Simultaneous removal of ammonia nitrogen, recovery of phosphate, and immobilization of nickel in a polyester fiber with shell powder and iron carbon spheres bioreactor: Optimization and pathways mechanism

Simultaneous removal of nitrogen, phosphorus, and organic matter from oligotrophic water in a system containing biochar and construction waste iron: Performances and biotic community analysis

The issue of combined pollution in oligotrophic water has garnered increasing attention in recent years. To enhance the pollutant removal efficiency in oligotrophic water, the system containing Zoogloea sp. FY6 was constructed using polyester fiber wrapped sugarcane biochar and construction waste iron (PWSI), and the denitrification test of simulated water and actual oligotrophic water was carried out for 35 days. The experimental findings from the systems indicated that the removal efficiencies of nitrate (NO3--N), total nitrogen (TN), chemical oxygen demand (COD), and total phosphorus (TP) in simulated water were 88.61%, 85.23%, 94.28%, and 98.90%, respectively. The removal efficiencies of actual oligotrophic water were 83.06%, 81.39%, 81.66%, and 97.82%, respectively. Furthermore, the high-throughput sequencing data demonstrated that strain FY6 was successfully loaded onto the biological carrier. According to functional gene predictions derived from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, the introduction of PWSI enhanced intracellular iron cycling and nitrogen metabolism.

Microbially driven Fe-N cycle: Intrinsic mechanisms, enhancement, and perspectives

The iron‑nitrogen (FeN) cycle driven by microbes has great potential for treating wastewater. Fe is a metal that is frequently present in the environment and one of the crucial trace elements needed by microbes. Due to its synergistic role in the microbial N removal process, Fe goes much beyond the essential nutritional needs of microorganisms. Investigating the mechanisms behind the linked Fe-N cycle driven by microbes is crucial. The Fe-N cycle is frequently connected with anaerobic ammonia oxidation (anammox), nitrification, denitrification, dissimilatory nitrate reduction to ammonium (DNRA), Feammox, and simultaneous nitrification denitrification (SND), etc. Although the main mechanisms of Fe-mediated biological N removal may vary depending on the valence state of the Fe, their similar transformation pathways may provide information on the study of certain element-microbial interactions. This review offers a thorough analysis of the facilitation effect and influence of Fe on the removal of nitrogenous pollutants in various biological N removal processes and summarizes the ideal Fe dosing. Additionally, the synergistic mechanisms of Fe and microbial synergistic N removal process are elaborated, covering four aspects: enzyme activity, electron transfer, microbial extracellular polymeric substances (EPS) secretion, and microbial community interactions. The methods to improve biological N removal based on the intrinsic mechanism were also discussed, with the aim of thoroughly understanding the biological mechanisms of Fe in the microbial N removal process and providing a reference and thinking for employing Fe to promote microbial N removal in practical applications.

Enhanced ammonia nitrogen and phenol removal by immobilized bacteria through composite mycelium pellet-driven quinone redox cycle

The composite mycelium pellet (CMP) was coupled with Pseudomonas sp. Y1 (CMP-Y1) to remove phenol and ammonia nitrogen (NH4+-N). The CMP was formed by the self-assembly of fungal mycelium with sponge iron (SIO), gallic acid (GA), and oxalic acid. The results showed that CMP with abundant pore size and successful internal loading of sponge iron containing iron nanoparticles. CMP could induce GA redox cycle to form Fenton-like reaction and thus achieve efficient phenol removal (93.32%, 24 h). Meanwhile, the removal efficiencies of phenol, NH4+-N, and chemical oxygen demand (COD) using CMP-Y1 at 12 h were 93.71, 92.40, and 89.00%, respectively. The increase in the electron transfer activity of strain Y1 by the addition of CMP could facilitate the nitrogen removal processes. In addition, high-throughput sequencing results indicated the abundance of antioxidant and repair genes was increased, which might be a strategy of strain Y1 to cope with oxidative stress. This strategy provided the possibility for the practical application of the combination of advanced oxidation and biological treatment, and offered new insights into the symbiotic system of fungi and bacteria.

Hydrogel bioreactor drives Feammox and synergistically removes composite pollutants: Performance optimization, microbial communities and functional genetic differences

Mixed pollutant wastewater has been a difficult problem due to the high toxicity of water bodies and the difficulty of treatment. Rice husk biochar modified with nano-iron tetroxide (RBC-nFe3O4) by polyvinyl alcohol cross-linking internal doping was used to introduce iron-reducing bacteria Klebsiella sp. FC61 to construct a bioreactor. The results of the long-term operation of the bioreactor showed that the removal efficiency of ammonia nitrogen (NH4+-N) and chemical oxygen demand best reached 90.18 and 98.49%, respectively. In addition, in the co-presence of Ni2+, Cd2+, and ciprofloxacin, the bioreactor was still able to remove pollutants efficiently by RBC-nFe3O4 and bio-iron precipitation inside the biocarrier. During the long-term operation, Klebsiella was always the dominant species in the bioreactor. And the sequencing data for functional prediction showed that the biocarrier contained a variety of enzymes and proteins involved in Feammox-related activities to ensure the stable and efficient operation of the bioreactor.

Nano iron tetroxide-modified rice husk biochar promoted Feammox performance of Klebsiella sp. FC61 and synergistically removed Ni2+ and ciprofloxacin

The iron reduction coupled with ammonia oxidation process (Feammox) is a biological reaction process associated with the nitrogen cycle that has been discovered in recent years. In this study, the iron-reducing bacterium Klebsiella sp. FC61 was attached by synthesizing nano-loadings of iron tetroxide (nFe₃O₄) onto rice husk biochar (RBC), and the RBC-nFe₃O₄ was used as an electron shuttle to participate in the biological iron reduction process of soluble and insoluble Fe³⁺ to improve the ammonia oxidation efficiency to 81.82%. This acceleration of electron transfer increased the carbon consumption rate and further tuned up the COD removal efficiency to 98.00%. The Feammox could be coupled with iron denitrification for internal nitrogen/iron cycling to reduce the accumulation of nitrate by-products and achieve the recycling of iron. In addition, pollutants such as Ni²⁺, ciprofloxacin, and formed chelates could be removed by pore adsorption and π-π interactions using bio-iron precipitates produced by iron-reducing bacteria.