Robert Nerenberg

University of Notre Dame | ND · Department of Civil and Environmental Engineering and Earth Sciences

This study explored the effect of extracellular polymeric substance (EPS) production on the performance of membrane-based biofilm reactors. Changing EPS production was induced by eliminating one of the main EPS polysaccharides, i.e., Pel. The studies were carried out using a pure culture of either Pseudomonas aeruginosa or an isogenic P. aeruginosa...

Nitrous oxide (N2O) is a potent greenhouse gas that can be produced by nitrifying and denitrifying bacteria. Yet the effects of N2O on microbial communities is not well understood. We used batch tests to explore the effects of N2O on mixed denitrifying communities. Batch tests were carried out with acetate as the electron donor and with the followi...

The membrane aerated biofilm reactor (MABR) is a novel technology based on gas-supplying membranes that supply dissolved O2 (DO) to biofilms growing on the membrane surface. The counter-diffusion of DO, supplied from base of the biofilm, and the electron donor, supplied from the bulk liquid, make membrane aerated biofilms (MABs) behave differently...

This research explored the effects of eukaryotic predation on nitrifying membrane-aerated biofilm reactor (MABR) biofilms. Past research on heterotrophic MABR biofilms showed that predation could create internal voids that promoted sloughing. However, the no past research addressed the effects of predation on nitrifying MABRs, even though nitrifica...

The membrane-aerated biofilm reactor (MABR) is an emerging wastewater treatment technology that uses O2-supplying membranes as a biofilm support. Because O2 is supplied from the biofilm base instead of the bulk liquid, MABR biofilms have distinct microbial community structures and behavior. Past research showed that protozoan predation in MABR biof...

The membrane aerated biofilm reactor (MABR) is an emerging wastewater treatment process that can greatly decrease energy requirements for aerating the water. It consists of cassettes of air-supplying, hollow-fiber membranes that can retrofit existing activated sludge processes. In order to maximize MABR nitrification fluxes, a basic understanding a...

The membrane-aerated biofilm reactor (MABR) is a novel wastewater treatment technology based on oxygen-supplying membranes. The counter diffusion of oxygen and electron donors in MABRs leads to unique behavior, and we hypothesized it also could impact predation. We used optical coherence tomography (OCT), microsensor analyses, and mathematical mode...

Abstract: Back-diffusion of inert gases into the lumen of Membrane-Aerated Biofilm Reactor (MABR) membranes decreases overall gas transfer rates and contaminant removal fluxes. However, most back-diffusion studies have neglected the effects of biofilms growth on the membranes, even though they are an integral part of the process. In this research,...

Peracetic acid (PAA) is an alternative disinfectant that may be effective for combined sewer overflow (CSO) disinfection, but little is known about the effect of particle size on PAA disinfection efficiency. In this work, PAA and hypochlorite were compared as disinfectants, with a focus on the effect of wastewater particles. Inactivation experiment...

The membrane-aerated biofilm reactor (MABR) is a novel treatment technology that employs gas-supplying membranes to deliver oxygen directly to a biofilm growing on the membrane surface. When operated with closed-end membranes, the MABR provides 100-percent oxygen transfer efficiencies (OTE), resulting in significant energy savings. However, closed-...

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...

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 stratificati...

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 b...

Elemental sulfur (So) can serve as an electron donor for denitrification. However, the mechanisms and rates of So-based denitrification, which depend on a biofilm development on the solid So surface, are not well understood. We used completely-mixed reactors packed with So chips to systematically explore the behavior of So-based denitrification as...

The membrane-biofilm reactor (MBfR), sometimes known as the membrane-aerated biofilm reactor (MABR), is an emerging treatment technology based on gas-transferring membranes. The membranes typically supply a gaseous electron donor or acceptor substrate, such as oxygen, hydrogen, and methane. The substrate diffuses through the membrane to a biofilm n...

A novel biofilm model is described which systemically couples bacteria, extracellular polymeric substances (EPS) and solvent phases in biofilm. This enables the study of contributions of rheology of individual phases to deformation of biofilm in response to fluid flow as well as interactions between different phases. The model, which is based on fi...

