Specific Nitrogen Removal Rate Research Articles

Response of aerobic granular sludge under acute inhibition by polystyrene microplastics: Activity, aggregation performance, and microbial analysis

In this study, the activity, aggregation performance, microbial community and functional proteins of aerobic granular sludge (AGS) in response to acute inhibition by different concentrations of polystyrene microplastics (PS-MPs) were investigated. As the PS-MPs concentration increased from 0 mg/L to 200 mg/L, the specific nitrogen removal rate and the activity of enzymes were inhibited. The inhibition of specific nitrite reduction rate (SNIRR) and specific nitrate reduction rate (SNRR) was most obvious at the PS-MPs concentration of 100 mg/L, and that of nitrite reductase (NIR) and nitrate reductase (NR) was most obvious at the concentration of 50 mg/L. But the inhibitory effects were mitigated at the concentration of 200 mg/L. The increase of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) indicated that the cells were damaged with the increase of PS-MPs concentration. The content of proteins and polysaccharides in extracellular polymeric substances (EPS) decreased, especially the polysaccharides were more affected. Analysis of zeta potential, hydrophobicity and surface thermodynamics of AGS revealed that addition of PS-MPs was unfavorable for AGS aggregation. It was also found that bacteria genera associated with EPS secretion and nitrogen removal functions were inhibited, while functions associated with cell metabolism, protein synthesis and cell repair were enhanced. This also confirmed that acute inhibition of PS-MPs had a detrimental effect on the nitrogen removal and aggregation performance of AGS. This study can provide theoretical support for the operation of AGS reactors under microplastics impact load.

Response of partial nitritation/anammox granules to biodegradable organic input in bacterial community and functions

Biodegradable organic input is considered as a critical factor influencing the stability of the partial nitritation/anammox (PN/A) process for autotrophic nitrogen removal. In this study, the response of PN/A granules to stepwise increasing the organic loading rate (OLR) was investigated in a continuous-flow reactor, according to the nitrogen removal activity, sludge morphology, bacterial community composition and nitrogen cycle pathways. Results show that the increased OLR from 0.47 to 3.36 kg·m−3·d−1 with different influent organic and nitrogen (COD/N) ratios from 0.25 to 1.0 caused the specific nitrogen removal rate of the granules to decrease by 60.9 %, which was accompanied by a looser granular structure and poor settling property. Inorganic feeding was then used to recover the performance of the granules, and the removal of total inorganic nitrogen rose to 78.4 % at a nitrogen loading rate of 3.36 kg·m−3·d−1. Based on high-throughput sequencing, biodegradable organics shaped the bacterial community structure in the granules by enriching symbiotic heterotrophs (such as Chloroflexi, Proteobacteria and Bacteroidetes) and washing out the anammox biomass. Candidatus Kuenenia dominated the anammox biomass, while Candidatus Brocadia was also found, which coordinated with aerobic ammonium-oxidizing bacteria (Nitrosomonas) in the PN/A process. Metagenomic analysis indicates that biodegradable organic stress and performance recovery significantly changed the composition of nitrogen cycle-related genes in the granules, in terms of a lower capacity of anammox and higher risk of nitrous oxide emission. These findings provide insight into the self-adaption strategy of PN/A granules in response to biodegradable organic input into wastewater treatment engineering applications.

PHA stimulated denitrification through regulation of preferential cofactor provision and intracellular carbon metabolism at different dissolved oxygen levels by Pseudomonas stutzeri

