Inhibited Anammox Activity Research Articles

Polystyrene nanoparticles regulate microbial stress response and cold adaptation in mainstream anammox process at low temperature

Nanoplastic pollution has become one of the most pressing environmental issues, and its bioaccumulation in aquatic environment also causes a great difficulty in treatment. Therefore, this work investigated the microbial dynamics of mainstream anaerobic ammonia oxidizing (anammox) process to treat the wastewater containing typical nanoplastics, as well as the fate and regulation mechanism of polystyrene nanoparticles (PS-NPs) with different concentrations. The results showed that 0.1–0.5 mg L-1 of PS-NPs had no significant effect on the nitrogen removal efficiency (NRE). When the concentration of PS-NPs increased from 0.5 mg L-1 to 2 mg L-1, the NRE of R1 with PS-NPs decreased from 94.9 ± 2.3 % to 77.0 ± 1.6 %, while the control reactor R0 maintained a stable NRE. Notably, the relative abundance of Ca. Kuenenia decreased from 17.4 % to 14.8 %, and that of Ca. Brocadia slightly decreased from 5.9 % to 5.0 % in R1. In addition, PS-NPs induced oxidative stress in anammox consortia, leading to the significant increase in reactive oxygen species (ROS) and lactate dehydrogenase (LDH) as well as cell membrane damage. PS-NPs also downregulated the content of heme c and further inhibited anammox activity. Based on the molecular docking simulation and western blotting, cold shock proteins (CSPs) could bind to PS-NPs and reduce the performance of anammox processes at low temperatures.

Performance evaluation of the effect of humic acid on Anammox granular sludge: Apparent morphology, nitrogen removal and microbial community

Humic acid (HA) is a typical refractory organic matter, so it is of great significance to investigate its effect on the performance of Anammox granular sludge. When the dosage of HA ≤ 50 mg/L, HA promotes the total nitrogen removal rate (NRR) to 1.45 kg/(m3·day). When HA was between 50 and 100 mg/L, the NRR of Anammox was stable. At this time, the adsorption of HA causes the sludge to gradually turn from red to brown, but the activities of heme and enzymes showed that its capacity was not affected. When HA levels reached 250 mg/L, the NRR dropped to 0.11 kg/(m3·day). Moderate HA levels promoted the release of extracellular polymeric substance (EPS), but excessive HA levels lead to a decrease in EPS concentrations. HA inhibited Anammox activity, which indirectly hindered the transmission of substrate and accumulated substrate toxicity. Although HA promoted the increase of heterotrophic microbial abundance in Anammox system, the microbial diversity decreased gradually. With the increase of HA concentration, the abundance of Candidatus_Brocadia, the main functional microorganism of Anammox system, decreased gradually, while the abundance of Candidatus_Kuenenia increased gradually.

Effects of Caffeine and COD from Coffee Wastewater on Anaerobic Ammonium Oxidation (Anammox) Activities

An anaerobic ammonium oxidation (anammox) process was employed to remove nitrogen from wastewater generated from a coffee brewing facility. The effects of caffeine and chemical oxygen demand (COD) in coffee wastewater on anammox activity were investigated. The anammox activity was inhibited in synthetic wastewater with a caffeine concentration greater than 350 mg/L. Daily additions of caffeine at 2.5 mg/L for 28 days to the same substrate did not inhibit anammox activity. However, daily additions of coffee wastewater with COD of ≥387 mg/L and caffeine at 2.5 mg/L significantly inhibited anammox activity. Because the pH was increased in the system, resulting in an increase in free ammonia (FA) concentration, one could postulate that FA is an inhibitor of anammox activity. Quantitative polymerase chain reaction (qPCR) analysis was employed to determine the populations of anammox and denitrifying bacteria. Coffee wastewater with bacterial COD to total nitrogen (bCOD:TN) ratios of 0.3–0.6:1 did not have any effect on the abundances of anammox and denitrifying bacteria. The results from this work suggest that biodegradable COD (bCOD) rather than total COD (TCOD) should be used for calculating the COD:TN ratio during the study of the effects of nitrogen removal from real wastewaters using the anammox process. A not-competitive model could fit the anammox inhibition with caffeine concentrations at 50–500 mg/L with maximum specific anammox activity (SAAmax) of 0.594 mg-N/mg-volatile suspended solids (VSS)/d and inhibitory constant (Ki) of 480.97 mg/L.

