Total Inorganic Nitrogen Research Articles

Improving the water quality in the Zandvlei Estuary, Cape Town, by retrofitting sustainable drainage systems in the Diep River catchment

The Zandvlei Estuary is the only functioning estuary along the False Bay coastline of Cape Town and is therefore of extreme local ecological importance. The most significant problems are eutrophication and siltation caused by the increased total inorganic nitrogen (TIN) and soluble ready phosphorus (SRP) levels due to urban development and the associated increased impervious surface area in the catchment that drains into it. In South Africa, stormwater drainage systems conventionally channel everything they collect into receiving water bodies without significant treatment. Sustainable drainage systems (SuDS) provide an alternative approach to managing stormwater runoff. They are designed to manage both stormwater quality and quantity while potentially improving biodiversity and amenity. This project modelled the potential improvement in the quality of the water entering Zandvlei Estuary resulting from the implementation of selected SuDS control measures in Zandvlei’s Diep River catchment using the software program, PCSWMM. SRP, TIN, total phosphorus (TP) and total suspended solids (TSS) were selected as pollutant indicators. Treatment trains that included a large, constructed wetland at the bottom of the catchment will likely provide the greatest improvements to the water quality entering Zandvlei – potentially reducing SRP, TIN, TP and TSS by approximately 59%, 53%, 53%, and 66%, respectively – as well as potentially reducing the runoff by 48%.

Comparation on the responses and resilience of single-anammox system and synergistic partial-denitrification/anammox system to long-term nutrient starvation: Performance and metagenomic insights

Starvation disturbance was a common problem in biological sewage treatment processes. However, understanding about the responses and resilience of different active anammox biomass in autotrophic and heterotrophic systems to long-term nutrient starvation remains limited. This study compared responses and potential recovery mechanisms of autotrophic single-Anammox and heterotrophic synergistic partial-denitrification/anammox (PD/anammox) systems to prolonged starvation (31–40 days). After starvation, total inorganic nitrogen (TIN) removal efficiency of single-Anammox and synergistic PD/anammox systems decreased to 62.16 % and 78.52 %, respectively, of their original level. After the nutrient resupply, the performance of both systems gradually recovered to a similar-to-pre-starvation level at the rate of 1.26 %/day and 1.89 %/day, respectively. Compared with single-Anammox system, complex synergistic relationship of microorganisms and effective quorum sensing (QS) regulation strategies might mitigate the negative influences were caused by starvation and ensure the performance quickly return of synergistic PD/anammox system. This study would contribute to promote the application of Anammox technology.

Novel control strategy employing anaerobic/aerobic/anoxic/aerobic/anoxic mode to enhance endogenous denitrification and anammox for municipal wastewater treatment

Anaerobic/Aerobic/Anoxic (AnOA) process utilizes endogenous denitrification to remove nitrogen. However, low endogenous denitrification activity critically restricts its application owing to insufficient carbon sources. In this study, a novel control strategy employing anaerobic/aerobic/anoxic/aerobic/anoxic (AOAOA) mode was introduced to treat low Carbon/Nitrogen (C/N) ratio municipal wastewater over 262 days. The concentration of total inorganic nitrogen (TIN) was only 3.9 ± 2.0 mg/L in the effluent, with a high nitrogen removal efficiency (NRE) of 94.3 %. The relative abundance of Candidatus Competibacter increased from 1.2 % to 2.3 %, ensuring an efficient endogenous denitrification process. Additionally, Candidatus Brocadia enriched from 0.02 % to 0.6 %, contributing to 63.1 % nitrogen removal during the anoxic stage in Phase Ⅲ. This study presents a promising approach for enhancing endogenous denitrification and anammox in the AnOA process, contributing to sustainable wastewater treatment.

