Nitrifying Biomass Research Articles

Biofiltration matrix optimization for efficient nitrogen removal from domestic onsite wastewater

Bench-scale columns were packed with marble chip, zeolite and gravel to treat septic tank effluent at elevated hydraulic loadings (0.48–0.64 m3 m−2 d−1) to challenge their hydraulic performance and ammonium (NH4+-N) removal performance. The results showed that higher NH4+-N removal efficiency was achieved in zeolite (75.8–94.1 %) and marble chip (54.9–83.9 %) columns than in sand (32.9–76.6 %) column without clogging during the experimental period (4 months). Biochar amendment (30 % v/v) resulted in a 23–29 % decrease of effluent NH4+-N in marble chip columns, while no impact was observed in the zeolite columns. Nitrification rather than adsorption contributed to the major NH4+-N removal (82–95 %) in zeolite, biochar amended zeolite and biochar amended marble chip columns. In addition, higher abundance of nitrifying microorganisms observed in the top layer of zeolite column (1.2 × 107 - 3.1 × 107amoA copies g−1, 3–10 times higher than marble chip) suggested NH4+-N was concentrated on zeolite surface by adsorption which then facilitated nitrification and promoted nitrifying biomass growth. Collectively, this study suggested that zeolite and biochar amended marble chip could serve as the filter materials for efficient NH4+-N removal from onsite wastewater at elevated wastewater loadings without clogging concerns.

Nitrification of the liquid phase of digestate: The transfer of the process from laboratory to pilot plant and full scale conditions

This paper aimed to verify the laboratory research results related to the liquid phase of digestate (LPD) treatment using nitrification at pilot scale conditions and to suggest an optimal method for full-scale system start-up. A reactor applying the nitrification of LPD was operated for 358 days. Significant free ammonia and free nitrous acid inhibition towards nitrite-oxidizing bacteria (NOB) increased N-NO2− concentrations up to 2300 mg/L in LPD. As a result of pH and a nitrogen loading rate control combined with the re-inoculation of the reactor, NOB activity was fully restored after 90 days, where the nitrogen oxidation rate and nitrogen oxidation efficiency reached up to 0.26 kg/(m3⋅d) and 99.9%, respectively, at N-NO2− concentrations not exceeding 45 mg/L. Thus, the feasibility of stable operation of the system even without any dilution of LPD was confirmed. The procedure of full-scale reactor start-up consisting of a separate unit serving to produce nitrifying biomass was suggested. It was shown that the volume of such a reactor could be divided into three compartments to optimize the start-up. Simple modeling proved the possibility of completing the start-up process in 34 days under specific conditions (total ammonia concentrations in LPD 2 kg/m3, daily production of LPD 20 m3/d, nitrogen loading rate reaching 0.25 kg/(m3⋅d)). The results could be used to accelerate the method transfer into practice.

Significance of enriched culture on the assessment of the acute inhibitory impact of sulfamethoxazole on nitrifying biomass

AbstractBACKGROUNDAutotrophic microorganisms are quite vulnerable to environmental conditions and to inhibitory actions that would upset nitrification mechanisms. A reliable numerical assessment of the adverse impact is needed for proper remedial action. This study focused on the kinetic response of the nitrifying fraction within the activated sludge biomass under acute exposure to sulfamethoxazole (SMX), utilizing and emphasizing the role of enriched culture. A mixed culture sustained with an enrichment technique was used to generate oxygen uptake rate profiles, where ammonia was the sole substrate with different SMX concentrations.RESULTSModel calibration studies yielded specific growth rates of 1.40/day for the ammonia oxidizing fraction and 0.65/day for the nitrite oxidizing fraction acting as the rate limiting step for the overall nitrification process. SMX did not appreciably affect the specific growth rates, but it induced a significant increase in half saturation coefficients. Moreover, increased endogenous decay rates were estimated.CONCLUSIONModel calibration values indicated that SMX induced competitive inhibition on microbial growth and enhanced endogenous respiration due to an increasing demand for the maintenance energy to activate antibiotic resistance. This underlines the merit of further studies on conditions to sustain resistant microorganisms capable of tolerating and even degrading antibiotics in biological systems. © 2022 Society of Chemical Industry (SCI).

