Activated Sludge Nitrification Research Articles

Analysis of full nitrification performance and optimization of reaction properties using N and O isotope fractionation

Isotopic fractionation properties have been successfully applied to identify the distribution and fate of nitrogen in ecosystems, revealing the dynamic response of N and O elements during nitrogen transport and transformation. However, only a few studies used the dual isotope technology in activated sludge treatment of domestic wastewater and many aspects of the process are unclear. Here, we use the dual isotope techniques to increase the understanding of the substrates required for nitrification reactions, nitrification performance, and process operation. Mixed sludge was successfully enriched with nitrifying bacteria in a continuous culture, and three dissolved oxygen (DO; 0.2–0.4, 3–4, and 7–8 mg/L) and three temperature levels (18 ± 1, 25 ± 1, and 33±1 °C) were tested for efficiency of nitrate nitrogen accumulation. Both δ15NNO3 and δ18ONO3 showed a gradual increase with an increase in DO or temperature, the increase in DO slowed down the fractionation effect of isotopes, and the increase in temperature reduced the variability in N and O utilization. The slope of δ15NNO3:δ18ONO3 gradually approached 1 with the increase in DO (<7 mg/L) or in temperature, and the optimal range of DO and temperature were accurately judged to strengthen the denitrification performance of nitrifying bacteria. δ18OH2O was successfully taken up to form NO2−-N and NO3−-N with 74 and 91% replacement rates, respectively, indicating that DO and H2O jointly completed the formation of nitrate nitrogen during the long nitrification process. In summary, the in situ dual isotope technology can help optimize the influence of environmental factors on nitrification performance to guide the long-term stable operation of nitrification reactions in sludge treatment and provide a reliable basis for complex activated sludge nitrification systems.

Denitrification of ammonium nitrate industrial wastewater using sulfur and limestone packed bioreactor

One of the ammonium nitrate industries in Indonesia, PT.X, is located in West Java. This industry produces wastewater containing 1890 mg/L ammonia-nitrogen, 1800 mg/L nitrate-nitrogen, and 51 mg/L nitrite-nitrogen. In industrial treatment, this wastewater is treated using activated sludge nitrification and anoxic denitrification by adding carbon sources such as methanol or glucose. Denitrification process using autotrophic bacteria is applied in wastewater treatment as an alternative method for reducing the cost of wastewater treatment. The bacteria can grow and develop on elemental sulfur. This paper presents the results of industrial wastewater treatment of ammonium nitrate by two processes: nitrification using activated sludge and denitrification using sulfur and limestone packed-bed bioreactors. Sulfur was used as an electron donor, reducing nitrate to nitrogen gas with sulfate as a by-product. Limestone was used as a material that could minimize the pH decrease caused by the sulfate formation. The residence time applied in this study was from 1 to 4 days; the longer the residence time, the higher the efficiency of nitrogen nitrate reduction. The highest efficiency of nitrate-nitrogen reduction was 97%, achieved at a residence time of 4 days at the nitrate-nitrogen initial concentration of 2,000 mg/L. The water pH during the denitrification process was in the range of 6.5-7.5, meeting the pH quality standard to be discharged into the environment.

The dissimilarity of antibiotic and quorum sensing inhibitor on activated sludge nitrification system: Microbial communities and antibiotic resistance genes

