Relevance of Organic Matter Fractions as Predictors of Wastewater Sludge Mineralization in Soil
Parnaudeau, V. (Virginie) | Nicolardot, Bernard | Pagès, Jérôme
Seventeen different wastewater sludges were characterized using both chemical and organic matter fractionation methods (water extraction, Van Soest method, and acid hydrolysis) and 6-mo incubation studies to assess their decomposition in soil. Simple correlation and multiple factor analysis (MFA) were then performed to establish relationships between composition and C and N mineralization of sludges. Carbon and N concentrations covered a wide range of values, but organic carbon (Cₒ) to organic nitrogen (Nₒ) ratios were relatively low (from 5 to 19). Carbon and N were mainly distributed in the most soluble fractions of the Van Soest method and in the water-insoluble fraction at 100°C. Carbon mineralization varied from 180 to 661 g C kg⁻¹ organic C added during the 168-d incubation. The addition of sludges led to different inorganic N dynamics: from −3.3 to +120.0 g N kg⁻¹ sludge organic C mineralized after the 168-d incubation. Fractionation studies showed that the most discriminating method was acid hydrolysis. Carbon mineralization was linked with the proportion of sludge N and C present in the lignin-like fraction (r = −0.68 and −0.65, respectively). Significant relationships were established between N mineralization and Nₒ to Cₒ ratio (0.88 < r < 0.95) and the Cₒ to Nₒ ratio of sludges, the C to N ratio of the soluble fraction obtained by the Van Soest method, the water-soluble fraction at 100°C, and the C and N present in the acid-hydrolyzable fraction. Finally, multiple factor analysis also enabled establishing a sludge typology using five clusters based on composition and mineralization characteristics.
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