Biological Nitrogen Removal Process Research Articles

Carbon emission calculation of three biological nitrogen removal processes: A case of rare earth element tailings wastewater in Southern Jiangxi, China

Global warming has been caused by greenhouse gases (GHGs) released by human activity. Traditional sewage treatment uses much energy to achieve discharge limits in the water treatment industry, producing many GHG emissions. In this study, the emission factor approach and mass balance method are used to calculate the carbon emission equivalent of nitrification and denitrification, anaerobic ammonia oxidation, and microalgae assimilation using a rare earth tailings (REEs) wastewater example. The results show that, among the three denitrification processes, the traditional nitrification and denitrification method has the greatest carbon emission equivalent (16.23 kgCO2/kgN). Direct causes include N2O emissions, which account for 48 % of the total carbon emission equivalent. The anaerobic ammonia oxidation process produces the carbon dioxide equivalent of 0.02 kgCO2/kgN. Carbon emission comparable to microalgal assimilation is −3.23 kgCO2/kgN. The anaerobic ammonia oxidation process can thus greatly reduce carbon emissions when compared to the conventional nitrification and denitrification processes, whilst microalgae assimilation can result in negative carbon emissions.

A novel derivative synchronous fluorescence method for the rapid, non-destructive and intuitive differentiation of denitrifying bacteria

It is challenging to differentiate bacteria residing in the same habitat by direct observation. This difficulty impedes the harvest, application and manipulation of functional bacteria in environmental engineering. In this study, we developed a novel method for rapid differentiation of living denitrifying bacteria based on derivative synchronous fluorescence spectroscopy, as exemplified by three heterotrophic nitrification-aerobic denitrification bacteria having the maximum nitrogen removal efficiencies greater than 90%. The intact bacteria and their living surroundings can be analyzed as an integrated target, which eliminates the need for the complex pre-processing of samples. Under the optimal synchronous scanning parameter (Δλ = 40 nm), each bacterium possesses a unique fluorescence spectral structure and the derivative synchronous fluorescence technique can significantly improve the spectral resolution compared to other conventional fluorescence methods, which enables the rapid differentiation of different bacteria through derivative synchronous fluorescence spectra as fast as 2 min per spectrum. Additionally, the derivative synchronous fluorescence technique can extract the spectral signals contributed by bacterial extracellular substances produced in the biological nitrogen removal process. Moreover, the results obtained from our method can reflect the real-time denitrification properties of bacteria in the biological nitrogen removal process of wastewater. All these merits highlight derivative synchronous fluorescence spectroscopy as a promising analytic method in the environmental field.

Effect of salinity on biological nitrogen removal from wastewater and its mechanism.

The nitrogen discharge from saline wastewater will cause significant pollution to the environment. As a high-efficiency and low-cost treatment method, biological treatment has a promising application prospect in the removal of nitrogen from high-salt wastewater. However, the inhibitory effect of high salt on microorganisms increases the difficulty of its treatment. This review discusses the influence of salinity on the nitrogen removal process, considering both traditional and novel biological techniques. Common methods to enhance the effectiveness of biological nitrogen removal processes and their mechanisms of action in engineering practice and research, including sludge acclimation and inoculation of halophilic bacteria, are also introduced. An outlook on the future development of biological nitrogen removal processes for high-salt wastewater is provided to achieve environmentally friendly discharge of high-salt wastewater.

Evaluation of aircraft deicing fluid as an external carbon source for denitrification

