Renewable natural gas derived from biogas presents a viable pathway for decarbonizing natural gas systems. Wastewater treatment plants equipped with anaerobic digesters often flare or utilize biogas for heat and electricity generation, missing the potential of renewable natural gas. This study investigates the techno-economic feasibility and emission impact of a renewable natural gas system at a small wastewater treatment plant in the Southwestern United States. Due to a lack of existing data on biogas composition and contaminants from plants originating within the United States, samples were tested seasonally for a year, and gas components are reported in this analysis. Using hourly biogas production data, the analysis incorporates costs and renewable fuel credits at 2022 market prices and the cost to remove the biogas contaminants. The results show a 15-year net present value of USD 16.3 million, with a payback period of three years, surpassing the economic performance of combined heat and power systems previously assessed for the same facility. Additionally, renewable natural gas systems achieve a 22% reduction in site emissions compared to combined heat and power systems. These findings highlight renewable natural gas as a profitable and environmentally superior alternative for biogas utilization in small-scale wastewater treatment plants, contingent on access to renewable fuel credits.

In this study, pillar shaped yttria-stabilized zirconia (YSZ) 3D microstructures with ∼60 to 90 μm diameter and 12 to 20 μm height are fabricated by 3D inkjet printing to improve the topology of the electrolyte/cathode interface. The microstructures increase the surface area of the cell by ∼2.4% to 4.0% and enhance the connection between the dense YSZ electrolyte and mixed YSZ-lanthanum strontium manganite (LSM) cathode. The morphology and microstructure of the YSZ interface are characterized with scanning electron microscopy. Polarization curves confirm that the power density improves by 47% to 107% at 0.55 V, depending on the dimensions of the microstructures, in comparison to a flat interface. The non-linear improvement in power density with the size of microstructures is confirmed by calculating the uncertainty with repeated tests. Based on electrochemical impedance spectroscopy and distribution of relaxation times analysis, the performance improvement is attributed to changes in the oxygen surface exchange kinetics and O²⁻ diffusivity in the cathode.

Ethylene epoxidation is an important reaction forming ethylene oxide (EO), which is a precursor to many other critical chemicals. This study links short-term EO production to the effects on the microstructure of Ag/yttria-stabilized zirconia cells with and without electrochemical promotion of catalysis (EPOC). Nano-scale features, called striations, were observed on the silver under all epoxidation reaction conditions tested, using a scanning electron microscope. While appearing in both cases, the striations for the EPOC case are finer in size (∼150 to 250 nm) compared to the no current case (∼400 to 500 nm). These features did not appear when epoxidation conditions were not present. Striation formation was further linked to the epoxidation reaction through electrochemical impedance spectroscopy and gas chromatography. Ethylene conversion to EO declines over the course of hours as striations form, indicating that striations have a negative influence on the reaction. Distribution of relaxation times was performed to determine the effect striation formation has on the electrochemical performance of the cells. It was observed that the low-frequency peaks in the DRT analysis significantly decrease as striations formed over the course of 10 h.