The stability of digestate organic matter is a key parameter for its use in agriculture. Here, the organic matter stability was compared between 14 post-treated digestates and the relationship between organic matter complexity and biodegradability was highlighted. Respirometric activity and CH yields in batch tests showed a positive linear correlation between both types of biodegradability (R=0.8). The accessibility and complexity of organic matter were assessed using chemical extractions combined with fluorescence spectroscopy, and biodegradability was mostly anti-correlated with complexity of organic matter. Post-treatments presented a significant effect on the biodegradability and complexity of organic matter. Biodegradability was low for composted digestates which comprised slowly accessible complex molecules. Inversely, solid fractions obtained after phase separation contained a substantial part of remaining biodegradable organic matter with a significant easily accessible fraction comprising simpler molecules. Understanding the effect of post-treatment on the biodegradability of digestates should help to optimize their valorization.
International audienceThe objective of this study was to correlate the chem. compn. and the odor concn. of emissions produced during storage and composting of pig slaughterhouse sludge (PSS). Seven exptl. conditions were monitored using composting reactors with forced aeration and cells designed to simulate storage. Sixty-six gas samples were collected and characterized by both GC-MS and olfactometry. Two types of correlation were investigated between the chem. compn. and the odor concn. (OC) of every gas sample. The odor activity value for a given emitted compd. (OAV) was computed as the ratio of its chem. concn. to its odor detection threshold (ODT). The correlation OAVMAX considered that the OC of a gas sample was equal to its highest OAV whereas the correlation OAVSUM considered that the odor of the gas sample was equal to the sum of the OAV of every compd. contained in the gas sample. As per Std. EN 13725, both OAVMAX and OAVSUM were compared using a confidence level for OC defined as [OC/1.65 to 1.65 × OC]. Whereas OAVMAX values were within the confidence level of OC for 62% of the 66 gas samples, OAVSUM values were within this confidence level for only 53%. Validating OAVMAX as a satisfying correlation between chem. compn. and OC, only three compds. among the 66 identified namely trimethylamine, hydrogen sulfide and methanethiol, accounted for the prediction of OC measured during composting and storage of PSS
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