Biodegradation of Carbon Nanotube/Polymer Nanocomposites using a Monoculture.

The biodegradation rates of carbon nanotube (CNT)/ polymer nanocomposites (PNCs) containing poly-ε-caprolactone (PCL) were investigated using Pseudomonas aeruginosa, a microorganism commonly found in the environment. CNT/PCL nanocomposite mass loss profiles revealed that the rate of PCL matrix biodegradation decreased systematically as the CNT loading increased from 0.1 to 10% w/w. Addition of even a low CNT loading (<1% w/w) caused the CNT/PCL biodegradation rate constant to decrease by more than 50%. Similar trends in biodegradation rate were observed for both pristine and oxidized multiwall CNTs embedded in PCL. During PCL matrix biodegradation, CNT accumulation was observed at the surface of CNT/PCL nanocomposites and single particle inductively coupled-mass spectrometry experiments revealed no measurable CNT release to the culture fluid. Experimental data indicated that biodegradation proceeded as a result of biofilm formation on the CNT/PCL nanocomposites and decreased as a function of CNT loading due to the cytotoxicity of CNTs toward P. aeruginosa and the physical barrier presented by the surface-accumulated CNTs to the underlying PCL substrate. As the CNT loading in the CNT/PCL nanocomposites increased, the microbial proliferation of planktonic cells in the surrounding media also decreased as did the biodegradation rate of PCL samples present in the same reactors. Results from this study demonstrate that the inclusion of CNTs into polymer matrices could increase the environmental persistence of polymers in lakes, landfills, and surface waters.

Influence of oxygenation on chromium redox reactions with manganese sulfide (MnS(s)).

Manganese sulfide (MnS(s)) minerals exist in sulfidic environments and can have unique reactive abilities because of sulfide, which is a known reductant, and Mn, the oxyhydroxides of which are known oxidants. This study elucidated the role of MnS(s) in controlling Cr speciation with implications on its fate and toxicity in the natural environment, specifically sulfidic sediments that undergo biogeochemical changes due to sediment resuspension during dredging, bioturbation, and flood events. In continuously mixed batch reaction experiments, aqueous CrVI reduction under anaerobic conditions occurred primarily on the surface of MnS(s) displaying a biphasic behavior- the initial rapid removal of CrVI from solution was followed by a slow decline due to surface passivation by reaction products, mainly sorbed or precipitated CrIII. The reaction progress increased with MnS(s) surface area loading but decreased on increasing CrVI concentration and pH, suggesting that surface site regeneration through product desorption was the rate-controlling mechanism. Below circum-neutral pH, higher solubility of MnS(s) resulted in additional CrVI reduction by reduced sulfur species in solution, whereas increased CrIII solubility lowered surface passivation allowing for more reactive sites to participate in the reaction. Aeration of MnS(s) at pH≥7 caused the formation of a heterogeneous MnIII(hydr)oxide that was composed of hausmanite and manganite. CrVI reoccurrence was observed on aeration of CrVI-spiked MnS(s) from the oxidation of product CrIII. The reoccurrence at pH≥7 was attributed to the oxidation of product CrIII by MnIII(hydr)oxide, whereas the reoccurrence at pH<7 was hypothesized from the oxidation of product CrIII by intermediate aqueous MnIII and/or sulfur species. Just as with Cr, MnS(s) may play an important role in speciation, fate, and transport of other environmental contaminants.

Bioprospecting of microalgae for integrated biomass production and phytoremediation of unsterilized wastewater and anaerobic digestion centrate.

Eighteen microalgae, including two local isolates, were evaluated for their ability to grow and remove nutrients from unsterilized primary or secondary wastewater effluents as well as wastewater supplemented with nutrient-rich anaerobic digester centrate (ADC). Most of the tested species except several phylogenetically clustered Chlorella sorokiniana including local isolates and Scenedesmus strains were unable to grow efficiently. This may reflect the presence of certain genetic traits important for robust growth in the unsterilized wastewater. The maximum algal-specific growth rates and biomass density obtained in these bacterial-contaminated cultures were in the range of 0.8-1 day(-1) and 250-350 mg L(-1), respectively. ADC supplementation was especially helpful to biologically treated secondary effluent with its lower initial macronutrient and micronutrient content. As a result of algal growth, total nitrogen and orthophosphate levels were reduced by as much as 90 and 70 %, respectively. Biological assimilation was estimated to be the main mechanism of nitrogen removal in primary and secondary effluents with ammonia volatilization and bacterial nitrification-denitrification contributing for cultures supplemented with ADC. Assimilation by algae served as the principal mechanism of orthophosphate remediation in secondary wastewater cultures, while chemical precipitation appeared also to be important for orthophosphate removal in primary wastewater. Overall, cultivation of microalgae in primary and primary + 5 % ADC may be more favorable from an economical and sustainability perspective due to elimination of the costly and energy-intensive biological treatment step. These findings demonstrate that unsterilized wastewater and ADC can serve as critical nutrient sources for biomass generation and that robust microalgae can be potent players in wastewater phytoremediation.