Efficient nitrogen removal from leachate by coupling Anammox and sulfur-siderite-driven denitrification

High concentrations of nitrate can be generated during anaerobic ammonium oxidation (Anammox) wastewater treatment processes. Addition of sulfur to Anammox reactors stimulates the growth of sulfur-driven denitrifying (SADN) bacteria that can reduce nitrate to nitrogen gas. However, protons released during the SADN process lower the pH of the system and inhibit Anammox activity. The system will keep stable when pH is in the range of 7.5–8.5. This study showed that addition of siderite stabilized the reactor system and significantly improved the nitrogen removal process. In fact, even when concentrations of total nitrogen were 477.15 ± 16.84 mg/L, the sulfur/siderite reactor maintained nitrogen removal efficiencies >90%, while efficiencies in the sulfur reactor were < 80%. Anammox accounted for 31% of the bacterial sequences in the sulfur/siderite reactor compared to only 14% in the sulfur reactor with the majority of sequences clustering with Ca. Brocadia. An abundance of c-type cytochromes in anammox aggregates in the sulfur-siderite reactor also indicated that anammox activity was higher in this system.

Metabolic potential of the imperfect denitrifier Candidatus Desulfobacillus denitrificans in an anammox bioreactor.

The imperfect denitrifier, Candidatus (Ca.) Desulfobacillus denitrificans, which lacks nitric oxide (NO) reductase, frequently appears in anammox bioreactors depending on the operating conditions. We used genomic and metatranscriptomic analyses to evaluate the metabolic potential of Ca. D. denitrificans and deduce its functional relationships to anammox bacteria (i.e., Ca. Brocadia pituitae). Although Ca. D. denitrificans is hypothesized to supply NO to Ca. B. pituitae as a byproduct of imperfect denitrification, this microbe also possesses hydroxylamine oxidoreductase, which catalyzes the oxidation of hydroxylamine to NO and potentially the reverse reaction. Ca. D. denitrificans can use a range of electron donors for denitrification, including aromatic compounds, glucose, sulfur compounds, and hydrogen, but metatranscriptomic analysis suggested that the major electron donors are aromatic compounds, which inhibit anammox activity. The interrelationship between Ca. D. denitirificans and Ca. B. pituitae via the metabolism of aromatic compounds may govern the population balance of both species. Ca. D. denitrificans also has the potential to fix CO2 via an irregular Calvin cycle and couple denitrification to the oxidation of hydrogen and sulfur compounds under chemolithoautotrophic conditions. This metabolic versatility, which suggests a mixotrophic lifestyle, would facilitate the growth of Ca. D. denitrificans in the anammox bioreactor.

Enhancing anammox resistance to low operating temperatures with the use of PVA gel beads

Low temperatures, or a sudden decrease in operating temperature, can seriously inhibit anammox activity, it is, therefore, important to maintain anammox activities at a low temperature. In this study, the use of gel beads to enhance the resistance of anammox biomass to a low temperature was investigated. The performance of three reactors: R1 without gel beads; R2 with polyvinyl alcohol/chitosan (PVA/CS); R3 with PVA/CS/Fe, was studied and compared in a temperature transition from 35 to 8 °C. When the operating temperature was ≥25 °C, there was little difference in nitrogen removal among the three reactors. Decreasing the temperature to < 25 °C created obvious difference between R1 and R2/R3. R1 had a nitrogen removal efficiency (NRE) of 33.1 ± 25.3% at 10 °C, significantly lower than that of R2 (90.5 ± 2.5%) or R3 (87.7 ± 11.1%). Unclassified Candidatus Brocadiaceae was the dominant genus at 10 °C, with an abundance of 44.4, 56.5 and 58.7% in R1, R2 and R3, respectively. These differences were attributed to the use of gel beads, which promoted the granulation of both the non-immobilized sludge and the immobilized biomass, resulting in higher anammox activities in R2/R3. The non-immobilized sludge of R1 was dominated by small particles (<300 μm) at 10 °C, while in R2 and R3 large particles (1000–2000 μm) were the main components. Furthermore, the immobilized biomass on gel beads exhibited much higher anammox activity and maintained a relatively high level of nitrate reductase and nitrite reductase in response to the temperature decrease. The Fe2+/Fe3+ in the PVA/CS/Fe gel beads further promoted microbial aggregation and led to an improved performance in R3 compared to R2. The results of this study demonstrate an effective approach to increase anammox resistance at low operating temperatures.

