Aerobic electrotrophic denitrification coupled with biologically induced phosphate precipitation for nitrogen and phosphorus removal from high-salinity wastewater: Performance, mechanism, and microbial community

Optimized feeding schemes of heterotrophic anodic denitrification coupled with cathodic phosphate recovery from wastewater using a microbial fuel cell

Enhanced water quality standards and increasing resource scarcity have prompted extensive research into low-cost nitrogen removal and phosphate recovery from wastewater. Microbial fuel cells (MFCs) offer a viable solution by simultaneously removing nitrogen, recovering phosphorus, and generating electrical energy. This study employed MFCs to achieve simultaneous nitrogen removal and phosphorus recovery, investigating the impact of different feeding schemes. The experimental results indicated that replacing the entire anode chamber solution and recycling the anode effluent to the cathode chamber effectively prevented the accumulation of nitrifying bacteria while achieving the highest pollutant removal performance. Under closed circuit conditions, the system consistently maintained low nitrite concentrations, achieving an average nitrate removal efficiency of 68.09 ± 1.86 % and phosphate recovery efficiency of 83.46 ± 5.30 %. Furthermore, this feeding scheme facilitated microbial growth and reproduction while also improving operational convenience. The study utilized metagenomics and other technologies to comprehensively analyze the system's operation mechanism and reasons for its excellent performance.

Contribution of Microbial Metabolism to Geogenic Phosphorus Enrichment in Groundwater: Insights from Metagenomic Sequencing and Organic Molecular Characterization

Microbial mediation in the enrichment of geogenic phosphorus (P) is often mentioned but rarely explored, especially in P enrichment processes through the mineralization of dissolved organic matter (DOM) containing natural P. To bridge the theoretical gap, this study investigated the mechanisms of P enrichment through microbially mediated mineralization of natural P-containing DOM by adopting an approach combining comprehensive field investigation with hydrochemical and molecular biological analyses. The co-analysis of the dominant microbial community compositions and genomics revealed that the microbial metabolism pathways involved in the biodegradation of P-containing DOM were associated with the enrichment level of dissolved inorganic phosphorus (DIP). Specifically, dephosphorylation was more pronounced under conditions of limited DIP, while C-P bond cleavage was the primary metabolic pathway under sufficient DIP. Co-occurrence network analysis further indicated that the substrates for DIP enrichment differed between dephosphorylation and C-P bond cleavage, namely CHONSP1 compounds in the region of highly unsaturated-low O compounds (AI ≤ 0.5, H/C < 1.5, and O/C < 0.4) and CHOP1 compounds in the region of highly unsaturated-high O compounds (AI ≤ 0.5, H/C < 1.5, and O/C ≥ 0.4), respectively. These findings provide new insights into geogenic P enrichment in groundwater from the perspective of microbial metabolism and have potential implications for the bioremediation of P-contaminated groundwater at different contamination levels.

Current intensity and hydraulic retention time play differential roles in functional gene expression or electron transfer pathways in a pyrite-filled three-dimensional biofilm electrode reactor (P3DBER)

This study developed a pyrite-filled three-dimensional biofilm electrode reactor (P3DBER) to treat nitrate wastewater with a low carbon/nitrogen ratio. Meanwhile, the joint effect of current intensity (CI) and hydraulic retention time (HRT) on the performance of the P3DBER was investigated. Results indicated that under the optimal conditions (CI = 30 mA, HRT = 4.9 h), the total inorganic nitrogen removal efficiency (TINRE) reached a maximum of 93.5 ± 1.4%, with a low electrical consumption of 0.075 kW h/g TIN. Increasing CI under different HRTs significantly enhanced the nitrogen removal capacity of the P3DBER. However, at high CI (30 mA), prolonging HRT did not further improve the nitrogen removal efficiency. The introduction of pyrite not only increased the types of electron donors but also could effectively maintain the stability of pH in the P3DBER. Variation partitioning analysis (VPA) showed that CI had a greater impact on the microbial community/functional genes than HRT. In addition, network analysis demonstrated a strong interconnection among microorganisms/functional genes within the P3DBER. This study offers valuable information for optimizing the operating parameters of the P3DBER.

