Total Inorganic Nitrogen Removal Efficiency Research Articles

Resourceful application and mechanism of oyster shell-microalgae synergistic system：Sustainable treatment of harsh low carbon nitrogen ratio actual wastewater

Microalgal technology holds great promise for both low C/N wastewater treatment and resource recovery simultaneously. Nevertheless, the advancement of microalgal technology is hindered by its reduced nitrogen removal efficiency in low C/N ratio wastewater. In this work, microalgae and waste oyster shells were combined to achieve a total inorganic nitrogen removal efficiency of 93.85% at a rate of 2.05 mg L−1 h−1 in low C/N wastewater. Notably, over four cycles of oyster shell reuse, the reactor achieved an average 85% ammonia nitrogen removal extent, with a wastewater treatment cost of only $0.092/ton. Moreover, microbial community analysis during the reuse of oyster shells revealed the critical importance of timely replacement in inhibiting the growth of non-functional bacteria (Poterioochromonas_malhamensi). The work demonstrated that the oyster shell - microalgae system provides a time- and cost-saving, environmental approach for the resourceful treatment of harsh low C/N wastewater.

Analyzing the nitrogen removal performance and cold adaptation mechanism of immobilized cold-acclimation ANAMMOX granules at low temperatures.

To improve the treatment performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, the immobilized cold-acclimation ANAMMOX granules (R3) were prepared and their low-temperature nitrogen removal ability as well as the cold adaptation mechanism were analyzed. The results indicated that the total inorganic nitrogen (TIN) removal efficiency of R3 was significantly higher than that of R2 (cold-acclimation granules without immobilization) and R1 (common granules), especially at 11 ± 2 and 7±2°C (68% and 54%). These were attributed to the remarkable biomass retention capacity of R3, high up to 4.3-4.9mg/gVSS even at 5-18°C. Besides, higher protein (PN) content of tightly bound extracellular polymeric substances (TB-EPS) also facilitated microbial aggregation in R3. Meanwhile, R3 granules retained higher ANAMMOX activity and heme c content at 5-25°C. The original dominant ANAMMOX genus (Candidatus Kuenenia) in R3 kept higher abundance (49%-57%) at 23 ±2 and 16 ±2°C, whereas Candidatus Brocadia became the dominant ANAMMOX genus (25%-32%) in R3 at 11 ±2 and 7±2°C. Notably, different ANAMMOX genera in R3 may adapt to cold environment by regulating the expression of cold-stress proteins (CspA, CspB, PpiD, and UspA). PRACTITIONER POINTS: Immobilized cold-acclimation ANAMMOX granules showed higher nitrogen removal efficiency at 23°C → 5°C. Immobilization method effectively retained biomass (Candidatus Kuenenia and Candidatus Brocadia). Immobilization facilitated TB-EPS release and biological aggregation in cold-acclimation granules. Expression of cold-stress proteins in immobilized cold-acclimation granules was more active.

Decrease in Oxygen Concentration for the Fast Start-Up of Partial Nitritation/Anammox without Inoculum Addition

Initiating the partial nitritation and anammox (PN/A) process without inoculation poses a significant challenge. Thus, there is a notable amount of interest in devising a straightforward strategy for the start-up of PN/A. This study demonstrates the feasibility of achieving the rapid start-up of a one-stage PN/A process within a moving-bed sequencing batch biofilm reactor (MBSBBR) by reducing the oxygen concentrations: 3.0 mg O2/L (Stage I), 2.0 mg O2/L (Stage II), and 1.0 mg O2/L (Stage III). The anammox activity was observed 15 days after a gradual decrease in the oxygen concentration and confirmed using a specific anammox activity test (5.9 mg N/gVSS∙h). During Stage III, the average total inorganic nitrogen (TIN) removal efficiency was 60.6%. The relative abundance of planctomycetes, a typical phylum representing anammox microorganisms, increased almost three times from Stage I (2.8%) to Stage III (7.1%). These results demonstrate the potential of a decrease in oxygen concentration for the fast start-up of the one-stage partial nitritation and anammox process without inoculation. The implementation of the studied DO strategy has practical implications for wastewater treatment plant operators, particularly in the start-up of the PN/A processes. Additionally, batch assays allow for the rapid assessment of treatment plant performance, providing real-time insights into its functionality and, thereby, optimizing wastewater treatment practices.

