Algal-mediated nitrogen removal and sustainability of algal-derived dissolved organic matter supporting denitrification.

Algae-mediated nitrogen removal from low carbon vs. nitrogen (C/N) wastewater techniques has garnered significant attention due to its superior autotrophic assimilation properties. This study investigated the ammonium-N removal potential of four algae species from low C/N synthetic wastewater. Results showed that 95 % and 99 % of ammonium-N are eliminated at initial concentrations of 11.05 ± 0.98 mg/L and 42.51 ± 2.20 mg/L with little nitrate and nitrite accumulation. The compositions of secreted algal-derived dissolved organic matter varied as C/N decreased and showed better bioavailability for nitrate-N removal by Pseudomonas sp. SZF15 without pre-oxidation, achieving an efficiency of 99 %. High-throughput sequencing revealed that the aquatic microbial communities, dominated by Scenedesmus, Kalenjinia, and Micractinium, remain relatively stable across different C/N, aligning with the underlying metabolic pathways. These findings may provide valuable insights into the sustainable elimination of multiple nitrogen contaminants from low C/N wastewater.

Tuning electronic structure of the carbon skeleton to accelerate electron transfer for promoting the capture of gold.

The efficient and selective recovery of gold from secondary sources is key to sustainable development. However, the complexity of the recovery environment can significantly complicate the compositions of utilized sorbents. Here, we report a straw-derived mesoporous carbon as an inexpensive support material. This mesoporous carbon is modified by anions (sulfur modulation, C-S-180) to improve its electron-transfer efficiency and tune the electronic structure of its skeleton toward enhanced gold reduction. The high surface area of C-S-180 (989.4 m2/g), as well as the presence of abundant C-S in the porous structure of the adsorbent, resulted in an outstanding Au3+-uptake capacity (3422.75 mg/g), excellent resistance to interference, and favorable Au3+ selectivity. Dissimilar to most existing carbon-based adsorbents, electrochemistry-based studies on the electron-transfer efficiencies of adsorbents reveal that sulfur modulation is crucial to optimizing their adsorption performances. Furthermore, the density functional theory reveals that the optimization mechanism is attributable to the adjustment of the electronic structure of the carbon skeleton by C-S, which optimizes the band-gap energy for enhanced Au3+ reduction. These findings offer a strategy for constructing green and efficient adsorbents, as well as a basis for extending the applications of inexpensive carbon materials in gold recovery from complex environments.

Phosphorus biorecovery from wastewater contaminated with multiple nitrogen species by a bacterial consortium.

Recovering finite and non-substitutable phosphorus from liquid waste streams through bio-mediated techniques has attracted increasing interest, but current approaches are incredibly dependent on ammonium. Herein, a process to recover phosphorus from wastewater under multiple nitrogen species conditions was developed. This study compared the effects of nitrogen species on the recovery of phosphorus resources by a bacterial consortium. It found that the consortium could not only efficiently utilize ammonium to enable phosphorus recovery but also utilize nitrate via dissimilatory nitrate reduction to ammonium (DNRA) to recover phosphorus. The characteristics of the generated phosphorus-bearing minerals, including magnesium phosphate and struvite, were evaluated. Furthermore, nitrogen loading positively influenced the stability of the bacterial community structure. The genus Acinetobacter was dominant under nitrate and ammonium conditions, with a relatively stable abundance of 89.01% and 88.54%, respectively. The finding may provide new insights into nutrient biorecovery from phosphorus-containing wastewater contaminated with multiple nitrogen species.

Efficient adsorption of dyes from aqueous solution using a novel functionalized magnetic biochar: Synthesis, kinetics, isotherms, adsorption mechanism, and reusability.

In this study, a novel adsorbent, dodecylbenzene sulfonic acid (DBSA) functionalized magnetic biochar (DBSA-Fe3O4@BC), was synthesized and used to efficiently remove dyes from aqueous solution. The results indicated that DBSA-Fe3O4@BC exhibited an excellent adsorption capacity for Rhodamine B (RhB), and the maximum adsorption capacity for RhB at 298 K was 367.67 mg/g, which was approximately 2.3-1.2 folds than that of BC, dodecylsulfonic acid functionalized biochar (DSA@BC), DBSA@BC, Fe3O4@BC, and DSA-Fe3O4@BC. The possible adsorption mechanisms for RhB adsorption by DBSA-Fe3O4@BC included pore filling, electrostatic attraction, H bond, and surface complexation. Importantly, structural control presented that the simultaneous introduction of alkyl and phenyl groups significantly enhanced RhB adsorption by DBSA-Fe3O4@BC through hydrophobic and π-π interaction. Combined ethanol (EtOH) desorption and H2O2 oxidation regeneration, DBSA-Fe3O4@BC remained high-performance for RhB adsorption after six cycles (97.44%), indicating its outstanding reusability. In summary, DBSA-Fe3O4@BC exhibited a prospective application for dyeing wastewater treatment.

Bioreduction performance of Cr(VI) by microbial extracellular polymeric substances (EPS) and the overlooked role of tryptophan.