Electrochemical removal of nitrate in high-salt wastewater with low-cost iron electrode modified by phosphate

Nitrate (NO3-) is a widespread pollutant in high-salt wastewater and causes serious harm to human health. Although electrochemical removal of nitrate has been demonstrated to be a promising treatment method, the development of low-cost electro-catalysts is still challenging. In this work, a phosphate modified iron (P-Fe) cathode was prepared for electrochemical removal of nitrate in high-salt wastewater. The phosphate modification greatly improved the activity of iron, and the removal rate of nitrate on P-Fe was three times higher than that on Fe electrode. Further experiments and density functional theory (DFT) calculations demonstrated that the modification of phosphoric acid improved the stability and the activity of the zero-valent iron electrode effectively for NO3- removal. The nitrate was firstly electrochemically reduced to ammonium, and then reacted with the anodic generated hypochlorite to N2. In this study, a strategy was developed to improve the activity and stability of metal electrode for NO3- removal, which opened up a new field for the efficient reduction of NO3- removal by metal electrode materials.

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.

Unraveling the mechanisms and responses of aniline-degrading biosystem to salinity stress in high temperature condition: Pollutants removal performance and microbial community

To explore the intrinsic influence of different salinity content on aniline biodegradation system in high temperature condition of 35 ± 1 °C, six groups at various salinity concentration (0.0%-5.0%) were applied. The results showed that the salinity exerted insignificant impact on aniline removal performance. The low-level salinity (0.5%-1.5%) stimulated the nitrogen metabolism performance. The G5-2.5% had excellent adaptability to salinity while the nitrogen removal capacity of G6-5.0% was almost lost. Moreover, high throughput sequencing analysis revealed that the g__norank_f__NS9_marine_group, g__Thauera and g__unclassified_f__Rhodobacteraceae proliferated wildly and established positive correlation each other in low salinity systems. The g__SM1A02 occupying the dominant position in G5 ensured the nitrification performance. In contrast, the Rhodococcus possessing great survival advantage in tremendous osmotic pressure competed with most functional genus, triggering the collapse of nitrogen metabolism capacity in G6. This work provided valuable guidance for the aniline wastewater treatment under salinity stress in high temperature condition.

Monodispersed and Organic Amine Modified La(OH)3 Nanocrystals for Superior Advanced Phosphate Removal

Advanced phosphate removal is critical for alleviating the serious and widespread aquatic eutrophication, strongly depending on the development of superior adsorption materials to overcome low chemical affinity and sluggish mass transfer at low phosphate concentrations. Herein, the first synthesis of monodispersed and organic amine modified lanthanum hydroxide nanocrystals (OA-La(OH)3) for advanced phosphate removal by modulating inner Helmholtz plane (IHP), is reported. These OA-La(OH)3 nanocrystals with positively charged surfaces and abundant exposed La sites exhibit specific affinity toward phosphate, delivering a maximum adsorption capacity of 168 mg P g⁻1 and a wide pH adaptability from 3.0 to 11.0, as well as a robust anti-interference performance, far surpassing those of documented phosphate removal materials. The superior phosphate removal performance of OA-La(OH)3 is attributed to its protonated organic amine in IHP, which enhances the electrostatic attraction around the adsorbent-solution interface. Impressively, OA-La(OH)3 can treat ≈5 000 and ≈3 200 bed volumes of simulated and real phosphate-containing wastewater to below extremely strict standard (0.1 mg L⁻1) in a fixed-bed adsorption mode, exhibiting great potential for advanced phosphate removal. This study offers a facile modification strategy to improve phosphate removal performance of nanoscale adsorbents, and sheds light on the structure-reactivity relationship of La-based materials.

Effect of salinity on biological nitrogen removal from wastewater and its mechanism

The nitrogen discharge from saline wastewater will cause significant pollution to the environment. As a high-efficiency and low-cost treatment method, biological treatment has a promising application prospect in the removal of nitrogen from high-salt wastewater. However, the inhibitory effect of high salt on microorganisms increases the difficulty of its treatment. This review discusses the influence of salinity on the nitrogen removal process, considering both traditional and novel biological techniques. Common methods to enhance the effectiveness of biological nitrogen removal processes and their mechanisms of action in engineering practice and research, including sludge acclimation and inoculation of halophilic bacteria, are also introduced. An outlook on the future development of biological nitrogen removal processes for high-salt wastewater is provided to achieve environmentally friendly discharge of high-salt wastewater.