Enhancing nitrogen removal performance through intermittent aeration in continuous plug-flow anaerobic/aerobic/anoxic process treating low-strength municipal sewage

Advanced nitrogen removal cannot be achieved through the conventional biological nitrogen removal process, which requires higher carbon sources and aeration energy. The proposal of intermittent aeration in the aerobic chambers offered an innovative approach to enhance nitrogen removal in low carbon-to-nitrogen ratio (C/N) municipal sewage, using a plug-flow reactor with anaerobic/aerobic/anoxic (AOA) process. Due to the effective utilization of internal carbon sources through the intermittent aeration, the total inorganic nitrogen removal efficiency (NRE) increased to 77.9 ± 3.2 % with the mean aerobic hydraulic retention time of only 3.2 h and a low C/N of 3.3 during the operation of 210 days. Polyhydroxyalkanoates dominated the nitrogen removal in this AOA system, accounting for 48.0 %, primarily occurring in the alternant aerobic/anoxic chambers. Moreover, the microbial community structure remained unchanged while the NRE increased to 77.9 %. This study provided an efficient and economic strategy for the continuous plug-flow AOA process.

Effect of free ammonia on partial denitrification: Long-term performance, mechanism, and feasibility of PD/Anammox-FBBR for mature landfill leachate treatment.

As a stable and effective approach for NO2--N accumulation, partial denitrification (PD) could significantly cut down operation cost, and PD/Anammox (PD/A) is a promising nitrogen removal process in wastewater treatment. The biotoxicity of free ammonia (FA) to nitrifying bacteria and anammox bacteria has been demonstrated, while whether FA affects PD bacteria is an open question. Here, long-term operation of PD-fixed bed biofilm reactor (PD-FBBR) treating synthetic wastewater and mature landfill leachate was conducted to reveal the mechanism concerning the effect of FA on PD bacteria. Stable NO2--N accumulation was achieved with NO3--N to NO2--N transformation ratio (NTR) of 60-70% during 280-day operation with FA ranged from 0 to 20.71 ± 0.23 mg/L, while NTR decreased and maintained at ∼30% when FA reached 40.59 ± 0.19 mg/L. Specific NOx--N reduction rate improved at low FA concentration (< 12 mg/L), while high FA level (> 25 mg/L) had inhibitory effect on PD bacteria. Under FA stress, more extracellular polymeric substances (EPS) were secreted, and the glnA gene abundance, glutamine synthase concentration, and glutamine concentration in cell and EPS significantly increased, indicating the enhancement of glutamine biosynthesis in PD bacteria for ammonia assimilation played an important role in response to FA stress. Metagenomic sequencing showed that FA stimulated the upregulation of narK (NO3--N/NO2--N antiporter) gene abundance and enhanced uptake of NO3--N and extrusion of NO2--N. Comamonas, unclassified_f__Comamonadaceae and Thauera were highly enriched in biofilm, which played a key role in the stable NO2--N accumulation. Furthermore, a novel two stage PD/A-FBBR was applied to mature landfill leachate treatment, and satisfactory total inorganic nitrogen removal efficiency ranged from 81.38 ± 3.56% to 89.16 ± 1.57% was obtained at relatively low COD/NO3--N of 2.57-2.84. Overall, these findings demonstrated how PD bacteria respond to FA stress and confirmed the feasibility of PD/A process in high FA wastewater treatment.

Impact of Influent Composition and Operating Conditions on Carbon and Nitrogen Removal from Urban Wastewater in a Continuous-Upflow (Micro)Aerobic Granular Sludge Blanket Reactor

