Nitrogen Removal Rate Research Articles

Iron sulfide mineral/polylactic acid mixotrophic biofilter for simultaneous nitrate and phosphate removal

Heterotrophic denitrification based on polylactic acid (PLAHD) can remove nitrate effectively, but it is expensive and can't remove phosphate. Autotrophic denitrification based on iron sulfide (ISAD) can simultaneously remove nitrate and phosphate cost-effectively, but its nitrate rate is slow. So, iron sulfide mineral/polylactic acid mixotrophic biofilter (ISPLAB) was constructed to combine advantages of ISAD and PLAHD. ISPLAB achieved nitrogen and phosphorus removal rates of 98.04 % and 94.12 %, respectively, at a hydraulic retention time (HRT) of 24 h. The study also revealed that controlling molecular weight (Mw) of PLA improved the release of soluble organic matter; adding iron sulfide enhanced the hydrolysis of PLA and precipitated PO43− of Fe2+/Fe3+, thereby facilitated simultaneous nitrogen and phosphorus removal. Microbial community analysis resulted that denitrifying bacterias (Phaeodactylibacter and Methylotenera), sulfur-reducing bacterias (Hyphomicrobium), sulfur-oxidizing bacteria (Denitratisoma), iron-reducing bacteria (Romboutsia) and hydrolyzed bacterias (norank_f_norank_o_1–20 and norank_f_Caldilineaceae) coexisted in the ISPLAB system. Organics and iron sulfide drived the denitrification process in ISPLAB.

Promoting the ecological restoration of black and odorous water by Fe/C internal electrolysis

Three ecological restoration systems vegetated with Vallisneria natans, containing ceramisite (VC), bio-carrier and ceramisite (BVC) or Fe/C filler, bio-carrier and ceramisite (FBVC) as functional substrates were constructed for black and odorous water restoration. The average ammonia nitrogen (NH4+-N) conversion rate of FBVC (90.51 %) was similar to that of BVC (88.49 %) and significantly higher than that of VC (53.35 %). However, the average total nitrogen (TN) removal rate of FBVC (84.93 %) was much higher than that of BVC (73.02 %) and VC (52.06 %). Additionally, the average COD removal efficiencies for VC, BVC and FBVC were 52.54 %, 71.84 % and 80.59 %, respectively; while they were 69.72 %, 74.79 % and 97.38 % for total phosphorus (TP). High-throughput sequencing revealed that the richness and diversity of autotrophic denitrifying bacteria, such as Pseudomonas, Pseudoxanthomonas, Arenimonas and Hydrogenophaga increased significantly in FBVC, while the plant growth-promoting bacterium Rhodobacter was dominant. Overall, this study demonstrated that a Vallisneria natans based ecological restoration system coupled with Fe/C internal electrolysis (Fe/C-IE) effectively improved the quality of black and odorous water. In addition, the mechanism of nitrogen, phosphorus and carbon removal was proposed.

Bibliometric Analysis of Nitrogen Removal in Constructed Wetlands: Current Trends and Future Research Directions

Nitrogen pollution in water environments has reached critical levels globally, primarily stemming from agricultural runoff, industrial discharges, and untreated sewage. The excessive presence of nitrogen compounds poses a significant threat to water quality, leading to adverse impacts on ecosystems and human health. Reaching a breakthrough in the technology of constructed wetlands (CWs) for mitigating nitrogen pollution is hindered by existing knowledge gaps regarding the mechanisms involved in the removal process. Reaching this understanding, we offer a comprehensive summary of current advancements and theories in this research field. Initially, bibliometric techniques were employed to identify yearly patterns in publications and areas of research focus. Subsequently, the chosen documents underwent statistical analysis using VOSviewer_1.6.20 to determine countries’ annual productivity, significant publication years, influential authors, keyword clustering analysis, and more. Finally, a comprehensive overview is provided on the elimination of nitrogen through CWs, encompassing insights into microbial communities and structure types. This analysis aims to uncover potential strategies for optimizing the rate of nitrogen removal. Furthermore, this study elucidates the current research trend concerning the nitrogen removal performance of CWs and identifies challenges and future research directions in this field.