Denitrification, a typical biological process mediated by complex environmental factors, i.e., carbon sources and dissolved oxygen (DO), has attracted great attention due to its contribution to the control of eutrophication and the biochemical cycling of nitrogen. However, the effects of carbon source on electron distribution and enzyme expression for enhanced denitrification under competition of electron acceptors (DO and nitrate) remain unclear. Here, we profile the carbon metabolic pathway of polyhydroxybutyrate (PHB) and glucose (Glu) at high and low DO levels (50% and 10% saturated DO, respectively). It was found that PHB enhanced the growth of Pseudomonas stutzeri (model denitrifying bacterium) and improved the specific nitrogen removal rate (SNRR) at all DO levels. The functional proteins had a better affinity for the cofactor nicotinamide-adenine dinucleotide (NADH) than for nicotinamide adenine dinucleotide phosphate (NADPH); thus, more electrons were involved in nitrogen reduction and intracellular PHB production in the PHB groups than in the Glu groups. Furthermore, the expression difference of enzymes in glucose and PHB metabolism was demonstrated by metaproteomic and target protein analysis, implying that PHB-driven intracellular carbon accumulation could optimize the intracellular electron allocation and correspondingly promote nitrogen metabolism. Our work integrated the mechanisms of intracellular carbon metabolism with preferences for electron transfer pathways in denitrification, providing a new perspective on how the selective parameters regulated microbial functions involved in denitrification.

Nitrogen removal characteristics of biofilms in each area of a full-scale AAO oxidation ditch process.

Plastic carriers were installed in different areas of a full-scale anaerobic/anoxic/aerobic (AAO) oxidation ditch process, and the dynamics of nitrogen removal, biofilm morphologies, and microorganism species were investigated. The results showed that the biofilm at the front of the aerobic area (dissolved oxygen [DO]=0.93mgL-1) provided the best denitrification, with specific nitrate and nitrite reduction rates of 10.16 and 3.78mg·(g·h)-1, respectively. The biofilm in the middle of the aerobic area (DO=1.27mgL-1) exhibited the best nitrification performance, with a maximum specific ammonia oxidation rate of 3.21mg·(g·h)-1. The biofilm at the end of the aerobic area (DO=0.01mgL-1) exhibited the highest anammox potential with a maximum specific anammox rate of 0.67mg·(g·h)-1. No correlation was observed between the specific nitrogen removal rates and abundance of nitrogen-removing microorganisms at the genus level. Biofilm denitrification during the process was primarily completed by heterotrophic denitrifying bacteria (Thauera, Acinetobacter, Hyphomicrobium, and Thermomonas). Aerobic denitrifying bacteria (0.19% Thauera and 0.34% Hyphomicrobium) were identified as the main denitrifying bacteria in the middle of the aerobic area. The dominant nitrifying microorganisms in the middle of the aerobic area were Nitrosomonas (0.50%) and Nitrospira (1.04%). A biofilm in the end of the aerobic area exhibited specific anammox potential, which may have been related to the dominance of 0.024% Candidatus Brocadia. Kinetic analysis revealed that adding plastic carriers to the front and middle of the aerobic area contributed to stable nitrogen removal efficiency.

Kinetic of nitrogen consumption by Anammox process in membrane biofilm reactors operated in sequential batch

