Search

Mainstream partial denitrification/anammox MBBR with nitrate-based carbon dosing control.

PAD reduces nitrogen and solids following anaerobic digestion without external carbon supplements.

Implementing an aerobic digestion step after anaerobic digestion, referred to as "post aerobic digestion" (PAD), can remove ammonia without the need for an external carbon source and destroy volatile solids. While this process has been documented at the lab-scale and full-scale, the mechanism for N removal and the corresponding microbial community that carries out this process have not been established. This research gap is important to fill because the nitrogen removal pathway has implications on aeration requirements and carbon demand, that is, short-cut N-removal requires less oxygen and carbon than simultaneous nitrification-denitrification. The aims of this research were to (i) determine if nitrite (NO

The Wisconsin Rapids Wastewater Treatment Plant (WRWWTP) is faced with a more stringent effluent phosphorus requirement that will drive capital investment between 2020 and 2025. The facility will need to achieve a monthly average value of 0.36 mg L

The wastewater treatment sector embraces mixed-culture biotechnologies for sanitation, environmental protection, and resource recovery. Bioprocess design, monitoring and control thrive on microbial processes selected in complex microbial communities. Microbial ecology and systems microbiology help access microbiomes and characterize microorganisms, metabolisms and interactions at increased resolution and throughput. Big datasets are generated from the sequencing of informational molecules extracted from biomasses sampled across process schemes. However, they mostly remain on science benches and computing clusters, without reaching the industry in a clear engineering objective function. A bilateral bridge should actionize this information. As systems microbiologists, we miss that engineering designs and operations rely on stoichiometry and kinetics. The added-value provided by microbial ecology and systems microbiology to improve capital (CAPEX) and operating expenditures (OPEX) needs to be addressed. As engineers, we miss that microbiology can be provide powerful microbial information on top of physical-chemical measurements for quantitative process design (e.g., nutrient removal systems) with detailed scientific description of phenomena inside microbiomes. In this perspective article, we allied academia and industry to address the state of shared knowledge, successes and failures, and to establish joint investigation platforms. Our roadmap involves three milestones to (i) elaborate an essential list of microbiological information needed to implement methods at the process line; (ii) characterize microbiomes from microorganisms to metabolisms, and shape conceptual ecosystem models as primer for process ecology understanding; (iii) bridge engineering and mathematical models with an analytical toolbox for fast- vs. high-throughput analyses to discover new microbial processes and engineer assemblies. We praise for a harmonized "language of love"(incorporating common vocabulary, units, protocols) across the water and environmental biotechnology sector to team up mindsets for a sewer- and plant-wide integration of systems microbiology and engineering.

Polyelectrolyte complex (PEC) materials show promise in the development of tunable membranes for aqueous and organic solvent separations, as well as in the creation of surface layers for fouling control. In this study, we developed a polyelectrolyte complex (PEC) functionalized by negatively charged carboxymethyl chitosan (CMC-) and positively charged quaternized chitosan (QC+) to tailor its surface properties and antibacterial efficacy. CMC- and QC+ were prepared and characterized using FT-IR and 1H NMR, which confirmed the presence of the carboxymethyl group and trimethylammonium group in CMC- and QC+ with 65.6% and 83.9% substitution, respectively. The CMC- functionalized PEC (CMC-/PEC) and QC+ functionalized PEC materials (QC+/PEC) were evaluated for their stability in water, resistance to organic and inorganic adsorption, and antibacterial action against a model microorganism, Pseudomonas putida. The results showed no release of chitosan derivatives after adsorption, and CMC-/PEC and QC+/PEC exhibited charge-based, selective repulsion of model organic and inorganic substances. Moreover, the functionalized PEC surfaces displayed lower bacterial attachment due to their smoother surfaces as compared to the bare ceramic membrane and their antimicrobial properties. Among the PEC samples, CMC-/PEC had the lowest cell attachment, while QC+/PEC showed the highest attachment due to electrostatic attraction. The ceramic and bare PEC surfaces were negligibly bactericidal, while cell viability decreased to 34.4 ± 10.2% and 30.6 ± 8.2% with the CMC-/PEC and QC+/PEC surfaces, respectively. In the filtration experiments, the unmodified PEC and CMC-/PEC showed lower rates of flux decline due to organic fouling than did the bare ceramic or QC+/PEC due to electrostatic repulsion. Furthermore, PECs as protective layers promoted much higher flux recoveries than simply backwashing the uncoated membranes. This surface tunability, then, enhances the potential of PECs either as fouling resistant materials or as a method to create a sacrificial, protective layer on surfaces that once fouled can be dissolved and re-established.

