| Summary: | The purpose of this project is to investigate the effect on the sewer network system if food waste disposers (MAK) are connected directly to the sewer system. Through tests, contacts with other municipalities and a literature study, the project investigated the importance of relevant aspects, see Table 1. Municipalities' attitude to MAK is, however, not only dependent on possible effects on the sewer system but also on the subsequent treatment and handling of the sludge from the sewage treatment plant. Digestion and biogas production do not take place at all sewage treatment plants, for example not in Kiruna. The possibilities for using the digestate from sewage treatment plants and digestion plants also differ. According to experience from municipalities with a large number of installed MAKs directly connected to the sewer system in households, these do not give any major negative effect if the function is satisfactory from the beginning. In this report, the use of the sewer network system for distribution / transport of food waste was in focus, not subsequent treatment steps, compatibility with environmental goals, etc. In the test carried out in Kiruna, two different disposers were tested in two food businesses. At the Lokeldaren preschool, the disposer was installed directly in a sink. In Jägarköket, the drain from the food waste disposer was passed through the grease separator. It was gradually concluded that the grease separator does not work optimally with the increased load that a MAK entails. Thus, in future installations in restaurant operations, MAK should either 1) be led past the grease separator where such is installed, 2) the grease separator be emptied more frequently or 3) a sludge tank or a separate tank be installed. In the new Kiruna, distance, slope and slumps are no problem as a new pipe network is built for the central sewage treatment plant. In older parts of the Kiruna urban area connected to the central sewage treatment plant, however, an investigation area by area is proposed according to proposals in the literature before introduction of MAK. From the sewer system perspective, there is no reason to limit the introduction of MAK to only food operations. A possible release should thus also include households and, for example, workplaces where food waste is generated.
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