Environmental Protection Agency Limits Research Articles

Rapid Single-Step Detection of Polyfluoroalkyl Substances (PFAS) Using Electropolymerized Phenoxazine Dyes.

Per- and polyfluoroalkyl substances (PFAS) are highly stable ubiquitous contaminants that have been recently added to the list of regulated chemicals. While methods for PFAS detection exist, analysis is difficult, involving a tedious protocol and expensive instrumentation. Here, we demonstrate the first implementation of a phenoxazine dye as a sensing probe that facilitates rapid and inexpensive detection of representative PFAS, e.g., perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), at sensitivity levels covering the recently established Environmental Protection Agency (EPA) limits. The method comprises an electrode modified with a stable redox film of Meldola blue (MB) in its electropolymerized form (epMB), which provides amino sites for electrostatic interactions with PFAS. Long-chain PFAS bind specifically to the epMB, inducing a hydrophobic-type cluster formation through ion-pair and F-F interactions. This binding generates concentration-dependent changes in the epMB/epMB+ oxidation, enabling rapid and sensitive quantification in a single step with high sensitivity, reaching a limit of detection of 0.4 ppt for PFOS and 1.65 ppt for PFOA. The sensor demonstrates good selectivity toward common interfering compounds like humic acid, sodium chloride and fluoride, metallic ions (Cu, Hg, As), as well as pesticides. In addition to PFOS and PFOA, the sensors can measure other perfluoroalkyl compounds, demonstrating potential as a tool for rapid quantification of a total PFAS index, with affinity for long-chain PFAS. This work highlights the integration of redox receptors into an electrochemical sensor to solve the grand challenge of PFAS analysis using a rapid and inexpensive procedure, with potential for field deployment.

Evaluation of Airborne Lead Pollution and Its Association with Children's Urinary Lead Levels

Despite the measures taken by most countries, lead pollution still poses an environmental and health risk to humans, especially children. Therefore, the current study aims to evaluate lead in the air and its impact on children's health. Lead samples from the air and children's urine were collected from three different areas within Kerbala Governorate: the urban city center residential areas, and rural areas as a reference area for comparison. A suspended dust collector was used to collect lead samples, and then the lead concentration was measured using an atomic spectrometer after digesting them with acids. The results of the study showed that the highest concentration of lead was in the center of the urban area (3.150 ?g/m3) and its mean concentration in the air was 1.703 (?g/m3), which is higher than the US Environmental Protection Agency limits, with statistically significant differences between the study areas p < 0.01. The mean concentration of lead in children's urine was 0.622 (?g/dL) with statistically significant differences between the areas p < 0.01. Pearson's correlation coefficient indicated a significant positive correlation between the concentration of lead in the air and children's urine (r = 0.651; p < 0.05). This means that high lead concentrations in children's urine are due to lead air pollution and are an indicator of lead pollution in the environment and warn of potential risks to children's health. Therefore, the study recommends reducing lead emission sources and conducting periodic examinations.

Utilizing Microbial Fuel Cells For Simultaneous Treatment Of Solid Waste Water And Energy Generation

The proposed biocatalyst utilized in the microbial fuel cell (MFC) experiment demonstrated exo-electrogenic activity, with species such as Mycobacterium and Shewanella (Pseudomonas) sourced from sewer wastewater. Chemical parameters from the initial experimental trial did not comply with Environmental Protection Agency (EPA) limits. The total suspended solids (TSS) in the second MFC trial were the only parameter to meet the EPA threshold of 50 ppm, with influent and effluent concentrations of 96 ppm and 23.1 ppm, respectively. Consequently, supplementary treatment methods are required to achieve EPA discharge standards. The second trial indicated that the MFC setup effectively reduced metal concentrations, including Cr, Mn, Pb, and Zn, to levels that satisfy EPA surface water effluent discharge criteria. Keywords: microbial fuel cell, anode chamber, cathode chamber, wastewater, energy generation. Aims Research Journal Reference Format: Adeniyi O. A., Bakri A.J., Samuel O. Fadipe, Shakirat B. A., Adebayo O.C. & Oyetunde R.A. (2024): Utilizing Microbial Fuel Cells For Simultaneous Treatment Of Solid Waste Water And Energy Generationelta. Advances in Multidisciplinary and Scientific Research Journal Vol. 10. No. 2. Pp 55-69. www.isteams.net/aimsjournal. dx.doi.org/10.22624/AIMS/V10N2P6

