The coexistence of nitrate (NO3−-N) and tetracycline (TC) in recirculating aquaculture wastewater poses a serious challenge to biological treatment. In this study, a magnetic biochar-enhanced pyrite-based biofilm electrode reactor (MB-PBER) was constructed to simultaneously remove NO3−-N and TC. The effects of MB preparation methods and ratios on reactor performance were investigated. Long-term operation results revealed that MB prepared by coprecipitation significantly outperformed that prepared by mechanical mixing in enhancing system performance. Further optimization showed that the optimal performance was achieved at an Fe3O4/biochar mass ratio of 1:4 (R7), with the effluent NO3−-N concentration decreasing to 1.44 ± 2.26 mg/L, a total inorganic nitrogen (TIN) removal efficiency of 91.42 ± 8.15%, and a TC removal efficiency of 94.37 ± 1.83%. Under the optimal conditions, higher extracellular polymeric substance (EPS) content and electron transport system activity (ETSA) were detected, thereby enhancing the extracellular electron transfer capacity within the coupled system. Microbial community analysis revealed that stochastic dispersal and environmental selection jointly drove community assembly in the MB-PBER system, leading to the directional enrichment of key functional genera such as Thiobacillus, Thermomonas, and Desulfobacillus, as well as the formation of a more interconnected microbial association network. Mechanistic analysis demonstrated that MB enhanced extracellular electron transfer through the synergistic effects of electron shuttling and conductive network construction. This study elucidates the mechanism by which MB enhances electron transfer and pollutant removal in MB-PBER, providing a promising strategy for the simultaneous removal of nitrogen and antibiotic contaminants from low C/N ratio recirculating aquaculture wastewater.

A study was conducted to enhance pyrite autotrophic denitrification (PAD) for low C/N wastewater using anthraquinone-2,6-disulfonate (AQS) immobilized on granular activated carbon (AQS-GAC). Two reactors were operated under varying C/N ratios (1-2) and hydraulic retention times (HRT: 6-10 h) to evaluate nitrogen removal. Enhanced performance was achieved with AQS-PAD. Under optimal conditions (C/N = 2, HRT = 6 h), nitrate removal efficiency exceeded 80% and nitrite accumulation was effectively controlled below 0.5 mg/L. Sulfate production increased by 67-167% in AQS-PAD, attributed to accelerated sulfur intermediate oxidation. The enhancement was attributed to: 1) accelerated electron transfer via the quinone mediator, improving nitrite reduction by 89.5%; 2) microbial community restructuring favouring Thiobacillus and Dechloromonas; and 3) increased extracellular polymeric substances (EPS) secretion and biofilm stability. AQS-GAC coupled with pyrite was concluded to be an efficient solution.

Pyrite autotrophic denitrification (PAD) faces challenges in electron utilization efficiency for treating low C/N wastewater. Here, we proposed a short-circuited microbial fuel cell (SMFC) integrated with a pyrite-packed bioreactor to overcome these limitations. Unlike conventional MFCs requiring external circuits, the SMFC employed an internal short-circuited design (direct anode-cathode connection via titanium wires), eliminating external power supply while enabling spontaneous electron transfer from the anode to the cathode. This configuration enhanced total nitrogen (TN) removal by 7.93 % compared to standalone PAD, with effluent NO2-- N stably below 1 mg/L. High-throughput sequencing revealed that Phycisphaerae (27 % abundance on the cathode) was a key genus, utilizing bioelectrons from the SMFC to drive complete nitrite reduction via dissimilatory Onr genes. The SMFC-PAD system achieved a 28.4 % increase in electron utilization efficiency by optimizing electron flux between pyrite oxidation (anode) and denitrification (cathode), overcoming intermediate accumulation of nitrite in traditional PAD. This work demonstrated a cost-effective strategy for denitrification by leveraging spatial electron regulation and microbial-electrochemical synergies.

This study evaluated a pyrite-based biofilm-electrode reactor (PBER) for nitrate removal under varying C/N ratios. Optimal performance occurred at a C/N ratio of 3.0, achieving a NO3--N removal efficiency (NRE) of 94.20 % (corresponding effluent NO3--N concentration <0.5 mg/L) with a minimal NH4+-N accumulation or effluent COD concentration below discharge standard (<50 mg/L, GB18918-2002, China). Moreover, EPS production peaked at a C/N ratio of 3, enhancing microbial stability and nitrogen removal. Excessive C/N ratio (>4.5) reduced EPS secretion and microbial resilience. Microbial analysis revealed that the C/N ratio significantly influenced iron metabolism gene expression, sulfate reduction, and microbial interactions. Functional genes such as korBC and napA were key in nitrogen-sulfur-iron cycling. Increasing C/N enriched more bacteria for heterotrophic denitrification (Bacteroidota, Actinobacteriota), sulfate reduction (Desulfobacterota), or iron autotrophic denitrification (Acidobacteriota), and resulted in insignificant NH4+-N accumulation. These findings offer valuable insights into the mechanisms of optimal nitrate removal in PBER affected by varying C/N.

