Systems analysis of small-scale systems for food supply and organic waste management

In this thesis, systems for recycling of household organic waste (easily degradable food waste and sewage water) and small-scale systems for food supply were evaluated to see if they could be environment and energy-conserving options. They were evaluated using simulation of static substance-flow models (SFA) combined with life cycle assessment methodology (LCA) for aggregation and interpretation of the results. Three systems were modelled and simulated: i) organic waste management (including transport, spreading on arable land and cropping of grain), ii) bread processing and distribution and finally iii) liquid milk processing and distribution. The results were found to be very dependent on factors such as choice of system boundaries, transport distances and type of technology. Thus, it was not possible to draw general conclusions regarding the organic waste management system and the scale of food supply system which were most beneficial. However, for the organic waste management system, it was concluded that toilet water-separating sewage systems are a means to increase the rate of nutrient recycling. Furthermore, it was found that urine-separating toilet systems increase nitrogen-recycling rate and decrease energy consumption. The results indicated that anaerobic digestion of organic wastes from society and animal manure could be a system for farmers (or communities) to become more energy self-supporting. With regard to the food supply system (the transport and processing chain of foodstuffs), it was concluded that energy optimised small-scale food processing and distribution systems could have lower environmental impacts and energy consumption than large-scale systems. However, this requires that the advantages of small-scale be utilised in the entire system, i.e. they should be combined with a nearby local market in order to minimise all transport. The results obtained indicate that the processing step and the private-car transport of food from shop to consumer's home are the most essential parts of the food supply system with respect to environmental impacts and energy consumption.