Reducing the solids retention time (SRT) of the enhanced biological phosphorus removal (EBPR) process can increase organic carbon diversion to the sidestream for energy recovery, thereby realizing some of the benefits of the high rate activated sludge (HRAS) process. Determining the washout (i.e. minimum) SRT of polyphosphate accumulating organisms (PAOs), therefore, allows for simultaneous phosphorus and carbon diversion for energy recovery from EBPR systems. However, few studies have investigated the washout SRT of PAOs in real wastewater, and little is known of the diversity of PAOs in high rate EBPR systems. Here we demonstrate efficient phosphorus removal (83% orthophosphate removal) in a high rate EBPR sequencing batch reactor fed real primary effluent and operated at 20 °C. Stable operation was achieved at a total SRT of 1.8 ± 0.2 days and hydraulic retention time of 3.7–4.8 hours. 16S rRNA gene sequencing data demonstrated that Accumulibacter were the dominant PAO throughout the study, with a washout aerobic SRT between 0.8 and 1.4 days. qPCR targeting the polyphosphate kinase gene revealed that Accumulibacter clades IIA, IIB and IID dominated the PAO community at low SRT operation, while clade IA was washed out at the lowest SRT values.

Mathematical modelling of N2O emissions is of great importance for the understanding and reduction of the environmental impact of wastewater treatment systems. This chapter reviews the current status of the modelling of N2O emissions from wastewater treatment. The existing mathematical models describing all known microbial pathways for N2O production are reviewed and discussed. These include N2O production and consumption by heterotrophic denitrifiers, N2O production by ammoniaoxidizing bacteria (AOB) through the hydroxylamine oxidation pathway and the AOB denitrification pathway and the integration of these pathways in single-pathway N2O models. The two-pathway models are compared to single-pathway models. The calibration and validation of these models using lab-scale and full-scale experimental data is also reviewed. The mathematical modelling of N2O production, while still being enhanced by new knowledge development, has reached a maturity that facilitates the estimation of site-specific N2O emissions and the development of mitigation strategies for wastewater treatment plants taking into account the specific design and operational conditions of the plant.

Water resource recovery facilities are faced with stringent effluent phosphorus limits to reduce nutrient pollution. Enhanced biological phosphorus removal (EBPR) is the most common biological route to remove phosphorus; however, many facilities struggle to achieve consistent performance due to limited carbon availability in the influent wastewater. A promising process to improve carbon availability is through return activated sludge (RAS) fermentation via sidestream EBPR (S2EBPR). In this study, a full-scale S2EBPR pilot was operated with a sidestream plus carbon configuration (SSRC) at a carbon-limited facility. A model based on the pilot test was developed and calibrated in the SUMO platform and used to explore routes for improving orthophosphate (OP) effluent compliance. Modeling results showed that RAS diversion by itself was not sufficient to drive OP removal to permit limits of 1 mg L

While enhanced biological phosphorus removal (EBPR) is widely utilized for phosphorus (P) removal from wastewater, understanding of efficient process alternatives that allow combined biological P removal and shortcut nitrogen (N) removal, such as nitritation–denitritation, is limited. Here, we demonstrate efficient and reliable combined total N, P, and chemical oxygen demand removal (70%, 83%, and 81%, respectively) in a sequencing batch reactor (SBR) treating real mainstream wastewater (primary effluent) at 20 °C. Anaerobic – aerobic cycling (with intermittent oxic/anoxic periods during aeration) was used to achieve consistent removal rates, nitrite oxidizing organism (NOO) suppression, and high effluent quality. Importantly, high resolution process monitoring coupled to ex situ batch activity assays demonstrated that robust biological P removal was coupled to energy and carbon efficient nitritation–denitritation, not simultaneous nitrification–denitrification, for the last >400 days of 531 total days of operation. Nitrous oxide emissions of 2.2% relative to the influent TKN (or 5.2% relative to total inorganic nitrogen removal) were similar to those measured in other shortcut N bioprocesses. No exogenous chemicals were needed to achieve consistent process stability and high removal rates in the face of frequent wet weather flows and highly variable influent concentrations. Process modeling reproduced the performance observed in the SBR and confirmed that nitrite drawdown via denitritation contributed to suppression of NOO activity.