Interspecies electron transfer and microbial interactions in a novel Fe(II)-mediated anammox coupled mixotrophic denitrification system

This study effectively coupled anammox and mixotrophic denitrification at a high nitrogen load rate of 6.84 g N/L/d with 40 mg/L Fe(II). Fe(II) enhanced the activity of nitrate reductase, nitrite reductase, and hydrazine dehydrogenase enzymes, facilitating accelerated ATP synthesis. Through electrochemical experiments, interspecies electron transfer processes in coupled system were explored. Fe(II) promoted flavin mononucleotide secretion, enhancing electron-donating and electron-accepting capacity by 2.8 and 1.3 times, respectively. Fe(II) triggered the enrichment of autotrophic denitrifying bacteria (Azospira and Hydrogenophaga), transitioning from single organic nutrient to mixotrophic denitrification. Meanwhile, Fe(II) increased Candidatus_Kuenenia abundance from 35.2 % to 49.0 %, establishing the competitive advantage of anammox bacteria over completed denitrifying bacteria (Comamonas). The synergistic interactions between anammox and various denitrification pathways achieved a nitrogen removal rate of 5.88 g N/L/d, with anammox contribution rate of 88.3 %. This study provides insights into broadening the application of partial denitrification /anammox and electron transfer in multi-bacterial coupling systems.

Novel insights into intrinsic mechanisms of magnetic field on long-term performance of anaerobic ammonium oxidation process

The performance of an anaerobic ammonium oxidation (anammox) reactor with the magnetic field of 40 mT was systematically investigated. The total nitrogen removal rate was enhanced by 16% compared with that of the control group. The enhancing mechanism was elucidated from the improved mass transfer efficiency, the complicated symbiotic interspecific relationship and the improved levels of functional genes. The magnetic field promoted formation of the loose anammox granular sludge and the homogeneous and well-connected porous structure to enhance the mass transfer. Consequently, Candidatus Brocadia predominated in the sludge with an increase in abundance of 13%. Network analysis showed that the positive interactions between Candidatus Brocadia and heterotrophic bacteria were strengthened, which established a more complicated stable microbial community. Moreover, the magnetic field increased the levels of hdh by 26% and hzs by 35% to promote the nitrogen metabolic process. These results provided novel insights into the magnetic field-enhanced anammox process.

Revealing sulfur-iron coupling mechanism for enhanced autotrophic denitrification in ecological floating beds

A sulfur-iron coupled ecological floating bed (EFB-SFe) was developed to enhance the denitrification capability of sulfur-based ecological floating beds (EFB-S). The denitrification performance, kinetic process and microbial community composition were explored. Results showed that sulfur-iron coupling effectively enhanced the denitrification performance of EFB, surpassing the sum of their individual effects. The average total nitrogen removal rate ranged from 1.56 to 4.56 g·m−2·d-1, with a removal efficiency of 22–84 %. The k value for the S + Fe group increased from 0.04 to 0.18 d-1 to 0.40–0.46 d-1 relative to the S group. The sulfur-iron coupling promoted the enrichment of denitrifying bacteria (Thiobacillus and Ferritrophicum). The denitrification genes in EFB-SFe were upregulated, being 12–22 times more abundant than in EFB-S. Sulfur and iron autotrophic denitrification were identified as the main nitrogen removal processes in EFB-SFe. Overall, sulfur-iron coupling showed the potential to enhance the denitrification capacity of EFB-S for treating low-pollution water.

