Total Nitrogen Removal Efficiency Research Articles

Lab-scale evaluation of Microalgal-Bacterial granular sludge as a sustainable alternative for brewery wastewater treatment

Microalgal-bacterial granular sludge (MBGS) could offer a sustainable alternative to traditional aerobic methods in brewery wastewater (BWW) treatment. This study compared MBGS with conventional activated sludge (AS) in treating real BWW and highlighted its advantages and challenges. MBGS achieved comparable chemical oxygen demand removal efficiency (93%) compared to AS (89%). Additionally, MBGS exhibited higher phosphate removal capabilities than AS. Extra nitrogen was added to influent to balance C/N ratio of BWW. MBGS was robust in handling C/N ratio fluctuations with an 82% total nitrogen removal efficiency. Metagenomic analysis further indicated that most of the genes involved in carbon, nitrogen and phosphorus metabolism were up-regulated in MBGS compared to AS. Despite changes in the microbial community and settling ability due to high starch and sugar content in BWW, MBGS demonstrated high efficiency and sustainability. Further research should optimize MBGS operation strategies to fully realize its potential for sustainable BWW treatment.

Bioretention cells filled with epoxy resin-modified loess for stormwater purification

As a filler material in bioretention cells, loess has a good ability to remove nitrogen and phosphorus. However, its low permeability can easily trigger cell blockage. To improve permeability, the modification of loess has become important in the construction of bioretention cells. This study tested water-soluble epoxy resin-modified loess and investigated its feasibility as a filler for bioretention cells. Its purification performance under different rainfall conditions, including intensity and dry periods, was analyzed and compared with traditional sand bioretention cells both with and without a submerged zone. Epoxy-modified loess could be used as a bioretention cell filler, significantly increasing the permeability coefficient of the cell. Although modification with epoxy resin did not affect the crystal composition of the loess, the cross-linking reaction that occurred on its surface increased the C content, decreased the Si content, and made the texture rougher. When the amount of epoxy resin was 2.5 % (SZ25), the resulting loess met the permeability coefficient design requirements; its maximum adsorption capacity for ammonium-nitrogen was at least 1.92 times more than that of sand. For phosphate, the maximum adsorption capacity reached 5.17 mg/g. The average removal efficiencies of ammonium-nitrogen, nitrate-nitrogen, total nitrogen, and total phosphorus in the epoxy-modified loess bioretention cells were 91.67 %, −12.42 %, 39.91 %, and 91.97 %, respectively, 3.14 %, 28.91 %, 20.07 %, and 9.59 % higher than those in the sand bioretention cell. Microbiological analyses revealed that modified loess filler promoted the enrichment of denitrifying bacteria to a relative abundance 14.31 %–26.47 % higher than that in traditional sand filler. Based on the Functional Annotation of Prokaryotic Taxa analysis, the modified loess bioretention cell had stronger C and N cycling than that of the traditional sand bioretention cell, indicating that microbial metabolism and denitrification were stronger and nitrogen removal was improved.

Effects of potassium-mediated electrical communication inhibition on nitrogen removal in microbial fuel cells

Potassium ion signaling mediates microbial communication in electroactive biofilms within microbial fuel cells (MFCs), but its role in nitrogen removal remains unclear. This study investigated the impact of inhibiting potassium signaling on nitrogen removal in MFCs using tetraethylammonium chloride (TEA) as an inhibitor. Results demonstrated that 5 mM and 10 mM TEA reduced the maximum power generation of MFCs from 77.95 mW/cm2 to 57.18 mW/cm2 and 48.23 mW/cm2, respectively. Correspondingly, total nitrogen (TN) removal efficiency was decreased from 46.57 ± 1.01% to 35.93 ± 0.63% and 38.97 ± 0.74%, respectively. This decline was attributed to inhibited potassium ion signaling, which compromised the electrochemical performance of the MFC and hindered the nitrogen removal process. The relative abundance of exoelectrogen Geobactor decreased from 15.37% to 5.17% and 8.05%, while the relative abundance of cathodic nitrifying bacteria Nitrosomonas decreased from 17.87% to 4.92% and 3.63% under 5 mM and 10 mM TEA. These findings underscore the crucial role of potassium ion signaling in enhancing the bioelectrochemical nitrogen removal process in MFCs.

