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TECHNICAL REPORTS

Waste Management

Evaluation of Extracted Organic Carbon and Microbial Biomass as Stability Parameters in Ligno-Cellulosic Waste Composts

^a CRA-Instituto Sperimentale per la Nutrizione delle Piante, sezione di Gorizia, Via Trieste 23, I-34170 Gorizia, Italy
^b CEBAS-CSIC, Departamento de Conservación de Suelos y Agua y Manejo de Residuos Orgánicos, Campus Universitario de Espinardo, E-30100 Espinardo, Murcia, Spain

^* Corresponding author (claudio.mondini{at}entecra.it)

Received for publication February 8, 2006. Extracted organic C and microbial biomass were evaluated as stability parameters in 3 different ligno-cellulosic waste composts. Organic C was extracted by both water and alkali and further separated in humic-like carbon (HLC) and nonhumic carbon (NHC). Conventional humification parameters, such as humification index and degree of humification were calculated from NHC and HLC. Microbial biomass carbon (B_C) was determined as an indicator of the degree of biochemical transformation, whereas ninhydrin reactive N (B_NIN) was measured to obtain the stability parameter B_NIN/N_TOT (N_TOT, total N). The water-extracted organic C did not provide reliable information on the transformations underwent by the ligno-cellulosic wastes during composting, since its content remained almost unaltered during the whole process. In contrast, parameters based on the alkali-extracted organic C and microbial biomass clearly reflected organic matter (OM) changes during the process. There was an increase in the net amount of HLC in the alkali extracts throughout composting, especially in the first 7 to 12 wk of the process, as well as a relative enrichment of HLC with respect to NHC. Values of humification index and degree of humification in end products were consistent with an adequate level of compost stability. The stability parameter B_NIN/N_TOT showed to be a reliable indicator of stability in ligno-cellulosic wastes. Parameters based on the alkali-extracted C and microbial biomass clearly reflected the transformation of the OM during composting and can be used as stability parameters in ligno-cellulosic waste composts.

Abbreviations: B_C, microbial biomass carbon • B_NIN, microbial biomass ninhydrin-reactive nitrogen • C_ORG, total organic carbon • DH, degree of humification • HI, humification index • HLC, humic-like carbon • OM, organic matter • NHC, nonhumic carbon • N_TOT, total nitrogen • TEC, total alkali-extracted organic carbon • WEOC, water-extracted organic carbon