Improving ammonia nitrogen removal and recovery by BMED stack optimization: The effect of ion exchange membrane thickness

Bipolar membrane electrodialysis (BMED) has emerged as an efficient and promising technology for the removal and recovery of ammonia nitrogen. Despite its potential, the optimization of BMED systems for enhanced performance and energy efficiency remains a critical challenge, particularly in the context of varying ion exchange membrane (IEM) thicknesses. Membranes with a thickness of < 80 µm have low resistance and are mainly used for processes requiring low energy consumption. Membranes with a thickness of 80–250 µm have moderate resistance and high ion selectivity and are widely used for electrodialysis applications. Membranes with a thickness of > 250 µm have higher ion selectivity than commercial membranes with a thickness of 80–250 µm and are suitable for processes that demand high purity. This study investigates the effect of IEM thickness ranging from 16–400 µm on BMED performance for ammonia nitrogen removal and recovery, and energy consumption. The BMED configuration comprising five cell triplets consisting of a cation exchange membrane, bipolar membrane, and anion exchange membrane was employed. The thickness of IEMs was divided into three categories: 16–17 µm (PCEM/ PAEM), 100–150 µm (CD100/AD100, InnoSep-C/InnoSep-A), and 380–400 µm (MC-3470/MA-3475). In membranes with a thickness of 100–150 µm, the ammonia nitrogen removal was exceptionally high at 99.2 %, with a recovery of 98.7 % (CD100/AD100: 100 µm) at a current density of 80 mA/cm2, and the system exhibited low specific energy consumption (SEC) of 8.87 kWh/kg-N (InnoSep-C/InnoSep-A: 150 µm) at a current density of 20 mA/cm2. However, when using the thinnest IEMs (PCEM: 16 µm, PAEM: 17 µm), an increase in total ammonia nitrogen loss (10.21–22.01 %) led to a reduction in ammonia nitrogen recovery. Conversely, when using the thickest IEMs (MC-3470: 380 µm, MA-3475: 400 µm), the SEC was extremely high (30.98–126.67 kWh/kg-N), making them unsuitable for the BMED process for ammonia nitrogen removal and recovery. Based on these experimental results, it is suggested to use an optimal thickness of IEM within the range of 80–250 µm in the BMED systems to achieve a balanced performance, maximizing ammonia nitrogen removal and recovery while minimizing the SEC. Consequently, the present study provides a comprehensive understanding of the effects of the IEM thicknesses on the BMED systems and could offer a practical perspective for optimizing the BMED stack with respect to improving the removal and recovery rate of ammonia nitrogen and reducing the energy consumption.

Strategies for efficient enrichment of anaerobic ammonia oxidizing bacteria in activated sludge

Anaerobic ammonia oxidation (Anammox) is an economical and sustainable wastewater nitrogen removal technology, and its application in the mainstream process is the inevitable trend of the development of Anammox. However, how to effectively enriching Anammox bacteria from the activated sludge remains challenging and restricts its extensive applications. In this study, the rapid and efficient enrichment of Anammox bacteria was achieved by raising the reflux ratio and nitrogen loading rate (NLR) using conventional activated sludge as the inoculant. In the screening phase (days 1–90), the reflux ratio was increased to discharge partial floc sludge, resulting in the relative abundance of Candidatus Brocadiaceae increased from 0.04% to 22.54%, which effectively reduced the matrix and spatial competition between other microorganisms and Anammox bacteria. On day 90, the stoichiometric ratio of the Anammox process closely approached the theoretical value of 1:1.32:0.26, indicating that the Anammox reaction was the primary nitrogen removal process in the system. In the enrichment phase (days 91–238), the NLR increased from 0.43 to 1.20 kgN/(m3·d) and removal efficiency was 71.89%, resulting in the relative abundance of Candidatus Brocadiaceae increased to 61.27% on day 180. The reactor operated steadily from days 444 to 498, maintaining the nitrogen removal rate (NRR) of 3.00 kgN/(m3·d) and achieving successful sludge granulation with the particle size of 392.4 µm. In short, this study provided a simple and efficient approach for enriching Anammox bacteria from the activated sludge, supporting to start an Anammox process efficiently.

Microalgae cultivation trials in a membrane bioreactor operated in heterotrophic, mixotrophic, and phototrophic modes using ammonium-rich wastewater: The study of fouling.