Aerobic granular sludge is an interesting alternative to the conventional activated sludge (CAS) system and modified-Ludzack–Ettinger (MLE) process for biological wastewater treatment, as it allows a more cost-effective and simultaneous removal of carbon (C) and nitrogen (N) compounds in a single stage. In this study, (micro)aerobic C and N removal from synthetic urban wastewater was investigated in a continuous-double-column-upflow aerobic granular sludge blanket (UAGSB) system. The UAGSB reactor was operated under different dissolved oxygen (DO) ranges (0.01–6.00 mg∙L−1), feed C/N ratios (4.7–13.6), and hydraulic retention times (HRTs) (6–24 h). At a DO range of 0.01–0.30 mg∙L−1, feed C/N ratio of 13.6, and HRT of 24 h, the UAGSB achieved the highest chemical oxygen demand (COD), N-NH4+, and total inorganic nitrogen (TIN) removal efficiencies of 86, 99, and 84%, respectively. A preliminary assessment of the energy and economic savings associated with the process investigated was also carried out. The impact of capital and operating costs mainly related to the energy consumption of the aeration was taken into account. The assessment reveals that the capital and energy expenses of the UAGSB reactor would result in cost savings of around 14 and 7%, respectively, compared with a MLE system.

Municipal wastewater treatment with limited carbon sources: The significance and advantages of transformation from partial denitrification to partial nitrification coupling with anammox

Anaerobic ammonium oxidation (anammox) combined with partial nitrification (PN) is expected to achieve energy self-sufficiency in wastewater treatment, while its advantages have not been fully revealed. An anaerobic/aerobic/anoxic (AOA) system was established to treat low chemical oxygen demand (COD)-total inorganic nitrogen (TIN) (C/N) ratio (3.08) municipal wastewater. Anammox bacteria were enriched from 7 × 106 to 3 × 108 copies/gSS during partial denitrification coupling with anammox (PDA) phase. With the PN achievement, the anammox hotspot zone transformed from the anoxic zone through PDA (37%) to the aerobic zone by partial nitrification coupled with anammox (PNA) (12%). As the nitrite accumulation rate increased to 97%, the TIN removal efficiency and rate increased to 95% and 0.12 kgN/(m3·d). Although anammox performance weakened after this transformation, the carbon sources saved by PN drove more nitrogen removal. PNA was beneficial for advanced and efficient nitrogen removal in carbon-limited wastewater treatment and was less dependent on higher anammox contribution.

Nitrogen reclamation from aquaculture wastewater as potential fish feed additives via bacterial and algal-bacterial granular sludge systems

In this study, the potentials of aerobic granular sludge (AGS) and algal-bacterial granular sludge (ABGS) systems for the recovery of nitrogen from aquaculture wastewater as protein-rich fish feed additive were assessed. During 88 days' cultivation, the average chemical oxygen demand (COD), total phosphorus (TP) and total inorganic nitrogen (TIN) removal efficiencies were determined to be 96.7 %, 75.7 %, and 73.2 % in the AGS system, 96.8 %, 82.5 %, and 76.6 % in the ABGS system, respectively. The net biomass yield of ABGS was 24.0 % higher than that of AGS. About 11.3 % and 14.1 % of the TIN in wastewater were recovered as organic nitrogen in AGS and ABGS, respectively. The two granules had a similarly high content of total proteins (52 %, dry matter based), both containing 9 essential amino acids for fish and 7 non-essential amino acids, these features enabled them to serve as a low-cost substitute for conventional protein-rich additives in the fish diets.

The Recovery of a Sequencing Biofilm Batch Reactor—Anammox System: Performance, Metabolic Characteristics, and Microbial Community Analysis

The mainstream application of the anammox process is often hindered by its long recovery phase and instability under disturbance. In this study, a lab-scale anammox sequencing biofilm batch reactor (SBBR) was rapidly recovered within 85 days by gradually increasing the influent nitrogen concentration, and the total inorganic nitrogen (TIN) removal efficiency achieved 83.44 ± 0.03%. During the recovery process, the nitrogen removal rate (NRR) increased from 0.05 to 0.34 kg/(m3·d), with the nitrogen loading rate (NLR) changing from 0.08 to 0.40 kg/(m3·d) in the anammox system. The activities of hydrazine oxidase (HZO) in the biofilm also increased from 0.17 to 10.80 μmol Cyt-c/(g VSS·s). Also, the dominant anammox genera in the biofilm were Candidatus Kuenenia and Candidatus Brocadia. The results of this study suggested that an SBBR–anammox system filled with a microbial carrier could facilitate the enrichment of anammox bacteria and contribute to performance recovery.