Removal of pharmaceuticals and personal care products during water recycling: microbial community structure and effects of substrate concentration.

Many pharmaceuticals and personal care products (PPCPs) have been shown to be biotransformed in water treatment systems. However, little research exists on the effect of initial PPCP concentration on PPCP biotransformation or on the microbial communities treating impacted water. In this study, biological PPCP removal at various concentrations was assessed using laboratory columns inoculated with wastewater treatment plant effluent. Pyrosequencing was used to examine microbial communities in the columns and in soil from a soil aquifer treatment (SAT; a method of water treatment prior to reuse) site. Laboratory columns were supplied with different concentrations (0.25, 10, 100, or 1,000 µg liter(-1)) of each of 15 PPCPs. Five PPCPs (4-isopropyl-3-methylphenol [biosol], p-chloro-m-xylenol, gemfibrozil, ketoprofen, and phenytoin) were not removed at any tested concentrations. Two PPCPs (naproxen and triclosan) exhibited removals independent of PPCP concentration. PPCP removal efficiencies were dependent on initial concentrations for biphenylol, p-chloro-m-cresol, chlorophene, diclofenac, 5-fluorouracil, ibuprofen, and valproic acid, showing that PPCP concentration can affect biotransformation. Biofilms from sand samples collected from the 0.25- and 10-µg liter(-1) PPCP columns were pyrosequenced along with SAT soil samples collected on three consecutive days of a wetting and drying cycle to enable comparison of these two communities exposed to PPCPs. SAT communities were similar to column communities in taxonomy and phylotype composition, and both were found to contain close relatives of known PPCP degraders. The efficiency of biological removal of PPCPs was found to be dependent on the concentration at which the contamination occurs for some, but not all, PPCPs.

Mineral and non-carbon nutrient utilization and recovery during sequential phototrophic-heterotrophic growth of lipid-rich algae.

A critical factor in implementing microalgal biofuels for mass production is the nutrient requirements. The current study investigated the fate of macro- and micronutrients and their availability in a sequential phototrophic-heterotrophic production process for the lipid rich microalga Auxenochlorella protothecoides. More than 99 % (by weight) of overall process nutrients were supplied during the initial photoautotrophic stage reflecting its significantly larger volume. Under photoautotrophic growth conditions only 9-35 % of supplied Mn, S, Fe, N, Mg, and Cu and less than 5 % of P, Mo, Co, B, Zn, and Ca were consumed by the algae. The rest of these nutrients remain in the spent growth media during the culture concentration-down from an 800 L phototrophic pond to a 5 L heterotrophic fermenter. In contrast, Zn, Mo, Mn, Mg, Ca, and N were exhausted (90-99 % removal) during the first 25 h of the heterotrophic growth stage. The depletion of these key nutrients may have ultimately limited the final biomass density and/or lipid productivity achieved. Approximately 10-20 % of the total supplied S, Mn, Fe, N, and Cu and 5 % of Ca and Zn were assimilated into algal biomass. Several elements including N, P, Mn, B, Cu, Ca, Mg, S, and Fe were released back into the liquid phase by anaerobic digestion (AD) of the residual biomass after lipid extraction. The nutrients recovered from the AD effluent and remaining in the spent medium should be recycled or their initial concentration to the phototrophic stage decreased to enhance process economics and sustainability for future commercialization of algal-derived biofuels.

Biogeochemical controls on hexavalent chromium formation in estuarine sediments.

