Molecular Characterization of Compost at Increasing Stages of Maturity. 1. Chemical Fractionation and Infrared Spectroscopy

Composted organic biomasses at 60, 90, and 150 days of maturity were studied for changes in molecular composition. Compost samples were subjected to a mild sequential fractionation based on (1) organic solvent extraction, (2) transesterification with boron trifluoride in methanol (BF3−CH3OH), and (3) methanolic alkaline hydrolysis (KOH−CH3OH). The general chemical variations in compost residues following fractionation were monitored by DRIFT spectroscopy, whereas the molecular components separated along the fractionation steps were identified by GC-MS. DRIFT spectra suggested a progressive decrease of biolabile compounds such as alkyls, carbohydrates, and proteinaceous materials with compost maturity. Extraction of unbound components in an organic solvent indicated a considerable reduction of linear and branched alkanoic acids, both saturated and unsaturated, n-alkanes, and n-alkanols with enhancing compost maturity. Extracts of weakly bound molecules by transesterification revealed a decrease, with compost maturity, of components from more recalcitrant plant polyesters, such as ω-, di-, and trihydroxy acids, dioic acids, and n-alkanols. Extracts of strongly bound molecules by alkaline hydrolysis indicated a lower decrease of the same components, suggesting their reduced availability when in stable hydrophobic domains of progressively mature compost. The largest decrease in molecular components occurred when compost was stabilized from 60 to 90 days, whereas its composition did not significantly vary after stabilization at 150 days. The molecular structures of a number of steroids and terpenes appeared to be less susceptible to transformation with composting maturity, thereby resulting as useful biomarkers to trace the fate of composted organic matter in the environment. This work showed that a detailed molecular characterization of compost by a stepwise chemical fractionation enables the evaluation of compost maturity and origin of composted biomasses, as well as the identification of environmental tracers. Keywords: Compost maturity; biomass recycling; molecular characterization; sequential molecular fractionation; hydrophobic component

Binding of Phenol and Differently Halogenated Phenols to Dissolved Humic Matter As Measured by NMR Spectroscopy

1H- and 19F-NMR measurements of spin−lattice (T1) and spin−spin (T2) relaxation times and diffusion ordered spectroscopy (DOSY) were applied to investigate the association of nonsubstituted (phenol (P)) and halogen-substituted (2,4-dichlorophenol (DCP); 2,4,6-trichlorophenol (TCP), and 2,4,6-trifluorophenol (TFP)) phenols with a dissolved humic acid (HA). T1 and T2 values for both 1H and 19F in phenols decreased with enhancing HA concentration, indicating reduction in molecular mobility due to formation of noncovalent interactions. Moreover, correlation times (τC) for different hydrogen and fluorine atoms in phenols showed that anisotropic mobility turned into isotropic motion with HA additions. Changes in relaxation times suggested that DCP and TCP were more extensively bound to HA than P and TFP. This was confirmed by diffusion measurements which showed full association of DCP and TCP to a less amount of HA than that required for entire complexation of P and TFP. Calculated values of binding constants (Ka) reflected the overall NMR behavior, being significantly larger for DCP- and TCP-HA (10.04 ± 1.32 and 4.47 ± 0.35 M−1, respectively) than for P- and TFP-HA complexes (0.57 ± 0.03 and 0.28 ± 0.01 M−1, respectively). Binding increased with decreasing solution pH, thus indicating a dependence on the fraction of protonated form (α) of phenols in solution. However, it was found that the hydrophobicity conferred to phenols by chlorine atoms on aromatic rings is a stronger drive than α for the phenols repartition within the HA hydrophobic domains

Reduced Toxicity of Olive Mill Waste Waters by Oxidative Coupling with Biomimetic Catalysis

Large quantities of environmentally toxic olive mill waste waters (OMWW) result from olive oil production worldwide. A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride (FePha) was used as biomimetic catalyst to oxidatively couple toxic phenols in OMWW fractions obtained by micro-, ultra-, and nanofiltration, and reverse osmosis. The occurrence of oxidative coupling in different OMWW size-fractions was assessed by high performance size exclusion chromatography (HPSEC), before and after conformational disruption with acetic acid, and measurements of proton spin−lattice relaxation time in the rotating frame (T1ρH) through 13C-CPMAS-NMR spectroscopy. The concurrent reduction in toxicity of OMWW size-fractions brought about by the FePha treatment was monitored by an algal bioassay. HPSEC chromatograms of OMWW samples subjected to catalyzed coupling showed apparent weight-average molecular weight (Mwa) values varying from 18 to 185% larger than for control. Moreover, when such FePha-treated fractions were added to acetic acid prior to HPSEC, the Mwa values still ranged from 14 to 162% larger than for control fractions similarly treated with acetic acid. This evidence of polymerization among toxic phenols was confirmed by T1ρ(H) values which were significantly enhanced by the FePha treatment, thereby indicating an increased conformational rigidity of OMWW materials. These molecular changes were reflected in a significantly reduced toxicity exerted on microalgae by the OMWW size-fractions subjected to catalyzed oxidative couplings. Our results suggest that OMWW can be effectively treated with a biomimetic catalyst to induce oxidative phenol polymerization and reduce their toxicity before amendments to soils or other disposal means