Combined activated sludge and sand filtration for purification of UASB effluent with high suspended solids from water hyacinth juice

Rapid biogasification of water hyacinth, a globally overgrown species, using compression and up-flow anaerobic sludge blanket (UASB) treatment of the juice has recently been proposed. This study aimed to establish a post-purification system for UASB-treated juice to effectively utilize the remaining nutrients for valuable products, such as vegetables and microalgae. To easily remove hard-to-degrade suspended solids (SS) and organic matter from UASB-treated juice, the activated sludge (AS) and sand filtration processes—conventional biological treatments—were introduced, with a focus on their physical treatment properties.Over 76% of SS and 43% of the organic carbon were removed from UASB-treated juice during the process. The hydraulic retention time of the AS was reduced to one day, indicating the potential of minimizing the facility size. The light transmittance, which is crucial for microalgae mediums, improved sevenfold. Even after most of the SS was removed by the AS, the sand filtration further increased the light transmittance by 1.4 times. The AS effectively removed most of the SS and organic matter, whereas sand filtration enhanced the treatment stability and further improved the light transmittance. NH4+ was mostly oxidized to NO3-, which is less toxic to plants. The total inorganic nitrogen content remained high after treatment, suggesting that UASB effluents from water hyacinth can be used as a nutrient source for hydroponics and microalgae cultivation in developing countries.

Start-up of a full-scale two-stage partial nitritation/anammox (PN/A) process treating reject water from high solid anaerobic sludge digestion (HSAD)

High solid anaerobic digestion (HSAD) achieves the benefits of high volumetric loading rates and lower reject water production, which, however, results in much more concentrated reject water with a remarkable increase in organics and nitrogen compared with that from conventional AD with low solid content. The high concentrations of ammonium (2000–3500 mg/L) and COD (3000–4000 mg/L) were reported to exert inhibition on anammox bacteria (AnAOB), posing challenges to the application of the partial nitritation/anammox (PN/A). To date, no cases of PN/A process start-up for sludge HSAD reject water were reported. This study demonstrated the start-up process of a 480 m3/d PN/A project without anammox sludge inoculation and treating HSAD reject water from a centralized dewatered sludge treatment plant. The project did not construct new infrastructures but utilized previously constructed tanks to upgrade the process from existing short-cut nitrification-denitrification to a two-stage PN/A process. Although no external anammox sludge inoculation was performed to save seeding sludge cost, the start-up was successfully achieved in about 9 months (273 days) based on a three-step method of “AnAOB enrichment - sludge acclimation - capacity doubling”. During start-up, the relative abundance of AnAOB (Candidatus_Kuenenia) increased from near zero to 12.0%. After start-up, the total inorganic nitrogen (TIN) removal load reached 0.74 kgN/(m3•d), with a total nitrogen removal efficiency of over 90%. Compared to the traditional nitrification-denitrification process, the PN/A process remarkably reduces the addition of organic chemicals and aeration energy consumption, saving approximately 4.2 million yuan (RMB) in operational costs annually. In summary, this research provides a full-scale reference for the start-up of the PN/A process treating sludge HSAD reject water.

Optimizing nitrogen removal in PD/A reactors: Effects of influent composition and temperature on system stability and microbial dynamics

This study investigates the performance and microbial community dynamics in two partial denitrification/anammox (PD/A) reactors with different influent wastewater compositions (differ in the presence/absence of NO2−) subjected to a controlled temperature gradient reduction from mesophilic (30 °C) to room temperature (20.92 °C) over 76 days. Two lab-scale PD/A reactors (R1 and R2), both operated with a total inorganic nitrogen (TIN) concentrations of 70 mg N/L. R1 maintained a NH4+/NO2−/NO3− ratio of 3:3:1 and a COD/NO3− ratio of 2.0, while R2 had an NH4+/NO3− ratio of 3:4, and COD/NO3− ratios of 2.0 and 2.5. Our findings reveal distinct responses to the temperature transitions: the optimization of the NH4+/NO2−/NO3− ratio at 3:3:1 facilitated more stable nitrogen removal as temperatures decreased. This stability can be attributed to the enhanced synchronization between anammox bacteria and denitrifiers, promoting a balanced bioconversion process that is less susceptible to temperature-induced disruptions. Notably, the specific anammox activity (SAA) in both reactors declined linearly with the decrease in temperature, but the relative abundance of anammox bacteria (Ca. Brocadia) in R1 increased from 2.1 % to 9.7 %. Furthermore, the percentage of anammox-related key genes was higher in R1 than in R2, suggesting a microbial mechanism underlying the stable performance of R1. These results underscore the significant impact of influent nitrogen composition on PD/A performance amid temperature gradients and highlight the critical role of optimizing influent ratios for maintaining efficient nitrogen removal. This study offers valuable insights into enhancing the stability of PD/A systems under varying thermal conditions.