Biological nitrogen removal via Anammox is an advantageous technology in the nitrogen treatment effluents with a low Carbon/Nitrogen ratio, a process that makes this route interesting for the most different types of industries, agribusinesses, and urban effluent treatment plants. Achieving robust Anammox biomass for use in full-scale plants is still a challenge that motivates studies of biomass enrichment and the search for kinetic parameters of substrate consumption rate that help optimize the conduction of reactors. According to the previously mentioned, this work aimed to carry out the kinetic study of nitrogen consumption by the Anammox process in a membrane aerated biofilm reactors operated in sequential batches (MABR-BS). 6 MABR-BS reactors were used, each one of them inoculated with a specific Anammox sludge, obtained from the enrichment of anaerobic and aerobic sludges coming from 3 different sludge sources, namely, a municipal wastewater treatment plant, a landfill leachate treatment plant, and a swine slaughterhouse effluent treatment plant. For the kinetic study, 6 reactors were used, made in glass flasks with a total volume of 1L, with a useful volume of 500 mL, with the 300:200mL ratio between synthetic effluent (with 100mgN-NH4+.L-1) and sludge from the sources: R1 - anaerobic sludge from a UASB reactor for urban sewage treatment; R2 - mixed sludge from a UASB reactor, consisting of waste sludge and supernatant scum; R3 - anaerobic sludge from landfill leachate treatment; R4 - mixed sludge consisting of aerobic and anaerobic sludge from landfill leachate treatment plant; R5 - anaerobic sludge from the swine slaughter effluent treatment plant and R6 - aerobic and anaerobic sludge from the swine slaughter effluent treatment plant. The experimental apparatus had 3 aerators coupled to 3 flowmeters with an air flow regulated at 1.0 L.min-1; 30 cm of silicone membrane in a curved shape with one of the inlets connected to the aerator and flowmeter, the other outlet was immersed in a 75 cm water column, exerting negative pressure on the air inside the tubular silicone membrane, forcing the air to exit through the microporosity of the membrane. Aeration was intermittent, with an interval of 0.16 h between each minute of aeration, the reactors were shaken in a water bath at 30 rpm and temperature of 32°C. The kinetic test had a duration of 24 hours with sampling every 2.5 hours. The nitrogen removal efficiencies (%) determined in the kinetic test were 61.36 (R1); 61.01(R2); 59.03 (R3); 56.70 (R4); 62.77 (R5) and 64.40 (R6). Regarding pH, all reactors had an initial pH above 8.0 and a final pH close to neutral. The specific nitrogen removal rates (in mgN.gVSS-1h-1), were on average 29.43 (R1); 33.50 (R2); 33.62 (R3); 33.42 (R4); 28.90 (R5) and 30.34 (R6). The best performance in the kinetic assay was obtained in the R1 reactor, obtaining a specific activity of maximum nitrogen removal of 57.61 mgN.gVSS-1h-1 and molar generation of residual nitrate with a stoichiometric coefficient of 0.018 mol.

Evaluation of long-term preservation and reactivation efficiency of anaerobic ammonium oxidation (anammox) microorganisms based on activation energy

The preservation efficiency of mainstream (M−ANA) and sidestream anaerobic ammonium oxidation (anammox) (S-ANA) were evaluated based on their activation energy (Ea). The Ea of M−ANA cultivated under low nitrogen loads was lower than that of S-ANA, which greatly contributed to enhancing the viability of anammox during preservation at 4 °C. After preservation for 140 d, the decay rate (bAN) of M−ANA ranged from 0.0012 to 0.0013/d; the bAN of S-ANA was 0.0036–0.0041/d. The addition of hydrazine, which requires minimal energy to activate anammox metabolism, is highly beneficial for the viability of microorganisms. The low Ea of anammox contributes to efficient reactivation with rapid reactivation of heme c, and the addition of hydrazine makes the process more beneficial. Although the specific nitrogen removal rate of the M−SNA seed sludge was much lower than that of S-ANA, the rate of M−ANA became higher after 48 days of reactivation.

A comprehensive root cause analysis of anammox bioreactor performance decline

The cultivation of anaerobic ammonia oxidizing bacteria (anammox) has gained enormous awareness over the last few decades. Although numerous studies focus massively on successfully growing these anammox to different enrichment environments, in reality, the failure rates are somewhat comparable to the reported success rates. This study combines a variety of measurement techniques to observe and monitor the sequence of a bioreactor performance decline following elevated influent substrate concentration. After attaining stable substrate removal throughout a nitrogen loading rate (NLR) range of 0.691 to 1.669 kg-N·m−3·d−1, the performance of the lab-scale anammox-sequencing batch reactor (SBR) abruptly broke down as the NLR reached 2.01 kg-N·m−3·d−1. The gathered information showed that the increased NLR firstly caused a significant and unfavorable change in the free ammonia (FA) and free nitrous acid (FNA) concentration in the bioreactor. A subsequent drop in N2 production and a decline from a peak high of 0.381 to a low of 0.012 kg-N·kg-VSS−3·d−1 of the specific nitrogen removal rate (SNRR) led to an 82% absurd decline in microbial cellular energy production. Prior to these anammox switching to survival mode and secreting larger quantities (32% higher) of extracellular polymeric substances (EPS), the activity of syntrophic decomposers increased substantially leading to the internal production of excess CO2 in the bioreactor and thereby diverging the bioreactor pH to lower levels. The purposes of this study are to understand the reason an anammox process shows different signals during a decline phase and to enable immediate response to performance deterioration.

