This study investigates the pyrolysis behavior and reaction kinetics of two different types of solid digestates from: (i) sewage sludge and (ii) a mixture of sewage sludge and lignocellulosic biomass—Typha latifolia plant. Thermogravimetric data in the temperature range 25–800 °C were analyzed using Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose kinetic methods, and the thermodynamic parameters ($\mathsf{\Delta }H$, $\mathsf{\Delta }G$, and $\mathsf{\Delta }S$) were also determined. Biochars were characterized using different chemical methods (FTIR, SEM–EDS, XRD, heavy metal, and nutrient analysis) and tested as soil enhancers using a germination test. Finally, their potential for biosorption of NH₄⁺, PO₄³⁻, Cu²⁺, and Cd²⁺ ions was studied. Kinetic and thermodynamic parameters revealed a complex degradation mechanism of digestates, as they showed higher activation energies than undigested materials. Values for sewage sludge digestate were between 57 and 351 kJ/mol, and for digestate composed of sewage sludge and T. latifolia between 62 and 401 kJ/mol. Characterizations of biochars revealed high nutrient content and promising potential for further use. The advantage of biochar obtained from a digestate mixture of sewage sludge and lignocellulosic biomass is the lower content of heavy metals. Biosorption tests showed low biosorption capacity of digestate-derived biochars and their modifications for NH₄⁺ and PO₄³⁻ ions, but high biosorption capacity for Cu²⁺ and Cd²⁺ ions. Modification with KOH was more efficient than modification with HCl. The digestate-derived biochars exhibited excellent performance in germination tests, especially at concentrations between 6 and 10 wt.%.

This article presents a comprehensive on-site bioremediation of an excavated diesel fuel-contaminated soil aided by various soil amendments and plant species. In the first 125 days, the excavated soil was placed in a land treatment unit, mixed with compost, and seeded with white clover (Trifolium repens). In the next 155 days, the land treatment unit was re-established and divided into four experimental plots. Experimental plots 2 and 3 were seeded with a mixture of plant seeds (Trifolium alexandrinum, Fagopyrum esculentum Moench, Trifolium incarnatum, Phacelia tanacetifolia, Sinapis alba, Trifolium repens), while experimental plots 1 and 4 were left without seeded vegetation. Moreover, a zeolite and an Ascophyllum nodosum-based biostimulant were added to experimental plots 3 and 4. The objectives were to select the most beneficial plant species for the plant-based bioremediation process, to evaluate applicability of different soil amendments for an enhanced hydrocarbon biodegradation, and to study their effects on the microbial community in soil. Our results showed an overall reduction in hydrocarbon pollution by more than 95% within 280 days. The rates of hydrocarbon degradation and changes in the microbial population were not affected by the presence of the zeolite and the biostimulant. In addition, the use of different plant species did not have a statistically significant effect on hydrocarbon degradation but affected microbial population dynamics, confirming stabile and diverse indigenous hydrocarbon-degrading microbial community in the native soil.

The petroleum industry is often faced with accidental spills and discharges that pollute valuable natural resources such as soil. The purpose of this study was to assess bioremediation potential of an on-site landfarming unit (LU), a highly economical solution that complies with the zero-waste policy, for bioremediation of the contaminated soil after an actual diesel fuel leakage in a fuel depot. The first aim was to evaluate the effects of different climates on hydrocarbon bioremediation. For this reason, a part of the contaminated soil was moved from the initial location with a sub-Mediterranean climate to an LU at another location with a temperate continental climate. Our results demonstrated that remediation in sub-Mediterranean climate is less effective than the remediation in a temperate continental climate. The second aim of this study was to evaluate the effect of different plant species on the microbial population during bioremediation. For that purpose, 365-day monitoring of phospholipid fatty acids (PLFA) was performed. Our results support the hypothesis that plant-assisted bioremediation can diminish toxic effects of diesel-polluted soil and that the changes in plant species during bioremediation cause changes in the microbial population. The main objective of this study was to implement a landfarming bioremediation technique after an actual diesel fuel pollution in the sub-Mediterranean climate and diminish toxic effects of pollutants in soil. Since soil bioremediation is performed by soil microorganisms, their communities are primarily affected by the growing vegetation and climatic conditions. For future bioremediation strategies or ex situ approaches, it is crucial to assess the influence of a specific climate on the degradation rate of hydrocarbons in soil and select the most efficient plant species for this purpose.

Due to its complex composition and toxicity, the waste liquid from hydrothermal carbonization (HTC) poses a serious environmental challenge that must be addressed before disposal. In this study, the photochemical treatment of HTC liquid in a microreactor flow system was investigated. The effects of wavelength, the presence of atmospheric oxygen, oxidizing agent (H₂O₂) and catalyst (FeSO₄), residence time and pH on the efficiency of the photo-treatment were investigated. In addition, the influence of the addition of deep eutectic solvent (DES) on photo-treatment was studied. The results showed that the photochemical treatment was more efficient at 365 nm than at 420 nm, and that the acidic conditions gave better results than the basic ones. UV₃₆₅ treatment in the presence of H₂O₂ (at a dosage of 1 vol%) resulted in removal efficiencies of 31.6% for COD, 17.6% for TOC, 16.9% for NH₄-N and 17.2% for PO₄-P. The addition of FeSO₄ caused coagulation/flocculation effects, but improved phosphorus removal. The addition of DES resulted in slight discolouration of the liquid and proved unsuccessful in COD removal. The GC-MS analysis and 3D-EEM spectra showed significant changes in the fate of organics and in the fluorescence intensity of aromatic proteins and humic acid-like substances. Photochemical treatment in a microreactor flow system in the presence of H₂O₂ under the selected operating conditions reduced the content of organics and nutrients in the HTC liquid, but the process liquids still showed toxic effects on the organisms V. fischeri and Daphnia magna.