Denitrifying polyphosphate accumulating organisms (DPAOs) are capable of nitrate (NO3−) and/or nitrite (NO2−) reduction coupled to phosphorus (P) uptake when subjected to alternating anaerobic/anoxic conditions. However, accumulation of the denitrification intermediate nitrous oxide (N2O), a potent greenhouse gas, has been previously observed in DPAO enrichments. To date, denitrification capability and denitrifying P uptake rates of DPAOs using different electron acceptors (NO3−, NO2−, and N2O) after long-term exposure and adaptation to elevated concentrations of NO2− characteristic of shortcut N removal systems have not been examined. To address this knowledge gap, we operated a lab-scale sequencing batch reactor under alternating anaerobic/anoxic conditions with high NO2− feed for over a year to obtain an enrichment of “Candidatus Accumulibacter phosphatis” capable of denitrifying P uptake. Ex situ batch assays were performed to clarify capacity for reduction of various nitrogen oxides and simultaneous P uptake by the DPAO enrichment culture under both decoupled (internal COD as electron donor) and coupled (external COD as electron donor) feeding conditions. These batch assays revealed distinct nitrogen oxides reduction and denitrifying P uptake capabilities, with significantly elevated kinetics when NO2− was supplied as the electron acceptor for P uptake. Surprisingly, N2O reduction was extremely slow when only internal storage polymers were present as an electron donor (decoupled feeding), as is typical for PAOs in practical enhanced biological P removal processes. This pattern held when N2O was the sole electron acceptor supplied, and when N2O was supplied with NO3− or NO2−. We documented a particularly strong propensity for N2O accumulation in the presence of NO2− under both decoupled and coupled scenarios. The formation of granular microbial aggregates in the reactor was observed without intentional granule selection. High-throughput 16S rRNA gene sequencing revealed selective enrichment of putative DPAOs in large granular biomass. qPCR-based profiling of denitrification functional genes demonstrated that smaller floccular aggregates had higher genomic potential for N2O production, while large granular aggregates likely played a role as a putative sink for N2O.

Elemental sulfur (S0 ) can serve as an electron donor for water and wastewater denitrification, but few researchers have addressed the kinetics of S 0 -based reduction of nitrate (NO 3- ), nitrite (NO 2- ), and nitrous oxide (N 2 O). In addition, S 0 -based denitrifying biofilms are counter-diffusional. This is because the electron donor (S 0 ) is supplied from the biofilm attachment surface while the acceptor, for example, NO 3- , is supplied from the bulk liquid. No existing mathematical model for S 0 -based denitrification considers this behavior. In this study, batch tests were used to determine the kinetic parameters for the reduction of NO 3- , NO 2- , and N 2 O. Additionally, a biofilm model was developed to explore the effects of counter-diffusion on overall fluxes, that is, the mass of NO 3- or NO 2- removed per unit biofilm support area per unit time. The maximum specific substrate utilization rates ( qˆ ) for NO 3- , NO 2- , and N 2 O were 3.54, 1.98, and 6.28 g N g COD -1 ·d -1 , respectively. The maximum specific growth rates ( µˆ ) were 0.71, 1.21, and 1.67 d -1 for NO 3- to NO 2- , NO 2- to N 2 O, and N 2 O to N 2 , respectively. Results suggest that the observed NO 2- accumulation during S 0 -based denitrification results from a low qˆ for NO 2- relative to that for NO 3- . The high qˆ for N 2 O, relative to that for NO 3- and NO 2- , suggest that little N 2 O accumulation occurs during denitrification. A counter-diffusional biofilm model was used to predict trends for NO 3- fluxes, and confirmed NO 2- accumulation in S 0 -based denitrification biofilms. It also explains the observed detrimental effects of biofilm thickness on denitrification fluxes. This study allows a more accurate prediction of NO 3- , NO 2- , and N 2 O transformations in S 0 -based denitrification.