Effects of NaCl and phenol on anammox performance in mainstream reactors with low nitrogen concentration and low temperature

In this study, the effects of NaCl and phenol on anammox performance at low temperature (20 °C) were tested. In Reactor 1, an increase in NaCl concentration from 2 to 10 g/L decreased anammox activity. When the temperature was elevated to 35 °C and NaCl lowered to 8 g/L, the activity was restored. When the temperature was again decreased to 20 °C, anammox activity decreased sharply. This suggested that low temperature after activity recovery at high temperature was not beneficial to the anammox operation. In Reactor 2, 6 g/L NaCl inhibited anammox activity, which then recovered gradually. In the presence of 8 g/L NaCl, glycine betaine was helpful for relieving inhibition of activity. However, when NaCl was increased to 10 g/L, glycine betaine was not beneficial. The effect of phenol was tested in Reactor 3. The results showed that anammox activity was only 22% of the seed sludge in the presence of 35 mg/L phenol. By discharging a certain amount of sludge and adding new sludge every day, the reactor was stabilized with higher activity in the presence of 20 mg/L phenol. Both NaCl and phenol increased the production of extracellular polymeric substances and decreased settling velocity.

Effect of salinity on anammox nitrogen removal efficiency and sludge properties at low temperature

ABSTRACT Anaerobic ammonium oxidation (Anammox) process is a new type of biological nitrogen removal technology that is highly efficient, consumes low energy, and is cost-effective. However, from a practical perspective, there are operational problems involved with the technology, due to its special low temperature environmental conditions. As such, the technology is currently a key research direction in the field of sewage control engineering. This study investigated the effect of salinity on the performance of the anammox process at the stress of a low temperature (15℃) and the role salinity has on extracellular polymeric substance (EPS) secretion and by extension, anammox activated sludge. The study tested the technology used to adjust and control salinity at a low temperature. The study found that at a low temperature of 15℃, low salinity can promote the nitrogen removal efficiency of anammox bacteria. Low salinity can also activate anammox bacteria activity. However, in contrast with low salt concentrations, high salt concentrations can inhibit anammox activity. When the temperature was 15℃ and the salinity was 4 g/L, the nitrogen removal efficiency of the reactor was 1.79 times higher than in the environment with unadjusted salinity at 15℃. At a low temperature, as salinity increased, the water binding capacity and flocculation capacity of sludge also increased. Salinity can promote the secretion of EPS and changes its composition. Under low temperature stress, the concentration of salt was less than 12 g/L, and the anammox activity improved. However, a high salinity level significantly inhibited anammox activity.

Comparison of short-term dosing ferrous ion and nanoscale zero-valent iron for rapid recovery of anammox activity from dissolved oxygen inhibition

As obligate anaerobes, anammox bacteria are sensitive to oxygen, which might hinder the maximization of anammox activity. However, there are very few effective strategies to rapidly recover anammox activity after its deterioration under exposure of oxygen. In this study, the activity recovery of anammox bacteria encountering dissolved oxygen (DO) exposure (0.2 and 2.0 mg L−1) were compared by three strategies in short-term experiments, nZVI, Fe(II) dosing, and N2 purging. nZVI is more effective in recovering anammox activity with a high DO exposure (2 mg L−1), compared to a low DO exposure (0.2 mg L−1). After inhibiting by 2.0 mg L−1 DO, anammox activity recovery (normalized to the control) was ranked in the order of nZVI (5 mg L−1) addition (63 ± 8.2%) > Fe(II) (5 mg L−1) addition (41 ± 8.0%) >N2 purging (39 ± 4.0%). In contrast to Fe(II) ion additions, the shell structure of nZVI combined with the buffering effect of biomass-extracellular polysaccharide (EPS) prevented the sharp pH variation and excessive dissolved Fe(II)/Fe(III) in solution. Under such circumstances, nZVI addition (5 and 25 mg L−1) increased the intracellular reactive oxygen species (ROS) to a moderate level (<200%), which might be responsible for the better activity recovery of anammox than that of Fe(II) addition and N2 purging. Specifically, 5 mg L−1 nZVI dosage moderately enhanced the intracellular O2− production (∼150% of the control) after scavenging 2.0 mg L−1 DO, and the anammox activity recovered better than that of both 5 and 25 mg L−1 Fe(II) ions additions. However, high dosage nZVI (75 mg L−1) inhibited anammox activity in spite of low or high DO exposure. Our findings elucidate that appropriate amount of nZVI (short-term dosing) can rapidly recover anammox activity when anammox bacteria encountering oxygen exposure accidentally and could be useful in facilitating the robust operation of anammox-based processes.

