Faecal separation for nutrient management––evaluation of different separation techniques

The aim of this study was to evaluate the potential of different separation techniques for local recovery of faecal nutrients. Separation by Aquatron, filtration, flotation and sedimentation was tested in the laboratory. Only the separation of faecal matter from flushwater was investigated. For efficient nutrient capture, the system has to be combined with urine-diverting toilets.

In this study we found that the extraction of nutrients from the faeces to the liquid occurred rapidly. Therefore, to effectively separate the faecal nutrients and particles from the flushwater, the separation has to be performed locally, preferably at house level.

The Aquatron and the filtration gave a fraction of separated solids with 10% dry matter, which contained 70–80% of the incoming plant nutrients nitrogen, phosphorus and potassium. The other two methods investigated did not prove effective for local separation of faeces.

Using urine-diverting toilets, where all the urine is diverted, and collected and 70% of the faecal nutrients are separated locally, the potential for local nutrient recovery from the household wastewater is 88% for nitrogen, 75% for phosphorus and 55% for potassium, mainly in the form of directly plant available nutrients.