Aerobic decomposition and stabilization of organic matter during the composting of waste materials is primarily due to the biochemical transformation of water-soluble compounds in the liquid phase by the microbial biomass. For this reason water-soluble organic matter represents the most active fraction of compost, both biologically and chemically, and thus should directly reflect the biochemical alteration of organic matter. In light of the variety of parameters generally utilized to study composting processes, this work aims at identifying the major chemical transformations that occur in solution and their influence on the attainment of stability and maturity with composting time. Compost stability, assessed by means of respirometric analysis which determined oxygen demand as a result of mineralization of the compost’s organic matter, and compost maturity evaluated with Lepidium sativum L. seed bioassays, were found to be highly related to the nature and content of water-soluble organic matter. Compost dissolved organic C is composed of various organic compounds having different susceptibilities to microbial degradation. The evaluation of the changes in dissolved organic C biodegradability with composting time and liability of different chemical compounds, have shown that during the initial stages of composting, soluble organic C is highly degradable under aerobic conditions, particularly due to the predominance of labile, hydrophilic compounds such as carbohydrates, amino acids and proteins. As these compounds are degraded more resistant aromatic moieties accumulate in solution resulting in a reduction in the degradability of dissolved organic C with composting time. This decrease in degradability was found to be highly correlated with microbial oxygen demand, and could have important implications in the evaluation of the composting process. Moreover, this work aims to elucidate the microbial-mediated processes responsible for the distribution of soluble organic matter between stable and labile pools with composting time. Accordingly, chemical analysis as well as UV absorption, and 1H and 13C-NMR spectroscopy of samples collected during the industrial composting of urban waste revealed microbial induced transformation of water-extractable organic matter over time. The chemical composition changed from labile, hydrophilic, plant-derived organic compounds at the beginning to predominately stable, hydrophobic moieties comprising lignin-derived phenols and microbially-derived carbohydrates at later stages of composting.
Biochemical transformation of dissolved organic matter during composting and its influence on compost stability and maturity
SAID PULLICINO, DANIEL
2006-01-01
Abstract
Aerobic decomposition and stabilization of organic matter during the composting of waste materials is primarily due to the biochemical transformation of water-soluble compounds in the liquid phase by the microbial biomass. For this reason water-soluble organic matter represents the most active fraction of compost, both biologically and chemically, and thus should directly reflect the biochemical alteration of organic matter. In light of the variety of parameters generally utilized to study composting processes, this work aims at identifying the major chemical transformations that occur in solution and their influence on the attainment of stability and maturity with composting time. Compost stability, assessed by means of respirometric analysis which determined oxygen demand as a result of mineralization of the compost’s organic matter, and compost maturity evaluated with Lepidium sativum L. seed bioassays, were found to be highly related to the nature and content of water-soluble organic matter. Compost dissolved organic C is composed of various organic compounds having different susceptibilities to microbial degradation. The evaluation of the changes in dissolved organic C biodegradability with composting time and liability of different chemical compounds, have shown that during the initial stages of composting, soluble organic C is highly degradable under aerobic conditions, particularly due to the predominance of labile, hydrophilic compounds such as carbohydrates, amino acids and proteins. As these compounds are degraded more resistant aromatic moieties accumulate in solution resulting in a reduction in the degradability of dissolved organic C with composting time. This decrease in degradability was found to be highly correlated with microbial oxygen demand, and could have important implications in the evaluation of the composting process. Moreover, this work aims to elucidate the microbial-mediated processes responsible for the distribution of soluble organic matter between stable and labile pools with composting time. Accordingly, chemical analysis as well as UV absorption, and 1H and 13C-NMR spectroscopy of samples collected during the industrial composting of urban waste revealed microbial induced transformation of water-extractable organic matter over time. The chemical composition changed from labile, hydrophilic, plant-derived organic compounds at the beginning to predominately stable, hydrophobic moieties comprising lignin-derived phenols and microbially-derived carbohydrates at later stages of composting.
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