Synergistic removal of nitrate by a cellulose-degrading and denitrifying strain through iron loaded corn cobs filled biofilm reactor at low C/N ratio: Capability, enhancement and microbiome analysis

Simultaneous removal of ammonia nitrogen, calcium and cadmium in a biofilm reactor based on microbial-induced calcium precipitation: Optimization of conditions, mechanism and community biological response

With the enhancement of environmental governance regulations, the discharge requirements for reverse osmosis wastewater have become increasingly stringent. This study proposes an innovative approach utilizing heterotrophic nitrification and aerobic denitrification (HNAD)-based biomineralization technology, combined with coconut palm silk loaded biochar, to offer a novel solution for resource-efficient and eco-friendly treatment of reverse osmosis wastewater. Zobellella denitrificans sp. LX16 were loaded onto modified coir silk and showed removal efficiencies of up to 97.38, 94.58, 86.24, and 100% for NH4+-N (65 mg L-1), COD (900 mg L-1), Ca2+ (180 mg L-1), and Cd2+ (25 mg L-1). Analysis of the metabolites of microorganisms reveals that coconut palm silk loaded with deciduous biochar (BCPS) not only exerts a protective effect on microorganisms, but also enhances their growth, metabolism, and electron transfer capabilities. Characterization of precipitation phenomena elucidated the mechanism of Cd2+ removal via ion exchange, precipitation, and adsorption. Employing high-throughput and KEGG functional analyses has confirmed the biota environmental response strategies and the identification of key genes like HNAD.

Denitrification driven by additional ferrous (Fe2+) and manganous (Mn2+) and removal mechanism of tetracycline and cadmium (Cd2+) by biogenic Fe-Mn oxides

Zoogloea sp. MFQ7 achieved excellent denitrification of 91.71% at ferrous to manganous ratio (Fe/Mn) of 3:7, pH of 6.5, nitrate concentration of 25 mg L-1 and carbon to nitrogen ratio of 1.5. As the Fe/Mn ratio increasd, the efficiency of nitrate removal gradually decreased, indicating that strain MFQ7 had a higher affinity for Mn2+ than Fe2+. In situ generated biogenic Fe-Mn oxides (BFMO) contained many iron-manganese oxides (MnO2, Mn3O4, FeO(OH), Fe2O3, and Fe3O4) as well as reactive functional groups, which play an significant part in tetracycline (TC) and cadmium (Cd2+) adsorption. The adsorption of TC and Cd2+ by BFMO can better fit the pseudo-second-order and Langmuir models. In addition, multiple characterization results of before and after adsorption indicated that the removal mechanism of BFMO on TC and Cd2+ was probably surface complexation adsorption and redox reactions.

Simultaneous removal of calcium, cadmium and tetracycline from reverse osmosis wastewater by sycamore deciduous biochar, shell powder and polyurethane sponge combined with biofilm reactor

The treatment of reverse osmosis concentrate generated from urban industrial sewage for resource recovery has been hot. In this research, a biofilm reactor was constructed by combining sycamore deciduous biochar, shell powder, and polyurethane sponge loaded with Zobellella denitrificans sp. LX16. For ammonia nitrogen (NH4+-N), calcium (Ca2+), chemical oxygen demand (COD), cadmium (Cd2+), and tetracycline (TC), the removal efficiencies were 98.69 %, 83.95 %, 97.26 %, 98.34 %, and 69.12 % at a hydraulic retention time (HRT) of 4 h, pH of 7.0, and influent salinity, Ca2+, and TC concentrations of 1.0, 180.0, and 3.0 mg/L, respectively. The biofilm reactor packing has a three-dimensional structure to ensure good loading of microorganisms while promoting electron transfer and metabolic activity of microorganisms and increasing the pollutant tolerance and removal efficiency. The reactor provides a practical reference for the sedimentation of reverse osmosis concentrate to remove Cd2+ and TC by microbial induced calcium precipitation (MICP).

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.

Microbial induced calcium precipitation by Zobellella denitrificans sp. LX16 to simultaneously remove ammonia nitrogen, calcium, and chemical oxygen demand in reverse osmosis concentrates

In recent years, with the rapid development of industrial revolution and urbanization, the generation and treatment of a large number of salt-containing industrial wastewater has attracted wide attention. A novel salt-tolerant Zobellella denitrificans sp. LX16 with excellent nitrogen removal and biomineralization capabilities was isolated in this experiment. Kinetic experiments were conducted to determine the optimal condition. Under this condition, chemical oxygen demand (COD) can be entirely removed together with ammonia nitrogen, and the removal efficiency of calcium was 88.09%. Growth curves and nitrogen balance tests showed that strain LX16 not only had good HNAD and MICP capabilities, but also had high nitrite reductase and nitrate reductase activities during this process. Three-dimensional fluorescence results reflected that when external carbon sources were lacking or salinity was high, humic acid could effectively enhance the metabolic activity of heterotrophic nitrifying aerobic denitrifying microorganisms through extracellular electron transfer, and the substances produced in the metabolic process could promote biommineralization. Moreover, combined with SEM, SEM-EDS, XRD and FTIR analysis, it is concluded that the microbial surface can provide nucleation sites to form calcium salts, and with the increase of alkalinity to generate Ca5(PO4)3OH. The theoretical basis for the use of biological treatment in reverse osmosis wastewater have been proved by this experiment.

Liquid-gas phase transition enables microbial electrolysis and H2-based membrane biofilm hybrid system to degrade organic pollution and achieve effective hydrogenotrophic denitrification of groundwater

Electron-donor Lacking was the limiting factor for the denitrification of oligotrophic groundwater and hydrogenotrophic denitrification provided an efficient approach without secondary pollution. In this study, a hybrid system with microbial electrolysis cell (MEC) assisted hydrogen-based membrane biofilm reactor (MBfR) was established for advanced groundwater denitrification. The liquid-gas phase transition prevented the potential pollution from organic wastes in MEC to groundwater, while the bubble-free diffusion of MBfR promoted hydrogen utilization efficiency. The negative-pressure extraction from MEC and the positive pressure for gas supply into MBfR increased the hydrogen proportion and current density of MEC, and improved the kinetic constant K of the denitrification reaction in MBfR. With actual groundwater, the MEC-MBfR hybrid system achieved a nitrate reduction of 97.8% with an effluent NO₃^--N of 2.2 ± 1.0 mg L^-1. The hydrogenotrophic denitrifiers of Thauera, Pannonibacter, and Azonexus, dominated the denitrification biofilm on the membrane and elastic filler in MBfR.