Predicting the aquatic and human health impacts of chromium (Cr) necessitates one to determine its speciation as either relatively nontoxic Cr(III) or toxic Cr(VI) and elucidate the influence of biogeochemical changes on its behavior and fate. In the Baltimore Harbor, Cr predominantly exists as Cr(III) associated with sediments. While reduction of Cr(VI) to Cr(III) is dominant in these anoxic sediments, the potential of Cr(III) oxidation and Cr(VI) reoccurrence during sediment resuspension and oxygenation resulting from dredging, bioturbation, and flood events poses a serious concern. In batch experiments, aqueous Cr(VI) spiked into continuously mixed anoxic suspensions was reduced to product Cr(III) under anaerobic conditions. No Cr(VI) reoccurrence was observed when conditions remained anaerobic. Aeration caused Cr(VI) reoccurrence from the abiotic oxidation of product Cr(III). Rates of aeration-driven Cr(VI) reoccurrence increased with pH, and Cr(VI) reoccurrence positively correlated with dissolved manganese (Mn) decline at pH ≥ 7. Aeration-driven oxidation of Mn(II) to Mn(III,IV)(hydr)oxides was the underlying mechanism causing product Cr(III) oxidation. Cr(VI) reoccurrence decreased with sediment loading and negatively correlated with the acid volatile sulfide (AVS) concentration. Although sediment resuspension and oxygenation may create temporary conditions conducive to Cr(VI) formation, long-term Cr(VI) persistence is unlikely in the presence of sediment reductants. While such natural attenuation in reducing environments mitigates the risk associated with Cr toxicity, this risk may still persist in Mn-rich and reductant-deficient environments.

Determination of pharmaceuticals and antiseptics in water by solid-phase extraction and gas chromatography/mass spectrometry: analysis via pentafluorobenzylation and stable isotope dilution.

A sensitive yet robust analytical method is presented for the simultaneous determination of 12 human pharmaceuticals (valproic acid, phenytoin, ibuprofen, gabapentin, acetaminophen, gemfibrozil, naproxen, ketoprofen, secobarbital, phenobarbital, 5-fluorouracil, and diclofenac) and 6 antiseptics (biosol, biphenylol, p-chloro-m-cresol, p-chloro-m-xylenol, chlorophene, and triclosan). The method employs solid-phase extraction (SPE) followed by a novel pentafluorobenzylation using a mixture of acetontrile/water (1/1, v/v). The method is simple to perform (derivatization can be completed in a single test tube) and eliminates the need for any solvent/SPE cartridge drying or blow-down. It affords excellent resolution, high sensitivity and reproducibility, and freedom from interference even for matrices as complex as untreated sewage. The method was applied to the analysis of sewage samples using 15 isotopically labeled surrogates, which resulted in the detection of 10 of the 12 pharmaceuticals and all of the antiseptics sought. Ten of 15 surrogates were synthesized from pure analytes by a simple H-D exchange reaction employing D(2)O and D(2)SO(4). Measured recoveries were sensitive to matrix effects and varied substantially among analytes, indicative of the limitations associated with using a single surrogate standard.

Combination of diffusive gradient in a thin film probe and IC-ICP-MS for the simultaneous determination of CH3Hg+ and Hg2+ in oxic water.

A diffusive gradient in thin film technique (DGT) was combined with ion chromatography and inductively coupled plasma mass spectrometry (IC-ICP-MS) for the in situ simultaneous quantification of CH(3)Hg(+) and Hg(2+) in aquatic environments. After diffusing through an agarose diffusive layer, the Hg species accumulated in a thiol-functionalized resin layer and were extracted using acidic thiourea solution to form stable thiourea-Hg complexes that were separated and detected via ion chromatography and ICP-MS, respectively. The effective diffusion coefficients of CH(3)Hg(+) and Hg(2+) complexes in the agarose diffusion layer with chloride were 5.26 (±0.27) × 10(-6) and 4.02 (±0.10) × 10(-6) cm(2) s(-1), respectively. The effective diffusion coefficients of CH(3)Hg(+) and Hg(2+) complexes in the agarose diffusion layer with dissolved organic matter was 3.57 (±0.29) × 10(-6) and 2.16 (±0.19) × 10(-6) cm(2) s(-1), respectively. The practical method detection limits are 0.1 and 0.7 ng L(-1) for CH(3)Hg(+) and Hg(2+) respectively for three weeks deployment. Lower detection limits would be possible by employing a thinner agarose diffusive layer and/or by deploying the probes longer. The method can measure time averaged CH(3)Hg(+) and Hg(2+) concentrations simultaneously in oxic water, making it useful as an in situ monitoring tool.