How Comamonas testosteroni and Rhodococcus ruber enhance nitrification in the presence of quinoline

Because many wastewater-treatment plants receive effluents containing inhibitory compounds from chemical or pharmaceutical facilities, the input of these inhibitors can lead to failure of nitrification and total-N removal. Nitrification de facto is the more important process, as it is the first step of nitrogen removal and involves slow-growing autotrophic bacteria. In this work, quinoline, the target compound severely inhibited nitrification: The biomass-normalized nitrification rate decreased four-fold in the presence of quinoline. The inhibition was relieved by bioaugmenting Comamonas testosteroni or Rhodococcus ruber to the nitrifying biomass. Because the inhibition was derived from a quinoline intermediate, 2‑hydroxyl quinoline (2HQ), not quinoline itself, nitrification was accelerated only after 2HQ disappeared due to the addition of R. ruber or C. testosteroni. R. ruber was superior to C. testosteroni for 2HQ biodegradation and accelerating nitrification. Besides accelerating nitrification, adding C. testosteroni or R. ruber led to the enrichment of Nitrospira, which appeared to be carrying out commamox metabolism, since ammonium-oxidizing bacteria were not enriched.

Rapid nitrification using nitrifying biomass acclimated to sulfamethoxazole (SMX)

Antibiotics often are input to biological-treatment systems for domestic sewage, and they can inhibit nitrifying bacteria and impair nitrification performance. In this work, activated sludge was acclimated to either a high or a low ammonium concentration in the continuous presence of 10 mg/L the antibiotic sulfamethoxazole (SMX). The high ammonium concentration led to nitrifying activated sludge (NAS), while the low ammonium concentration led to conventional activated sludge (CAS). After acclimation, the NH4+-removal rate for NAS was 8-fold greater than the rate for CAS when 10 mg/L SMX also was present in the medium. NAS also biotransformed SMX faster than did CAS. The removal kinetics for NH4+ and SMX were well represented by the Aiba self-inhibition model: The NAS biomass had a much faster maximum removal rate for NH4+, and it had better affinity for NH4+ and less inhibition from SMX. The NAS biomass also had faster biotransformation kinetics for SMX, with the main impact being a much faster maximum specific biotransformation rate (rmax). Analysis of microbiological community documented that the NAS biomass was enriched in nitrifying bacteria and also had more heterotrophic bacteria likely to be able to biotransform SMX.

Characterization of Bacterial and Archaeal Communities by DGGE and Next Generation Sequencing (NGS) of Nitrification Bioreactors Using Two Different Intermediate Landfill Leachates as Ammonium Substrate

Nitrification–denitrification is an environmentally friendly and cost-effective way to treat landfill leachates. Special attention has been given to the nitrification step, usually the limiting one due to its special sensitivity to environmental factors. Here, the effect of the acclimatization of the nitrifying biomass to two different intermediate landfill leachates with different salt concentrations, COD and BOD5 has been studied. Despite the complete nitrification being successfully performed, the specific nitritation rates were reduced after the biomass adaptation to both landfill leachates caused by the presence of heavy metals and the high salt concentration. NGS analysis of the biomass samples revealed that Proteobacteria (48.5%), Actinobacteriota (14.4%) and Chloroflexi (9.5%) were the dominant phyla in the non-adapted biomass. The leachate feeding led to a decrease in OTU diversity and favored the growth of the phyla Bacteroidetes (27.2%), Euryarchaeota (26.6%) and Proteobacteria (20.0%) accounting for more than 70% of relative abundance. Several OTUs capable of performing the nitritation belong to the Xanthobacteraceae and the Xanthomonadaceae families, the Saccharimonadales order, and the genus Nitrosomonas, Nitrosospira and Paracoccus. In the nitratation process, the Xanthobacteraceae family and Lautropia and Nitrolancea genera were found.Graphical

