Is ammonification the rate limiting step for nitrification kinetics?

Fulvic acid mediated highly efficient heterotrophic nitrification-aerobic denitrification by Paracoccus denitrificans XW11 with reduced C/N ratio

Reducing the C/N ratio requirements for heterotrophic nitrification-aerobic denitrification (HNAD) is crucial for its practical application; however, it remains underexplored. In this study, a highly efficient HNAD bacterium, Paracoccus denitrificans XW11, was isolated. The HNAD characteristics of XW11 were studied, and the redox mediator fulvic acid (FA) was used to reduce the C/N requirements. Whole-genome sequencing revealed multiple denitrification genes in XW11; however, nitrification genes were not identified, because heterotrophic nitrification-related gene sequences were not included in the database. However, the nitrogen removal related enzyme activity test revealed complete nitrification and denitrification pathways. Reverse transcription PCR showed that the membrane-bound nitrate reductase (NarG), rather than the periplasmic nitrate reductase, was responsible for aerobic denitrification. The conventional nitrite reductase (NirS) also does not mediate nitrite denitrification. When the C/N ratio was 10, the ammonia removal efficiency of the Control was 71.71 % and the addition of FA increased it to 86.12 %. Transcriptomic analysis indicated electron flow from the carbon source to FA without proton transmembrane transport, and the presence of FA constructs another electron transfer system. The redox potential of oxidized FA/reduced FA is 0.3679 V, avoiding competition for electrons from Complex III. Thus, ammonia monooxygenase obtains electrons more easily, thereby promoting nitrification. The enzyme activity test of the nitrification process confirmed this view. In addition, NarG expression increased, and the denitrification process was enhanced. Overall, FA improved HNAD efficiency by facilitating electron transfer to the nitrogen dissimilation process, offering a novel approach to reduce the C/N requirement of HNAD.

Microbial communities and denitrification mechanisms of pyrite autotrophic denitrification coupled with three-dimensional biofilm electrode reactor

Denitrification is of great significance for low C/N wastewater treatment. In this study, pyrite autotrophic denitrification (PAD) was coupled with a three-dimensional biofilm electrode reactor (BER) to enhance denitrification. The effect of current on denitrification was extensively studied. The nitrate removal of the PAD-BER increased by 14.90% and 74.64% compared to the BER and the PAD, respectively. In addition, the electron utilization, extracellular polymeric substances secretion, and denitrification enzyme activity (NaR and NiR) were enhanced in the PAD-BER. The microbial communities study displayed that Dokdonella, Hydrogenophaga, Nitrospira, and Terrimonas became the main genera for denitrification. Compared with the PAD and the BER, the abundance of the key denitrification genes narG, nirK, nirS, and nosZ were all boosted in the PAD-BER. This study indicated that the enhanced autotrophic denitrifiers and denitrification genes were responsible for the improved denitrification in the PAD-BER. PRACTITIONER POINTS: PAD-BER displayed higher nitrate removal, EPS, NAR, and NIR activity. The three types of denitrification (HD, HAD, and PAD) and their contribution percentage in the PAD-BER were analyzed. HAD was dominant among the three denitrification processes in PAD-BER. Microbial community composition and key denitrification genes were tested to reveal the denitrification mechanisms.

Effects of dairy processing sludge and derived biochar on greenhouse gas emissions from Danish and Irish soils

Globally, to ensure food security bio-based fertilizers must replace a percentage of chemical fertilizers. Such replacement must be deemed sustainable from agronomic and greenhouse gas (GHG) emission perspectives. For agronomic performance several controlled protocols are in place but not for testing GHG emissions. Herein, a pre-screening tool is presented to examine GHG emissions from bio-waste as fertilizers. The various treatments examined are as follows: soil with added mineral nitrogen (N, 140 kg N ha^-1) fertilizer (MF), the same amount of MF combined with dairy processing sludge (DS), sludge-derived biochar produced at 450 °C (BC450) and 700 °C (BC700) and untreated control (CK). These treatments were combined with Danish (sandy loam) or Irish (clay loam) soils, with carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions and soil inorganic-N contents measured on selected days. During the incubation, biochar mitigated N₂O emissions by regulating denitrification. BC450 reduced N₂O emissions from Danish soil by 95.5% and BC700 by 97.7% compared to emissions with the sludge application, and for Irish soil, the N₂O reductions were 93.6% and 32.3%, respectively. For both soils, biochar reduced CO₂ emissions by 50% as compared to the sludge. The lower N₂O reduction potential of BC700 for Irish soil could be due to the high soil organic carbon and clay content and pyrolysis temperature. For the same reasons emissions of N₂O and CO₂ from Irish soil were significantly higher than from Danish soil. The temporal variation in N₂O emissions was correlated with soil inorganic-N contents. The CH₄ emissions across treatments were not significantly different. This study developed a simple and cost-effective pre-screening method to evaluate the GHG emission potential of new bio-waste before its field application and guide the development of national emission inventories, towards achieving the goals of circular economy and the European Green Deal.