Optimizing the efficiency of a three‐step fed anoxic/aerobic sequencing batch reactor using response surface methodology

AbstractIn this study, the removal of chemical oxygen demand (COD), ammonium nitrogen (NH4+‐N) and total inorganic nitrogen (TIN) in a three‐step fed anoxic/aerobic sequencing batch reactor was investigated. Response surface methodology (RSM) was used to determine and optimize the effect of operating parameters such as the ratio of aerobic/anoxic (Ae/Ax) phase durations, percentage of feeding to the first anoxic phase (R1) and ratio of feeding percentages to the third and second anoxic phases (R3:R2). The results of the analysis of variance (ANOVA) showed that the three independent variables were statistically highly significant (p &lt; 0.0001). The values of the determination coefficient (R2) for the removal efficiency of COD, NH4+‐N and TIN was 0.9558, 0.9334 and 0.9963, respectively, indicating a good agreement between the experimental results and the predicted values. The quadratic model was valid in predicting experimental results. The optimum conditions obtained using the desirability function were found to be 2.05 for the ratio of Ae/Ax phase durations, 43.09% for R1 and 0.86 for R3:R2, where the COD, NH4+‐N and TIN removal efficiency was 94.29, 97.83 and 86.86%, respectively. As a result of the evaluation of the interactive effect of the independent variables, it was determined that R1 was the most effective factor. The results showed that RSM could be used for optimization of operating parameters and improvement of efficiency in a three‐step fed anoxic/aerobic sequencing batch reactor.

Improving stability and nitrogen removal performance of pilot-scale autotrophic process for mature landfill leachate treatment utilizing in-situ organics

This study established a stable and efficient pilot-scale denitrification (DN) and partial nitritation (PN) combined with autotrophic nitrogen removal process for mature landfill leachate treatment. A total inorganic nitrogen removal efficiency (TINRE) of 95.3% was achieved without any external carbon source input, including 17.1%, 1.0% and 77.2% of nitrogen removal contributed by the DN, PN and autotrophic processes, respectively. ANAMMOX genus, Ca_Anammoxoglobus (19.4%) was dominant in autotrophic reactor. Moreover, denitrifying bacteria could utilize in-situ organics, including poorly degradable organics, to enhance the nitrogen removal performance of autotrophic process, contributing 3.4% of TINRE. This study provides new insights for the economical, low-carbon, and efficient treatment of mature landfill leachate.

Optimization of synthetic domestic wastewater treatment performance in anoxic/aerobic sequencing batch reactor with zeolite addition

In this study, treatment performance was investigated based on chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), total inorganic nitrogen (TIN) and simultaneous nitrification and denitrification (SND) parameters in a zeolite-added anoxic/aerobic sequencing batch reactor. Response surface methodology (RSM) was used to model treatment performance, determine the impact of operating conditions, and optimize them. The effect of zeolite size, dosage and COD/NH4 +-N (C/N) ratio as operating parameters were evaluated in the central composite design (CCD). Variance analysis (ANOVA) results of the quadratic model, high coefficients of determination and low values of the root mean square error (RMSE) for dependent variables indicated the validity of the model in predicting experimental results. The desirability function showed that optimum conditions were 0.80 mm for zeolite size, 3.05 g/L for zeolite dosage and 9.8 for C/N. Under these conditions, the maximum COD, NH4 +-N, TIN removal efficiencies and SND efficiency were 92.85%, 93.3%, 77.33% and 82.96%, respectively. The results of the study showed that the most effective independent variable on dependent variables was the C/N ratio.

Effects of superficial gas velocity on the performance of an air-lift internal circulation partial nitrification-anammox granular sludge reactor

