Comparison of carbon footprints and eutrophication impacts of rural on-site wastewater treatment plants in Finland

In many sparsely populated areas, such as the Finnish countryside, most houses are not connected to centralized sewers due to excessive distances. On-site wastewater treatment plants are therefore necessary to reduce local emissions to meet the legislatory limits. Dozens of on-site wastewater treatment applications are marketed to households, with varying operating costs and pollution reduction potentials. The installation and use of these systems will cause environmental impacts outside the site, through their supply chains. The aim of this study is to analyze the potential tradeoff between the reduction of local emissions and the increase in life cycle impacts. Six alternatives were chosen for comparison, including the energy-demanding small sewage treatment plants and the various types of soil systems (including source separation systems). The results show that the dry toilet in combination with gray-water treatment had the least impact and the package plants the greatest. However, which is the optimal on-site system solution for a certain property is strongly dependent on the local conditions and, therefore, appropriate guidance is definitely needed.