Efficient removal of organic matter and nitrogen from municipal wastewater in multi-module biochar filters for onsite wastewater treatment

ABSTRACT Biochar is a promising material for wastewater treatment. This study assessed multi-module biochar filters (MmBFs) as onsite wastewater treatment systems (OWTSs), comprising movable modules filled with biochar to remove chemical oxygen demand (COD), nitrogen, phosphorus, and Escherichia coli (E. coli) in wastewater. The MmBF treats wastewater sequentially through six modules: three aerobic modules (M1-M3) for organic matter oxidation and nitrification, two anoxic modules (M4-M5) for denitrification, and an additional module (M6) for the removal of faecal bacteria using biochar and bark. The experiments ran for 381 days using three identical MmBF pilots with two distinct sampling periods, conducted under conditions relevant to OWTSs using municipal wastewater as influent. Water samples were taken from the influent, final effluent, and effluent of each module to evaluate the removal efficiency of organic matter, nitrogen, phosphorus, and E. coli. During the second sampling period, the results showed a 95 ± 2.1% removal of COD, along with a substantial removal of total inorganic nitrogen (71 ± 6.6%). However, phosphate removal was limited (3.4 ± 30.4%). E. coli removal decreased from 2.63 ± 0.93 log10 removal in the first sampling period to 1.8 ± 0.73 log10 removal in the second sampling period. In summary, the MmBFs showed promising potential in treating organic matter, nitrogen, and E. coli, making it an alternative option for OWTS. However, further exploration is needed to assess long-term performance, micropollutant removal, and biological activities. Design enhancements, especially for phosphorus removal are necessary.

Advanced N removal from low C/N sewage via a plug-flow anaerobic/oxic/anoxic (AOA) process: Intensification through partial nitrification, endogenous denitrification, partial denitrification, and anammox (PNEnD/A)

Achieving low-cost advanced nitrogen (N) removal from municipal wastewater treatment plants (WWTPs) remains a challenge. A plug-flow anaerobic/oxic/anoxic (AOA) system with a mixtures bypass (MBP) integrating partial nitrification (PN), endogenous carbon denitrification (EnD), partial denitrification (PD), and anaerobic ammonium oxidation (Anammox), was constructed to treat actual sewage with a low C/N ratio. The effluent concentrations and removal efficiency of total inorganic nitrogen (TIN) during stable operation were 2.9 ± 0.9 mg/L and 93.1 ± 2.0 %, respectively. EnD was enhanced by the MBP through the efficient utilization of polyhydroxyalkanoates generated in the anaerobic zone. PD was promoted by the addition of carries and sodium acetate to the anoxic tank and the subsequent implantation of the Anammox biofilm successfully coupled PD/A. Stable PN was obtained with a satisfactory nitrite accumulation ratio of 92.6 %, facilitated by carriers and the introduction of hydroxylamine in the oxic zone. Mass balance analysis revealed that EnD and Anammox contributed 40.8 % and 48.2 % of TIN removal, respectively. The enrichment and synergistic effects of ammonia-oxidizing bacteria, denitrifying bacteria, glycogen-accumulating organisms, and anaerobic ammonia-oxidizing bacteria formed a diverses bacterial basis for the establishment of PN, EnD, PD, and Anammox (PNEnD/A) in the AOA system. The successful integration of PNEnD/A into the AOA process provides an innovative approach for low-cost advanced N removal in WWTPs.