R Radiological Risk Assessment Of 222 Radon Concentration And Annual Effective Dose Calculation In Groundwater From Zakho, Iraq

Radon, the heaviest of noble gases in the periodic table, is a naturally occurring radioactive nuclide found in rocks, soil, and water. It has gained increasing attention in recent research due to its association with cancer. This study focused on assessing the potential radioactive risks associated with water usage in Zakho, Iraq, by analyzing 16 groundwater samples collected from the primary water source. Alpha spectrometry with RAD7 and RAD-H2O accessories from Durridge CO was employed for assay purposes. The measured 222Rn concentrations ranged from 0.21 ± 0.1 to 19.75 ± 4.8 BqL−1, with an average of 8.90 Bq. −1. The recorded values indicate that 31% of the data surpasses the specified United States Environmental Protection Agency (USEPA) limit of 11.1 BqL−1. Notably, the evaluation of the total annual effective dose revealed significant age-related variations. Specifically, 62% of infant samples and 68% of children samples exceeded the acceptable limit of 100 μSv/y, while 25% of adult samples surpassed the World Health Organization (WHO) recommended threshold. The obtained data align with similar studies conducted globally, emphasizing the need for continuous radon monitoring during water consumption. The findings advocate for proactive measures to ensure the safety of these water sources, addressing the pressing concern of radon-related health risks.

Deep separation of arsenic and alkali from alkaline arsenic containing solution using hydrothermal lime precipitation method

A new strategy of lime precipitation of arsenic (As) under hydrothermal conditions was proposed for the treatment of alkaline arsenic-containing wastewater (AAW). On the basis of theoretical analysis, a study was conducted on the reaction law and mechanism of lime precipitation of arsenic in hydrothermal systems, as well as the environmental stability of precipitation products. Results of theoretical calculations showed that increasing the reaction temperature was beneficial the formation of insoluble Ca5(AsO4)3OH, which promoted the removal of arsenic. It is shown that the arsenic concentration could be reduced from 35.38 mg/L to 9.16 mg/L with increasing the reaction temperature from 90 °C to 210 °C. The experimental results further confirmed the above conclusion. When the reaction temperature was increased from 90 °C to 210 °C, the arsenic concentration in the final liquid decreased from 706.21 mg/L to 15.21 mg/L. The leaching toxicity evaluation results of the products showed that the stability of the arsenic precipitates was improved significantly with the hydrothermal conditions. The arsenic leaching concentration for the products obtained at 170 °C was only 2.1 mg/L, which was lower than the U.S. Environmental Protection Agency (USEPA) limit of 5 mg/L for solid waste containing hazardous arsenic. It is found that the improved stability of the arsenic precipitates could be attributed to the increased crystallinity and crystal size of the product obtained under hydrothermal conditions.

Trace metals in CO 2 -rich Green River springs, Utah, USA: an analogue for engineered storage

Abstract Sedimentary rocks with high natural CO 2 concentrations provide invaluable analogues for the long-term engineered storage of CO 2 . Some previous studies have reported high trace metal concentrations in sandstone aquifers exposed to CO 2 , a cause for concern should stored CO 2 leak into underground sources of drinking water. However, the intensively studied Jurassic sandstone aquifer in the San Rafael–Green River (Utah, USA) area has trace metal concentrations that are within US Environmental Protection Agency's limits for drinking water. Exceptions are As which is plausibly introduced into the aquifer by saline brines external to the aquifer, and salinity which largely is. This shows that CO 2 in aquifers does not inevitably cause trace metal contamination. CO 2 –water–rock batch experiments elucidated the controls on the trace metal concentrations. After the addition of CO 2 , the experiments reproduce Cu, Cd, Hg, Ni and Zn well, with less good agreement for Cr and Pb although these are still low compared to drinking water standards. Major cations used as fingerprints for mobilization mechanisms suggest that the trace metals are largely derived by desorption, possibly from grain-coating Fe-oxides, rather than by the dissolution of mineral phases. Possible exceptions are Pb and Ni, plus As which is derived from saline brines.