Recent findings show that a subset of bacteria affiliated withNitrospira, a genus known for its importance in nitrite oxidation for biological nutrient removal applications, are capable ofcompleteammoniaoxidation (comammox) to nitrate. Early reports suggested that they were absent or present in low abundance in most activated sludge processes, and thus likely functionally irrelevant. Here we show the accumulation of comammoxNitrospirain a nitrifying sequencing batch reactor operated at low dissolved oxygen (DO) concentrations. Actual mainstream wastewater was used as influent after primary settling and an upstream pre-treatment process for carbon and phosphorus removal. The ammonia removal rate was stable and exceeded that of the treatment plant’s parallel full-scale high DO nitrifying activated sludge reactor. 16S rRNA sequencing showed a steady accumulation ofNitrospirato 53% total abundance and a decline in conventional ammonia oxidizing bacteria to Nitrospirabeginning around day 200, to eventually comprise 94% of all detectedamoAand 4% of total bacteria by day 407. Quantitative fluorescence in-situ hybridization confirmed the increasing trend and high relative abundance ofNitrospira. These results demonstrate that comammox can be metabolically relevant to nitrogen transformation in wastewater treatment, and can even dominate the ammonia oxidizing community. Our results suggest that comammox may be an important functional group in energy efficient nitrification systems designed to operate at low DO levels.

Wastewater treatment plants (WWTPs) are among the major anthropogenic sources of N2O, a major greenhouse gas and ozone-depleting agent. We recently devised a zero-energy zero-carbon biofiltration system easily applicable to activated sludge-type WWTPs and performed lab-scale proof-of-concept experiments. The major drawback of the system was the diminished performance observed when fully oxic gas streams were treated. Here, a serial biofiltration system was tested as a potential improvement. A laboratory system with three serially positioned biofilters, each receiving a separate feed of artificial wastewater, was fed N2O-containing gas streams of varied flow rates (200-2000 mL·min-1) and O2 concentrations (0-21%). Use of the serial setup substantially improved the reactor performance. Fed fully oxic gas at a flow rate of 1000 mL·min-1, the system removed N2O at an elimination capacity of 0.402 ± 0.009 g N2O·m-3·h-1 (52.5% removal), which was approximately 2.4-fold higher than that achieved with a single biofilter, 0.171 ± 0.024 g N2O·m-3·h-1. These data were used to validate the mathematical model developed to estimate the performance of the N2O biofiltration system. The Nash-Sutcliffe efficiency indices ranged from 0.78 to 0.93, confirming high predictability, and the model provided mechanistic insights into aerobic N2O removal and the performance enhancement achieved with the serial configuration.

Biofilms are soft multicomponent biological materials composed of microbial communities attached to surfaces. Despite the crucial relevance of biofilms to diverse industrial, medical, and environmental applications, the mechanical properties of biofilms are understudied. Moreover, most of the available techniques for the characterization of biofilm mechanical properties are destructive. Here, we detail a model-based approach developed to characterize the viscoelastic properties of soft materials and bacterial biofilms based on experimental data obtained using the nondestructive dynamic optical coherence elastography (OCE) technique. The model predicted the frequency- and geometry-dependent propagation velocities of elastic waves in a soft viscoelastic plate supported by a rigid substratum. Our numerical calculations suggest that the dispersion curves of guided waves recorded in thin soft plates by the dynamic OCE technique are dominated by guided waves, whose phase velocities depend on the viscoelastic properties and plate thickness. The numerical model was validated against experimental measurements in agarose phantom samples with different thicknesses and concentrations. The model was then used to interpret guided wave dispersion curves obtained by the OCE technique in bacterial biofilms developed in a rotating annular reactor, which allowed the quantitative characterization of biofilm shear modulus and viscosity. This study is the first to employ measurements of elastic wave propagation to characterize biofilms, and it provides a novel framework combining a theoretical model and an experimental approach for studying the relationship between the biofilm internal physical structure and mechanical properties.

Wastewater treatment processes are subject to numerous disturbances during biological treatment of wastewater. In order to achieve and sustain suitable conditions of the process, basic wastewater parameters should be frequently monitored. While great improvements have been made in the automatization of treatment process, little is known about automatic measuring systems that can detect unusual process conditions in a bioreactor. Tracking these parameters can be difficult and the time required for the determination might vary from several minutes to few days. The objective of this study is to evaluate the use of an electronic nose in-house device (based on a non-selective gas sensor array) for the detection of process disturbances in a lab-scale sequencing batch reactor (SBR) during biological treatment of wastewater with activated sludge. Measurements were performed during a 12-hours working cycle. Continuous analyses of the headspace were performed using a sensor array based on the resistive Metal Oxide Semiconductor type (MOS) gas sensor. Based on the data obtained and the PCA analysis, this study showed that the e-nose technology can be used to predict or retrieve information about potential disruptions during wastewater processes using the e-nose technology.