The airlift internal circulation reactor for partial nitrification-anammox (PNA-ALR) has the advantages of a small footprint, high mass transfer efficiency, and the ease of formation of granular sludge, thus making it an effective biological treatment for ammonia-containing wastewater. Although superficial gas velocity (SGV) is an essential parameter for PNA-ALR, it is unclear how the magnitude of SGV impacts nitrogen removal performance. In this study, the nitrogen removal efficiencies of five PNA-ALRs with different SGV were measured during feeding with synthetic municipal wastewater. At an optimal SGV of 2.35 cm s−1, the PNA-ALR consistently maintained the total inorganic nitrogen (TIN) removal efficiency at 76.31% and the effluent TIN concentration was less than 10 mg L−1. By increasing or decreasing the SGV, the nitrogen removal efficiency decreased to a range between 30% and 50%. At lower SGV, the dead space in the PNA-ALR was increased by 21.15%, and the feast/famine ratio of sludge increased to greater than 0.5, which caused a disruption in the structure, and a large loss of, granular sludge. Computational fluid dynamics (CFD) simulations showed operation at a higher SGV, resulting in excessive shear stress of 3.25 N m−2 being generated from bubble rupture in the degassing section. Fluorescent staining determined a decrease of 26.5% in viable bacteria. These results have improved our understanding of the effects of SGV on a PNA-ALR during mainstream wastewater treatment.

Insights on nitrogen and phosphorus removal mechanism in a single-stage Membrane Aeration Biofilm Reactor (MABR) dominated by denitrifying phosphorus removal coupled with anaerobic/aerobic denitrification

In the study, the denitrifying phosphorus removal process coupled with anaerobic/aerobic denitrification was started in a single-stage Membrane Aeration Biofilm Reactor (MABR). When the influent NO3−-N was 50.2 mg/L and the total phosphorus (TP) was 30.5 mg/L, the maximum Total Inorganic Nitrogen Removal Efficiency (TINRE) can reach 99.79 % and the Total Phosphorus Removal Efficiency (TPRE) can reach 82.62 % without the addition of any flocculant or precipitant. The phosphorus content in the substrate sludge was 4.10 %–6.15 %, which was higher than that in the initial biofilm or activated sludge (1.27 %–1.83 %). Based on 16S rRNA sequencing technology, it was found that Phosphorus-Accumulating Organisms (PAOs, Acinetobacter, relative abundance 0.02 % to 1.92 %) and Denitrifying Phosphorus-Accumulating Organisms (DPAOs, Flavobacterium (0.26 % to 5.39 %), Bdellovibrio (0.12 % to 1.48 %), and Pseudomonas (2.29 % to 1.28 %)) played pivotal roles in phosphorus removal. The enzyme gene reads of Complex I and Complex V processes were much more than that of Complex II- Complex IV, which indicated that Complex I and Complex V can be the main process for oxidative phosphorylation in the MABR. Moreover, four inorganic nitrogen metabolic processes, Dissimilatory Nitrate Reduction to Ammonium (DNRA), Assimilatory Nitrate Reduction Ammonium (ANRA), nitrification, and denitrification were found. Nitrifiers (Nitrosomonas (0.09 % to 0.19 %), Nitrospira (2.48 % to 0.06 %)), denitrifiers (Dokdonella (6.95 % to 2.11 %), Denitratisoma (0.42 % to1.48 %)), and aerobic denitrifiers (Pseudomonas (2.29 % to 1.28 %) and Thauera (4.75 % to 1.78 %)) contributed to nitrogen removal in the MABR. This study provided insights into the removal mechanism of nitrogen and phosphorus in a single-stage MABR.

Achieving deep autotrophic nitrogen removal from low strength ammonia nitrogen wastewater in aeration sponge iron biofilter: Simultaneous nitrification, Feammox, NDFO and Anammox