Heterogeneous multi-population competitive algorithm and its application in ASM1 parameter estimation

Activated sludge model 1 (ASM1) is a biokinetic model of the activated sludge wastewater treatment process, which has several uncertain parameters and complex chemical reaction processes. This model is often used in simulations to assess whether the effluent quality of wastewater meets discharge standards. Accurate and rapid estimation of the parameters of ASM1 is a necessary prerequisite for its successful application in industrial practice. However, ASM1-based parameter estimation is difficult to implement in practical operations due to the slow convergence rate and low convergence accuracy of most parameter estimation algorithms as well as the non-uniqueness of parameter estimation. In view of this, a novel metaheuristic optimization algorithm combining Legendre function network and dynamic partitioning strategy, named heterogeneous multi-group competitive algorithm (HMCA), is proposed to overcome the problem of low algorithmic efficiency and poor practicality in parameter estimation. The performance of the algorithm in terms of convergence speed, convergence accuracy and applicability is verified by two sets of test functions and eight state-of-the-art comparison algorithms. The superior performance of the algorithm in parameter estimation is then validated in conjunction with Benchmark Simulation Model no. 1 (BSM1) and four sets of operational data.

Assessment of the Impact of Selected Industrial Wastewater on the Nitrification Process in Short-Term Tests

Many chemical compounds can inhibit the nitrification process, especially organic compounds used in the chemical industry. This results in a decrease in the nitrification intensity or even a complete termination of this process. As the technological design of the selected municipal and industrial wastewater treatment plant (WWTP) assumed the dephosphation process, without taking into account nitrification, it was necessary to reduce the concentration of ammonium nitrogen in the treated sewage supplied to the Vistula River. Therefore, the aim of the research was to determine the inhibition of nitrification in the activated sludge method under the influence of industrial wastewater from the production of various organic compounds and to select the most toxic wastewater in relation to nitrifiers. The assessment of nitrification inhibition was carried out on the basis of the method of short-term (4-h) impact of the tested sewage on nitrifying bacteria in the activated sludge. The research covered nine different types of chemical sewage, including wastewater from the production of synthetic rubbers, styrene plastics, adhesives, solvents and emulsifiers. The nitrification process was inhibited to the highest degree by wastewater from the production of styrene-butadiene rubbers (72%). Only wastewater from the production of methacrylate (polymethyl methacrylate) had the lowest degree of inhibition: 16%. These wastewaters also have a toxic effect on the entire biocenosis and adversely affect the structure of activated sludge flocs. The attempts to filter toxic wastewater through the ash basins significantly relieved the inhibition of nitrification.

A bioreactor and nutrient balancing approach for the conversion of solid organic fertilizers to liquid nitrate-rich fertilizers: Mineralization and nitrification performance complemented with economic aspects

Due to the high water- and nutrient-use efficiency, hydroponic cultivation is increasingly vital in progressing to environment-friendly food production. To further alleviate the environmental impacts of synthetic fertilizer production, the use of recovered nutrients should be encouraged in horticulture and agriculture at large. Solid organic fertilizers can largely contribute to this, yet their physical and chemical nature impedes application in hydroponics. This study proposes a bioreactor for mineralization and nitrification followed by a supplementation step for limiting macronutrients to produce nitrate-based solutions from solid fertilizers, here based on a novel microbial fertilizer. Batch tests showed that aerobic conversions at 35 °C could realize a nitrate (NO₃^--N) production efficiency above 90% and a maximum rate of 59 mg N L^-1 d^-1. In the subsequent bioreactor test, nitrate production efficiencies were lower (44-51%), yet rates were higher (175-212 mg N L^-1 d^-1). Calcium and magnesium hydroxide were compared to control the bioreactor pH at 6.0 ± 0.2, while also providing macronutrients for plant production. A mass balance estimation to mimic the Hoagland nutrient solution showed that 92.7% of the NO₃^--N in the Ca(OH)₂ scenario could be organically sourced, while this was only 37.4% in the Mg(OH)₂ scenario. Besides, carbon dioxide (CO₂) generated in the bioreactor can be used for greenhouse carbon fertilization to save operational expenditure (OPEX). An estimation of the total OPEX showed that the production of a nutrient solution from solid organic fertilizers can be cost competitive compared to using commercially available liquid inorganic fertilizer solutions.

