Food Waste Disposers, the Sewers and the Circular Economy

Domestic food waste is generated through avoidable and unavoidable waste when preparing food in the household. One option of managing domestic food waste is through the use of food waste disposers (FWDs). FWDs are under-sink grinding units used to dispose of domestic food waste via the sewer network. This thesis assesses potential risk and benefit of FWD usage using an evidence based approach. The characteristics of the ground food particles, from a wide range of foods are measured using a series of laboratory studies. Particle size distributions and maximum settling velocity characteristics were measured with settling velocities generally being higher for larger particles, except when particle density and sphericity changes. Due to their high water content, most food types have a particle specific gravity close to unity. The transport behaviour of the particles from food waste disposers is assessed using a hydrodynamic network model of the field site, calibrated and validated using flow survey data, to model particle transport. This allows for the risk of deposition of every particle size of every food type to be assessed in every pipe in the sewer. The transformation of organic food waste in the sewer network is also estimated. For this purpose, COD values of the characterised foods were measured and a rate of transformation of food within wastewater was measured, a modified BOD test was undertaken using potato wherein the rate of biochemical oxygen consumption was measured over a 24h period with and without potato to quantify the degradation of the food waste in-sewer. Using the data collected, the potential for the use of food waste disposers in the circular economy is also examined using the field site as a case study and also the wider implications of the data discussed.