Effect of elemental sulfur on anaerobic ammonia oxidation: Performance and mechanism

Biological nitrogen removal processes provide effective means to mitigate nitrogen-related issues in wastewater treatment. Previous studies have highlighted the collaborative efficiency between sulfur autotrophic denitrification and Anammox processes. However, the trigger point induced the combination of nitrogen and sulfur metabolism is unclear. In this study, elemental sulfur (S0) was introduced to Anammox system to figure out the performance and mechanism of S0-mediated autotrophic denitrification and Anammox (S0SAD-A) systems. The results showed that the nitrogen removal performance of the Anammox reactor decreased with the increasing concentrations of NH4+-N and NO2−-N in influent, denitrification occurred when NH4+-N concentration reached 100 mg/L. At stage ⅳ (150 mg/L NH4+-N), the total nitrogen removal efficiency in S0SAD-A system (95.99%) was significantly higher than that in the Anammox system (77.22%). Throughout a hydraulic retention time, the consumption rate of NH4+-N in S0SAD-A was faster than that in Anammox reactor. And there existed a nitrate-concentration peak in S0SAD-A system. Metagenomic sequencing was performed to reveal functional microbes as well as key genes involved in sulfur and nitrogen metabolism. The results showed that the introduction of S0 elevated the abundance of Ca. Brocadia. Moreover, the relative abundance of Anammox genes, such as hao, hzsA and hzsC were also stimulated by sulfur. Notably, unclassified members in Rhodocyclaceae acted as the primary contributor to key genes involved in the sulfur metabolism. Overall, the interactions between Anammox and denitrification were stimulated by sulfur metabolism. Our study shed light on the potential significance of Rhodocyclaceae members in the S0SAD-A process and disclosed the relationship between anammox and denitrification.

One-stage anammox and thiocyanate-driven autotrophic denitrification for simultaneous removal of thiocyanate and nitrogen: Pathway and mechanism

The coupled process of anammox and reduced-sulfur driven autotrophic denitrification can simultaneously remove nitrogen and sulfur from wastewater, while minimizing energy consumption and sludge production. However, the research on the coupled process for removing naturally toxic thiocyanate (SCN-) is limited. This work successfully established and operated a one-stage coupled system by co-cultivating mature anammox and SCN--driven autotrophic denitrification sludge in a single reactor. In this one-stage coupled system, the average total nitrogen removal efficiency was 89.68±3.33 %, surpassing that of solo anammox (81.80±2.10 %) and SCN--driven autotrophic denitrification (85.20±1.54 %). Moreover, the average removal efficiency of SCN- reached 99.50±3.64 %, exceeding that of solo SCN--driven autotrophic denitrification (98.80±0.65 %). The results of the 15N stable isotope tracer labeling experiment revealed the respective reaction rates of anammox and denitrification as 106.38±10.37 μmol/L/h and 69.07±8.07 μmol/L/h. By analyzing metagenomic sequencing data, Thiobacillus_denitrificans was identified as the primary contributor to SCN- degradation in this coupled system. Furthermore, based on the comprehensive analysis of nitrogen and sulfur metabolic pathways, as well as the genes associated with SCN- degradation, it can be inferred that the cyanate (CNO) pathway was responsible for SCN- degradation. This work provided a deeper insight into coupling anammox with SCN--driven autotrophic denitrification in a one-stage coupled system, thereby contributing to the development of an effective approach for wastewater treatment involving both SCN- and nitrogen.

Pilot-scale conditioning of starch-based flocculant for cyanobacterial thickening and dewatering: Mechanism investigation and effect verification

Existing cyanobacteria thickening and dewatering processes in Taihu Lake commonly use conventional inorganic flocculants to condition the cyanobacteria, which poses certain environmental risks. In this study, three different types of typical flocculants, namely polymerized aluminum chloride (PAC), cationic polyacrylamide (CPAM) and starch-based flocculant (St-CTA), were selected to investigate their flocculant effects on cyanobacteria and the mechanism of action. The analysis showed that the dosage of St-CTA was low, the flocculation efficiency was high, and it could form flocs with large particle size and high strength. The adsorption and precipitation effect of St-CTA on protein and polysaccharide in flocculated EPS was stronger than that of CPAM and PAC, and it was able to act on the protein structure of EPS favorable for flocculation, improve the hydrophilic effect of S-EPS and LB-EPS, and reduce the content of bound water in EPS from 2.08 to 1.22 g/g DS, thus improving the efficiency of algae-water separation. The free energy and energy barrier of the EPS surface in each layer of the cyanobacterial floc after flocculation by St-CTA were significantly reduced, which resulted in the tendency of the cyanobacterial particles to aggregate and thus flocculate and settle. The pilot validation of St-CTA for cyanobacteria dewatering showed that the water content of algal residue could be reduced to 93.48 %, and the removal efficiencies of total nitrogen (TN), total phosphorus (TP), ammoniacal nitrogen (NH3-N), and chemical oxygen demand (COD) in the air-floated water could be up to 27.3 %, 76.6 %, 27.4 %, and 56.4 %, respectively. In conclusion, this study provides scientific knowledge and demonstration for promoting the use of St-CTA to condition cyanobacterial thickening and dewatering, which is a new idea to solve the problem of cyanobacterial resourcefulness and safe utilization.