Partial nitrification and anammox process is considered to be a good choice for nitrogen removal. Nevertheless, it is difficult to achieve in low ammonia wastewater because of the need to control further oxidation of nitrite. Nitrification combined with Feammox (anaerobic ammonia oxidation coupled to Fe (III) reduction) and NDFO (nitrate/nitrite-dependent Fe (II) oxidation) can achieve autotrophic removal of low ammonia. And sponge iron can avoid the disadvantage of continuously adding iron sources in this process. Therefore, a sponge iron biofilter (SIBF) treating low ammonia wastewater under aeration was explored in this study. The optimal operating conditions for SIBF were hydraulic retention time (HRT) of 9 h and gas–water ratio (R) of 9:1, at which the total inorganic nitrogen removal efficiency was up to 77.2 %, and effluent ammonia and total inorganic nitrogen concentrations were less than 5 mg/L and 15 mg/L, respectively. This met the 1A discharge standard of municipal wastewater in China. Stable ratio isotope results indicated that Feammox, NDFO and Anammox resulted in high nitrogen loss in SIBF. And different nitrogen transformation contribution tests indicated NDFO had the dominant contribution, which accounted for 55.7 %. Besides, the production of N2O was minimum under HRT of 9 h and R of 9:1, in which the N2O emission factor was 0.7 %. Stable isotope tracing analysis showed that 92.8 % of N2O was derived from ammonia and the dominant production pathway was nitrifier denitrification. The results of microbial community showed that the nitrification bacteria-Nitrosomonas, Nitrotoga, Nitrospira, Feammox bacteria-Dechloromonas, NDFO bacteria-Thiobacillus and anammox bacteria-Brocadia played major roles in SIBF. Therefore, SIBF shows superior performance and application potential in autotrophic nitrogen removal from low-ammonia nitrogen wastewater under aeration.

Performance characteristics and bacterial community analysis of a novel two-step-feed three-stage A/O-MBBR system for nitrogen removal in municipal wastewater

To obtain a high nitrogen removal efficiency and fully use the carbon sources in raw wastewater, a novel two-step-feed three-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR) system with ten chambers was established for municipal wastewater treatment. The designed ten chambers in the 2F-3S-A/O-MBBR system played different roles in nitrogen and organic removals, and they accomplished the task of achieving stable high nitrogen removal efficiency at different temperatures together. Concretely, the average total inorganic nitrogen (TIN) removal efficiency was improved to 72.88 % from 61.55 % without any external carbon sources by the second-stage A/O-MBBR subsystem due to the two-step-feed configuration, and it was further improved to 91.42 % by the third-stage A/O-MBBR subsystem due to the use of the external carbon sources. Specific functional biofilms with different bacterial communities (r = 0.85, P ≤ 0.001) and functional genes of denitrification and nitrification (r = 0.63, P ≤ 0.001) were formed in 4 groups of functional zones, including the first-stage anoxic, second-stage anoxic, third-stage anoxic and oxic chambers. This study developed an efficient 2F-3S-A/O-MBBR biological nitrogen removal process and investigated the performance characteristics and bacterial community to provide fundamental support for the application of this process.

Low energy-consumed process of integrated anammox and in-situ fermentation-based denitrification for ultra-efficient nitrogen removal from mainstream domestic sewage

Anammox is a promising biotechnology for nitrogen removal and gaining popularity in mainstream wastewater treatment. The efficient and low energy-consumed elimination of the intrinsic byproduct nitrate in anammox-mediated process is still a tough barrier and urgently demands resolving. To explore a newly green alternative for advanced nitrogen removal from domestic sewage, this study proposed a novel Integrated Anammox, Fermentation and Denitrification (IAFD) process. After 215-day operation, total inorganic nitrogen (TIN) removal efficiency markedly increased from 72.6% to 94.1% and effluent TIN dropped from 7.9 mg L−1 to 1.8 mg L−1 with influent TIN of 56 mg L−1. Through in-situ activated sludge fermentation, 37.341 mg COD·L−1·d−1 organics was yielded, causing a COD/NO3−-N of 8.9, Soluble protein (63.8%), polysaccharide (10.6%) and acetic acid (13.9%) were primary components. Candidatus_Brocadia (0.8%) and Candidatus_Competibacter (4.6%) were dominant functional bacteria, which contributed 81.1% and 18.9% to nitrogen elimination, respectively. Robust anammox (3.37 mg N·g VSS−1·h−1), fermentation-assisted denitrification and denitritation synergistically boosted N removal. The novel process required no external carbon, reduced 59.5% aeration and 35.8% external sludge. The novel process showed significantly environmental and economical advantages of low operation expenses and energy cost with no external carbon requirement, 59.5% aeration and 35.8% external sludge reduction. This work provided an energy-neutral and sustainable scheme for the advanced nitrogen removal of municipal wastewater and sludge disposal in WWTPs.

