Filter conditions:

After the process of coagulation and precipitation, the secondary effluent still contains some particulate matter, phosphorus and other pollutants. If the pollutants are further removed, filtration process should be adopted.

Definition of filtering:

The sewage evenly and slowly through a layer or several layers of filter material, the removal of pollutants in the process, called filtration. In the advanced sewage treatment system, the filtration process can remove some fine suspended particles and colloidal particles which can not be removed by the pre-stage biological treatment process and coagulation and precipitation process, so that the concentration of SS, turbidity, BOD5, COD, phosphorus, heavy metals, bacteria and viruses in the sewage is further reduced.

Coagulation and precipitation process + filtration water quality

• SS & lt; 5mg /L

• BODS< 8mmg /L

• COD< 20-35 mg/L

• NH3 – N< 15-30 mg/L

• TP< 0.2 mg IL

Direct filtration process and microflocculation filtration process

· Direct filtration process: secondary effluent can also be removed from coagulation and precipitation

Direct filtration is called direct filtration process.

· Micro-flocculation filtration: a small amount of coagulant is added as a filter aid before filtration.

To improve the filtration effect, this is called microflocculation filtration.

· The effluent quality of direct filtration and micro-flocculation filtration is slightly lower than that of the flocculation and precipitation filtration process, but it can reduce the capital construction cost and operation cost. In most of the established wastewater reuse projects abroad, direct filtration or micro-flocculation filtration process is adopted, because the effluent has met most of the reuse requirements.