Molecular Characterization of a Compost and Its Water-Soluble Fractions

A sequential chemical fractionation was applied to a compost, with its dissolved organic matter (DOM) extracted in water and separated in hydrophilic (HiDOM) and hydrophobic (HoDOM) components and a water extract, following oxidation of compost suspension with an oxygen flux (TEA). The components sequentially isolated by mild extractions and hydrolyses as structurally unbound (SU), weakly bound (WB), and strongly bound (SB) to the matrix of the bulk compost and its water-soluble fractions were identified in their molecular structure. The bulk compost was rich with components derived from both aromatic (phenolic compounds) and aliphatic (long-chain fatty acids, hydroxy acids, diacids, and alcohols) structures of suberins, whereas components derived from cutins were especially extracted from TEA, HoDOM, and HiDOM. The TEA sample also yielded a significant amount of oxidized products that was dominated by dehydroabietic acids. The fractionation sequence highlighted the different intermolecular interactions that bound the isolated molecular components to the compost complex matrix. While a significant part of the bulk compost was still present as a solid residue at the end of the sequential fractionation, all water-soluble fractions were almost completely hydrolyzed. These results indicate that the water-soluble components of compost may be readily separated from the compost matrix and contribute to the environmental dynamics of natural organic matter

MOESM1 of Decomposition of bio-degradable plastic polymer in a real on-farm composting process

Additional file 1. Supporting information

PCA and Heatmap of plant metabolites as a function of <i>Trichoderma</i> inoculum.

(a) PCA score-plot based on GC-MS and 1H NMR data of leaves harvested from maize plants inoculated with Trichoderma (B2) and treated with different P-based fertilizers (P0-P4). Names and direction of most significant PCA loading vectors involved in the differentiation of treatments are reported along the score-plot borders. (b) Heatmap visualization of most discriminant variables.</p

Plant shoots dry weight, chlorophyll, P and N content.

Plant shoots dry weight (a), chlorophyll content (b), leaf phosphorus content (c), leaf nitrogen content (d), in control (B0) and inoculated maize plants (B2) treated with different P-based fertilizers (P0-P4). Error bars indicate standard deviation (n = 5) and different letters indicate significant differences by the Tukey’s test (p ≤ 0.05 at a significance of 0.05).</p

PCA and Heatmap of plant metabolites as a function of different treatments.

(a) PCA score-plot based on GC-MS and 1H NMR data of leaves harvested from maize plants treated with different P-based fertilizers (P0-P4), with and without microbial inoculum (B2, B0). Names and direction of most significant PCA loading vectors involved in the differentiation of treatments are reported along the score-plot borders. (b) Heatmap visualization of most discriminant variables.</p

Remediation of Waters Contaminated with MCPA by the Yeasts <i>Lipomyces starkeyi</i> Entrapped in a Sol−Gel Zirconia Matrix

A single-stage sol−gel route was set to entrap yeast cells of Lipomyces starkeyi in a zirconia (ZrO2) matrix, and the remediation ability of the resulting catalyst toward a phenoxy acid herbicide, 4-chloro-2-methylphenoxyacetic acid (MCPA), was studied. It was found that the experimental procedure allowed a high dispersion of the microorganisms into the zirconia gel matrix; the ZrO2 matrix exhibited a significant sorption capacity of the herbicide, and the entrapped cells showed a degradative activity toward MCPA. The combination of these effects leads to a nearly total removal efficiency (>97%) of the herbicide at 30 °C within 1 h incubation time from a solution containing a very high concentration of MCPA (200 mg L−1). On the basis of the experimental evidence, a removal mechanism was proposed involving in the first step the sorption of the herbicide molecules on the ZrO2 matrix, followed by the microbial degradation operated by the entrapped yeasts, the metabolic activity of which appear enhanced under the microenvironmental conditions established within the zirconia matrix. Repeated batch tests of sorption/degradation of entrapped Lipomyces showed that the removal efficiency retained almost the same value of 97.3% after 3 batch tests, with only a subsequent slight decrease, probably due to the progressive saturation of the zirconia matrix

Antioxidant activity of HS-FEN at different concentration (50, 30, 25 μg mL^-1).

Vertical bars represent the standard deviation (s.d.). Different capital letters indicate significant differences according to Tukey test (p ≤ 0.05).</p