Lab-Scale Treatment of Anaerobic Co-Digestion Liquor from Kitchen Waste, Human Feces, and Municipal Sludge Using Partial Nitritation-Anammox Process

Effective nitrogen removal from anaerobic co-digestion is a major challenge to achieving dual-carbon goals. This study explored the acclimatization process of a lab-scale two-stage partial nitritation and anammox process of a stepwise increase in the percentage of raw anaerobic co-digestion liquor from kitchen waste, human feces, and municipal sludge in a venous industrial park in China, which has not been reported yet. Under limited dissolved oxygen (below 0.5 mg/L) and high ammonia levels (200–1500 mg/L), based on adjusting aeration rates, partial nitritation rapidly started up in 50 days. After acclimatization, partial nitritation still performed efficiently and stably, with the final total nitrogen loading rate (TNLR) of 1.24 ± 0.09 gN/L/d, nitrite accumulation rate of 99 ± 4%, and ratio of eff. nitrite/ammonia of 1.32 ± 0.13. In the anammox process, the final total nitrogen removal efficiency, total nitrogen removal rate, and TNLR reached 94 ± 5%, 1.27 ± 0.03 gN/L/d, and 1.36 ± 0.05 gN/L/d, respectively. Chemical oxygen demand (COD) was also reduced in both reactors, with COD removal rates of 0.7 gCOD/L/d in the partial nitritation and 0.4 gCOD/L/d in the anammox process. Overall, the PNA system demonstrated its feasibility in adapting to high ammonia, salinity, and iron levels, when treating anaerobic co-digestion liquor, particularly regarding resource recovery in venous industrial parks.

Gel beads prepared by polyvinyl alcohol cross-linking with phytic acid and Fe as novel microbial carriers for simultaneous partial nitrification, anammox and denitrification

Enhancing the stability of biomass and ensuring a stable activity of anaerobic ammonia oxidizing bacteria are crucial for successful operation of the simultaneous partial nitrification, Anammox, and denitrification (SNAD) process. In this study, gel beads of polyvinyl alcohol/phytic acid (PVA/PA) and polyvinyl alcohol/phytic acid/Fe (PVA/PA/Fe) were prepared as innovative bio-carriers. Theoretical simulations and analyses revealed that these carriers are predominantly connected via hydrogen and borate bonds, with PVA/PA/Fe also featuring metal coordination bonds. The total nitrogen removal efficiency of reactors with PVA/PA/Fe and PVA/PA increased by 13.5 % and 9.0 %, respectively, compared to reactor without carriers. The iron-enriched PVA/PA/Fe carriers significantly improve SNAD by promoting Anammox, Feammox, and nitrate-dependent Fe2+ oxidation reactions, leading to faster nitrogen conversion and higher nitrogen removal rate than reactor without carriers and with PVA/PA. Using of PVA/PA and PVA/PA/Fe gel beads as bio-carriers offers benefits to the SNAD process, including cost-effective and low carbon requirement.