Effects of antibiotics (azithromycin, AZM, 1–40 mg/L) and quorum sensing inhibitor (QSI, 2(5H)-furanone, 1–40 mg/L) combined pollution with environmental concentration of copper on bacterial/archaeal community and antibiotic resistance genes (ARGs) in activated sludge system were explored. QSI inhibited nitrification more obviously than AZM. AZM and QSI were synergistic inhibitions on bacterial diversity, and AZM inhibited bacterial compositions more than QSI. While, QSI had more impacts on archaeal diversity/compositions. Less interactions among bacteria and archaea communities with Aquimonas as keystone genus. Functional differences in bacteria/archaea communities were little, and AZM had more effects on metabolism. AZM mainly affected nitrifying bacteria (Candidatus Nitrospira nitrificans and Nitrosomonas). Specific denitrifying bacteria were enriched by AZM (Brevundimonas, 1.76–31.69%) and QSI (Comamonas, 0.61–9.61%), respectively. AZM enriched ARGs more easily than QSI and they were antagonistic to proliferation of ARGs. Bacteria were main hosts of ARGs (macrolide-lincosamide-streptogramin B, other/efflux, etc.) and archaea (Methanosphaerula, Methanolobus) carried multiple ARGs.

Response of microbial communities based on full-scale classification and antibiotic resistance genes to azithromycin and copper combined pollution in activated sludge nitrification laboratory mesocosms at low temperature

This study aimed to investigate the short-term response of abundant-rare genera and antibiotic resistance genes (ARGs) to azithromycin (AZM, 0.05–40 mg/L) and copper (1 mg/L) combined pollution in activated sludge nitrification system at low temperature. Nitrification was as expected inhibited in stress- and post-effects periods under AZM concentration higher than 5 mg/L. Abundant and rare taxa presented dissimilar responses based on full-scale classification. Conditionally rare or abundant taxa (CRAT) were keystone taxa. Relative abundance of ammonia-oxidizing archaea increased, and three aerobic denitrifying bacteria (Brevundimonas, Comamonas and Trichococcus) were enriched (from 9.83% to 68.91% in total). Ammonia nitrogen assimilating into Org-N and denitrification may be nitrogen pathways based on predict analysis. 29 ARGs were found with more co-occurrence patterns and high concentration of AZM (greater than 5 mg/L) caused their proliferation. Importantly, expect for some abundant taxa, rare taxa, potential pathogens and nitrogen-removal functional genera were the main potential hosts of ARGs.

Nitrification performance evaluation of activated sludge under high potassium ion stress during high-ammonia nitrogen organic wastewater treatment

The recycling reverse osmosis (RO) membrane concentrate of some high-ammonia nitrogen (NH4+-N) organic wastewater to the biological unit could cause potassium ion (K+) accumulation, thereby affecting the removal of NH4+-N by activated sludge. Thus, the effects of high K+ stress on activated sludge nitrification performance was studied. The results showed that the high K+ stress promoted the floc sludge to produce more extracellular polymers (EPS), which accelerated the sludge sedimentation and enriched the biomass in sequential batch reactors (SBRs). The ammonia oxidation process and nitrite (NO2--N) oxidation process were further analyzed in the nitrification process. High K+ stress enriched ammonia oxidizing bacteria (AOB), which ensured the efficient ammonia oxidation process in SBRs, and ensured the removal rate of NH4+-N was maintained above 93%. However, high K+ stress (15g/L KCl) inhibited the activity of NO2−-N oxidizing bacteria (NOB) and reduced the abundance of NOB, thus leading to the accumulation of NO2−-N, and finally worsened the nitrification performance of activated sludge. In short, the performance of activated sludge will not be inhibited when the K+ in the wastewater does not exceed 5.23 g/L. The results could provide a reference for the optimization of the biological performance in treating high-NH4+-N organic wastewater with activated sludge coupled RO membrane treatment process.

Stoichiometric and kinetic characterization of an acid-tolerant ammonia oxidizer ‘Candidatus Nitrosoglobus’

