Investigations of nitrogen removal pathways in a biological packed bed reactor using elementary mass balances

Nitrogen cycle involves a complex set of potential biochemical pathways with reactions catalyzed by different microorganisms. Elementary mass balances for COD, DO, NH4-N and alkalinity were conducted and stoichiometric relationships were investigated to explain possible pathways of the nitrogen removal mechanisms in a lab-scale submerged down flow biological packed bed (BPB) reactor. Four sets of experiments were performed by modifying the organic loading and C/N ratio in comparison with steady-state conditions. Approximately 90% of COD and NH4-N removal occurred in two upper sections occupying 1/5 of the reactor height. The elementary mass balances could not explain all the experimental results with respect to nitrogen removal and oxygen consumption by known mechanisms. The mass balance calculations, excluding the possibility of nitrification, were in general in accordance with the observations indicating no or minimal NO3-N production. The theoretical stoichiometric requirements for nitrification reaction were satisfied in 6 experiments and in another 8 experiments nitrification may have occurred, but stoichiometry was not satisfied. Using C/N ratio as the variable, only at C/N ratio = 10, the predictions confirmed the possibility of nitrification in the same 3 (out of 4) assays as observed in practice. The results of this study reveal that the nitrogen transformations occurring in the studied reactor are complex and cannot be explained by simple mechanisms of microbial assimilation and nitrificatio

Impact of aeration conditions on the removal of low concentrations of nitrogen in a tertiary partially aerated biological filter

A submerged biological aerated filter (BAF) partially aerated was used to study the removal of low concentrations of ammonia nitrogen (0.3 g N/m3 to 30.5 g N/m3) typically found in nutrient enriched river and lake waters, and treated effluents. Four series of experiments were performed with a synthetic wastewater at ammonia loading rates between 6 g N/m3 d and 903 g N/m3 d and C/N ratios from 2 to 20. The results showed that ammonia removal rates reached higher values (172 g N/m3 d to 564 g N/m3 d) for C/N = 2 and lower values (13.6 g N/m3 d to 34.6 g N/m3 d) for C/N = 20. Between 50% and 70% of the ammonia was removed in the upper section of the BAF, where the dissolved oxygen (DO) concentration was over 2.1 g O2/m3 and the biofilm depth ranged from 0.4 to 0.6 mm. At the bottom section of the reactor, simultaneous removal of ammonia and nitrate was observed at the DO concentrations in the range 0.4 g O2/m3 to 0.8 g O2/m3. There was no removal of ammonia nitrogen for loads below 15 g N/m3.d. The results indicate that the removal of nitrogen in partially aerated BAF may not only be explained by the conventional mechanisms of nitrification/denitrification

Performance of microbial fuel cells operated under anoxic conditions

Nowadays, microbial fuel cells (MFC) stand up as a promising renewable energy source. Due to the ability of the MFC to oxidize a wide spectrum of substrates, wastewater seems to be one of the most interesting fuels. Unfortunately, wastewater could contain electron acceptors such as nitrate, which could interfere with the electrical performance of the MFC. In this work, the influence of oxidised nitrogen forms on the electricity production of an air breathing MFC was studied. It was observed that power generation was not significantly influenced when operated at nitrate concentrations below 0.9 mg N-NO3 L−1. However, when the nitrate concentrations were above this value, the electricity generation was reduced. In order to investigate the causes of this reduction, an electrochemical characterization of the MFC was performed. The results of polarization curves were fitted to an empirical mathematical model. From the results it was observed that, when nitrate was present, the denitrifiers outcompeted the electrogenic microorganisms for substrate, causing mass transfer limitations to the electrogenic process.Hoy en día, las pilas de combustible microbianas (MFC) se erigen como una fuente de energía renovable prometedora. Debido a la capacidad del MFC para oxidar un amplio espectro de sustratos, las aguas residuales parecen ser uno de los combustibles más interesantes. Desafortunadamente, las aguas residuales podrían contener aceptores de electrones como el nitrato, lo que podría interferir con el rendimiento eléctrico del MFC. En este trabajo, se estudió la influencia de las formas de nitrógeno oxidado en la producción de electricidad de un MFC que respira aire. Se observó que la generación de energía no se veía significativamente influenciada cuando se operaba a concentraciones de nitrato por debajo de 0.9 mg N-NO 3  L -1. Sin embargo, cuando las concentraciones de nitratos estuvieron por encima de este valor, se redujo la generación de electricidad. Para investigar las causas de esta reducción, se realizó una caracterización electroquímica del MFC. Los resultados de las curvas de polarización se ajustaron a un modelo matemático empírico. A partir de los resultados se observó que, cuando estaba presente el nitrato, los desnitrificantes superaban a los microorganismos electrogénicos por sustrato, provocando limitaciones de transferencia de masa al proceso electrogénico

A grey box model of glucose fermentation and syntrophic oxidation in microbial fuel cells

In this work, the fermentative and oxidative processes taking place in a microbial fuel cell (MFC) fed with glucose were studied and modeled. The model accounting for the bioelectrochemical processes was based on ordinary, Monod-type differential equations. The model parameters were estimated using experimental results obtained from three H-type MFCs operated at open or closed circuits and fed with glucose or ethanol. The experimental results demonstrate that similar fermentation processes were carried out under open and closed circuit operation, with the most important fermentation products being ethanol (with a yield of 1.81 mol mol−1 glucose) and lactic acid (with a yield of 1.36 mol mol−1 glucose). A peak in the electricity generation was obtained when glucose and fermentation products coexisted in the liquid bulk. However, almost 90% of the electricity produced came from the oxidation of ethanol