Performance and mechanism of a novel woodchip embedded biofilm electrochemical reactor (WBER) for nitrate-contaminated wastewater treatment

In this study, a woodchip biofilm electrode reactor (WBER) with woodchips embedded anode and cathode was developed, and its denitrification mechanism was analyzed by investigating the denitrification performance, organic matter change, redox environment and microbial community. The results show that the WBER with a carbon rod as anode (C-WBER) had a higher denitrification efficiency (2.58 mg NO- 3-N/(L·h)) and lower energy consumption (0.012 kWh/g NO- 3-N) at 350 mA/m². By reducing the hydroxyl radical and dissolved oxygen concentrations, anode embedding technology effectively decreased the inhibition on microorganisms. Lignin decomposition, nitrification and aerobic denitrification were carried out in anode. Additionally, hydrogen autotrophic denitrification and heterotrophic denitrification were occurred in cathode. The WBER effectively removed nitrate and reduced the cost, providing a theoretical basis and direction for further develop BERs.

Pollutant dynamics between The Black Sea and The Marmara Sea: Basis for wastewater management strategy

The study evaluated pollutant dynamics between The Black Sea and The Marmara Sea using data collected during a marine survey of the region around The Bosphorus strait, in the last five years. A hydraulic model was utilized to define two-layered water exchange in The Bosphorus. Analysis of pollutant exchange indicated The Black Sea as major polluter for the marine environment in The Marmara Sea. Four wastewater outfalls are located along The Bosphorus; Mass balances between the two ends of The Bosphorus indicated losses of 44 t/d total N and 138 t/d COD in the lower layer before reaching The Black Sea. This was explained with a simultaneous nitrification-denitrification process sustained in the low oxygen or anoxic zones around the outfalls, implying that a sustainable wastewater strategy should preclude additional treatment for The Bosphorus discharges, since they do not have an appreciable impact on the water quality of the lower flow.

The Kinetics of Pollutant Removal through Biofiltration from Stormwater Containing Airport De-Icing Agents

The present study aimed to determine the kinetics of pollutant removal in biofilters with LECA filling (used as a buffer to prevent de-icing agents from being released into the environment with stormwater runoff). It demonstrated a significant effect of temperature and a C/N ratio on the rate of nitrification, denitrification, and organic compound removal. The nitrification rate was the highest (0.32 mg N/L·h) at 25 °C and C/N = 0.5, whereas the lowest (0.18 mg N/L·h) at 0 °C and C/N = 2.5 and 5.0. Though denitrification rate is mainly affected by the available quantity of organic substrate, it actually decreased as the C/N increased and was positively correlated with the temperature levels. Its value was found to be the highest (0.31 mg N/L·h) at 25 °C and C/N = 0.5, and the lowest (0.18 mg N/L·h) at 0 °C and C/N = 5.0. As the C/N increased, so did the content of organic compounds in the treated effluent. The lowest organic removal rates were noted for C/N = 0.5, ranging between 11.20 and 18.42 mg COD/L·h at 0 and 25 °C, respectively. The highest rates, ranging between 27.83 and 59.43 mg COD/L·h, were recorded for C/N = 0.5 at 0 and 25 °C, respectively.

Inhibitory effect of phenol on wastewater ammonification

This study aimed to elucidate inhibitory effect of phenol on ammonification of dissolved organic nitrogen (DON) in wastewater. Laboratory incubation experiments were conducted using primary and secondary effluent samples spiked with phenol (100-1000 mg/L) and inoculated with mixed cultures, pure strains of phenol-degrading bacteria (Acinetobacter sp. and Pseudomonas putida F1), and/or an ammonia oxidizing bacterium (Nitrosomonas europaea). DON concentration was monitored with incubation time. Phenol suppressed the ammonification rate of DON up to 62.9%. No or minimal ammonification inhibition was observed at 100 mg/L of phenol while the inhibition increased with increasing phenol concentration from 250 to 1000 mg/L. The inhibition was curtailed by the presence of the phenol-degrading bacteria. DON was ammonified in the samples inoculated with only N. europaea and the ammonification was also inhibited by phenol. The findings suggest that high phenol in wastewater could result in low ammonification and high DON in the effluent.

