Civl & Environmental Engineering

The objective was to evaluate anion exchange (IEX) resins to remove organic acids and thus reduce fouling in low-pressure membrane filtration. A secondary objective was to demonstrate the usefulness of a new fractionation strategy for identifying the organic components of wastewater effluent organic matter (EfOM). We previously showed that organic acids (14-60% of EfOM) caused almost all short-term fouling in polyethersulfone (PES) UF. Investigators using different fractionation strategies (without strict removal of colloids and with dramatic pH changes during fractionation) reported that the hydrophilic base/neutral fraction of EfOM was the most important foulant, but colloids were present or had formed in that fraction during processing. In this work we report that resistance to filtration was partially reduced with removal of colloids but nearly all short-term fouling was eliminated with removal of organic acids for PES-UF and for polyvinylidene fluoride (PVDF) MF. Critical flux was increased from 75 to 200 L m −2 h −1 after fixed-bed treatment with weak-base DEAE or strong-base MIEX. Strong-base IRA-958 or non-ionic DAX-8 in column operation, or MIEX with in-line addition, were less effective in reducing fouling and increasing critical flux. These results confirmed our earlier observation that organic acids were primarily responsible for short-term fouling from EfOM and also demonstrated that IEX was effective for removal of organic acids, reducing fouling, and increasing critical flux.

Background: Microalgal biomass contains a high level of carbohydrates which can be biochemically converted to biofuels using state-of-the-art strategies that are almost always needed to employ a robust pretreatment on the biomass for enhanced energy production. In this study, we used an ultrasonic pretreatment to convert microalgal biomass (Scenedesmus obliquus YSW15) into feasible feedstock for microbial fermentation to produce ethanol and hydrogen. The effect of sonication condition was quantitatively evaluated with emphases on the characterization of carbohydrate components in microalgal suspension and on subsequent production of fermentative bioenergy. Method: Scenedesmus obliquus YSW15 was isolated from the effluent of a municipal wastewater treatment plant. The sonication durations of 0, 10, 15, and 60 min were examined under different temperatures at a fixed frequency and acoustic power resulted in morphologically different states of microalgal biomass lysis. Fermentation was performed to evaluate the bioenergy production from the non-sonicated and sonicated algal biomasses after pretreatment stage under both mesophilic (35°C) and thermophilic (55°C) conditions. Results: A 15 min sonication treatment significantly increased the concentration of dissolved carbohydrates (0.12 g g -1 ), which resulted in an increase of hydrogen/ethanol production through microbial fermentation. The bioconvertibility of microalgal biomass sonicated for 15 min or longer was comparable to starch as a control, indicating a high feasibility of using microalgae for fermentative bioenergy production. Increasing the sonication duration resulted in increases in both algal surface hydrophilicity and electrostatic repulsion among algal debris dispersed in aqueous solution. Scanning electron microscope images supported that ruptured algal cell allowed fermentative bacteria to access the inner space of the cell, evidencing an enhanced bioaccessibility. Sonication for 15 min was the best for fermentative bioenergy (hydrogen/ethanol) production from microalga, and the productivity was relatively higher for thermophilic (55°C) than mesophilic (35°C) condition. Conclusion: These results demonstrate that more bioavailable carbohydrate components are produced through the ultrasonic degradation of microalgal biomass, and thus the process can provide a high quality source for fermentative bioenergy production.

Calcium loading onto granular activated carbon (GAC) was evaluated in batch reactor tests for a series of single ring aromatic compounds. In the pH range from 7 to 9 when these aromatic rings contained adjacent carboxyl and hydroxyl groups, the level of calcium loaded was always greater than with compounds that did not contain this arrangement. Also with these compounds, the presence of calcium increased the loading of the organic onto GAC. When rings contained only carboxyls, only hydroxyls or carboxyl and hydroxyl groups not adjacent to one another, the calcium loading was much lower. For the compounds evaluated with only carboxyl groups (benzoic acid and phthalic acid), calcium loading onto GAC at pH greater than 8 was the same as when no organic compound was present in the system. It was noted that there was not a relationship between the ability of a ligand to form aqueous complexes and the effect of that ligand on calcium loading. Specifically phthalate was the strongest complexing ligand evaluated, but it did not cause significant calcium loading onto GAC. Calcium loading was found to increase in relation to the acidity constants of the organic ligands: increasing calcium loading was observed as the value (pKa 2 -pKa 1 ) increased. These results are consistent with the formation of hydrophobic Ca-ligand assemblages within the GAC.