Integrated membrane bioreactors modelling: A review on new comprehensive modelling framework

Integrated Membrane Bioreactor (MBR) models, combination of biological and physical models, have been representing powerful tools for the accomplishment of high environmental sustainability. This paper, produced by the International Water Association (IWA) Task Group on Membrane Modelling and Control, reviews the state-of-the-art, identifying gaps for future researches, and proposes a new integrated MBR modelling framework. In particular, the framework aims to guide researchers and managers in pursuing good performances of MBRs in terms of effluent quality, operating costs (such as membrane fouling, energy consumption due to aeration) and mitigation of greenhouse gas emissions

Improvements in Modeling Dissolved Oxygen in Activated Sludge Systems

The aim of this research was to show the impact of the flow conditions and variations in the aeration intensity on changes in the predicted dissolved oxygen (DO) concentrations in a full-scale activated sludge reactor. The Activated Sludge Model No. 1 was used to describe the biochemical processes. The studies were performed at the Rock Creek wastewater treatment plant in Hillsboro, OR (USA). The simulation results were compared with data originating from two 24-hour experiments. The model that best reflected the spatial and diurnal distributions of the DO concentrations was the one-dimensional advection-dispersion equation with a variable overall oxygen mass transfer coefficient in the source term for dissolved oxygen

Application of Mathematical Modeling and Computer Simulation for Solving Water Quality Problems

Deteriorated water resources in Central and Eastern Europe call for actions that should be undertaken to improve current conditions and to protect human and environmental health. Mathematical modeling and computer simulation is often an integral part of the decision-making process. Models and simulations allow rapid and varied evaluation of causes and effects and the principal advantage is that they enable an analysis of even long-term actions with limited investment costs. This paper provides an overview of popular models used for simulation of major elements of a water quality system: surface water quality (QUAL2E), wastewater treatment (Activated Sludge Model No.1), sewer network (SWMM), and water distribution network (EPANET). Model uses are illustrated by specific examples both in the U.S. or in Central and Eastern Europe

Improvements In Modelling Dissolved Oxygen In Activated Sludge Systems

The aim of this research was to show the impact of the flow conditions and variations in the aeration intensity on changes in the predicted dissolved oxygen (DO) concentrations in a full-scale activated sludge reactor. The Activated Sludge Model No. 1 was used to describe the biochemical processes. The studies were performed at the Rock Creek wastewater treatment plant in Hillsboro, OR (USA). The simulation results were compared with data originating from two 24-hour experiments. The model that best reflected the spatial and diurnal distributions of the DO concentrations was the one-dimensional advection-dispersion equation with a variable overall oxygen mass transfer coefficient in the source term for dissolved oxygen

Modelization of Nutrient Removal Processes at a Large WWTP Using a Modified ASM2d Model

The biodegradation of particulate substrates starts by a hydrolytic stage. Hydrolysis is a slow reaction and usually becomes the rate limiting step of the organic substrates biodegradation. The objective of this work was to evaluate a novel hydrolysis concept based on a modification of the activated sludge model (ASM2d) and to compare it with the original ASM2d model. The hydrolysis concept was developed in order to accurately predict the use of internal carbon sources in enhanced biological nutrient removal (BNR) processes at a full scale facility located in northern Poland. Both hydrolysis concepts were compared based on the accuracy of their predictions for the main processes taking place at a full-scale facility. From the comparison, it was observed that the modified ASM2d model presented similar predictions to those of the original ASM2d model on the behavior of chemical oxygen demand (COD), NH4-N, NO3-N, and PO4-P. However, the modified model proposed in this work yield better predictions of the oxygen uptake rate (OUR) (up to 5.6 and 5.7%) as well as in the phosphate release and uptake rates

Evaluation of Partial Nitritation/Anammox (PN/A) Process Performance and Microorganisms Community Composition under Different C/N Ratio

A one-stage partial nitritation/anammox (PN/A) process with intermittent aeration is possible under sidestream conditions, but implementation in a mainstream is a challenge due to increased Carbon/Nitrogen (C/N) ratios in domestic wastewater. This study investigated the effect of C/N ratios on process efficiency and the effect of narrowing non-aeration time on process improvement at high chemical oxygen demand (COD) load. An increase in TN removal efficiency was achieved in both series with gradual change of C/N ratio from 1 to 3, from 65.1% to 83.4% and 63.5% to 78% in 1st and 2nd series, respectively. However, at the same time, the ammonium utilization rate (AUR) value decreased with the increase in C/N ratio. At a high COD (C/N = 3) concentration, the process broke down and regained productivity after narrowing the non-aeration time in both series. Shifts in the system performance were also connected to adaptive changes in microbial community revealed by data obtained from 16S rRNA NGS (next-generation sequencing), which showed intensive growth of the bacteria with dominant heterotrophic metabolism and the decreasing ratio of autotrophic bacteria. The study shows that deammonification is applicable to the mainstream provided that the C/N ratio and the aeration/non-aeration time are optimized