Carbide lime as substrates to boost energy recuperation and dyestuff removal in constructed wetland-microbial fuel cell integrated with copper oxide/carbon cloth cathode

Methylene blue (MB) was regarded as a highly toxic and hazardous substance owing to its irreparable hazard and deplorable damage on the ecosystem and the human body. The treatment of this colorant wastewater appeared to be one of the towering challenges in wastewater treatment. In this study, a microbial fuel cell coupled with constructed wetland (CW-MFC) with effective MB elimination and its energy recuperation concurrently based on the incorporation of carbide lime as a substrate in a new copper oxide-loaded on carbon cloth (CuO/CC) cathode system was studied. The crucial influencing parameters were also delved, and the MB degradation and chemical oxygen demand (COD) removal efficiencies were correspondingly incremented by 97.3% and 89.1% with maximum power output up to 74.1 mW m-2 at optimal conditions (0.2 g L-1 carbide lime loading and 500 Ω external resistance). The carbide lime with high calcium ion content was greatly conducive for the enrichment of critical microorganism and metabolic activities. The relative abundances of functional bacteria including Proteobacteria and Actinobacteriota were vividly increased. Moreover, the impressive results obtained in printed ink wastewater treatment with a COD removal efficiency of 81.3% and a maximum power density of 58.2 mW m-2, which showcased the potential application of CW-MFC.

The synthesis of ectoine enhance the assimilation of ammonia nitrogen in hypersaline wastewater by the salt-tolerant assimilation bacteria sludge

In contrast to nitrification-denitrification microorganisms that convert ammonia nitrogen in hypersaline wastewater into nitrogen for discharge, this research utilizes sludge enriched with salt-tolerant assimilation bacteria (STAB) to assimilate organic matter and ammonia nitrogen in hypersaline wastewater into ectoine - a biomass with high economic value and resistance to external osmotic pressure. The study investigates the relationship between the synthesis of ectoine and nitrogen removal efficiency of STAB sludge in three sequencing batch reactors (SBR) operated at different salinities (50, 75, and 100 g/L) and organic matter concentrations. The research reveals that, under low concentration carbon sources (TOC/N = 4, NH4+-N = 60 mg/L), the ammonia nitrogen removal efficiency of SBR reactors increased by 14.51 % and 17.25 % within 5 d and 2 d, respectively, when salinity increased from 50 g/L to 75 g/L and 100 g/L. Under high concentration carbon sources (TOC/N = 8, NH4+-N = 60 mg/L), the ammonia nitrogen removal efficiency of STAB sludge in the three reactors stabilized at 80.20 %, 76.71 %, and 72.87 %, and the total nitrogen removal efficiency was finally stabilized at 80.47 %, 73.15 %, and 65.53 %, respectively. The nitrogen removal performance by ammonium-assimilating of STAB sludge is more sustainable under low salinity, while it is more short-term explosive under high salinity. Moreover, the intracellular ectoine concentration of STAB sludge was found to be related to this behavior. Empirical formulas confirm that STAB sludge synthesizes ectoine from nutrients in wastewater through assimilation, and intracellular ectoine has a threshold defect (150 mg/gVss). The ectoine metabolism pathways of STAB sludge was constructed using the Kyoto Encyclopedia of Genes and Genomes (KEGG). The ammonia nitrogen in sewage is converted into glutamic acid under the action of assimilation genes. It then undergoes a tricarboxylic acid cycle to synthesize the crucial precursor of ectoine - aspartic acid. Subsequently, ectoine is produced through ectoine synthase. The findings suggest that when the synthesis of intracellular ectoine reaches saturation, it inhibits the continuous nitrogen removal performance of STAB sludge under high salinity. STAB sludge does not actively release ectoine through channels under stable external osmotic pressure.

