Abiotic Parameters and microbial Counts as stability indicators during composting of organic waste

The implementation of the EU Directives concerning the Integrated Pollution Prevention and Control (2008/1/EC) andthe water policy (2000/80/EC) have oriented the waste management operations at minimization via recycling andrecovery strategies. In the case of the industrial and agricultural waste, composting is often placed within the mostfeasible options. The performance of the composting process and the some important quality aspects of the end-product(the compost), mainly assessed by stability, are governed by both the composition - biological and elemental- of thewastes and the management strategies.

In order to postulate the optimization of the quality of the compost, thecombined application of independent methodologies for the determination of microbial activity is needed: theapplication of well-integrated perspectives and methodologies might hold a key to identify stability indices forcomposting.This study reports on assessing compost stability during composting of a variety of organic waste: poultry manure;source separated biowaste; mixtures of sludge and garden clippings sprayed with certain pesticides; mixture with sludgederived from beverage production, paper pulp, mushroom substrate, horse manure; mixture with beverage sludge,mushroom substrate, horse and chicken manure. The different substrates were composted using windrow pilot or fullscale systems and monitored, from raw material to mature compost (for approximately 3-5 months). The compostingprocess was monitored through the microflora population evolution and the microbial activity, assessed through thedetermination of the respiration activity (using the Specific Oxygen Uptake Rate - SOUR test - Lasaridi & Stentiford,1998a,b) and the stable isotope fractionation. To better interpret the results, a number of abiotic parameters(temperature, pH, electrical conductivity, moisture and volatile solids content) were also recorded throughout eachcomposting process. The succession of the microbial community was studied as assessed by microbial counts. Standardprocedures for compost sampling and selective substrates were used for the cultivation and enumeration of the differentgroups of microorganisms (total bacteria, amylolytic, cellulolytic and proteolytic bacteria, enterobacteria, fungi andyeasts, nitrifying bacteria, bacteria with resistance to antibiotics, total coliforms and Ε. coli).In all runs, the compost temperature reached thermophilic levels (above 55 oC) within the first few days of processingregardless of the inherent differences of the raw materials. The physical and chemical parameters examined varieddepending on the composting material. The respiration rate, as determined via the SOUR test, for all substratesincreased at the beginning of the active composting phase, as complex compounds were broken down to simpler, moreeasily degradable ones. Thereafter, the respiration rate gradually declined as to reach values below 2.0 mgO2·g-1VS·hr-1.Moreover, results indicated that there was a correlation between composting time and some physical and chemicalparameters, such as intensity of water evaporation and volatile solids reduction. The temporal evolution of the microbialcommunity structure seems to depict well, albeit in a qualitative manner, the changes in the composting matrix duringthe process. Results of the microbial community dynamics analysis suggested that for all materials examined themicroflora characterising the process was spontaneously developed, with no signs of inhibition, as their metabolicactivity drives the process and overrides substrate differences. The observed pattern for δ13C did not show anystatistically significant variation during the composting process, as opposed to findings reported elsewhere. Overall, theSOUR test and the δ15N signature seemed to offer a good indication of the progress of the organic matter Stabilisation process during composting.



Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 7
Preis inkl. MwSt.: € 7,00
Autor: Christina Chroni
A. Kyriacou
Dr. Katia Lasaridi

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