Discharge of inadequately treated waste water containing nutrients such as phosphorus and nitrogen as well as organic matter and bacteria is associated with a risk of eutrophication and contamination. The Swedish government has decided upon several Environmental Quality Objectives aiming to reduce the emissions of nutrients to water bodies. In Sweden, there are between 675 000 to 1 000 000 on-site sewage systems. Recent studies have shown that the function of small sewage treatment plants is in many cases insufficient. To prevent this regular service and supervision by a professional is needed. The focus of this study are small sewage treatment plants which use a technique where mechanical, chemical and/or biological reduction of pollutants is being used in the same facility to reduce nutrients in household wastewater. The aim of the study is to investigate how different municipalities ensure that small sewage treatment plants fulfill the requirements and reduce pollutants as efficient as the manufacturers claim. To do this, a survey was carried out, leading to a data-set that is covering more than 90 municipalities. The results show that many municipalities lack resources to ensure that small sewage treatment plants work properly. Operation and maintenance of the plants is an important issue, and should be given much more attention. Therefore the municipalities should request more documentation from the owners both before and after installation to make sure that the small sewage treatment plant can fulfill the required standard. About half of the municipalities demand that the owners acquire some kind of service agreement with the manufacturer.  If small sewage treatment plants should be a wastewater treatment solution that we can rely on in the future, there is a need of evaluating and analyzing these facilities more systematically.

Water is crucial for all life on this planet. Despite this much of our aquatic environments have become affected by pollution and nutrient-loading. One large contributor to the problem is privately owned sewers, also called on-site sewage systems. Currently there are approximately 691 000 on-site sewage systems in Sweden, which carry the infamous distinction of representing one of the largest point sources of phosphorus and nitrogen. Furthermore roughly 180 000 of these sewers are by legal definitions unlawful, because of substandard wastewater treatment. The purpose of this study was to investigate how Sweden’s 290 municipalities conduct their supervision towards privately owned sewages and what inventory and administration rates they have. A hypothesis was there should be a correlation between municipalities’ inventory and administration rates. The study was conducted by a web-survey sent out to all municipal environmental and health offices. The results show a majority of the municipalities have an inventory ongoing, or have already conducted one. Administration and inventory rates at which on-site sewage systems are being controlled are rather low, numbering 3.1 respectively 3.6 percentages per year. Surprisingly there was also a low correlation between the inventory and administration rates, with an r-value of only 0.29 (r2 ≈ 0.085). Overall, the results indicate a need to increase oversight of inadequate and non-regulatory on-site sewage systems if we are to meet our national environmental goals and our global sustainable development goals.