Granular biofilms are dense spherical complex biological systems composed mainly of multi-microbial cells, water, and extracellular polymeric substances (EPS). They facilitate efficient purification and settling of activated sludge in wastewater treatment processes. The viscoelastic properties of these complex biofilm systems are important characteristics that control their growth and dictate how they respond to hydrodynamic forces and chemical stimuli. However, the viscoelastic properties of granular biofilms are poorly understood. In this paper, we study granular biofilms' viscoelastic properties using optical coherence elastography (OCE), a nondestructive method that integrates optical coherence tomography (OCT) with elastic wave propagation. While quantitative viscoelastic characterization of granular biofilms is challenging due to their heterogeneous properties, we show that elastic waves are suitable for this purpose. First, we employ guided elastic waves in a thin section of a granular biofilm to reveal a two-layered profile for the viscoelastic properties. Next, we utilize circumferential elastic waves that propagate near the surface of a non-sectioned spherical biofilm to quantify the layered system's viscoelastic properties. To the best of our knowledge, this work is the first quantitative study that characterizes the layered viscoelastic properties of granular biofilms. The measurement approach may provide a platform to study the interplay between the viscoelastic properties and other characteristics of granular biofilms such as the complex microbial system, morphology, and oxygen distribution.

Nitrous oxide (N2 O) is a potent greenhouse gas that can be formed in wastewater treatment processes by ammonium oxidizing and denitrifying microorganisms. While N2 O emissions from suspended growth systems have been extensively studied, and some recent studies have addressed emissions from nitrifying biofilms, much less is known about N2 O emissions from denitrifying biofilm processes. This research used modeling to evaluate the mechanisms of N2 O formation and reduction in denitrifying biofilms. The kinetic model included formation and consumption of key denitrification species, including nitrate (NO3-), nitrite (NO2-), nitric oxide (NO), and N2 O. The model showed that, in presence of excess of electron donor, denitrifying biofilms have two distinct layers of activity: an outer layer where there is net production of N2 O and an inner layer where there is net consumption. The presence of oxygen (O2 ) had an important effect on N2 O emission from suspended growth systems, but a smaller effect on biofilm systems. The effects of NO3- and O2 differed significantly based on the biofilm thickness. Overall, the effects of biofilm thickness and bulk substrate concentrations on N2 O emissions are complex and not always intuitive. A key mechanism for denitrifying biofilms is the diffusion of N2 O and other intermediates from one zone of the biofilm to another. This leads to zones of N2 O formation or consumption transformations that would not exist in suspended growth systems.

Groundwater contamination is an ever-growing environmental issue, that has attracted much and undiminished attention for the past half century. Groundwater contamination originates from anthropogenic (e.g. hydrocarbons), natural compounds (e.g. nitrate and arsenic), or both; to tackle these contaminants different technologies have been tested during the years. Recently, bioelectrochemical systems (BESs) have emerged as a potential treatment for groundwater contamination, with in situ applications reported, that showed promising results. Nitrate and hydrocarbons (toluene, phenanthrene, benzene, BTEX and light PAHs) have been successfully removed, due to the interaction of microbial metabolism with poised electrodes, other than physical migration due to the electric field generated in BES. The selection of proper BESs relies on several factors and problems such as complexity of the groundwater, scale-up and energy requirements that need to be taken into account. Modelling efforts could help predict case scenarios and choose an ideal design and approach to solve these issues. In this review, we critically analyze in situ BES applications for groundwater remediation, focusing in particular on the different setups proposed, and we identify and discuss the existing research gaps in the field.

Biofilms are biological materials composed of microbial communities encased in a self-produced extracellular polymeric substance (EPS). The viscoelastic properties of biofilms are related to the cross-link density in the EPS and ultimately the cohesiveness of biofilms. Accurate measurement of biofilm viscoelastic properties at the mesoscale remains a challenge. Rheological measurements, although being more common, provide only global properties, do not permit in-situ characterization, and are not amenable to complex sample geometries. To address these challenges, our work seeks to develop a nondestructive framework for characterizing biofilm viscoelastic properties using elastic wave propagation measured by the optical coherence elastography technique. The framework holds great potential to elucidate spatially varying mechanical properties and their correlation with sample morphology and composition.

