Paul H. Fallgren

Bioelectrochemical system platform for sustainable environmental remediation and energy generation.

The increasing awareness of the energy-environment nexus is compelling the development of technologies that reduce environmental impacts during energy production as well as energy consumption during environmental remediation. Countries spend billions in pollution cleanup projects, and new technologies with low energy and chemical consumption are needed for sustainable remediation practice. This perspective review provides a comprehensive summary on the mechanisms of the new bioelectrochemical system (BES) platform technology for efficient and low cost remediation, including petroleum hydrocarbons, chlorinated solvents, perchlorate, azo dyes, and metals, and it also discusses the potential new uses of BES approach for some emerging contaminants remediation, such as CO2 in air and nutrients and micropollutants in water. The unique feature of BES for environmental remediation is the use of electrodes as non-exhaustible electron acceptors, or even donors, for contaminant degradation, which requires minimum energy or chemicals but instead produces sustainable energy for monitoring and other onsite uses. BES provides both oxidation (anode) and reduction (cathode) reactions that integrate microbial-electro-chemical removal mechanisms, so complex contaminants with different characteristics can be removed. We believe the BES platform carries great potential for sustainable remediation and hope this perspective provides background and insights for future research and development.

Removal of bacteria and viruses from waters using layered double hydroxide nanocomposites

Abstract We have identified synthetic layered double hydroxides (LDH) nanocomposites as an effective group of material for removing bacteria and viruses from water. In this study, LDH nanocomposites were synthesized and tested for removing biological contaminants. LDH was used to remove MS2 and øX174 (indicator viruses), and Escherichia coli (an indicator bacterium) from synthetic groundwater and to remove mixed communities of heterotrophic bacteria from raw river water. Our results indicate that LDH composed of magnesium–aluminium or zinc–aluminium has a viral and bacterial adsorption efficiency ≥99% at viral concentrations between 5.9 × 106 and 9.1 × 106 plaque forming units (pfu)/L and bacterial concentrations between 1.6 × 1010 and 2.6 × 1010 colony forming units (cfu)/L when exposed to LDH in a slurry suspension system. Adsorption densities of viruses and bacteria to LDH in suspension ranged from 1.4 1010 to 2.1 1010 pfu/kg LDH and 3.2 × 1013–5.2 × 1013 cfu/kg LDH, respectively. We also tested the efficiency of LDH in removing heterotrophic bacteria from raw river water. While removal efficiencies were still high (87–99%), the adsorption capacities of the two kinds of LDH were 4–5 orders of magnitude lower than when exposed to synthetic groundwater, depending on if the LDH was in suspension or a packed column, respectively.

Enhanced bioremediation of hydrocarbon-contaminated soil using pilot-scale bioelectrochemical systems

Two column-type bioelectrochemical system (BES) modules were installed into a 50-L pilot scale reactor packed with diesel-contaminated soils to investigate the enhancement of passive biodegradation of petroleum compounds. By using low cost electrodes such as biochar and graphite granule as non-exhaustible solid-state electron acceptors, the results show that 82.1-89.7% of the total petroleum hydrocarbon (TPH) was degraded after 120 days across 1-34 cm radius of influence (ROI) from the modules. This represents a maximum of 241% increase of biodegradation compared to a baseline control reactor. The current production in the BESs correlated with the TPH removal, reaching the maximum output of 70.4 ± 0.2 mA/m(2). The maximum ROI of the BES, deducting influence from the baseline natural attenuation, was estimated to be more than 90 cm beyond the edge of the reactor (34 cm), and exceed 300 cm should a non-degradation baseline be used. The ratio of the projected ROI to the radius of BES (ROB) module was 11-12. The results suggest that this BES can serve as an innovative and sustainable technology for enhanced in situ bioremediation of petroleum hydrocarbons in large field scale, with additional benefits of electricity production and being integrated into existing field infrastructures.

