Larger on-Site Sewage Treatment Plants in Sweden : - A literature and an interview study to find appropriate solutions

Abstract: There are no general recommendations of how a larger on-site sewage treatment plant should be designed; most research studies have been conducted on smaller ones. The purpose of this thesis is to investigate what type of design that is appropriate for an on-site sewage treatment plant built to manage the hydraulic load from between 50 and 200 human equivalents. Phosphorus is the main parameter of interest for this thesis, but nitrogen, biological oxygen demand (BOD ) and chemical oxygen demand (COD) is also included. To find appropriate solutions of this, both a literature study and a qualitative interview study have been done. The combined knowledge from this has then been used to describe what solutions are appropriate according to both environmental and economic aspects. The interview study included four participants with different designs of a larger on-site sewage treatment plant. For the analysis on the data from the interviews, content analysis was used, five main categories was found: Design of the on-site sewage treatment plant, Maintenance work to make the on-site sewage treatment plant well-functioning, Supervision and regulation, Environmental awareness and Economy. Infiltration, filter bed, phosphorus filter, precipitation of phosphorus, small sewage treatment plant and constructed wetlands, are the designs of an on-site sewage treatment plant that has been described in this thesis. Of these designs, infiltration or filter beds are appropriate solutions. These can be combined with a phosphorus filter, if higher phosphorus reductions are required. Also, a small sewage treatment plant could be an appropriate solution of a larger on-site sewage treatment plant, this solution requires more maintains work and has higher costs.