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Planted soil filters, also referred to as constructed wetlands or reed bed systems, are natural systems treating solid-free wastewater. This can be pre-treated wastewater from a flush toilet or faecal wastewater from a urine diversion toilet, either combined with wastewater from the kitchen and bathroom, or separate from it. A planted soil filter, preceded by a settling and watertight storage tank, consists of a sand and gravel matrix (sealed at the bottom) planted with wetland plants like reeds. Solid free wastewater is discharged from the storage tank on top of the filter or though an underground inlet-system and flows through (vertical) the filter. Horizontal-flow soil filters are commonly found, and easier to construct than vertical flow filters, but they are less efficient at eliminating nitrogen. Wastewater is treated through several processes, in which bacteria play an important role. After treatment, the effluent can be discharged into surface water, used for irrigation or groundwater recharge.