary infiltration area (option 6)”, select the correct area required per person based on the subsurface/surface value. In our example, the value is >3.75 m2.

Then take your PE value (6) x per the area required per person (3.75m2) = 22.50m2 total required area.

Step 2: Base gravel calculator for Sandcel sand polishing filter

Using the formula below, you can calculate how much gravel you need for your site once you have calculated its area. Please note two tonnes of 10mm pea gravel is required per m3.

Formula = Area in m2 (calculated above) x 0.3 (300mm depth) x 2 (2 tonnes / m3).


Step 3: Sandcel infill gravel calculator

350mm of pea gravel sprayed over different layers (see above sketch of the Sandcel stratified layers) is required to fill in the inside of the GRP panels.

Formula = 350mm x area in m2 x 2 (2 tonnes / m3).


Total sand required for Sandcel installation = results step 2 + results step 3 = tonnes of 10mm pea gravel required.

Gravel requirements for standard size Sandcel sand polishing filters

See below examples of standard Sandcel dimensions and gravel quantities in tonnes.


NOTE: Dimensions add 150mm to the below dimensions to include the GRP panel enclosure

Dimensions of the areaSandcel 900Sandcel 1200Sandcel 1500Sandcel 1800
3850mm * 4000mm6.08m3 or
13 tonne
5000mm * 4000mm8m3 or
16 tonne
6350mm * 4000mm10.4m3 or
21 tonne
7500mm * 4000mm12m3 or
24 tonne

Who supplies the sands and gravel?

Builders and installers are responsible for pea gravel during a Tricel Sandcel installation, while Tricel is responsible for the sand. Sand used throughout has been certified compliant with the EPA Code of Practice, and these particles are washed and graded to ensure that little or no binding occurs during use.

Tricel is responsible for the delivery and installation of the Sandcel sand polishing filter.

The contractor carries out all other works, such as excavation, concrete surround, pumping main, etc.

Images of an installation

Base gravel & panels assembled & first Layer of Sand, Placed

Base gravel & panels assembled & first Layer of Sand, Placed

First Layer of Pea Gravel, Placed

First Layer of Pea Gravel, Placed

Second Layer of Sand, Placed

Second Layer of Sand, Placed

Second Layer of Pea Gravel, being placed

Second Layer of Pea Gravel, being placed

Final Layer of Sand, Placed

Final Layer of Sand, Placed

Base layer of gravel distribution layer and distribution pipework

Base layer of gravel distribution layer and distribution pipework

Gravel capping layer

Gravel capping layer & geotextile


Gravel capping layer & geotextile

Key Features

Reliable & long-lasting

Reliable & long-lasting

SMC panels, strong & lightweight

Fast delivery

Fast delivery

Manufactured in Ireland, short lead time



Designed to the EPA Code of Practice

Get in touch

    Type of request*


    Tricel (Killarney) Unlimited Company
    Ballyspillane Industrial Estate, Killarney, Co. Kerry, V93 PN84, Ireland
    Tel: 00353 (0)64 6632421