The adsorption of Fe(II) onto hematite was measured as a function of pH, surface area, and time. The effects of anions (chloride, sulfate, or nitrate) and of Zn(II) were also determined. All experiments were conducted under strict anoxic conditions with 5 or 30 days for equilibration. Results showed that immobilization of Fe(II) on hematite consists of a fast sorption process and one or more slow processes, which probably include both sorption and formation of new phases. Sorption occurred at pH values as low as 4, which has not been reported in existing literature. Some Fe(II) could not be extracted after 20 h with 0.5 N HCl. In the presence of 0.01 M NaCl, all of the added Fe(II) was recovered when pH was below 6, but either 100% or less than 25% of added Fe(II) was recovered when pH was greater than 6. These results are consistent with auto-catalytic formation of magnetite, which was stable relative to hematite for pH above 5.9. However, when sulfate was greater than 1 mM, unextracted Fe(II) was observed at pH above 5 where only approximately 15% of added Fe(II) was recovered by a 0.5 N HCl extraction; these results could not be explained by precipitation of magnetite nor of known sulfate phases. Based on these results, existing models for adsorption of Fe(II) onto ferric oxides (based on experiments of several hours to a day) are not accurate for prediction of environmentally significant Fe(II) reactions with ferric oxides, when much longer times are available for reaction. There was no competition between Zn(II) and Fe(II) for 0.25 mM or less and 90 m 2 l − 1 hematite. Zn(II) was completely recovered using 0.5 N HCl for every condition that was tested.

Acid-mine drainage (AMD) is difficult and costly to treat. We investigated a new approach to AMD treatment using fuel cell technologies to generate electricity while removing iron from the water. Utilizing a recently developed microbial fuel cell architecture, we developed an acid-mine drainage fuel cell (AMD-FC) capable of abiotic electricity generation. The AMD-FC operated in fed-batch mode generated a maximum power density of 290 mW/m 2 at a Coulombic efficiency greater than 97%. Ferrous iron was completely removed through oxidation to insoluble Fe(III), forming a precipitate in the bottom of the anode chamber and on the anode electrode. Several factors were examined to determine their effect on operation, including pH, ferrous iron concentration, and solution chemistry. Optimum conditions were a pH of 6.3 and a ferrous iron concentration above ∼0.0036 M. These results suggest that fuel cell technologies can be used not only for treating AMD through removal of metals from solution, but also for producing useful products such as electricity and recoverable metals. Advances being made in wastewater fuel cells will enable more efficient power generation and systems suitable for scale-up.

Natural organic matter (NOM) enhancement of the biological reduction of hematite (R-Fe 2 O 3 ) by the dissimilatory iron-reducing bacterium Shewanella putrefaciens strain CN32 was investigated under nongrowth conditions designed to minimize precipitation of biogenic Fe(II). Hydrogen served as the electron donor. Anthraquinone-2,6-disulfonate (AQDS), methyl viologen, and methylene blue [quinones with an E w 0 (pH 7) of 0.011 V or less], ferrozine [a strong Fe(II) complexing agent], and characterized aquatic NOM (Georgetown NOM or Suwannee River fulvic acid) enhanced bioreduction in 5-day experiments whereas 1,4benzoquinone (E w 0 value ) 0.280 V) did not. A linear relationship existed between total Fe(II) produced and concentrations of ferrozine or NOM but not quinones, except in the case of methylene blue. Such a linear relationship between Fe(II) and methylene blue concentrations could be due to the systems being far undersaturated with respect to methylene blue or the loss of the thermodynamic driving force. A constant concentration of AQDS and variable concentrations of ferrozine produced a linear relationship between total Fe(II) produced and the concentration of ferrozine. Enhancement effects of both AQDS and ferrozine were additive. NOM may serve as both an electron shuttle and an Fe(II) complexant; however, the concentration dependence of hematite reduction with NOM was more similar to ferrozine than quinones. NOM likely enhances hematite reduction initially by electron shuttling and then further by Fe(II) complexation, which prevents Fe(II) sorption to hematite and cell surfaces.

