Annually, the olive oil industry generates a significant amount of by-products, such as olive pomace, olive husks, tree prunings, leaves, pits, and branches. Therefore, the recovery of these residues has become a major challenge in Mediterranean countries. The utilization of olive industry residues has received much attention in recent years, especially for energy purposes. Accordingly, this primary experimental study aims at investigating the potential of olive biomass waste for energy recovery in terms of synthesis gas (or syngas) production using the thermal arc plasma gasification method. The olive charcoal made from the exhausted olive solid waste (olive pomace) was chosen as a reference material for primary experiments with known composition from the performed proximate and ultimate analysis. The experiments were carried out at various operational parameters: raw biomass and water vapour flow rates and the plasma generator power. The producer gas involved principally CO, H₂, and CO₂ with the highest concentrations of 41.17%, 13.06%, and 13.48%, respectively. The produced synthesis gas has a lower heating value of 6.09 MJ/nm³ at the H₂O/C ratio of 3.15 and the plasma torch had a power of 52.2 kW.

The depletion and usage of fossil fuels causes environmental issues and alternative fuels and technologies are urgently required. Therefore, thermal arc water vapor plasma for a fast and robust waste/biomass treatment is an alternative to the syngas method. Waste cooking oil (WCO) can be used as an alternative potential feedstock for syngas production. The goal of this experimental study was to conduct experiments gasifying waste cooking oil to syngas. The WCO was characterized in order to examine its properties and composition in the conversion process. The WCO gasification system was quantified in terms of the produced gas concentration, the H₂/CO ratio, the lower heating value (LHV), the carbon conversion efficiency (CCE), the energy conversion efficiency (ECE), the specific energy requirements (SER), and the tar content in the syngas. The best gasification process efficiency was obtained at the gasifying agent-to-feedstock (S/WCO) ratio of 2.33. At this ratio, the highest concentration of hydrogen and carbon monoxide, the H₂/CO ratio, the LHV, the CCE, the ECE, the SER, and the tar content were 47.9%, 22.42%, 2.14, 12.7 MJ/Nm³, 41.3% 85.42%, 196.2 kJ/mol (or 1.8 kWh/kg), and 0.18 g/Nm³, respectively. As a general conclusion, it can be stated that the thermal arc-plasma method used in this study can be effectively used for waste cooking oil gasification to high quality syngas with a rather low content of tars.

A gliding arc discharge (GAD) plasma device has been developed and tested. Possible applications areas for GAD plasma could be microalgae suspension treatments and the creation of plasma-activated water. To understand its behavior, the influence of the input power on the electrical characteristics of the generated GAD plasma was investigated using an oscilloscope. The waveforms of the voltage and current of GAD plasma are presented. The duration of the discharge time and the evolution of the arc during discharge were determined and investigated. It was revealed that the increase in the output voltage prolonged the duration of the arc discharge. The composition of the air plasma was investigated using a flame-emission spectrometer and acousto-optic emission spectrometer. It was revealed that the main species in the emission spectra of the GAD air plasma were N₂, N₂⁺, N⁺, NO, and O species. Furthermore, the increase in the input power enhanced the ionization degree of the air plasma and increased the intensities of the emission lines associated with N₂⁺, NO, and O species. An increase in the conductivity of the BG-11 medium was observed. Physicochemical analyses of the plasma-activated BG-11 medium indicated an increase in the concentration of nitrite and nitrate ions and hydrogen peroxide with an enhancement of the voltage.

In this work, gliding arc discharge (GAD) was used to produce air plasma and investigate the influence of the discharge parameters on the composition of the air plasma, vibrational temperatures, and the production of NO_x. It was demonstrated that the main particles obtained in the GAD air plasma were N₂*, N₂⁺, N⁺, NO_γ, and O. It was observed that the reduction in the discharge frequency increased the intensity of the excited nitrogen molecules lines and reduced the nitric oxide (NO) and nitrogen dioxide (NO₂) gas concentrations. The increase in the output voltage prolonged the duration of arc discharge and enhanced the intensities of the emission lines of the N₂⁺, O, and NO_γ species and the concentrations of NO and NO₂ gasses. It was shown that the increase in the air flow rate from 6.7 L/min to 15.6 L/min decreased the concentration of the produced NO gas by 24%. Additionally, the line intensities of all main species in air plasma were enhanced. Studies have shown that the NO and NO₂ gas concentrations (selectivity of NO and NO₂) can be controlled by varying the air flow, output voltage, and discharge frequency. The highest NO_x concentration of 2380 ppm was produced at 250 V, when the direct air flow was 11.2 L/min.

The global coronavirus (COVID-19) pandemic in early 2020 caused the amount of medical waste, especially plastic waste, to increase. The pandemic exacerbated the plastic waste management problem, including the need to find more sustainable treatment methods. This study investigated the sustainable conversion of plastic waste (FFP2-type face masks) to syngas via pure CO₂ plasma gasification to recover energy and reduce environmental pollution. A direct current (DC) thermal arc plasma torch of 40.6–68.4 kW power generated the plasma stream. Carbon dioxide (CO₂), as a greenhouse gas (GHG), was used as the main plasma-forming gas and gasifying agent. The 140_thermal feedstock input plasma gasification system was used in the study. The effect of the CO₂-to-C ratio on the gasification performance efficiency was investigated. The best CO₂ plasma gasification process performance was obtained at a CO₂-to-C ratio of 2.34. In these conditions, the main syngas components (H₂ + CO) comprised 80.46 vol.% (H₂: 24.62 vol.% and CO: 55.84 vol.%) and the following values were seen for the heating value of the syngas (LHV_syngas: 13.88 MJ/Nm³), the syngas yield (3.13 Nm³/kg_FFP2), the tar content in the syngas (23.0 g/Nm³), the carbon conversion efficiency (CCE: 70.6%), and the cold gas efficiency (CGE: 47.8%). Additionally, the plasma gasification process mass and energy balance were evaluated. It was demonstrated that CO₂ plasma gasification could be a promising thermochemical treatment technology for sustainable plastic waste disposal and the simultaneous utilization of greenhouse gases, such as carbon dioxide.