Modeling nitrogen behavior in Tigris River using system dynamics approach

Nitrogen behavior across multimedia environment like Tigris River is complex process resulting in a number of interactions of the biogeochemical processes. A solid understanding of the interacted processes is critical to evaluate river system performance. Inorganic nitrogen including ammonium ion (NH4+), free ammonia (NH3), total ammoniacal nitrogen (NHx), nitrite (NO2−), nitrate (NO3−), total oxidized nitrogen (NOx), and total inorganic nitrogen (TIN) in Tigris River were examined from April 2018 to March 2020. A simple system model was implemented to simulate and to help interpret the trend of inorganic N forms based on datasets collected from the river system. It is indicated that the obtained results revealed that the dynamic model was able to represent and predict NHx and NOx behavior in Tigris River. Root mean squared errors between actual and predicted concentrations for NHx and NOx were 0.053 and 0.312 g m−3, respectively. Modeling analysis confirmed the steady-state dynamics of NHx and NOx over the course of the study. Average concentration for NHx was 0.37 ± 0.05 g m−3, while mean value of NOx levels was 2.18 ± 0.33 g m−3 in the Tigris river water. The results from this study also supported by the changes of the water budget, chemical oxygen demand, pH, dissolved oxygen, electrical conductivity, and water temperature in the river system. The results suggest that the microbial mechanisms are the principal N transformation processes in the river system. Findings presented in this research could help to improve conceptual understanding of N behavior in Tigris River, and therefore could assist decision makers to select best management practices and to develop mitigation strategies to sustain water quality in Tigris River.

Enhanced nitrogen removal from low C/N municipal wastewater through nitrification, partial denitrification and anammox via a step-feed strategy: Synergistic contribution by bacteria in biofilm and floc sludge

Energy-efficient nitrogen removal from carbon-limited municipal wastewater poses challenges. This study developed a novel partial denitrification and anammox (PD/A) process using a step-feed strategy in a single-stage integrated fixed-biofilm activated sludge (IFAS) system operated under sequencing batch mode. Despite relatively low temperatures (15.9–21.6 °C), biological nitrogen removal efficiency reached 80.5 % without the addition of external carbon sources. With the total inorganic nitrogen (TIN) of 48.9 ± 1.2 mg N/L, and C/N of 4.0 in influent, the TIN in effluent achieved 9.6 ± 1.5 mg N/L. Anammox bacteria (AnAOB) activity in the biofilm was 27.96 mg N/(g VSS·d), which was threefold greater than in floc sludge. Candidatus Brocadia (AnAOB) presented a high relative abundance in biofilm (0.53 %), whereas denitrifying bacteria including Thauera and Candidatus Competibacter were mainly retained in floc sludge. Overall, the coupling of step-feed strategy and IFAS offers novel insights into the efficient nitrogen removal from low C/N domestic sewage for retrofitting of municipal wastewater treatment plants, not only saving the energy consumption for aeration, but also fully utilizing carbon sources and ammonium in the influent for the PD/A process.

Integration of batch assays and microbial community analysis for partial nitritation and anammox process monitoring

This study investigates the feasibility of using batch assays combined with microbial community analysis to control the partial nitritation/anammox (PN/A) process. A Moving Bed Sequencing Batch Biofilm Reactor (MBSBBR) was operated over 130 days with varying ammonia influent concentrations. The highest anammox activity (22.4 mg N/gVSS∙h) was observed at an influent concentration of 200 mg N-NH4/L, correlating with high total inorganic nitrogen (TIN) removal efficiency. However, increasing the ammonia influent concentration to 340 mg N/L led to decreased anammox and nitrifying bacteria activities and reduced TIN removal efficiency. Sequencing revealed Candidatus Brocadia as the predominant genus, with its abundance correlating with TIN removal performance. High correlation coefficients (above 0.76) among batch tests highlighted the interdependence of key bacterial activities in the PN/A, emphasizing the need for a balanced microbial community for effective nitrogen removal. Batch assays provided immediate data on metabolic activities, while sequencing offered comprehensive insights into microbial community structure. Integrating these methods allowed for a holistic understanding of the microbial dynamics and their impact on process stability. This approach enhances the accuracy of wastewater treatment monitoring, aiding in the development of effective management strategies for optimizing PN/A processes.