Optimization of Aeration Rate—Low Cost but High Efficiency Operation of Aniline-Degrading Bioaugmentation Reactor

In this work, two sequencing batch reactors (R0 and R1) were built for treating 600 mg·L−1 aniline-containing wastewater. R1 was a bioaugmentation system with the addition of highly efficient aniline-degrading strain AD4 (Delftia sp.), while R0 served as a control system. The effects of aeration rates on R1 and R0 were investigated in the range of 300 to 800 mL·min−1. Results showed that the increase in aeration rates promoted the degradation of aniline in both R1 and R0. Under bioenhancement, the highest removal efficiency of aniline was stabilized above 99.7% in R1 while it was lower than 95.6% in R0. As for nitrogen removal, increasing aeration rates reduced the NH4+-N released from aniline degradation but caused the accumulation of NO3−-N and NO2−-N. R1 had a better total inorganic nitrogen removal efficiency than R0. The alpha biodiversity of both R1 and R0 reached the highest at 400 mL·min−1 and decreased at higher aeration rates. However, R1 always kept higher biodiversity than R0. Furthermore, the abundance of various functional bacteria was also higher in R1. This study revealed the high efficiency of bioenhanced activated sludge for the treatment of refractory wastewater and illustrated the importance of aeration control from the angle of energy saving, which demonstrated the potential of biofortification to help energy conservation and emission reduction.

Spontaneous granulation of moderately halophilic sludge inoculated with saltern sediments from single granule into multi-granule aggregation

There is very limited research on the application of moderate halophiles for biotreatment of hypersaline wastewater widely generated from some industries. This study demonstrated the development of moderate halophiles inoculated from saltern sediments into aerobic granule sludge (AGS) to treat hypersaline wastewater with a salinity of 100 g/L. The granulation of moderate halophiles can occur without applying the settling velocity selective pressure. The saltern sediment initially aggregated into single small granules and finally developed into 1200 ± 50 μm multiparticle granules. The halophiles affiliated in Halomonas was dominant in the granular bacterial community, with a relative abundance of 94.52%. Halomonas ventosae secreted sulfated polysaccharides. The sulfated polysaccharides content accounted for 63.95 ± 2.10% in the polysaccharides (PS), having an adhesive role in connecting single granules. Multiparticle granules showed the clear stratified structure, with α-D-glucopyranose polysaccharides in the inner bounders and β-D-glucopyranose polysaccharides in the outer. The moderately granular sludge showed the stable chemical oxygen demand (COD) removal efficiency of >90% and the aerobic total inorganic nitrogen (TIN) removal efficiency (equal to ammonia removal) of 70 ± 5.00%. This paper contributes new insight into the formation of moderately halophilic granular sludge and accelerates the application of moderately halophilic granular sludge to treat hypersaline wastewater.

Aerobic nitrous oxide emission in anoxic/aerobic and intermittent aeration sequencing batch reactors

ABSTRACT This study characterized nitrogen removal and nitrous oxide (N2O) emissions from lab-scale anoxic/aerobic sequencing batch reactor (AOSBR) and intermittent aeration sequencing batch reactor (IASBR), respectively, for treating synthetic municipal wastewater. The N2O emission was evaluated in a simulated cycle, and batch conditions of aerobic nitrification, simultaneous nitrification and denitrification (SND), and aerobic denitrification. The results show that nitrogen removal was enhanced in IASBR compared to AOSBR, with 94.2% and 67.9% of total inorganic nitrogen removal efficiency in IASBR and AOSBR, respectively. In the simulated cycle, the emission factors (of oxidized ammonium) were 4.9% and 0.6% in AOSBR and IASBR, respectively. Under batch conditions, the N2O emission factors during SND were obviously higher than that during aerobic nitrification and denitrification. The N2O emission factors during SND ranging 0.68–11.68% in AOSBR and 1.25–5.13% in IASBR. Furthermore, N2O emission under batch conditions was affected by the aeration ratios. Moderate and high aeration ratios used in this study stimulated the N2O emission from SND. The N2O emission was enhanced with the nitrite accumulation during aerobic nitrification when the nitrite-oxidizing bacteria was inhibited by a chemical inhibitor. Aerobic denitrification via nitrite could be the main pathway of N2O generation from SND processes. The findings from our study can help further understand N2O emission mechanisms and guide the optimization of the current wastewater treatment process for minimizing N2O emission.