Start-up of granule-based denitrifying reactors with multiple magnesium supplementation strategies

Aerobic granulation and resource production under continuous and intermittent saline stress

Three sequential batch reactors (SBR) were operated to evaluate salt addition's impact on granulation, performance, and biopolymer production in aerobic granular sludge (AGS) systems. System R1 was fed without adding salt (control); system R2 operated with saline pulses, i.e., one cycle with salt (2.5 g NaCl/L) addition followed by another without salt; and R3 received continuous supplementation of 2.5 g NaCl/L. The results indicated that the reactors supplemented with salt presented higher concentrations of mixed liquor volatile suspended solids (MLVSS) and better settleability than R1, showing that osmotic pressure contributed to biomass growth, accelerated granulation, and improved physical characteristics. The faster granulation occurred in R2, thus proving the beneficial effects of intermittent salt addition through alternating pulses. Salt addition did not impair the simultaneous removal of carbon, nitrogen, and phosphorus. In fact, R2 showed better carbon removals. In conclusion, continuous or intermittent (pulsed) supplementation of 2.5 g NaCl/L did not lead to increased production of extracellular polymeric substances (EPS) and alginate-like exopolymers (ALE). This outcome could be attributed to the low saline concentration employed, a higher food-to-microorganism (F/M) ratio observed in R1, and possibly greater endogenous consumption of biopolymers in the famine period in R2 and R3 due to the greater solids retention time (SRT). Therefore, this study brings important results that contribute to a better understanding of the effect of salt in continuous dosing or in pulses as a selection pressure strategy to accelerate granulation, as well as the behavior of the AGS systems for saline effluents.

Reason and control strategy for denitrification and anammox sludge flotation in nitrogen removal process: Mechanisms, strategies and perspectives

Anaerobic biological treatment technology, especially denitrification and anaerobic ammonia oxidation (anammox) technology as mainstream process, played dominant role in the field of biological wastewater treatment. However, the above process was prone to sludge floating during high load operation and thereby affecting the efficient and stable operation of the system. Excessive production of extracellular polymeric substance (EPS) was considered to be the main reason for anaerobic granular sludge flotation, but the summaries in this area were not comprehensive enough. In this review, the potential mechanisms of denitrification and anammox sludge floatation were discussed from the perspective of granular sludge structural characteristics, nutrient transfer, and microbial flora change respectively, and the corresponding control strategies were also summarized. Finally, this paper indicated that future research on sludge flotation should focus on reducing the negative effects of EPS in sludge particles.

Anoxic granular activated sludge process for simultaneous removal of hazardous perchlorate and nitrate

An airtight, anoxic bubble-column sequencing batch reactor (SBR) was developed for the rapid cultivation of perchlorate (ClO₄^-) and nitrate (NO₃^-) reducing granular sludge (GS) in this study. Feast/famine conditions and shear force selection pressures in tandem with a short settling time (2-min) as a hydraulic section pressure resulted in the accelerated formation of anoxic granular activated sludge (AxGS). ClO₄^- and NO₃^- were efficiently (>99.9%) reduced over long-term (>500-d) steady-state operation. Specific NO₃^- reduction, ClO₄^- reduction, chloride production, and non-purgeable dissolved organic carbon (DOC) oxidation rates of 5.77 ± 0.54 mg NO₃^--N/g VSS·h, 8.13 ± 0^.74 mg ClO₄^-/g VSS·h, 2.40 ± 0.₄0 mg Cl^-/g VSS·h, and 16.0 ± 0.06 mg DOC/g VSS·h were recorded within the reactor under steady-state conditions, respectively. The AxGS biomass cultivated in this study exhibited faster specific ClO₄^- reduction, NO₃^- reduction, and DOC oxidation rates than flocculated biomass cultivated under similar conditions and AxGS biomass operated in an up-flow anaerobic sludge blank (UASB) bioreactor receiving the same influent loading. EPS peptide identification revealed a suite of extracellular catabolic enzymes. Dechloromonas species were present in high abundance throughout the entirety of this study. This is one of the initial studies on anoxic granulation to simultaneously treat hazardous chemicals and adds to the science of the granular activated sludge process.

