Organic matter (OM), and dissolved organic matter (DOM), have a major influence upon biogeochemical processes; most significantly, the carbon cycle. To date, very few studies have examined the spatial heterogeneity of DOM in paddy soils. Thus, very little is known about the DOM molecular profiles and the key environmental factors that underpin DOM molecular chemodiversity in paddy soils. Here, Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry was applied to unambiguously resolve 11 361 molecular formulas in 16 paddy soils; thereby elucidating the molecular characteristics of paddy soil DOM. Soil pH, iron complexing index (Fep/FeR) and C/N ratio were established to be key factors controlling DOM profiles. Polycyclic aromatics (derived from combustion) and polyphenols (derived from plants) increased with increasing pH, while polyphenols molecules, pyrogenic aromatics, and carboxylic compounds decreased with increasing iron complexing index. Patterns in molecular profiles indicated DOM in paddy soils to become more recalcitrant at higher soil C/N ratio and higher pH. Furthermore, plant-derived polyphenols and pyrogenic DOM were retained favorably by iron and the chemodiversity of DOM in paddy soil increased with increasing soil C/N ratios. This study provides critical information about DOM characteristics at a molecular level and will inform better global management of soil carbon in paddy soil ecosystems.

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Hydrochar is a carbonaceous material derived from hydrothermal liquefaction, and it carries good potential as a new material for environmental applications. However, little is known about the dissolved organic matter (DOM) associated with hydrochar and the consequences of its release. The relationship between the production temperature and the characteristics of DOM released from hydrochar as well as the associated biotoxicity was investigated using a suite of advanced molecular and spectroscopic tools. With the increase in production temperature, the resulted hydrochar-based DOM contained a higher content of phenols and organic acids but less sugars and furans. Meanwhile, the molecular structure of DOM shifted to lower molecular weight with higher organic contents containing <6 O atoms per compound, aromatics, and N-containing substances. While low-temperature hydrochar-derived DOM showed minimal biotoxicity, increase in production temperature to 330 °C led to a great rise in toxicity. This might be attributed to the increased contents of phenols, organic acids, and organics containing <6 O atoms and 1 N atom per compound. These results suggest that hydrochar-derived DOM have more negative impacts on the environment than the organics associated with biochar production. Such understanding highlights the importance of controlling the hydrochar production process.

Anaerobic biodegradationAerobic biodegradation Oxidation by bio-aeration Activated carbon filtration Refinery wastewater 284.95 285.00 285.05 285.10 285.15 285.20ABSTRACT A set of wastewaters sampled in a stream-by-stream flow of the process in a refinery wastewater treatment plant were characterized to investigate the molecular composition and transformation of dissolved organic matter (DOM). The samples were separated into organic and aqueous phase DOMs by solvent extraction and solid phase extraction (SPE). Volatile and semi-volatile compounds in the organic phase were characterized by gas chromatography -mass spectrometry (GC-MS); DOMs in the organic and aqueous phase were characterized by negative ion electrospray (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The aqueous phase DOMs exhibited more complex molecular composition than other complex mixtures investigated by far, in which there were totally 76 compound class species identified in a single mass spectrum. Refinery wastewater DOMs have lower values of double bond equivalent (DBE) and O/C ratio than those of natural organic matters (NOMs) in fresh and marinewaters. The organic phase DOM occupied the major TOC value, but was liable to be degraded in the biological process. Some humic-like substances presented in the aqueous DOM were found resistant for the treatment processes by the ESI FT-ICR MS based semi-quantitative results.