Enhancement of biological nitrogen removal performance from low C/N municipal wastewater using novel carriers based on the nano-Fe3O4

Promoting mechanism of nitrogen removal by Fe3O4 magnetic particles during the start-up phase in sequencing batch reactor

In this paper, a magnetic sequencing batch reactor (SBR) was constructed, and the influence rule of magnetic particle dosing performance of denitrification was investigated. The diversity, structure, and potential functions of the microbial community were comprehensively explored. The results showed that the particle size and the dosage of Fe3O4 magnetic particles were the main parameters affecting the sedimentation performance of activated sludge. The start-up phase of the SBR reactor with Fe3O4 magnetic particles was 5 days less than the control. Moreover, total nitrogen removal efficiency during the start-up phase was improved, with the maximum value reaching 91.93%, surpassing the control by 9.7% with the Fe3O4 dosage of 1.2 g L-1. In addition, the activated sludge concentration and dehydrogenase activity were improved, compared to the control. High-throughput sequencing showed that the denitrifying bacterium Saccharimonadales dominated the reactor and was enriched by magnetic particles. According to predicted functions, the abundance of genes for denitrification increased with the addition of magnetic particles, suggesting the capacity of nitrogen removal was enhanced in the microbial community. Overall, the Fe3O4 magnetic particles provide great potential for enhanced wastewater nitrogen removal.

Bidirectional Enhancement of Nitrogen Removal by Indigenous Synergetic Microalgal-Bacterial Consortia in Harsh Low-C/N Wastewater

Conventional microalgal-bacterial consortia have limited capacity to treat low-C/N wastewater due to carbon limitation and single nitrogen (N) removal mode. In this work, indigenous synergetic microalgal-bacterial consortia with high N removal performance and bidirectional interaction were successful in treating rare earth tailing wastewaters with low-C/N. Ammonia removal reached 0.89 mg N L-1 h-1, 1.84-fold more efficient than a common microalgal-bacterial system. Metagenomics-based metabolic reconstruction revealed bidirectional microalgal-bacterial interactions. The presence of microalgae increased the abundance of bacterial N-related genes by 1.5- to 57-fold. Similarly, the presence of bacteria increased the abundance of microalgal N assimilation by 2.5- to 15.8-fold. Furthermore, nine bacterial species were isolated, and the bidirectional promotion of N removal by the microalgal-bacterial system was verified. The mechanism of microalgal N assimilation enhanced by indole-3-acetic acid was revealed. In addition, the bidirectional mode of the system ensured the scavenging of toxic byproducts from nitrate metabolism to maintain the stability of the system. Collectively, the bidirectional enhancement system of synergetic microalgae-bacteria was established as an effective N removal strategy to broaden the stable application of this system for the effective treatment of low C/N ratio wastewater.

Simultaneous denitrification enhancement and sludge reduction based on novel suspended carrier modified using activated carbon and magnetite at low carbon/nitrogen ratio

A novel suspended carrier was prepared by sticking activated carbon (AC) and magnetite (Fe3O4) onto polypropylene slices. Although this carrier could not reverse the decreased denitrification capacity trends under anoxic conditions at an influent carbon/nitrogen (C/N) ratio of 2, it enhanced denitrification by stimulating sludge reduction and accelerating electron transfer to certain extent. The carrier stuck by mixed AC/Fe3O4 exhibited better performance in terms of sludge reduction, extracellular polymeric substances (EPS) secretion, and denitrification than that merely stuck by AC and Fe3O4 at an influent C/N ratio of 2. The carrier stuck by mixed AC/Fe3O4 increased the total nitrogen removal efficiency by 24.6 % ± 12.5 % in a 72-h denitrification batch experiment compared to the common polypropylene carrier. Moreover, the carrier improved EPS secretion and nitrogen metabolism and promoted the growth of Trichococcus and some denitrifying genera. This study provides a reference for the treatment of low C/N ratio sewage.

Comprehensive analysis of effects of magnetic nanoparticles on aerobic granulation and microbial community composition: From the perspective of acyl-homoserine lactones mediated communication

As dosing additives benefit for aerobic granular sludge (AGS) cultivation, effects of different concentrations (0, 10, 50 and 100 mg/L) of magnetic nanoparticles (Fe3O4 NPs) on aerobic granulation, contaminant removal and potential microbial community evolution related to acyl-homoserine lactones (AHLs) mediated bacterial communication were investigated with municipal wastewater. Results showed that the required time to achieve granulation ratio > 70 % was reduced by 60, 90 and 30 days in phase II with addition of 10, 50, 100 mg/L Fe3O4 NPs, respectively. 50 mg/L Fe3O4 NPs can improve contaminant removal efficiency. The promotion of relative abundance of AHLs-producing and AHLs-producing/quenching populations and AHLs-related functional genes accompanied with faster granulation. Iron-cycling-related bacteria were closely related with AHLs-related bacteria during AGS formation. Co-occurrence network analyses showed that AHLs-mediated communication may play an important role in coordinating microbial community composition and functional bacteria participating in nitrogen and polyphosphate metabolisms during aerobic granulation process.

