Applications of solid-state NMR spectroscopy in environmental science

Stochastic image spectroscopy: a discriminative generative approach to hyperspectral image modelling and classification

This paper introduces a new latent variable probabilistic framework for representing spectral data of high spatial and spectral dimensionality, such as hyperspectral images. We use a generative Bayesian model to represent the image formation process and provide interpretable and efficient inference and learning methods. Surprisingly, our approach can be implemented with simple tools and does not require extensive training data, detailed pixel-by-pixel labeling, or significant computational resources. Numerous experiments with simulated data and real benchmark scenarios show encouraging image classification performance. These results validate the unique ability of our framework to discriminate complex hyperspectral images, irrespective of the presence of highly discriminative spectral signatures.

Enhancing Phosphorus Release from Sewage Sludge in Anaerobic Digestion via Thermal Hydrolysis Pretreatment: Insights from Phosphorus Speciation and Molecular Biological Pathways

This study explores the mechanisms enhancing phosphorus (P) release from sludge in anaerobic digestion (AD) with thermal hydrolysis pretreatment (THP) using sequential chemical extraction, X-ray absorption near-edge structure spectroscopy (XANES), 31P NMR, and multiomics. THP-treated sludge notably increased liquid-phase P by 53.8% over 3 days compared to sewage sludge (SS), identifying solid-phase Fe-P as the primary P source. The THP+AD also provided a higher abundance of bacteria that contributed to P release through multiple pathways (MPRPB), whereas SS+AD enriched some microbial species with single P release pathway. Moreover, species co-occurrence network analysis underlined the pivotal role of P-releasing bacteria in THP+AD, with 8 out of 16 keystones being P-releasers. Among the 63 screened genes that were related to P transformations and release, the poly beta-hydroxybutyrate (PHB) synthesis genes associated with polyphosphate bacteria-mediated P release were more abundant in THP+AD than in SS+AD. Furthermore, the upregulation of genes involved in methyl phosphonate metabolism in the THP-treated sludge enhanced the methane production potential of the AD process. These findings suggested that MPRPB were indeed the main contributors to P release, and enrichment in the THP+AD process enhanced their capability for P liberation.

Variation in Phosphorus Speciation of Sewage Sludge throughout Three Wastewater Treatment Plants: Determined by Sequential Extraction Combined with Microscopy, NMR Spectroscopy, and Powder X-ray Diffraction

The variation in phosphorus (P) speciation of sewage sludge throughout three wastewater treatment plants (WWTPs) was obtained by combining sequential P extraction with optical and scanning electron microscopy (SEM), chemical analyses, powder X-ray diffraction (PXRD), and ²⁷Al and ³¹P nuclear magnetic resonance (NMR) spectroscopy. The WWTPs combine chemical P removal (CPR) and enhanced biological P removal (EBPR) and were compared to understand the effect of iron (Fe) dosing with and without codosing of aluminum (Al) and thermal hydrolysis on the P speciation. ³¹P NMR showed comparable inorganic orthophosphate (ortho-P, 53-60% of total P) and organophosphate (organic-P, 37-45%) in primary sludge, whereas polyphosphate (poly-P, 23-44%) from poly-P accumulating organisms (PAOs) was mainly observed in the secondary sludge. Inorganic ortho-P (90-98%) dominated after anaerobic digestion, which degraded poly-P and most organic-P. The inorganic ortho-P was mainly Fe bound P (Fe-P), especially after anaerobic digestion (71%). Codosing of Fe and Al led to two comparable fractions: Fe-P (38%) and P sorbed on amorphous Al (hydr)oxides (38%). Vivianite was identified in all samples by microscopy and chemical extraction but was PXRD amorphous in 12 out of 17 samples. Thus, vivianite may be more common in sewage sludge than previously known.