The role of influent organic carbon-to-nitrogen (COD/N) ratio in removal rates and shaping microbial ecology in soil aquifer treatment (SAT)

Soil columns simulating soil aquifer treatment (SAT), fed with synthetic secondary effluent by intermittent infiltration of flooding/drying cycles, were characterized for nitrogen and organic carbon removal, and microbial ecology and biokinetics. The columns differed in the concentration ratio of chemical oxygen demand (COD) to the summed NH₄⁺, NO₂^- and organic nitrogen-2 (C/N2) or 5 (C/N5). Chemical profiles along the column demonstrated a preference for COD oxidation over nitrification and coupled denitrification, with higher nitrogen loss (57% vs. 16%) in the C/N5 column. Unexpectedly, significant dominance of the genus Nitrospira over the genus Nitrobacter and ammonia-oxidizing bacteria (AOB) was strongly correlated at column depths where NH₄⁺ removal occurred. Moreover, the Nitrospira profile had the strongest correlation to the profile of NH₄⁺ (positive) and NO₃^- (negative), strongly indicating complete ammonia oxidation. 16S sequencing analysis of the topsoil in C/N2 vs. C/N5 columns revealed double the abundance of microbial aerobic potential (64% vs. 32%) vs. one-third the denitrification potential (13% vs. 31%). The concentrations and degradability levels of organic carbon were the most influential parameters shaping community structure. Niche differentiation within the biofilm attached to the soil is suggested to have an important role in the process's anoxic activity and nitrogen removal.

Integrating novel (thermophilic aerobic membrane reactor-TAMR) and conventional (conventional activated sludge-CAS) biological processes for the treatment of high strength aqueous wastes

A combination of thermophilic aerobic membrane reactor (TAMR) and conventional activated sludge (CAS) was studied by means of two pilot plants at semi-industrial scale in order to simulate the new configuration adopted in a full-scale facility for the treatment of high strength aqueous wastes. Aqueous wastes with high contents of organic pollutants were treated by means of the TAMR technology, progressively increasing the organic load (3-12 kg_COD m^-3 d^-1). A mixture of municipal wastewater and thermophilic permeate was fed to the CAS plant. The main results are the following: achievement of a high COD removal yield by both the TAMR (78%) and the CAS (85%) plants; ammonification of the organic nitrogen under thermophilic conditions and subsequent mesophilic nitrification; capacity of the downstream mesophilic process to complete the degradation of the organic matter partially obtained by the TAMR process and precipitation of phosphorus as vivianite and carbonatehydroxylapatite in the TAMR plant.

Impact of electro-stimulation on denitrifying bacterial growth and analysis of bacterial growth kinetics using a modified Gompertz model in a bio-electrochemical denitrification reactor

This study aimed to investigate the effect of electro-stimulation on denitrifying bacterial growth in a bio-electrochemical reactor, and the growth were modeled using modified Gompertz model under different current densities at three C/Ns. It was found that the similar optimum current density of 250mA/m² was obtained at C/N=0.75, 1.00 and 1.25, correspondingly the maximum nitrate removal efficiencies were 98.0%, 99.2% and 99.9%. Moreover, ATP content and cell membrane permeability of denitrifying bacteria were significantly increased at optimum current density. Furthermore, modified Gompertz model fitted well with the microbial growth curves, and the highest maximum growth rates (µ_max) and shorter lag time were obtained at the optimum current density for all C/Ns. This study demonstrated that the modified Gompertz model could be used for describing microbial growth under different current densities and C/Ns in a bio-electrochemical denitrification reactor, and it provided an alternative for improving the performance of denitrification process.