Parametric optimization of the CNG/ethanol-induced RCCI profiles in biodiesel combustion through a robust design space foray

To attain a “net-zero carbon footprint,” plant-based biodiesel should be used in conventional IC engines with naturalizing other important emission characteristics like nitrogen oxide and carbon footprint. This study uses a statistical modeling-based multi-objective optimization approach to find the compromise parametric solution for the combustion, performance, stability, and emissions of a diesel engine powered by Mahua biodiesel mixed with compressed natural gas (CNG)/ethanol. This current study was conducted through an advanced injection strategy called the split injection approach, followed by various energy shares from ethanol or CNG enrichment through port fuel injection strategies. Hence the engine operation was conducted with the fuel mixture of various reactivity in different proportions. However, the injection angle was counted as an effective input parameter along with the variation in energy share for different injection angles. A robust ‘design of experiment’ (DoE) approach was incorporated here by a novel strategy developed by Scott Kowalski, John Cornell, and Geoff Vining (KCV) to investigate this multi-factor approach which combines both reactivity phasing and injecting phasing strategies. The Response Surface Methodology (RSM) based statistical modeling was incorporated here to predict the corresponding responses in continuous design space. It is pertinent to mention that the combination of this novel DoE-RSM-based injection and reactivity phasing is a first-of-a-kind in this paradigm as per the current literature. The robust model’s best desirable responses showed improved combustion, performance, and emission characteristics while remaining within US Environmental Protection Agency (EPA) limits. The NHC & CO footprint of the best optimal strategy was almost 15% and 60% lower for ethanol enriched biodiesel operation and 50% & 80% lower for PFI-CNG operation, respectively, the experimental values corresponding to the highest LNVIMEP & lowest COVIMEP. PM footprint has also illustrated an almost 40% lower footprint corresponding to the lowest ROPRMAX for ethanol enriched strategy and 5% reduced emission for CNG-BD operation corresponding to maximum CD. Improved EQ_BTE and CO2 footprint were registered by almost 6 % & 60% for PFI of ethanol and 20% and 10% for CNG-BD operation, respectively, compared to their experimental values corresponding to the lowest ROPRMax.

A highly sensitive, easy-and-rapidly-fabricable microfluidic electrochemical cell with an enhanced three-dimensional electric field

An NP-μFEC is a reusable, novel microfluidic electrochemical cell with multiple non-planar interdigitated microelectrode arrays, minimal sample volume, and enhanced electric field penetration for highly sensitive electrochemical analysis. (i) The NP-μFEC features spatial 3-electrode architecture, and a small sample volume (∼4 μL). (ii) Here, [Fe(CN)6]3-/4- redox couple are used as an electrochemical reporter. The effects on the electrochemical properties of NP-μFEC due to the change in the reference electrode (RE) and counter electrode (CE)'s position with respect to the working electrode (WE) position are analyzed. For NP-μFEC, the position of the RE with respect to the WE does not affect the CV, DPV electrochemical profiles. However, the spacing between the CE and WE plays a significant role. (iii) The enhanced three-dimensional electric field penetration in NP-μFEC is validated by finite element analysis simulation using COMSOL Multiphysics. (iv) Without electrode surface modifications, NP-μFEC shows a detection limit (DL) of ∼2.54 × 10−6 M for aqueous [Fe(CN)6]3-/4- probe. (v) The DL for Cu2+, Fe3+, and Hg2+ are 30.5±9.5 μg L−1, 181±58.5 μg L−1, and 12.4±1.95 μg L−1, respectively, which meets the US Environmental Protection Agency (EPA)'s water contamination level for Cu, Fe, and is close to that for Hg (EPA limits are 1300 μg L−1, 300 μg L−1, and 2 μg L−1, respectively). (vi) Further, using a pressure-sensitive adhesive layer to form the channel and create the NP-μFEC configuration simplifies the manufacturing process, making it cost-effective and allowing for rapid adoption in any research lab. NP-μFEC is used to detect heavy metal ions in water. This demonstrates that cost-effective, easy-to-fabricate NP-μFEC can be a new sensitive electrochemical platform.