In this study, a constructed wetland–Fe3O4/granular activated carbon anode microbial electrolysis cell (CW-FMEC) was constructed to enhance denitrification in low COD/N ratio wastewater. The introduction of Fe3O4 boosted the expression of functional genes involved in the denitrification pathway, and the abundance of narG, nirS, and nosZ increased by 99.29%, 70.54%, and 132.18%, respectively, compared to CW. In addition, the content of c-type cytochromes (c-Cyts) and EPS were also enhanced in the CW-FMEC. The microbial communities study displayed that Thauera, Dechloromonas, and Arenimonas became the main genera for denitrification. The denitrification performance at different COD/N ratios was investigated in depth. Under optimal working circumstances, the CW-FMEC had an excellent nitrate removal rate (88.9% ± 1.12%) while accumulating nearly no NO2−-N or NH4+-N in the effluent. This study provides a new direction for the development of CW-MEC and accelerates its implementation.

Antibiotics frequently exist in nitrate wastewater and seriously threaten biological denitrification. This study investigated the impact of enrofloxacin (ENR) on autotrophic, heterotrophic, and mixotrophic denitrification processes at various filling heights. The experiments were conducted across four consecutive phases with ENR concentrations of 0, 0.1, 1, and 10 mg/L. As the influent ENR concentration increased, the denitrification performance of the FeS2-based 2-based autotrophic denitrification (PAD) system was significantly inhibited at different filling heights, with nitrate removal efficiency (NrE) dropping to 30.42 %. In contrast, the polycaprolactone (PCL)-based heterotrophic denitrification (PHD) and mixotrophic denitrification (PAD+PHD) +PHD) systems only affected NrE in the lower layer, whereas the middle and upper layers maintained high NrE levels, largely unaffected by ENR stress, reaching up to 98.28 % and 94.02 % respectively. Sulfate reduction was more prominent in the upper and middle layers of the mixotrophic denitrification bioreactor (PHD system). Bacterial diversity indices initially increased and then decreased as ENR concentration rose from 0 to 10 mg/L, with the PHD system showing lower diversity compared to the PAD system. Redundancy analysis (RDA) revealed that the relative abundances of Proteobacteria and Actinobacteriota in the PAD system, and Bacteroidota and Firmicutes in the PHD system, were negatively correlated with ENR concentration. Overall, the PAD system experienced significant stress from ENR at various filling heights, whereas the upper-middle layer of the PHD system demonstrated greater resistance. This highlighted the impact of antibiotic contamination along with the performance of different filling heights and emphasized the need for tailored strategies in wastewater treatment.

Vertical spatial denitrification performance, microbial community and key denitrification genes in a biofilter coupled with water electrolysis were studied to explain the mechanisms of heterotrophic–hydrogen autotrophic denitrification.

Denitrification is of great significance for low C/N wastewater treatment. In this study, pyrite autotrophic denitrification (PAD) was coupled with a three-dimensional biofilm electrode reactor (BER) to enhance denitrification. The effect of current on denitrification was extensively studied. The nitrate removal of the PAD-BER increased by 14.90% and 74.64% compared to the BER and the PAD, respectively. In addition, the electron utilization, extracellular polymeric substances secretion, and denitrification enzyme activity (NaR and NiR) were enhanced in the PAD-BER. The microbial communities study displayed that Dokdonella, Hydrogenophaga, Nitrospira, and Terrimonas became the main genera for denitrification. Compared with the PAD and the BER, the abundance of the key denitrification genes narG, nirK, nirS, and nosZ were all boosted in the PAD-BER. This study indicated that the enhanced autotrophic denitrifiers and denitrification genes were responsible for the improved denitrification in the PAD-BER.Practitioner Points PAD-BER displayed higher nitrate removal, EPS, NAR, and NIR activity. The three types of denitrification (HD, HAD, and PAD) and their contribution percentage in the PAD-BER were analyzed. HAD was dominant among the three denitrification processes in PAD-BER. Microbial community composition and key denitrification genes were tested to reveal the denitrification mechanisms. Pyrite autotrophic denitrification (PAD) coupled with a three-dimensional biofilm electrode reactor (BER) improved denitrification by enhancement of denitrifying bacteria and denitrification genes, extracellular polymeric substances (EPS) secretion, and denitrification enzymes activity (NAR and NIR).image

