The Associate Professor Arve Heistad, from the Norwegian University of Life Sciences, was the discussion leader at the seminar. The Licentiate’s work dealt with the investigation of existing small on-site systems in terms of phosphorus and bacterial removal, and included a theoretical comparison between different solutions based on sustainability indicators.
Small on-site sanitation systems for wastewater collection and treatment are prevalent in suburban and rural areas in many countries. However, these systems often underperform, causing potential impact to the receiving waters and increasing the risks to public health, thus hindering the overall sustainability of the systems. Understanding the different sustainability dimensions and trade-offs between assessment indicators can support the planning of sustainable on-site sanitation systems for a specific context. In this thesis, the sustainability and function of on-site sanitation systems was assessed by defining a set of indicators and by investigating the treatment efficiency of on-site facilities for domestic wastewater treatment in a field study. Particular attention was given to the removal of phosphorus and indicator bacteria due to their relevance in terms of eutrophication risk and public-health concern.
Multi-criteria analysis methodology, including LCA, literature review and mass balances, was used to compare sanitation alternatives such as soil-based systems, source-separation and package plants. Moreover, manual flow-proportional sampling of wastewater was performed in the field and further analyzed for organic matter content, phosphorus, indicator bacteria, suspended solids and pH.
The multi-criteria analysis showed that the greywater–blackwater separation system was the most sustainable option in the baseline scenario and in the scenario when nutrient-related indicators were important, together with the urine diversion system. The sand filter and drain field were ranked the highest when nutrient removal and recycling was not important (Scenario 1), and (in combination with chemical P-removal) when the indicators related to energy and climate change had the highest weights (Scenario 3). The field study showed that the investigated sand filters generally had low P-removal capacity and sometimes exceeded the criteria for excellent water quality set by the EU bathing water directive with regard to intestinal enterococci and E. coli. In contrast, alkaline P-filters generally removed P efficiently but the collected data did not generally confirm a further reduction of the bacterial content of the wastewater in the P-filters.
Overall, the robustness of the systems plays an important role when assessing their sustainability and treatment efficiency. Sufficient removal of nutrients and pathogens must be ensured by an appropriate construction, operation and maintenance.