Small-scale reactors (<10 l) have been employed in composting research, but few attempts have assessed
the performance of composting considering the transformations of organic matter. Moreover, composting
at small scales is often performed by imposing a fixed temperature, thus creating artificial conditions, and
the reproducibility of composting has rarely been reported. The objectives of this study are to design an
innovative small-scale composting device safeguarding self-heating to drive the composting process and
to assess the performance and reproducibility of composting in small-scale pilots. The experimental
setup included six 4-l reactors used for composting a mixture of sewage sludge and green wastes. The
performance of the process was assessed by monitoring the temperature, O2 consumption and CO2 emissions,
and characterising the biochemical evolution of organic matter. A good reproducibility was found
for the six replicates with coefficients of variation for all parameters generally lower than 19%. An intense
self-heating ensured the existence of a spontaneous thermophilic phase in all reactors. The average loss
of total organic matter (TOM) was 46% of the initial content. Compared to the initial mixture, the hot
water soluble fraction decreased by 62%, the hemicellulose-like fraction by 68%, the cellulose-like fraction
by 50% and the lignin-like fractions by 12% in the final compost. The TOM losses, compost stabilisation
and evolution of the biochemical fractions were similar to observed in large reactors or on-site experiments,
excluding the lignin degradation, which was less important than in full-scale systems. The reproducibility
of the process and the quality of the final compost make it possible to propose the use of this
experimental device for research requiring a mass reduction of the initial composted waste mixtures.
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