Wastewater management data for impact assessment in Finland : scalability of national and regional data in the case site of Tana River catchment

Abstract

Governance of wastewater in Finland often places emphasis on connecting to the sewage network rather than treating wastewater on-site. Centralized wastewater treatment focuses the source to a single point, while decentralized is a nonpoint source of pollution. In sparsely populated areas, such as the case site Tana River catchment area, connecting to sewage networks typically is not possible for a major portion of the population, mainly due to long distances. There well-functioning on-site systems are crucial for the sanitation. However, environmental impact estimation is difficult for decentralized sanitation due to the lack of real-life data and monitoring (OWTSs).

The aim of this thesis was to compare the loads from on-site wastewater treatment systems (OWTSs) and wastewater treatment plants (WWTPs) and be able to scale them according to the population and the type and processes of the wastewater treatment systems. The thesis utilized data of wastewater load from previous studies to calculate the load for the case site, the Tana River catchment area, where data were well available. For the case site, a previously collected survey of the current state of wastewater treatment in Utsjoki municipality was used as a base to count and locate different OWTSs in the area. ArcGIS software was used in mapping the different systems and their load.

The calculations show that general estimation with national data can easily over or underestimate the environmental impact of decentralized sanitation. The results also point out that increasing the proportion of centralized sanitation can reduce the total environmental load in terms of organic matter, total phosphorus and total nitrogen. Results emphasize the significance of enhanced monitoring of OWTSs in Finland.