Chronic impact of sulfamethoxazole on the metabolic activity and composition of enriched nitrifying microbial culture

This study investigated the chronic impact of sulfamethoxazole (SMX) on activated sludge sustaining an enriched nitrifying biomass. For this purpose, a laboratory scale fill and draw reactor was operated with 100 mg COD/L of peptone mixture and 50 mg N/L of ammonia at a sludge age of 15 days. Additionally, the biomass was exposed to a daily SMX dose of 50 mg/L once the reactor reached steady-state conditions. The reactor performance and microbial composition were monitored for 37 days with conventional parameters and molecular techniques based on the gene for ammonia monooxygenase subunit A (amoA) and the prokaryotic 16S rRNA gene. Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene cloning analyses suggested a microbial community change concurrent with the addition of SMX. Specifically, quantitative polymerase chain reaction analyses (qPCR/RT-qPCR) revealed a significant reduction in the levels and activity of ammonia oxidizing bacteria (AOB). However, the acclimation period ended with high amoA mRNA levels and improved nitrification efficiency. Partial degradation of SMX by heterotrophic bacteria was also observed.

Nitrification at full-scale municipal wastewater treatment plants: Evaluation of inhibition and bioaugmentation of nitrifiers

Batch nitrification tests were conducted with sludge and wastewater streams obtained from field implementations to evaluate nitrification inhibition and efficiency of a nitrifiers bioaugmentation technology at full-scale municipal wastewater treatment plants (WWTPs). The results showed that the substrate organic carbon and pH of wastewater streams were inhibitory factors to nitrification and the low pH was the cause of the WWTP experiencing poor nitrification. An ammonia-nitrogen removal rate of 0.21mg-N/gMLVSS-h was observed at pH 6.5, while the rate increased to 0.54mg-N/gMLVSS-h with an introduction of 6% bioaugmented nitrifiers, indicating that the integrated side-stream nitrifiers bioaugmentation process was beneficial in improving nitrification efficiency, even under low pH conditions not conducive to nitrification. The study provides new insights into effective upgrading of municipal WWTPs exposed to poor nitrification.

Chronic impact of tetracycline on nitrification kinetics and the activity of enriched nitrifying microbial culture

This study evaluated the chronic impact of tetracycline on biomass with enriched nitrifying community sustained in a lab-scale activated sludge system. For this purpose, a fill and draw reactor fed with 100 mg COD/L of peptone mixture and 50 mg N/L of ammonia was sustained at a sludge age of 15 days. At steady-state, the reactor operation was continued with a daily tetracycline dosing of 50 mg/L for more than 40 days, with periodic monitoring of the microbial composition, the nitrifying bacteria abundance, as well as the amoA and 16S rRNA gene activity, using molecular techniques. Changes in the kinetics of nitrification were quantified by modelling concentration profiles of major nitrogen fractions and oxygen uptake rate profiles derived from parallel batch experiments. Activated sludge modeling results indicated inhibitory impact of tetracycline on the growth of nitrifiers with a significant increase of the half saturation coefficients in corresponding rate equations. Tetracycline also inactivated biomass components of the enriched culture at a gradually increasing rate with time of exposure, leading to total collapse of nitrification. Molecular analyses revealed significant changes in the composition of the microbial community throughout the observation period. They also showed that continuous exposure to tetracycline inflicted significant reduction in amoA mRNA and 16S rRNA levels directly affecting nitrification. The chronic impact was much more pronounced on the ammonia oxidizing bacteria (AOB) community. These observations explained the basis of numerical changes identified in the growth kinetics of nitrifiers under stress conditions.

Acute impact of erythromycin and tetracycline on the kinetics of nitrification and organic carbon removal in mixed microbial culture

The study evaluated acute impact of erythromycin and tetracycline on nitrification and organic carbon removal kinetics in mixed microbial culture. Acclimated biomass was obtained from a fill and draw reactor fed with peptone mixture selected as synthetic substrate and operated at a sludge age of 10 days. Acute inhibition was tested in batch reactors involving a control unit started solely with substrate and the others with additional doses of each antibiotic. Modeling indicated that both steps of nitrification were totally blocked by erythromycin. Tetracycline inhibited and retarded nitrification kinetics at 50 mg/L and stopped nitrite oxidation at 200 mg/L, leading to nitrite accumulation. Both antibiotics also affected organic carbon removal by inducing partial inactivation of the heterotrophic community in the culture, increased substrate storage and accelerated endogenous respiration, with a relatively slight impact on heterotrophic growth. Major inhibitory effect was on process stoichiometry, leading to partial utilization of organic substrate.