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Waste Management

Dynamic Respiration Index as a Descriptor of the Biological Stability of Organic Wastes

Dipartimento di Produzione Vegetale, Università degli Studi di Milano, Via Celoria 2, 20133, Milan, Italy

^* Corresponding author (fabrizio.adani{at}unimi.it).

Received for publication August 7, 2003. Analytical methods applicable to different organic wastes are needed to establish the extent to which readily biodegradable organic matter has decomposed (i.e., biological stability). The objective of this study was to test a new respirometric method for biological stability determination of organic wastes. Dynamic respiration index (DRI) measurements were performed on 16 organic wastes of different origin, composition, and biological stability degree to validate the test method and result expression, and to propose biological stability limits. In addition, theoretical DRI trends were obtained by using a mathematical model. Each test lasted 96 h in a 148-L-capacity respirometer apparatus, and DRI was monitored every hour. The biological stability was expressed as both single and cumulative DRI values. Results obtained indicated that DRI described biological stability in relation to waste typology and age well, revealing lower-stability waste characterized by a well-pronounced DRI profile (a marked peak was evident) that became practically flat for samples with higher biological stability. Fitting indices showed good model prediction compared with the experimental data, indicating that the method was able to reproduce the aerobic process, providing a reliable indication of the biological stability. The DRI can therefore be proposed as a useful method to measure the biological stability of organic wastes, and DRI values, calculated as a mean of 24 h of the highest microbial activity, of 1000 and 500 mg O₂ kg^–1 volatile solids (VS) h^–1 are proposed to indicate medium (e.g., fresh compost) and high (e.g., mature compost) biological stabilities, respectively.

Abbreviations: DRI, dynamic respiration index • DRI_cum, cumulative dynamic respiration index value for 96 h • DRI_cumadj, cumulative dynamic respiration index value for 96 h minus the lag phase • DRI_DiProVe, average instantaneous dynamic respiration index value taken during the 24 h of the most intense biological activity • DRIh_cumadj, cumulative dynamic respiration index value for 96 h minus the lag phase and standardized with respect to the number of hours • DRI_imax, maximum instantaneous dynamic respiration index value measured during the entire test • MSW, municipal solid waste • OUR, oxygen uptake rate • VS, volatile solids

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This Issue in Journal of Environmental Quality

JEQ 2004 33: 1589-1599. [Full Text]  

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