Recently, acidic (i.e. pH<5) nitrification in activated-sludge is attracting attention because it enables stable nitritation (NH4+ → NO2−), and enhances sludge reduction and stabilization. However, the key acid-tolerant ammonia oxidizers involved are poorly understood. In this study, we performed stoichiometric and kinetic characterization of a new acid-tolerant ammonia-oxidizing bacterium (AOB) belonging to gamma-proteobacterium, Candidatus Nitrosoglobus. Ca. Nitrosoglobus was cultivated in activated-sludge in a laboratory membrane bioreactor over 200 days, with a relative abundance of 55.1 ± 0.5% (indicated by 16S rRNA gene amplicon sequencing) at the time of the characterization experiments. Among all known nitrifiers, Ca. Nitrosoglobus bears the highest resistance to nitrite, low pH, and free nitrous acid (FNA). These traits define Ca. Nitrosoglobus as an adversity-strategist that tends to prosper in acidic activated-sludge, where the low pH (< 5.0) and high levels of FNA (at parts per million levels) sustained and inhibited all other nitrifiers. In contrast, in the conventional pH-neutral activated-sludge process, Ca. Nitrosoglobus is less competitive with canonical AOB (e.g. Nitrosomonas) due to the relatively slow specific growth rate and low affinities to both oxygen and total ammonia. These results advance our understanding of acid-tolerant ammonia oxidizers, and support further development of the acidic activated-sludge process in which Ca. Nitrosoglobus can play a critical role.

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.

Effect evaluation of microplastics on activated sludge nitrification and denitrification

A large amount of microplastics have entered conventional wastewater treatment plants, and their effects on activated sludge nitrification and denitrification are rarely reported. This study investigated the effects of microplastics on activated sludge nitrification and denitrification using five typical microplastics, namely, polyvinyl chloride (PVC), polypropylene, polyethylene, polystyrene, and polyester (PES) with concentrations of 0, 1000, 5000, and 10,000 particles/L. Results indicated that microplastics had negative effects on ammonia oxidation rate and low effect on nitrite oxidation rate during nitrification. The total inorganic nitrogen did not have much difference during 3 h nitrification under all the tested conditions. The addition of microplastics showed positive effects on denitrification, especially for PVC and PES at microplastic concentration of 5000 particles/L. Nitrification and denitrification did not evidently stop under all the tested conditions, indicating that the selected microplastic types and concentrations were not toxic to nitrification and denitrification within 3 h. The high abundance of PVC microplastics remarkably increased the nitrous oxide (N2O) emission during denitrification. The N2O emission in the test with 10,000 particle/L of PVC was 4.6times higher than the blank control. This study indicated that microplastics with <10,000 particle/L concentration in wastewater had low effects on nitrification and denitrification, whereas they had high effects on the N2O emission during denitrification.

Estimating the impact of inhibitory substances on activated sludge denitrification process

Abstract Industrial wastewater frequently contains substances which inhibit activated sludge treatment processes. Inhibitory characteristics of different substances are usually evaluated based on testing the impact of respective substance on activated sludge nitrification or oxygen uptake rates. However, denitrification is always before aerobic processes in conventional activated sludge treatment plants and thereby more exposed to inhibitory compounds. There is no easily applicable and validated method available for determination of denitrification process efficiency and inhibition. In this study, a method for evaluation of inhibition on the activated sludge denitrification process was developed and validated using 3,5-dichlorophenol (3,5-DCP) as a model inhibitory compound and additionally controlled with real wastewater produced in the shale oil industry. Average IC50 value (5.5 ± 2.2 mg L−1) for 3,5-DCP showed that denitrifiers were less sensitive than nitrifiers (IC50 = 2.9 ± 0.7 mg L−1) and more sensitive than aerobic heterotrophs (IC50 = 7.2 ± 2.4 mg L−1). Methodological aspects like accumulation of nitrite nitrogen, acclimatization of biomass and technical issues were discussed. Achieved validation characteristics were similar with ISO Standards estimating activated sludge nitrification and oxygen uptake rates, which proves the reliability of the method: standard deviation, 95.4% confidence level, relative standard deviation were calculated to be 2.2 mg L−1, 1.2 … 9.8 mg L−1 and 39.2%, respectively.

Insights gained into activated sludge nitrification through structural and functional profiling of microbial community response to starvation stress

An improved understanding of nitrifying microbial communities in wastewater treatment is imperative for proper design and operation of biological nutrient removal systems.

