The initial wave of manufactured treatment devices (MTDs) were generally simpler than options available today. With few exceptions, early MTDs were comprised predominantly of swirl/vortex and other types of gravity separators that targeted solids and floating pollutants. State and local stormwater programs were in their infancy and were predominantly focused on reducing suspended solids loads. Our knowledge of particle size distributions and other common pollutants carried by stormwater paled in comparison to what we know today. MTD testing protocols were non-existent leaving early MTD providers to devise their own and make their case for acceptance. Regulators recognizing the need for underground solutions, especially in urban areas, implemented crude MTD performance criteria typically rooted in demonstrating removal of coarse solids in the laboratory.
Current stormwater design guidance typically recommends starting with preservation of the natural landscape and hydrology wherever feasible. But, even with preservation, new stormwater management facilities are likely to be required to capture and clean runoff from pollution generating surfaces. These new stormwater facilities are likely to include imported soil or soil amendments that add permeability and/or optimize soil structure for vegetative growth. For many years, the industry has characterized media in vegetated facilities generically as soil, sand, compost, etc.
The EPA selected a removal standard of 80% total suspended solids (TSS) removal as the target pollutant of concern due to high TSS concentrations impact on water quality and degradation to aquatic habitat. Many other pollutants of concern are particle-bound, and TSS is thereby a surrogate for other pollutants. Testing methodologies for stormwater control measures (SCMs) in respects to TSS can vary greatly. In part two, we’ll continue our look at stormwater sediment and discuss particle shape and density and their affect on TSS removal.
There are a vast number of stormwater separators on the market which can make it challenging when selecting the ideal solution for each project. Hydrodynamic separators and oil/water separators are often used interchangeably in the industry but each system is unique and one may be better suited for the overall treatment goals of the project. So what is the difference between a hydrodynamic separator and an oil water separator and how can you determine which one is best suited for your project?
Stormwater regulations are increasing calling for an increased level of treatment. This often takes the form of filtration systems. Two types of filtration systems used in stormwater are media filtration and membrane filtration.
Media Filtration systems are defined as filters that function through the use of physical capturing of pollutants, as well as absorption of pollutants through chemical reactions. Typical media based filtration systems are composed of sand, stone, organics, or other materials. The media utilized is typically chosen to target specific pollutants for removal.
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