The membrane biofilm reactor (MBfR) is a novel technology that can safely deliver hydrogen to the base of a denitrifying biofilm via gas-supplying membranes. While hydrogen is an effective electron donor for denitrifying bacteria (DNB), it also supports sulfate-reducing bacteria (SRB) and methanogens (MET), which consume hydrogen and create undesir...

Wastewater treatment plants can be a significant source of nitrous oxide (N2O), a potent greenhouse gas. While researchers have addressed N2O emissions from suspended-growth processes, little is known about the emissions from biofilm processes. Biofilms may behave differently due to substrate gradients and microbial stratification. We explored N2O...

Wastewater treatment plants (WWTPs) engaging in biological nutrient removal (BNR) including nitrification and denitrification can be a significant source of nitrous oxide (N2O) emissions. Most studies on N2O emission from BNR processes have explored suspended-growth systems. Few studies have addresses biofilm processes. This study used mathematical...

Peracetic acid and hypochlorite were compared as disinfectants, with a focus on the disinfection of particulate-containing combined sewer overflows (CSOs). Hypochlorite is widely used to disinfect water and wastewater, although its use for disinfection of CSO discharges raises concerns regarding safety and efficiency. Peracetic acid (PAA) is an alt...

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...

We present a novel approach, based on image analysis and modelling, to study the impact of morphological variability (roughness) and fluid dynamics on substrate mass fluxes in biofilms. Specifically, we used this method to assess substrate fluxes in counter-diffusional autotrophic biofilms in a hydrogen-based membrane biofilm reactor. The physical...

We used modeling to predict the energy and cost savings associated with the air-based, hybrid membrane-biofilm reactor (hybrid MfBR). This process is obtained by replacing fine-bubble diffusers in conventional activated sludge with air-supplying, hollow-fiber membrane modules. Evaluated processes included removal of chemical oxygen demand (COD), co...

A two-dimensional, particle-based biofilm model coupled with mass transport and computational fluid dynamics was developed to simulate autotrophic denitrification in a spiral-wound membrane biofilm reactor (MBfR), where hydrogen is supplied via hollow-fiber membrane fabric. The spiral-wound configuration consists of alternating layers of plastic sp...

An archaeon with an unusual perchlorate-reducing metabolism raises questions about the diversity and evolution of perchlorate-reducing microorganisms.

In this research, we used modeling to assess the impact of irregular fouling-layer surface morphology (i.e., roughness) on permeate fluxes. Two membrane filtration models, each based on Darcy's Law, were used to predict fluxes for fouling layers with varying degrees of surface irregularity. One of the models considered the arithmetic mean thickness...

The membrane biofilm reactor (MBfR), an emerging technology for water and wastewater treatment, is based on pressurized membranes that supply a gaseous substrate to a biofilm formed on the membrane's exterior. MBfR biofilms behave differently from conventional biofilms due to the counter-diffusion of substrates. MBfRs are uniquely suited for numero...

Bacteria have their own form of "twitter" communication, described as quorum sensing (QS), where bacteria emit and sense chemical signal molecules as a means to gauge population density and control gene expression. Many QS-controlled genes relate to biofilm formation and function and may be important for some water and wastewater treatment biofilms...

The membrane biofilm reactor (MBfR) is an emerging technology for water and wastewater treatment based on gas-supplying membranes. Unlike conventional filtration membranes, MBfRs do not separate solids from liquids. Rather, a gaseous substrate is transferred across the membrane, while a biofilm, naturally formed on the outer membrane surface, catal...

Nitrous oxide is a potent greenhouse gas that can be formed in wastewater treatment, and there is increasing interest in its fate in treatment processes. In this research, kinetic parameters and denitrification-gene expression levels were determined for Paracoccus pantotrophus, a common denitrifying bacterium. Batch tests were carried out with acet...

Many utilities are seeking more cost effective, safe, and reliable electron donors for biological nutrient removal (BNR). Elemental sulfur (So) may be an attractive option, but little is known about the feasibility of So-based denitrification and its kinetics. This study furthered our investigations into the kinetics and stoichiometry of So based d...

