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Grit particles settling in water

North America regional grit gradation data now available

News & Opinion
3 October 2016

New grit gradation data available

Following comprehensive testing, grit gradation data is now available at a regional level to help North American wastewater engineers, owners and operators to design and optimize grit removal systems for wastewater treatment plants.

The data sets, which have been compiled from over 120 tests conducted across the United States and Canada, contain average physical size data as well as settling velocity data, making them the most comprehensive resources available on grit and its behavior.

The best way to analyze grit is by settling velocity

Virtually all conventional grit removal processes rely on gravity sedimentation to achieve the separation of grit from wastewater, and most conventional grit removal processes are designed based on the assumption that grit is spherical and has a specific gravity of 2.65. Not all grit maintains a specific gravity of 2.65, however, and other factors - such as particle shape, and encapsulation by fats, oils and grease (FOG) - significantly impact its settling velocity. Therefore, the best means to analyze grit is to determine the settling velocity for given particle size ranges.

Settling velocity data can be correlated to the measured settling velocity of a clean sand sphere. The settling velocity is expressed as the Sand Equivalent Size (SES), which is the sand particle size having the same settling velocity as the more buoyant grit particle. The correlated particle size or SES can then be used for accurate design of an effective grit removal process.

When true settling velocity is considered in the design, real-world removal efficiency of grit particles can be estimated more realistically. These data sets will help US and Canadian wastewater professionals to achieve this objective.

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Regional data sets

State and province data sets

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