Pile Composting of Two-phase Centrifuged Olive Husks: Bioindicators of the Process
Composting is a process largely used to solve the organic material disposal problem, but composting of the olive husks produced by two-phase technology remains largely unknown. Because of their high content of salts, polyphenols, fatty acids and tannins,
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Introduction The present work was developed within the EC project FAIRS-CT97 3620 named Husks, whose aim is to solve in an energetically, economically and environmentally acceptable way the problem of the olive husk disposal. The Mediterranean EC countries contribute 96% of world production of olive oil (about 1.7 millions of tons year-I). Olive oil can be produced by different extraction systems, the traditional discontinuous pressing process and the continuous centrifugation process being the most usual. In the continuous process a decanter is used, adding a high volume of water to the crushed olive and obtaining three phases: olive oil, olive oil wastewater and pulp with about 47% moisture. Recently, a new kind of centrifuge decanter was introduced; this new two-phase process produces olive oil and a husk mixed with olive oil mill wastewater. The new two-phase centrifugation technology solves the problem of olive milling wastewaters by dramatically reducing their production, but in the meantime shifts the problem to husks, which have more water content and higher phenols concentration.
ImSTAAM, University of Molise, 86100 Campobasso, Italy 2mSTAM, University of Milan, 20133 Milan, Italy 3DPVTA, University of Udine, 33100 Udine, Italy
H. Insam, N. Riddech, S. Klammer {Eds.} Microbiology of Compo sting © Springer-Verlag Berlin Heidelberg 2002
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Ranallietal.
Composting is a process largely used to solve the organic materials disposal problem, but very little is known about compo sting of the husks produced by twophase technology. Because of their content of fatty acids, phenols and tannins (highly phytotoxic compounds), husk utilisation as fertiliser is not possible. Composting of the husks could permit the degradation of toxic compounds. Recent literature reports that the compost obtained by husks shows good characteristics in relation to both phytotoxicity and germination tests, and to agronomic evaluation (Sciancalepore et al. 1996; Epstein 1997). It is in any case necessary to extend the knowledge about the conditions of starting up, running of the plants, the degradation of toxic compounds and the fertiliser and hygienic characteristics of the mature compost. The main purposes of this investigation were to compare simplified composting technologies and to utilise bioindicators other than microbial counts, for process monitoring. In particular, ATP content and several enzyme activities were tested as bioindicators of the process in a two-pile composting process on a pilot scale for olive husk treatment. The addition of separate solids or animal manure as inoculum to start up the process could introduce pathogen microorganisms to the raw material (Hussong et al. 1985). The safety of the cured compost (absence of Salmonella spp.) required by European regulations was evaluated by traditional culturable and biomolecular non-culturable techniques.
Materials and Methods Plants The experiments were carried out utilising two static piles (Fig. 1). The piles were set up in a greenhouse to be protected from atmo
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