A strategy for the addition of plant biomass to constructed wetlands to increase nitrogen removal in treating sewage: A full-scale experiment

Plant biomass has been widely used as an exogenous carbon source for constructed wetlands to increase nitrogen removal efficiency, but a convenient and efficient addition strategy is lacking. In this study, a new strategy was developed and tested in full-scale horizontal subsurface flow constructed wetlands, i.e., designing a decomposition zone in front of the constructed wetland, adding plant biomass directly to the decomposition zone, and re-adding the refractory parts to the decomposition zone after removal from the decomposition zone and treatment with alkaline leachate. Adding straw significantly increased the average total nitrogen removal efficiency from 36.0% to 44.9% without a significant increase in the chemical oxygen demand concentration. The refractory straw significantly increased the total nitrogen removal efficiency after it was removed, treated with alkaline leachate, and re-added to the system. Every 1 g of raw straw or refractory straw removed 0.088 g or 0.038 g of nitrate, respectively. The relative abundances of Bacillacea, Gemmatimonadaceae, Blastocatellaceae, and Caldilineaceae, which are associated with denitrification, increased after straw addition. The relative abundances of the functional groups of the bacterial community associated with organic matter degradation increased with straw addition, and the functional groups of the bacterial communities associated with nitrogen cycling were positively correlated with the nitrogen concentration. The strategy developed in this study is convenient and efficient for increasing the nitrogen removal efficiency by increasing plant biomass and can be applied in several scenarios.

Activation of denitrification potential within anammox consortia to exceed nitrogen removal thresholds via Fe-Mn functionalized biochar: Enhanced interspecies electron transfer and metabolite cross-feeding

Anammox exerts a crucial role in nitrogenous effluents remediation; nevertheless, nitrogen removal efficiency thresholds triggered by additional nitrate production poses a critical obstacle for anammox performance. Herein, Fe-Mn functionalized biochar (FeMn#BC) was synthesized and incorporated into anammox consortia to elicit the exogenous organics-independent metabolic potential of denitrifying bacteria, which decreased nitrate accumulation and achieved up to 90.69 ± 0.48 % total nitrogen removal efficiency. Enzyme content analysis indicated that FeMn#BC bolstered biometabolic vigour and electron transport system activity by stimulating the synthesis of heme c and NADH. Microbial community succession results demonstrated that FeMn#BC facilitated the proliferation of anammox bacteria (AnAOB) and nitrate-reducing functional bacteria. Metagenomic analysis uncovered that FeMn#BC increased the relative abundance of genes related to energy metabolism, nutrient-substrate ingestion, cofactor synthesis, and iron-manganese transport pathways. Candidatus Brocadia sp013360945 interacted nitrogen metabolism substrates and electrons with dominated denitrifying species PR03 sp. (dependent on endogenous organics and FeMn#BC-released Fe(II)), while interacted cofactors with other mutualistic bacteria possessing nitrate-reducing potential (e.g. ATM1 sp003577165). FeMn#BC-released Mn(II) served as an additional electron donor, augmenting electron availability for non-dominant anammox species like Candidatus Jettenia caeni and Candidatus. Kuenenia stuttgartiensis. This research highlights the critical mechanism of Fe-Mn synergism for overcoming the bottleneck of anammox nitrogen removal efficiency, and demonstrates the substantial potential of Fe-Mn functionalized materials to revolutionize the existing wastewater treatment technologies towards a carbon-free approach.

The efficacy of integrated vermifiltration technology for treatment of food analysis laboratory wastewater

The macrophyte-assisted vermifiltration (MAVF) technology was applied for treatment of food analysis laboratory wastewater at Industrial Technology Institute (ITI), Sri Lanka for the first time. Three laboratory-scale sub-surface vertical flow units were established:1) without earthworms and plants (Control unit), 2) with earthworms (Eisenia fetida) (vermi-filtration unit (VF unit), 3) with both earthworms and macrophytes (Canna indica) (MAVF unit). Wastewater was fed batch-wise with a feeding rate of 10 mL/min and seven days hydraulic retention time (HRT) for eight consecutive batches. Physiochemical parameters, Chemical Oxygen Demand (COD), Total Phosphorus (TP), Total Nitrogen (TN), pH, of the influent and effluent of all three units were analyzed to investigate the treatment efficiencies. One-Way ANOVA was performed to evaluate the significant differences in treatment efficiencies. The mean COD removal efficiencies of the control unit, VF unit, and MAVF unit were 60.2 % ± 10.7, 71.6± 8.07 %, and 72.0 % ± 8.86, respectively. Average TN removal efficiencies of the control unit, VF unit, and MAVF unit were 8.05 % ± 5.75, 10.9±6.4 %, and 24.9 % ±12.84, respectively. Average TP removal efficiencies were 35.84 % ± 17.5, 35.84 % ± 17.5 %, and 40.0 % ±16.76, respectively. The COD removal displayed promising results, whereas the means for enhancing TP and TN removal should be further studied. The findings of this study sensitizes the testing laboratories to go green by adopting in-house cost effective laboratory wastewater treatment systems.

