Artificial filled natural river sand (natural river sand is selected with a certain particle size distribution) is adopted, and a certain amount of functional special filler is added to ensure high hydraulic load and meet the effluent treatment target. When the polluted river water is treated, the hydraulic load is above 2 m/(m2 d), and the effluent quality can meet the national Class III water quality standard for surface water, so it can be used as drinking water source. For domestic sewage, the hydraulic load can reach more than 1 m/(m2 d), and the effluent quality can meet or exceed the effluent standard of secondary treatment. The CODCr is generally below 4 mg/L, and the minimum is less than 2 mg/L; BOD5 is generally below 2 mg/L, which can be used as reclaimed water.
CRI system adopts dry-wet alternate operation mode, that is, flooding and drying alternate in each infiltration pond. Automatic control and manual management can be combined, and ploughing can be carried out regularly. The purification mechanism of CRI system includes three processes: filtration, biofilm action and adsorption. The removal of organic pollutants is mainly accomplished by filtration interception, adsorption and biodegradation. SS was removed by pretreatment and filtration. Ammonia nitrogen is removed by nitrification (drying) and denitrification (flooding); Phosphorus and the special filler in the infiltration filter form calcium phosphate precipitation and are removed.