Squaramide-Immobilized Carbon Nanoparticles for Rapid and High-Efficiency Elimination of Anthropogenic Mercury Ions from Aquatic Systems

Water pollution due to environmental remediation and poor waste administration in certain areas of the globe signifies a serious problem in acquiring safe and clean drinking water. This problem is especially critical in rural areas, where advanced water purification techniques are deficient, and it remains a daunting task for ecosystem and public health protection. This critical task can be addressed herein by developing scalable poly squaramide-phenyl methacrylamide (PSQ)-functionalized carbon nanoparticles (CNPs) (PSQ-CNPs) with densely populated chelating sites with strong Hg2+-binding capacity. The PSQ-CNPs have shown high efficiency in removing Hg2+ from aqueous solution, providing a Hg2+ capacity of 2840 mg g-1, surpassing all the amine and thiol-based adsorbents reported hitherto. More significantly, the adsorbent reveals the largest distribution coefficient value (Kd) of 9.09 × 1010 mL g-1, which allows it to reduce Hg2+ content from 10 ppm to less than 0.011 ppb, well below the United States Environmental Protection Agency (EPA) limits for drinking water standards (2 ppb). The adsorption measurements of the adsorbent followed the Langmuir isotherm model and pseudo-second order. The practical applicability of PSQ-CNPs was verified with the real samples (the lake, river, and industrial wastewater) and has been proven to be excellent. The adsorbent could still retain its Hg2+ removal efficacy even after 12 sorption cycles. It is attributed that the remarkable performance of PSQ-CNPs arises from the high-density chelating sites and pores on the surface of CNPs. The present work shows a new benchmark for Hg2+-removal adsorbents and presents a novel practical approach for decontaminating Hg2+ and other heavy metal ions from wastewater.

Distribution and source of and health risks associated with polybrominated diphenyl ethers in dust generated by public transportation

Carcinogenic and neurotoxic polybrominated diphenyl ethers (PBDEs) are environmentally ubiquitous and have been widely investigated. However, little is understood regarding their pollution status, sources, and potential risk to persons in public transportation microenvironments (PTMs). We collected 60 dust samples from PTMs and then selected four materials typical of bus interiors to determine the sources of PBDEs in dust using principal component analysis coupled with Mantel tests. We then evaluated the risk of PBDEs to public health using Monte Carlo simulations. We found that PBDE concentrations in dust were 2-fold higher in buses than at bus stops and that brominated diphenyl ether (BDE)-209 was the main pollutant. The number of buses that passed through a bust stop contributed to the extent of PBDE pollution, and the primary potential sources of PBDEs in dust were plastic handles and curtains inside buses; BDE-209 and BDE-154 were the main contributors of pollution. We found that health risk was 8-fold higher in toddlers than in adults and that the reference doses of PBDEs in dust were far below the United States Environmental Protection Agency limits. Our findings provide a scientific basis that may aid in preventing PBDE pollution and guiding related pollution management strategies in PTMs.

Lead Sequestration from Halide Perovskite Solar Cells with a Low-Cost Thiol-Containing Encapsulant.

Perovskite solar cells (PSCs) are being studied and developed because of the outstanding properties of halide perovskites as photovoltaic materials and high conversion efficiencies achieved with the best PSCs. However, leaching out of lead (Pb) ions into the environment presents potential public health risks. We show that thiol-functionalized nanoparticles provide an economic way of minimizing Pb leaching in the case of PSC module damage and subsequent water exposure (at most, ∼2.5% of today’s crystal silicon solar panel production cost per square meter). Using commercial materials and methods, we retain ∼90% of Pb without degrading the photovoltaic performance of the cells, compared with nonencapsulated devices, yielding a worst-case scenario of top-soil pollution below natural Pb levels and well below the U.S. Environmental Protection Agency limits.

Spatial distribution, sources identification, and health risk assessment polycyclic aromatic hydrocarbon compounds and polychlorinated biphenyl compounds in total suspended particulates (TSP) in the air of South Pars Industrial region-Iran.

South Pars Industrial Energy Zone, located in the southwest of Iran along the Persian Gulf coast, encompasses many industrial units in the vicinity of urban areas. This research study investigated the effects of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) on human health and the environment. Suspended particulate matters (SPM) in the air sampled, in summer and winter 2019, from ten stations next to industrial units and residential areas. The samples were analyzed by gas chromatography-mass spectrometry (GC-MS). Spatial distribution maps of pollutants in the region were prepared using GIS software. The highest carcinogenic risk due to PAHs and PCBs measured as ([Formula: see text]) and ([Formula: see text], respectively. According to the US Environmental Protection Agency limit ([Formula: see text]), the cancer risks from PAH compounds were significant and need further investigation. The PCB cancer risks were within acceptable ranges. The highest adsorption ratios for PAHs were obtained through skin and PCBs by ingestion. The maximum measured non-carcinogenic hazard indexes (HI) turned out to be 0.037 and 0.023 for PAH and PCB, respectively, and were reported as acceptable risks. The predominant source of PAH in industrial areas was liquid fossil combustion, and in urban areas replaced by coal-wood-sugarcane combustion. Petrochemical complexes, flares, power plants (69%), electric waste disposal sites, and commercial pigments (31%) were reported as PCB sources. Industries activities were the most effective factors in producing the highest level of carcinogenic compounds in the region, and it is necessary to include essential measures in the reform programs.

