VF should probably be called 'vertical downflow' because there are also systems where the wastewater is brought to the filter bottom and the wastewater passes the filter in upward direction and treated water is collected at the top of the bed. These systems have commonly been used in
Brazil since 1980s. The beds are filled with crushed rock on the bottom, the next layer is coarse gravel, and the top layer is local soil planted with rice (Oryza sativa). This treatment system is called 'filtering soil' in Brazil (Figure 32). Other systems were also studied under experimental conditions in Australia, New Zealand, or Sweden. However, outside Brazil, the layer of soil is usually not used and beds are filled with gravel and usually planted with species commonly used for HSSF wetlands. At present, there is a very limited information on treatment effect of these systems with the exception of systems in Brazil where the results show good treatment performance.
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