This work investigates olive pomace from olive mill factories as an adsorbent for the removal of total phenols from olive mill effluent (OME). This pathway of valorization of olive pomace reduces the environmental impact of OME while providing a sustainable and cost-effective wastewater treatment approach for the olive oil industry. Olive pomace was pretreated with water washing, drying (60 °C) and sieving (<2 mm) to obtain the raw olive pomace (OPR) adsorbent material. Olive pomace biochar (OPB) was obtained via carbonization of OPR at 450 °C in a muffle furnace. The adsorbent materials OPR and OPB were characterized using several basic analyzes (Scanning Electron Microscopy–Energy-Dispersive X-ray SEM/EDX, X-ray Diffraction XRD, thermal analysis DTA and TGA, Fourier transform infrared FTIR and Brunauer, Emmett and Teller surface BET). The materials were subsequently tested in a series of experimental tests to optimize the sorption of polyphenols from OME, investigating the effects of pH and adsorbent dose. Adsorption kinetics showed good correlation with a pseudo-second-order kinetic model as well as Langmuir isotherms. Maximum adsorption capacities amounted to 21.27 mg·g⁻¹ for OPR and 66.67 mg·g⁻¹ for OPB, respectively. Thermodynamic simulations indicated spontaneous and exothermic reaction. The rates of total phenol removal were within the range of 10–90% following 24 h batch adsorption in OME diluted at 100 mg/L total phenols, with the highest removal rates observed at pH = 10. Furthermore, solvent regeneration with 70% ethanol solution yielded partial regeneration of OPR at 14% and of OPB at 45% following the adsorption, implying a significant rate of recovery of phenols in the solvent. The results of this study suggest that adsorbents derived from olive pomace may be used as economical materials for the treatment and potential capture of total phenols from OME, also suggesting potential further applications for pollutants in industrial wastewaters, which can have significant implications in the field of environmental technologies.

Batch biochemical methane potential (BMP) assays to evaluate the methane yield of biogas substrates such as energy crops are usually carried out with undiluted inoculum. A BMP assay was performed on two energy crops (green cuttings and grass silage). Anaerobic digestion was performed both with and without supplementation of three commercial additives containing trace metals in liquid, solid or adsorbed form (on clay particles). In order to reveal positive effects of trace metal supplementation on the methane yield, besides undiluted inoculum, 3-fold and 10-fold dilutions of the inoculum were applied for substrate digestion. Diluted inoculum variants were supplemented with both mineral nutrients and pH-buffering substances to prevent a collapse of the digestion process. As expected, commercial additives had no effect on the digestion process performed with undiluted inoculum, while significant increases of methane production through trace element supplementation could be observed on the diluted variants. The effect of inoculum dilution may be twofold: (1) decrease in trace metal supplementation from the inoculum and (2) reduction in the initial number of bacterial cells. Bacteria require higher growth rates for substrate degradation and hence have higher trace element consumption. According to common knowledge of the biogas process, periods with volatile fatty acids accumulation and decreased pH may have occurred in the course of anaerobic digestion. These effects may have led to inhibition, not only of methanogenes and acetogenes involved in the final phases of methane production, but also of fibre-degrading bacterial strains involved in polymer hydrolysis. Further research is required to confirm this hypothesis.

Poultry farms with floor-standing poultry generate large amounts of poultry litter waste. The direct application of this waste as an organic fertilizer does not ensure sustainable and cost-efficient utilization of all waste fractions, and can also be linked to environmental hazards. Therefore, the development of new technologies is required for processing poultry litter into a safe product with higher added value. In this work, the characteristics of activated carbon derived from hydrochar, along with the liquid products obtained from hydrothermal carbonization (HTC) and the wet torrefaction (WT) of poultry litter, were investigated. Poultry litter (PL) was applied in a mixture with sawdust (SD) in the following ratios: 1:0 (PL/SD 1:0), 1:1 (PL/SD 1:1), 1:2 (PL/SD 1:2), and 2:1 (PL/SD 2:1). WT processing took place in an innovative fluidized bed system in a superheated steam medium with low overpressure (less than 0.07 MPa) at 300 °C and 350 °C for 30–45 min. Conventional HTC processing was performed in a water medium at 220 °C for 1–4 h. The hydrochar produced in the experiments was activated with steam for 1 h at 450–750 °C. The porosity characteristics of activated hydrochar were measured, including pore size, pore volume, and specific surface area, in view of potential industrial applications as an adsorbent. Additionally, the contents of 5-hydroxymethylfurfural (HMF), as high-value product, were determined in the liquid products obtained from HTC processing, as well as in the condensate obtained after WT processing. Specific surface areas of the activated hydrochars may still be too low for application as adsorbent material. Hence, its use as a biofertilizer and soil improver should be preferred. Interestingly, the liquid fraction obtained from the innovative WT process displayed a significantly higher 5-HMF content compared to the conventional HTC process.