Comparison of different aerobic granular sludge types for activated sludge nitrification bioaugmentation potential

Three types of nitrifying granules were grown on media simulating anaerobic digestion dewatering reject water and compared for their potential to increase nitrification capacity when added to mainstream flocculent activated sludge treatment. An advantage of nitrification bioaugmentation with sidestream granules instead of flocculent biomass is that the granules can be selectively maintained at longer retention times than flocs and thus provide higher nitrification capacity from bioaugmentation. The three granule types and feeding conditions were: nitrifying granules with aerobic feeding, nitrifying-denitrifying granules with anoxic feeding, and nitrifying-denitrifying/phosphate-accumulating (NDN-PAO) granules with anaerobic feeding. NDN-PAO granular sludge showed the highest potential for nitrification bioaugmentation due to its better treatment performance, granule physical characteristics, and much greater production of granular mass and nitrification capacity. Dechloromonas-associated organisms were dominant in these granules; Candidatus Accumulibacter-related organisms were also present. Nitrosomonas was the dominant ammonia-oxidizing bacteria, while Candidatus Nitrotoga was an abundant nitrite-oxidizer in all granule types.

Acute impact of dimethyl phthalate on activated sludge nitrification kinetics

This study involved model evaluation of acute impact of dimethyl phthalate (DMP) on substrate utilization kinetics of aerobic nitrifying activated sludge biomass. A laboratory scale fill/draw reactor acclimated to peptone-meat extract mixture, supplying the biomass, was maintained throughout the study and four sets of batch experiments were conducted to determine the acute impact. After nitrification and carbon removal kinetics of the acclimated biomass were determined as a baseline to the acute inhibitory impact studies, 1 g/L DMP concentration was applied. Related experimental data were derived and simulated for model calibration to determine the necessary process kinetics. Model evaluation provided unique information on blockage of nitrification under impact of DMP, and its biological degradation by a fraction of heterotrophic biomass as carbon source at a slower rate than peptone-meat extract mixture.

Inhibition of the nitrification process in activated sludge by trivalent and hexavalent chromium, and partitioning of hexavalent chromium between sludge compartments

The input of wastewater treatment plants (WWTPs) may contain high concentrations of Cr(III) and Cr(VI), which can affect nitrogen removal. In the present study the influence of different Cr(III) and Cr(VI) concentrations towards activated sludge nitrification was studied. To better understand the mechanisms of Cr(VI) toxicity, its reduction, adsorption and uptake in activated sludge was investigated in a batch growth system. Quantification of Cr(VI) was performed by speciated isotope dilution inductively coupled plasma mass spectrometry. It was found that Cr(VI) concentrations above 1.0mgL−1 and Cr(III) concentrations higher than 50mgL−1 negatively affected nitrification. Speciation studies indicated almost complete reduction of Cr(VI) after 24h of incubation when Cr(VI) concentrations were lower than 2.5mgL−1, whereas for Cr(VI) added to 5mgL−1 around 40% remained unreduced. The study of the partitioning of Cr in the activated sludge was performed by the addition of Cr(VI) in concentrations of 2.5 and 5.0mgL−1. Results revealed that Cr was allocated mainly within the intercellular compartments, whereas intracellular and adsorbed Cr represented less than 0.1% of the Cr sludge concentrations. Cr(VI) was reduced in all compartments, the most efficiently (about 94%) within the intracellular and intercellular fractions. The extent of reduction of adsorbed Cr was 92% and 80% for 2.5 and 5.0mg of Cr(VI) L−1, respectively. The results of present investigation provide a new insight into the toxicity of Cr species towards activated sludge nitrification, which is of significant importance for the management of WWTPs in order to prevent them from inflows containing harmful Cr(VI) concentrations.

