Changes In Composition Of Organic Compounds Research Articles

Hydrochar stability: understanding the role of moisture, time and temperature in its physiochemical changes

Limited information is available about potential physicochemical changes that can occur in hydrochar post-production, e.g. during drying and storage. Understanding these changes is crucial not just for shaping future research plans, but also for future practical applications. Here we studied the effect of moisture (69.2% and 2.4%) and three storage temperatures (− 18, 4, and 20 °C) over a year on selected organic and inorganic compounds in hydrochar produced from the Hydrothermal carbonization (HTC) of digested cow manure. Comparison of the control wet hydrochars (WHs) and dry hydrochars (DHs) showed changes in organic compound composition due to drying. Overall, the total amount of the selected organic compounds was notably greater in WH (15.2 g kg−1 DM) compared to DH (11.8 g kg−1 DM), with variations observed in individual compound concentrations. Drying, however, had no significant influence on the identified inorganic compounds. Storage caused significant changes in both WH and DH, particularly in organic compounds after 12 weeks. Sugars (2–sevenfold), acids (36–371%), and aromatics (58–120%) in stored samples at week 52 were significantly higher than their control values. Changes in the inorganic elements (e.g., Co, K, Mg, Mn, P, S, Sr, and Zn) occurred faster in WH, with significant differences starting from week 1 compared to their control values, while DH showed fewer changes. Based on these changes in both organic and inorganic content, we recommend the optimal storage conditions for future HTC studies to preserve hydrochar properties. Finally, we discussed potential applications for stored hydrochars, with DH showing greater stability, especially at − 18 °C, making it suitable for various applications.Graphical

Elevated atmospheric CO2 drives decreases in stable soil organic carbon in arid ecosystems: Evidence from a physical fractionation and organic compound analysis.

The increasing concentration of CO2 in the atmosphere is perturbing the global carbon (C) cycle, altering stocks of organic C, including soil organic matter (SOM). The effect of this disturbance on soils in arid ecosystems may differ from other ecosystems due to water limitation. In this study, we conducted a density fractionation on soils previously harvested from the Nevada Desert FACE Facility (NDFF) to understand how elevated atmospheric CO2 (eCO2 ) affects SOM stability. Soils from beneath the perennial shrub, Larrea tridentata, and from unvegetated interspace were subjected to a sodium polytungstate density fractionation to separate light, particulate organic matter (POM, <1.85 g/cm3 ) from heavier, mineral associated organic matter (MAOM, >1.85 g/cm3 ). These fractions were analyzed for organic C, total N, δ13 C and δ15 N, to understand the mechanisms behind changes. The heavy fraction was further analyzed by pyrolysis GC/MS to assess changes in organic compound composition. Elevated CO2 decreased POM-C and MAOM-C in soils beneath L. tridentata while interspace soils exhibited only a small increase in MAOM-N. Analysis of δ13 C revealed incorporation of new C into both POM and MAOM pools indicating eCO2 stimulated rapid turnover of both POM and MAOM. The largest losses of POM-C and MAOM-C observed under eCO2 occurred in soils 20-40 cm in depth, highlighting that belowground C inputs may be a significant driver of SOM decomposition in this ecosystem. Pyrolysis GC/MS analysis revealed a decrease in organic compound diversity in the MAOM fraction of L. tridentata soils, becoming more similar to interspace soils under eCO2 . These results provide further evidence that MAOM stability may be compromised under disturbance and that SOC stocks in arid ecosystems are vulnerable under continued climate change.

Changes in organic compound composition in soil following heating to maximum soil water repellency under anoxic conditions

