Food Waste Disposers (FWD) - Long term impact on sewerage (2010-2011)
One alternative to reduce the amount of solid residues originating from household food preparation is to install food waste disposers (FWD) under the kitchen sink. These will then grind leftovers which are in turn transported with the existing sewerage to the local wastewater treatment plant. The environmental service could here be twofold: (i) the demand for vehicle transportation of solid waste will be reduced and (ii) an increased biogas production due to the increased load of organic material reaching the anaerobic digester at the wastewater treatment plant.
FWD has been widely used in the US since the first half of the 20th century but has never reached the same market penetration rate in Sweden and other European countries. This could partly be explained by the negative effect the system is theorized to have on the condition of existing sewerage. Views that the application of FWD will lead to elevated levels of clogging, hydrogen sulphide production and flooding are fairly common among engineers in Swedish municipalities. Surahammar and Smedjebacken, situated to the west of Stockholm, are among the vast minority that have made directed efforts to introduce the system on a large scale, with a number of installed FWD of about 2000 and 650 respectively. The performance of these systems has been examined, but the focus have been on impact on the wastewater treatment plant, only short term impacts have been examined in the literature on sewerage. Hence there is a need for a systematic study which aims to adequately respond the question what the impact is of a long term usage of FWD.
As Surahammar and Smedjebacken are among the municipalities with the highest number of FWD connected to the sewerage in Sweden (about 50 and 25 % respectively of the households), the study will explore long term effects of this extensive use on the existing sewerage. When impacts have been discovered, statistical methods will be applied to verify if this can be derived to specific underlying factors such as the material, dimension, inclination and age of the pipe. Short term impacts will also be further elucidated in Gällivare municipality which recently introduced the system. Furthermore it will also be within the scope of this project to measure the levels of hydrogen sulphide and water consumption to examine if a large scale introduction of FWD signifies elevated levels of respective category. Finally, attempts will also be undertaken to classify composition and origin of deposition of fat and other depositions within the sewerage.
A large number of municipalities are considering an introduction of the FWD-system and it would be of great significance to these to have the issues raised in this project adequately answered. Another LTU project, New GIRON, will examine how to design a new integrated water and wastewater system for the city of Kiruna. Here the FWD device could be considered as an integral part. It is thus important that the outcome of this project can facilitate in answering the question if FWD is possible as a solution given the local conditions of the Kiruna area.