Integrated process of Tetrasphaera-dominated in-situ waste activated sludge fermentation, biological phosphorus removal and endogenous denitrification in single reactor for treatment of wastewater with limited carbon sources

An integrated process of sludge in-situ fermentation, biological phosphorus removal and endogenous denitrification (ISFPR-ED) was developed to treat low ratio of chemical oxygen demand to nitrogen (COD/N) wastewater and waste activated sludge (WAS) in a single reactor. Nutrient removal and WAS reduction were achieved due to Tetrasphaera-dominated sludge fermentation provided organic carbon in extending the anaerobic duration. The WAS reduction efficiency, effluent orthophosphate (PO43−-P) and total inorganic nitrogen reached 28.1 %, less than 0.4 and 7.2 mg/L, respectively. While organic carbon was reduced by 67 %. Tetrasphaera, conventional polyphosphate accumulating organisms (PAOs) stored glycogen, amino acids, and PHA for nutrient removal. Excess energy from fermentation enhanced anaerobic PO43−-P uptake by Tetrasphaera. Tetrasphaera was the dominant PO43−-P removal and fermentation bacteria, working synergistically with conventional PAOs and fermenting microorganisms. This integrated process improves nutrient removal efficiency and reduces operating costs for carbon addition and WAS disposal in wastewater treatment.

Carbon-efficient Nutrients removal from real municipal wastewater under conditions of highly variable influent quality and low temperature

In order to maximize carbon efficient nutrient removal of real primary effluent under the conditions of highly variable influent quality and low temperature, this study integrated four advanced bioprocesses, namely partial nitrification, endogenous denitrification, partial denitrification-anammox, enhanced biological phosphorus removal, into one advanced pilot design. The pilot system has been on-site operated for 212 days and was able to handle highly variable conditions with the aid of automatic feedback and feedforward controllers nested in secondary and tertiary treatment. Comparing to the case when full nitrification and full dentification technologies had to be used to meet the effluent requirement of total inorganic nitrogen (TIN) ≤ 3 mg/L and orthophosphate phosphorus ≤ 0.1 mg/L, the pilot results showed that 100 wt% carbon and 55.5 wt% oxygen could be saved in the secondary process and another 45.2 wt% carbon could be saved in the tertiary process. 44.5 wt% influent TIN was removed through endogenous denitrification in the secondary treatment with another 39.5 wt% TIN polished by partial denitrification-anammox in tertiary treatment. Because post-anoxic endogenous denitrification has removed majority of the NOX-N, it was concluded that the energy intensive mixed liquor recirculation that has been popular in traditional design for pre-anoxic zone denitrification can be eliminated.

Atmospheric deposition patterns in bulk open field precipitation and throughfall in Aleppo pine forest and black pine forest on the eastern Adriatic coast

The Mediterranean region, with its unique ecological characteristics, is particularly sensitive to global environmental changes, including climate change and impact of air pollution.Although Aleppo pine and black pine forests are the most abundant on the eastern Adriatic coast, atmospheric deposition in these forests is poorly studied. Changes in the chemical composition of precipitation as it passes through the tree canopy can lead to soil and groundwater eutrophication, and soil acidification, which affects plant vitality. In this study, the dynamics of ion deposition in Aleppo pine forest (Pinus halepensis Mill.) and black pine forest (Pinus nigra Arnold) on the eastern Adriatic coast are investigated, focusing on throughfall and bulk open field depositions.The aim of our research was to fill the gaps in understanding the influence of tree canopies on deposition fluxes in two different Mediterranean pine stands and to compare total inorganic nitrogen loads with critical loads. Over a period of two years, bulk open field precipitation and throughfall were sampled, measured and analysed using the ICP Forest methodology.The results indicate significant differences in ion deposition between bulk open field and throughfall, with throughfall showing higher values for almost all ions. The highest enrichment ratio was determined for K+. The comparison of the actual inorganic nitrogen load with the critical nitrogen load for Mediterranean pine forests revealed that the inorganic nitrogen load exceeded the critical load in the Aleppo pine forest. Ion deposition increased in the throughfall compared to bulk precipitation, which can be attributed to the seasonality of precipitation, including leaching and long dry periods. These findings enhance our understanding of ion deposition fluxes in vulnerable Mediterranean pine ecosystems and emphasize the need for long-term research on this topic in the actual changing environmental conditions.

