Prediction of household wastewater treatment systems' in situ performance based on standardized tests

This paper presents a comparative analysis on operating conditions of onsite wastewater treatment systems. Actual EU Member States' national regulations require in situ treatment thresholds expressed in effluent concentrations. CE marking of onsite wastewater treatment system is mandatory according to standardized test (EN 12566-3 + A2) with performance declared in removal efficiency. Recent study indicates that in situ raw sewage concentrations are 1.5 times higher than those on test platforms. In this context, performance comparison between platform tests and in situ discharge threshold cannot be based on effluent concentrations but rather on removal efficiency to fulfill environmental and health requirements. This study compares: (i) results from eight standardized tests, (ii) over 300 measurements of in situ raw sewage, and (iii) several national-level thresholds focusing on carbon parameters. To meet French effluent thresholds, a minimum removal efficiency of 96% in SS and 95% in BOD5 is required. A beta law model assesses the efficiency measured during standardized testing and establishes a robustness characteristic with a probability above 80%. When a septic tank is used, its efficiency can be incorporated into the prediction. Although the new performance criteria are more stringent, some of the eight products evaluated still meet the requirements.