A three-dimensional (3D) anode is essential for high-performance microbial fuel cells (MFCs). In this study, 3D porous carbon monoliths from a wax gourd (WGCM) were obtained by freeze-drying and carbonization. Nano-TiO2 was further coated onto the surface of WGCM to obtain a nano-TiO2/WGCM anode. The WGCM anode enhanced the maximum power density of MFCs by 167.9% compared with the carbon felt anode, while nano-TiO2/WGCM anode additionally increased the value by 45.8% to achieve 1396.2 mW/m2. WGCM enhancement was due to the 3D porous structure, the good conductivity and the surface hydrophilicity, which enhanced electroactive biofilm formation and anodic electron transfer. In addition, nano-TiO2 modification enhanced the enrichment of Acinetobacter, an electricigen, by 31.0% on the anode to further improve the power production. The results demonstrated that the nano-TiO2/WGCM was an effective anode for power enhancement in MFCs.

With pyrite (FeS2) and polycaprolactone (PCL) as electron donors, three denitrification systems, namely FeS2based autotrophic denitrification (PAD) system, PCL-supported heterotrophic denitrification (PHD) system and split-mixotrophic denitrification (PPMD) system, were constructed and operated under varying hydraulic retention times (HRT, 1-48 h). Compared with PAD or PHD, the PPMD system could achieve higher removals of NO3  -N and PO43--P, and the effluent SO42  concentration was greatly reduced to 7.28 mg/L. Similarly, the abundance of the dominant genera involved in the PAD (Thiobacillus, Sulfurimonas, and Ferritrophicum, etc.) or PHD (Syntrophomonas, Desulfomicrobium, and Desulfovibrio, etc.) process all increased in the PPMD system. Gene prediction completed by PICRUSt2 showed that the abundance of the functional genes involved in denitrification and sulfur oxidation all increased with the increase of HRT. This also accounted for the increased contribution of autotrophic denitrification to total nitrogen removal in the PPMD system. In addition, the analysis of metabolic pathways disclosed the specific conversion mechanisms of nitrogen and sulfur inside the reactor.

A three-dimensional biofilm-electrode reactor (3D-BER) that combined heterotrophic and autotrophic denitrification (HAD) was developed to remove nitrate. The denitrification performance of the 3D-BER was evaluated under different experimental conditions, including current intensities (0-80 mA), COD/N ratios (0.5-5), and hydraulic retention times (2-12 h). The results showed that excessive current limited the nitrate removal efficiency. However, a longer hydraulic retention time was not required to achieve a better denitrification effect in the 3D-BER. Moreover, the nitrate could be effectively reduced over a broad range of COD/Ns (1-2.5), and its removal rate peaked at 89% at I = 40 mA, HRT = 8 h, and COD/N = 2. Although the current reduced the diversity of microorganisms in the system, it promoted the growth of dominant species. Nitrification microorganisms were enriched in the reactor, especially Thauera and Hydrogenophaga, which were crucial to the denitrification process. Thus, the combination of autotrophic denitrification and heterotrophic denitrification was promoted by the 3D-BER system to increase the efficiency of nitrogen removal.

With pyrite (FeS2) and polycaprolactone (PCL) as electron donors, three denitrification systems, namely FeS2-based autotrophic denitrification (PAD) system, PCL-supported heterotrophic denitrification (PHD) system and split-mixotrophic denitrification (PPMD) system, were constructed. Compared with PAD or PHD, PPMD could achieve higher removal of NO3--N or PO43--P, and the effluent SO42- concentration was also greatly reduced to 7.28 mg/L. Similarly, the abundance of the dominant genera involved in the PAD (Thiobacillus, Sulfurimonas, and Ferritrophicum, etc.) or PHD (Syntrophomonas, Desulfomicrobium, and Desulfovibrio, etc.) all increased during the PPMD. High-throughput sequencing analysis showed that the abundance of functional genes involved in denitrification and sulfur oxidation all increased with the increase of hydraulic retention time (HRT, 1–48 h). This also explained the increased contribution of autotrophic denitrification to total nitrogen removal in the PPMD. In addition, the analysis of metabolic pathways explained the specific conversion mechanisms of nitrogen and sulfur inside the reactor.