Characterization of Sludge Morphology and Bacterial Community Evolution in the Rapid Activation of Freeze-stored PN/A Granular Sludge

Inoculating granular sludge is an alternative method for the quick start-up of a high-performance autotrophic nitrogen removal reactor. In order to establish the response relationship between sludge activation and reactor performance, the freeze-stored granular sludge was inoculated into a continuous-flow reactor, and a control strategy of the high loading rate and high hydraulic selective pressure was carried out in this study. As a result, a one-stage partial nitritation/ANAMMOX process was started up in 34 days, and the removal efficiency of total nitrogen was over 83%, with a removal loading rate of total nitrogen of 1.67 kg·(m3·d)-1. During this period, the Image pro-plus software was employed to analyze the evolution of the characteristic dimensions of particles. A good linear positive correlation (R2=0.988) between the projected area of the erythrine zone in the inner layer and the specific nitrogen removal rate of granules was found, which provide a simple method to estimate the activity of the PN/A granules. The results of MiSeq high-throughput sequencing showed that the enrichment of aerobic ammonia-oxidizing bacteria (Nitrosomonas) and the wash-out of heterotrophic bacteria (such as Denitratisoma and Haliangium, etc.) were achieved in the start-up of the reactor. Meanwhile, the improvement in granular compactness was in favor of activating anaerobic ammonia oxidizing bacteria (Candidatus_Kuenenia, abundance>30%) that colonized the inner layer of the granules.

Effect of hydraulic selection pressure on the characteristics of partial nitritation/anammox granular sludge in a continuous-flow reactor

Strong hydraulic selection pressure is a control co-factor for maintaining the stability of granular sludge in a continuous-flow bioreactor. In this study, efficient nitrogen removal was achieved in a continuous partial nitritation/anammox (PN/A) granular reactor in a short hydraulic retention time (HRT), decreasing from 100 to 40 min, where more than 95% of ammonium and 80% of total inorganic nitrogen (TIN) were removed at a constant nitrogen loading rate of 2.0 kg (m 3 d) −1 . Results showed that the decreased HRT substantially influenced the observed biomass growth curve, with a trade-off between the growth and washout of microbial populations. Further, sludge characterization indicated that shorter HRT improved granular compactness with the accumulation of extracellular polymeric substances and increased the specific nitrogen removal rate, reaching q (TIN) = 39.9 mg N g −1 VSS ⋅ h −1 . These observations were consistent with shifts in the bacterial community structure of the PN/A sludge with different particle sizes. High-throughput pyrosequencing revealed that strong hydraulic selection pressure promoted the niche segregation of aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AnAOB) and washout of nitrite-oxidizing species in the granules. The effective retention of k -strategists AnAOB (dominated by genus Candidatus Kuenenia) occupying the interior layer of the granules exhibited a solid retention time (SRT) 10-fold longer than that of AOB (identified as Nitrosomonas ) enriched in the aerobic zone. A strategy involving HRT and SRT coordination in operation can enhance the efficiency and stability of PN/A systems, considering the potential development of small aggregates into mature granules. • Strong hydraulic selection pressure was applied in a CSTR with PN/A granules. • NH 4 + -N removal ≥ 95% and TIN removal ≥ 80% were achieved at an HRT of 40 min. • HRT influenced the observed biomass growth curve and granular functional activity. • Shorter HRT promoted niche segregation of AOB and AnAOB in PN/A sludge.

