Grit removal, which involves separating foreign particles such as sand and gravel is very important and needs to be carried out in every wastewater treatment system. In order to accomplish this, a Grit Chamber is usually constructed for this purpose, as this is needed to protect major mechanical equipment from wear and tear including damage. Other than that, it also ensures that formation of deposit especially in pipelines can be avoided and overall this can save the time that otherwise would be spent to clean the accumulation of waste.
A grit chamber is usually installed before primary sedimentation tanks and it is sensible to say that it should be placed well before wastewater pumps. There are basically three different types of grit chambers. One is called the horizontal flow type, another is the aerated grit chamber and the last one is the vortex type. The design of a horizontal flow type is such that as wastewater flows through in horizontal direction at a certain velocity (0.3m/s) particles will start to settle at the channel before reaching the outlet point. Normally it is constructed with consideration put in mind to remove particles that would otherwise be trapped on a 0.21 diameter mesh size. Once the grit settles to the bottom of the chamber, it can then be removed out from the system, using conveyor with buckets or plows.
Aerated grit chamber consists of an aeration tank, which is designed to create a spiral flow of wastewater as it moves through the chamber. With the velocity created from the movement of water, a certain particle sized grit will settled at the bottom. A well-designed system should have the incoming velocity travelling at a precise speed in order to avoid the grit exiting out of the chamber with the wastewater as well. A trial and error observation can be carried out to determine the right adjustment on the feeding of air to the system. Similar like a horizontal flow type, the accumulated particles which settled at the bottom can then be removed using conveyor buckets.
A vortex type grit chamber operates on similar principal and basically it has a cylindrical tank, which is designed to create a vortex flow pattern. In order to achieve this, wastewater basically has to enter the chamber tangentially and as such a centrifugal force will ensure that the grit is taken out. Find out more about other forms of physical treatment in wastewater plant such as the use of Dissolved Air Flotation System.