Successful mainstream nitritation through NOB inactivation

The development of new wastewater treatment processes can assist in reducing the impact of wastewater treatment on the environment. The recently developed partial nitritation anammox (PNA) process, for example, consumes less energy for aeration and reduces nitrate in the effluent without requiring additional organic carbon. However, achieving stable nitritation (ammonium oxidation; NH4+ → NO2−) at mainstream conditions (T = 10–25 °C, C:N > 10, influent ammonium < 50 mgNH4-N/L and effluent < 1 mgNH4-N/L) remains challenging. This study explores the potential and mechanism of nitrite-oxidizing bacteria (NOB) suppression in a bottom-fed sequencing batch reactor (SBR). Two bench-scale (11 L) reactors and a pilot-scale reactor (8 m3) were operated for over a year and were fed with organic substrate depleted municipal wastewater. Initially, nitratation (nitrite oxidation; NO2− → NO3−) occurred occasionally until an anaerobic phase was integrated into the operating cycle. The introduction of the anaerobic phase effectively suppressed the regrowth of NOB while nitritation was stable over 300 days, down to 8 °C and at ammonium influent concentrations < 25 mgNH4-N/L. Batch experiments and process data revealed that parameters typically affecting NOB growth (e.g., dissolved oxygen, alkalinity, trace elements, lag-phase after anoxia, free nitrous acid (FNA), free ammonia (FA), pH, sulfide, or solids retention time (SRT)) could not fully explain the suppression of nitratation. Experiments in which fresh nitrifying microbial biomass was added to the nitritation system indicated that NOB inactivation explained NOB suppression better than NOB washout at high SRT. This study concludes that bottom-fed SBRs with anaerobic phases allow for stable nitritation over a broad range of operational parameters. Coupling this type of SBR to an anammox reactor can enable efficient mainstream anammox-based wastewater treatment.

Ammonium oxidation activity promotes stable nitritation and granulation of ammonium oxidizing bacteria

Two-stage partial nitritation/anammox (PN/AMX) processes have been pointed out as a feasible configuration for achieving mainstream anammox. For two-stage configurations, stable partial nitritation has been reported feasible in granular sludge reactors. This study aimed to explore the operating conditions involved in the development of an autotrophic aerobic granular sludge using floccular sludge as inoculum. The influence of different parameters such as free ammonia concentration, settling time, superficial gas flow velocity and ammonium oxidation rate was investigated. Enhancing ammonium oxidation activity since the early phase of the operation (i.e. using conventional activated sludge as inoculum enriched with a fraction of a floccular nitrifying biomass) promoted a fast development (ca. 30 days) of an autotrophic aerobic granular sludge performing stable nitritation. When the seeded sludge presented a low nitrifying activity (lower than 0.1 g N L−1 d−1), the increase of the air-flow rate triggered the formation of an autotrophic aerobic granular sludge since ammonium oxidation activity was promoted. Contrarily, imposing low settling times (10 min) or strong free ammonia inhibitory conditions (FA concentrations higher than 50 mg N L−1) were shown to negatively influence the achievement of high ammonium oxidation rates, hampering the development of an autotrophic aerobic granular sludge. This study demonstrated the importance of ensuring high ammonium oxidation rates (higher than 0.2 g N L−1 d−1) for the proper development of an autotrophic partial nitritation granular sludge.

Effect of two different intermediate landfill leachates on the ammonium oxidation rate of non-adapted and adapted nitrifying biomass

A widely employed approach to minimize the detrimental effect of landfill leachates (LL) on nitrifying biomass is to adapt it to these contaminated effluents prior to use. In the study reported here the impact of different intermediate landfill leachates (intermediate 1 (ILL1) and intermediate 2 (ILL2)) and synthetic medium (SM) on the nitritation rates of non-adapted and adapted nitrifying biomass were evaluated and modeled. The models, based on previously reported models (Haldane, Edwards and Aiba), considered the effect of three different heavy metals (Cu, Ni and Zn) present in both landfill leachates. The proposed models fitted well with the different biomasses. The highest specific substrate oxidation rate (qS) of the present study (41.85 ± 1.09 mg N–NH4+ g TSS−1 h−1) was obtained by the non-adapted biomass using SM. The non-adapted biomass was characterized by ~5- and ~28-fold higher nitritation rates on using the different ammonium sources tested (SM, ILL1 and ILL2) when compared to the other biomasses adapted to ILL1 (~9 mg N–NH4+ g TSS−1 h−1) and ILL2 (~1.3 mg N–NH4+ g TSS−1 h−1), respectively. The calculated inhibition constants indicate that the inhibitory effect of the heavy metals followed the order Ni>Zn>Cu. The results reported here bring into question the commonly accepted idea that an adaptation period of the biomass is required to treat landfill leachate.

Effect of Amoxicillin on Nitrogen Oxidation Bacteria Present in Activated Sludge: Respirometry Investigation.