Manganese-induced Parkinsonism in mice is reduced using a novel contaminated water sediment exposure model.

Heavy metals enter the aquatic environment and accumulate within water sediments, but these metal-sediment interactions remain to be explored within toxicity studies. We developed an exposure model in mice that encapsulates the aquatic microenvironment of metals before exposure. Male and female C57/BL6 mice were exposed via their drinking water to manganese contaminated sediment (Sed_Mn) or to manganese without sediment interaction (Mn) for six weeks. Sediment interaction did not alter weekly manganese ingestion from water in males or females. We analyzed motor impairment, a common feature in manganese-induced Parkinsonism, using the beam traversal, cylinder, and accelerating rotarod tests. Sed_Mn mice performed better overall compared to Mn mice and males were more sensitive to manganese than females in both Sed_Mn and Mn treatment groups. Our study indicates that metal-sediment interactions may alter metal toxicity in mammals and introduces a new exposure model to test the toxicity of metal contaminants of drinking water.

Influence of polymer type and carbon nanotube properties on carbon nanotube/polymer nanocomposite biodegradation.

The interaction of anaerobic microorganisms with carbon nanotube/polymer nanocomposites (CNT/PNC) will play a major role in determining their persistence and environmental fate at the end of consumer use when these nano-enabled materials enter landfills and encounter wastewater. Motivated by the need to understand how different parameters (i.e., polymer type, microbial phenotype, CNT characteristics) influence CNT/PNC biodegradation rates, we have used volumetric biogas measurements and kinetic modeling to study biodegradation as a function of polymer type and CNT properties. In one set of experiments, oxidized multiwall carbon nanotubes (O-MWCNTs) with a range of CNT loadings 0-5% w/w were incorporated into poly-ε-caprolactone (PCL) and polyhydroxyalkanoates (PHA) matrices and subjected to biodegradation by an anaerobic microbial community. For each CNT/PNC, complete polymer biodegradation was ultimately observed, although the rate of biodegradation was inhibited above certain critical CNT loadings dependent upon the polymer type. Higher loadings of pristine MWCNTs were needed to decrease the rate of polymer biodegradation compared to O-MWCNTs, an effect ascribed principally to differences in CNT dispersion within the polymer matrices. Above certain CNT loadings, a CNT mat of similar shape to the initial PNC was formed after polymer biodegradation, while below this threshold, CNT aggregates fragmented in the media. In situations where biodegradation was rapid, methanogen growth was disproportionately inhibited compared to the overall microbial community. Analysis of the results obtained from this study indicates that the inhibitory effect of CNTs on polymer biodegradation rate is greatest under conditions (i.e., polymer type, microbial phenotype, CNT dispersion) where biodegradation of the neat polymer is slowest. This new insight provides a means to predict the environmental fate, persistence, and transformations of CNT-enabled polymer materials.

Sequential biodegradation of 1,2,4-trichlorobenzene at oxic-anoxic groundwater interfaces in model laboratory columns.

Halogenated organic solvents such as chlorobenzenes (CBs) are frequent groundwater contaminants due to legacy spills. When contaminated anaerobic groundwater discharges into surface water through wetlands and other transition zones, aeration can occur from various physical and biological processes at shallow depths, resulting in oxic-anoxic interfaces (OAIs). This study investigated the potential for 1,2,4-trichlorobenzene (1,2,4-TCB) biodegradation at OAIs. A novel upflow column system was developed to create stable anaerobic and aerobic zones, simulating a natural groundwater OAI. Two columns containing (1) sand and (2) a mixture of wetland sediment and sand were operated continuously for 295 days with varied doses of 0.14-1.4 mM sodium lactate (NaLac) as a model electron donor. Both column matrices supported anaerobic reductive dechlorination and aerobic degradation of 1,2,4-TCB spatially separated between anaerobic and aerobic zones. Reductive dechlorination produced a mixture of di- and monochlorobenzene daughter products, with estimated zero-order dechlorination rates up to 31.3 µM/h. Aerobic CB degradation, limited by available dissolved oxygen, occurred for 1,2,4-TCB and all dechlorinated daughter products. Initial reductive dechlorination did not enhance the overall observed extent or rate of subsequent aerobic CB degradation. Increasing NaLac dose increased the extent of reductive dechlorination, but suppressed aerobic CB degradation at 1.4 mM NaLac due to increased oxygen demand. 16S-rRNA sequencing of biofilm microbial communities revealed strong stratification of functional anaerobic and aerobic organisms between redox zones including the sole putative reductive dechlorinator detected in the columns, Dehalobacter. The sediment mixture column supported enhanced reductive dechlorination compared to the sand column at all tested NaLac doses and growth of Dehalobacter populations up to 4.1 × 108 copies/g (51% relative abundance), highlighting the potential benefit of sediments in reductive dechlorination processes. Results from these model systems suggest both substantial anaerobic and aerobic CB degradation can co-occur along the OAI at contaminated sites where bioavailable electron donors and oxygen are both present.