Mechanisms underlying the detrimental impact of micro(nano)plastics on the stability of aerobic granular sludge: Interactions between micro(nano)plastics and extracellular polymeric substances

Microplastics (MPs) and nanoplastics (NPs) present in wastewater can pose a negative impact to aerobic granular sludge (AGS). Herein, this study found that MPs and NPs (20 mg/L) deteriorated the sludge settleability and granule integrity, resulting in a 15.7 % and 21.9 % decrease in the total nitrogen removal efficiency of the AGS system, respectively. This was possibly due to the reduction of the extracellular polymeric substances (EPS) content. The subsequent analysis revealed that tyrosine, tryptophan, and humic acid-like substances in EPS exhibited a higher propensity for chemisorption and inhomogeneous multilayer adsorption onto NPs compared to MPs. The binding of EPS onto the surface of plastic particles increased the electronegativity of the MPs, but facilitated the aggregation of NPs through reducing the electrostatic repulsion, thereby mitigating the adverse effects of MPs/NPs on the AGS stability. Additionally, comprehensive analysis of the extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the suppressed aggregation of microorganisms was the internal mechanisms contributing to the inadequate stability of AGS induced by MPs/NPs. This study provides novel insights into the detrimental mechanisms of MPs/NPs on the AGS stability, highlighting the key role of EPS in maintaining the structural stability of AGS when exposed to MPs/NPs.

Performances of a novel BAF with ferromanganese oxide modified biochar (FMBC) as the carriers for treating antibiotics, nitrogen and phosphorus in aquaculture wastewater.

In this paper, a biological aerated filter (BAF) based on ferromanganese oxide-biochar (FMBC) was constructed to investigated the removal performance and mechanism for conventional pollutants and four kinds of antibiotic, in contrast of conventional zeolite loaded BAF (BAF-A) and bamboo biochar filled BAF (BAF-B). Results showed that the average removal efficiency of total nitrogen (TN), total phosphorus (TP) and antibiotics in a FMBC-BAF (named by BAF-C) were 52.97 ± 2.27%, 51.58 ± 1.92% and 70.36 ± 1.00% ~ 81.65 ± 0.99% respectively in running period (39-100 d), which were significantly higher than those of BAF-A and BAF-B. In the BAF-C, the expression of denitrification enzyme activities and the secretion of extracellular polymeric substance (EPS) especially polyprotein (PN) were effectively stimulated, as well as accelerated electron transfer activity (ETSA) and lower electrochemical impedance spectroscopy (EIS) were acquired. After 100 days of operation, the abundance of nitrogen, phosphorus and antibiotic removal functional bacteria like Sphingorhabdus (4.52%), Bradyrhizobium (1.98%), Hyphomicrobium (2.49%), Ferruginibacter (7.80%), unclassified_f_Blastoca tellaceae (1.84%), norank_f_JG30-KF-CM45 (6.82%), norank_f_norank_o_SBR1031 (2.43%), Nitrospira (2.58%) norank_f_Caldilineaceae (1.53%) and Micropruina (1.11%) were enriched. Mechanism hypothesis of enhanced performances of nutrients and antibiotics removal pointed that: The phosphorus was removed by adsorption and precipitation, antibiotics removal was mainly achieved through the combined action of adsorption and biodegradation, while nitrogen removal was realized by biologic nitrification and denitrification in a FMBC-BAF for aquaculture wastewater treatment.

New insights and enhancement mechanisms of activated carbon in autotrophic denitrification system utilizing zero-valent iron as indirect electron donors

Zero-valent iron acts as an indirect electron donor, supplying ferrous iron for the nitrate-dependent ferrous oxidation (NDFO) process. The addition of activated carbon (AC) increased the specific NDFO activity in situ and ex situ by 0.4 mg-N/(d·g VSS) and 2.2 mg-N/(d·g VSS), respectively, due to the enrichment of NDFO bacteria. Furthermore, AC reduced the nitrous oxide emission potential of the sludge, a mechanism that metagenomic analysis suggests may act as a cellular energy storage strategy. During a 196-day experiment, a total nitrogen removal efficiency of 53.7 % was achieved, which may be attributed to the upregulation of key genes involved in iron oxidation and denitrification. Based on these findings, a model involving pilin, ’nanowires,’ and a cyc2/?→/(FoxE→FoxY)/?→cymA/Complex III/?-mediated pathway for extracellular electron uptake was proposed. Overall, this work provides a feasible strategy for enhancing the nitrogen removal performance of the ZVI-NDFO process.

