Effect of active substances on dissolved organic matter properties in uncontaminated soil during non-thermal discharge plasma process

Abstract

Discharge plasma technology has received widespread attention for soil remediation as it has high efficiency and does not cause secondary pollution. However, its effect on soil quality is unclear. The chemical composition and fluorescence properties of soil dissolved organic matter (DOM) are key indicators of its quality. Here, we conducted a non-thermal discharge plasma (NTP) experiment with different treatment times and studied how NTP influences the composition, characteristics, and ecological functions of DOM. NTP significantly affected DOM decomposition and transformation by generating reactive oxygen and nitrogen species and ultraviolet radiation. Short-term NTP promoted the formation of low-molecular-weight DOM components, and increased the DOC, DON, and DTP concentrations. Meanwhile, it enhanced the DOM stability and compositional complexity. Therefore, it increased the soil nutrient supply capacity and improved the DOM chelation ability with heavy metal ions and organic pollutant adsorption capacity. Additionally, long-term NTP (＞100 min), increased the NH₄⁺-N content and decreased the NO₃⁻-N content by inhibiting nitrification and promoting ammonification. NTP treatment preferentially degraded DOM precursors in difficult-to-degrade plant residues. Short-term NTP (≤100 min) increased UVA humic-like material to 47% and decreased tryptophan-like to 6%. It had little effect on terrestrial humic-like material, showing limited impact on stable aromatics. Changes in fluorescence index (FI), humicity index (HIX), biogenicity index (BIX) and freshness index (β:α) further confirmed DOM transformation processes. Therefore, an appropriate treatment duration can optimise the composition and pollution remediation capability of DOM in practical applications, but excessive treatment may affect the soil microbial balance and nutrient cycling.

Graphical abstract

Keywords

Non-thermal discharge plasma / Dissolved organic matter / Three-dimensional fluorescence / Soil quality

Highlight

	● NTP preferentially degraded DOM precursors in difficult-to-degrade plant residues.
	● Short treatment duration raised DOM complexity, stability and LMW DOM formation.
	● Long treatment duration inhibited nitrification and promoted ammonification.
	● Excessive NTP treatment can affect soil microbes and nutrient cycling.

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