Amoxicillin (AMX) is one of the most widely used antibiotics in the world and its presence in wastewater is of great concern for its potential to bacteria selection. However, there is still a gap about the toxicity effect of AMX in nitrifier biomass from activated sludge (AS). This study is based on the implementation of respirometric tests in batches in order to evaluate the toxic effluent toxicity in the nitrification process of AS. The tests were conducted by comparing respiration rates with effluent containing ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2--N) called "reference" and batches containing toxic effluent doped with different concentrations of AMX here called "process." Results with effluent containing concentrations greater than 100mg L-1 showed that AMX negatively affected the specific growth rate (μm) of ammonia-oxidizing bacteria (AOB) (from 0.50 d-1 to 0.13 d-1) and nitrite-oxidizing bacteria (NOB) (from 0.64 d-1 to 0.15 d-1). Although there is no total inhibition of populations, these μm values are limiting for a feasible development of the nitrification process in AS systems. The removal of AMX decreased from 99 to 37% (liquid phase) when the concentration of AMX increased (20mg L-1 to 200mg L-1). A decrease in the microbial community AOB and NOB was observed through fluorescent in situ hybridization (FISH), corroborating the results of respirometry. In summary, the study showed that the inhibition of the AS nitrification process occurs in the presence of high concentrations of AMX and the most susceptible group are the NOB.

Oxygen diffusivity and reaction rate in spherical gel entrapping ammonia-oxidizing bacteria

Nitrifying biomass immobilized in a gel has been applied in wastewater treatment, as immobilization results in a high bacterial cell density in the reactor and facilitates easy solid–liquid separation in the settling tank. Herein, the diffusivity, reaction rate, and concentration profile of oxygen in a spherical gel entrapping ammonia-oxidizing bacteria (AOB) were investigated. Calcium alginate gel and 2,2-bis[4-(methacryloxy polyethoxy)phenyl] propane (BPE) gel were used as models to prepare millimeter-sized spherical gels. A novel method involving controlled oxygen transfer into/out of the spherical gel with alternative flow of air and N2 gas, measurement of oxygen concentration at the center of the spherical gel using an oxygen microsensor, and analysis using the Fickian diffusion equation was developed to determine oxygen diffusivity in the gel. Ammonia oxidation in the AOB-entrapping gel was also monitored by measuring the oxygen concentration at the center of the gel using an oxygen microsensor. The oxygen concentration profile in the gel was estimated based on the oxygen diffusivity and Michaelis–Menten model parameters determined for suspended AOB cells. The kinetic rate-determining step in the AOB-entrapping gel was identified using the effectiveness factor. The results would be useful for the development of aerobic bacteria-entrapping gels and the design of wastewater treatment processes using these gels.

Nitrifying biomass can retain its acclimation to 2,4,6-trichlorophenol

Many municipal wastewater treatment plants in China receive industrial wastewater that contains inhibitory organic chemicals, such as chlorinated phenols. For the common aerobic biological treatment, nitrification is a key step, but nitrifying bacteria are notably sensitive to inhibition by chlorinated phenols. In this work, normal activated sludge (containing nitrifying biomass) was acclimated to 2,4,6-trichlorophenol (TCP). The acclimated biomass had more than 2-fold faster nitrification kinetics than normal biomass when exposed to TCP, and it also achieved effective TCP removal in parallel. When suddenly exposed to TCP after as much as two months without TCP input, the acclimated nitrifying biomass retained effective nitrification and TCP biodegradation: The nitrification rate and TCP removal rate were 0.325 mM/h and 0.049 mM/h for the acclimated biomass, compared to only 0.165 mM/h and 0.001 mM/h for normal biomass. Resistance to TCP inhibition also was retained for 5 generations of sub-culturing without TCP exposure. High-throughput sequencing confirmed that the acclimated biomass contained nitrifying bacteria and heterotrophic bacteria capable of degrading TCP, although the key genera changed during sub-culturing.