The membrane-aerated biofilm reactor (MABR) is a novel, energy-efficient technology that provides wastewater treatment by passively supplying dissolved oxygen directly to a biofilm, without the formation of bubbles. Significant energy savings may be obtained by using the MABR for wastewater treatment, as compared to the conventional activated sludg...

The heavy use of fertilizers in agricultural lands can result in significant nitrate (NO3−) loadings to the aquatic environment. We hypothesized that biological denitrification in agricultural ditches and streams could be enhanced by adding elemental sulfur (So) to the sediment layer, where it could act as a biofilm support and electron donor. Usin...

Research has shown that biological nutrient removal (BNR) processes may be significant sources of nitrous oxide (N2O) and nitric oxide (NO) emissions. However, most research has focused on suspended growth systems. Little is known about emissions from biofilm systems, where substrate gradients and microbial stratifications within the biofilm can co...

Given the concerns over nitrous oxide (N2O) formation during biological nutrient removal, a better and more quantitative understanding of N2O reduction by denitrifying bacteria is needed to predict the fate of N2O in wastewater treatment processes. In this research, kinetic parameters and yields were determined for a mixed culture of denitrifying b...

Many utilities are seeking more cost effective, safe, and reliable electron donors for biological nutrient removal (BNR). Elemental sulfur (S°) may be an attractive option, but little is known about the feasibility of S°-based denitrification and its kinetics. In this research, we used bench–scale, S° packed–bed reactors to determine denitrificatio...

A hydrogen–based membrane biofilm reactor (MBfR) in a spiral-wound configuration is being developed to remove nitrate and other oxidized contaminants from water and wastewater. The MBfR uses membranes to provide a gaseous substrate to a biofilm growing on the membrane's outer surface. This study investigated the spatial distribution and performance...

Perchlorate is an emerging surface water and groundwater contaminant, and it is of concern because of its mobility in the environment and its inhibitory effect on thyroid function. Microbial fuel cells (MFCs) may be a suitable method for its treatment. We investigated a MFC with a denitrifying biocathode for perchlorate reduction and utilized the s...

Microbial fuel cells (MFCs) can be built with layered electrode assemblies, where the anode, proton exchange membrane (PEM), and cathode are pressed into a single unit. We studied the performance and microbial community structure of MFCs with layered assemblies, addressing the effect of materials and oxygen crossover on the community structure. Fou...

The hybrid membrane biofilm process (HMBP) is a new approach to achieving total nitrogen removal from wastewater. Air-filled, hollow-fiber membranes are placed into an activated sludge basin and bulk aeration is suppressed. A nitrifying biofilm develops on the membranes, exporting nitrate and nitrite to the bulk liquid. The nitrate and nitrite are...

In this study, we use extended X-ray absorption fine structure (EXAFS) spectroscopy measurements to examine the atomic environment of Cd bound onto two experimental bacterial consortia: one grown from river water, and one grown from a manufacturing gas plant site. The experiments were conducted as a function of pH and demonstrate that the complex m...

Bromate is a carcinogenic disinfection by-product formed from bromide during ozonation or advanced oxidation. We previously observed bromate reduction in a hydrogen-based, denitrifying hollow fiber membrane biofilm reactor (MBfR). In this research, we investigated the potential existence of specialized bromate-reducing bacteria. Using denaturing gr...

Membrane aerated biofilms (MABs) are an emerging technology for wastewater treatment. Several bench scale and pilot scale studies have help to highlight the benefits of this technology. This paper will discuss experiments that examined the impact of oxygen gradients and the impact of BOD gradients on the performance of MABs, and discusses how an MA...

We evaluated two microbial fuel cell (MFC) configurations that potentially can be used to remove BOD and total nitrogen from wastewater. The first was a two-chamber MFC with a denitrifying biocathode, where exoelectrogenic bacteria used the cathode as an electron donor and nitrate as the electron acceptor. This system could be used for tertiary den...

Agricultural headwater streams are a major pathway for the export of nitrate (NO3 ?) into the environment. These streams may also be well-suited for removing NO3 ?, via microbial denitrification, thereby preventing export to downstream ecosystems. Since denitrification is often limited by the lack of readily degradable electron donor, we explored t...

