ABSTRACT
Natural treatment systems differ from conventional processes in that they require comparatively little or no energy either in their construction or in their operation, making them highly sustainable with a small carbon footprint. They are constructed using the minimum of synthetic materials and rely on renewable energy. Oxygen is supplied by either natural diffusion or photosynthesis or a combination of the two. This results in silent, almost odourless processes that are very robust and simple to construct and operate. However, such systems offset the need for energy and expensive electromechanical equipment by utilizing greater areas of land, making them more important in warmer climates where land is comparatively cheap (Table 13.1). Natural treatment systems include land treatment (e.g. surface irrigation, sub-surface irrigation, infiltration–percolation and overland flow), macrophyte-based systems including floating macrophytes (e.g. duckweed, hyacinth ponds) and wetlands (e.g. reed beds), and stabilization ponds that are classed as either anaerobic lagoons or oxidation ponds (e.g. facultative ponds, maturation ponds and purification lakes).
