Bioresources and Bioproducts

Methane is a potent greenhouse gas that requires its emissions to be mitigated. A significant source for methane emissions is in the form of the biogas that is produced from anaerobic digestion in wastewater reclamation and landfill facilities. Biogas has a high valorization potential in the form of its bioconversion into ectoines, an active ingredient in skin care products, by halotolerant alkaliphilic methanotrophs. Cultures of Methylotuvimicrobium alcaliphilum 20Z were grown in bench scale stirred-tank reactors to determine factors to improve methane uptake and removal. Tangential flow filtration was also implemented for a bio-milking method to recover ectoine from culture media. Methane uptake and reactor productivity increased, with a temperature of 28 °C compared with 21 °C. Decreasing the methane gas bubble diameter by decreasing the sparger pore size from 1 mm to 0.5 µm significantly improved methane removal and reactor productivity by increasing mass transfer. Premixing methane and air before sparging into the reactor saw a higher removal of methane, while sparging methane and air separately created an increase in reactor productivity. Maximum methane removal efficiency was observed to be 70.56% ± 0.54 which translated to a CH₄-EC of 93.82 ± 3.36 g CH₄ m⁻³ h⁻¹. Maximum ectoine yields was observed to be 0.579 mg ectoine L⁻¹ h⁻¹.

Spontaneous combustion of charcoal is still not fully understood, generating uncertainties among producers, regulatory agencies, and the scientific community. This study evaluated the influence of final pyrolysis temperature (350, 450, 550, and 650 °C) on the properties of Eucalyptus spp. charcoal and its relation to ignition behavior. Gravimetric yield, proximate composition, calorific value, and ignition temperature were determined. Charcoal yield decreased by 31% between 350 °C and 650 °C. Fixed carbon content increased from ~65% to ~93%, accompanied by a reduction in volatile matter (~35% to ~6%) and a corresponding rise in calorific value. Step-heating experiments, conducted in a furnace with infrared camera monitoring, showed that ignition temperature increased from ~273 °C in charcoal produced at 350 °C to ~424 °C in charcoal produced at 650 °C. Strong correlations indicated that higher fixed carbon and lower volatile matter contents are directly associated with higher ignition temperatures. These results demonstrate that increasing the final pyrolysis temperature improves both the thermal stability and the energy quality of charcoal, although at the expense of gravimetric yield. Since the methodology was based on forced heating rather than spontaneous combustion under near-ambient conditions, complementary tests are required to evaluate spontaneous combustion propensity. Overall, the findings provide practical insights to balance yield, quality, and safety while reinforcing the importance of standardized assessment protocols to ensure safer storage and transport of charcoal.

The growing challenge of managing end-of-life creosote-treated railroad ties, along with the increasing demand for effective water treatment solutions, has highlighted the potential of converting railroad tie biomass into functional biochar through pyrolysis. Pyrolysis temperatures ranging from 250 °C to 700 °C were evaluated to determine their influence on biochar yield, physicochemical properties, and adsorption performance for nitrate and phosphate. The findings revealed that increasing pyrolysis temperature enhanced biochar surface area and porosity, reaching 454.9 m²/g at 700 °C. Elemental analyses showed maximum carbonization at 550 °C, with carbon content peaking at 80%, reflecting the development of more stable aromatic structures. SEM and FTIR analyses confirmed these structural changes, including the emergence of extensive pore networks and aromatic frameworks. Biochar produced at 600 °C demonstrated high nitrate (80%) and phosphate (79%) removal efficiencies, following Freundlich isotherm models. Magnesium-modified biochar further improved nitrate adsorption, reaching 90% removal at 5 ppm. Importantly, polycyclic aromatic hydrocarbons in the biochar decreased significantly at higher temperatures, ensuring environmental safety. This work demonstrates the dual environmental benefits of converting hazardous railroad tie waste into value-added biochar for nutrient removal in water treatment applications, offering a sustainable and scalable solution for circular waste management.