Shortcut nitrogen removal, that is, removal via formation and reduction of nitrite rather than nitrate, has been observed in membrane-aerated biofilms (MABs), but the extent, the controlling factors, and the kinetics of nitrite formation in MABs are poorly understood. We used a special MAB reactor to systematically study the effects of the dissolve...

The hybrid membrane biofilm process (HMBP) is a new approach to achieving total nitrogen removal from wastewater, with great potential for retrofitting into existing plants. It incorporates air-supplying hollow-fiber membranes into a conventional activated sludge tank. By using passive aeration, energy consumption may be greatly reduced. A nitrifyi...

Perchlorate (ClO4-) contamination of surface and ground waters is a significant environmental concern in the United States. Unfortunately, perchlorate is very soluble and stable in water, and it is not removed by conventional drinking water treatment processes (i.e., flocculation, coagulation, sedimentation, and filtration). Advanced treatment proc...

In 2008, molecular methods continue to be mainstream in environmental engineering research. Fingerprinting techniques such as denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) analysis continue to be popular tools to track differences in microbial community composition over time and space....

Membrane-aerated biofilms (MABs) are an effective means to achieve nitrification and denitrification of wastewater. In this research, microsensors, fluorescence in situ hybridization (FISH), and modeling were used to assess the impact of bulk liquid biological oxygen demand (BOD) concentrations on the activity and microbial community structure of n...

The hybrid (suspended and attached growth) membrane biofilm process (HMBP) is a novel method to achieve total nitrogen removal from wastewater. Air-filled hollow-fiber membranes are incorporated into an activated sludge tank, and a nitrifying biofilm develops on the membranes, producing nitrite and nitrate. By suppressing bulk aeration, the bulk li...

Kinetics parameters for perchlorate and chlorate reduction were determined for Dechlorosoma sp. HCAP-C, also known as Dechlorosoma sp. PCC, a novel perchlorate-reducing bacterium (PCRB) that accumulates significant amounts of chlorate during perchlorate reduction. This is the first report of such behavior, and we hypothesized the perchlorate reduct...

The hybrid membrane biofilm process (HMBP) is a new approach to achieving total nitrogen removal from wastewater, with great potential for retrofitting into existing plants. It incorporates air-supplying hollow-fiber membranes into a conventional activated sludge tank. The HMBP utilizes both attached and suspended growth to achieve TN removal. At t...

The hydrogen-based membrane biofilm reactor (MBfR) has been shown to reduce perchlorate to below 4 microg/L, but little is known about the microbial ecology of this or other hydrogen-based reactors, especially when influent perchlorate concentrations are much lower than the influent oxygen and nitrate concentrations. Dissimilatory (per)chlorate-red...

The hybrid membrane biofilm process (HMBP) is a novel approach to achieving total nitrogen removal from wastewater. It incorporates air-supplying, hollow-fiber membranes into a conventional activated sludge tank, where bulk aeration is suppressed. A nitrifying biofilm grows on the membranes and exports nitrite and nitrate to the anoxic bulk liquid,...

Perchlorate is widely used as a propellant in the aerospace and defense industries, and is of environmental concern due to its high mobility and inhibiting effect on thyroid function. An ideal treatment approach is bioreduction to chloride via dissimilatory perchlorate-reducing bacteria (PCRB). PCRB are ubiquitous in the environment, and are mainly...

The hybrid membrane biofilm process (HMBP) is a novel technology for removing total nitrogen (TN) from municipal wastewater. Air-filled, hollow-fiber membranes are placed in an activated sludge basin, and the bulk liquid is left anoxic. Membranes support an aerobic, nitrifying biofilm, while produced nitrate is exported to the bulk liquid and reduc...

The extensive use of nitrogen fertilizers in agriculture has led to widespread eutrophication. We explored sulfur-based autotrophic denitrification in agricultural headwater streams as means to remove nitrogen near the source. A stream mesocosm, simulating a headwater drainage ditch, was amended with elemental sulfur chips. Nitrate removal efficien...

