Små avlopp – provtagning i fält
A model for establishing effluent limitations for small scale wastewater treatment is presented in this article. The effluent limitations are based on the publication HVMFS 2016:17 from the Swedish Agency for Marine and Water Management. The proposed limitations have been adjusted based on waste content, water consumption and uncertainty of measurement. In addition, an analysis of field sampling of Swedish small scale wastewater treatment units have been made. Based on the results for various techniques models for how to calculate upper one-sided confidence intervals are presented. These confidence intervals can then be used for comparison with the effluent limitations. Variations in water consumption have a large impact on the effluent. It could at least differ a factor of 5 for different households. Hence there is an obvious risk that households with low water consumption are investigated though they meet expected reductions. On the other end households with a high consumption are let go even though the process is malfunctioning. Techniques for so called high protection level, i.e. higher demand on reduction of nitrogen and phosphorus, are showing a large spread of data and hence continuous sampling in combination with a water meter should be applied.