Integration of mixotrophic denitrification and anammox in Thiothrix-hydroxyapatite coupled particles treating municipal wastewater against low temperature and organic load shocks

Sulfur-driven autotrophic denitrification coupled with anammox (SPDA) is a promising process for autotrophic nitrogen removal, but autotrophic microorganisms are challenging to retain in wastewater treatment units. In this study, a single-stage mixotrophic denitrification coupled with anammox (MDA) process was established in an up-flow anaerobic sludge bed reactor with Thiothrix-hydroxyapatite coupled particles. The advancement of the sludge granulation process effectively strengthened the resistance of the MDA system to environmental stresses, and the SPDA-dominated nitrogen removal process achieved a total nitrogen removal efficiency of 88.6 %, a nitrogen removal rate of 0.432 KgN/m3/d at temperatures as low as 12.8 °C and an organic loading rate of 0.63 KgCOD/m3/d. Interestingly, the ecological niche integration of sulfur oxidizing bacteria (SOB), anammox bacteria and heterotrophic denitrifying bacteria in the granular sludge was observed during long-term operation. The FISH-CLSM results revealed the spatial distribution of functional microorganisms in the granular sludge and the potential pollutant transformation mechanism. The aggressive growth of SOB dominated by Thiothrix constructed a biological wall at the periphery of the granules, which ensured their priority for nitrate acquisition, supplied nitrite to the internal anammox bacteria, and acted as an important barrier against the shock of organic loads. Overall, this study presents a novel granulation approach for the biological treatment of sulfur-containing wastewater, highlighting the efficacy of functional integration within Thiothrix-hydroxyapatite coupled particles as an effective strategy to resist environmental stress.

Nitrogen removal pathways in lake restoration using microalgal-bacterial granular sludge: Unraveling influence of organics and carbon to nitrogen ratio

This study investigated the performance of microalgal-bacterial granular sludge (MBGS) in the restoration of Qingling Lake and Huangjia Lake, focusing on nitrogen removal under varying water quality conditions. Significant color changes in MBGS and differences in granule characteristics were observed, with Qingling Lake demonstrating superior removal efficiencies for ammonia nitrogen, nitrate nitrogen, and total nitrogen compared to Huangjia Lake. Stoichiometric analysis revealed that when the chemical oxygen demand (COD) and carbon-to-nitrogen (C/N) ratios were less than 20 mg/L and 20, respectively, assimilatory nitrate reduction was positively correlated with both, whereas denitrification was negatively correlated. Gene function analysis showed that Qingling Lake had a more active microbial community supporting efficient nitrogen metabolism. The findings highlighted the enormous potential of MBGS in lake restoration, demonstrating its ability to adapt to different COD concentrations and C/N ratios by altering its nitrogen removal pathways.

Molecular evidence of internal carbon-driven partial denitrification in a mainstream pilot A-B system coupled with side-stream EBPR treating municipal wastewater

Achieving mainstream short-cut nitrogen removal via nitrite has become a carbon and energy efficient way, but still remains challenging for low-strength municipal wastewaters. This study integrated sidestream enhanced biological phosphorus removal system in a pilot-scale adsorption/bio-oxidation (A-B) process (named A-B-S2EBPR system) and nitrite accumulation was successfully achieved for treating the municipal wastewater. Nitrite could accumulate to 5.5 ± 0.3 mg N/L in the intermittently aerated tanks of B-stage with the nitrite accumulation ratio (NAR) of 79.1 ± 6.5 %. The final effluent concentration and removal efficiency of total inorganic nitrogen (TIN) were 4.6 ± 1.8 mg N/L and 84.9 ± 5.6 %, respectively. In-situ process performance of nitrogen conversions, routine batch nitrification/denitrification activity tests and functional gene abundance of nitrifiers collectively suggested that the nitrite accumulation was mainly caused by partial denitrification rather than out-selection of nitrite oxidizing bacteria (NOB). Moreover, the single-cell Raman spectroscopy analysis first demonstrated that there was a specific microbial population that could utilize polyhydroxyalkanoates (PHA) as the potential internal carbon source during the partial denitrification process. The integration of S2EBPR brings unique features to the conventional A-B process, such as extended anaerobic retention time, lower oxidation–reduction potential (ORP), much higher and complex volatile fatty acids (VFAs) etc., which can largely reshape the microbial communities. The dominant genera were Acinetobacter and Comamonadaceae, which accounted for (17.8 ± 15.5)% and (6.7 ± 3.4)%, respectively, while the relative abundance of conventional nitrifiers was less than 0.2%. This study provides insights into phylogenetic and phenotypic shifts of microbial communities when incorporating S2EBPR into the sustainable A-B process to achieve mainstream short-cut nitrogen removal.