Model-based analysis of sulfur-based denitrification in a moving bed biofilm reactor

ABSTRACT In this study, a biofilm model was developed for sulfur-based denitrification in a moving bed biofilm reactor (MBBR), including mass transport as well as the conversion kinetics of sulfur-oxidizing bacteria (SOB). The experimental reactor simulated received a synthetic wastewater containing nitrate, sulfide and thiosulfate. The substrate affinity of SOB for intermediary elemental sulfur (S0) was found the most sensitive parameter. After estimating this single parameter, the model could adequately describe the steady state performance of the experimental MBBR. The experimental and simulated mass balances indicated that a fraction of influent sulfur accumulated into intermediate S0. Furthermore, the simulations showed that SOB were active over the entire thickness of a 200 µm biofilm. The simulation results allowed to quantify the extent of diffusion and substrate limitation. Scenario analyses indicated that the specific nitrogen loading rate could be increased from 0.05 to 0.20 kg N.kg−1 VSS.day−1 (corresponding to 0.22–0.86 kg N.m−2.day−1 expressed per biofilm surface area) while maintaining nitrogen removal efficiencies above 70%. An increasing specific nitrogen loading rate in this range resulted in an almost linearly increasing specific nitrogen removal rate, independent from whether it was realized through a decreasing HRT, carrier filling ratio or biofilm thickness.

An investigation into the optimal granular sludge size for simultaneous nitrogen and phosphate removal

An aerobic granular sludge (AGS) pilot plant fed with a mixture of acetate amended centrate and secondary effluent was used to investigate the optimal granule size range for simultaneous nitrification and denitrification (SND) and ortho-phosphate removal. The anaerobic phase was mixed to understand how AGS will perform if integrated with a continuous flow activated sludge system that cannot feed the influent through the settled sludge bed. Five different granule size fractions were taken from the pilot (operated at DO setpoint of 2mgO2/L) and each size was subjected to activity tests in a well-controlled lab-scale AGS reactor at four dissolved oxygen (DO) concentrations of 1, 2, 3, and 4 mgO2/L. The size fractions were: 212 – 600 µm, 600 – 1000 µm, 1000 – 1400 µm, 1400 – 2000 µm, and >2000 µm. The smallest size range (212 – 600 µm) had the highest nitrification and phosphate removal rates at DO setpoints from 1 – 3 mgO2/L, which was attributed to the higher aerobic volume fraction in small granules and hence a higher abundance of phosphorus accumulating organisms (PAO) and ammonia oxidizing bacteria (AOB). In comparison, large granules (>1000 µm) had 1.4 – 4.7 times lower ammonia oxidation rates than the smallest size range, which aligned with their lower AOB abundance relative to granule biomass. The granules with the highest anoxic volume fraction had the highest abundance of nitrite reductase genes (nir gene) but did not show the highest specific nitrogen removal rate. Instead, smaller granules (212 – 600 and 600 – 1000 µm), which had a lower nir gene abundance, had the highest specific nitrogen removal rates (1.2 – 3.1 times higher than larger granules) across all DO values except at 4 mgO2/L. At a DO setpoint of 4 mgO2/L, nitrite production by ammonia oxidation (ammonia monooxygenase) exceeded nitrite reduction by nitrite reductase in granules smaller than 1000 µm, in addition, some denitrifying heterotrophs switched to oxygen utilization in deeper layers hence suppressing denitrification activity. At the DO range of 2 – 4 mg/L, granular size had a greater effect on nutrient removal than DO. Therefore, for AGS developed at an average DO setpoint of 2 mgO2/L, selecting for size fractions in the range of 212 – 1000 µm and avoiding DO values higher than 3 mgO2/L can achieve both a higher nitrogen removal capacity and energy savings. This study is the first to investigate the influence of different DO values on SND and biological phosphorus removal performance of different aerobic granular sludge sizes.