Water resource recovery facilities (WRRFs) performing biological nitrogen removal (BNR) often require external carbon sources for meeting nitrogen discharge permit limits. This brings an additional financial burden to the facilities considering the continuous need of these external carbon sources. This paper evaluates the utilization of airport stormwater, which in the winter season is rich in aircraft deicing fluid (ADF) as an alternative external carbon source. Denitrification and nitrification bench scale experiments were performed to assess the efficacy of external carbon sources to remove nitrogen in WRRFs. Experimental results showed that ADFs achieve denitrification rates of 0.064–0.066 d−1, higher than what achieved by a commercial carbon source, MicroC 2000A, with corresponding value of 0.058 d−1 at low temperatures, as low as 13 °C, which is considered a worst-case scenario for nitrogen removal efficiency. Furthermore, no inhibition to nitrification associated with the ADFs was observed. Subsequently a dynamic modeling study was conducted to assess the performance of ADFs as external carbon sources for denitrification and compared them to the conventional source that was being used in a full-scale BNR process. Results from the dynamic modeling study revealed that if 40 % of the spent-ADF at LaGuardia airport, New York City, could be collected with the stormwater and conveyed to a WRRF via the sewer collection system, an approximate reduction of 30 % of the commercial external carbon source could be accomplished by repurposing a waste product. This study contributes to the potential of ADF as a denitrification aid and an alternative for commercially available carbon sources with comparable nitrogen removal efficiencies.

Biofilm colonization and succession in a full-scale partial nitritation-anammox moving bed biofilm reactor

BackgroundPartial nitritation-anammox (PNA) is a biological nitrogen removal process commonly used in wastewater treatment plants for the treatment of warm and nitrogen-rich sludge liquor from anaerobic digestion, often referred to as sidestream wastewater. In these systems, biofilms are frequently used to retain biomass with aerobic ammonia-oxidizing bacteria (AOB) and anammox bacteria, which together convert ammonium to nitrogen gas. Little is known about how these biofilm communities develop, and whether knowledge about the assembly of biofilms in natural communities can be applied to PNA biofilms.ResultsWe followed the start-up of a full-scale PNA moving bed biofilm reactor for 175 days using shotgun metagenomics. Environmental filtering likely restricted initial biofilm colonization, resulting in low phylogenetic diversity, with the initial microbial community comprised mainly of Proteobacteria. Facilitative priority effects allowed further biofilm colonization, with the growth of initial aerobic colonizers promoting the arrival and growth of anaerobic taxa like methanogens and anammox bacteria. Among the early colonizers were known ‘oligotrophic’ ammonia oxidizers including comammox Nitrospira and Nitrosomonas cluster 6a AOB. Increasing the nitrogen load in the bioreactor allowed colonization by ‘copiotrophic’ Nitrosomonas cluster 7 AOB and resulted in the exclusion of the initial ammonia- and nitrite oxidizers.ConclusionsWe show that complex dynamic processes occur in PNA microbial communities before a stable bioreactor process is achieved. The results of this study not only contribute to our knowledge about biofilm assembly and PNA bioreactor start-up but could also help guide strategies for the successful implementation of PNA bioreactors.8NUh31NTQCwxAXZWHM2SHSVideo

Optimization of step-feed anoxic-oxic-membrane bioreactor (AO-MBR) with methanol addition for biological nitrogen removal in wastewater using BioWin and response surface methodology (RSM)

The study optimized a step-feed anoxic-oxic membrane bioreactor (AO-MBR) with methanol addition, an existing biological nitrogen removal (BNR) process, to improve total nitrogen (TN) removal and to reduce operating costs. Methanol, utilized as an external carbon source, was costly, which led to examining ways to reduce its usage by adjusting the operational parameters and modifying the configuration. The BioWin’s built-in activated sludge model underwent calibration through biokinetic batch experiments and numerical adjustments of stoichiometric and kinetic parameters to create the BNR process model. Dynamic simulations validated the calibrated model. Using the model, a modified configuration with a 20.8% increase in total anoxic volume was proposed. This increased the anoxic hydraulic retention time, improving the denitrification process. The response surface methodology (RSM) was then used to optimize the operating parameters of the modified configuration for maximum TN removal efficiency and minimum operating cost. The optimized parameters found were 0.5 mg/L dissolved oxygen, 45 days of solid retention time, 0:1 methanol distribution ratio, and 1,794.29 L/d methanol, which all enhanced the denitrification process. This resulted in a 16% increase in TN removal efficiency, a 4.12% decrease in operating costs, and an 8.96% reduction in methanol usage.

