Composting of different agro-food wastes: Effects of the phenolic and lignocellulosic fractions on greenhouse gases emissions

Currently, society faces a number of challenges related to the large amounts of organic wastes generated and accumulated by the increasing expansion of agroindustrial activities1. Most of these wastes are rich in lignocellulosic compounds, which represents a major fraction of all plant biomass (of above 90%), so, its degradation is crucial for global carbon cycle2. These organic wastes may be introduced directly on agriculture sector as soil organic amendment, however, these might contain phytochemicals, such as phenolic compounds which may introduce toxic effects to soil and to beneficial organisms. Transformation and degradation of these renewable organic wastes into composts (COMPOSTING) is a possible solution for these problems and an environmentally friendly processes that allows make use of natural resources efficiently3. The main potential handicap is generation and emission of greenhouse gases such as carbon dioxide (CO2 ), methane (CH4 ) and nitrous oxide (N2O) and another ones which may led serious problems like nitric oxide (NO) and ammonia (NH3) 4. For this reason, quantification of GHG emissions from composting and finding possible relations with the chemical and structural composition of the wastes used is crucial to the development of technologies for mitigating emissions and should help to make decisions concerning waste management.

Characterization of MSW rejected fractions to fulfill RDF requirements and utilization

In order to fulfil European and Portuguese legal requirements, adequate alternatives to traditional municipal waste landfilling must be found namely concerning organic wastes and others susceptible of valorisation. According to the Portuguese Standard NP 4486:2008, refuse derived fuels (RDF) classification is based on three main parameters: lower heating value (considered as an economic parameter), chlorine content (considered as a technical parameter) and mercury content (considered as an environmental parameter). The purpose of this study was to characterize the rejected streams resulting from the mechanical treatment of unsorted municipal solid waste, from the plastic municipal selective collection and from the composting process, in order to evaluate their potential as RDF. To accomplish this purpose six sampling campaigns were performed. Chemical characterization comprised the proximate analysis – moisture content, volatile matter, ashes and fixed carbon, as well as trace elements. Physical characterization was also done. To evaluate their potential as RDF, the following parameters established in the Portuguese standard were also evaluated: heating value and chlorine content. As expected, results show that the refused stream from mechanical treatment is rather different from the selective collection rejected stream and from the rejected from the compost screening in terms of moisture, energetic matter and ashes, as well as heating value and chlorine. Preliminary data allows us to conclude that studied materials have a very interesting potential to be used as RDF. In fact, the rejected from selective collection and the one from composting have a heating value not very different from coal. Therefore, an important key factor may be the blending of these materials with others of higher heating values, after pre-processing, in order to get fuel pellets with good consistency, storage and handling characteristics and, therefore, combustion behavior.