Role of cyclic diguanylate in affecting microbial community shifts at different pH during the operation of simultaneous partial nitrification, anammox and denitrification process

The intracellular cyclic diguanylate acid (c-di-GMP) has emerged as a prominent second signal molecule that coordinates sessile-motile transition and biofilm formation in many bacteria. Herein, we study the role of c-di-GMP in affecting microbial community shifts at different pH levels during simultaneous partial nitrification, anammox and denitrification process (SNAD) in integrated fixed film activated sludge (IFAS) reactor. The results demonstrated that the contents of c-di-GMP notably decreased in suspended sludge, whereas the contents of c-di-GMP in biofilm had no significant change as pH gradually increased from 7.5 to 8.5. Most of the bacteria (Blastocatella, Brevundimonas) with flagella that have been reported to be regulated by c-di-GMP were present in suspended sludge, and the microbial community structure of suspended sludge had obvious change than biofilm. The increased alkaline pH reduced intracellular c-di-GMP content for increasing the motility of bacteria to be washed out from the reactor, causing the microbial community shifts in suspended sludge. This change would lead to the increase of nitrite-oxidizing bacteria which would inhibit anammox activity. Overall, this study provided more comprehensive information regarding the shifts of microbial community induced by c-di-GMP in SNAD-IFAS reactor.

Quantitative evaluation of inhibitory effect of various substances on anaerobic ammonia oxidation (anammox)

The inhibitory effect of 20 substances of various chemical species on the anaerobic ammonia oxidation (anammox) activity of an enrichment culture, predominated by Candidatus Brocadia, was determined systematically by using a 15N tracer technique. The initial anammox rate was determined during first 25min with a small-scale anaerobic batch incubation supplemented with possible inhibitors. Although Cu2+ and Mn2+ did not inhibit anammox, the remaining 18 substances [Ni2+, Zn2+, Co2+, [Formula: see text] , Fe2+, 4 amines, ethylenediaminetetraacetic acid (EDTA), ethylenediamine-N,N'-bis (2-hydroxyphenylacetic acid) (EDDHA), citric acid, nitrilotriacetic acid (NTA), N,N-dimethylacetamide (DMA), 1,4-dioxane, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and tetrahydrofuran (THF)] were inhibitory. Inhibitory effect of NTA, EDDHA, THF, DMF, DMA and amines on anammox was first determined in this study. Inhibitory effects of metals were re-evaluated because chelators, which may interfere inhibitory effect, have been used to dissolve metal salts into assay solution. The relative anammox activities as a function of concentration of each substance were described successfully (R2>0.91) either with a linear inhibition model or with a Michaelis-Menten-based inhibition model. IC50 values were estimated based on either model, and were compared. The IC50 values of the 4 chelators (0.06-2.7mM) and 5 metal ions (0.02-1.09mM) were significantly lower than those of the 4 amines (10.6-29.1mM) and 5 organic solvents (3.5-82mM). Although it did not show any inhibition within 25min, 0.1mM Cu2+ completely inhibited anammox activity in 240min, suggesting that the inhibitory effect caused by Cu2+ is time-dependent.

Determine the operational boundary of a pilot-scale single-stage partial nitritation/anammox system with granular sludge.