Use of magnetic powder to effectively improve the denitrification employing the activated sludge fermentation liquid as carbon source

Nitrogen removal is often limited in municipal wastewater treatment due to the lack of sufficient carbon source. Utilizing volatile fatty acids (VFAs) from waste activated sludge (WAS) fermentation broth as a carbon source is an ideal alternative to reduce the cost for wastewater treatment plants (WWTPs) and improve denitrification efficiency simultaneously. In this study, an anaerobic system was applied for simultaneous denitrification and WAS fermentation and the addition of magnetic microparticles (MMP) were confirmed to enhance both denitrification and WAS fermentation. Firstly, the addition of MMP increased the nitrate reduction rate by over 25.36% and improve the production of N2. Additionally, the equivalent chemical oxygen demand (COD) of the detected VFAs increased by 7.06%-14.53%, suggesting that MMP promoted the WAS fermentation. The electron transfer efficiency of denitrifies was accelerated by MMP via electron-transporting system (ETS) activity and cyclic voltammetry (CV) experiments, which might result in the promotional denitrification and WAS fermentation performance. Furthermore, the high-throughput sequencing displayed that, MMP enriched key microbes capable of degrading the complex organics (Chloroflexi, Synergistota and Spirochaetota) as well as the typical denitrifies (Bacteroidetes_vadinHA17 and Denitratisoma). Therefore, this study provides a novel strategy to realize simultaneous WAS utilization and denitrification for WWTPs.

Role of Nano-Fe3O4 for enhancing nitrate removal in microbial electrolytic cells: Characterizations and microbial patterns of cathodic biofilm

Conductive magnetite nanoparticle (Nano-Fe3O4) can facilitate numerous biological reduction reactions as an outstanding electron mediator for electron transfer. The positive role of Nano-Fe3O4 for nitrate removal has gradually gained attention recent years, however, it has not been clarified for the persistence of the promoting effect under different concentrations addition. Performance of nitrogen removal and characteristics of cathodic biofilm were evaluated in this study after Nano-Fe3O4 addition with gradient concentration of 100∼500 mg L-1 in microbial electrolytic cells (MEC). Our study illustrated that the optimal concentration was 200 mg L-1 as the removal rate of nitrate increased by 24.76% and the removal rate of total dissolved nitrogen by 29.72%. At the optimal concentration, Nano-Fe3O4 increased cathodic biofilm DNA concentration by 61.04%, enhanced electron transport system activity, enriched iron redox bacteria, denitrifying bacteria and genes, as well as increased extracellular polymeric substances (EPS) amount, especially the protein content of soluble-EPS. However, promoting effect on nitrate removal was not visible in high concentration (500 mg L-1) addition, its electron transport system activity and EPS content were even declined. XPS results indicated that high concentration of Nano-Fe3O4 may reduce the availability of electrons to cathodic biofilm by competing for electrons, which inhibit nitrate removal.

Characterization of the microbial community and prediction of metabolic functions in an anaerobic/oxic system with magnetic micropolystyrene as a biocarrier

Polystyrene (PS) and magnetic polystyrene (MPS) materials have been used extensively in wastewater treatment. In this research, a 55-day anaerobic/oxic process was carried out to evaluate the effects of PS and MPS on microorganisms under aerobic and anaerobic conditions. Scanning electron microscopy results revealed differences in the entanglement state of the sludge with the biocarrier due to differences in surface morphology. High-throughput sequencing analysis showed that the microbial communities differed considerably in the presence of PS and MPS addition under both aerobic and anaerobic conditions. The highest abundance and diversity were observed in the PS reactor, with 929 observed species and a PD_whole_tree index of 91.58 under anaerobic conditions. MPS promoted the enrichment of bacteria related to nitrogen recycling such as Nitrospirota which increased from 1.13% in the seeding sludge to 3.48% and 10.07% in the aerobic reactors with PS and MPS, respectively. Moreover, advanced analysis showed that PS inhibited many microbial functions (e.g., protein export, nitrogen metabolism), and MPS alleviated this inhibition. This study provides significant insights into the microbial effects of PS and MPS and may shed light on biocarrier selection in future studies.

From anaerobic digestion to single cell protein synthesis: A promising route beyond biogas utilization

The accumulation of a large amount of organic solid waste and the lack of sufficient protein supply worldwide are two major challenges caused by rapid population growth. Anaerobic digestion is the main force of organic waste treatment, and the high-value utilization of its products (biogas and digestate) has been widely concerned. These products can be used as nutrients and energy sources for microorganisms such as microalgae, yeast, methane-oxidizing bacteria(MOB), and hydrogen-oxidizing bacteria(HOB) to produce single cell protein(SCP), which contributes to the achievement of sustainable development goals. This new model of energy conversion can construct a bioeconomic cycle from waste to nutritional products, which treats waste without additional carbon emissions and can harvest high-value biomass. Techno-economic analysis shows that the SCP from biogas and digestate has higher profit than biogas electricity generation, and its production cost is lower than the SCP using special raw materials as the substrate. In this review, the case of SCP-rich microorganisms using anaerobic digestion products for growth was investigated. Some of the challenges faced by the process and the latest developments were analyzed, and their potential economic and environmental value was verified.