Hydration development of blended cement paste with granulated copper slag modified with CaO and Al2O3

Granulated copper slag (GCS) is currently applied to partial cement replacement as a supplementary cementitious material (SCM), but with a low rate due to its low pozzlanic activity. In this contribution we introduce an approach to enhance the reactivity of GCS by modifying the mineral structure using calcium oxide (CaO) and aluminum oxide (Al2O3) both by 10 wt.%, in a molten state. Blended cement pastes were formulated using cement (70 wt.%) and the modified GCS (30 wt.%). The development of hydration heat and strength were examined using isothermal calorimetry and strength tests, respectively. The mineral composition and microstructure of hydration products for different reaction periods were examined using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Also, toxicity characteristic leaching procedure (TCLP) was performed on the samples. Results showed an increase in the hydration heat emission rate from the early hydration and the compressive strength of blended cement paste after curing for 28 days, indicating that the addition of CaO and Al2O3 in GCS improves pozzolanic activity. XRD and SEM-EDS analysis indicated that the modified GCS consumed more calcium hydroxide (CH) accompanied by increased generation of calcium silicate hydrate (C–S–H) gels in blended cement with a microstructure containing more gel phases and fewer pores, forming a more compact structure. Leaching of heavy metals of paste samples was lower than Environmental Protection Agency (EPA) limit. It is possible to apply the modified GCS as a sustainable material to promote cleaner production for cement and concrete industries.

Stabilization of heavy metals in soil and leachate at Dompoase landfill site in Ghana

The levels of heavy metals pollution in water and soil around landfill sites are increasing due to the indiscriminate dumping of domestic and industrial wastes at these sites. This research was conducted to study the characterisation and stabilisation of heavy metals in soils and leachate at the Dompoase landfill site, Kumasi-Ghana. Nine surface composite soil samples (< 40 cm deep) were collected at Dompoase landfill site from the middle (hotspot) of the landfill site through a 15 m radius away from the landfill cell where there were no dumping activities. Untreated leachate sample was also collected from a dugout around the landfill cell at a 4 m distance. This untreated leachate sample is estimated to be over 10 years and has a pH of 7.5. Physicochemical properties (i.e., electrical conductivity, pH, temperature, moisture and clay contents) and heavy metals (i.e., Cu, Cd, Fe, Ni and Zn) analyses were conducted on the collected samples. The results showed that the mean concentrations of all the heavy metals in soil studied were all above the Ghana Environmental Protection Agency (EPA) and WHO guidelines with the exception of Ni. All the psychochemical parameters were also within the EPA guidelines. Concentrations of Ni and Cd in the leachate sample were low and could not be detected. Cu and Zn recorded concentrations below the EPA and WHO guidelines while Fe recorded concentrations above the EPA and WHO limits. The contamination factor revealed that Cu (CF = 0.00) can be classified as exhibiting low contamination with Fe (CF = 1.50), Cd (CF = 1.80) and Zn (CF = 2.35) showing moderate contaminations. Low-grade CaO in varying quantities was utilised as stabilising agent to stabilise the heavy metals within various samples for a 21-day period. The physicochemical properties were monitored within the 21-day period during the heavy metal stabilisation. The results showed a percentage reduction in concentrations of metals within the period. The work shows that low-grade CaO can effectively be used in the remediation of contaminated sites as a result of anthropogenic activities.