In this work, microalgae cultivation trials were carried out in a membrane bioreactor to investigate fouling when the cultures of Chlorellavulgaris were grown under mixotrophic, heterotrophic, and phototrophic cultivation regimes. The Chlorella cultures were cultivated in wastewater as a source of nutrients that contained a high concentration of ammonium. In mixotrophic cultivation trials, the results showed that the elevated contents of carbohydrates in the soluble microbial product and proteins in extracellular polymeric substances probably initiated membrane fouling. In this case, the highest protein content was also found in extracellular polymeric substances due to the high nitrogen removal rate. Consequently, transmembrane pressure significantly increased compared to the phototrophic and heterotrophic regimes. The data indicated that cake resistance was the main cause of fouling in all cultivations. Higher protein content in the cake layer made the membrane surface more hydrophobic, while carbohydrates had the opposite effect. Compared to a mixotrophic culture, a phototrophic culture had a larger cell size and higher hydrophobicity, leading to less membrane fouling. Based on our previous data, the highest ammonia removal rate was reached in the mixotrophic cultures; nevertheless, membrane fouling appeared to be the fundamental problem.

Carbon slow-release and enhanced nitrogen removal performance of plant residue-based composite filler and ecological mechanisms in constructed wetland application

Stable carbon release and coupled microbial efficacy of external carbon source solid fillers are the keys to enhanced nitrogen removal in constructed wetlands. The constructed wetland plant residue Acorus calamus was cross-linked with poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) to create composite solid carbon source fillers (Ac-BDPs). The study demonstrated the slow release of carbon sources from Ac-BDPs with 35.27 mg/g under an average release rate of 0.88 mg/(g·d). Excellent denitrification was also observed in constructed wetlands with Ac-BDPs. Moreover, the average removal rate of nitrate nitrogen (NO3−-N) was increased by 1.94 and 3.85 times of the blank groups under initial NO3−-N inputs of 5 and 15 mg/L, respectively. Furthermore, the relatively high abundances of nap, narG, nirKS, norB, qnorZ and nosZ guaranteed efficient denitrification performance in constructed wetlands with Ac-BDPs. The study introduced a reliable technique for biological nitrogen removal by using composite carbon source fillers in constructed wetlands.

Iron particle-integrated anammox granules in baffled reactor: Enhanced settling property and nitrogen removal performance

This study evaluates iron particle-integrated anammox granules (IP-IAGs) to enhance wastewater treatment efficiency. The IP-IAGs resulted in notable improvements in settleability and nitrogen removal. The settling velocity of IP-IAGs increased by 17.91 % to 2.92 ± 0.20 cm/s, and the total nitrogen removal efficiency in batch mode improved by 6.82 %. These changes indicate enhanced biological activity for effective treatment. In continuous operation, the IP-IAGs reactor showed no accumulation of nitrite until 40 d, reaching a peak nitrogen removal rate (NRR) of 1.54 kg-N/m3·d and a nitrogen removal efficiency of 82.61 %. Furthermore, a partial nitritation-anammox reactor that treated anaerobic digestion effluent achieved a NRR of 1.41 ± 0.09 kg-N/m3·d, proving the applicability of IP-IAGs in real wastewater conditions. These results underscore the potential of IP-IAGs to enhance the efficiency and stability of anammox-based processes, marking a significant advancement in environmental engineering for wastewater treatment.

Optimization of nitrogen removal by immobilized heterotrophic nitrification aerobic denitrifying bacterium using response surface methodology

An innovative bacterial carrier complex embedded with polyvinyl alcohol and sodium alginate complex (P.S.) was developed, using the heterotrophic nitrification-aerobic denitrification (HN-AD) strain Paracoccus sp. QD-21, which was carefully selected from activated sludge. The performance of the immobilized bacterium on ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen was thoroughly analyzed, aiming to investigate the synergistic effects of the P.S.-encapsulated bacterial carrier on the HN-AD strain QD-21. To assess the adaptability of the immobilized bacterium, various single-factor analysis experiments were conducted, including the assessment of carbon source, C/N, temperature, pH, rotational speed, and salinity. Subsequently, response surface methodology was employed to conduct further optimization, leading to the identification of optimum conditions (147.31 rpm, 36°C, C/N 8.72, pH 8). Under these conditions, an impressive ammonia nitrogen removal rate of 94.82 ± 0.82% was achieved. Furthermore, practical wastewater treatment experiments were carried out, demonstrating a remarkable 63.31% increase in ammonia nitrogen removal when the carrier with HN-AD bacterium attached was employed. Notably, the addition of a specific carbon source remarkably enhanced the treatment efficiency, resulting in a complete removal rate of 100%. These significant findings lay a solid foundation for the engineering application of the HN-AD bacterium and highlight the promising potential of the P.S.-encapsulated bacterial carrier complex in various applications.