Control of Filamentous Bacteria overgrowth by Changing the Hydraulic Flow Distribution of a Step-feed Biological Nitrogen Removal (SFBNR) Process-based WWTP: A Full-scale Study

To facilitate the wastewater recycling process while adhering to environmental and industrial regulations, it becomes imperative to meet stringent standards. This necessitates the effective elimination of organic substances, with particular emphasis on nitrogen-based compounds. To this end, activated sludge methods, particularly the step-feed biological nitrogen removal (SFBNR) process, are employed. Although various operational measures are employed in SFBNR systems, including the elimination of complex substrates, modifications in aeration conditions, the utilization of piston hydraulic flow, and the appropriate distribution of substrates, these systems remain susceptible to the excessive growth of filamentous bacteria. The current study aimed to examine the change in the distribution of the hydraulic flow entering this system on a real scale over a period of five years. It was observed that the quality of sludge settling improved and accordingly the overgrowth of filamentous Microthrix parvicella declined, thereby enhancing the quality of the effluent.

Denitrification Capacity of Volatile Fatty Acids from Sludge Fermentation: Lab-Scale Testing and Full-Scale Assessment

This work provides insights into the possibility of integrating recovered volatile fatty acids (VFAs) into biological nitrogen removal processes. VFAs are the main products of the acidogenic fermentation of waste sludge and are an effective carbon source for denitrification in activated sludge processes. The assessment of denitrification rates and the utilisation hierarchy of different VFAs are relevant to evaluating the possibility of replacing external carbon sources with the fermented liquid, FL, from acidogenic fermentation. To this scope, single VFAs, FL collected from a full-scale waste sludge fermenter, and commercial hydroalcoholic solutions have been tested with manometric lab-scale tests. Regarding single acids, acetic acid showed the highest denitrification rates, up to 4 mg N-NO3 g VSS−1 h−1, while more complex acids usually showed a lower denitrification rate. The synthetic VFA mixture and FL showed a higher denitrification rate than the sole acetate (up to 134% of the acetate denitrification rate). Mass balances across the full-scale wastewater treatment plant demonstrated the positive role of FL dosage in enhancing the denitrification process in the activated sludge treatment, with an average nitrogen removal equal to 57% and 78% without and with FL dosage, respectively. Batch manometric tests proved to be an efficient and reliable tool to assess the quality of the carbon sources as well as the activity of denitrifying bacteria in activated sludge samples.

Characterization of the microplastic photoaging under the action of typical salt ions of biological nitrogen removal processes

Microplastics (MPs) are one of the most prevalent and diverse contaminants, and wastewater treatment plants are significant MP aggregators. Controlling the pollution caused by microplastics requires an understanding of how they age. The properties of the MPs photoaging process under the influence of salt ions typical of biological nitrogen elimination processes were disclosed in this work. The aging process of polyvinyl chloride microplastics (PVC-MPs) was greatly slowed down by greater HCO3− and NO2− concentrations, according to a comparison of the carbonyl index changes that occurred during photoaging. The carbonyl index had a negative correlation with the thermal stability of the photo-aged PVC-MPs, and aging accelerated the elimination of chlorine from the water. The samples were aged by UV radiation after 36 h at 40 °C, and the amount of chlorine eliminated was 10.13 times greater than that of the original MPs samples. It was discovered that the leachate concentration of aged MPs dramatically increased with decreasing particle size and was positively connected with the level of aging by comparing the concentration of leachate for two particle sizes (1 mm and 100 m). Photoaging caused MPs to become rougher, which in turn improved the NO3−-N, NH4+-N, and NO2−-N adsorption by PVC-MPs.

