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Pretreatment Unit

Stormwater pretreatment system for settling

The configuration of the different pretreatment models allows a minimum accumulation of 25 % of its volume in sediment.

The Soleno pretreatment unit is a stormwater treatment system designed to be installed upstream of a retention basin, infiltration system or stormwater management structure. It captures sediment, oils and floating debris before they migrate toward the main system, helping reduce clogging risks and protect long-term performance.

By reducing the contaminant load upstream, the pretreatment unit contributes to the quality control of urban runoff water. Its settling-based design helps retain particles of 100 microns and larger, ranging from very fine sand to very coarse sand, while effectively removing total suspended solids.

As a result of Stokes’ law*, fine particles remain trapped in the pretreatment unit. It is used to control the quality of runoff water in urban areas. The pretreatment unit retains particles of 100 microns or more, from very fine to very coarse sand, and effectively removes total suspended solids (TSS).

Model shown: 900 mm (36 in) model, with 4 outlets of 300 mm (12 in)
* Stokes law defines the behaviour of settling solid particles in a fluid.

 

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Pretreatment Unit
Unité_prétraitement

Advantages and Benefits

  • Monolithic system without interior moving parts.
  • The pretreatment unique design prevents the dispersion of hydrocarbons and floating debris.
  • Is an economical solution for the upstream treatment of some types of pollutants and for removing sand particles.
  • The pretreatment unit is easy to maintain because it provides direct surface access to the sediment accumulated in the reservoir.
  • This system eliminates work in confined spaces.
  • Installed upstream of a system, it ensures its sustainability.
  • The pretreatment unit is made from durable, lightweight and corrosion-resistant high-density polyethylene (HDPE).
  • Provides excellent resistance to de-icing salts, abrasives, chemicals and vibration.
  • The pretreatment unit can be easily adapted to all types of pipe while maintaining network watertightness.
  • Is easy to install on site, as it is much lighter than traditional systems.
  • Withstands CL-625, H-25 and HS-25 loads.

Technical Documents

Data Sheet

Data Sheet – Pretreatment Unit

Specifications

Specs – Pretreatment Unit

Maintenance Guide

Maintenance Guide – Pretreatment Unit

Operation

Steps

1. When it rains, surface runoff carries suspended sediments, oils and floating debris. Collection systems direct water to a storm water sewer which channels it to a pretreatment unit.

2. When water carrying suspended pollutants enters the tank, its velocity is reduced to begin the settling process.

3. Suspended solids are deposited through settling at the bottom of the unit.

4. Because of its permanently submerged water intakes, the pretreatment unit ensures retention and accumulation of floating pollutants.

5. The pretreatment unit acts directly at the source to prevent pollutants dispersing through the whole storm water sewer network.

Why Choose a Pretreatment Unit?

A stormwater pretreatment solution designed to protect downstream systems

The pretreatment unit helps protect retention basins, infiltration systems and stormwater management structures by reducing the amount of sediment, oils and floating debris that reaches them. Installed upstream, it acts before pollutants migrate into the main system, helping reduce clogging risks and preserve long-term performance.

Its operation is based on settling. When stormwater runoff enters the unit, water velocity is reduced, allowing suspended solids to settle at the bottom of the structure. Floating pollutants are retained through permanently submerged water intakes, helping prevent their dispersion toward the downstream system.

Because the unit is made from HDPE, it provides a durable, lightweight and corrosion-resistant alternative to traditional systems. Its direct surface access makes inspection and maintenance easier, while helping eliminate confined-space work during periodic servicing.

Common Applications

  • Pretreatment Upstream of a Retention Basin

The pretreatment unit is especially useful when a stormwater retention basin must be protected from sediment, oils and floating debris. Installed upstream, it helps reduce the contaminant load before water enters the main retention system.

  • Protection of Infiltration Systems

By retaining sand particles and suspended solids, the pretreatment unit can help reduce clogging risks in infiltration systems. This is particularly important when long-term system performance depends on the quality of the water entering the structure.

  • Storm Sewer Networks

The pretreatment unit can be integrated into storm sewer networks to improve runoff quality before water is conveyed toward a retention basin, infiltration system, outlet or other stormwater management structure.

  • Commercial, Institutional and Urban Sites

Parking areas, commercial sites, institutional properties and other paved surfaces can generate runoff containing sediment, oils and floating debris. The pretreatment unit helps capture these pollutants before they migrate downstream.

Stormwater pretreatment system removing sediment before entering the retention basin

Pretreatment Unit or Settling and Separation Tank?

Understanding the difference to choose the right stormwater treatment solution

The pretreatment unit is designed to be installed upstream of a retention basin, infiltration system or stormwater management structure. Its primary role is to reduce the migration of sediment, oils and floating debris toward the main system in order to protect performance and limit clogging risks.

A settling and separation tank follows a dedicated stormwater treatment approach focused on separating suspended solids, oils and floating debris within a treatment structure. It may be recommended when the project requires a more complete settling and separation solution based on flow rates, target particle size and applicable treatment requirements.

The right choice depends on the project objectives, the system to be protected, flow rates, runoff quality, site conditions and regulatory requirements.

More Information

Inspection and maintenance: inspection and maintenance are facilitated by one or two chimneys providing access to recover oils and sediments.

Pipe connections: our systems are custom designed with a range of entry diameters at various configuration angles. Fittings for inlets and outlets are available to facilitate connections.

Separation by settling: gravity is used to separate suspended solids and oils.

Retention capacity: the volume of contaminants retained by the pretreatment unit is related to the diameter and length of the unit.

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Validate the Right Pretreatment Solution for Your Project

Need to protect a retention basin, infiltration system or stormwater management structure from sediment, oils and floating debris? Our team can help you validate the right pretreatment unit configuration based on flow rates, target particles, pipe connections and site constraints.

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FAQ - Frequently Asked Questions about our pretreatment unit

What is a stormwater pretreatment unit?

A stormwater pretreatment unit is a structure installed upstream of a retention basin, infiltration system or stormwater management structure to capture sediment, oils and floating debris before they migrate toward the main system.

What is the purpose of a pretreatment unit?

The purpose of a pretreatment unit is to protect downstream stormwater infrastructure by reducing the contaminant load carried by runoff. It can help limit clogging risks, reduce sediment accumulation and support the long-term performance of retention or infiltration systems.

What pollutants can the pretreatment unit retain?

The pretreatment unit is designed to retain sediment, sand particles, suspended solids, oils and certain floating debris found in stormwater runoff.

Where should a pretreatment unit be installed?

A pretreatment unit is typically installed upstream of a retention basin, infiltration system, green infrastructure system or stormwater management structure to reduce the contaminant load before water enters the main system.

What is the difference between a pretreatment unit and a treatment catch basin?

A treatment catch basin acts at a collection point and adds a localized pretreatment function. A pretreatment unit is a dedicated structure, generally installed upstream of a main system, to handle larger flows or protect downstream stormwater infrastructure.

Does the pretreatment unit make maintenance easier?

Yes. Access to accumulated sediment and oils is provided from the surface through one or two access chimneys, making inspection and periodic maintenance easier.

How do you choose the right pretreatment unit configuration?

The right configuration depends on flow rates, target particle size, downstream system type, pipe connections, available space, regulatory requirements and site constraints. For project-specific validation, it is recommended to consult a Soleno expert.