The production of volatile fatty acids (VFAs) from waste stream has been recently getting attention as a cost-effective and environmentally friendly approach in mechanical–biological treatment plants. This is the first study to explore the use of a functional bacterium, AM5 isolated from forest soil, which is capable of enhancing the production of VFAs in the presence of soil bacteria as a co-digester in non-strict anaerobic fermentation processes of food waste leachates. Batch laboratory-scale trials were conducted under thermophilic conditions at 55 °C and different pH values ranging from approximately 5 to 11, as well as under uncontrolled pH for 15 days. Total solid content (TS) and volatile solid content (VS) were observed with 58.42% and 65.17% removal, respectively. An effluent with a VFA concentration of up to 33,849 mg/L (2365.57 mg/g VS; 2244.45 mg/g chemical oxygen demand (COD)-VFA VS; 1249 mg/g VSremoved) was obtained at pH 10.5 on the second day of the batch culture. The pH resulted in a significant effect on VFA concentration and composition at various values. Additionally, all types of VFAs were produced under pH no-adjustment (approximately 5) and at pH 10.5. This research might lead to interesting questions and ideas for further studies on the complex metabolic pathways of microbial communities in the mixture of a soil solution and food waste leachate.

The carbon dioxide (CO2) methanation reaction is a process that produces methane (CH4) by reacting CO2 and H2. Many studies have been conducted on this process because it enables a reduction of greenhouse gases and the production of energy with carbon neutrality. Moreover, it also exhibits a higher efficiency at low temperatures due to its thermodynamic characteristics; thus, there have been many studies, particularly on the catalysts that are driven at low temperatures and have high durability. However, with regards to employing this process in actual industrial processes, studies on both toxic substances that can influence catalyst performance and regeneration are still insufficient. Therefore, in this paper, the activity of a Ni catalyst before and after hydrogen sulfide (H2S) exposure was compared and an in-depth analysis was conducted to reveal the activity performance through the regeneration treatment of the poisoned catalyst. This study observed the reaction activity changes when injecting H2S during the CO2 + H2 reaction to evaluate the toxic effect of H2S on the Ni-Ce-Zr catalyst, in which the results indicate that the reaction activity decreases rapidly at 220 °C. Next, this study also successfully conducted a regeneration of the Ni-Ce-Zr catalyst that was poisoned with H2S by applying H2 heat treatment. It is expected that the results of this study can be used as fundamental data in an alternative approach to performance recovery when a small amount of H2S is included in the reaction gas of industrial processes (landfill gas, fire extinguishing tank gas, etc.) that can be linked to CO2 methanation.

It is urgent to determine suitable municipal sludge treatment solutions to simultaneously minimize the environmental negative impacts and achieve sustainable energy benefits. In this study, different sludge pretreatment techniques were applied and investigated to enhance the sludge solubility and, subsequently, facilitate the anaerobic biodegradation performance of the mixed sludge under different sludge concentrations and pretreatment techniques. The sludge characteristics before and after pretreatment and batch experiments of anaerobic digestion of sludge samples under different conditions were analyzed and discussed. The results showed that the mechanical pretreatment method, alone and in combination with low-temperature heat treatment, significantly improved the sludge solubility, with the highest solubility at 39.23%. The maximum biomethane yield achieved was 0.43 m3/kg after 10 d of anaerobic digestion of a 3% sludge sample subjected to mechanical and thermal pretreatment prior to anaerobic biodegradation. In comparison, it took more than 28 d to achieve the same biomethane production with the unpretreated sludge sample. Mechanical pretreatment and subsequent heat treatment showed a high ability to dissolve sludge and, subsequently, accelerate anaerobic digestion, thereby providing promising prospects for increasing the treatment capacity of existing and new sludge treatment plants.

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In this study, a pilot-scale reactor was designed and compared using computational fluid dynamics (CFD) for a high-efficiency CO2 methanation reaction. The trends of the CO2 methanation catalyst efficiency at a pilot or industrial scale could be lower than those measured at the laboratory scale, owing to the flow of fluid characteristics. Therefore, the CO2 methanation reactor was designed based on the results of the CFD analysis to minimize the above phenomenon. Ni–Ce–Zr was used to manufacture a CO2 methanation catalyst in the form of pellets. The catalyst successfully produced about 43.3 Nm3/d of methane from the reactor. This result shows that CO2 methanation, which is known as an exothermic reaction, was stable at the pilot scale. It is believed that the self-supply of energy will be possible when this CO2 methanation technology is applied to industrial processes generating large amounts of CO2 and H2 from by-product gases.