A sensitive electrochemical analysis for cadmium and lead based on Nafion-Bismuth film in a water sample

This study presents a simple, low-cost, sensitive and environmentally friendly approach for the simultaneous electrochemical determination of lead and cadmium based on a commercial screen-printed gold electrode (SPGE) with Nafion and an in situ bismuth film. The developed sensor was coated with a Nafion polymer to reduce the interference and enhance the stability and reproducibility of the gold working electrode and an in situ bismuth film to increase the sensitivity and achieve a low detection limit. Electrochemical properties were investigated using anodic stripping square voltammetry. The composite film was characterized using cyclic voltammetry, and scanning electron microscopy was carried out for the morphological characterization of the modified electrode. It was found that the prepared electrode has high sensitivity and good repeatability with a limit of detection below the Environmental Protection Agency limits (5 µg/L Cd and 10 µg/L Pb). The linear calibration curves for Pb(II) ranged from 20 ppb to 300 ppb, and for Cd(II), they ranged from 50 ppb to 300 ppb. The detection limits (S/N = 3) were estimated to be 3 ppb for Pb(II) and 4 ppb for Cd(II). This method was effectively applied in the application of river and tap water samples, and the results were compared with flame-atomic absorption spectroscopy analysis.

Parts per trillion detection of heavy metals in as-is tap water using carbon nanotube microelectrodes

Heavy metal contamination of drinking water is a major global issue. Research reports across the globe show contamination of heavy metals higher than the set standards of the World Health Organization (WHO) and US Environmental Protection Agency (EPA). To our knowledge, no electrochemical sensor for heavy metals with parts per trillion (PPT) limits of detection (LOD) in as-is tap water has been reported or developed. Here, we report a microelectrode that consists of six highly densified carbon nanotube fiber (HD-CNTf) cross sections called rods (diameter ∼69 μm and length ∼40 μm) in a single platform for the ultra-sensitive detection of heavy metals in tap water and simulated drinking water. The HD-CNTf rods microelectrode was evaluated for the individual and simultaneous determination of trace level of heavy metal ions i.e. Cu2+, Pb2+ and Cd2+ in Cincinnati tap water (without supporting electrolyte) and simulated drinking water using square wave stripping voltammetry (SWSV). The microsensor exhibited a broad linear detection range with an excellent limit of detection for individual Cu2+, Pb2+ and Cd2+ of 6.0 nM, (376 ppt), 0.45 nM (92 ppt) and 0.24 nM (27 ppt) in tap water and 0.32 nM (20 ppt), 0.26 nM (55 ppt) and 0.25 nM (28 ppt) in simulated drinking water, respectively. The microelectrode was shown to detect Pb2+ ions well below the WHO and EPA limits in a broad range of water quality conditions reported for temperature and conductivity in the range of 5 °C–45 °C and 55 to 600 μS/cm, respectively.

In Situ Preconcentration and Quantification of Cu2+ via Chelating Polymer-Wrapped Multiwalled Carbon Nanotubes.

Trace analysis of heavy metals in complex, environmentally relevant matrices remains a significant challenge for electrochemical sensors employing stripping voltammetry-based detection schemes. We present an alternative method capable of selectively preconcentrating Cu2+ ions at the electrode surface using chelating polymer-wrapped multiwalled carbon nanotubes (MWCNTs). An electrochemical sensor consisting of poly-4-vinyl pyridine (P4VP)-wrapped MWCNTs anchored to a poly(ethylene terephthalate) (PET)-modified gold electrode (r = 1.5 mm) was designed, produced, and evaluated. The P4VP is shown to form a strong association with Cu2+ ions, permitting preconcentration adjacent to the electrode surface for interrogation via cyclic voltammetry. The sensor exhibited a detection limit of 0.5 ppm with a linear range of 1.1–13.8 ppm (16.6–216 μM) and a relative standard deviation (RSD) of 4.9% at the Environmental Protection Agency (EPA) limit of 1.3 ppm. Evaluation in tap water, lake water, ocean water, and deionized water rendered similar results, highlighting the generalizability of the presented preconcentration strategy. The advantages of electrochemical analysis paired with polymeric chelation represent an effective platform for the design and deployment of heavy metal sensors for continuous monitoring of natural waters.