Start-up of a Three-stage PN/A Granular Sludge Reactor for Treating Wastewater with High Concentrations of Ammonia

In order to apply partial nitritation-ANAMMOX (PN/A) technology to treat wastewater with high concentrations of ammonia, autotrophic nitrogen-removing granular sludge was crushed and inoculated into a three-stage continuous flow reactor. The nitrogen loading rate (NLR), dissolved oxygen (DO) concentration, and free ammonia (FA) levels in each compartment of the reactor were controlled over a 106-day period. Results showed that the nitritation process occurred with the inoculated granules during the initial phase. A limited aeration strategy was employed in the reactor at relatively high NLRs. Given the effective suppression of nitrite-oxidizing bacteria and the prevention of ANAMMOX bacteria from high DO conditions, the compact structure and nitrogen-removal activity of the granules could be improved. When the ammonia-nitrogen concentration was increased in the influent to 350 mg·L-1, the adverse impacts of high FA concentrations on the functional microbe activity in the first compartment should be eliminated. This occurs by reducing the influent pH and alkalinity dosage. This occurs by reducing the influent pH and degree of alkalinity. As a result, a total nitrogen removal rate of 7.2 kg·(m3·d)-1 was achieved in the reactor, which is 50 to 100 times higher than that of conventional activated sludge systems. The consistent improvement in the nitrogen-removal activity of the granules was demonstrated by batch testing at different aeration intensities. This showed that activity was greatest in the first compartment, which showed the highest granular maturity. In addition, a clear linear correlation (R2>0.97) was observed between the amount of extracellular polymeric substance and the specific nitrogen removal rate. This indicated that the dense granules played a positive role in enhancing the performance of the reactor.

Impacts of different morphologies of anammox bacteria on nitrogen removal performance of a hybrid bioreactor: Suspended sludge, biofilm and gel beads

The difficulties in the anaerobic ammonium oxidation (anammox) process mainly consist of low microbial growth rates and long start-up times of bioreactors. The morphologies of anammox bacteria might affect nitrogen removal performance and microbial community. In this study, three morphologies of anammox bacteria, namely, suspended sludge, biofilm and suspended sludge embedded in gel beads, were compared in a hybrid bioreactor under anoxic conditions (DO concentration < 0.1 mg L−1). The results show that the average total inorganic nitrogen removal efficiency of a hybrid bioreactor reached 67 ± 15% with a maximum value of 80% for continuous synthetic wastewater feeding, and that the specific total inorganic nitrogen removal rate reached 15.75 mg·(gVSS·h)−1 regardless of the organic matter stress. Batch tests indicate that mainly suspended sludge (67%) and biofilm (26%) contributed to the anammox process, with the specific total inorganic nitrogen removal rate reaching 10.55 and 4.05 mg·(gVSS·h)−1, respectively. However, the embedding of sludge in gel resulted in nitrification instead of anammox with a nitrification rate of 0.20 ± 0.01 mg·(L·h)−1 due to the expansion of gel beads floating on the water surface. Therefore, a pore-forming technique was developed to produce more channels for gas dispersion inside the gel beads. In terms of microbial community, Candidatus Kuenenia involved in the anammox group was the most abundant genus in biofilm (43.4%) and suspended sludge (15.7%), while Nitrospira occupied the largest proportion in gel beads (25.6%). This study offers useful information for the selection of anammox bacteria morphology.

Effects of Environmental Factors on the Synergy of Functional Bacteria in Completely Autotrophic Granular Sludge

To obtain experimental evidences for optimizing a completely autotrophic nitrogen removal process based on granules, the effects of dissolved oxygen (DO) concentration, temperature (t), initial ammonium (NH4+-N) concentration, and solution pH conditions on the synergy between the aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AMX) were investigated using a single factor batch experiment, while the analysis of the microbial community structure within them was conducted using MiSeq high-throughput pyrosequencing. Results revealed that AOB (genus Nitrosomonas) and AMX (genus Candidatus Kuenenia) dominated in the granules, representing relative abundances of 32.9% and 9.8%, respectively. For the granules, the highest specific nitrogen removal rate of q(TN)=(17.7±1.0) mg·(g·h)-1 was obtained at a DO concentration of 2 mg·L-1, while the initial NH4+-N concentration was set at 100 mg·L-1. And a lower DO level resulted in partial nitritation became the rate-limiting step of process, otherwise, it would be the ANAMMOX reaction instead. According to the free energy of the reactions, the activity of AMX was more sensitive to low temperature than that of AOB. When the reaction temperature was lower than 30℃, nitrite accumulation could be observed in bulk liquid, with the significant decrease of q(TN) for the granules. Under the same oxygen supply conditions, an initial NH4+-N concentration lower than 100 mg·L-1 could inhibit the activity of AMX partly. However, with an initial NH4+-N concentration over 150 mg·L-1, either oxygen-limiting or high free ammonia concentration could lead to the dramatic decrease of q(TN). In addition, the effective synergy of the two types of ammonium oxidizers in granules was always achieved at solution pH in the range of 7.0-8.5.