While enhanced biological phosphorus removal (EBPR) is widely utilized for phosphorus (P) removal from wastewater, understanding of efficient process alternatives that allow combined biological P removal and shortcut nitrogen (N) removal, such as nitritation-denitritation, is limited. Here, we demonstrate efficient and reliable combined total N, P, and chemical oxygen demand removal (70%, 83%, and 81%, respectively) in a sequencing batch reactor (SBR) treating real mainstream wastewater (primary effluent) at 20°C. Anaerobic – aerobic cycling (with intermittent oxic/anoxic periods during aeration) was used to achieve consistent removal rates, nitrite oxidizing organism (NOO) suppression, and high effluent quality. Importantly, high resolution process monitoring coupled toex situbatch activity assays demonstrated that robust biological P removal was coupled to energy and carbon efficient nitritation-denitritation, not simultaneous nitrification-denitrification, for the last >400 days of 531 total days of operation. Nitrous oxide emissions of 2.2% relative to the influent TKN (or 5.2% relative to total inorganic nitrogen removal) were similar to those measured in other shortcut N bioprocesses. No exogenous chemicals were needed to achieve consistent process stability and high removal rates in the face of frequent wet weather flows and highly variable influent concentrations. Process modeling reproduced the performance observed in the SBR and confirmed that nitrite drawdown via denitritation contributed to suppression of NOO activity.

Microbial granular biofilms are spherical, multi-layered aggregates composed of communities of bacterial cells encased in a complex matrix of hydrated extracellular polymeric substances (EPS). While granular aggregates are increasingly used for applications in industrial and municipal wastewater treatment, their underlying mechanical properties are poorly understood. The challenges of viscoelastic characterization for these structures are due to their spherical geometry, spatially heterogeneous properties, and their delicate nature. In this study, we report a model-based approach for nondestructive characterization of viscoelastic properties (shear modulus and shear viscosity) of alginate spheres with different concentrations, which was motivated by our measurements in granular biofilms. The characterization technique relies on experimental measurements of circumferential elastic wave speeds as a function of frequency in the samples using the Optical Coherence Elastography (OCE) technique. A theoretical model was developed to estimate the viscoelastic properties of the samples from OCE data through inverse analysis. This work represents the first attempt to explore elastic waves for mechanical characterization of granular biofilms. The combination of the OCE technique and the theoretical model presented in this paper provides a framework that can facilitate quantitative viscoelastic characterization of samples with curved geometries and the study of the relationships between morphology and mechanical properties in granular biofilms.

Biological denitrification typically requires the addition of a supplemental electron donor, which can add a significant operating expense to wastewater treatment facilities. Most common electron donors are organic, but reduced inorganic sulfur compounds (RISCs), such as sulfide (HS−) and elemental sulfur (S0), may be more cost-effective. S0 is an inexpensive and well characterized electron donor, but it provides slow denitrification rates due to its low solubility. A lesser-known RISC is sulfite ( $${\text{SO}}_{3}^{2 - }$$ ), which can be easily produced from S0 by a simple combustion process. Unlike S0, $${\text{SO}}_{3}^{2 - }$$ is highly soluble, and therefore may provide higher denitrification rates. However, very little is known about microbial denitrification with $${\text{SO}}_{3}^{2 - }$$ . Also, $${\text{SO}}_{3}^{2 - }$$ is a strong reductant that reacts abiotically with oxygen and has toxic effects on microorganisms. This paper reviews $${\text{SO}}_{3}^{2 - }$$ in the environment, $${\text{SO}}_{3}^{2 - }$$ chemistry, microbiology, toxicity, and its potential use for denitrification. Since $${\text{SO}}_{3}^{2 - }$$ is an intermediate in the sulfur oxidation pathway of most sulfur-oxidizing microorganisms, it is an energetic electron donor and it should select for a $${\text{SO}}_{3}^{2 - }$$ -oxidizing community. Our review of the literature, as well as our own lab experience, suggests that $${\text{SO}}_{3}^{2 - }$$ can effectively serve as an electron donor for denitrification. Further research is needed to determine the kinetics of $${\text{SO}}_{3}^{2 - }$$ -based denitrification, its toxic threshold for sulfur-oxidizing microorganisms, and its potential inhibition of sensitive species such as nitrifying microorganisms and potential formation of nitrous oxide. Its effect on sludge settling efficiency also should be explored.