The Inhibition of Engineered Nano-ZnO in the Biological Nitrogen Removal Process: A Review

Engineered nano-ZnO is extensively utilized in both production and daily life, leading to its inevitable entry into the wastewater treatment system through various pathways. Nitrogen removal microorganisms in wastewater treatment systems are highly susceptible to environmental impacts. The antibacterial properties of nano-ZnO can impede the biological nitrogen removal (BNR) process and adversely affect the nitrogen removal performance. A comprehensive understanding of the inhibitory effect and mechanism of nano-ZnO on the BNR process is crucial in devising appropriate countermeasures to ensure optimal nitrogen removal performance. This review provides an overview of the sources of nano-ZnO in the environment, its impact on the BNR process, and the inhibition mechanism, and proposes potential methods that can mitigate the inhibitory effect of nano-ZnO. Additionally, future prospects are also discussed. This review serves as a foundation for a deeper understanding of the inhibition of engineered nano-ZnO on the BNR process and aids in guiding efforts to maintain the nitrogen removal performance in the presence of engineered nano-ZnO.

Mechanisms of signaling molecules regulating microbial community succession and metabolic pathways in partial nitrification of a composite zeolite-biofilm under low salinity

The low salinity caused by the substitution of seawater and the overuse of deicing salt hinders the treatment of mainstream wastewater by conventional biological nitrogen removal process. In this experiment, the start-up and stable operation of partial nitrification were achieved based on a composite zeolite biofilm (CZB) and 94.1 % of nitrite accumulation efficiency was obtained at low salinity. CZB could still maintain high biofilm proportion, strong adhesion and robust structure to resist the impact of 0.6 % salinity. The enhanced release of C8-HSL from the aqueous phase of the CZB increased the oxygen transfer resistance of the sludge layer, thus reducing the oxygen mass transfer efficiency of the sludge layer and inhibiting NOB more effectively. The augmented release of C6-HSL and C12-HSL in the sludge phase (SP) leads to elevated production of protein and polysaccharides, culminating in the development of a more resilient microbial structure. Meanwhile, C6-HSL and C8-HSL in the SP of CZB promoted gene expression, especially nitrate reductase (Nar), to stabilize the supply of NO2–-N. Meanwhile, CZB reinforced the microbial impact resistance by enhancing the tricarboxylic acid cycle, and awakened important gene (nrfA, associated with dissimilatory nitrate reduction to ammonium). This activation played a vital role in maintaining the appropriate NH4+-N to NO2–-N ratio in the effluent. Finally, CZB eliminated Nitrospira from the system and increased the relative abundance of Nitrosomonas to 12.8 % at 0.6 % salinity. This method offered valuable theoretical insights for design and optimization of the partial nitrification process for treating mainstream low-salinaty wastewater.

N2O emission reduction in the biological nitrogen removal process for wastewater with low C/N ratios: mechanisms and strategies

Urban wastewater, as the main influent type of Waste Water Treatment Plants (WWTPs), has the characteristic of low carbon to nitrogen ratio (C/N). In the biological nitrogen removal (BNR) process, insufficient carbon source often affects the nitrogen removal efficiency and leads to more N2O emissions. We review recent researches on N2O emissions in the BNR process of wastewater with low C/N. The availability of carbon sources affects heterotrophic denitrification (HD) and autotrophic nitrification/denitrification processes, which are the main reasons for N2O emissions in BNR. For the sustainable development of BNR in WWTPs, we introduce strategies suitable for reducing N2O emissions in the BNR process of low C/N wastewater from two aspects: traditional process innovation and new process development. These strategies mainly include carbon source addition, adjustment of aeration strategy, optimization of oxidation ditch and biofilm facilities, and application of Anammox related processes. In the future, it is still necessary to further deepen this research direction through the normalization of N2O emission quantification standards, exploration of N2O metabolism mechanisms, assessment of environmental effects of emission reduction strategies, and practical application of new processes.

Enhancing nitrogen removal performance through intermittent aeration in continuous plug-flow anaerobic/aerobic/anoxic process treating low-strength municipal sewage

Advanced nitrogen removal cannot be achieved through the conventional biological nitrogen removal process, which requires higher carbon sources and aeration energy. The proposal of intermittent aeration in the aerobic chambers offered an innovative approach to enhance nitrogen removal in low carbon-to-nitrogen ratio (C/N) municipal sewage, using a plug-flow reactor with anaerobic/aerobic/anoxic (AOA) process. Due to the effective utilization of internal carbon sources through the intermittent aeration, the total inorganic nitrogen removal efficiency (NRE) increased to 77.9 ± 3.2 % with the mean aerobic hydraulic retention time of only 3.2 h and a low C/N of 3.3 during the operation of 210 days. Polyhydroxyalkanoates dominated the nitrogen removal in this AOA system, accounting for 48.0 %, primarily occurring in the alternant aerobic/anoxic chambers. Moreover, the microbial community structure remained unchanged while the NRE increased to 77.9 %. This study provided an efficient and economic strategy for the continuous plug-flow AOA process.