This work investigated the effect of experimental conditions of dry and wet torrefaction on the properties of olive leaves and olive pomace. Torrefaction improved the fuel properties of olive waste. According to Van Krevelen parameters (O/C and H/C ratios), torrefied biomass, tested as solid biofuel, achieved a similar quality threshold to lignite. For example, dry torrefaction conducted at 230 °C for 80 min reduced the O/C and H/C ratios of olive leaves from 0.51 and 1.51 for raw biomass to 0.25 and 1.17 for torrefied biomass, respectively. Under the same conditions, the O/C and H/C ratios of olive pomace were also reduced from 0.34 and 1.60 to 0.27 and 1.36, respectively. Calorific values of raw olive leaves and olive pomace amounted to 18.0 and 23.2 MJ/kg, respectively. Following dry torrefaction and biomass conversion into biochar, calorific values of olive leaves and olive pomace increased by 24% and 14% up to 22.2 and 26.3 MJ/kg through dry torrefaction, compared with 17% and 23% increments up to 21.1 and 28.5 MJ/kg through wet torrefaction, respectively. Interestingly, biomass processing through wet torrefaction performed in a fluidized bed powered by superheated steam could be completed 8- to 12-fold more rapidly than dry torrefaction. SEM analysis indicated a breakdown of the surface structure of olive waste following the torrefaction process. According to the Brunauer–Emmett–Teller (BET) method, total pore surface areas of biochar obtained from wet torrefaction of olive pomace and olive leaves amounted to 3.6 m²/g and 0.8 m²/g, with total pore volumes amounting to 0.0225 cm³/g and 0.0103 cm³/g, respectively. Maximal contents of 5-hydroxymethylfurfural and furfural in liquid by-products from dry torrefaction amounted to 1930 and 1880 mg/1 kg, respectively. Alternately, in liquid by-products from wet torrefaction, concentrations of these high-value compounds remained very low.

Torrefaction is a technology for the preliminary thermochemical treatment of biomass in order to improve its fuel characteristics. The aim of this work is to conduct comparative studies and select the optimal operating conditions of fluidized bed torrefaction for the processing of poultry litter (PL) into an environmentally friendly fuel. PL torrefaction was evaluated according to three different process configurations: (1) torrefaction of PL pellets in a fixed bed in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT1, NT2 and NT3); (2) torrefaction of PL pellets in a fluidized bed of quartz sand in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT4, NT5 and NT6); and (3) torrefaction of PL pellets in a fluidized bed of quartz sand in an environment of superheated steam at temperatures of 250 °C, 300 °C and 350 °C (ST1, ST2 and ST3). The duration of the torrefaction process in all experiments was determined by the time required for completion of CO₂, CO, H₂, and CH₄ release from the treated biomass samples. The gas analyzer (Vario Plus Syngaz) was used to measure the concentration of these gases. The torrefaction process began from the moment of loading the PL sample into the reactor, which was heated to the required temperature. After the start of the torrefaction process, the concentration of CO₂, CO, H₂, and CH₄ in the gases leaving the reactor initially increased and, subsequently, dropped sharply, indicating the completion of the torrefaction process. The chemical composition of the obtained biochar was studied, and it was found that the biochar contained approximately equal amounts of oxygen, carbon, nitrogen, hydrogen and ash, regardless of the torrefaction method. Furthermore, the biogas yield of the liquid condensate, obtained from the cooling of superheated steam used in the torrefaction process, was evaluated. The results highlight the efficiency of fluidized bed torrefaction, as well as the performance of superheated steam as a fluidization medium.