In soil rapid infiltration wastewater treating systems(which is abbreviated as RI system), the wastewater will be imported to the highly permeable land surface,so as to experience the different physical,chemical and biological actions in the course of its trickling down, and finally reaches the purpose of wastewater purification.
      This technique has some effect in removing BOD,COD,NH3-N,P, and possesses the advantages of economical investment and low operational fee.
      However, the technique has the following shortcomings, as it is selective in local space, and occupies large area. Besides, it has a bad activity performance in winter.Moreover,the influent water should not contain matters that would endanger microorganisms。