In-situ electrochemical upcycling ammonia from wastewater-level nitrate with a natural hematite electrode: Regulation, performance, and application

Electrochemical reduction of nitrate (NO3-RR) to ammonia (NH4+/NH3) offers promising prospects for NO3- treatment. However, this process still suffers from NH4+ causing secondary pollution and catalyst deactivation in high-concentration NO3- wastewater. Herein, a high-performance system comprising a hematite (α-Fe2O3) electrode and a water-resistant membrane achieved 97.6 % NO3- removal and 81.6 % NH4+ as (NH4)2SO4in situ recovery at wastewater-level NO3-. The system exhibited an energy consumption of 62.2 kWh·KgNH3−1 and a Faradaic efficiency of 85.9 %. In-situ spectroscopy and electrochemical measurements revealed that α-Fe2O3 acted as both an electron transfer mediator for reducing NO3- to NO2- and an active center for NH3 formation via NO2-/Fe(Ⅱ) redox. Density functional theory calculations identified *HNO3 to *NO2 as potential-determining step of NO3-RR. Natural hematite-based system exhibited 74.8 % total inorganic nitrogen removal and 77.1 % NH4+ recovery for actual photovoltaic wastewater. This study provides insights into the development of electrochemical systems for resourcefully treating NO3--containing wastewater.

Simultaneous carbon, nitrogen and phosphorus removal in sequencing batch membrane aerated biofilm reactor with biofilm thickness control via air scouring aided by computational fluid dynamics

Membrane aerated biofilm reactor (MABR) is challenged by biofilm thickness control and phosphorus removal. Air scouring aided by computational fluid dynamics (CFD) was employed to detach outer biofilm in sequencing batch MABR treating low C/N wastewater. Biofilm with 177–285 µm thickness in cycle 5–15 achieved over 85 % chemical oxygen demand (COD) and total inorganic nitrogen (TIN) removals at loading rate of 13.2 gCOD/m2/d and 2.64 gNH4+-N/m2/d. Biofilm rheology measurements in cycle 10–25 showed yield stress against detachment of 2.8–7.4 Pa, which were equal to CFD calculated shear stresses under air scouring flowrate of 3–9 L/min. Air scouring reduced effluent NH4+-N by 10 % and biofilm thickness by 78 µm. Intermittent aeration (4h off, 19.5h on) and air scouring (3 L/min, 30 s before settling) in one cycle achieved COD removal over 90 %, TIN and PO43−-P removals over 80 %, showing great potential for simultaneous carbon, nitrogen and phosphorus removals.

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.

Influence of residual anaerobic granular sludge (AnGS) from anaerobically digested molasses wastewater in aerobic granular sludge reactor

This study investigated the impact of residual anaerobic granular sludge (AnGS) from anaerobic digesters treating molasses wastewater on ammonium reduction in a downstream aerobic granular sludge (AGS) reactor. Two conditions were tested: raw (high AnGS concentration) and settled (low AnGS concentration) anaerobically digested molasses wastewaters were fed into the AGS reactor. With the introduction of raw wastewater, enhanced nitrite accumulation at 30 % and improved total inorganic nitrogen (TIN) removal at 11 % were observed compared to 1 % nitrite accumulation and 8 % TIN removal with the introduction of settled wastewater. However, AnGS adversely affected other aspects of reactor performance, increasing effluent solid content and decreasing soluble chemical oxygen demand removal efficiency from 20 % in the low AnGS condition to 11 % in the high AnGS condition. Despite the observed retention of AnGS in the reactor, no significant bioaugmentation effects on the microbial community of the AGS were observed. Aerobic granular sludge was consistently observed in both conditions. The study suggests that AnGS may act as a nucleus for granule formation, helping to maintain granule stability in a disturbed environment. This study offers a systematic understanding of the impact of AnGS on subsequent nitrogen removal process using AGS, aiding in the decision making in the treatment of high solid anaerobic digestate.

