Hou-Yun Yang

Bioelectromethanogenesis, the microbial conversion of carbon dioxide (CO₂) into methane (CH₄) using a cathode, offers a promising route for biogas upgrading and renewable energy storage. The flow field is an essential factor influencing the performance of bioelectromethanogenesis, and the stability and efficiency of the biocathode play important roles in this process. This study systematically investigated the effect of different internal-circulation flow rates on the biocathode initiated without the electric field and the reactor effluent. It was found that the methane production of the biocathode initiated without the electric field was increased by around 30% at an internal-circulation flow rate of 18 mL/min, which was stronger than that of the biocathode initiated by the reactor effluent. The relative content of the extracellular polymeric substance (EPS) heme was increased by 4%, while the EPS electron accepting capacity was much higher than that initiated by reactor effluent. Furthermore, the microbial community analysis showed that the functional methanogen on the biocathode initiated without an electric field was Methanosaeta (17%) and Methanobacterium (8%). This study could provide support for the dynamic operation of biogas upgrading in microbial electrolysis cells.

Poly(butylene adipate-co-terephthalate) (PBAT) wastewater, characterized by high chemical oxygen demand (COD) and acidity, poses significant challenges to anaerobic digestion (AD) due to toxicity and volatile fatty acids (VFAs) accumulation. This study coupled granular activated carbon (GAC) and waste iron scraps (WISs) to synergistically enhance AD performance. Batch experiments demonstrated that, compared with the control, the GAC/WISs group achieved a COD removal efficiency of 53.18% and a methane production of 207.53 ± 5.80 mL/g COD, which were 5.48- and 12.14-fold increases, respectively, while reducing the accumulation of total VFAs by 98.48% (to 15.09 mg/L). Mechanistic analysis revealed that GAC adsorbed inhibitors and enriched methanogens, while WISs buffered pH and promoted direct interspecies electron transfer (DIET) through hydrogenotrophic methanogenesis. Metagenomic sequencing showed shifts in microbial communities, with enrichment of syntrophic bacteria (Syntrophobacter) and functional genes (pta, bcd, and pccA), indicating metabolic reprogramming. This study provided a theoretical foundation and engineering strategy for the anaerobic treatment of PBAT wastewater.

Constructed wetland-microbial fuel cell (CW-MFC) has excellent effect and potential in wastewater treatment based on many factors, such as fillers, hydraulic retention time (HRT), influent chemical oxygen demand (COD) concentration, and plants. This study explored the influence of fillers, influent COD concentrations, and HRT on the performance of CW-MFC systems to optimize the operation. Two CW-MFCs with pyrite and activated carbon as anode materials (PCW-MFC and ACW-MFC) were set up, respectively. The results showed that prolonging HRT of the systems could improve the nutrients’ removal efficiency and voltage output. The influent COD concentration had a positive import on the removal efficiency of COD, nitrate-nitrogen (NO ₃ ⁻ -N), and total phosphorus (TP) in CW-MFCs. On the contrary, the removal efficiency of ammonia-nitrogen (NH ₄ ⁺ -N) decreased and the voltage change showed a trend of increasing first and then decreasing with the increase of COD concentration. The optimal operating conditions of CW-MFCs were COD of 200 mg/L and HRT of 24 h. Moreover, it found that the overall performance of PCW-MFC was better than that of ACW-MFC. Microbial community analysis evaluated that the abundance of autotrophic denitrifying bacteria Thiobacillus , Dechloromonas , and Pseudomonas in the cathode layer of PCW-MFC was higher than that of ACW-MFC, indicating that pyrite could effectively promote the bacterial reproduction of nitrogen and phosphorus removal and electrogenesis.

Oxidation ditch and Anaerobic–Anoxic–Oxic (A²/O) processes have been applied in urban wastewater treatment plants for decades, but the differences between two processes in engineering applications are less studied. Based on the continuous monitoring of Ningyang’s sewage treatment plant (Shandong, China) for one year, this study systematically analyzed the removal efficiencies of nutrients in the oxidation ditch and the modified high-efficiency multi-cycle A²/O processes. The results showed that chemical oxygen demand (COD) and total phosphorus (TP) removal in the modified high-efficiency multi-cycle A²/O process of the Phase II project was better than that in the oxidation ditch process of the Phase I project, and the average concentration of COD and TP in the effluent was 49.9% and 51.7% lower than that in the oxidation ditch process, respectively. The removal rate of ammonia nitrogen (NH₄⁺-N) by the two processes was basically the same, while the total nitrogen (TN) effluent concentration of the oxidation ditch process was 31.4% lower than that in the high-efficiency multi-cycle A²/O process. In summary, the high-efficiency multi-cycle A²/O process had a better treatment performance regarding nutrient removal than the oxidation ditch process under the same conditions. Furthermore, the engineering and operational costs of the high-efficiency multi-cycle A²/O process were lower.

Under the background of carbon neutrality, the constructed wetland-microbial fuel cell coupled system (CW-MFC) has attracted more and more attention in wastewater treatment. This study, the CW-MFC was developed for promoting nutrients removal in wastewater and electricity generation. The results showed that the average removal efficiencies of COD, NH₄⁺-N and TP in CW-MFC were 85.20%, 75.99% and 59.20%, respectively. While the average removal efficiencies of COD, NH₄⁺-N and TP in CW were 78.05%, 70.88% and 50.80%, which were all lower than those in CW-MFC. In addition, the maximum output voltage of 331 mV was achieved in CW-MFC, which could be used for the running of wastewater treatment plant in turn and further reduce the consumption of fossil fuel. Accordingly, the maximum power density of the CW-MFC system reached to 107.54 mW m^-3.