Dr Roberto Quirós. Supervisors: Dr. Xavier Gabarrell and Dra. Gara Villalba. 2014

The present thesis entitled “Environmental assessment of technologies to treat municipal solid waste and the organic matter cycle to produce compost and its application in horticultural crop” has been carried out at the Institute of Environmental Science and Technology (ICTA) at the Universitat Autònoma de Barcelona (UAB) under the supervision of Dr. Xavier Gabarrell and Gara Villalba, from the ICTA and the Department of Chemical Engineering at the UAB. Furthermore, the thesis was developed with the collaboration of Grupo de Investigación en Compostage (GICOM) at the UAB and the Environmental Horticulture Unit at the Institute of Agriculture and Food Research and Technology (IRTA). Bellaterra, September 2014. The increased generation of municipal solid waste (MSW) due to population growth and new patterns of consumption is an important issue for European Union (EU) and countries around the world. Policies for managing MSW in a sustainable manner have been key components of EU directives (Directives 1999/31/EC and 2008/98/EC). This doctoral thesis aims to study technologies for the treatment of MSW and assess the environmental impacts of using organic waste to fertilize crop in order to optimize resources and reduce waste. The studies are based on life cycle analysis using CML and ReCipe methodologies. Chapter 2 is dedicated to the assessment of autoclaving, a technology normally used for the sterilization of pharmaceutical waste. This technology offers the possibility of recovering the valuable portion of mixed MSW such as the organic fiber (OF). The processes of autoclaving, sorting and biological treatment were compared to two known technologies: incineration and landfill. The results showed that the systems which considered the anaerobic digestion had the lowest impacts in eutrophication potential and global warming potential. Meanwhile, incineration had the best results for the remainder five impact categories studied. On the other hand, landfill had the highest impact in all studied categories. Chapter 3, the second case study was carried out to compare the environmental and agronomical results of two composts (industrial and home) with mineral fertilizers. Fertilizers were applied to horticultural cauliflower crops. The results showed a better yield (fruit · ha-1) for the crops fertilized with mineral fertilizers but the best environmental performance was for the crops fertilized with home compost. Chapter 4, the third case study, two home composts were produced by two different methods (i.e. production management), resulting in significant differences in terms of emissions. Emissions of methane, nitrous oxides and ammonia were experimentally measured for both composts. The results showed that nitrous oxides and methane emissions contributed considerably the category of global warming potential. While ammonia emissions contributed to the categories of acidification potential, eutrophication and photochemical oxidation. It was observed that these gaseous emissions depend on the management practices employed when producing the compost such as: quality and type of waste stream, frequency mixing of the composting material, rigorous control of some physico-chemical characteristics (humidity, pH, temperature, etc.), among others. Chapter 6, the fourth case study was carried out to compare the environmental performance of organic and mineral fertilizer in a crop sequence of cauliflower and tomato. Furthermore, two procedures for allocating life cycle impacts to crops were also studied. The first one was based on time allocation and the other one in the mineralization N degree in soil. In general, the results showed a better environmental performance for cauliflower crop than tomato in all impact categories considered. Meanwhile, in both crops, the fertilization treatment with home compost showed the lowest impacts than industrial compost and mineral fertilizers in the most impact categories studied. Additionally, the total impacts for the crop sequence (sum of impacts of cauliflower and tomato) were lower than single (i.e. cauliflower and tomato) impacts for the three fertilization treatments. Finally, the dissertation also includes guidelines for organic waste management (Chapter 5). These guidelines focused on domestic compost production and its application in horticulture. The guidelines show the V2V “vegetables to vegetables” model, a closed loop model starting from food waste (e.g. vegetables and fruits) compost until it is again transformed in organic fertilizer to be applied to crops. The guidelines are targeted towards farmers and anyone interested in domestic compost production.