Insights into the effects of exogenous folate on the recovery of SPNA system after starvation: Performance, microbial community and metabolism

To investigate the effects of folate addition on the recovery process of the single-stage partial nitritation-anammox (SPNA) system, two continuous stirred tank reactors (CSTRs), named R1 (adding folate) and R2 (control group), were operated for 105 days at room temperatures. The highest nitrogen removal rate (NRR) observed in R1 was 0.47 kg N/(m3·d) with the addition of 3.0 mg/L folate. Additionally, the activities of HZO and HZS in R1 were higher than those in R2. The relative abundance of Candidatus Brocadia reached 23.7% in R1 and 18.2% in R2. Moreover, the relative abundance of nitrogen metabolism genes and carbon metabolism genes increased with folate addition. However, 3.0 mg/L folate addition reduced the relative abundance of nirK/S and the activity and growth of ammonia-oxidizing bacteria, which was not conducive to continually improving the NRR. This study provided a novel perspective on improving the activity and abundance of anammox bacteria during the restoration process.

Comammox Nitrospira cooperate with anammox bacteria in a partial nitritation–anammox membrane bioreactor treating low-strength ammonium wastewater at high loadings

Research has revealed that comammox Nitrospira and anammox bacteria engage in dynamic interactions in partial nitritation–anammox reactors, where they compete for ammonium and nitrite or comammox Nitrospria supply nitrite to anammox bacteria. However, two gaps in the literature are present: the know-how to manipulate the interactions to foster a stable and symbiotic relationship and the assessment of how effective this partnership is for treating low-strength ammonium wastewater at high hydraulic loads. In this study, we employed a membrane bioreactor designed to treat synthetic ammonium wastewater at a concentration of 60 mg N/L, reaching a peak loading of 0.36 g N/L/day by gradually reducing the hydraulic retention time to 4 hr. Throughout the experiment, the reactor achieved an approximately 80 % nitrogen removal rate through strategically adjusting intermittent aeration at every stage. Notably, the genera Ca. Kuenena, Nitrosomonas, and Nitrospira collectively constituted approximately 40 % of the microbial community. Under superior intermittent aeration conditions, the expression of comammox amoA was consistently higher than that of Nitrospira nxrB and AOB amoA in the biofilm, despite the higher abundance of Nitrosomonas than comammox Nitrospira, implying that the biofilm environment is favorable for fostering cooperation between comammox and anammox bacteria. We then assessed the in situ activity of comammox Nitrospira in the reactor by selectively suppressing Nitrosomonas using 1-octyne, thereby confirming that comammox Nitrospira played the primary role in facilitating the nitritation (33.1 % of input ammonium) rather than complete nitrification (7.3 % of input ammonium). Kinetic analysis revealed a specific ammonia-oxidizing rate 5.3 times higher than the nitrite-oxidizing rate in the genus Nitrospira, underscoring their critical role in supplying nitrite. These findings provide novel insights into the cooperative interplay between comammox Nitrospira and anammox bacteria, potentially reshaping the management of nitrogen cycling in engineered environments, and aiding the development of microbial ecology-driven wastewater treatment technologies.