Exposure of sulfur-driven autotrophic denitrification to hydroxylamine/hydrazine: Underlying mechanisms and implications for promoting partial denitrification and N2O recovery

Hydroxylamine (NH2OH) and hydrazine (N2H4) are crucial intermediates in biological nitrogen removal processes, but their potential effects on the nitrogen-related metabolic pathway during the sulfur-driven autotrophic denitrification (SDAD) process remain unclear and were thus explored in this work. The results of dedicated batch tests indicated that the accumulation ratio of NO2− was positively correlated with the NH2OH concentration, reaching 86.2 ± 2.6% at the NH2OH concentration of 2.0 mg-N/L, while it was barely affected by the N2H4 concentration. Furthermore, the joint inhibition of NH2OH and free nitrous acid led to the substantial accumulation of N2O (up to 32.9 ± 1.3%) during the NO2− reduction phase. In contrast, N2H4 exhibited great potential for facilitating N2O accumulation in both the NO3− reduction and NO2− reduction phases with an accumulation ratio of 13.0 ± 0.3% and 27.5 ± 1.5%, respectively, at the N2H4 concentration of 2.0 mg-N/L. Total enzyme activity analyses revealed that the presence of NH2OH inhibited the activity expression of all denitrifying enzymes, with the downstream enzymes (such as NO2− reductase and N2O reductase) being more susceptible to NH2OH. The addition of N2H4 did not cause a significant decrease in the activity of NO3− reductase and NO2− reductase, but notably curbed the activity of N2O reductase. Based on the responses of the SDAD-related nitrogen metabolic pathway to NH2OH/N2H4, this work provided effective technical means for i) the promotion of NO2− accumulation which might enable the coupling of SDAD with Anammox and ii) the efficient recovery of N2O via the SDAD process.

Microbial electrolysis drives ammonium removal from saline wastewater through marine anammox bacteria

Currently, ammonium removal from saline wastewater still poses a challenge to conventional biological nitrogen removal process. Herein, the conversion of NH4+-N to N2 was successfully driven by marine anammox bacteria (MAB) in a single chamber microbial electrolytic cell (MEC) using NH4+-N as the sole substrate. Compared with no ammonium removal in the abiotic reactor with applied voltage (0–1.5 V), the maximum ammonium and total nitrogen removal rate (ARR and TNRR) of 55 and 50 g/m3•d were obtained at the voltage of 1.1 V, which were 78 % and 76 % higher than that of 0.5 V, respectively. At the voltage ≥ 1.1 V, the accumulation of NO2–-N and NO3–-N was observed in the MEC, and the nitrifying bacteria Nitrosmonas and Nitrospira were detected on the anode surface with the relative abundances of 0.84 % and 0.21 %, respectively. It was proved that the production of NO2–-N and NO3–-N was an electrochemical biological process by electroactive nitrifying bacteria. Candidatus Scalindua was the main functional genus for ammonium removal at anode biofilm with the relative abundance of 19.27 %. Therefore, ammonium was successfully removed by integrating anodic anammox and anodic nitrification. Applied voltage increased the microbial diversities at anode surface and promoted the formation of electrode biofilm. These findings indicated a promising saline wastewater treatment by employing salt-tolerant MAB for ammonium removal.