This paper presents and validates a new paradigm for modeling complex biogeochemical systems using a diagonalized reaction-based approach. The bioreduction kinetics of hematite (␣-Fe 2 O 3 ) by the dissimilatory metal-reducing bacterium (DMRB) Shewanella putrefaciens strain CN32 in the presence of the soluble electron shuttling compound anthraquinone-2,6-disulfonate (AQDS) is used for presentation/validation purposes. Experiments were conducted under nongrowth conditions with H 2 as the electron donor. In the presence of AQDS, both direct biological reduction and indirect chemical reduction of hematite by bioreduced anthrahydroquinone-2,6-disulfonate (AH 2 DS) can produce Fe(II). Separate experiments were performed to describe the bioreduction of hematite, bioreduction of AQDS, chemical reduction of hematite by AH 2 DS, Fe(II) sorption to hematite, and Fe(II) biosorption to DMRB. The independently determined rate parameters and equilibrium constants were then used to simulate the parallel kinetic reactions of Fe(II) production in the hematite-with-AQDS experiments. Previously determined rate formulations/parameters for the bioreduction of hematite and Fe(II) sorption to hematite were systematically tested by conducting experiments with different initial conditions. As a result, the rate formulation/parameter for hematite bioreduction was not modified, but the rate parameters for Fe(II) sorption to hematite were modified slightly. The hematite bioreduction rate formulation was first-order with respect to hematite "free" surface sites and zero-order with respect to DMRB based on experiments conducted with variable concentrations of hematite and DMRB. The AQDS bioreduction rate formulation was first-order with respect to AQDS and first-order with respect to DMRB based on experiments conducted with variable concentrations of AQDS and DMRB. The chemical reduction of hematite by AH 2 DS was fast and considered to be an equilibrium reaction. The simulations of hematite-with-AQDS experiments were very sensitive to the equilibrium constant for the hematite-AH 2 DS reaction. The model simulated the hematite-with-AQDS experiments well if it was assumed that the ferric oxide "surface" phase was more disordered than pure hematite. This is the first reported study where a diagonalized reaction-based model was used to simulate parallel kinetic reactions based on rate formulations/ parameters independently obtained from segregated experiments.

A low-temperature O 2 trap was designed in order to achieve strict anoxic conditions. The work was motivated by observation of slow oxidation of Fe͑II͒ in an anaerobic chamber, leading to an estimated 3.8ϫ 10 −7 atm O 2 (well below the O 2 monitor detection limit) despite recirculation of the N 2 :H 2 atmosphere across a Pd catalyst. Very low O 2 activity inside an "anaerobic" chamber can result in erroneous conclusions regarding oxidation-reduction reactivities in anoxic environments. The O 2 trap consisted of two sequential barrier suspensions with 93.2 mM Fe͑III͒ as ferric hydroxide, 0.90 mM FeCl 2 , and pH 8.1. The partial pressure of O 2 was estimated to be less than 7.5ϫ 10 −9 atm O 2 when reactors were attached to the traps, based on no observed oxidation of Fe͑II͒.

A force balance model was developed to predict the effects of particle size, particle size distribution and surface potential on the structure of the ®lter cake. The model predicts that a stable ®lter cake is formed at low surface potentials and that the ®lter cake becomes unstable when the surface potential is larger than 30 mV. The model predicts a minimum porosity and permeability for ®lter cakes formed at intermediate surface potential. The surface potential that produces the lowest porosity increases with increasing particle size in the system. The speci®c resistance of the ®lter cake was a function of particle size and surface potential. The surface potential for the maximum speci®c resistance in the uniform particle system agreed with reports in the literature. #

The objective was to determine the effects of wastewater effluent organic materials (EfOM) on fouling of ultrafilters (100 kDa polyethersulfone (PES)). EfOM constituents were sequentially removed, first by removing particles down to the approximate ultrafilter pore size and then by removing dissolved EfOM based on functionality. Particles and colloids 420 nm accounted for 19% of total organic carbon (TOC), including 96% of EfOM 4100 kDa.

The sorption of uranyl onto hydrous ferric oxide (HFO) or hematite was measured by discontinuously titrating the suspensions with uranyl at pH 5.9, 6.8, and 7.8 under P CO2 ) 10 -3.5 atm (sorption isotherms). Batch reactors were used with equilibration times up to 48 days. Sorption of 1 µM uranyl onto HFO was also measured versus pH (sorption edge). A diffuse double layer surface complexation model was calibrated by invoking three sorption species that were consistent with spectroscopic evidence for predominance of bidentate complexes at neutral pH and uranyl-carbonato complexes: >SOH:UO 2 OH +1 , (>SO) 2 : UO 2 CO 3 -2 , and (>SO) 2 :(UO 2 ) 3 (OH) 5 -1 . The model was consistent with previously published isotherm and edge data. The model successfully predicted sorption data onto hematite, only adjusting for different measured specific surface area. Success in application of the model to hematite indicates that the hydrated surface of hematite has similar sorptive reactivity as HFO.