Wastewater treatment plants can be significant sources of nitrous oxide (N2O), a potent greenhouse gas. While our understanding of N2O emissions from suspended-growth processes has advanced significantly, less is known about emissions from biofilm processes. Biofilms may behave differently due to their substrate gradients and microbial stratification. In this study, we used mathematical modeling to explore the mechanisms of N2O emissions from nitrifying and denitrifying biofilms. Our ammonia-oxidizing bacteria biofilm model suggests that N2O emissions from biofilm can be significantly greater than from suspended-growth systems. The driving factor is the diffusion of hydroxylamine, a nitrification intermediate, from the aerobic to the anoxic regions of the biofilm. The presence of nitrite-oxidizing bacteria further increased emissions. For denitrifying biofilms, our results suggest that emissions are generally greater than for suspended-growth systems. However, the magnitude of the difference depends on the bulk dissolved oxygen, chemical oxygen demand, and nitrate concentrations, as well as the biofilm thickness. Overall, the accumulation and diffusion of key intermediates, i.e. hydroxylamine and nitrite, distinguish biofilms from suspended-growth systems. Our research suggests that the mechanisms of N2O emissions from biofilms are much more complex than suspended-growth systems, and that emissions may be higher in many cases.

In this study, the bioaugmentation of a sequencing batch reactor (SBR) for the treatment of reject water from wastewater treatment plant was evaluated. For the bioaugmentation step a product containing an enrichment of microorganisms from the Archaea domain was used to enhance the performance of the reactor for treating reject water. The experiment was carried out in two parallel lab-scale sequencing batch reactors. The first one (SBR A) was bioaugmented with a suspension of microorganisms from the Archaea domain, while the second reactor (SBR B) was not bioaugmented. The results here presented show that the SBR technology could sustain efficient NH 4 + –N and chemical oxyden demand removal rates and can be applied for the treatment of reject water. Moreover, the addition of microorganisms belonging to the Archaea domain improved the SBR overall operation, especially when the loading in the influent was increased. Administering Archaea to the reactor had also a positive effect on ammonia oxidation as well as on the nitrite removal.

Water bodies often suffer from the discharge of nutrient loading from agricultural and urban areas that compromises the quality of water. This study presents the application of the Hotelling test to evaluate the impacts of treated wastewater, discharged from a municipal wastewater treatment plant (WWTP), on the quality of river water. The quality of water was described by different pollution indicators, including COD, BOD5, TSS, NH4-N, NO2-N, NO3-N, TKN, TN and TP. The water samples were collected at three different locations: 500 m above the discharge point, at the wastewater discharge point and 1000 m below the wastewater discharge point. The tests of single pollution indicator showed differences between the two locations. Specifically, the results show that each single comparison controlled type I error at 0.05, while the family-wise error rate for the tests of all marginal hypotheses was controlled at 0.37. Testing for single indicators separately may not reveal true multivariate differences. In order to overcome this limitation, a modified version of T2 Hotelling test was used with robust James-Stein type estimators of covariance matrix. Major differences in the overall water quality were observed mainly for the concentration of nitrogenous compounds and found to significantly influence the water quality of the receiving river.

Wastewater treatment plants can be significant sources of nitrous oxide (N2O), a potent greenhouse gas. However, little is known about N2O emissions from biofilm processes. We adapted an existing suspended-growth mathe- matical model to explore N2O emissions from nitrifying biofilms. The model included N2O formation by ammonia- oxidizing bacteria (AOB) via the hydroxylamine and the nitrifier denitrification pathways. Our model suggested that N2O emissions from nitrifying biofilms could be significantly greater than from suspended growth systems under similar conditions. The main cause was the formation and diffusion of hydroxylamine, an AOB nitrification intermediate, from the aerobic to the anoxic regions of the biofilm. In the anoxic regions, hydroxylamine oxidation by AOB provided reducing equivalents used solely for nitrite reduction to N2O, since there was no competition with oxygen. For a continuous system, very high and very low dissolved oxygen (DO) concentrations resulted in lower emissions, while intermediate values led to higher emissions. Higher bulk ammonia concentrations and greater biofilm thicknesses increased emissions. The model effectively predicted N2O emissions from an actual pilot-scale granular sludge reactor for sidestream nitritation, but significantly underestimated the emissions when the NH2OH diffusion coefficient was assumed to be minimal. This numerical study suggests an unexpected and important role of hydroxylamine in N2O emission in biofilms.