Performance evaluation, enzymatic activity change and metagenomic analysis of sequencing batch reactor under divalent zinc stress

Divalent zinc (Zn2+) are widely detected in domestic and industrial wastewater, and it is essential to evaluate the effect of Zn2+ on wastewater biological treatment process due to its bio-toxicity. In this study, the nitrogen removal rates and their corresponding enzymatic activities of sequencing batch reactor decreased with the increase of Zn2+ concentration. The Zn2+ accumulation in activated sludge caused significant antioxidant response, and the reactive oxygen species (ROS) production and antioxidant enzymatic activities were positively correlated with Zn2+ concentration. The presence of Zn2+ inhibited the metabolic pathways related to energy production and electron transport. The abundance decreases of nitrification and denitrification functional genes led to the deterioration of nitrogen removal performance under Zn2+ stress. The correlation analysis between functional gene modules and microbial genera revealed that Zoogloea had obvious Zn2+ resistance. This study can provide the insights into the influencing mechanism of Zn2+ on the biological nitrogen removal process.

Enhanced nutrients removal and microbial mechanisms in a pilot-scale anaerobic-oxic-anoxic (A/O/A) system: Synergistic roles of denitrifying polyphosphate accumulating organisms and endogenous denitrifiers

The realization of low-cost and high-standard nutrients removal are not acquired effectively in conventional pre-denitrification biological nitrogen removal processes (e.g., anaerobic/anoxic/oxic (A/A/O) process) for the treatment of domestic sewage. In this study, a pilot-scale bioreactor system based on the synergism of denitrifying phosphorus removal (DPR) and endogenous denitrification (ED) was proposed for advanced nutrients removal, which was operated under alternating anaerobic/oxic/anoxic (A/O/A) mode with no extracellular carbon source in the anoxic stage. The results showed that A/O/A and A/A/O systems were successfully established and operated in four stages with different mixed liquor suspended solid (MLSS, I: 3.32 ± 0.25 g/L, II: 5.89 ± 0.94 g/L, III: 8.66 ± 0.51 g/L, IV: 9.11 ± 5.72 g/L). Compared with the A/A/O system, the A/O/A system showed significantly higher nitrogen and phosphorus removal effectiveness within hydraulic retention time of 10 h. At MLSS of 8.66 ± 0.51 g/L, the A/O/A system could achieve simultaneously efficient removal of COD (91.47% ± 2.06%, 2.97 ± 0.26 mg COD/(g MLSS·h)), NH4+-N (97.27% ± 1.23%, 0.37 ± 0.06 mg NH4+-N/(g MLSS·h)), TN (89.94% ± 1.47%, 0.45 ± 0.03 mg TN/(g MLSS·h)), and PO43--P (96.67% ± 0.88%, 0.04 ± 0.01 mg PO43--P/(g MLSS·h)), and the effluent concentrations of COD, NH4+-N, TN, and PO43--P were 24.0 ± 3.1, 0.9 ± 0.4, 4.4 ± 0.6, and 0.13 ± 0.03 mg/L, respectively. In addition, microbial community results indicated that denitrifying polyphosphate accumulating organisms and endogenous denitrifiers synergistically enhanced the nutrients removal capacity in the A/O/A system. Overall, this work provides new insight for further scaling and optimization of the A/O/A system.

A comprehensive literature mining and analysis of nitrous oxide emissions from different innovative mainstream anammox-based biological nitrogen removal processes

The biological nitrogen removal (BNR) process in wastewater treatment plants generates a substantial volume of nitrous oxide (N2O), which possesses a potent greenhouse gas effect. A limited number of studies have systematically investigated the N2O emissions of anammox-based systems with different BNR processes under mainstream conditions. Based on extensive big data statistical analysis, it had been revealed that simultaneous nitritation, anammox and denitrification (SNAD), partial nitritation anammox (PNA) and partial denitrification anammox (PDA), exhibit significantly lower N2O emission factors when compared to traditional BNR processes. The median values for N2O emission factors were determined to be 1.01 %, 1.15 % and 1.43 % for SNAD, PNA and PDA, respectively. Based on nitrogen removal data and N2O emission factors, the N2O emissions from PNA, SNAD and PDA processes were calculated to be 0.016 g·d−1, 0.037 g·d−1 and 0.008 g·d−1, respectively. Furthermore, the machine learning models (SVM and ANN) exhibited excellent predictive performance for N2O emissions in the BNR processes. However, after removing environmental factors, the R2 value of the SVM model sharply decreased. The SHAP feature analysis demonstrated the significant impact of environmental factors on the accuracy of predictive performance in machine learning models. Spearman correlation analysis was employed to investigate the relationship between N2O emissions and operational factors as well as microbial communities. The results demonstrated a negative correlation between HRT, temperature and C/N with N2O emissions. Moreover, strong associations were observed between Nitrosomonas, Nitrospira, Denitratisoma, Thauera species and N2O emissions. The contribution of N2O production via AOB pathways played a key role that was quantitatively calculated to be 93 %, 80 % and 48 % in the PNA, SNAD and PDA processes, respectively. These findings highlight the potential of these innovative BNR processes in mitigating N2O emissions.

