Features
Water Remediation Using the Soil Percolation System
Masataka Sugahara

Department of Human Environment,
Osaka Sangyo University

The soil percolation system is a method applied intentionally to function as infiltration and purification, which a natural soil ecosystem has in itself an innate system of water processing or environmental purification. The soil, formed as the result of various activities of animals, plants, and natural physicochemical action, consists of three phases, specifically solid, liquid, and gas. The solid phase is the main substance of soil. The soil grains in the solid phase are classified into gravel, sand, silt, and clay by its particle diameter. The porosity occupied by the liquid and gas phases are expressed as porosity of the soil. This porosity is changed by the diameter of a soil grain, the aggregated soil that is mutually combined by the particles, and the degree of soil tamping or consolidation. Its value ranges between 30% and 70%.
The permeability of the water in soil has a very close relation to the composition of the soil porosity. If the aggregated soil is fully formed, even in silty soil with a small particle diameter, there is great improvement characterized in water permeability. It can be ascertained that the permeability of water plays a main role in the physical and chemical reaction of soil.
Water purification is performed during the course of sewage water permeation into the soil. Therefore, unless suitable permeable conditions are applied, the expected effect is not acquired. As regards to water movement in soil, two types of permeation are taking place and these are: the saturated osmosis occurs when the porosity is saturated completely with water, and the unsaturated osmosis which takes place when gas filters through the porosity, as well.
The organic component of soil cannot be decomposed easily by microorganisms if soil is saturated with water. When air (oxygen) is supplied, porosity of the soil can function efficiently, and the moderate balance of the three phases of soil is required.
The mechanisms of the soil percolation are as follows: filtration, in which the soil particles mainly play a role as filters [Physical effect]; adsorption, that clay mineral and humic substances in soil play a role as an adsorbent [Chemical effect]; and biologic decomposition by the action of living organism in soil [Biological effect].
The effect of concrete remediation of soil is obtained by using the mechanisms mentioned above such as filtration of suspended matters, decomposition of organic matter and nitrogenous compounds, fixation of phosphorous, etc.It goes without saying that such a percolation system which the soil possesses originally is outstanding but its function has a limitation. The performance, on the other hand, can be improved by adding various kinds of additives to the soil, which is the main substance. This new soil is made of composite soil that can heighten water permeability and removal capability. Making the soil layer composition, wherein water transmission and permeability are greatly different, is also effective. In this special feature, we introduce the latest soil percolation systems.


before
4 Challenge to Energy-Independent Treatment forLivestock and Food Wastes
top of contents next
1 History of Technical Developments of Soil Percolation System for Wastewater and River Water Treatment in Japan