Biodegradation and removal of pharmaceuticals and personal care products in treatment systems: a review.

Pharmaceuticals and personal care products (PPCPs) have been the focus of much recent research as concerns rise about their occurrence in bodies of water worldwide. In an effort to characterize the risk and determine the prevalence of these micropollutants in lakes and rivers, many researchers are examining PPCP removal from impaired water during wastewater treatment and water recycling (soil passage) processes. Biodegradation studies and projects considering combinations of biodegradation and other removal processes have been conducted over a wide range of compound categories and therapeutic classes, as well as across different systems and scales of study. This review summarizes the extent of PPCP removal observed in these various systems.

Chromium occurrence and speciation in Baltimore harbor sediments and porewater, Baltimore, Maryland, USA.

Industrial activities in the Baltimore Harbor, Baltimore, Maryland, USA, have resulted in widespread chromium contamination of sediments. A comprehensive analysis of Cr speciation in sediment and porewater collected from 22 locations in the Baltimore Harbor was completed to understand Cr bioavailability and probability of toxicity due to Cr in sediments. The analysis employed a reverse-phase ion-pair high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) method. Sub-microgram-per-liter determination of Cr(III) and Cr(VI) in environmental samples was found, with method validation revealing broad method applicability of HPLC-ICP-MS to a wide range of sample types. The major limitation of the method was poor Cr species separation in high ionic strength solutions (greater than 0.1 M NaCl). Total Cr concentrations in Baltimore Harbor sediments ranged from 2.5 to 1,050 mg/kg with 11 of the 22 sites containing total Cr in excess of the 370 mg/ kg effects range-median (ER-M) sediment quality guideline. The Cr(VI) concentrations in sediments, however, were markedly lower, ranging from 0.10 to 0.38 mg/kg with Cr(VI) not detected in 14 of the 22 stations. Porewater concentrations, both for total Cr and Cr(VI), were quite low, with total Cr ranging from 0.20 to 2.16 microg/L and Cr(VI) ranging from 0.73 to 1.17 microg/L. The Cr(VI)-reducing capacity of the sediments, based on a sediment-spiking experiment, was found to be strongly correlated with the acid volatile sulfides content of the sediment. Overall, our results provide field validation of the hypothesis that Cr(VI) will not persist in sediments with excess acid volatile sulfides. Given the low concentrations of Cr(VI) in sediment and porewater, it appears unlikely that Cr in Baltimore Harbor sediments contributes appreciably to previously observed sediment toxicity.

Production of lipid-containing algal-bacterial polyculture in wastewater and biomethanation of lipid extracted residues: Enhancing methane yield through hydrothermal pretreatment and relieving solvent toxicity through co-digestion.