Adapting to seasonal temperature variations: A dynamic multi-subunit strategy for sulfur autotrophic denitrification bioreactors

Elemental sulfur autotrophic denitrification (S0AD) processes are temperature-sensitive, presenting a substantial challenge for the practical implementation of S0AD bioreactors. In this study, a comprehensive methodology for designing and operating S0AD bioreactors was developed, effectively managing fluctuations in nitrogen removal efficiency caused by seasonal temperature variations. Initially, the nitrate removal rate was correlated with simulated on-site temperature and nitrate loading, revealing correlation coefficients of k1, k2, k3, and A as 5.42×10-4, -0.41, 0.04, and 0.13, respectively, to establish a mathematical model for predicting S0AD efficiency. Subsequently, by considering influence factors such as dissolved oxygen and dynamic sulfur consumption, the model was employed to accurately design a pilot-scale S0AD bioreactor for a case study. By utilizing an alternative multi-subunit operation, a stable effluent nitrate concentration of less than 8 mg-N/L was maintained throughout the year. Importantly, this approach resulted in a substantial reduction of 76.8% in excessive nitrate removal, sulfur consumption, and sulfate production. This study aims to provide an optimal design and operation strategy for the practical application of S0AD bioreactors, thereby enhancing reliability and cost-effectiveness in the face of seasonal temperature changes.

Effect of calcium ion concentration on the ORR performance of Pd/C catalysts

Noble metal electrocatalysts prepared by microbial methods have attracted extensive attention because of their environmental protection and easy preparation. However, the preparation of electrocatalysts by microbial methods has problems such as large nanoparticles size and low loading rate. In this study, the porous gel co-embedded with Shewanella and alginate is prepared as the adsorption matrix to further enhance its mass transfer and adsorption efficiency. The effect of calcium ion concentration on catalyst performance is explored by optimizing the CaCl2 concentration to expose more adsorption sites. The results show that when the Ca2+ concentration is 0.025 mmol L-1, the prepared catalyst has the smallest size and the highest Pd loading, and exhibits the best electrochemical activity and stability. This provides a new idea for the preparation of electrocatalysts by microbial methods.

Extracellular electron transfer for aerobic denitrification mediated by the bioelectric catalytic system with zero-carbon source

The slow rate of electron transfer and the large consumption of carbon sources are technical bottlenecks in the biological treatment of wastewater. Here, we first proposed to domesticate aerobic denitrifying bacteria (ADB) from heterotrophic to autotrophic by electricity (0.6 V) under zero organic carbon source conditions, to accelerate electron transfer and shorten hydraulic retention time (HRT) while increasing the biodegradation rate. Then we investigated the extracellular electron transfer (EET) mechanism mediated by this process, and additionally examined the integrated nitrogen removal efficiency of this system with composite pollution. It was demonstrated that compared with the traditional membrane bioreactor (MBR), the BEC displayed higher nitrogen removal efficiency. Especially at C/N = 0, the BEC exhibited a NO3--N removal rate of 95.42 ± 2.71 % for 4 h, which was about 6.5 times higher than that of the MBR. Under the compound pollution condition, the BEC still maintained high NO3--N and tetracycline removal (94.52 ± 2.01 % and 91.50 ± 0.001 %), greatly superior to the MBR (10.64 ± 2.01 % and 12.00 ± 0.019 %). In addition, in-situ electrochemical tests showed that the nitrate in the BEC could be directly converted to N2 by reduction using electrons from the cathode, which was successfully demonstrated as a terminal electron acceptor.

Microalgae-assisted heterotrophic nitrification-aerobic denitrification process for cost-effective nitrogen and phosphorus removal from high-salinity wastewater: Performance, mechanism, and bacterial community

A microalgae-assisted heterotrophic nitrification-aerobic denitrification (HNAD) system for efficient nutrient removal from high-salinity wastewater was constructed for the first time as a cost-effective process in the present study. Excellent nutrient removal (∼100.0 %) was achieved through the symbiotic system. The biological removal process, biologically induced phosphate precipitation (BIPP), microalgae uptake, and ammonia stripping worked together for nutrient removal. Furthermore, the biological removal process achieved by biofilm contributed to approximately 55.3-71.8 % of nitrogen removal. BIPP undertook approximately 45.6-51.8 % of phosphorus removal. Batch activity tests confirmed that HNAD fulfilled an extremely critical role in nitrogen removal. Microalgal metabolism drove BIPP to achieve efficient phosphorus removal. Moreover, as the main HNAD bacteria, OLB13 and Thauera were enriched. The preliminary energy flow analysis demonstrated that the symbiotic system could achieve energy neutrality, theoretically. The findings provide novel insights into strategies of low-carbon and efficient nutrient removal from high-salinity wastewater.