Modeling Nitrous Oxide Production during Biological Nitrogen Removal via Nitrification and Denitrification: Extensions to the General ASM Models

Nitrous oxide (N(2)O) can be formed during biological nitrogen (N) removal processes. In this work, a mathematical model is developed that describes N(2)O production and consumption during activated sludge nitrification and denitrification. The well-known ASM process models are extended to capture N(2)O dynamics during both nitrification and denitrification in biological N removal. Six additional processes and three additional reactants, all involved in known biochemical reactions, have been added. The validity and applicability of the model is demonstrated by comparing simulations with experimental data on N(2)O production from four different mixed culture nitrification and denitrification reactor study reports. Modeling results confirm that hydroxylamine oxidation by ammonium oxidizers (AOB) occurs 10 times slower when NO(2)(-) participates as final electron acceptor compared to the oxic pathway. Among the four denitrification steps, the last one (N(2)O reduction to N(2)) seems to be inhibited first when O(2) is present. Overall, N(2)O production can account for 0.1-25% of the consumed N in different nitrification and denitrification systems, which can be well simulated by the proposed model. In conclusion, we provide a modeling structure, which adequately captures N(2)O dynamics in autotrophic nitrification and heterotrophic denitrification driven biological N removal processes and which can form the basis for ongoing refinements.

Savings with upgraded performance through improved activated sludge denitrification in the combined activated sludge–biofilter system of the Southpest Wastewater Treatment Plant

The purpose of the experiments was to increase the rate of activated sludge denitrification in the combined biological treatment system of the Southpest Wastewater Treatment Plant in order to gain savings in cost and energy and improve process efficiency. Initial profile measurements revealed excess denitrification capacity of the preclarified wastewater. As a consequence, flow of nitrification filter effluent recirculated to the anoxic activated sludge basins was increased from 23,000 m3 d(-1) to 42,288 m3 d(-1) at an average preclarified influent flow of 64,843 m3 d(-1), Both simulation studies and microbiological investigations suggested that activated sludge nitrification, achieved despite the low SRT (2-3 days), was initiated by the backseeding from the nitrification filters and facilitated by the decreased oxygen demand of the influent organics used for denitrification. With the improved activated sludge denitrification, methanol demand could be decreased to about half of the initial value. With the increased efficiency of the activated sludge pre-denitrification, plant effluent COD levels decreased from 40-70 mg l(-1) to < 30-45 mg l(-1) due to the decreased likelihood of methanol overdosing in the denitrification filter.

Enhancing activated sludge nitrification through seeding from a downstream nitrifying fixed-film reactor

An ASM1-based mathematical model was developed for the description of the combined activated sludge-biofilter system of the Southpest Wastewater Treatment Plant, Budapest, Hungary. This model includes the interactions of the activated sludge and biofilter units, i.e. the influence of both the clarified activated sludge effluent and the backwashed nitrifying and denitrifying microorganisms. Concentration profile measurements have been carried out throughout the combined system in order to track the biological processes. Optimization possibilities of the existing combined plant were investigated by mathematical simulations under the different detected operational conditions. In these studies concentration data measured on separate days and the appropriate flow rates of the preclarified influent and the recycled streams registered at the treatment plant were used. Simulation results showed that N-removal of the activated sludge unit could be highly intensified by appropriate aeration, that would facilitate the e fficient growth of backwashed biomass. However, in some cases, shortage of readily biodegradable carbon source proved to be the limit of the benefits available.

Evaluation of the Persistence of Micropollutants Through Pure‐Oxygen Activated Sludge Nitrification and Denitrification

The persistence of pharmaceuticals, hormones, and household and industrial chemicals through a pure-oxygen activated sludge, nitrification, denitrification wastewater treatment facility was evaluated. Of the 125 micropollutants that were tested in this study, 55 compounds were detected in the untreated wastewater, and 27 compounds were detected in the disinfected effluent. The persistent compounds included surfactants, fire-retardant chemicals, pesticides, fragrance compounds, hormones, and one pharmaceutical. Physical-chemical properties of micropollutants that affected partitioning onto wastewater solids included vapor pressure and octanol-water partition coefficients.