Microhabitat-differentiated distribution of culturable and antagonistic bacteria in marine ecosystem: Seawater as the original microbial provider

Abstract: Due to the typical tropical climatic characteristics, the Xisha archipelago in the South China Sea has derived typical biological treasures, particularly culturable bacteria. Microbial resources in nature will be valuable resources for industrial application only after being culturable microorganisms. Herein, the global distribution of culturable and antagonistic bacteria against aquatic pathogenic vibrios, including Vibrios parahaemolyticus, Vibrios harveyi, Vibrios alginolyticus, Vibrios campbellii, and Vibrios owensii, in thirty-nine stations of the Xisha archipelago across four main microhabitats of sediment, seawater, corals, and marine organisms were investigated by cultivation-based strategies. Vibrio was the dominant genus (68.98%) among the culturable bacteria, followed by Pseudoalteromonas (9.36%) and Alteromonas (4.91%). Only four targeted antagonistic strains with an antagonistic specificity of a certain Vibrio were obtained, namely the strains of SP52, C219 and W198, which provided a new insight of precise disease prevention/treatment by further revealing the targeted antagonistic mechanism. The correlations between the abundance of culturable bacteria and environmental factors in the whole Xisha archipelago and four microhabitats showed that salinity as the main factor significantly affected the distribution of 6 microbial genera, while total inorganic nitrogen (TIN), total carbon (TC), and PO43− significantly related to 3 genera, 2 genera, and 1 genus, respectively. Importantly, we found that microhabitat discrepancy rather than distance discrepancy of environmental factors made a greater contribution to the distribution of culturable bacteria and antagonistic bacteria and the capability of antagonistic bacteria, which was emphasized as an important factor in shaping bacterial communities. Additionally, seawater was the original microbial provider of other microhabitats in the marine ecosystem, which was the opposite of the terrestrial ecosystem in that the soil is the original microbial provider.

Metagenomic insights into microbial metabolic mechanisms of a combined solid-phase denitrification and anammox process for nitrogen removal in mainstream wastewater treatment

To overcome the significant challenges associated with nitrite supply and nitrate residues in mainstream anaerobic ammonium oxidation (anammox)-based processes, this study developed a combined solid-phase denitrification (SPD) and anammox process for low-strength nitrogen removal without the addition of nitrite. The SPD step was performed in a packed-bed reactor containing poly-3-hydroxybutyrate-co-3-hyroxyvelate (PHBV) prior to employing the anammox granular sludge reactor in the continuous-flow mode. The removal efficiency of total inorganic nitrogen reached 95.7 ± 1.2% under a nitrogen loading rate of 0.18 ± 0.01 kg N·m3·d−1, and it required 1.02 mol of nitrate to remove 1 mol of ammonium nitrogen. The PHBV particles not only served as biofilm carriers for the symbiosis of hydrolytic bacteria (HB) and denitrifying bacteria (DB), but also carbon sources that facilitated the coupling of partial denitrification and anammox in the granules. Metagenomic sequencing analysis indicated that Burkholderiales was the most abundant HB genus in SPD. The metabolic correlations between DB (Betaproteobacteria, Rhodocyclaceae, and Anaerolineae) and anammox bacteria (Candidatus Brocadiac and Kuenenia) in the granules were confirmed through microbial co-occurrence networks analysis and functional gene annotations. Additionally, the genes encoding nitrate reductase (Nap) and nitrite reductase (Nir) in DB primarily facilitated nitrate reduction, thereby supplying nitric oxide to anammox bacteria for subsequent nitrogen removal with hydrazine synthase (Hzs) and hydrazine dehydrogenase (Hdh). The findings provide insights into microbial metabolism within combined SPD and anammox processes, thus advancing the development of mainstream anammox-based processes in engineering applications.