On 4 February 2015 Caterina Maulini defended his doctoral thesis entitled «Study of gaseous emissions in biological processes intended for solid waste material recovery. Volatile organic compounds emissions characterization. The thesis supervisors were Dra. Adriana Artola and Dr. Xavier Font.
The Thesis Committee was chaired by Dr. Arturo Chica from Universidad de Córdoba, Dra. Estel·la Pagans from the company Odournet and Dr. David Gabriel from Universitat Autònoma de Barcelona.
World economic growth during the second half of the XX century has caused a great increase in waste generation. This fact has been reflected in European policies which define the objective of recycling, at least, 50% of municipal waste before 2020. In the case of biodegradable organic wastes, this purpose can be achieved mainly through biological treatments such as composting and anaerobic digestion. In order to achieve the proposed target, the current European scenario in terms of organic waste valorisation facilities and the emergence of these new policies, suggest a future proliferation of biological treatment facilities, among which there will be a lot of composting plants.
Given this upcoming proliferation of composting facilities (and waste treatment plants in general), the environmental impacts associated with the composting process must be taken into account, paying special attention to gaseous emissions resulting from biological degradation of organic matter. The main contaminants in these emissions are methane, ammonia, nitrous oxide and volatile organic compounds (VOC). Methane and nitrous oxide are considered greenhouse gases, while ammonia and VOC are the main cause of odours associated with these treatment facilities.
The Composting Research Group (GICOM), where this thesis has been developed, has a wide research experience in composting, either studying the biological process itself, process control or process gaseous emissions at full scale. Besides, in recent years GICOM has started a new research line exploring the potentiality of solid state fermentation (SSF) as another way to valorise organic wastes, commonly from industrial processes, with the aim of obtaining value_added products (enzymes, biopesticides, biosurfactants, etc.). In this thesis the research experience of the group has been used to analyse in depth the gaseous emissions from biological valorisation processes of solid organic wastes, determining emission factors for VOC, CH4, N2O, NH3 and characterizing, by identification and quantification, VOC emissions during the treatment of different wastes at pilot scale.
To achieve this overall objective, a methodology to identify and quantify VOC by gas chromatography coupled to mass spectrometry has been set_up. Also, VOC emissions during a conventional composting process under different aeration strategies have been studied. Thus, two methodological issues essential for the development of this thesis have been defined on one hand, the process strategy and on the other hand, the gaseous emission sampling methodology and analysis. From this methodological basis, gaseous emissions from the composting process of urban wastes, such as WWTP sludge, either raw or digested, and also de Organic Fraction of Municipal Solid Wastes (OFMSW) have been analysed, quantitatively and qualitatively. The OFMSW composting process and its emissions have been compared to non_source selected Municipal Solid Wastes (MSW). Also, the contribution of wood chips (used as bulking agent) to the composting process emissions has been determined. Finally, the emissions associated to the material valorisation of specific wastes such as orange peel, hair wastes and residue of winterization in order to produce various enzymes through SSF, have also been studied.
In addition to the scientific interest of this thesis, which is reflected by the papers published in high impact journals in the field of Environmental Engineering, it increases the research group know-how on the treatment of different wastes at pilot scale. The definition of a methodology for gaseous emissions determination that can be implemented in future experiments performed in the GICOM pilot plant is also relevant. This methodology will allow the quantification of CH4, N2O and NH3, the qualitatively determination of VOC emissions and the quantification of the most commonly found compounds. This last point will permit to include data on the emissions of the material valorisation processes carried out in the research group pilot plant, reporting valuable information on the environmental impact of the process also useful in the design of the required emissions equipment.
The following papers have been published from this Thesis:
- VOC emissions from the composting of the organic fraction of municipal solid waste using standard and advanced aeration strategies. Maulini-Duran, C., Puyuelo, B., Artola, A., Font, X., Sánchez, A., Gea, T. Journal of Chemical Technology & Biotechnology.
- A systematic study of the gaseous emissions from biosolids composting: raw sludge versus anaerobically digested sludge. Maulini-Duran, Artola, A., Font, X., Sánchez, A. Bioresource Technology. 147, 43-51 (2013).
- Gaseous emissions in municipal wastes composting: effect of the bulking agent. Maulini-Duran, C., Font, X., Artola, A. Sánchez, A. Bioresource Technology. 172, 260-268 (2014).
- Gaseous emissions during the solid state fermentation of different wastes for enzyme production at pilot scale. Maulini-Duran, C., Abraham, J., Rodríguez-Pérez, S., Cerda, A., Jiménez-Peñalver, P., Gea, T., Barrena, R., Artola, A., Font, X., Sánchez, A. Bioresource Technology, 179, 211-218 (2015).