In conventional wastewater treatment plants, primary treatment is implemented after the headworks and before secondary treatment. Primary treatment is typically accomplished via the clarifiers and focuses on the removal of solid particulate not captured by screens and grit removal.
Clarifiers are large tanks that are used to separate and remove solid particles from the wastewater. They work by allowing the wastewater to flow into the top of the tank through the draft tube, where it is then slowed and forced to settle by sets of inclined plates known as baffles. The solid particles in the wastewater, such as dirt and debris, will drop to the bottom of the tank, while the cleaner water is allowed to flow out of the tank and move on to the next stage of treatment.
The removal efficiency of clarifiers can vary depending on a number of factors, including the design of the clarifier, the flow rate of the wastewater, and the type and amount of solid particles present in the wastewater. In general, clarifiers are able to remove around 50-70% suspended solids and 40-50% BOD (organics) inherent in solids.
One of the main advantages of using clarifiers in primary wastewater treatment is that they are relatively simple and low-cost to operate and maintain. They are also capable of handling large volumes of wastewater, making them an ideal solution for storing and treating the wastewater produced by large communities and industries.
In terms of their capabilities, clarifiers are typically used to remove a wide range of solid particles from wastewater, including dirt, debris, and other suspended solids. They are also able to remove some dissolved pollutants, such as heavy metals, from the wastewater.
While clarifiers and primary treatment are an important component of wastewater treatment, it is important to note that they are not able to remove all pollutants from the wastewater. Secondary and tertiary treatment methods, such as biological treatment and advanced filtration, are typically required to remove the remaining pollutants and purify the wastewater to a level that is safe for release back into the environment.