Development of a Novel Hydrodynamic Sequencing Batch Reactor for Landfill Leachate Treatment by Shortcut Biological Nitrogen Removal

This study introduced an alternative shortcut biological nitrogen removal (SBNR) process for landfill leachate treatment by developing a novel hydrodynamic sequencing batch reactor (H-SBR). The reactor could enhance the oxygen transfer rate (OTR) and nitrite accumulation ratio (NAR) by modifying internal hydrodynamic turbulence intensity. The average chemical oxygen demand (COD) and total nitrogen (TN) concentrations introduced into the reactor were 660 and 250 mg L−1, respectively, and the average removal efficiencies were 93% (COD) and 96% (TN). The effect of geometric parameters on oxygen transfer was estimated by performing a hydrodynamic model and a nonlinear least square analysis. After correcting the constants (α and β) of mass transfer coefficients (KLa) to values of 0.7361 and 1.2639, the model data fit the experiment well with an R-squared value of 0.99. The OTR improved by up to 30%, and hence, increased the NAR by up to 20% with a reduction of about 0.5 kg N kW−1 for power efficiency. The H-SBR development is innovative because the oxygen transfer efficiency was improved by the hydrodynamic modification of internal turbulence intensity, although not by mechanical equipment or chemical supplements. For the SBNR process, the modification of the reactor configuration for OTR enhancement could significantly improve nitrogen removal efficiency with successful nitrite accumulation. In addition to landfill leachate treatment, the H-SBR process can be employed in the treatment of low C/N ratio wastewaters.

Influence of growth media and internal recycle rate on nitrogen removal from high-strength wastewater in a low footprint anoxic-upflow/aerobic process

This research investigated the use of integrated fixed-film media in comparison to suspended-growth in a low-footprint upflow biological nitrogen removal (BNR) process to find a robust solution for treatment of high-strength dairy farm wastewater (DFW). Using real DFW and synthetic wastewater (SWW), two juxtaposed anoxic upflow bioreactor/aerobic systems (UBR-A) were operated under different internal recycle ratios (R) of 3 and 4 in both modes. Performance of the UBR-A system was sensitive to R, particularly in suspended-growth. The denitrification efficiency (ηD) and nitrate removal rates in this mode were significantly lower (p < 0.05) at R= 4 compared to R= 3 with both real DFW and SWW. With DFW, this was observed despite a higher COD/NO3-N of 20–50. In integrated fixed-film, ηD at R= 4 significantly improved to ∼95 % with both feeds. Whereas a COD/NO3-N > 9 was required to offset the imbalance caused by increased NO3-N loading at R= 4. Modeling of the denitrification potential controlled by R (PD-IR) and COD availability (PD-COD) showed that denitrification reciprocated with PD-IR. From the multiple regression analysis, nitrate removal was linearly correlated with growth medium, R, and wastewater type (p < 0.00001) accounting for 43 % of the variation. Nitrification efficiency was consistently higher > 90 % under all conditions but specific nitrification rates nearly doubled in integrated fixed-film mode. Correspondingly, the total nitrogen removal increased from 67 % to 80 % in DFW-system and 59–84 % in SWW-system at R= 4 compared to suspended growth at the same R. The study results add to the understanding of integrated media in BNR processes for high-strength wastewater treatment.