Enhanced aquaculture wastewater treatment in a biofilm reactor filled with sponge/ferrous oxalate/biochar composite (Sponge-C2FeO4@NBC) biocarriers: Performance and mechanism

Fabricating low-cost and efficient biofilm carriers for moving bed biofilm reactors in wastewater treatment is crucial for achieving environmental sustainability. Herein, a novel sponge biocarrier doped with NaOH-loaded biochar and nano ferrous oxalate (sponge-C₂FeO₄@NBC) was prepared and evaluated for nitrogenous compounds removal from recirculating aquaculture systems (RAS) wastewater by stepwise increasing ammonium nitrogen (NH₄⁺-N) loading rates. The prepared NBC, sponge-C₂FeO₄@NBC, and matured biofilms were characterized using SEM, FTIR, BET, and N₂ adsorption-desorption techniques. The results reveal that the highest removal rates of NH₄⁺-N reached 99.28 ± 1.3% was yielded by the bioreactor filled with sponge-C₂FeO₄@NBC, with no obvious nitrite (NO₂^--N) accumulation in the final phase. The reactor packed with sponge-C₂FeO₄@NBC biocarrier had the highest relative abundance of functional microorganisms responsible for nitrogen metabolism than in the control reactor, confirmed from 16S rRNA gene sequencing analysis. Our study provides new insights into the newly developed biocarriers for enhancing RAS biofilters treatment performance in keeping water quality within the acceptable level for the rearing of aquatic species.

The degradation of high emulsified oil wastewater in an intermittently-aerated MBBR packed with magnetic polystyrene particles

This work aims to explore the effects of the magnetic polystyrene particles (MPS) on contaminants removal of the high emulsified oil wastewater. 26 days intermittently-aerated progress illustrated that COD removal efficiency and the resistance to the shock loading was promoted in the presence of MPS. Gas chromatography (GC) results also indicated that MPS enhanced the number of organic species reduced. According to the cyclic voltammetry test, conductive MPS appeared special redox performance which was considered could to facilitate the extracellular electron transfer. Furthermore, MPS dosing accelerated the electron-transporting system (ETS) activity by 24.91% compared the control. Based on the superior performance above, the conductivity of MPS is considered to be responsible for the enhanced organic removal efficiency. Moreover, the high-throughput sequencing displayed that electroactive Cloacibacterium and Acinetobacter accounted for a higher proportion in the MPS reactor. Additionally, Porphyrobacter and Dysgonomonas which were capable of degrading organics were also enriched more by MPS. To sum up, MPS is a promising additive to enhance the organic substances removal for the high emulsified oil wastewater.

Performance of anammox enchanced by pulsed electric fields under added organic carbon sources using integrated network and metagenomics analyses

This paper aims to investigate the function of a pulsed electric field (PEF) in the anaerobic ammonia oxidation (anammox) process after adding certain chemical oxygen demand (COD) through integrated network and metagenomics analyses. The findings showed that the presence of COD was detrimental to anammox, but PEF could significantly reduce the adverse effect. The total nitrogen removal in the reactor for applying PEF was 16.99% higher on average than the reactor for only dosing COD. Additionally, PEF upgraded the abundance of anammox bacteria subordinate to the phylum Planctomycetes by 9.64%. The analysis of molecular ecological networks promulgated that PEF resulted in an increase in network scale and topology complexity, thereby boosting the potential collaboration of the communities. Metagenomics analyses demonstrated that PEF dramatically promoted anammox central metabolism in the presence of COD, specifically enhancing pivotal N functional genes (hzs, hdh, amo, hao, nas, nor and nos).

Synergistic analysis of performance, functional genes, and microbial community assembly in SNDPR process under Zn(II) stress

One of the most prevalent heavy metals found in rural sewage is Zn(II), while its effect on simultaneous nitrification, denitrification and phosphorus removal (SNDPR) remains unclear. In this work, the responses of SNDPR performance to long-term Zn(II) stress were investigated in a cross-flow honeycomb bionic carrier biofilm system. The results indicated that Zn(II) stress at 1 and 5 mg L^-1 could increase nitrogen removal. Maximum ammonia nitrogen, total nitrogen, and phosphorus removal efficiencies of up to 88.54%, 83.19%, and 83.65% were obtained at Zn(II) concentration of 5 mg L^-1. The functional genes, such as archaeal amoA, bacterial amoA, NarG, NirS, NapA, and NirK, also reached the highest value at 5 mg L^-1 Zn(II), with the absolute abundances of 7.73 × 10⁵, 1.57 × 10⁶, 6.68 × 10⁸, 1.05 × 10⁹, 1.79 × 10⁸, and 2.09 × 10⁸ copies·g^-1 dry weight, respectively. The neutral community model demonstrated that deterministic selection was responsible for the system's microbial community assembly. Additionally, response regimes with extracellular polymeric substances and cooperation among microorganisms facilitated the stability of the reactor effluent. Overall, the findings of this paper contribute to improving the efficiency of wastewater treatment.