The Role of Grit Chambers in Wastewater Treatment

Grit chambers are long narrow tanks which play a crucial role in wastewater treatment. They slow down the flow of the effluent so that the solid wastes, like sand, slit, and gravel settle in the water. Removing inorganic particles prevent damage to the pumps as well as their accumulation in the sludge digesters.

They are particularly important for the cities which have a combined sewer system and carry a good amount of gravel that gets washed off streets and land.

Let us know something more about them as they are an important part of treatment optimization and design.

Types of grit chambers

Grit chambers come in two versions - mechanically cleaned and manually cleaned. In the first type, grit chamber collects the grit on the floor of the grit chamber. This collected grit is elevated to the ground level by different mechanisms, like bucket elevators, air lift or jet pump. Grit effluent mechanism also comes in multiple designs, most of which are agitation devices used with either water or air to create washing action. Manually cleaned grit chambers are cleaned at least once a week. One simple method to do so is to use shovel.

Aerated grit chamber

An aerated grit chamber is provided with a standard spiral flow aeration tank which consists of air diffusion tubes on one side of the tank. The grit particles settle down at the bottom of the grit chamber. The rates depend on the particle size and the velocity of the spiral flow at the bottom which is majorly decided by the rate of air diffusion through diffuser tubes and shape of the aeration tank. Heavier particles settle down easily, and the lighter organic particles are carried through the roll of spiral motion.

Operation of grit chamber

Grit chambers are very similar to sedimentation tanks that are designed to separate the heavier inorganic material and let lighter organic material pass through. Therefore, the velocity of the effluent should neither be too low as it may make lighter organic matter settle; not it should be too high as it may make slit and grit present in the sewage unsettle.

Therefore, the velocity of the effluent in the grit chamber is kept controlled. In addition, this particular velocity is maintained at all fluctuation of flow to make sure that only organic solid is flowed out from the bottom.

All these points clearly state the importance of grit chamber in wastewater plants.