Markbaserad rening – en studie av funktion i fält / Soil-based wastewater treatment – a field study
Soil-based wastewater treatment, i.e. septic tanks followed by an infiltration or a sandfilter bed is the most common solution for small scale wastewater treatment in Sweden. In this project four students have surveyed 217 households in a field study. Grab samples have been taken on both suspended solids from the septic tank and on the effluent from sandfilter beds. Visual inspection camera was used to determine the status in the infiltration pipe. The analysis of the biological performance shows that soil-based systems are robust and fulfill the limit for reduction of organic matter set by the Swedish authorities. One out of 10 systems in the study did not perform according to expected levels due to mistakes during design and construction. It is not possible to disqualify a system based on the status in the ventilation pipe. Instead the entire infiltration pipe should be inspected by camera in order to gather enough information. It cannot be concluded that suspended solids are passing through the septic tanks on such levels that the process in the following steps are disturbed. The technique with using a visual inspection camera yields plenty of useful information.