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Multivariate analysis of the physicochemical, chemical and biological parameters of winery and distillery composts could point the way to improving the use of these generally intractable waste materials. Marian Bustamante, Concha Paredes, and Raul Moral of the Department of Agrochemistry and Environment at the Miguel Hernandez University, in Alicante, Spain and Javier Morales, Asuncion Mayoral of the Applied Statistical Unit, point out a growing problem faced by the liquer trade. Wineries and distilleries generate enormous amounts of solid and liquid wastes, everything from grape stalk, grape marc, wine lees, exhausted grape marc and vinasse to the byproducts of maturation and distillation. Bustamente points out that these materials have such different characteristics that it is difficult to find a way to manage and dispose of them. Low pH and high phytotoxic content makes it difficult to compost them. Similarly, the presence of antibacterial phenolic substances also resist biological degradation. These problems make the use of these waste products as naturally derived fertilisers untenable because of the detrimental effects such acidic and toxic materials would have on soil. Moreover, the nitrogen content is essentially immobilised within the materials because of their subsequent resistance to break down even in the soil. If the waste products were composted prior to application to the soil, however, that could eradicate toxicity problems and free nutrients from the material. "Composting is defined as a biological treatment in which aerobic thermophilic and mesophilic indigenous microorganisms use organic matter as a substrate, obtaining as a result a stabilised, deodorized, hygienic material, free of pathogens and plant seeds and rich in humic substances," the researchers explain. However, understanding stability and maturity of such waste once it has been composted presents its own problems. For instance, several analytical techniques would be needed to obtain a profile of such a complex material. Now, Bustamente and colleagues have taken a cheminformatics approach to wine waste. They have studied the various physico-chemical, chemical and biological parameters of the composting process for four winery and distillery composts. Using multivariate techniques: factorial analysis (FA) and linear discriminant analysis (LDA), they have classified these parameters in order to establish which best describes the composting process. Their study reveals just four factors that account for almost 90% of the variability in the compost, which means that determining maturity and stability can be greatly simplified. Without this simplification dozens of other factors would have to be determined and incorporated into the assessment. The parameters associated with compost maturity are agronomic character, water-soluble fraction, increase in ammonia and rise in temperature. Further linear discriminant analysis of these factors then allowed the researchers to classify the four different composts to an accuracy of 95%. The researchers explain that their approach is quite generic. Studying different properties at the beginning and end of the composting process can reveal whether or not a particular waste stream is viable for fertilising soil perhaps in conjunction with sewage sludge, cattle manure and poultry manure.
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