Filter materials - a possible method to optimise the reduction and recycling of phosphorus in smallscale wastewater treatment systems?

One of the environmental goals adopted by the Swedish Parliament concerns the reductionand extended recycling of nutrients, especially phosphorus (P). Phosphorus is discharged intothe environment through poorly treated wastewater, especially in sparsely populated areaswhere few people are connected to the municipal sewer-system. In these areas, small-scalewastewater treatment systems such as constructed wetlands and infiltration systems have beenused as treatment facilities. These systems have shortcomings and the recycling of phosphorus is very limited. New methods have therefore been searched for. One interestingmethod is the use of filter materials that efficiently sorb high amounts of phosphorus and,when P-saturation is achieved, could be used as soil conditioner or P-fertilisers. The criteriasuch materials have to fulfil are that they have a high P-sorption capacity, are available andthat sorbed phosphorus is available for uptake by plants. Different filter materials, naturalmaterials as well as anthropogenic ones have been tested in different kinds of investigations.Most materials have been tested in batch experiments, others have been selected for furtherstudies in column experiments and a few materials have also been tested in field experiments.A few materials have also been investigated with regard to plant availability of sorbedphosphorus. The results from the different investigations are promising, even though theknowledge still is scarce. In order to learn more about these materials, further studies aresuggested.