Sensitivity analysis on a three-phase plant-wide water and resource recovery facility model for identification of significant parameters

Water and resource recovery facility (WRRF) mathematical models have been advancing towards their widespread application for sizing and operation of treatment plants to minimize energy consumption and cost while maximizing nutrient recovery and effluent quality. Effective utilisation of these models requires that they are well calibrated. However, difficulties (with important parameters not identified and uncertainties in interpretation of model output results) can be experienced in model calibration, especially due to (i) the intricate relationships of model output variables with model input factors (where parameters are inter-related to various model outputs), resulting in non-linearity, and (ii) the limitations (due to expensive and/or time-consuming experimental methods) experienced in procuring and reconciling data required for determination of the model input factors. This paper presents the performance of a sensitivity analysis, reinforced with expert-based reasoning, on a three-phase (aqueous-gas-solid) plant-wide model (PWM_SA, Ikumi et al., 2015), for identification of significant parameters, and highlights the ones requiring experimental determination, specific to the system. The sensitivity analysis exercise was performed using two methods – i.e., Morris screening (screening method) and standardised regression coefficient (SRC; based on regression). This process was useful towards detection of the parameters, which are not normally measured at WRRFs, but may require attention for future application of mathematical models in decision-making processes for WRRFs. These included the influent fractions of unbiodegradable and readily biodegradable organics, the kinetic constants for hydrolysis of biodegradable particulates, the elemental composition of the organics and the specific growth rate of autotrophic nitrifying biomass.

Aerobic granular sludge formation in a sequencing batch reactor treating agro-industrial digestate

ABSTRACT Most of nitrogen emissions can be ascribed to agro-industrial activities. Since digestate produced by fermentation of agro-industrial residues can be difficult to dispose of due to its high ammonium content, advanced technical- and cost-effective technologies must be developed and applied in order to significantly reduce its impact on the environment. In this study, aerobic granules were successfully cultivated in a granular sludge sequencing batch reactor (GSBR) fed with the ammonium-rich (approx. 2500 mg L−1) effluent of a 3-stage anaerobic digester treating agro-industrial residues. The peculiar characteristics of such wastewater required a 2-step operating strategy aimed at the selection of nitrifying biomass (Step 1) and the formation of aerobic granular sludge (Step 2). During Step 1, nitrifying biomass selection was achieved by properly regulating the cycle length: removal rates progressively increased from 42 to 109 mgN L−1d−1, and a corresponding increase in specific removal rates from 8 to 24 mgN gVSS −1d−1 was also observed. During Step 2, the increase in selective pressures (i.e. minimum settling velocity and volumetric organic loading rate) led to the formation of compact (average diameter, 1.02 ± 0.43 mm) and well-settling granules (SVI5, 28.6 ± 3.8 mL gTSS −1), which were able to remove up to 89 ± 2% of organic matter (as COD), 79 ± 3% of and 59 ± 4% of nitrogen (as a sum of , and ). The 2-step operating strategy played a key role in biomass selection and subsequent granule formation and maintenance in the GSBR, and may be successfully adopted for the treatment of different ammonium-rich wastewaters.

Improving and upgrading an existing activated sludge with a compact MBBR – disc filters parallel line for municipal wastewater treatment in touristic alpine areas

Abstract Many wastewater treatment plants (WWTP) in touristic areas struggle to achieve the effluent requirements due to seasonal variations in population. In alpine areas, the climate also determines a low wastewater temperature, which implies long sludge retention time (SRT) needed for the growth of nitrifying biomass in conventional activated sludge (CAS). Moreover, combined sewers generate high flow and dilution. The present study shows how the treatment efficiency of an existing CAS plant with tertiary treatment can be upgraded by adding a compact line in parallel, consisting of a Moving Bed Biofilm Reactor (MBBR)-coagulation-flocculation-disc filtration. This allows the treatment of influent variations in the MBBR and a constant flow supply to the activated sludge. The performance of the new 2-step process was comparable to that of the improved existing one. Regardless significant variations in flow (10,000–25,000 m3/d) and total suspended solids (TSS) (50–300 mg/L after primary treatment) the effluent quality fulfilled the discharge requirements. Based on yearly average effluent data, TSS were 11 mg/L, chemical oxygen demand (COD) 27 mg/L and total phosphorus (TP) 0.8 mg/L. After the upgrade, ammonium nitrogen (NH4-N) dropped from 4.9 mg/L to 1.3 mg/L and the chemical consumption for phosphorus removal was reduced.

