Integration of complete elemental mass-balanced stoichiometry and aqueous-phase chemistry for bioprocess modelling of liquid and solid waste treatment systems − Part 2: Bioprocess stoichiometry

Bioprocesses interact with the aqueous environment in which they take place. Integrated bioprocess and three-phase (aqueous−gas−solid) multiple strong and weak acid/base system models are currently being developed for a range of wastewater treatment applications including anaerobic digestion, biological sulphate reduction, autotrophic denitrification, biological desulphurization and plant-wide water and resource recovery facilities. In order to model, measure and control such integrated systems, a thorough understanding of the interactions between the bioprocesses and aqueous phase multiple strong and weak acid/bases are required. In the first of this series of five papers, the generalized procedure for deriving bioprocess stoichiometric equations was explained. This second paper presents the stoichiometric equations for the major biological processes and shows how their structure can be analysed to provide insight into how bioprocesses interact with the aqueous environment. Such insight is essential for confident, effective and reliable use of model development protocols and algorithms. It shows that the composite parameters, total oxygen demand (TOD, electron donating capacity) and alkalinity (proton accepting capacity), are conserved in bioprocess stoichiometry and their changes in the aqueous phase can be calculated from the bioprocess components. In the third paper, the measurement of the organics composition is presented. The link between the modelling and measurement frameworks of the aqueous phase, which uses the composite parameter alkalinity, is described in the fourth paper. Aqueous ionic speciation modelling is described in detail in the fifth.

Fluoride ions in groundwater of the Turkana County, Kenya, East Africa

Groundwater samples were evaluated throughout Turkana County (Kenya, East Africa) while looking for drinking water sources. Some samples showed high concentrations of fluoride with values in the range of 0.15–5.87 mg/L. Almost 50% of the samples exceeded the WHO and Kenyan potable water standard guideline value of 1.5 mg/L for drinking water quality. The hydrogeochemical studies revealed that the dominant cation in water is Na+ and the dominant anion is HCO3− resulting in Na-HCO3 type of groundwater, followed by Ca/Mg-HCO3 or Na-SO4 and Na-Cl in a few cases. Speciation modelling revealed that the groundwater is undersaturated with respect to gypsum and anhydrite, mostly undersaturated with respect to fluorite (6 samples are at equilibrium), and supersaturated or at equilibrium with respect to calcite (CaCO3). Precipitation of calcite favours the dissolution of F-rich minerals in the alkaline medium. Simultaneously, groundwater is enriched with sodium and bicarbonate, probably as a result of chemical weathering of Na-feldspar. Investigated groundwater can be presumably used for drinking purposes from 17 wells, but a detailed investigation of other trace element concentrations is necessary.

Volatile metal emissions from volcanic degassing and lava–seawater interactions at Kīlauea Volcano, Hawai’i

Volcanoes represent one of the largest natural sources of metals to the Earth’s surface. Emissions of these metals can have important impacts on the biosphere as pollutants or nutrients. Here we use ground- and drone-based direct measurements to compare the gas and particulate chemistry of the magmatic and lava–seawater interaction (laze) plumes from the 2018 eruption of Kīlauea, Hawai’i. We find that the magmatic plume contains abundant volatile metals and metalloids whereas the laze plume is further enriched in copper and seawater components, like chlorine, with volatile metals also elevated above seawater concentrations. Speciation modelling of magmatic gas mixtures highlights the importance of the S2− ligand in highly volatile metal/metalloid degassing at the magmatic vent. In contrast, volatile metal enrichments in the laze plume can be explained by affinity for chloride complexation during late-stage degassing of distal lavas, which is potentially facilitated by the HCl gas formed as seawater boils.

Rare earth elements, aluminium and silicon distribution in the fern Dicranopteris linearis revealed by μPIXE Maia analysis

Background The fern Dicranopteris linearis is a hyperaccumulator of rare earth elements (REEs), aluminium (Al) and silicon (Si). However, the physiological mechanisms of tissue-level tolerance of high concentrations of REE and Al, and possible interactions with Si, are currently incompletely known. Methods A particle-induced X-ray emission (μPIXE) microprobe with the Maia detector, scanning electron microscopy with energy-dispersive spectroscopy and chemical speciation modelling were used to decipher the localization and biochemistry of REEs, Al and Si in D. linearis during uptake, translocation and sequestration processes. Results In the roots >80 % of REEs and Al were in apoplastic fractions, among which the REEs were most significantly co-localized with Si and phosphorus (P) in the epidermis. In the xylem sap, REEs were nearly 100 % present as REEH3SiO42+, without significant differences between the REEs, while 24–45 % of Al was present as Al-citrate and only 1.7–16 % Al was present as AlH3SiO42+. In the pinnules, REEs were mainly concentrated in necrotic lesions and in the epidermis, and REEs and Al were possibly co-deposited within phytoliths (SiO2). Different REEs had similar spatial localizations in the epidermis and exodermis of roots, the necrosis, veins and epidermis of pinnae of D. linearis. Conclusions We posit that Si plays a critical role in REE and Al tolerance within the root apoplast, transport within the vascular bundle and sequestration within the blade of D. linearis.

