Working principle of mechanical filter in pure water equipment

The mechanical filter is mainly used for reducing the turbidity of the raw water. The raw water is sent into the mechanical filter filled with various grades of matched quartz sand. By utilizing the pollutant interception ability of the quartz sand, larger suspended particles and colloids in the water can be effectively removed, and the turbidity of the effluent will be less than 1mg/L, ensuring the normal operation of subsequent treatment processes.

Coagulants are added to the pipeline of the raw water. The coagulant undergoes ion hydrolysis and polymerization in the water. The different products from hydrolysis and aggregation are strongly adsorbed by the colloid particles in the water, reducing the particle surface charge and diffusion thickness simultaneously. The particle repulsion ability decreases, they will get closer and coalesce. The polymer produced by hydrolysis will be adsorbed by two or more colloids to produce bridging connections between particles, gradually forming larger flocs. When the raw water passes through the mechanical filter, they will be retained by the sand filter material.

The adsorption of the mechanical filter is a physical adsorption process, which can be roughly divided into a loose area (coarse sand) and a dense area (fine sand) according to the filling method of the filter material. Suspension substances mainly form contact coagulation in the loose area by flowing contact, so this area can intercept larger particles. In the dense area, the interception mainly depends on the inertia collision and absorption between suspended particles, so this area can intercept smaller particles.

When the mechanical filter is affected by excessive mechanical impurities, it can be cleaned by backwashing. Reverse inflow of water and compressed air mixture is used to flush and scrub the sand filter layer in the filter. The trapped substances adhering to the surface of the quartz sand can be removed and carried away by the backwash water flow, which helps to remove sediment and suspended substances in the filter layer and prevent filter material blockage. The filter material will restore its pollutant interception capacity fully, achieving the goal of cleaning. The backwash is controlled by the inlet and outlet pressure difference parameters or timed cleaning, and the specific cleaning time depends on the turbidity of the raw water.