Caitlyn S. Butler

Bioelectrochemical perchlorate reduction in a microbial fuel cell

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 system to identify putative biocathode-utilizing perchlorate-reducing bacteria (PCRB). Perchlorate reduction in the MFC was established by increasing the perchlorate loading to the biocathode, while decreasing nitrate loading. Perchlorate reduction was obtained without the need for exogenous electron shuttles or fixed electrode potentials, achieving a maximum perchlorate removal of 24 mg/L-d and cathodic conversion efficiency of 84%. The perchlorate-reducing biocathode bacterial community, which contained putative denitrifying Betaproteobacteria, shared little overlap with a purely denitrifying biocathode community, and was composed primarily of putative iron-oxidizing genera. Despite differences in cathodic function, the anode communities from the perchlorate-reducing MFC and the denitrifying MFC were similar to each other but different than their corresponding biocathode community. These data indicate that PCRB can utilize a cathode as an electron donor, and that this process can be harnessed to treat perchlorate while producing usable electrical power.

Simplifying microbial electrosynthesis reactor design

Microbial electrosynthesis, an artificial form of photosynthesis, can efficiently convert carbon dioxide into organic commodities; however, this process has only previously been demonstrated in reactors that have features likely to be a barrier to scale-up. Therefore, the possibility of simplifying reactor design by both eliminating potentiostatic control of the cathode and removing the membrane separating the anode and cathode was investigated with biofilms of Sporomusa ovata. S. ovata reduces carbon dioxide to acetate and acts as the microbial catalyst for plain graphite stick cathodes as the electron donor. In traditional ‘H-cell’ reactors, where the anode and cathode chambers were separated with a proton-selective membrane, the rates and columbic efficiencies of microbial electrosynthesis remained high when electron delivery at the cathode was powered with a direct current power source rather than with a potentiostat-poised cathode utilized in previous studies. A membrane-less reactor with a direct-current power source with the cathode and anode positioned to avoid oxygen exposure at the cathode, retained high rates of acetate production as well as high columbic and energetic efficiencies. The finding that microbial electrosynthesis is feasible without a membrane separating the anode from the cathode, coupled with a direct current power source supplying the energy for electron delivery, is expected to greatly simplify future reactor design and lower construction costs.

Ecological and Transcriptional Responses of Anode-Respiring Communities to Nitrate in a Microbial Fuel Cell

A poorly understood phenomenon with a potentially significant impact on electron recovery is competition in microbial fuel cells (MFC) between anode-respiring bacteria and microorganisms that use other electron acceptors. Nitrate is a constituent of different wastewaters and can act as a competing electron acceptor in the anode. Studies investigating the impact of competition on population dynamics in mixed communities in the anode are lacking. Here, we investigated the impact of nitrate at different C/N ratios of 1.8, 3.7, and 7.4 mg C/mg N on the electrochemical performance and the biofilm community in mixed-culture chemostat MFCs. The electrochemical performance of the MFC was not affected under electron donor non-limiting conditions, 7.4 mg C/mg N. At lower C/N, electron donor limiting and ratio electron recovery were significantly affected. The electrochemical performance recovered upon removal of nitrate at 3.7 mg C/mg N but did not at 1.8 mg C/mg N. Microbial community analysis showed a decrease in Deltaproteobacteria accompanied by an increase in Betaproteobacteria in response to nitrate at low C/N ratios and no significant changes at 7.4 mg C/mg N. Transcriptional analysis showed increased transcription of nirK and nirS genes during nitrate flux, suggesting that denitrification to N2 and not facultative nitrate reduction by Geobacter spp. might be the primary response to perturbation with nitrate.