Nitrous oxide (N

One-dimensional (1-D) biofilm models have been demonstrated reliable for specific types of biofilm reactor design. Limitations using mechanistic biofilm models for engineering design do not rely on improved biofilm models, but rely on improved biofilm reactor models. This is important when considering that biofilm reactors containing submerged, free-moving biofilm carriers are the most widely applied biofilm system(s) for municipal wastewater treatment. This paper presents a new biofilm reactor model that considers the impact of submerged free-moving biofilm carrier (Xcarrier) movement on system performance. The model accounts for a hydrodynamic condition characterized as plug flow with back mixing (to model axial dispersion). The relevance of this new biofilm reactor model to engineering situations is evaluated by applying it to relevant scenarios and comparing model results.

Wastewater treatment plants can be significant sources of nitrous oxide (N2O), a potent greenhouse gas. However, little is known about N2O emissions from biofilm processes. We adapted an existing suspended-growth mathematical model to explore N2O emissions from nitrifying biofilms. The model included N2O formation by ammonia-oxidizing bacteria (AOB) via the hydroxylamine and the nitrifier denitrification pathways. Our model suggested that N2O emissions from nitrifying biofilms could be significantly greater than from suspended growth systems under similar conditions. The main cause was the formation and diffusion of hydroxylamine, an AOB nitrification intermediate, from the aerobic to the anoxic regions of the biofilm. In the anoxic regions, hydroxylamine oxidation by AOB provided reducing equivalents used solely for nitrite reduction to N2O, since there was no competition with oxygen. For a continuous system, very high and very low dissolved oxygen (DO) concentrations resulted in lower emissions, while intermediate values led to higher emissions. Higher bulk ammonia concentrations and greater biofilm thicknesses increased emissions. The model effectively predicted N2O emissions from an actual pilot-scale granular sludge reactor for sidestream nitritation, but significantly underestimated the emissions when the NH2OH diffusion coefficient was assumed to be minimal. This numerical study suggests an unexpected and important role of hydroxylamine in N2O emission in biofilms.

Nitrous oxide (N2O) is a powerful greenhouse gas emitted from wastewater treatment, as well as natural systems, as a result of biological nitrification and denitrification. While denitrifying bacteria can be a significant source of N2O, they can also reduce N2O to N2. More information on the kinetics of N2O formation and reduction by denitrifying bacteria is needed to predict and quantify their impact on N2O emissions. In this study, kinetic parameters were determined for Paracoccus pantotrophus, a common denitrifying bacterium. Parameters included the maximum specific reduction rates, $$\hat{q}$$ , growth rates, $${\hat{\upmu }}$$ , and yields, Y, for reduction of NO3 − (nitrate) to nitrite (NO2 −), NO2 − to N2O, and N2O to N2, with acetate as the electron donor. The $$\hat{q}$$ values were 2.9 gN gCOD−1 d−1 for NO3 − to NO2 −, 1.4 gN gCOD−1 d−1 for NO2 − to N2O, and 5.3 gN gCOD−1 d−1 for N2O to N2. The $${\hat{\upmu }}$$ values were 2.7, 0.93, and 1.5 d−1, respectively. When N2O and NO3 − were added concurrently, the apparent (extant) kinetics, $$\hat{q}_{\text{app}}$$ , assuming reduction to N2, were 6.3 gCOD gCOD−1 d−1, compared to 5.4 gCOD gCOD−1 d−1 for NO3 − as the sole added acceptor. The $${\hat{\upmu }}_{\text{app}}$$ was 1.6 d−1, compared to 2.5 d−1 for NO3 − alone. These results suggest that NO3 − and N2O were reduced concurrently. Based on this research, denitrifying bacteria like P. pantotrophus may serve as a significant sink for N2O. With careful design and operation, treatment plants can use denitrifying bacteria to minimize N2O emissions.