Correlation of structural extracellular polymeric substances in the mesh biofilms with solids retention time and biofilm hydraulic resistance in dynamic membrane bioreactors

Dynamic membrane bioreactor (DMBR), which mainly relied on the in-situ formed biofilms on support materials with large aperture (e.g., nylon mesh) to separate fine particles in wastewater, has attracted a lot of attentions due to low cost. The filtration performance of DMBR is mainly determined by the structure and hydraulic resistance of biofilms formed on the mesh. Therefore, understanding the correlation of operation conditions with mesh biofilm compositions and permeability are critically important for optimizing DMBR operation. In present study, how structural extracellular polymeric substances, including alginate-like extracellular polysaccharide (ALE) and amyloid-like protein (AP), in mesh biofilms correlate to solids retention time (SRT) and biofilm structures was explored in DMBRs. At 5d-SRT, compact and gel-like mesh biofilms were formed with a high specific filtration resistance (SFR) of 459 × 10⁹ m/g, while at 40d-SRT porous mesh biofilms were developed with a low SFR of 24 × 10⁹ m/g. Consequently, the 5d-SRT MBR experienced more rapid rise in transmembrane pressure. Further studies found that the 5d-SRT mesh biofilms had a higher AP content, which was positively correlated to biofilm hydraulic resistance. On the contrary, the 40d-SRT mesh biofilms contained a higher content of ALE, suggesting that ALE was negatively correlated to biofilm hydraulic resistance. Therefore, AP instead of ALE likely played a more important role in the formation of compact and gel-like mesh biofilms.

Deciphering the toxic effects of antibiotics on denitrification: Process performance, microbial community and antibiotic resistance genes

The extensive application of antibiotics, and the occurrence and spread of antibiotic resistance genes (ARGs) shade health risks to human and animal. The long-term effects of sulfamethoxazole (SMX) and tetracycline (TC) on denitrification process were evaluated in this study, with the focus on nitrogen removal performance, microbial community and ARGs. Results showed that low-concentration SMX and TC (<0.2 mg L^-1) initially caused a deterioration in nitrogen removal performance, while higher concentrations (0.4-20 mg L^-1) of both antibiotics had no further inhibitory influences. The abundances of ARGs in both systems generally increased during the whole period, and most of them had significant correlations with intI1, especially efflux-pump genes. Castellaniella, which was the dominant genus under antibiotic pressure, might be potential resistant bacteria. These findings provide an insight into the toxic effects of different antibiotics on denitrification process, and guides future efforts to control antibiotics pollution in ecosystems.

Performance enhancement of H2S-based autotrophic denitrification with bio-gaseous CO2 as sole carbon source through new pH adjustment materials

H₂S-based denitrification could achieve synchronous removal of nitrate and H₂S and had been regarded as an efficient way for biogas desulfurization and wastewater denitrification. Using CO₂ in biogas as carbon source had a potential of saving cost further, but the performance deteriorated due to the drop in pH. Two kinds of nature ore, medical stone and phosphate ore, were added as new pH adjustment materials in this study, and feasibility of using CO₂ as sole carbon source for H₂S-based denitrification was investigated. As a result, both materials could increase the pH from 4.5 to above 6.0. Compared with medical stone, higher level of pH (up to 6.39) and nitrate removal efficiency (99.1%) were obtained with phosphate ore. In addition, ATP increased more rapidly than the control, reflecting improvement on microbial activities. Therefore, phosphate ore as the pH adjustment material could improve H₂S-based denitrification performance obviously.

Mass transfer of nanobubble aeration and its effect on biofilm growth: Microbial activity and structural properties

It is necessary to improve the performance and reduce the aeration cost is of wastewater treatment by aerobic biofilm systems. Nanobubble aeration is supposed to be a promising method to achieve these goals. Compared with coarse bubbles, dissolved oxygen profiling showed that the nanobubbles provided more oxygen to biofilms, offering superior oxygen supply capacity and 1.5 times higher oxygen transfer efficiency. Nanobubble aeration accelerated the growth of the biofilm and achieved better removal efficiencies of chemical oxygen demand and ammonia, with as maximum as six times higher dehydrogenase activity, and more extracellular polymeric substance content than when using the traditional aeration mode. This is attributed to the enhancement of metabolism and the proliferation of microorganisms. Confocal laser-scanning microscopy imaging confirmed that nanobubble aeration affected the components of biofilm by shifting the microbial community and changing its metabolic pathways of biofilms, such as carbohydrate synthesis. Nanobubble aeration resulted in an energy saving of approximately 80%. The assessment of nanobubble aerated biofilm growth suggests that this technique can offer a rapid-initiation, high efficiency, and low-cost strategy for aerobic biofilm systems in wastewater treatment.