The feasibility of generating a lipid-containing algal-bacterial polyculture biomass in municipal primary wastewater and enhancing biomethanation of lipid-extracted algal residues (LEA) through hydrothermal pretreatment and co-digestion with sewage sludge (SS) was investigated. In high-rate algal ponds, the polyculture of native algal and bacteria species demonstrated a monthly average net and gross biomass productivity of 30 ±â€¯3 and 36 ±â€¯3 gAFDW m-2 day-1 (summer season). The algal community was dominated by Micractinium sp. followed by Scenedesmus sp., Chlorella sp., pennate diatoms and Chlamydomonas sp. The polyculture metabolic activities resulted in average reductions of wastewater volatile suspended solids (VSS), carbonaceous soluble biochemical oxygen demand (csBOD5) and total nitrogen (Ntotal) of 63 ±â€¯18%, 98 ±â€¯1% and 76 ±â€¯21%, respectively. Harvested biomass contained nearly 23% lipid content and an extracted blend of fatty acid methyl esters satisfied the ASTM D6751 standard for biodiesel. Anaerobic digestion of lipid extracted algal residues (LEA) demonstrated long lag-phase in methane production of 17 days and ultimate methane yield of 296 ±â€¯2 mL/gVS (or ~50% of theoretical), likely because to its limited biodegradability and toxicity due to presence of the residual solvent (hexane). Hydrothermal pretreatment increased the ultimate methane yield and production rate by 15-30% but did not mitigate solvent toxicity effects completely leading to less substantial improvement in energy output of 5-20% and diminished Net Energy Ratio (NER < 1). In contrast, co-digestion of LEA with sewage sludge (10% to 90% ratio) was found to minimize solvent toxicity and improve methane yield enhancing the energy output ~4-fold, compared to using LEA as a single substrate, and advancing NER to 4.2.

Neutral degradates of chloroacetamide herbicides: occurrence in drinking water and removal during conventional water treatment.

Treated drinking water samples from 12 water utilities in the Midwestern United States were collected during Fall 2003 and Spring 2004 and were analyzed for selected neutral degradates of chloroacetamide herbicides, along with related compounds. Target analytes included 20 neutral chloroacetamide degradates, six ionic chloroacetamide degradates, four parent chloroacetamide herbicides, three triazine herbicides, and two neutral triazine degradates. In the fall samples, 17 of 20 neutral chloroacetamide degradates were detected in the finished drinking water, while 19 of 20 neutral chloroacetamide degradates were detected in the spring. Median concentrations for the neutral chloroacetamide degradates were approximately 2-60ng/L during both sampling periods. Concentrations measured in the fall samples of treated water were nearly the same as those measured in source waters, despite the variety of treatment trains employed. Significant removals (average of 40% for all compounds) were only found in the spring samples at those utilities that employed activated carbon.

Neutral chloroacetamide herbicide degradates and related compounds in Midwestern United States drinking water sources.

Recent studies have revealed the presence of neutral degradates of chloroacetamide herbicides in the Chesapeake Bay at concentrations greatly in excess of the parent compounds. As some degradates are being considered for regulation in drinking water, exposure of human populations to such micropollutants is of interest. Here we report the results of a survey of source waters used by 12 drinking water utilities in the Midwestern United States. Analytes included 20 neutral and six ionic chloroacetamide degradates, four parent chloroacetamide herbicides, three triazine herbicides, and two triazine degradates. Samples were collected during Fall 2003 and Spring 2004. In the fall samples, 16 of 20 neutral chloroacetamide degradates were detected, while 18 of 20 neutral chloroacetamide degradates were detected in the spring samples. Concentrations of most parent chloroacetamides and neutral degradates were somewhat to substantially higher in the spring than in the fall, with median concentrations of approximately 10-100 ng/L. Groundwater sources tended to have lower concentrations of parents and neutral degradates than surface water sources in the fall, although concentrations of parents and degradates in groundwater were similar to those in surface water in the spring.

Synergistic co-digestion of wastewater grown algae-bacteria polyculture biomass and cellulose to optimize carbon-to-nitrogen ratio and application of kinetic models to predict anaerobic digestion energy balance.

This study investigated enhancing methane production from algal-bacteria biomass by adjusting the C/N ratio through co-digestion with a nitrogen-poor co-substrate - cellulose. A biomethane potential test was used to determine cumulative biogas and methane production for pure and co-digested substrates. Four kinetic models were evaluated for their accuracy describing experimental data. These models were used to estimate the total energy output and net energy ratio (NER) for a scaled AD system. Increasing the algal C/N ratio from 5.7 to 20-30 (optimal algae:cellulose feedstock ratios of 35%:65% and 20%:80%) improved the ultimate methane yield by >10% and the first ten days production by >100%. The modified Gompertz kinetic model demonstrated highest accuracy, predicting that co-digestion improved methane production by reducing the time-lag by ∼50% and increasing rate by ∼35%. The synergistic effects increase the AD system energy efficiency and NER by 30-45%, suggesting potential for substantial enhancements from co-digestion at scale.