Efficient degradation of tetracycline by activated peroxymonosulfate with high permeate flux FeTiOx reactive ceramic membrane: Membrane preparation, real wastewater application, and mechanism insight

Antibiotic residue in wastewater is one of the most worrying environmental pollution problems. In this study, innovative bimetallic nanocatalysts of FeTiOx were prepared. Benefiting from the synergistic effect between Ti and Fe, FeTiOx exhibited an excellent performance in activating peroxymonosulfate (PMS) for tetracycline (TC) degradation. Within 60 min, the TC treatment efficiency can reach 96 %. Mechanism study confirmed that the non-free radical pathway (1O2) and free radical pathway (O2−, OH, SO4−) co-participated during the TC treatment process. To further improve the separation function and efficiency, FeTiOx nanocatalyst was loaded on the ceramic membrane (CM) by a facile spraying method and a self-designed experimental device was constructed, which can be used to degrade TC with large volume. In the designed device, 2 L 40 mg/L TC wastewater can be degraded at one time with an efficiency of 85 % and a permeate flux of 1011.66 kg/m2·h when the transmembrane pressure (TMP) was 20 kPa. Finally, real pharmaceutical wastewater was treated and found that the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3−N) and total organic carbon (TOC) were 70.3 %, 62.85 % and 32.8 %, respectively. The study provides a new strategy for treating wastewater pollutants by combining CM technology with advanced oxidation processes (AOPs).

Management of eutrophication using combined the “flock &amp; sink” mitigation technique and submerged plants restoration: a mesocosm study

Abstract Currently, the issue of eutrophication and cyanobacterial blooms persists in water bodies worldwide, prompting the exploration of various treatment methods. This study conducted a comparative analysis of eutrophic water bodies using ferric chloride-modified zeolite (FMZ) and calcium hydroxide-modified zeolite (CMZ) combined with Elodeanuttallii (E. nuttallii) for removal and purification effects. The results revealed that the addition of E. nuttallii had a sustained inhibitory effect on phosphorus release, maintaining stability with lower Turbidity(Tur) and stabilized pH within the range of 8.5-9. FMZ demonstrated rapid reduction in dissolved phosphorus concentration, achieving a removal rate of 96% within 3 days. The combined plant group of CMZ and FMZ exhibited synergistic effects with E. nuttallii, achieving an impressive total phosphorus (TP) removal rate of 80.13% and a total nitrogen (TN) removal rate of 48.77%. Additionally, chlorophyll a (Chl a) concentration decreased from 100.74 ± 24.72 μg/L to 49.96 ± 2.08 μg/L. The phytoplankton community composition indicated that diatoms thrived in low temperatures and high NH4 conditions. Under the same low Total Nitrogen to Total Phosphorus (TN:TP) ratio, high TP concentrations were associated with cyanobacteria dominance, while green algae dominated in other scenarios. This comprehensive approach demonstrates the potential efficacy of CMZ and FMZ combined with E. nuttallii in addressing eutrophic water bodies and mitigating cyanobacterial blooms.

Mechanism of catalytic subcritical water oxidation of m-nitroaniline and nitrogen conversion by CuCo2O4 catalyst

Catalytic subcritical water oxidation (CSWO) of M−nitroaniline (M−NA) was investigated in a fused quartz tube reactor (FQTR) to determine the effects of reaction parameters on M−NA mineralization rate, total nitrogen (TN) removal rate and nitrogen-containing products distribution. The results indicated that the TN removal rate was only 26.36 % at 200 °C, 200 % excess oxidant and 15 min residence time, while the TN removal rate reached 67.83 % at 360 °C in SWO of M−NA. Compared with SWO of M−NA, the mineralization rate and TN removal rate of CSWO of M−NA increased by about 10 % and 17.83 %, respectively. The main reason is mainly attributed to CuCo2O4 catalyzing the preferential reaction of ·NO2 with ·NH4, hastening N2 generation. Alternatively, the CuCo2O4 catalyst may induce a direct reaction between the nitro and amino groups on M−NA within the benzene ring to form N2. Moreover, degradation pathways and nitrogen migration mechanism of M−NA under SWO/CSWO conditions were proposed. These crucial findings are expected to guide the development of environmentally sustainable catalytic technologies towards addressing significant water pollution challenges.

Treatment of electroplating wastewater using electrocoagulation and integrated membrane.

