Respiration and microbial community succession as compost stability indicators

Since the new Paradigm in biodegradable waste management promotes resource recovery, composting still remains one of the main options. However, the assessment of compost stability, both as a product quality indicator and a process evolution index, is still a problem resisting intensive research efforts. Although a large variety of stability indexes has been proposed in the literature and some have been adopted in national regulations, the question of identifying parameters effectively reflecting the stabilisation process of organic matter during composting still remains.

In the present work we aimed at gaining a more complete picture of the microflora evolution and the microbial activity, as assessed through the respiration rate, during composting of a variety of organic waste in order to evaluate their potential to serve as stability indicators. As an attempt to identify suitable microbial indicators of compost maturity, the process performance of windrow composting of source seperated biowaste, green waste and poultry manure was studied with regard to abiotic factors, respiration activity and the functional microflora. The composting process went through typical changes in temperature, moisture content and microbial properties, despite differences in the initial substrate used. Respiration activity reflected well the process stage ,while some microbial groups have also shown a potential to serve as stability indicators. Green waste, source separated biowaste and poultry manure have been composted in turned pilot systems and monitored, from raw material to mature compost (approximately 3-5 months), with regard to abiotic factors, microbial activity and succession of functional and taxonomic groups. The succession of the microbial community was studied using traditional techniques. Temperature of the composting material, moisture and volatile solids content, C:N ratio, pH, and O2 consumption of water extracts (SOUR test, expressed as mg O2/g VS/hr) were measured during the composting process. A standard procedure for sampling of the compost and selective substrates was used for the enumeration of the different groups of microorganisms (total bacteria, amylolytic, cellulolytic and proteolytic bacteria, enterobacteria, fungi and yeasts). Mesophilic and thermophilic microorganisms were incubated at 30°C and 55°C respectively. The compost temperature reached thermophilic levels (above 55oC) within the first few days of processing for all materials. The physical and chemical parameters examined varied in accordance with the composting material and system used. Results indicate that there is a correlation between composting time and some physicochemical parameters, such as intensity of water evaporation and volatile solids reduction. The temporal evolution of the microbial community structure seems to depict well, albeit in a qualitative manner, the changes in the composting matrix during the process, with nitrobacter and pathogen indicators varying as a monotonous function of processing time. The potential of specific microbial groups to serve as fingerprints of the different process stages requires further investigation. The SOUR value correlated well with composting time and demonstrated a potential for quantitative estimate of the stabilisation process.



Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2008 (Oktober 2008)
Seiten: 10
Preis inkl. MwSt.: € 10,00
Autor: Christina Chroni
A. Kyriacou
T. Manios
Dr. Katia Lasaridi

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