Iron-retrofitted anaerobic baffled reactor system for rural wastewater treatment: Stable performance of nutrients removal with phosphorus recovery and minimal sludge production

An iron-retrofitted anaerobic baffled reactor (ABR) system was developed for the effective treatment of rural wastewater with reduced maintenance demand and aeration costs. Average removal efficiencies of chemical oxygen demand, total nitrogen and total phosphorus of 99.4%, 62.7% and 92.6% were achieved respectively, when the ABR system was operating at steady state. With effective bioreduction of FeIII in the anaerobic chambers, phosphorus was immobilized in the sludge as vivianite, the sole phosphorus-carrying mineral. The FeIII in the recirculated sludge induced Feammox in the ABR reactor, contributing 14.8% to total nitrogen removal. Biophase separation and enrichment of microorganisms associated with iron and nitrogen transformations were observed in the system after Fe dosing, which enhanced the removal of pollutants. The coupling of Feammox and vivianite crystallization to remove nitrogen and phosphorus in an iron-retrofitted ABR would appear to be a promising technology for rural wastewater treatment.

Firmicutes and Bacteroidetes as the dominant microorganisms for ammonium nitrogen wastewater treatment with a low C/N ratio in BCOR

Improving nitrogen removal is a significant concern in the biological treatment of ammonium nitrogen (NH4+-N) wastewater with low chemical oxygen demand (COD)/NH4+-N (C/N) ratio, and microorganisms are the critical factor affecting nitrogen removal. In this study, a laboratory-scale biological contact oxidation reactor (BCOR) system was successfully started up (day 1 to day 47) and stabilized (day 48 to day 320). A 16S rRNA gene sequencing analysis showed that the phyla Firmicutes and Bacteroidetes were first observed as the dominant microorganisms in the BCOR for the ammonium nitrogen wastewater treatment with a low C/N ratio. The genera Bacteroides (phylum Bacteroidetes), Porphyromonas (phylum Bacteroidetes), Dialister (phylum Firmicutes), and Anaerococcus (phylum Firmicutes) also became the main microorganisms in this system for the first time. These microbial communities enabled the system to achieve an average ammonium nitrogen removal efficiency and total nitrogen removal efficiency of 95.8 % and 88.1 %, respectively, during the operational period. It indicated that these dominant microorganisms in the BCOR system played an essential role in improving the performance of biological nitrogen removal. This conclusion will play a critical role in promoting the microbial mechanism research and technology engineering application of the BCOR system for treating ammonium nitrogen wastewater with a low C/N ratio.

Enhancing simultaneous nitrification and denitrification in a plant-scale integrated fixed-film activated sludge system: Focusing on the cooperation between activated sludge and biofilm

To further remove nutrients through simultaneous nitrification and denitrification (SND), the integrated fixed-film activated sludge (IFAS) system has become one of the most efficient pathways for modifying the existing wastewater treatment plants. This study investigated the cooperation between suspended activated sludge and carrier-attached biofilm for promoting SND in different seasons in a plant-scale IFAS system. The results showed that the involvement of biofilm could stimulate SND, removing 23.9 % of influent total nitrogen (TN) in the aerobic IFAS system. The nitrification rate and the SND ratio were much influenced by the temperature, resulting in higher TN removal efficiency in summer (90.3 %) than that in winter (86.4 %). The highest SND ratio of 67 % could be achieved at the temperature of 23 °C. Additionally, the SND ratio also depended on a variety of operational parameters (such as dissolved oxygen (DO), COD/NH4+-N, and mixed liquor suspended solids (MLSS)). High-throughput sequencing technology further confirmed that the composition of the functional bacterial communities in activated sludge significantly differed from that in biofilm. Nitrifying bacteria were mostly detected in biofilm samples, while more denitrifying bacteria existed in activated sludge, thus resulting in the enhancement of synergic nitrogen removal via SND in the IFAS system.