Total ammonia nitrogen (TAN) removal performance of a recirculating down-hanging sponge (DHS) reactor operated at 10 to 20 °C with activated carbon

Removal of total ammonium nitrogen (TAN) is essential during transportation of live seafood due to its high toxicity to aquatic cultures. Recirculating TAN removal system has been proposed and installed for the transportation of live seafood, while TAN removal performance often deteriorates at low temperature range (10–20 °C) due to the decrease of nitrifying activity. The authors have previously developed down-hanging sponge (DHS) reactors as a recirculating TAN removal system, which is a trickling filter system that uses polyurethane-sponge media to retain nitrifying biomass. The present study aimed to examine TAN removal performance of DHS reactor operated at 10 and 20 °C, and the following 4 DHS reactors were operated for the purpose; the DHS reactor operated 1) at 20 °C, 2) at 20 °C with addition of powdered activated carbon (AC) as an additional biomass carrier, 3) at 10 °C, and 4) at 10 °C with AC (designated as 20 °C-DHS, 20 °C-DHS-AC, 10 °C-DHS, and 10 °C-DHS-AC reactors, respectively). The DHS reactors were operated for 472 d with feeding of artificial seawater media, and TAN loading rates increased stepwisely up to 200 mg-N L-sponge media−1 d−1. TAN removal performance was examined by determining the concentrations of TAN, nitrite and nitrate in influent and effluent. Additionally, amplicon sequencing of prokaryotic 16S rRNA gene sequence was performed at Day 34, 212 and 374 to identify the nitrifying bacteria involved in the TAN removal. Both the 20 °C-DHS and 20 °C-DHS-AC reactors showed 200 mg-N L-sponge media−1 d−1 of TAN removal rate, whereas the 10 °C-DHS reactor showed only 15 mg-N L-sponge media−1 d−1. Notably, the addition of AC enhanced TAN removal performance of the DHS reactor operated at 10 °C. The 10 °C-DHS-AC reactor showed 60 mg-N L-sponge media−1 d−1 of TAN removal rate, which was 4-folds higher than those found in the 10 °C-DHS reactor. The amplicon sequencing analysis revealed that ammonia-oxidizing (i.e., Nitrosomonas) and nitrite-oxidizing (Nitrospira and Nitrospina) bacteria (AOB and NOB, respectively) proliferated in the operated DHS reactors, and the relative abundance of those AOB and NOB were greater in the DHS reactors with AC addition (i.e., the 20 °C-DHS-AC and 10 °C-DHS-AC reactors). Intriguingly, temperature difference (20 °C and 10 °C) resulted in occurrence of different NOB communities, and Nitrospira and Nitrospina were prominent in the DHS reactors operated at 20 °C and 10 °C, respectively. DHS reactor is capable of removing TAN even at 10 °C, which is applicable as a recirculating TAN removal system for transportation of live seafood.

FULL-SCALE APPLICATION OF MABR TECHNOLOGY FOR UPGRADING AND RETROFITTING AN EXISTING WWTP: PERFORMANCES AND PROCESS MODELLING

MABR (Membrane Aerated Biofilm Reactor) consists in an attached-growth process in which a gas permeable membrane is used as a biofilm carrier, and bubble-less oxygen transfer allows for a counter-diffusional mechanism where the electron donor (NH4+, biodegradable organics) and electron acceptor (O2) reach the biofilm from opposing sides. The paper reports results form the largest MABR installation in the world, demonstrating the beneficial impact of the technology in terms of improved process resilience under different operational conditions, through the key performance indicator oxygen transfer rate (OTR), which ranged between 7 and 16 gO2/m2/d. The OTR monitoring over the considered operational period shows (i) a weak impact of sludge temperature on the oxygen transfer within the considered range (9-22 degC) and also (ii) proves the reliability of OTR as an indicator of the improved resilience of the entire wastewater plant in the new MABR configuration, under peak loading conditions. Finally, a mathematical model was developed in the BioWin software platform, to evaluate its use as support tool for model-aided process optimization. The model was calibrated in terms of hydrodynamic behaviour of the MABR zone and seeding effect on the nitrifying biomass, which was expressed as solids retention time (SRT) of the attached growth biomass; the calibrated mathematical tool was then successfully validated in terms of prediction of ammonia concentration in the MABR zone.