In this study, SnO2-Sb2O3/GAC particle electrodes were prepared using the dip-calcination method. The particle electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer Emmett Teller (BET), thermogravimetric test and linear sweep voltammetry (LSV), which proved that the metal oxide was successfully loaded on the granular activated carbon and exhibited high electrocatalytic activity and thermal stability. The effects of initial pH, electrolytic voltage, electrolyte concentration, initial phenol concentration and particle electrode dosage on the performance of the three-dimensional (3D) electrocatalytic oxidation in phenol degradation were investigated. The results showed that under the optimal conditions, the removal rates of phenol and chemical oxygen demand (COD) were 99.65% and 67.16%, respectively. Finally, it was found that the novel particle electrodes had the ability of stable operation, maintaining high-efficiency operation no less than 15 times, which further highlights their robustness and durability.

Anode materials were vital for power production in microbial fuel cells (MFCs). By freeze-drying and carbon-ization, porous carbon monolith derived from wax gourd (WGCM) was prepared. WGCM was then coated by nano-Fe3O4 to obtain the nano-Fe3O4/WGCM anode. WGCM anode increased the maximum power density of the MFCs from 430.6 mW/m2 to 906.6 mW/m2, while nano-Fe3O4/WGCM anode further promoted it to 1438.8 mW/ m2. WGCM had a three-dimensional (3D) microporous network structure, a hydrophilic surface and good con-ductivity, which enhanced biofilm formation and reduced internal resistance. Fe3O4 increased Geobacter enrichment on anode surface, a popular electricigen in MFCs. Calculated from anode surface microbial cell density and the relative abundance, Geobacter on the nano-Fe3O4/WGCM increased by 41.4% compared with the WGCM anode. The results demonstrated that the preparation of carbon monolith coated with nano-Fe3O4 was a promising method for anode enhancement in MFCs.

Wastewater contains a significant quantity of organic matter, continuously causing environmental pollution. Timely and accurate detection of organic content in water can facilitate improved wastewater treatment and better protect the environment. Microbial fuel cells (MFCs) are increasingly recognized as valuable biological monitoring systems, due to their ability to swiftly detect organic indicators such as biological oxygen demand (BOD) and chemical oxygen demand (COD) in water quality. Different types of MFC sensors are used for BOD and COD detection, each with unique features and benefits. This review focuses on different types of MFC sensors used for BOD and COD detection, discussing their benefits and structural optimization, as well as the influencing factors of MFC-based biomonitoring systems. Additionally, the challenges and prospects associated with the development of reliable MFC sensing systems are discussed.

Aquaculture wastewater can be efficiently treated by sequencing batch biofilm reactor (SBBR) via simultaneous nitrification and denitrification (SND), which is heavily influenced by different aeration strategies. The triangular associations among functional microbial abundance, key enzymes, and purification performance can be helpful to explain their influence mechanism on nitrogen removal from SBBR. For the present study, ten such systems for aquaculture wastewater polishing were operated under the pre-aeration (Pre-A) or post-aeration (Post-B) mode with different ratios of aeration to non-aeration or non-aeration to aeration. It was found that the average percent removals of ammonium (NH4+-N) and total inorganic nitrogen (TIN) were 84.72% and 61.98% in Pre-A, and were 93.84% and 55.29% in Post-B, with no obvious nitrite accumulation (0.13 +/- 0.07 mg/L in Pre-A and 0.6 +/- 0.2 mg/L in Post-B). The proteomic analysis illustrated that the aeration sequence affected the intermediary effect of ammonia monooxygenase (EC1.14.99.39) and hydroxylamine dehydrogenase (EC1.7.2.6). Post-aeration was beneficial to the consistency of the nitrifier abundance, the key nitrifying enzyme abundance, and NH4+-N removal. Meanwhile, the aeration sequence influenced the triangular associations among the heterotrophic denitrifier abundance, the denitrifying enzyme abundance, and TIN removal. In addition, nitrous-oxide reductase (EC1.7.2.4) was inhibited in the Post-B treatment. The different aeration strategies had no obvious impact on the taxonomic composition of autotrophic nitrifiers in these SBBR systems, but greatly influenced the taxonomic composition of heterotrophic denitrifiers at the genus level, especially affecting the proportion of denitrifying polyphosphate accumulating organisms (PAOs).