Treatment of coking wastewater by using manganese and magnesium ores

This study investigated a wastewater treatment technique based on natural minerals. A two-step process using manganese (Mn) and magnesium (Mg) containing ores were tested to remove typical contaminants from coking wastewater. Under acidic conditions, a reactor packed with Mn ore demonstrated strong oxidizing capability and destroyed volatile phenols, chemical oxygen demand (COD)(,) and sulfide from the coking wastewater. The effluent was further treated by using Mg ore to remove ammonium-nitrogen and phosphate in the form of magnesium ammonium phosphate (struvite) precipitates. When pH of the wastewater was adjusted to 1.2, the removal efficiencies for COD, volatile phenol and sulfide reached 70%, 99% and 100%, respectively. During the second step of precipitation, up to 94% of ammonium was removed from the aqueous phase, and precipitated in the form of struvite with phosphorus. The struvite crystals showed a needle-like structure. X-ray diffraction and transmission electron microscopy were used to characterize the crystallized products.

Energy and Performance Comparison of Microbial Fuel Cell and Conventional Aeration Treating of Wastewater

Microbial fuel cell (MFC) technology provides a low cost alternative to conventional aerated wastewater treatment, however, there has been little comparison between MFC and aeration treatment using real wastewater as the substrate. This study attempts to directly compare the wastewater treatment efficiency and energy consumption and generation among three reactor systems-a traditional aeration process, a simple submerged MFC configuration, and a control reactor acting similar as natural lagoons. Results showed that all three systems were able to remove >90% of COD, but the aeration used shorter time (8 days) than the MFC (10 days) and control reactor (25 days). Compared to aeration, the MFC showed lower removal efficiency in high COD concentration, but much higher efficiency when the COD is low. Only the aeration system showed complete nitrification during the operation, reflected by completed ammonia removal and nitrate accumulation. Suspended solid measurements showed that MFC reduced sludge production by 52-82% as compared to aeration, and it also saved 100% of aeration energy. Furthermore, though not designed for high power generation, the MFC reactor showed a 0.3 Wh/g COD/L or 24 Wh/m3 (wastewater treated) net energy gain in electricity generation. These results demonstrate that MFC technology could be integrated into wastewater infrastructure to meet effluent quality and save operational cost.

Electrically induced reduction of trichloroethene in clay.

Chlorinated compounds such as trichloroethene (TCE) are recalcitrant contaminants commonly detected in soil and groundwater. Contemporary remedies such as electron donor amendment tend to be less or ineffective in treating chlorinated compounds in matrix of lower permeability, such as clay. In this study, electrically induced reduction (EIR) was tested by inserting electrodes in saturated clay containing 122.49-125.43 mg TCE kg(-1). Weak electric potentials (E) of 6, 9, and 12 V m(-1) were applied, and up to 97% of TCE were depleted during the study period. Corresponding increases in chloride concentrations was observed during TCE depletion, indicating a reductive dechlorination pathway. No migration of TCE was observed between the two electrodes, neither were intermediate compounds such as dichloroethene (DCE) or vinyl chloride (VC). Results were also tested against a mathematical equation we previously established for field applications. Electrically induced reduction may offer a novel method for in situ degradation of chlorinated contaminants, especially in low-permeable media such as clay.

Nitrate removal from groundwater in columns packed with reed and rice stalks

Nitrate leaching contaminates groundwater. The objective of this study was to determine if reed and rice stalks could enhance denitrification and reduce nitrate leaching into groundwater. Artificial groundwater spiked with nitrate and field groundwater samples were tested in the columns in sand reactors packed with either reed or rice stalks. The maximum nitrate removal rates were determined to be 1.93 and 1.97 mg nitrate‐N l−1 h−1, respectively, in the reed and rice stalk‐packed columns. The maximum nitrate‐nitrogen removal rate in reactors packed with reed stalk was 1.33 mg nitrate‐N l−1 h−1 when experimented with natural groundwater. Chemical oxygen demand consumption was higher when rice stalk (176.1 mg l−1) was used as the substrate, compared to reed stalk (35.2 mg l−1) at the same substrate dosage. No nitrite accumulation was detected during the test. The results demonstrate that agricultural byproducts, such as reed and rice stalks, may be used as substrate amendments for enhanced denitrification in natural settings, such as lakeside lagoons, ditches or wetlands.

