Discharge of bacteria from on-site wastewater treatment units (2015-2016)

In this project the occurrence of bacteria in the outlets of small-scale on-site wastewater treatment units is investigated. The project is funded by the Swedish Agency for Marine and Water Management.

Small on-site wastewater treatment facilities are often located at small receiving water courses and there is a risk for spread of pathogens. Yet, the reduction of pathogens in small wastewater systems has not been comprehensively studied. Sand filters and alkaline filters are likely to have a good potential for pathogen reduction. However, pathogen reduction might decrease over time.

The project aims at investigating the occurrence of bacteria in the outlet of sand filters and alkaline filters considering the filter materials’ age and hydraulic load.

Both sand filters and alkaline filters of different age and hydraulic load are selected for sampling. Three sampling campaigns are carried out during 2015-2016. The samples are analyzed with regard to two indicator bacteria: enterococci and E. coli. Both are included in the EU bathing water directive for assessing bathing water quality. Additionally, pH and total suspended solids are analyzed to assess the facilities’ status and function. The collected data is statistically evaluated to identify difference between the facilities. Further, it is investigated how the facilities’ age and hydraulic load affects the discharge of bacteria.

The project is funded by the Swedish Agency for Marine and Water Management. It is a collaboration between Luleå University of Technology, the County Administrative Board of Västerbotten, Region Västerbotten (a co-operative body which is responsible of regional development in Västerbotten County), Umeå municipality, Vännäs municipality, Robertsfors municipality and Skellefteå municipality.

Annelie Hedström, Inga Herrmann and Kerstin Nordqvist