How to sustainably feed a microbe: Strategies for biological production of carbon-based commodities with renewable electricity

As interest and application of renewable energy grows, strategies are needed to align the asynchronous supply and demand. Microbial metabolisms are a potentially sustainable mechanism for transforming renewable electrical energy into biocommodities that are easily stored and transported. Acetogens and methanogens can reduce carbon dioxide to organic products including methane, acetic acid, and ethanol. The library of biocommodities is expanded when engineered metabolisms of acetogens are included. Typically, electrochemical systems are employed to integrate renewable energy sources with biological systems for production of carbon-based commodities. Within these systems, there are three prevailing mechanisms for delivering electrons to microorganisms for the conversion of carbon dioxide to reduce organic compounds: (1) electrons can be delivered to microorganisms via H2 produced separately in a electrolyzer, (2) H2 produced at a cathode can convey electrons to microorganisms supported on the cathode surface, and (3) a cathode can directly feed electrons to microorganisms. Each of these strategies has advantages and disadvantages that must be considered in designing full-scale processes. This review considers the evolving understanding of each of these approaches and the state of design for advancing these strategies toward viability.

Nitrite accumulation in a denitrifying biocathode microbial fuel cell

Microbial fuel cells (MFCs) are a potential treatment technology-energy requirements for treatment can be offset with electricity production, biomass yield can be minimized, and microbial electron donors can be decoupled from acceptors, expanding treatment options. One potential MFC configuration uses an organic-oxidizing anode biofilm and a denitrifying cathode biofilm. However nitrite, a denitrification intermediate with environmental and public health impacts, has been reported to accumulate. In this study, before complete denitrification was achieved in a bench-scale, batch denitrifying cathode, nitrite concentrations reached 66.4 ± 7.5% of the initial nitrogen. Common environmental inhibitors such as insufficient electron donor, dissolved oxygen, insufficient carbon source, and pH, were considered. Improvement in these conditions did not mitigate nitrite accumulation. We present an Activated Sludge Model with an integration of the Nernst–Monod model and Indirect Coupling of Electrons (ASM–NICE) that effectively simulated the observed batch data, including nitrite-accumulation by coupling biocathodic electron transfer to intracellular electron mediators. The simulated half-saturation constants for mediated intracellular transfer of electrons during nitrate and nitrite reduction suggested a greater affinity for nitrate reduction when electrons are not limiting. The results imply that longer hydraulic retention times (HRTs) may be necessary for a denitrifying biocathode to ensure complete denitrification. These findings could play a role in designing full-scale MFC wastewater treatment systems to maximize total nitrogen removal.

A mastery-based learning approach for undergraduate engineering programs

We report the results of an action research study in which a modified mastery-based learning approach was implemented in three undergraduate engineering courses: engineering statistics, LabVIEW programming, and environmental engineering. In this paper, we describe both the action research and the modified mastery-based learning approach that was implemented. Findings from the analysis of data on student performance, and student and faculty perceptions of the approach are presented. In addition, we discuss our recommendations for modifications to the approach that could be used in future implementations.

The role of inorganic nitrogen in successful formation of granular biofilms for wastewater treatment that support cyanobacteria and bacteria

Recently, the use of phototrophs for wastewater treatment has been revisited because of new approaches to separate them from effluent streams. One manifestation uses oxygenic photogranules (OPGs) which are dense, easily-settleable granular biofilms of cyanobacteria, which surrounding populations of heterotrophs, autotrophs, and microalgae. OPGs can remove COD and nitrogenous compounds without external aeration. To better grow and maintain biomass in the proposed wastewater process, this study seeks to understand the factors that contribute to successful granulation. Availability of initial inorganic nitrogen, particularly ammonium, was associated with successful cultivation of OPGs. In the first days of granulation, a decrease in ammonium coupled with an increase in a cyanobacterial-specific 16S rRNA gene, may suggest that ammonium was assimilated in cyanobacteria offering a competitive environment for growth. Though both successful and unsuccessful OPG formation demonstrated a shift from non-phototrophic bacterial dominated communities on day 0 to cyanobacterial dominated communities on day 42, the successful community had a greater relative abundance (46%) of OTUs associated with genera Oscillatoria and Geitlernema than the unsuccessful community (27%), supporting that filamentous cyanobacteria are essential for successful OPG formation. A greater concentration of chlorophyll b in the unsuccessful OPG formation suggested a greater abundance of algal species. This study offers indicators of granulation success, notably availability of inorganic nitrogen and chlorophyll a and b concentrations for monitoring the health and growth of biomass for a potential OPG process.