Volatile metal emissions from volcanic degassing and lava-seawater interactions at Kīlauea Volcano, Hawai’i

Volcanoes represent one of the largest natural sources of metals to Earth’s surface. Emissions of these pollutants and/or nutrients have important implications for the biosphere. We compare gas and particulate chemistry, including metals, of the substantial magmatic (≥200 kt/day SO2) and lava-seawater interaction (laze) plumes from the 2018 eruption of Kīlauea, Hawai’i. The magmatic plume contains abundant volatile chalcophile metals (e.g. Se), whereas the laze is enriched in seawater components (e.g. Cl), yet Cu concentrations are 105 times higher than seawater. High-temperature speciation modelling of magmatic gases at the lava-air interface emphasises chloride’s critical role in metal/metalloid complexation during degassing. In the laze, concentrations of moderately (Cu, Zn, Ag) to highly volatile (Bi, Cd) metals are elevated above seawater. These metals have an affinity for chloride and are derived from late-stage degassing of distal lavas, potentially facilitated by the HCl gas formed as seawater boils. Understanding these processes yields insights into the environmental impacts of volcanism in the present day and geological past.

Regulation of dissolved phosphate through incorporation into schwertmannite

<p>Phosphate is known to absorb strongly to schwertmannite (Fe<sub>8</sub>O<sub>8</sub>(OH)<sub>6</sub>(SO<sub>4</sub>)·nH<sub>2</sub>O)<sup>1</sup> and as such, schwertmannite has been proposed to limit phosphate in solution in acid mine drainage (AMD) environments. This in turn will limit phosphate availability to the micro-organisms that live in and propagate AMD<sup>2</sup>. Here we have studied sediment samples from the Rio Tinto river in Spain collected during Europlanet field area visit to verify whether phosphate can be incorporated into sulphate-rich minerals in this river. The minerals were identified using X-ray diffraction. Our analyses show that the concentration of phosphate in the river is in the nM range. Digestion of modern sediments in nitric acid followed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis indicate that sites with sulphate-rich minerals are correlated with elevated phosphate concentrations. In addition, phosphate is also retained in ancient sediments that are dominated by goethite (FeO(OH)).</p><p>We have also conducted experiments to explore the competition between Fe<sup>3+</sup>, phosphate and sulphate ions in solution as well as the effect of this on schwertmannite nucleation. UV-Vis and Raman spectroscopy demonstrate that contact ion pairs form between Fe<sup>3+</sup> and phosphate or sulphate in solution. Particularly, phosphate and sulphate compete for Fe<sup>3+ </sup>in solution consistent with predictions by the solution speciation modelling program PHREEQC. Our experiments also show that above a critical concentration, phosphate retards the nucleation of schwertmannite. As this critical concentration is above that found in Rio Tinto river fluids, phosphate is expected to have a limited role in schwertmannite precipitation, but, its concentration is regulated by its incorporation into schwertmannite and other sulphate-bearing phases in AMD systems.</p><p>References</p><p><sup>1</sup>Eskandarpour et al. 2006, Material Transactions, 1832. <sup>2</sup>Chen et al. 2015, ISME, 1579.</p>

Thermodynamic models applied to CO2 absorption modelling

Carbon capture, utilisation, and storage (CCUS) is considered as the least cost-intensive option towards achieving the emission reduction target by 2050. One of the important technologies to remove CO2 from different gas streams is solvent-based CO2 capture. Modelling and simulation of solvent-based CO2 capture processes have been attracting a lot of attention in recent years. Thermodynamic models play a vital role in these modelling and simulation studies. Hence, this study critically reviews the thermodynamic models applied in the modelling of solvent-based CO2 capture systems over the past years, to provide a guideline for the selection of the optimum models for future studies. These models have wide applications in two main areas: equilibrium modelling [vapour-liquid equilibrium (VLE) (physical) and speciation equilibrium (chemical)], and calculation of some thermodynamic properties. VLE and speciation modelling methods are classified rigorously. VLE modelling methods are classified as homogeneous, heterogeneous, and empirical, and speciation modelling methods are classified as iterative (which could be stoichiometric and non-stoichiometric) and non-iterative. Thermodynamic models are categorised into three key families: activity-coefficient based, equation of state based, and quantum mechanical based. Theory and concepts of different thermodynamic models are presented. Some selected studies that used each family of thermodynamic models are reviewed.