Influence of Uranium Concentration and pH on U-Phosphate Biomineralization by Caulobacter OR37

Uranium contamination of soils and groundwater in the United States represents a significant health risk and will require multiple remediation approaches. Microbial phosphatase activity coupled to the addition of an organic P source has recently been studied as a remediation strategy that provides an extended release of inorganic P (Pi) into U-contaminated sites, resulting in the precipitation of meta-autunite minerals. Previous laboratory- and field-based biomineralization studies have investigated environments with relatively high U concentrations (>20 μM). However, most contaminated sites have much lower U concentrations (<2 μM). The Environmental Protection Agency (EPA) limit for U in drinking water is 0.126 μM. Reaching this regulatory limit becomes challenging as U concentrations approach autunite solubility. We studied the precipitation of U(VI)-phosphate minerals by an environmental isolate of Caulobacter sp. (strain OR37) from an Oak Ridge, Tennessee, U-contaminated site. Abiotic U(VI) solubility experiments reveal that U(VI)-phosphate minerals do not form in the presence of excess Pi (500 μM) when U(VI) concentrations are <1 μM and pH is <5. When OR37 cells are reacted under the same conditions with Pi or glycerol-2-phosphate, U(VI)-phosphate mineral formation was observed, along with the formation of intracellular polyphosphate granules. These results show that bacteria provide supersaturated microenvironments needed for U(VI)-phosphate mineralization while hydrolyzing organic P sources. This provides a pathway to lower U concentrations to below EPA limits for drinking water.

Nitrogen-fertilizer recovery from urban sewage via gas permeable membrane: Process analysis, modeling, and intensification

Feasibility of recovering nitrogen (N)-fertilizers from sewage has gained attention recently due to concerns about the sustainability of the Haber-Bosch process in producing N-fertilizers and of the nitrification–denitrification processes in removing N from wastewaters. This study proposes a non-pressurized gas permeable membrane reactor (GPMR) with the potential to recover high-purity N-fertilizer at lower energy demand than current technologies. Performance of the GPMR in recovering N-fertilizer from the following two waste streams of sewage-origin is demonstrated: 1) centrate generated by anaerobic digestion of primary and secondary sludge; and 2) aqueous phase generated by hydrothermal liquefaction of sewage-grown algal biomass. A process model developed for the GPMR was calibrated using test results on a synthetic feed, and validated using results from the tests on the above two waste streams. Temporal ammoniacal-N concentrations predicted by the model agreed well with the measured values (r2 = 0.82; n = 70). Tests conducted on the two wastes at 24–25 °C indicated that feed-side pH of 10 and mild mixing of the feed maximized N-fertilizer recovery. The GPMR was able to recover 80–100% of ammoniacal-nitrogen from both waste streams, yielding 2–86 g of ammonium sulfate from 1 L of the feed. Energy dispersive X-ray analysis and heavy metal analysis of ammonium sulfate recovered from both feeds confirmed compliance with the US Environmental Protection Agency limits for use as fertilizer. Confocal microscopic images of virgin and used membrane surfaces were examined to assess membrane fouling. A process intensification analysis was performed to relate the physical parameters to the performance of the GPMR and to identify areas for further studies.

Chemical characteristics and sources of ambient PM2.5 in a harbor area: Quantification of health risks to workers from source-specific selected toxic elements.

Samples of ambient PM2.5 were collected in the Qingdao harbor area between 21 March and May 25, 2016, and analyzed to investigate the compositions and sources of PM2.5 and to assess source-specific selected toxic element health risks to workers via a combination of positive matrix factorization (PMF) and health risk (HR) assessment models. The mean concentration of PM2.5 in harbor area was 48μgm-3 with organic matter (OM) dominating its mass. Zn and V concentrations were significantly higher than the other selected toxic elements. The hazard index (HI) and cancer risk (Ri) of all selected toxic elements were lower than the United States Environmental Protection Agency (USEPA) limits. There were no non-cancer and cancer risks for workers in harbor area. The contributions from industrial emissions (IE), ship emissions (SE), vehicle emissions (VE), and crustal dust and coal combustion (CDCC) to selected toxic elements were 39.0%, 12.8%, 24.0%, and 23.0%, respectively. The HI values of selected toxic elements from IE, CDCC, SE, and VE were 1.85×10-1, 7.08×10-2, 6.36×10-2, and 3.37×10-2, respectively; these are lower than the USEPA limits. The total cancer risk (Rt) value from selected toxic elements in CDCC was 2.04×10-7, followed by IE (6.40×10-8), SE (2.26×10-8), and VE (2.18×10-8). CDCC and IE were the likely sources of cancer risk in harbor area. The Bo Sea and coast were identified as the likely source areas for health risks from IE via potential source contribution function (PSCF) analysis based on the results of PMF-HR modelling. Although the source-specific health risks were below the recommended limit values, this work illustrates how toxic species in PM2.5 health risks can be associated with sources such that control measures could be undertaken if the risks warranted it.