The partial nitritation/anammox (PN/A) process has been applied to ammonium-rich wastewater treatment, but the operational boundary has not been well determined for long-term stability. This pilot-scale study was targeted at a single-stage PN/A process using a sequencing batch reactor (SBR) (volume: 53 m(3)) and granulated activated sludge. The maximum nitrogen removal rate reached 0.83 kg N/(m(3)·d). Microbial analysis suggested that ammonium oxidizing bacteria were mainly present in small sludge flocs while anammox bacteria were prone to grow in large sludge granules. The PN/A performance was enhanced when dissolved oxygen (DO) was increased from 0.25 to 0.76 mg/L, and deteriorated at DO higher than 1.15 mg/L. The PN/A was inhibited at free ammonia (FA) over 77.0 mg/L. High DO or FA concentrations inhibited anammox activity and further induced high and inhibitory nitrite concentrations. Therefore, appropriate DO and FA concentrations should be controlled to achieve single-stage PN/A in SBRs.

Evaluation of the inhibitory effects of heavy metals on anammox activity: A batch test study

This study evaluated the interactive effect of Cu(II) and Zn(II) on anaerobic ammonium oxidation (anammox) activity using response surface methodology with a central composite design. A regression model equation was developed and validated to predict the normalized anammox activity (NAA) of anammox granules exposed to various heavy metal concentrations. The joint inhibitory effect tended to exacerbate initially and reversed as the concentrations increased and then moderated again. The most severe inhibition, resulting in a NAA of 20.1%, occurred at Cu(II) and Zn(II) concentrations of 16.3 and 20.0mgL−1, respectively. Notably, the cumulative toxicity was mitigated with the aid of intermittent exposure acclimatization. Additionally, pre-exposure to Cu(II) in the absence of substrates strongly inhibited anammox activity. However, the presence of NO2− significantly enhanced Cu(II) inhibition. Therefore, such conditions should be avoided to minimize the disturbance of the anammox process.

When the smoke disappears: dealing with extinguishing chemicals in firefighting wastewater.

Water is not enough. Nowadays, numerous chemicals are used for fire extinction. After use, however, these may unintentionally enter sewerage systems. In order to safely treat firefighting wastewater (FFWW), knowledge of the potential effects of these chemicals on biological treatment processes is essential. This study characterized and mimicked the composition of FFWW containing two powders, three foams and one foam degrader. Nitrogen (162-370 mg NH4(+)-N L(-1)) and phosphorus (173-320 mg PO4(3-)-P L(-1)) concentrations exceeded discharge limits, whereas chemical and biological oxygen demand, suspended solids and detergent concentrations remained sufficiently low. Adequate nutrient removal could be obtained through FeCl3 addition and nitrification/denitrification with acetate as substrate. In batch tests, residual nitrifying activities of 84, 81, 89, 95 and 93% were observed in the presence of powders, foams, foam degrader, synthetic and real FFWW, respectively. All categories showed higher denitrification rates than the control. Although the powders at first seemed to inhibit anammox activity at 82%, after pH correction anammox was fully feasible, allowing nitrogen removal through oxygen-limited nitrification/denitrification (OLAND). Detailed cost calculations indicated that OLAND could save 11% of capital and 68% of operational costs compared to nitrification/denitrification, identifying OLAND as the most recommendable process for nitrogen removal from firefighting wastewaters.

Experimental evaluation of the nitrite sensitivity coefficient in granular anammox biomass

Nitrite is widely reported to inhibit anammox activity and growth. One modeling approach for nitrite impairment of anammox growth is the use of a nitrite sensitivity coefficient which increases the endogenous decay coefficient of anammox bacteria proportionally to nitrite concentration. The objective of this study was to measure nitrite concentration profiles within active anammox granules incubated at fixed bulk nitrite concentrations and to compare these with nitrite concentration profiles predicted by a biofilm model that incorporates the nitrite sensitivity coefficient. We developed an apparatus for the repeated measurement of nitrite concentration profiles along the radius of granular anammox biomass over a period of 6 days at fixed bulk nitrite concentrations. Granular anammox biomass was obtained from a two-stage bench-scale partial nitritation/anammox reactor system. There was no apparent effect of nitrite concentration on nitrite utilization kinetics after 6 days at exposures up to 90 mg NO(2)(-)-N/L. These findings suggest that anammox bacteria tolerate extended exposures to elevated nitrite concentrations, and in its present form, the nitrite sensitivity coefficient is not applicable for anammox growth modeling.