Bioremediation of benzene, ethylbenzene, and xylenes in groundwater under iron-amended, sulfate-reducing conditions.

Elevated concentrations of sulfide in groundwater (approximately 63 mg S(2-)/L in water and 500 mg dissolved H2S/L dissipating from the wellhead) at a field site near South Lovedale (OK, USA) were inhibiting the activity of sulfate-reducing bacteria (SRB) that are known to degrade contaminants, including benzene, toluene, ethylbenzene, and xylenes. Elevated concentrations of these contaminants, except for toluene, also were present in this groundwater. Microcosms were established in the laboratory using groundwater and sediment collected from the field site and amended with various nutrient, substrate, and inhibitor treatments. All microcosms initially were amended with FeCl2 to induce FeS precipitation and, thereby, to reduce aqueous sulfide concentrations. Complete removal of benzene, ethylbenzene, and m+p-xylenes (BEX; o-xylene not detected) was observed within 39 d in treatments with various combinations of nutrient and substrate amendments, including treatments with no amendments (other than FeCl2). This indicates that the elevated concentration of sulfide is the only limiting factor to BEX biodegradation at this site under anaerobic conditions and that treating the groundwater with FeCl2 may be a simple remedy to both facilitate and enhance BEX degradation by the indigenous SRB population.

Site-Specific Limitations of Using Urea as a Nitrogen Source in Biodegradation of Petroleum Wastes in Soil

Nutrient addition is important to achieving the carbon/nitrogen balance and successful biodegradation of petroleum contaminants. Urea has been considered as a preferred nitrogen source in enhancing biodegradation, because of its high nitrogen content and commercial availability. This study investigated urea in the biodegradation of petroleum-contaminated soils collected from an arid and sandy area in Egypt. Ammonium nitrate served as the nitrogen amendment control in this study. Biodegradation of petroleum-contaminated soils from Wyoming was monitored as a comparison. Addition of urea failed to improve the enhancement of biodegradation of petroleum-impacted soil from the Egyptian site; in addition, urea demonstrates an adverse effect on the biodegradation rates. Results indicate that urea or its intermediates may inhibit the microorganisms involved in petroleum degradation. Data from this study suggest that the application of urea in the enhancement of biodegradation of petroleum compounds should consider site specificity, and may not be applicable in geological areas or soils structures similar to those in this study.

Passivation of zero-valent iron by denitrifying bacteria and the impact on trichloroethene reduction in groundwater

Zero-valent iron (ZVI) application in groundwater remediation is limited by its vulnerability to passivation, which significantly decreases its surface reactivity. Both biological and chemical processes can potentially passivate ZVI, although the understanding of biological passivation is limited. This study was conducted in bench-scale reactors packed with fresh ZVI or ZVI pre-exposed to nitrate (NO3(-)) and in the presence or absence of a denitrifying bacterial enrichment (DNBE). The first-order rate coefficients (k) for NO3(-) reduction by ZVI in the presence and absence of DNBE were 0.20 and 0.09 s(-1), respectively, suggesting that both ZVI and microbes contribute to NO3(-) removal. Abiotic reduction of nitrate was observed in reactors with trichloroethene (TCE) if ZVI was present; however, it resulted in reduced rates of TCE reduction (k = 0.29 s(-1)) when compared to reactors with fresh ZVI and no nitrate (k = 0.55 s(-1)). The TCE reduction efficiency decreased by 49% (k = 0.15 s(-1)) in the presence of DNBE, suggesting that microbial growth on ZVI or catalyzed oxidation of ZVI surface can inhibit TCE reduction by ZVI. Contrary to the presumption that denitrification may decrease ZVI passivation by nitrate, results from this study suggest that denitrifying bacteria actually exacerbate ZVI passivation.