Nitrous oxide emissions from secondary activated sludge in nitrifying conditions of urban wastewater treatment plants: Effect of oxygenation level

In order to better understand the mechanisms of N 2O emissions from nitrifying activated sludge of urban WWTPs, sludge from the Valenton plant (Paris conurbation) are subjected to lab-scale batch experiments under various conditions of oxygenation. The results show that the highest N 2O emissions (7.1 μgN-N 2O gSS −1 h −1 in average) occur at a dissolved oxygen (DO) concentration of around 1 mgO 2 L −1. These high emissions at low oxygenation (from 0.1 to 2 mgO 2 L −1) are due to two processes: autotrophic nitrifier denitrification and heterotrophic denitrification. Nitrifier denitrification always dominates, representing from 58% to 83% of the N 2O production. This N 2O production originating from nitrifying activated sludge becomes 8 times higher when nitrite is added at a DO of 1 mgO 2 L −1; a decrease is observed both at higher and lower oxygenation. Heterotrophic denitrification represents less than 50% of the N 2O production, decreasing from 42% to 17% when oxygenation increases from 0.1 to 2 mgO 2 L −1. We show that ammonium oxidizing bacteria (AOB) can shift to nitrifier denitrification when oxygen is depleted in the environments including in the WWTPs, nitrite then plays the role of oxygen as the final electron acceptor. As opposed to what happens in nitrification, the end products of nitrifier denitrification are gaseous forms of nitrogen, where N 2O is not negligible compared to N 2. Overall, N 2O emissions represent 0.1–0.4% of oxidized NH 4 +, depending on the oxygenation level. N 2O emissions would range from 0.11 to 0.42 T N-N 2O day −1 for a tertiary treatment of the Paris wastewater effluents, consisting exclusively of activated sludge nitrification.

Effect of Selected Textile Effluents on Activated Sludge Nitrification Process

In this study, a recently developed methodology for the assessment of the inhibitory effect on nitrifying biomass was applied to several textile effluents from productive processes. Effluents are classified according to the degree of inhibition as EC50 (concentration producing 50% nitrification inhibition); the investigated textile effluents showed a wide range of EC50 ranging from 20 ml gVSS− 1 (83 ml l− 1) to values above 100 ml gVSS− 1 (300 ml l− 1) for effluents produced by rinsing phases. Taking into account biodegradability and toxicity evaluations, most of the effluents showed a good treatability in conventional biological wastewater treatment plant. On the other hand three textile effluents showed significant toxic effects towards nitrifying biomass. In any case, the proposed procedure represents an efficient tool to prevent treatment failures due to toxic discharges.

STUDIES OF VARIOUS WASTEWATER NITRIFICATION BIOREACTOR TYPES BASED ON MODELLING AND SIMULATION

In view of the importance of wastewater treatment, the purpose of this work is to study and simulate the behavior of various reactors used in wastewater biological treatment, under different working conditions, based on analytical models. The paper approaches the performances of some constructive types of reactors, in order to asses their competitiveness for the nitrification process. The studies were performed in the following systems: a single-stage activated sludge nitrification, a continuous nitrification with immobilized biomass, a fed-batch nitrification with immobilized biomass, a fluidized bed reactor with attached nitrifying microorganisms. The analytical models used for simulation are based on dynamic balance equations for ammonia and organic substrate, for organic stabilizing and nitrifying organisms. Also, nitrification kinetics involving a sequence of two steps of oxidation as well as oxygen transfer equations, as complementary relations are included. The computer simulations revealed that the analyzed bioreactors are different in terms of substrates and biomass dynamics. Also, simulation tools based on analytical models of the nitrification systems could be successfully applied in a preliminary phase of process synthesis for choosing the most appropriate nitrification system without experiments, thus saving time and money.