Wastewater flows in on-site wastewater treatment (2020-2021)

In this project we evaluate the wastewater flows to on-site wastewater treatment facilities. The results will help the Swedish Agency for Marine and Water Management to update the flow values given in current legislation. The study is funded by the Swedish Agency for Marine and Water Management.

The water consumption in households with on-site wastewater treatment (<200 PE) is today estimated to be 170 liters per person and day. This flow is used to calculate pollutant concentrations (BOD, tot-P, tot-N) in the wastewater that is treated in the facilities. Using the (estimated) influent concentration acceptable effluent concentrations for P, N and BOD are calculated using the current pollutant reduction requirements. In several studies it has been shown that the influent concentrations are in fact higher than the estimated ones which leads to that the treatment units’ treatment efficiency is underestimated. To be able to better assess the function of on-site wastewater units the flow value assumed in the regulation (170 liters per person and day) needs to be updated. This study supports this work by evaluating flows observed in a number of package plants.