Physical, chemical and biological processes involving interactions between water, soil, plants, micro-organisms, etc occur naturally in the environment. Natural treatment systems are designed to take advantage of these interactions and treat wastewater.
All natural treatment systems are preceded by some form of mechanical pre-treatment (e.g. screening, sedimentation).
Typical natural treatment systems include:
Slow Rate - Application of wastewater to vegetated land to provide treatment and to meet growth needs of vegetation.
Rapid Infiltration - Wastewater is applied intermittantly to shallow infiltration or spreading basins.
Overland Flow - Wastewater is distributed across the upper portions of carefully graded vegetated slopes and allowed to flow over the sloped surface to runoff collection ditches (generally used at sites with impermeable surface soils)
Wetlands - Land areas with water that support growth of vegetation. Vegetation provides surfaces for attachment of bacteria films, aids in filtration and adsorption of wastewater, transfers oxygen into the water and controls algal growth by limiting sunlight growth. There are two types of wetlands, namely:
- Natural Wetlands, and
- Constructed Wetlands - Free Water Surface (FWS) or Subsurface Flow Systems (SFS)