Reed bed treatment systems are self-contained, artificially engineered, wetland ecosystems. They are designed to optimise the microbiological, chemical and physical processes naturally occurring in the Reed Bed.  Wetland plants, such as reeds, transfer atmospheric oxygen down through their roots in order to survive in waterlogged conditions. This creates both aerobic and anaerobic soil conditions, allowing an extraordinary microbial species diversity to flourish.

These bacteria and fungi can use organic pollutants as a food source, breaking down a wide range of organic chemical products. So, chemicals are not simply stored in the reed bed; they are actually degraded into harmless components. Other contaminants, such as metals, are transformed from a toxic, mobile state and fixed in the soil via complex chemical reactions. The soil's adsorption capacity also provides a buffer for peak or shock effluent loads.
The complexity of microbial life and powerful reactions within the root zone of the soil based Reed Bed result in an extraordinary water cleaning capability. This capability is often far less constrained than in many chemical or physical wastewater treatment systems.

The Role of Plants
The specially selected plant species within the Reed Bed have three main functions:
· They provide the means for secondary restructuring of the soil system. The very extensive root and rhizome system creates channels for the water to pass through and also keeps the soil open through the constant growth and die back of the root system.
· The roots of the aquatic plant introduce atmospheric oxygen down into the body of soil, providing an environment which encourage an extraordinary quantity of species diversity of micro-organisms to flourish around the plant roots. These are needed for the effective breakdown of many types of compounds, such as the oxidation of ammonia to nitrate - the first step in the biological breakdown of this compound.
· The plants are capable of taking up a certain amount of nutrient from the wastewater themselves.