Today, one million, or 15 percent, of the Swedish household uses small sewer systems that are not connected to municipal wastewater treatment plants.
New methods for testing
Small sewage systems emit large amounts of phosphorus. Stronger criteria for phosphorus discharges demands for upgrading of small-scale sewage, in order to prevent overfeeding and to enable recycling of phosphorus which is a finite resource, vital for agriculture.
– Poor phosphorus removal in small wastewater facilities is a global problem, says PhD student Inga Herrmann who submitted her doctoral thesis on the subject in June. We work with a model to simulate the function of the so-called reactive filters and develop a single metod for simulate and testing of different filter material's ability to take care of phosphorus.
The advantage of reactive filters is that they require minimal maintenance. With better filter, we can reduce the eutrophication of lakes and streams, especially in the Baltic Sea,at the same time that it may help to recover phosphorus.
Expensive field experiment
Testing filters in field experiments are expensive. By computer simulation researchers can study chemical reactions in the filters or how water is transported through the filter and how it affects the emission of phosphorus, without having to pay for expensive field experiments.
Today, there is no single method to test the filters for small-scale sewage. This makes it difficult to compare different tests and the effectiveness of new filter materials.
The studies of filters for small drainage are performed by the research group in Sanitary Engineering at Luleå University of Technology and are carried out in collaboration with Ecotech, a company that manufactures mini treatment plants.