The effects of operational parameters such as carbon source, C/N ratio, initial nitrate concentration, temperature, and pH value on heterotrophic denitrification and functional denitrifying genes were evaluated. When methanol was used as the sole carbon source, complete denitrification was performed in a short time without nitrous oxide (N₂O) emission. Complete denitrification was performed at high C/N ratios (5.14 and 12.85) and low initial nitrate concentrations (75.9 and 151.6 mg N L⁻¹). The denitrification rate was not temperature-sensitive in the range of 25–35 °C, but tended to decrease at a low pH of 5–6. The relationships between N₂O emission and functional genes under various operational conditions were investigated by Pearson correlation and association network analyses. The C/N ratio was a key factor for N₂O emission during the heterotrophic denitrification process. This information on the denitrification performance and its association with functional gene dynamics under various operational conditions is useful for N₂O mitigation strategies for wastewater treatment processes.

Soils co-contaminated with petroleum hydrocarbons (PHs) and heavy metals pose significant challenges, such as reduced bioavailability of pollutants, toxic effects on soil microorganisms, and unpredictable chemical interactions. These complex interactions hinder effective remediation. Phytoremediation, which utilizes plant and microbial processes, offers a sustainable and eco-friendly approach. However, its effectiveness is often constrained by the intricate interplay among PHs, heavy metals, and soil components, which complicates pollutant degradation and microbial activity. This review explores the interactions between enhancement strategies, including soil amendments, plant growth-promoting bacteria (PGPB), and genetic engineering, which can synergistically enhance pollutant degradation and remediation efficiency. Key challenges include competition for soil adsorption sites among contaminants, microbial community disruptions, and environmental variability. Moreover, the limitations of these strategies, including their reliance on specific plant species, sensitivity to environmental variability, and the necessity for long-term monitoring, are discussed. The proposed solutions focus on integrating emerging technologies and interdisciplinary approaches to overcome these challenges and improve pollutant removal efficiency. Future advancements in interdisciplinary approaches, integrating biological techniques with technological innovations, are highlighted as key to addressing the complexities of co-contaminated environments and improving pollutant removal efficiency.

The chemical oxygen demand (COD) removal, electricity generation, and microbial communities were compared in 3 types of microbial fuel cells (MFCs) treating molasses wastewater. Single-chamber MFCs without and with a proton exchange membrane (PEM), and double-chamber MFC were constructed. A total of 10,000 mg L⁻¹ COD of molasses wastewater was continuously fed. The COD removal, electricity generation, and microbial communities in the two types of single-chamber MFCs were similar, indicating that the PEM did not enhance the reactor performance. The COD removal in the single-chamber MFCs (89–90%) was higher than that in the double-chamber MFC (50%). However, electricity generation in the double-chamber MFC was higher than that in the single-chamber MFCs. The current density (80 mA m⁻²) and power density (17 mW m⁻²) in the double-chamber MFC were 1.4- and 2.2-times higher than those in the single-chamber MFCs, respectively. The bacterial community structures in single- and double-chamber MFCs were also distinguishable. The amount of Proteobacteria in the double-chamber MFC was 2–3 times higher than those in the single-chamber MFCs. For the archaeal community, Methanothrix (96.4%) was remarkably dominant in the single-chamber MFCs, but Methanobacterium (35.1%), Methanosarcina (28.3%), and Methanothrix (16.2%) were abundant in the double-chamber MFC.