Effects of oxytetracycline on anammox activity

Batch experiments were conducted to investigate the effects of oxytetracycline on anaerobic ammonium oxidation (anammox) process. The short-and long-term effects on anammox activity were studied by measuring ammonium (NH4 +), nitrite (NO2 −), and nitrate (NO3 −) concentrations over time. Experiments were conducted at NH4 +and NO2 − concentrations of 60–90 mg N/L and 60–190 mg N/L, respectively (NH4 +:NO2 − ratio from 1:1–1:2.25), oxytetracycline concentrations of 10–100 mg/L, and biomass concentrations of 300–800 mg/L. In the short-term study, anammox activity was inhibited by all oxytetracycline concentrations studied. However, daily addition of oxytetracycline to a concentration of 5 ± 3.5 mg/L in the anammox sequencing batch reactor completely inhibited anammox activity in the fifth week. Fluorescent in situ hybridization was used to identify autotrophic ammonium oxidizing bacteria (Nitrosomonas spp., Nitrobacter spp., Nitrospira spp., Candidatus Brocadia anammoxidans, and Candidatus Kuenenia stuttgartiensis). The population of anammox culture was significantly decreased while Nitrosomonas spp. and Nitrospira spp. increased in the fifth week compared with the first week of experiment. A not-competitive model fit the anammox inhibition data at oxytetracycline concentrations of 0–100 mg/L quite well with Vmax of 0.0435 mg N/mg VSS-hr and Ki of 54.66 mg/L.

Innovative treatment system for digester liquor using anammox process

This study demonstrated that partial nitritation using nitrifying activated sludge entrapped in a polyethylene glycol (PEG) gel carrier, as a pretreatment to anammox process, could be successfully applied to digester liquor of biogas plant at a nitrogen loading rate of 3.0 kg-N/m 3/d. The nitritation process produced an effluent with a NO 2–N/NH 4–N ratio between 1.0 and 1.4, which was found to be suitable for the subsequent anammox process. A high SS concentration (2000–3000 mg/l) in the digester liquor did not affect partial nitritation treatment performances. Effluent from this partial nitritation reactor was successfully treated in the anammox reactor using anammox sludge entrapped in the PEG gel carrier with T-N removal rates of greater than 4.0 kg-N/m 3/d. Influent BOD and SS contents did not inhibit anammox activity of the anammox gel carrier. The combination of partial nitritation and anammox reactors using PEG entrapped nitrifying and anammox bacteria was shown to be effective for the removal of high concentration ammonium in the digester liquor of a biogas plant.

High nitrogen removal performance at moderately low temperature utilizing anaerobic ammonium oxidation reactions

High rates of nitrogen removal from wastewater have been reported using anammox bacteria at temperatures around 37 degrees C, but not at moderately low temperatures. In this study, nitrogen removal performance of an anaerobic biological filtrated (ABF) reactor, filled with porous polyester nonwoven fabric carriers as a fixed bed for anammox bacteria, was tested at 37 degrees C and at moderately low temperature (20-22 degrees C). To attain higher nitrogen removal performance, effects of influent nitrogen concentrations and hydraulic retention time (HRT) on nitrogen removal rates were investigated. Nitrogen removal rate increased with influent ammonium and nitrite concentrations, resulting in a removal rate of 3.3 kg-N/m(3)/d on day 32 for an HRT of 180 min at 37 degrees C. However, influent nitrite concentrations greater than 280 mg/l inhibited anammox activity. Therefore, the influent nitrite concentration was adjusted to be below 280 mg/l, and high-loading tests were performed for a shorter HRT. As a result, a nitrogen conversion rate of 11.5 kg-N/m(3)/d was achieved. Moreover, to evaluate long-term anammox activity at moderately low temperatures, ABF reactors were operated for 446 d. Anammox activity could be maintained at 20-22 degrees C, and stable nitrogen removal performance was observed. Furthermore, high nitrogen conversion rate of 8.1 kg-N/m(3)/d was attained. These results clearly show that an appropriate nitrite concentration in the influent and a shorter HRT resulted in high nitrogen conversion rates. The nitrogen removal performance we obtained at moderately low temperatures will open the door for application of anammox processes to many types of industrial wastewater treatment.