Research Progress of NMR in Natural Product Quantification

In the fields of medicine and health, traditional high-performance liquid chromatography or UV-visible spectrophotometry is generally used for substance quantification. However, over time, nuclear magnetic resonance spectroscopy (NMR) has gradually become more mature. Nuclear magnetic resonance spectroscopy has certain advantages in the quantitative analysis of substances, such as being nondestructive, having a high flux and short analysis time. Nuclear magnetic resonance spectroscopy has been included in the pharmacopoeiae of various countries. In this paper, the principle of nuclear magnetic resonance spectroscopy and the recent progress in the quantitative study of natural products by NMR are reviewed, and its application in the quantitative study of natural products is proposed. At the same time, the problems of using NMR alone to quantify natural products are summarized and corresponding suggestions are put forward.

Quantitative determination of vivianite in sewage sludge by a phosphate extraction protocol validated by PXRD, SEM-EDS, and 31P NMR spectroscopy towards efficient vivianite recovery

Vivianite (Fe₃(PO₄)₂⋅8H₂O) is a potential phosphorus (P) recovery product from wastewater treatment plants (WWTPs). However, routine methods for quantification of vivianite bound P (vivianite-P) are needed to establish the link between vivianite formation and operating conditions, as current approaches require specialized instrumentation (Mössbauer or synchrotron). This study modified a conventional sequential P extraction protocol by insertion of an extraction step (0.2% 2,2'-bipyridine + 0.1 M KCl) targeting vivianite-P (Gu et al., Water Research, 2016, 103, 352-361). This protocol was tested on digested and dewatered sludge from two WWTPs, in which vivianite (molar Fe:P ratios of 1.0-1.6) was unambiguously identified by optical microscopy, powder X-ray diffraction, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The results showed that vivianite-P was separated from iron(III)-bound P (Fe(III)-P) in the sludge. Vivianite-P constituted about half of the total P (TP) in the sludge from a Fe dosing chemical P removal (CPR) WWTP, but only 16-26% of TP in the sludge from a WWTP using a combination of Fe dosing CPR and enhanced biological P removal (EBPR). The modified protocol revealed that Fe-bound P (Fe-P, i.e., vivianite-P + Fe(III)-P) was the dominant P fraction, in agreement with quantitative ³¹P nuclear magnetic resonance (NMR) experiments. Moreover, it was shown that the conventional P extraction protocol underestimated the Fe-P content by 6-35%. The established protocol represents a reliable in-house analytical method that can distinguish and quantify vivianite-P and Fe(III)-P in sludge, i.e. facilitate optimized vivianite production at WWTPs.

ER, Venâncio T, Valderrama AC. Functionalization of an Alginate-Based Material by Oxidation and Reductive Amination

This research focused on the synthesis of a functional alginate-based material via chemical modification processes with two steps: oxidation and reductive amination. In previous alginate functionalization with a target molecule such as cysteine, the starting material was purified and characterized by UV-Vis, ¹H-NMR and HSQC. Additionally, the application of FT-IR techniques during each step of alginate functionalization was very useful, since new bands and spiked signals around the pyranose ring (1200–1000 cm⁻¹) and anomeric region (1000–750 cm⁻¹) region were identified by a second derivative. Additionally, the presence of C₁-H₁ of β-D-mannuronic acid residue as well as C₁-H₁ of α-L-guluronic acid residue was observed in the FT-IR spectra, including a band at 858 cm⁻¹ with characteristics of the N-H moiety from cysteine. The possibility of attaching cysteine molecules to an alginate backbone by oxidation and post-reductive amination processes was confirmed through ¹³C-NMR in solid state; a new peak at 99.2 ppm was observed, owing to a hemiacetal group formed in oxidation alginate. Further, the peak at 31.2 ppm demonstrates the presence of carbon -CH₂-SH in functionalized alginate—clear evidence that cysteine was successfully attached to the alginate backbone, with 185 μmol of thiol groups per gram polymer estimated in alginate-based material by UV-Visible. Finally, it was observed that guluronic acid residue of alginate are preferentially more affected than mannuronic acid residue in the functionalization.