The introduction of various concentrations of chemically modified humic compounds (HC) with different redox characteristics into the media with free and immobilized anaerobic consortia accumulating landfill gases was studied as approach to their functioning management. For this purpose, quinone (hydroquinone, naphthoquinone or methylhydroquinone) derivatives of HC were synthesized, which made it possible to vary the redox and antioxidant properties of HC as terminal electron acceptors in methanogenic systems. The highest acceptor properties were obtained with potassium humate modified by naphthoquinone. To control possible negative effect of HC on the cells of natural methanogenic consortia, different bioluminescent analytical methods were used. The addition of HC derivatives, enriched with quinonones, to nutrient media at concentrations above 1 g/L decreased the energetic status of cells and the efficiency of the methanogenesis. For the first time, the significant decrease in accumulation of biogas was reached as effect of synthetic HC derivatives, whereas both notable change of biogas composition towards increase in the CO2 content and decrease in CH4 were revealed. Thus, modification with quinones makes it possible to obtain low-potential HC derivatives with strongly pronounced acceptor properties, promising for inhibition of biogas synthesis by methanogenic communities.

Redox moieties, which are present in the molecular backbone of humic substances (HS), govern their antioxidant properties. We hypothesized that a directed modification of the humic backbone via incorporation of redox moieties with known redox properties might provide an efficient tool for tuning up antioxidant properties of HS. In this work, hydroquinonoid and hydronaphthoquinonoid centres were used, which possess very different redox characteristics. They were incorporated into the structure of coal (leonardite) humic acids CHA) and peat fulvic acids (PFA). For this goal, an oxidative copolymerization of phenols was used. The latter was induced via oxidation of hydroquinones and hydroxynapjtaquinones with a use of Fenton’s reagent. The structure of the obtained products was characterized using NMR and FTIR spectroscopy. H/D labelling coupled to FT ICR mass spectrometry analysis was applied for identification of the reaction products as a tool for surmising on reaction mechanism. It was shown that covalent -C-C- bond were formed between the incorporated redox centers and aromatic core of HS. The parent humic acids and their naphthoquinonoid derivatives have demonstrated high accepting capacity. At the same time, fulvic acids and their hydroquinonoid derivatives have possessed both high donor and high antioxidant capacities. The kinetic studies have demonstrated that both humic acids and their derivatives showed much slower kinetics of antioxidant reactions as compared to fulvic acids. The obtained results show, firstly, substantial difference in redox and antioxidant properties of the humic and fulvic acids, and, secondly, they can serve as an experimental evidence that directed chemical modification of humic substances can be used to tune and control antioxidant properties of natural HS.

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