利用茶叶渣制备原始生物炭TBC,并对其进行锌铁负载改性得到改性生物炭MBC,探究MBC吸附水溶液中Cr(VI)的吸附性能.SEM和XRD分析结果表明,MBC表面形貌结构复杂,且成功负载有化合物.FTIR结果表明改性提高了生物炭表面的官能团含量,增强了生物炭的吸附性能.XPS结果表明MBC对Cr(VI)的去除主要是以还原作用和螯合作用为主.对MBC进行了单因素实验、吸附动力学实验、等温吸附实验和热力学实验等,在pH值为2,Cr(VI)初始质量浓度为100 mg/L的条件下,MBC对Cr(VI)的最大吸附量能达到124.37 mg/g.MBC对Cr(VI)的吸附过程符合Langmuir等温吸附模型和准二级动力学模型,说明MBC对Cr(VI)的吸附原理是以单分子层的化学吸附为主,热力学结果表明MBC的吸附过程是自发的吸热反应.

Aquaculture usually produces a large amount of wastewater posing a serious threat to the receiving water environment. In this study, five morphologically identical sequencing batch biofilm reactors (SBBR) were established to treat simulated tilapia aquaculture wastewater under different aeration strategies, involving two dissolved oxygen (DO) concentrations (2 or 3 mg/L) and five aeration/non-aeration ratios (ANRs: 1 h/5 h, 2 h/4 h, 3 h/3 h, 4 h/2 h, 5 h/1 h). The nutrients under the different aeration strategies were mainly removed by simultaneous nitrification, denitrification and phosphorus removal (SNDPR), which was prone to occur under high DO conditions. High DO concentration and appropriate ANR were beneficial to phosphorus removal. High- throughput sequencing analysis revealed that the increase of DO or ANR favored the enrichment of Patesci-bacteria, but decreased the relative abundance of Proteobacteria. In addition, the relative abundance of nitri-fication functional genes (amoABC, hao, and nxrAB) responsible for nitrogen conversion was low, which was a critical and limiting factor in the nitrogen cycle. The SBBR achieved the highest performance at the ANR of 4/2 and DO of 3 mg/L

A heterotrophic and autotrophic denitrification (HAD) system shows satisfactory performance for groundwater with nitrate contamination. In this study, an HAD system combining solid-phase heterotrophic denitrification and electrochemical hydrogen autotrophic denitrification (SHD-EHD) was developed for the treatment of nitrate-contaminated groundwater, in which polycaprolactone (PCL) was used as the carbon source to enhance the nitrate removal performance and prevent secondary pollution of the electrochemical hydrogen autotrophic denitrification (EHD) system. The denitrification performance, microbial community structure and nitrogen metabolism were investigated. The results showed that a high nitrate removal rate of 99.04% was achieved with an influent nitrate concentration of 40 mg/L, a current of 40 mA and a hydraulic retention time (HRT) of 4 h. By comparing the performance with the EHD system, it was found that the HAD system with PCL promoted the complete denitrification and reduced the accumulation of NO2−-N. Analysis of the microbial community structure identified the key denitrifying bacteria: Dechloromonas, Thauera and Hydrogenophaga. A comparison of microbial communities from SHD-EHD and solid-phase heterotrophic denitrification (SHD) demonstrated that electrical stimulation promoted the abundance of the dominant denitrifying bacteria and the electroactive bacteria. Analysis of the nitrogen metabolic pathway revealed that the conversion of NO to N2O was the rate-limiting step in the overall denitrification pathway. The SHD-EHD developed in this study showed great potential for groundwater nitrate removal.

In this study, a heterotrophic/biofilm-electrode autotrophic denitrification reactor (HAD-BER) was constructed and nano-alpha-Fe2O3 was coated on granular activated carbon (GAC) as a third electrode to enhance the nitrate removal performance. The introduction of nano-alpha-Fe2O3 could stimulate microorganisms to secrete more extracellular polymeric substances (EPS), accelerating the electron transfer. Moreover, more denitrification bacteria were enriched on the particle electrodes, especially Pseudomonas and Thermomonas, which played a significant role in denitrification. The denitrification performance at different COD/N ratios (0.65-3.23) and current intensities (0-150 mA) was investigated in depth. When the nitrate concentration of the influent was 60 mg/L, nitrate was almost completely removed at the optimal current intensity (60 mA) and COD/N ratio (1.29). At the same time, there was almost no nitrite (<0.10 mg/L) and ammonia nitrogen (0 mg/L) accumulation in the effluent. This study provided a new direction for the advancement of HAD-BER and accelerated its implementation. Practitioner Points By introducing nano-a-Fe2O3 into HAD-BER, more denitrification bacteria were enriched on the particle electrodes.The increased contents of polysaccharide and protein content could accelerate the electron transfer.Almost completely denitrification could be achieved at current = 60 mA and COD/N = 1.29.The study provided a new direction for the further development of HAD-BERs.