Biodegradability of carbon nanotube/polymer nanocomposites under aerobic mixed culture conditions.

The properties and commercial viability of biodegradable polymers can be significantly enhanced by the incorporation of carbon nanotubes (CNTs). The environmental impact and persistence of these carbon nanotube/polymer nanocomposites (CNT/PNCs) after disposal will be strongly influenced by their microbial interactions, including their biodegradation rates. At the end of consumer use, CNT/PNCs will encounter diverse communities of microorganisms in landfills, surface waters, and wastewater treatment plants. To explore CNT/PNC biodegradation under realistic environmental conditions, the effect of multi-wall CNT (MWCNT) incorporation on the biodegradation of polyhydroxyalkanoates (PHA) was investigated using a mixed culture of microorganisms from wastewater. Relative to unfilled PHA (0% w/w), the MWCNT loading (0.5-10% w/w) had no statistically significant effect on the rate of PHA matrix biodegradation. Independent of the MWCNT loading, the extent of CNT/PNC mass remaining closely corresponded to the initial mass of CNTs in the matrix suggesting a lack of CNT release. CNT/PNC biodegradation was complete in approximately 20 days and resulted in the formation of a compressed CNT mat that retained the shape of the initial CNT/PNC. This study suggests that although CNTs have been shown to be cytotoxic towards a range of different microorganisms, this does not necessarily impact the biodegradation of the surrounding polymer matrix in mixed culture, particularly in situations where the polymer type and/or microbial population favor rapid polymer biodegradation.

Effects of initial solute distribution on contaminant availability, desorption modeling, and subsurface remediation.

Low permeability regions in which solute movement is governed by diffusion reduce the availability of pollutants for remediation and can function as long-term sources of groundwater contamination. The inherent difficulty in understanding mass transfer from these regions of sequestered contamination is further complicated by unknown solute distributions within the low-permeability regions (sequestering regions). When models are calibrated to reproduce temporal histories of solute release from a sequestering region (desorption), the fitted parameter values are used to infer the physical or chemical characteristics of the media; however, the calibrated parameters also reflect the case-specific initial conditions (i.e., the solute distribution within the sequestering region domain at the onset of desorption). This phenomenon is demonstrated using model simulations of solute diffusion from hypothetical solids with characteristics similar to those of the well studied Borden, Ontario aquifer system. Solute release from the solids is simulated using a batch diffusion model under different initial solute distributions within the solids. The results of these model simulations are used to calibrate parameters of a multiple first-order rate desorption model (MRM) to illustrate how the fitted MRM parameters increase or decrease depending on the initial "aging" of the solids. Further numerical simulations are conducted for a one-dimensional flow system under steady-state and variable-rate hydraulic flushing. These simulations show that although aging reduces desorptive mass flux during early stages of flushing, aged sites have greater desorptive mass flux (greater solute availability) than "freshly" contaminated media during the later stages of remediation. Overall, the results demonstrate why the physicochemical meaning of observed desorption rates cannot be accurately deduced without first understanding the initial solute distribution within the media.

Sorption and bioreduction of hexavalent uranium at a military facility by the Chesapeake Bay.

Directly adjacent to the Chesapeake Bay lies the Aberdeen Proving Ground, a U.S. Army facility where testing of armor-piercing ammunitions has resulted in the deposition of >70,000 kg of depleted uranium (DU) to local soils and sediments. Results of previous environmental monitoring suggested limited mobilization in the impact area and no transport of DU into the nation's largest estuary. To determine if physical and biological reactions constitute mechanisms involved in limiting contaminant transport, the sorption and biotransformation behavior of the radionuclide was studied using geochemical modeling and laboratory microcosms (500 ppb U(VI) initially). An immediate decline in dissolved U(VI) concentrations was observed under both sterile and non-sterile conditions due to rapid association of U(VI) with natural organic matter in the sediment. Reduction of U(VI) to U(IV) occurred only in non-sterile microcosms. In the non-sterile samples, intrinsic bioreduction of uranium involved bacteria of the order Clostridiales and was only moderately enhanced by the addition of acetate (41% vs. 56% in 121 days). Overall, this study demonstrates that the migration of depleted uranium from the APG site into the Chesapeake Bay may be limited by a combination of processes that include rapid sorption of U(VI) species to natural organic matter, followed by slow, intrinsic bioreduction to U(IV).