Co-culture of microalgae and enriched nitrifying bacteria for energy-efficient nitrification

The aim of this study was to investigate the possibility of using microalgae as an oxygen supplier for nitrification. In order to measure oxygen demands of nitrification, the activated sludge were cultured in a selective medium for 150 days, and enriched nitrifying biomass was successfully obtained. The enriched nitrifiers were used to estimate oxygen demands for nitrification and used for co-culturing with microalgae. Oxygen transfer rates (OTR) were also measured for various mixing conditions to determine if mixing without forced aeration could satisfy oxygen demands of nitrification. For all mixing conditions, OTR were lower than the oxygen uptake rates (OUR) of nitrifiers. As a result, nitrification without forced aeration was incomplete due to oxygen deficiency. Meanwhile, oxygen production rates (OPR) of 6 microalgae species were measured, and it was demonstrated that C. vulgaris, S quadricauda, D. communism and C. emersonii could supply sufficient oxygen for nitrification at all mixing modes. Based on these results, 4 species of microalgae with sufficient oxygen supplying capabilities were selected for co-culturing with enriched nitrifiers, and full nitrification was accomplished without forced aeration. Finally, the electric energy of co-culture was estimated and showed that energy consumption by co-culture was lower than that of aerated nitrifiers.

Nitrification in a biofilm-enhanced highly loaded aerated lagoon.

A full-scale biofilm-enhanced aerated lagoon using fixed submerged media was monitored using automated water quality monitoring stations over the span of one year to quantify its nitrification performance. The system was operating at a high organic loading rate averaging 5.8gtotalCBOD5 /m2 of media per day (23.9gtotalCBOD5 /m3 of lagoon per day), a total ammonia nitrogen loading rate averaging 0.9gNH4 -N/m2 day (3.7gNH4 -N/m3 day), and temperatures ranging from 1.6 to 20.8°C. The system showed an extended seasonal nitrification period compared with a simulated aerated lagoon system of the same dimensions. This extension of complete nitrification with approximately 1month was observed in the fall despite the decrease of operating temperature down to 4°C. During this maximum nitrification period, substantial denitrification occurred, and the effluent un-ionized ammonia ratio was reduced. A temporary loss of nitrification was also experienced in relation to an episode of elevated suspended solids concentration. Measured biofilm characteristics, namely the detachment dynamics and the biofilm thickness, were used to explain this temporary nitrification loss. During wintertime, a low nitrate production was still observed, suggesting year-long retention of nitrifying bacteria in the biofilm. PRACTITIONER POINTS: Nitrification in a highly loaded biofilm-enhanced aerated lagoon is mainly affected by operating temperature. Maximum nitrification is observed during the warmer months and occurs even at high organic loading rates (>5gCBOD5 /m2 day). Compared with a simulated suspended growth system, the biofilm-enhanced lagoon shows a significantly extended nitrification period. The extension is observed at the end of the summertime maximum nitrification period. Low amounts of nitrate still produced during winter in the biofilm-enhanced aerated lagoon suggest year-long retention of autotrophic nitrifying biomass in the biofilm. Nitrification in the biofilm-enhanced aerated lagoon is negatively impacted by the presence of important quantities of accumulated solids that resuspend when their digestion starts as temperature increases.

Acclimation of nitrifying biomass to phenol leads to persistent resistance to inhibition

It is common that biological wastewater-treatment processes are exposed to inputs of toxic compounds, such as phenolics. Due to their slow growth rate, nitrifying bacteria are most susceptible to inhibition that can lead to loss of nitrification capacity. Here, a microbial community containing nitrifying bacteria was acclimated to phenol, and it developed resistance to phenol inhibition and maintained nitrification activity. For the phenol-acclimated biomass, the NH4+–N removal rates were almost unaffected when it was suddenly exposed to phenol. Heterotrophic synthesis and nitrification rates contributed 76% and 24% of the total NH4+–N removal respectively during phenol removal, but the nitrification rate increased significantly once phenol was removed and mineralized. In contrast, the NH4+–N removal rates decreased sharply for normal (unacclimated) nitrifying biomass when it was exposed to phenol. The phenol-acclimated biomass retained its resistance to phenol inhibition for at least two months after acclimation, and addition of the phenol-acclimated biomass to the normal biomass conferred resistance to phenol inhibition. Community analysis of the phenol-acclimated biomass showed an increase in families known to contain strains able to biodegrade phenolics. Taken together, the results indicate that the main impact of phenol acclimation was enrichment of phenol-biodegrading bacteria, which allowed rapid removal and mineralization of phenol and, consequently, alleviation of phenol's inhibition of nitrification.