Microbial fuel cells (MFCs) are promising for energy-efficient wastewater treatment, but most research has focused on lab-scale configurations that are not easily be scaled up. A potentially scalable configuration may be obtained by layering MFC assemblies on air-filled hollow-fiber membranes (HFMs), called HFM-MFCs. The HFM-MFC would provide micro...

Bromate (BrO(3)(-)) is an oxidized contaminant produced from bromide (Br(-)) during ozonation and advanced oxidation of drinking water. Previous research shows that denitrifying bioreactors can reduce bromate to innocuous bromide. We studied a hydrogen-based, denitrifying membrane-biofilm reactor (MBfR) for bromate reduction, and report the first k...

Whereas ion exchange is an attractive technology for treating perchlorate and nitrate in drinking water, a major disadvantage is that the resin must be regenerated using a brine, producing wastes with high concentrations of nitrate, perchlorate, and salt. This study investigates the potential for simultaneous nitrate and perchlorate reductions in h...

We report on a novel process for total nitrogen (TN) removal, the hybrid membrane biofilm process (HMBP). The HMBP uses air-supplying hollow-fibre membranes inside an activated sludge tank, with suppressed aeration, to allow concurrent nitrification and denitrification. We hypothesised that a nitrifying biofilm would form on the membranes, and that...

The hybrid membrane biofilm process (HMBP) is a novel technology for removing total nitrogen (TN) from municipal wastewater. Air-filled, hollow-fiber membranes are placed in an activated sludge basin, and the bulk liquid is left anoxic. The membranes support an aerobic, nitrifying biofilm, while produced nitrite and/or nitrate is exported to the bu...

The hybrid membrane biofilm process (HMBP) is a novel technology for total nitrogen (TN) removal from municipal wastewater. In the HMBP, a bank of gas permeable, hollow fiber membranes is inserted into an activated sludge system. Oxygen supplied by the membranes is consumed by a nitrifying biofilm growing on the fibers, while the produced nitrate i...

This paper provides the first kinetic parameters for a hydrogen-oxidizing perchlorate-reducing bacterium (PCRB), Dechloromonas sp. PC1. The qmax for perchlorate and chlorate were 3.1 and 6.3 mg/mgDW-day, respectively. The K for perchlorate was 0.14 mg/L, an order of magnitude lower than reported for other PCRB. The yields Y on perchlorate and chlor...

Hexavalent chromium (Cr(VI)) is a mutagen and carcinogen that is a significant concern in water and wastewater. A simple and non-hazardous means to remove Cr(VI) is bioreduction to Cr(III), which should precipitate as Cr(OH)3(s). Since Cr(VI)-reducing bacteria can use hydrogen (H2) as an electron donor, we tested the potential of the H2-based membr...

A H2-based, denitrifying and sulfate-reducing membrane-biofilm reactor (MBfR) was shown to be effective for removing selenate (Se(VI)) from water or wastewater by reducing it to insoluble Se(0). When Se(VI) was first added to the MBfR, Se(VI) reduction--first to selenite (Se(IV)) and then mostly to Se(0)--took place immediately and then increased o...

Sustained biological bromate (BrO3-) reduction was demonstrated in a hydrogen-based membrane biofilm reactor (MBfR). With 1 mg/L bromate and 5 mgN/L nitrate in the influent, the effluent bromate was 0.12 mg/L and the bromate flux was 1.1 g BrO3- -m -2-day-1. When influent bromate was increased to 4 mg/L, the effluent bromate was 3.5 mg/L with a flu...

Certain gaseous substrates, such as hydrogen, methane, and oxygen, can act as electron donor or acceptors for desired microbial processes. These gases are inexpensive and can lead to effective processes, but their low water solubility can limit their use. The membrane biofilm reactor (MBfR) is a novel system that uses membranes to supply dissolved...

The H2-based membrane biofilm reactor (MBfR) delivers H2 gas to a biofilm that naturally accumulates on the outer surface of bubbleless membranes. Although the MBfR is proven for the reduction of nitrate and perchlorate in drinking-water and groundwater settings, its most extensive application may be for advanced nitrogen removal in wastewater trea...