¹³C solid‐state NMR assessment of decomposition pattern during co‐composting of sewage sludge and green wastes

Abstract

The fate of organic matter during composting is poorly understood. Therefore, we analysed composts of sewage sludges and green wastes (44 samples representative of 11 stages of biodegradation) by conventional chemical methods: pH, humic (HA) and fulvic acid (FA) content, C, N and organic matter (OM) content, and by 13 C CPMAS NMR to assess the decomposition process of the organic matter. Chemical changes clearly occurred in two phases: first, decomposition of OM during the first 2 months was characterized by decreased C/N ratios, OM content and increased pH; and second, a humification process with increased HA/FA ratios. NMR spectrum changes confirmed this pattern, with an increase in aromaticity and a decrease in alkyl C. A decrease of syringyl to guaiacyl ratio (S/G), a sign of lignin transformation, also indicated humification during composting. NMR spectroscopic properties of composts were also studied by means of principal components analysis (PCA) and revealed changes according to the degree of compost maturation. The factorial map presents a chronological distribution of composts on the two first principal components. The influences of eight chemical factors on the PCA ordination of composts as monitored by their evolution by NMR were also studied by multivariate analyses. PCA clearly indicated two phases: the rapid decomposition of organic matter followed by the formation of humic-like substances. The first phase, that is 'new' composts, was strongly correlated with OM contents, pH and C/N ratios whereas the second phase, corresponding to 'old' compost, was correlated with pH, HA content and HA/FA ratio. These results confirm that knowledge of the formation of humic substances is indispensable to suitable monitoring of the composting process.Correspondence: R. Albrecht.

Changes in chemical and biological parameters during co-composting of anaerobically digested sewage sludges with lignocellulosic material

“…After about one month, both the piles exhibited an organic carbon content close to 25%. These results are very close to those reported by Albrecht et al [18] during the composting of digested municipal sewage sludges and green wastes. The relatively low variation in the organic carbon content could be attributed to the more stable nature of the organic matter contained in anaerobic sludges as a consequence of the stabilization it had undergone in the treatment plant.…”

“…Similar results have been reported in composting of sewage sludges with green wastes [18] and maize straw. [20] C/N ratio The two mixtures exhibited a low C/N ratio (close to 11) at the beginning of the experiment.…”

“…[13] However, in the case of sewage sludges based mixtures several studies report a low initial C/N ratio and a reduced change in this parameter during the process in agreement with our results. [15,18,20,23] Several studies have been conducted in order to verify the effect of the initial C/N ratio on the composting process by using different compositions of starting materials. Eiland et al [24] observed that low initial C/N ratios caused a fast degradation of fibres during the first three months of composting of straw and pig manure (hemicellulose: 50-80%, cellulose: 40-60%).…”

Biomass, laccase and endoglucanase production by Lentinula edodes during solid state fermentation of reed grass, bean stalks and wheat straw residues

“…All measurements were made at room temperature. The 13 C chemical shifts were referenced to tetramethylsilane and calibrated with the glycine carbonyl signal, set at 172.5 ppm (Albrecht et al 2008).…”

Isolation, Characterization, and Environmental Application of Bio-Based Materials as Auxiliaries in Photocatalytic Processes

“…Their integration area almost equals that of the aromatic region (28.8%) and again derives from the selective enrichment of recalcitrant components [60]. 13 C solid-state nuclear magnetic resonance (NMR) spectroscopy offers the possibility of direct chemical characterization of organic materials in terms of content of different functional groups [57][58][59]. In the 13 C CPMAS solid-state NMR spectrum of BBS-HA (Figure 2 together with the deducted abundance of functional groups), the region between 160 and 220 ppm is dominated by a signal at 173 ppm, due to carboxyl C. The aromatic and phenolic region (110-160 ppm) represented 30% of C. Here, the signal at 129 ppm, indicating a relatively larger presence of non-substituted aromatic rings, may be due to aromatic lignin [60].…”