Natural Water Research Articles

Optimization of the electro-photocatalytic process for the removal of formaldehyde from water using the Taguchi model

The most significant environmental issue in many nations across the world is industrial wastewater contamination with formaldehyde (a priority pollutant). Any natural water that has had industrial effluent discharged into with formaldehyde concentrations between 100 and 1000 mg/l is deemed toxic to humans. This is an applied analytical research project aimed at examining formaldehyde removal from urban drinking water using a batch electro-photocatalytic (EPC) reactor that uses ultraviolet-A (UV-A) lamp dynode and immobilized ZnO NPs on a zinc sheet-copper electrode. pH, formaldehyde content, lamp intensity, radiation duration, lamp-electrode distance, ZnO NP stacking, and current density are the factors under investigation. They were found to be in the ranges 3–11, 110–330 mg/l, 480–720 mW/cm2, 8–32 min, 1.5 cm, 1–3, and 4–12 mA/cm2, respectively. The findings demonstrate the relationship between UV-A lamp intensity, radiation duration, and current density with the elimination of formaldehyde. The experimental data better fit a first-order reaction (R2 = 0.9982). The most optimal conditions elimination (0 mg/l) of formaldehyde are achieved at pH = 11, radiation period = 8 min, two layers of ZnO NPs, and current density = 8 mA/cm2 by the Taguchi model. The results show that increasing pH, radiation period, lamp intensity, and current density all increase removal efficiency. The results show that EPC is a practical and efficient method for treating formaldehyde-contaminated drinking water at high concentrations.

Au-modified metal-organic framework photonic heterostructure as a SERS sensor for enrichment and detection of trace organic dyes and pesticides

Surface enhanced Raman scattering (SERS) sensors with excellent sensitivity, stability and repeatability are essential for the ultrasensitive analysis of trace targets. In this study, a SERS sensor was developed using a photonic heterostructure composed of Au nanoparticles (AuNPs) & Zeolitic Imidazolate Framework-8 photonic crystals (ZIF-8 PCs). The sensor aims to enrich and detect organic dyes and pesticides, with enhanced detection capabilities achieved through adjustments in AuNPs content and the band-edge effects of ZIF-8 PCs. The sensor exhibited excellent performances in detecting 4-mercaptobenzoic acid. The detection limit was 1 × 10–12 mol·L−1, with a relative standard deviation of 5.0 % and the enhancement factor of 1.439 × 1011. Furthermore, the self-enrichment function of the sensor was verified through molecular dynamics simulations. This validation enabled the SERS sensor to be effectively utilized for the analysis of Rhodamine 6 G (R6G), methylene blue (MB), Thiabendazole (TBZ) and Parathion-methyl (PTM) without complex pretreatment. The detection limits achieved were 1 × 10–12 for R6G and MB, and 1 × 10–11 mol·L−1 for TBZ and PTM, respectively. This study presented an effective strategy for constructing high-performance SERS sensors, elucidated the mechanism of analyte enrichment and achieved the detection of samples in natural lake water, which offers a new option for on-site monitoring of contaminants with a portable Raman spectroscopy.

Towards portable kits for on-site colorimetric detection of aqueous hydrazine using piperidine-thiophene-barbituric acid push-pull probe.

Owing to the carcinogenicity and environmental risks as well as the wide industrial use of hydrazine, we report herein a colorimetric probe for its ratiometric detection in pure water. The developed probe possesses push-pull architecture with 2-(piperidyn-1-yl)thiophene as the donor, N,N'-dibutylbarbituric as the acceptor, and butadiene as the spacer. In contrast to weak solvatochromic behavior in organic solvents, the probe showed distinct optical photophysical properties in water resulting from the formation of nanoscopic aggregates. The probe underwent pronounced spectral changes upon the addition of hydrazine including an 11.5-fold decrease in absorbance and ~2.4-fold fluorescence quenching. The mechanistic investigation revealed the rapid formation of hydrazone upon the interaction of the probe with hydrazine via retro-Knoevenagel reaction as confirmed experimentally and corroborated with DFT calculations. The induced colorimetric and fluorometric changes were utilized in hydrazine sensing with excellent selectivity over other biologically relevant analytes with a detection limit of 0.76 µM in aqueous media. The practical utility of the probe was assessed in real-life natural water samples, while we have also developed a cost-effective portable kit for the on-site hydrazine detection both in the solution and vapor phases.