Metal oxide nanoparticles resonate to ammonium removal through influencing Mg2+ absorption by Pseudomonas putida Y-9

Most metal oxide nanoparticles (NPs) can impact ammonium removal, but the underlying mechanism remains unclear. In this study, high doses of NiO, CuO, ZnO and TiO₂ (>1 mg/L) inhibited the ammonium removal performance of Pseudomonas putida Y-9. Interestingly, low levels of CuO NPs (0.1, 0.5 mg/L) and NiO NPs (0.1 mg/L) enhanced ammonium removal efficiency. Moreover, a decrease in Mg²⁺ levels was significantly positively correlated with ammonium removal efficiency, while negatively correlated with the Ti²⁺, Zn²⁺, and Cu²⁺ release of NPs. Further research on effect of NPs and their corresponding cations on ammonium removal revealed that four NPs affected Mg²⁺ absorption in Y-9 via different routes, thus impacting NH₄⁺ removal efficiency, i.e., the effect of NiO NPs was caused by itself, TiO₂ NPs' impact was solely due to the release Ti⁴⁺, while the influence of CuO NPs and ZnO NPs was based on both the particles and released ions.

Ca(II) and Mg(II) significantly enhanced the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II)

This study investigated the impacts of alkaline-earth metals [Ca(II), Mg(II)] and heavy metals [Zn(II), Ni(II)] on the nitrogen removal capacity of Arthrobacter arilaitensis Y-10. StrainY-10 was able to tolerate 20 mg/L Ca(II) and its ammonium removal efficiency was 100%. 0.5 mg/L Ca(II) effectively promoted total nitrogen removal from wastewater containing nitrite. Mg(II) supplementation substantially enhanced the bacterial growth and nitrogen reduction. As Mg(II) concentrations increased from 0 to 2 mg/L, the ammonium, nitrate and nitrite removal efficiencies increased by 40.62%, 69.91% and 64.68%, respectively. Although the nitrogen removal ability of strain Y-10 was sharply hindered by Zn(II) and Ni(II), it occurred continuously even when the Zn(II) concentration reached 30 mg/L. However, the ammonium and total nitrogen removal almost stopped at 8 mg/L Ni(II), and the denitrification capacity was lost when the Ni(II) concentration exceeded 1 mg/L. The results demonstrate that Ca(II) and especially Mg(II) could significantly enhance the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II).

Investigating the effect of copper and magnesium ions on nitrogen removal capacity of pure cultures by modified non-competitive inhibition model

Copper, a common heavy metal, may be beneficial for or poisonous to microbial activity. The objective of this study was to determine the effect of different copper ion concentrations on the nitrogen removal performance of Arthrobacter arilaitensis strain Y-10 and Pseudomonas taiwanensis strain J488. The non-competitive inhibition model was employed to evaluate the 50% inhibition concentrations (IC₅₀ values) of copper ions toward the pure strains. In the absence of magnesium ions, a low concentration of copper (0.1 mg/L) significantly enhanced the ammonium removal ability of strain Y-10 and its removal efficiency increased by 10.88% compared with the control treatment. Copper ranging from 0 to 0.1 mg/L had no significant effect on the ammonium removal capacity of strain J488. After adding 9.90 mg/L of magnesium to the basal medium, the effects of copper on nitrification of ammonium or denitrification of nitrate or nitrite were also assessed. In these conditions, 0.25 mg/L copper ions could strongly inhibit the ammonium, nitrate and nitrite removal activities for strain Y-10. For strain J488, no clear deterioration in ammonium removal efficiency was observed at copper ion concentrations below 0.5 mg/L, but 0.25 mg/L copper ions significantly inhibited nitrate and nitrite removal efficiencies, which were only 45.88% and 6.35%, respectively. The IC₅₀ values of copper ions for nitrate and nitrite removal by strain Y-10 were 0.195 and 0.090 mg/L respectively; for strain J488, the IC₅₀ values were 0.175 and 0.196 mg/L. The magnesium ions could improve the cell growth, nitrogen removal efficiency and copper ion resistance of bacteria.

Transient disturbance of engineered ZnO nanoparticles enhances the resistance and resilience of anammox process in wastewater treatment

The increasing use of engineered nanoparticles (NPs) in consumer and industrial products raises concerns about their environmental impacts, but their potential influence on anaerobic ammonium oxidation (anammox) process in wastewater treatment remains unknown. In this study, the response of granule-based anammox reactor to different loads of ZnONPs was investigated. The introduction of 1-5mgL^-1 ZnONPs did not affect reactor performance, but 90% of the nitrogen removal capacity was deprived by a shock of 10mgL^-1 ZnONPs within 3days. Anammox activity was significantly inhibited, but no significant stimulation of intracellular reactive oxygen species (ROS) production or extracellular lactate dehydrogenase (LDH) activity was observed. The inhibition was thus mainly due to the accumulation of toxic Zn(II) ions in anammox biomass. However, the resistance and resilience of this anammox reactor to ZnONPs were enhanced by intermittent perturbations in the mode of "shock-recovery". The up-regulated abundance of Zn(II)-exporter ZntA might contribute to the enhanced resistance. In addition, these repeated transient disturbances improved the functional specificity of the anammox community despite the reduction of its diversity. Overall, these results may provide useful references for evaluating and controlling the risk of NPs to anammox process.