Extracellular polymeric substances (EPS) have exhibited promising advantages in mitigating heavy metal contamination, e.g., single-valent silver (Ag(I)), trivalent gold (Au(III)), and hexavalent chromium (Cr(VI)). However, knowledge of the specific substrate in EPSs that supports Cr(VI) reduction has remained elusive. Here, we isolated a novel Cr(VI)-reducing strain with self-mediating properties in an aquatic environment with various pH values to investigate the mechanisms. After analysis by a batch assay coupled with X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) spectroscopic techniques, it was found that Cr(VI) was reduced by the strain and soluble-EPS (S-EPS), and then, organo-trivalent chromium (organo-Cr(III)) was successfully formed. In addition, compared with other components of the strain, the strain and S-EPS completely removed Cr(VI), and the S-EPS exhibited a positive effect on Cr(VI) reduction with a strong monotonic correlation (R2 = 0.999, p = 9.03 × 10-5), indicating that the reduction is an EPS-dependent process. Specifically, the Cr(VI) reduction efficiency was enhanced to 48.85% and 99.4% after EPS and EPS plus tryptophan were added; their respective efficiencies were 3.94 and 8.02 times higher than that of the control assay in which the reductant was depleted. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis showed that the tryptophan concentration concomitantly decreased by 61.54%. These findings highlighted the importance of S-EPS and tryptophan and improved our understanding of EPS for Cr(VI) reduction, which might provide a novel strategy for decontaminating targeted heavy metals in future applications.

Rapid and efficient adsorption of tetracycline from aqueous solution in a wide pH range by using iron and aminoacetic acid sequentially modified hierarchical porous biochar.

The object of this work was to synthesize an iron and aminoacetic acid sequentially modified hierarchical porous biochar (AC-Fe@HPBC) for tetracycline (TC) removal from aqueous solution. Results showed that AC-Fe@HPBC had a larger surface area (362.5370 m2/g), developed microporous structure (0.1802 cm3/g), and numerous functional groups, which provided more adsorption sites. The maximum adsorption capacity towards TC by AC-Fe@HPBC was 457.85 mg/g, 1.43, 1.29 and 1.20-fold than that of HPBC, AC@PHBC and Fe@HPBC, respectively, and the super-fast adsorptive equilibrium was achieved within 10 min. Additionally, introducing amino and carboxyl functional groups on the AC-Fe@HPBC surface significantly broadened the operation pH range (3-11). Site energy analysis indicated TC and AC-Fe@HPBC had stronger adsorption affinity at a higher temperature. The adsorption mechanism involved pore filling, surface complexation, H-bond and π-π interaction. Moreover, the reusability experiments proved AC-Fe@HPBC as an effective adsorbent for TC removal from aqueous solution.

Enhanced adsorption of rhodamine B from water by Fe-N co-modified biochar: Preparation, performance, mechanism and reusability.

To adsorb rhodamine B (RhB) in wastewater by pristine biochar was limited, while the modified biochar has shown great potential adsorption performance. Here, coconut shell mixed with FeSO4·7H2O and urea was prepared to synthesize Fe-N co-modified biochar by once pyrolysis method at 500℃. The results showed Fe-N-BC had larger surface area (972.8714 m2·g-1), higher developed porous structure (0.65016 cm3·g-1), and more oxygen-containing groups, which collectively contributed to significantly improve the adsorption performance of the Fe-N-BC towards RhB. The maximum adsorption capacity of RhB reached 12.41 mg·g-1 by Fe-N-BC which was 1.58, 1.43 and 1.26 folds than that of BC, N-BC and Fe-BC, respectively. The mechanism of adsorption for Fe-N-BC towards RhB including ion exchange, pore filling, surface complexation, H-bond and π-π interaction. This study indicates that Fe-N-BC is an excellent adsorbent for RhB removal from wastewater.

Enhancing nitrate removal from wastewater by integrating heterotrophic and autotrophic denitrification coupled manganese oxidation process (IHAD-MnO): Internal carbon utilization performance.

Due to cause the deterioration of water quality and can produce toxic nitrite, the nitrate constituted of great threatens to human health and eco-systematic safety. Among most well-known biotechnology to remove nitrate, the integrated heterotrophic and autotrophic denitrification (IHAD) process is promising, especially for the organic-limited polluted water. In this work, the IHAD coupled manganese oxidation (IHAD-MnO) process was developed by using Pseudomonas sp. SZF15 (Gram negative strain, and rod-shaped morphology with 2.3 µm in length) in the glass serum bottles. It was found that limited organic content could accelerate nitrate removal rate, and manganese oxidation efficiency can reach up to 60.08%. To further explain carbon conversion characteristics of the process, pure heterotrophic condition assays were conducted, the results confirmed that inorganic carbon will be generated by organic carbon metabolism in heterotrophic condition, the maximum accumulation content of inorganic carbon was 142.21 mg/L (when the initial organic carbon level was 293 mg-C/L). Subsequently, since the consumption of organic carbon, biogenic inorganic carbon can be further utilized by microorganisms to support autotrophic denitrification (AuDN). Besides, X-ray photoelectron spectroscopy (XPS) was employed to analyze precipitation products produced from the process. The magnified Mn 2p spectra results showed that a typical characteristic peak of manganese dioxide was observed with the intense peak at 641.8 eV and a satellite peak at 653.7 eV, respectively. This showed that Mn(II) was oxidized to manganese dioxide by the process, which may be a functional material with adsorption properties. The process posed a highly efficient and cost effective solution with less carbon consumption and less greenhouse gas emission for sustainable water treatment technologies.