Fast start-up of anammox process with mixed activated sludge and settling option

ABSTRACTIn this study, successful start-up of the anaerobic ammonium oxidation (anammox) process in a sequencing batch reactor (SBR) was achieved by seeding mixed activated sludge which included aerobic sludge, anaerobic sludge, simultaneous partial nitrification, anammox and denitrification (SNAD) sludge, and anammox sludge with low activity at a 2200:2100:5:2 volume ratio. On day 15, the effective anammox activity was attained in SBR, with the specific total nitrogen removal rate (SRR) of 0.214 gNg−1 VSSd−1. The total nitrogen removal rate (NRR) increased to 230 gNm−3 d−1 by gradually reducing the setting time to 10 min. With the nitrogen loading rate (NLR) up to 506 gNm−3 d−1, the total NRR of the SBR reached 433 gNm−3 d−1 during stationary phase. Candidatus Brocadia was detected as predominant functional microbes in the anammox SBR. The results demonstrated the feasibility of seeding mixed activated sludge to start-up an anammox SBR by settling option.

Differentiation in Nitrogen-Converting Activity and Microbial Community Structure between Granular Size Fractions in a Continuous Autotrophic Nitrogen Removal Reactor.

The differentiations in nitrogen-converting activity and microbial community structure between granular size fractions in a continuous completely autotrophic nitrogen removal over nitrite (CANON) reactor, having a superior specific nitrogen removal rate of 0.24 g/(g VSS·d), were investigated by batch tests and high-throughput pyrosequencing analysis, respectively. Results revealed that a high dissolved oxygen concentration (>1.8 mg/l) could result in efficient nitrite accumulation with small granules (0.2-0.6 mm in diameter), because aerobic ammonium-oxidizing bacteria (genus Nitrosomonas) predominated therein. Meanwhile, intermediate size granules (1.4-2.0 mm in diameter) showed the highest nitrogen removal activity of 40.4 mg/(g VSS·h) under sufficient oxygen supply, corresponding to the relative abundance ratio of aerobic to anaerobic ammonium-oxidizing bacteria (genus Candidatus Kuenenia) of 5.7. Additionally, a dual substrate competition for oxygen and nitrite would be considered as the main mechanism for repression of nitrite-oxidizing bacteria, and the few Nitrospira spp. did not remarkably affect the overall performance of the reactor. Because all the granular size fractions could accomplish the CANON process independently under oxygen limiting conditions, maintaining a diversity of granular size would facilitate the stability of the suspended growth CANON system.

Investigating the nitrification and denitrification kinetics under aerobic and anaerobic conditions by Paracoccus denitrificans ISTOD1

Municipal wastewater contains multiple nitrogen contaminants such as ammonia, nitrate and nitrite. Two heterotrophic nitrifier and aerobic denitrifiers, bacterial isolates ISTOD1 and ISTVD1 were isolated from domestic wastewater. On the basis of removal efficiency of ammonia, nitrate and nitrite under both aerobic and anaerobic conditions, ISTOD1 was selected and identified as Paracoccus denitrificans. Aerobically, NH4+-N had maximum specific nitrogen removal rate (Rxi) of 7.6g/gDCW/h and anaerobically, NO3−N showed Rxi of 2.5*10−1g/g DCW/h. Monod equation described the bioprocess kinetic coefficients, µmax and Ks, obtained by regression. Error functions were calculated to validate the Monod equation experimental data. Aerobic NO3−N showed the highest YW of 0.372mg DCW/mg NO3−N among the five conditions. ISTOD1 serves as a potential candidate for treating nitrogen rich wastewater using simultaneous nitrification and aerobic denitrification. It can be used in bioaugmentation studies under varied condition.