Inhibitory effects of sulfamethoxazole on denitrifying granule properties: Short- and long-term tests

The broad-spectrum antibiotic sulfamethoxazole (SMX) was chosen to assess its short- and long-term effects on denitrifying granules. The SMX concentration and pre-exposure time in batch testing influenced the denitrifying granule activity. In the continuous-flow experiments, no inhibitory effects on the upflow anaerobic sludge blanket performance were observed at SMX concentrations up to 100mgL^-1, probably because of functional redundancy and long-term acclimation. The specific denitrifying activity first decreased to a minimum of 49.3% and then recovered to a level comparable to the initial level as the SMX concentration increased. The changing trend of the extracellular polymer content was consistent with the specific denitrifying activity throughout the process, and relatively high EPS loss ratios (maximum loss of 61.8%) were observed. Additionally, the diameter of the denitrifying granules monophonically increased to a final value of 35.0%. This research provided the application of denitrifying granules to treat wastewater that contained antibiotic.

Anoxic biodegradation of petroleum hydrocarbons in saline media using denitrifier biogranules

The total petroleum hydrocarbons (TPH) biodegradation was examined using biogranules at different initial TPH concentration and contact time under anoxic condition in saline media. The circular compact biogranules having the average diameter between 2 and 3mm were composed of a dense population of Bacillus spp. capable of biodegrading TPH under anoxic condition in saline media were formed in first step of the study. The biogranules could biodegrade over 99% of the TPH at initial concentration up to 2g/L at the contact time of 22h under anoxic condition in saline media. The maximum TPH biodegradation rate of 2.6 gTPH/gbiomass.d could be obtained at initial TPH concentration of 10g/L. Accordingly, the anoxic biogranulation is a possible and promising technique for high-rate biodegradation of petroleum hydrocarbons in saline media.

Successful start-up of the anammox process: Influence of the seeding strategy on performance and granule properties

Successful start-up of the anaerobic ammonium oxidation (anammox) process in up-flow sludge blanket reactor was achieved by seeding denitrifying (R0) or mixed denitrifying-anammox granular sludge at a 3:1 volume ratio (R1). The results demonstrated that R1 was successfully started-up on day 40 and had a nitrogen removal rate (NRR) of 0.55kgNm(-3)d(-1). By contrast, it took 98days to start up R0 (0.54kgNm(-3)d(-1)). R0 and R1 achieved maximum NRRs of 5.70 and 12.02kgNm(-3)d(-1), respectively. The biogranules from R1 generally possessed greater specific anammox activity (SAA), higher extracellular polymeric substance (EPS) and heme c content, larger granules and greater settling velocity. Quantitative PCR (qPCR) and high-throughput sequencing techniques were used to monitor the evolution of the bacterial community. These results demonstrated the feasibility of seeding mixed denitrifying-anammox granular sludge to start-up an anammox reactor.

Insight into the short- and long-term effects of Cu(II) on denitrifying biogranules

This study aimed to investigate the short- and long-term effects of Cu(2+) on the activity and performance of denitrifying bacteria. The short-term effects of various concentrations of Cu(2+) on the denitrifying bacteria were evaluated using batch assays. The specific denitrifying activity (SDA) decreased from 14.3 ± 2.2 (without Cu(2+)) to 6.1 ± 0.1 mg N h(-1)g(-1) VSS (100 mg Cu(2+)L(-1)) when Cu(2+) increased from 0 to 100 mg L(-1) with an increment of 10 mg Cu(2+)L(-1). A non-competitive inhibition model was used to calculate the 50% inhibition concentration (IC50) of Cu(2+) on denitrifying sludge (30.6 ± 2.5 mg L(-1)). Monod and Luong models were applied to investigate the influence of the initial substrate concentration, and the results suggested that the maximum substrate removal rate would be reduced with Cu(2+) supplementation. Pre-exposure to Cu(2+) could lead to an 18.2-46.2% decrease in the SDA and decreasing percentage of the SDA increased with both exposure time and concentration. In the continuous-flow test, Cu(2+) concentration varied from 1 to 75 mg L(-1); however, no clear deterioration was observed in the reactor, and the reactor was kept stable, with the total nitrogen removal efficiency and total organic carbon efficiency greater than 89.0 and 85.0%, respectively. The results demonstrated the short-term inhibition of Cu(2+) upon denitrification, and no notable adversity was observed during the continuous-flow test after long-term acclimation.