Novel applications of molecular biological and microscopic tools in environmental engineering

Molecular biological methods offer flexible and powerful tools to environmental practitioners and researchers interested in studying environmental challenges in natural and engineered systems. In recent years, these techniques have allowed investigators to connect the fate, transport, and transformation of environmental chemical contaminants and pathogens with biological processes of functionally diverse microorganisms or microbial communities. Indeed, the boundaries of microbial ecosystems are constantly refined as researchers discover new links that extend beyond ————————— 1 Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095. *Corresponding author: Phone: 310-794-9850, E-mail: mahendra@seas.ucla.edu 2 Department of Civil and Environmental Engineering, University of Utah, Salt Lake City, UT 84112. 3 Department of Civil, Architectural, and Environmental Engineering, Drexel University, Philadelphia, PA 19104 4 Department of Civil and Environmental Engineering, University of Massachusetts, Amherst, MA 01003. Bacteria to include Archaea and unicellular Eukarya. Quantitative polymerase chain reaction (qPCR) provides a rapid and sensitive approach to determine gene abundance and expression from a wide range of microorganisms from complex environments. Whole genome arrays (WGA) and functional gene arrays (FGA) are being used to elucidate transcriptional changes in response to environmental parameters. Antibiotic resistance profiling and microbial source tracking studies continue to benefit from the information provided by a molecular-based experimental design. Quantitative fluorescent in situ hybridization (qFISH) and next generation sequencing technologies are changing the way we view suspended solids in wastewater treatment. Innovative sensors are being developed that couple molecular biological, chemical, or physical properties to improve the sensitivity and specificity for intended targets. Thus, advanced molecular analysis complements conventional approaches to provide a more

The Oxygenic Photogranule Process for Aeration-Free Wastewater Treatment

This study presents the oxygenic photogranule (OPG) process, a light-driven process for wastewater treatment, developed based on photogranulation of filamentous cyanobacteria, nonphototrophic bacteria, and microalgae. Unlike other biogranular processes requiring airlift or upflow-based mixing, the OPG process was operated in stirred-tank reactors without aeration. Reactors were seeded with hydrostatically grown photogranules and operated in a sequencing-batch mode for five months to treat wastewater. The new reactor biomass propagated with progression of photogranulation under periodic light/dark cycles. Due to effective biomass separation from water, the system was operated with short settling time (10 min) with effective decoupling of hydraulic and solids retention times (0.75 d vs 21-42 d). During quasi-steady state, the diameter of the OPGs ranged between 0.1 and 4.5 mm. The reactors produced effluents with average total chemical oxygen demand less than 30 mg/L. Nitrogen removal (28-71%) was achieved by bioassimilation and nitrification/denitrification pathways. Oxygen needed for the oxidation of organic matter and nitrification was produced by OPGs at a rate of 12.6 ± 2.4 mg O2/g biomass-h. The OPG system presents a new biogranule process, which can potentially use simple mixing and natural light to treat wastewater.

Investigation of the Fate and Dynamics of Extracellular Polymeric Substances (EPS) during Sludge-Based Photogranulation under Hydrostatic Conditions

Oxygenic photogranules have received increasing interest due to their ability to treat wastewater without aeration and recover wastewaters chemical energy and solar energy. It has been reported that these photogranules can be produced under both hydrostatic and hydrodynamic conditions, and enrichment of filamentous cyanobacteria is required for this photogranulation to occur. Despite the critical role extracellular polymeric substances (EPS) play in granulation, EPS in photogranulation is yet virtually unknown. Here, we present the fate and dynamics of different fractions of EPS in sludge-based photogranulation under hydrostatic conditions. The study shows that during the transformation of activated sludge into a photogranular biomass, sludges base-extractable proteins selectively degrade. Strong correlations between base-extracted proteins and the growth of chlorophyll a and chlorophyll a/ b ratio suggest that the bioavailability of this organic nitrogen is linked with selection and enrichment of filamentous cyanobacteria under hydrostatic conditions. The results of soluble and sonication-extractable EPS and microscopy also show that the growth of filamentous cyanobacteria required large amounts of polysaccharide-based EPS for their motility and maintenance. With findings on the progression of photogranulation, the fate and dynamics of EPS, and microscopy on microstructures associated with EPS, we discuss potential mechanisms of photogranulation occurring under hydrostatic conditions.