Environmental contextHeating of soils under wildfires can substantially reduce their ability to absorb rainfall, causing reduced vegetation recovery and increased erosion and flooding. This study examines, for the first time, the chemical changes in soil organic matter associated with heating in the oxygen-limited conditions typical under many wildfires. There was a noticeable tendency for production of non-polar compounds, which may ultimately contribute to a more persistent form of soil water repellency with important implications for managing fire affected terrain. AbstractSoil heating, as experienced during wildfires or management burns, can lead to extreme soil water repellency (WR). Previous work has focussed on the chemical composition of soil organic matter (SOM) that may be associated with WR in natural soil samples or samples heated in air. Under wildfires, however, oxygen supply is typically reduced and previous work has shown that the extreme WR induced under such conditions resists eventual destruction at temperatures ~200 °C higher than that of the same soil heated in air. This study examines, for the first time, the chemical changes in SOM associated with extreme WR following heating under oxygen limited conditions. Extracts obtained by accelerated solvent extraction (ASE), using mixtures of isopropyl alcohol/aqueous ammonia (IPA/NH3) and dichloromethane/methanol (DCM/MeOH), were analysed using gas chromatography–mass spectrometry (GC/MS). The data were compared with the SOM composition of the same soil unheated and following heating in air. In the absence of oxygen during soil heating, phthalic acid esters, substituted benzaldehydes, unsaturated amides and organophosphate esters were produced. In comparison with extracts of the same soil heated in air, there was a decreased methoxyphenol/phenol ratio, suggesting progressive demethoxylation and synthesis of new aromatic structures likely to promote extreme WR in soil.

Changes in soil organic compound composition associated with heat-induced increases in soil water repellency

Soil heating, as for example experienced during vegetation fires, often increases soil water repellency; however, no detailed analysis of the soil chemical changes associated with this increase has been conducted to date. Here we characterize the changes in organic compound composition associated with heat-induced increases in water repellency for three Australian eucalypt-forest soils (one sandy loam, two sands). Laboratory heating (300C) strongly increased water drop penetration times (WDPTs) in all soils. Soils were extracted by accelerated solvent extraction (ASE) with an iso-propanol/ammonia mixture (IPA/NH 3 95:5) and pure iso-propanol (IPA). Extracts were fractionated into less and more polar fractions and analysed by GC-MS. Water repellency was eliminated in unheated and heated soils by IPA/NH 3 , but not by pure IPA. Before heating, total solvent extracts were dominated by n-alkanols, terpenoids, C 16 acid, C 29 alkane, β-sitosterol and polar compounds. After heating, dominant compounds were aromatic acids, aldehydes, levoglucosan, simple sugars and glycosides. Heating resulted in a sharp absolute decrease of homologous aliphatic series of alkanols and alkanes, a shift of fatty acid signature to members <C 20 and an increase in total content of aromatic compounds. Heating also caused the formation of complex high-molecular-weight compounds detected in the more polar fractionated extracts and low-molecular-weight oxo- and hydroxyacids and aromatics in the IPA/NH 3 solvent. We speculate that these compounds in conjunction with fatty acids of <C 12 interact with organic and mineral soil surfaces and cause the observed strong increases in soil water repellency following heating.

Sorption of the herbicide dichlobenil and the metabolite 2,6-dichlorobenzamide on soils and aquifer sediments.

The worldwide used herbicide dichlobenil (2,6-dichlorobenzonitrile) has resulted in widespread presence of its metabolite 2,6-dichlorobenzamide (BAM) in pore- and groundwater. To evaluate the transport of these compounds we studied the sorption of dichlobenil and BAM in 22 sediment samples of clayey till, sand, and limestone including sediments exhibiting varying oxidation states. Dichlobenil sorbed to all investigated sediments, with a high sorption in topsoils (Kd = 7.4-17.4 L kg(-1)) and clayey till sediments (Kd = 2.7-126 L kg(-1)). The sorption of the polar metabolite BAM was much lower than the sorption of dichlobenil but followed the same tendency with the highest sorption in the topsoils (Kd = 0.24-0.66 L kg(-1)) and in the clayey till sediments (Kd = 0.10-0.93 L kg(-1)). The sorption of both compounds was significantly higher (2-47 times) in the unoxidized (reduced) clayey till than in the weathered (oxidized) clayey till. Such a difference in sorption capacity could neither be explained by a higher organic carbon content, sorption to clay minerals, differences in clay mineralogy, nor by blocking of reactive surface sites on clay minerals by iron oxides. However, by removing an average of 81% of the organic carbon from the reduced clayey till with H2O2, the sorption decreased on average 50%. Therefore, most of the sorption capacity in the reduced clayey till was related to organic carbon, which indicates that sorption processes are affected by changes in organic compound composition due to weathering.