Electroplating wastewater contains heavy metal ions and organic matter. These contaminants not only endanger the environment but also pose risks to human health. Despite the development of various treatment processes such as chemical precipitation MBR, electrocoagulation (EC) ceramic membrane (CM), coagulation ultrafiltration (UF) reverse osmosis (RO), and CM RO. These methods are only effective for low concentrations of heavy metals and struggle with high concentrations. To address the challenge of treating electroplating wastewater with high heavy metal content, this study focuses on the wastewater from Dongfang Aviation Machinery Processing Plant. It introduces an EC and integrated membrane (IM) treatment process for electroplating wastewater. The IM comprises microfiltration (MF) membrane, nanofiltration (NF) membrane, and RO membrane. Results indicated that under specific conditions, such as a pH of 8, current density of 5 A/dm2, electrode plate spacing of 2 cm, 35 min of electrolysis time, and influent pH of 10 for the IM, removal rates of Zn2+, Cu2+, Ni2+, and TCr in the wastewater exceeded 99%. The removal rates of chemical oxygen demand (COD), suspended solids (SS), total phosphorus (TP), total nitrogen (TN), and petroleum in wastewater exceed 97%. Following a continuous cleaning process, the membrane flux can consistently recover to over 94.3%.

Effects and mechanisms of oxytetracycline and norfloxacin on microbial extracellular polymeric substances (EPS) in biological denitrification of aquaculture wastewater

The direct equalizing ray method was employed to design three groups of mixtures of oxytetracycline(OTC) and norfloxacin(NOR) with varying proportions(Group R1 had a higher proportion of OTC, while R2 had similar concentrations of both antibiotics, and R3 had a higher proportion of NOR).The effects of these mixtures on the content and properties of extracellular polymeric substances (EPS) in the biological denitrification process were investigated using an sequencing batch reactor activated sludge reactor (SBR). The results revealed that the removal rates of ammonia nitrogen(NH3-N) decreased in all three groups with the addition of antibiotics. As the antibiotic concentration increased, the EPS content decreased by 68.46%, 55.53%, and 65.03% in R1, R2, and R3, respectively. To understand the interaction mechanism of mixed antibiotics on EPS in activated sludge, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) techniques were employed. The findings demonstrated significant effects of mixed antibiotics on functional groups such as C-O, CO, and C-O-C. Specifically, hydrogen bonding was found to be the primary influencing factor in the R1 ratio, while Π-Π conjugation played a major role in the R3 ratio.

Response of aerobic granular sludge under acute inhibition by polystyrene microplastics: Activity, aggregation performance, and microbial analysis

In this study, the activity, aggregation performance, microbial community and functional proteins of aerobic granular sludge (AGS) in response to acute inhibition by different concentrations of polystyrene microplastics (PS-MPs) were investigated. As the PS-MPs concentration increased from 0 mg/L to 200 mg/L, the specific nitrogen removal rate and the activity of enzymes were inhibited. The inhibition of specific nitrite reduction rate (SNIRR) and specific nitrate reduction rate (SNRR) was most obvious at the PS-MPs concentration of 100 mg/L, and that of nitrite reductase (NIR) and nitrate reductase (NR) was most obvious at the concentration of 50 mg/L. But the inhibitory effects were mitigated at the concentration of 200 mg/L. The increase of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) indicated that the cells were damaged with the increase of PS-MPs concentration. The content of proteins and polysaccharides in extracellular polymeric substances (EPS) decreased, especially the polysaccharides were more affected. Analysis of zeta potential, hydrophobicity and surface thermodynamics of AGS revealed that addition of PS-MPs was unfavorable for AGS aggregation. It was also found that bacteria genera associated with EPS secretion and nitrogen removal functions were inhibited, while functions associated with cell metabolism, protein synthesis and cell repair were enhanced. This also confirmed that acute inhibition of PS-MPs had a detrimental effect on the nitrogen removal and aggregation performance of AGS. This study can provide theoretical support for the operation of AGS reactors under microplastics impact load.