Photoautotrophic Microalgae Screening for Tertiary Treatment of Livestock Wastewater and Bioresource Recovery

Photoautotrophic microalgae offer high promise for a tertiary treatment of livestock wastewater owing to their rapid growth and nutrient uptake. To screen better microalga for the tertiary treatment, batch photobioreactor tests were conducted using Chlorella emersonii, Chlorella sorokiniana, and Botryococcus braunii. This study evaluated their specific growth rates, CO2 utilization rates, and nutrient removal rates to provide appropriate selection guidelines. Based on statistical comparisons, results indicate that selecting the right microalgae was the key to success in the tertiary treatment since each microalga responded differently, even under the same light, temperature, and nutrient conditions. Among the tested species, Chlorella emersonii was found to present the fastest photoautotrophic growth, total inorganic carbon (TIC) utilization, and nutrient removal for livestock wastewater treatment. Regression results identified that its specific growth and total nitrogen removal rates were as high as 0.51 day−1 and 0.18 day−1, respectively. Estimated TIC utilization over the supplied TIC was much higher (~34%) than those of others (11%–18%). This systemic evaluation of rate-limiting factors provides a quantitative understanding of the kinetic-based selection strategy of microalgae to polish livestock wastewater with better effluent quality.

Efficient Utilization of Waste Carbon Source for Advanced Nitrogen Removal of Landfill Leachate

A modified single sequencing batch reactor (SBR) was developed to remove the nitrogen of the real landfill leachate in this study. To take the full advantage of the SBR, stir phase was added before and after aeration, respectively. The new mechanism in this experiment could improve the removal of nitrogen efficiently by the utilization of carbon source in the raw leachate. This experiment adopts the SBR process to dispose of the real leachate, in which the COD and ammonia nitrogen concentrations were about 3800 mg/L and 1000 mg/L, respectively. Results showed that the removal rates of COD and total nitrogen were above 85% and 95%, respectively, and the effluent COD and total nitrogen were less than 500 mg/L and 40 mg/L under the condition of not adding any carbon source. Also, the specific nitrogen removal rate was 1.48 mgN/(h·gvss). In this process, polyhydroxyalkanoate (PHA) as a critical factor for the highly efficient nitrogen removal (>95%) was approved to be the primary carbon source in the sludge. Because most of the organic matter in raw water was used for denitrification, in the duration of this 160-day experiment, zero discharge of sludge was realized when the effluent suspended solids were 30–50 mg/L.

Influence of light intensity on bacterial nitrifying activity in algal-bacterial photobioreactors and its implications for microalgae-based wastewater treatment

The influence of irradiance on the nitrifying activity in photobioreactors of a bacterial consortium enriched from a wastewater treatment bioreactor was assessed using independent ammonium oxidation kinetic batch tests and respirometric assays. Culture irradiance below 250 μmol m−2 s−1 did not show a significant effect on nitrification activity, while irradiance at 500 and 1250 μmol m−2 s−1 caused a decrease of 20 and 60% in the specific total ammonium nitrogen removal rates and a reduction of 26 and 71% in the specific NO3− production rates, respectively. However, no significant influence of irradiance on the affinity constant of NH4+ oxidation was observed. The increasing nitrite accumulation at higher light intensities suggested a higher light sensitivity of nitrite oxidizers. Additionally, NH4+ oxidation respirometric assays showed a decrease in the oxygen uptake of 14 and 50% at 500 and 1250 μmol m−2 s−1, respectively. The experimental determination of the light extinction coefficient (λ) of the nitrifying bacterial consortium (λ = 0.0003 m2 g−1) and of Chlorella sorokiniana (λ = 0.1045 m2 g−1) allowed the estimation of light penetration in algal-bacterial high rate algal ponds, which showed that photoinhibition of nitrifying bacteria can be significantly mitigated in the presence of high density microalgal cultures.