Clarifier is a device for water coagulation and removal of suspended solids and colloids in water. The medium used to intercept and separate impurity particles in the clarifier is suspended sludge. The coagulation treatment process of water and wastewater includes three stages: mixing of water and chemicals, reaction and separation of flocs and water. The clarifier is a special equipment to complete the above three processes.

Principle

The medium used to intercept and separate impurity particles in the clarifier is suspended sludge. In the clarifier, the sediment is lifted up and kept in a uniformly distributed suspended state, forming a stable active sludge layer with high concentration in the clarifier, and the concentration of suspended solids in this layer is about 3~10g/L. The raw water flows from bottom to top in the clarifier, and the sludge layer can be in a dynamic equilibrium state in the upflow due to gravity. When the raw water passes through the sludge suspension layer, the suspended solids in the raw water will be blocked by the sludge suspension layer using the contact flocculation principle, so that the water can be clarified. Clear water is collected in the upper part of the clarifier.

The rising velocity of the sludge suspension layer is related to the volume and concentration of the sludge. Therefore, the correct selection of the rising velocity and the maintenance of a good sludge suspension layer are the basic conditions for the clarifier to achieve a better treatment effect.

Classification

Clarifier can be divided into sludge suspension type and sludge circulation type. The commonly used clarifiers in wastewater treatment include mechanical accelerated clarifier, hydraulic circulating clarifier, suspension clarifier and pulse clarifier.

Hydraulic circulating clarifier

A type of hydraulic circulating clarifier. The mixing reaction in the pool, mud circulating reflux and water separation treatment are completed by the hydraulic energy of inlet water. Raw water enters the pool from the bottom of the pool center through a nozzle, on which a mixing chamber, a throat and a first reaction chamber are arranged. A large amount of alum in the conical bottom of the pool is sucked into the mixing chamber by nozzle jet to mix with raw water, and then overflows into the second reaction chamber. The first and second reaction chambers form a suspension layer area to clarify and treat raw water. The effluent from the second reaction chamber enters the separation chamber, and the clarified water equivalent to the inflow flows upward. The rest flows back into the mixing chamber with a reflux ratio of 4. This clarifier has the advantages of no mechanical mixing equipment, convenient operation and management, large cone bottom angle, good sludge discharge effect, but short reaction time makes the operation unstable and unsuitable for large water volume.

Accelerated clarifier

Accelerated clarifier is a clarifier integrating mixing, flocculation and sedimentation water treatment processes into one tank. A new rotary impeller is set in the tank to mix the raw water and added reagents with the return sludge settled in the clarification area, and then enter the separation area after reacting in the primary and secondary mixing reaction areas. The clear water overflows upward and flows out, and the remaining flow flows downward and flows back through the reflux joint to re enter the primary mixing reaction zone to mix with the fresh raw water.

Suspension clarifier

Suspension clarifier refers to the clarifier in which the raw water is added with coagulant to remove bubbles in the water and react through the suspended sludge layer. It belongs to suspended sludge clarifier. Suspension clarifier is a traditional water purification process. Its working principle is to make the mature flocs in the clarifier in a balanced static suspension state by using the rising water flow formed by the inlet water at the bottom of the clarifier to form the so-called suspended sludge layer. The raw water after adding coagulant generates micro flocs by mixing or water distribution, and then passes through the suspended sludge layer from bottom to top with the rising water flow. The micro flocs in the inlet water and the sludge in the suspended sludge layer conduct contact flocculation to make the small flocs polymerize with each other or be adsorbed by the sludge layer, while the clean water is separated upward, and the raw water is purified.

Pulse clarifier

Pulse clarifier is a sludge suspension clarifier. It uses the contact flocculation of sludge in the suspension layer on suspended particles in raw water to remove suspended impurities in raw water. It has the characteristics of small floor area, good treatment effect, high production efficiency, uniform water distribution and reagent saving. As the pulse clarifier adopts the way of inlet water from the bottom distribution pipe, it can also make the concentration distribution of the suspended layer more uniform and prevent particles from depositing at the bottom of the tank.