Filtration Manufactured Treatment Devices

Plan view of an upflow filtration MTD with filter cartridges. This example for the U.K provides four separate stages of treatment for influent water including: 1) oil retention, 2) chemical separation, 3) filtration and 4) sedimentation (Source: 3P Technik UK Ltd, 2023).

Overview

Filtration Manufactured Treatment Devices (MTDs) are structures with one or more chambers containing filtration media, membranes and/or filtration cartridges that remove solids and debris/trash from runoff. Some units may have oil separation functions and pretreatment chambers for coarse sediment and debris. The filter components are designed to remove the coarse and fine sediment fraction of suspended solids and associated pollutants in stormwater runoff and may also target removal of dissolved pollutants such as phosphorus or metals through biological and/or chemical processes.

Example of a high flow curb inlet filtration MTD with proprietary soil media installed and monitored at the Kortright Centre in Vaughan, Ontario. (Source: STEP, 2020).

Application

Filtration MTDs are suitable for pre-treatment or may be installed as stand alone if third party performance testing shows that they achieve enhanced level water quality protection (i.e. lower 95th percentile removal efficiencies of 80% or greater).

Since Filtration MTDs contain filters that restrict flow rates, they are normally designed for much lower hydraulic loading rates than Oil-Grit Separator MTDs and have longer detention times. Flow restriction occurs due to the small pore size openings of filters and the clogging of pores and/or the formation of films either on the surface of the filter or within the filter matrix filter. For this reason, inspection and maintenance intervals for Filtration MTDs are normally shorter than for OGS MTDs. The method of maintenance typically involves sediment removal with a hydro vacuum truck as well as filter cleaning or replacement.

Further guidance on how the data and information generated from verified laboratory testing of OGS technologies should be interpreted and factored into regulatory agency approvals and procurement decisions for stormwater management is provided in this publicly available specification Guidance on the Use and Application of Results from Verified Laboratory and Field Testing for Stormwater Manufactured Treatment Devices, developed by TRCA and the Standards Council of Canada that addresses both OGS and Filtration MTDs.

Testing and Verification

Testing of Filtration MTD performance must be based primarily on field monitoring. Field testing is particularly important for Filtration MTDs because stormwater sediments consist of a mixture of cohesive silts, clay, sand, and may include organic matter, emulsified oils, fine debris, bacteria and other pollutants that build up on filter surfaces and/or penetrate into the filter structure(s) resulting in clogging dynamics that may vary significantly across different filtration system designs. These clogging processes are not easily replicated in laboratory testing due to limitations on the type of test sediment that is used (non-cohesive ground silica) and other factors.

Field testing also allows for a more accurate assessment of filter performance for stormwater pollutants other than suspended solids. These pollutants are subject to complex physical, chemical, and biological interactions that are not easy to replicate in a laboratory.

In Canada, the Canadian Procedure for Field Testing of Filtration Manufactured Treatment Devices, developed by TRCA and the Standards Council of Canada stipulates field testing requirements for Filtration MTDs. This document was developed based on the Technology Assessment Protocol – Ecology (TAPE). TAPE provides a robust and scientifically defensible field evaluation methodology for proprietary and non-proprietary stormwater treatment technologies that is well regarded by stormwater practitioners, having been developed and continuously updated over the past two decades through an extensive third-party expert peer review process. It should be noted that several jurisdictions in Canada do not accept filtration MTDs without field monitoring due to the aforementioned concerns, even if a lab test has been verified through the ISO 14034 ETV process.

The technique of removing pollutants from runoff as it infiltrates through the soil.

Deposition of material of varying size, both mineral and organic away from its site of origin by the action of water, wind, gravity or ice.

Settling-out or deposition of particulate matter suspended in runoff.

The technique of removing pollutants from runoff as it infiltrates through the soil.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Sustainable Technologies Evaluation Program

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

The temporary storage of stormwater to control discharge rates, and allow for sedimentation.

Systems designed to remove trash, debris and some amount of sediment, oil and grease from stormwater runoff based on the principles of sedimentation for the grit and phase separation for the oil.

Toronto and Region Conservation Authority

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.