Let’s Talk – Gross Pollutant Traps

SPEL Vortceptor GPT

A gross pollutant trap (GPT) – categorized as a ‘primary treatment device’, is the first line of defense in a stormwater treatment system and removes much of the bulky pollutants from stormwater runoff. Traditionally we find GPTs fending off litter, cigarette butts, plastic bottles, leaves and sediment. A strong, robust GPT plays a key role in ensuring ‘tertiary treatment devices’ like biofilters, raingardens and proprietary filters can ‘polish’ or clean the stormwater, removing an additional layer of particles and dissolved pollutants.

What Gross Pollutant system works best?

An interesting study was conducted by the CSIRO in 2010 surveying council employees and GPT cleaning contractors on their perception of different device types. Summarised in the graph below, the continuous reflective separation unit consistently rated higher in comparison to other GPTs on the market.

Not all GPTs are the same

There are several different GPTs in the market today – all removing gross pollutants from our stormwater system in different ways. Most GPTs fall into one of the below categories:

Difference in specific gravity traps – 

systems which use gravity to separate pollutants that float and settle without the use of screens. Water quality is achieved by incorporating baffles/booms in a series of chambers.

Direct screening – devices which incorporate screens in various orientations to manage the flow. These are not self-cleansing.

Vortex type devices – devices that direct flow to produce vortices/hydrodynamic separation, but do not have a screen.

Devices that combine a vortex/hydrodynamic separation with a non-blocking screening system – these are known as ‘continuous deflective separation’ units. The SPEL Vortceptor GPT is a vortex separation unit with a non-blocking screen system.

cleaning frequency for GPT
cleaning frequency for GPT

The Launch of the 'Continuous Deflective Separation' GPT

CDS Technologies pioneered the use of the ‘Continuous Deflective Separation’ GPT in Australia during the mid-90s. The rights were then acquired by Rocla Pty Ltd in 2007 allowing them exclusive patents to CDS GPT technology until 2015. These units were, and still are, housed in precast concrete segments. Once installed, they are reliable and councils benefit from the merit of their proven performance and reliability.

vortceptor inline

Explanation Video

Installation Video

The SPEL Vortceptor

Without a doubt CDS units were the way forward as an effective GPT, yet the concrete unit was often difficult and costly to install. 


In 2019 SPEL release the Vortceptor – a light weight, one-piece alternative to the current concrete tanks. This exclusively designed and manufactured GPT with a hydrodynamic separator producing vortex conditions, resulted in excellent pollutant removal ratings and high-quality outcomes. 


With its non-blinding screen, the Vortceptor was cutting edge technology. As founder Stephen Hales recalls ‘we knew we had a good product. This lightweight, easy to install system would save our customers time and money.


SPEL manufactures the Vortceptor as a single piece, pre-assembled fibreglass  chamber. No laborious on-site assembly. No hefty installation costs. The remarkable strength to weight ratio achieved by this structure gives us a product a fraction of the weight, while still structurally robust underground. Fibreglass is also durable and resistant to chemicals, saltwater acid sulfate soils.

Timeless Innovation - Two Decades On

The world of GPTs has changed dramatically since the mid 90’s. While technology has advanced and improvements have been made, the principals of the continuous defection technology have remained timeless. SPEL continues to innovate, looking for further improvements and field testing on the Vortceptor.

As Stephen Hales would say 'it's a constant evolution' bringing us closer every day to the clean water future we all envisage.

The flow

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