In sparsely populated areas, sand filter beds play an important role in wastewater treatment. As the need to improve the removal of nutrients increases, reactive filter materials represent one potential way to improve the reliability of current systems. We tested a pilot-scale multi-layer biotite filter for its ability to remove phosphorus, nitrogen, organic matter and enteric microorganisms with the importance of each layer in a multi-layer biotite filter being examined. In the experimental setup, the filters were fed with a raw wastewater influent mimicking the usual daily rhythm of water consumption and the reduction effects of the variable loads were examined during the experiment time of 54 weeks. It was observed that the reduction efficiency of the phosphorus was good (87%) during normal and under loading sequences but the reduction achieved for nitrogen was poor (27%). During and after overloading sequences, the phosphorus reduction was poor (46.5%) whereas the nitrogen reduction improved (to 66.7%). The reduction of organic matter was good during all sequences. The reductions of enteric microorganisms were at a level of 2-3 log10 units already after a single sand layer. For Escherichia coli, reductions of more than 5 log10 units were found after the wastewater had passed through a multilayer biotite filter during all sequences. It is concluded that the inclusion of a biotite layer improves the reliability of the filter bed. However, the proper scaling of the unit is essential in order to guarantee that the filter remains in aerobic conditions.
Keywords: biotite; microorganisms; nutrients; sand filter bed; wastewater treatment.