Biogenic Sulfide-Mediated Iron Reduction at Low pH

Acid mine drainage (AMD) pollutes natural waters, but some impacted systems show natural attenuation. We sought to identify the biogeochemical mechanisms responsible for the natural attenuation of AMD. We hypothesized that biogenic sulfide-mediated iron reduction is one mechanism and tested this in an experimental model system. We found sulfate reduction occurred under acidic conditions and identified a suite of sulfate-reducing bacteria (SRB) belonging to the groups Desulfotomaculum, Desulfobacter, Desulfovibrio, and Desulfobulbus. Iron reduction was not detected in microcosms when iron-reducing bacteria or SRB were selectively inhibited. SRB also did not reduce iron enzymatically. Rather, the biogenic sulfide produced by SRB was found to be responsible for the reduction of iron at low pH. Addition of organic substrates and nutrients stimulated iron reduction and increased the pH. X-ray diffraction and an electron microprobe analysis revealed that the polycrystalline, black precipitate from SRB bioactive samples exhibited a greater diversity of iron chalcogenide minerals with reduced iron oxidation states, and minerals incorporating multiple metals compared to abiotic controls. The implication of this study is that iron reduction mediated by biogenic sulfide may be more significant than previously thought in acidic environments. This study not only describes an additional mechanism by which SRB attenuate AMD, which has practical implications for AMD-impacted sites, but also provides a link between the biogeochemical cycling of iron and sulfur.

Explainable Ensemble Learning Approaches for Predicting the Compression Index of Clays

Accurate prediction of the compression index (cc) is essential for geotechnical infrastructure design, especially in clay-rich coastal regions. Traditional methods for determining cc are often time-consuming and inconsistent due to regional variability. This study presents an explainable ensemble learning framework for predicting the cc of clays. Using a comprehensive dataset of 1080 global samples, four key geotechnical input variables—liquid limit (LL), plasticity index (PI), initial void ratio (e0), and natural water content w—were leveraged for accurate cc prediction. Missing data were addressed with K-Nearest Neighbors (KNN) imputation, effectively filling data gaps while preserving the dataset’s distribution characteristics. Ensemble learning techniques, including Random Forest (RF), Gradient Boosting Decision Trees (GBDT), Extreme Gradient Boosting (XGBoost), and a Stacking model, were applied. Among these, the Stacking model demonstrated the highest predictive performance with a Root Mean Squared Error (RMSE) of 0.061, a Mean Absolute Error (MAE) of 0.043, and a Coefficient of Determination (R2) value of 0.848 on the test set. Model interpretability was ensured through SHapley Additive exPlanations (SHAP), with e0 identified as the most influential predictor. The proposed framework significantly improves both prediction accuracy and interpretability, offering a valuable tool to enhance geotechnical design efficiency in coastal and clay-rich environments.

A green procedure for the determination of bioavailable forms of aluminum in natural waters by electrothermal atomic absorption spectroscopy combined with microextraction technique.

Aluminum is a prevalent element in nature, but bioavailable forms of aluminum are toxic to plants, animals, and humans. The present study is dedicated to the development of an ecologically friendly, fast, simple, reliable, sensitive, and accurate improved procedure for the determination of subtrace concentrations of bioavailable forms of aluminum in natural waters. The procedure includes the separation and pre-concentration of bioavailable forms of aluminum using vortex-assisted liquid-liquid microextraction (VALLME) of ionic associates with salicylaldehyde 4-picolinhydrazone (SAPH) and sodium dodecyl sulfate (DDSNa) by isoamylacetate (200μl) and direct electrothermal atomic absorption spectroscopy (ETAAS). The SAPH reagent interacts only with water-soluble forms of aluminum. SAPH is used for the pre-concentration of bioavailable forms of aluminum as well as a chemical modifier; it increases the absorbance and the precision of the analytical signal of aluminum. The calibration curve shows the linear dependence in the range of 0.05-86μg⋅L-1 of the aluminum concentration (R2 = 0.992), with the limit of detection at 0.015μg⋅L-1 and the limit of quantification at 0.05μg⋅L-1. The accuracy of the proposed procedure for bioavailable forms of aluminum determination was verified on model solutions and against a reference method on natural samples of river and lake waters (RSD 3.2-5.2%, recovery 97.1-103.4%).

Evaluating the efficacy of microalgal-bacterial granular sludge system in lake water remediation.

The microalgal-bacterial granular sludge (MBGS) process is attracting attention as a green wastewater treatment technology. However, research on the application of MBGS in lake water remediation is limited. Thus, this experiment investigated the feasibility and the efficacy of the MBGS process for the treatment of natural lake water in a continuous-flow tubular reactor. The averageremoval efficiencies of COD, NH4+-N, NO3--N, NO2--N, TN, PO43--P, TP, and turbidity by MBGS system in the day/night cycles were 50.10/61.39%, 63.52/75.23%, 43.37/73.57%, 90.72/93.48%, 78.30/80.02%, 71.13/74.62%, 65.08/70.57%, 92.32/89.84%, respectively. As the experiment progressed, the total chlorophyll content in MBGS decreased as the granule size increased, while the extracellular polymeric substances content increased, suggesting that thelake water contributed to bacterial growth and favored the stability of MBGS. Moreover, the eukaryotic microorganisms were dominated by Chlorophyta and Rotifera, and prokaryotic microorganisms were dominated by Proteobacteria in MBGS. By promoting the decomposition of various organic compounds in the lake water and inhibiting sludge expansion, these microorganisms helpthe MBGS system tomaintain excellent granular characteristics and performance. Overall, the MBGS system proved to be a feasible option for the remediation of natural lake waters.

Electro-peroxone process for triclocarban and triclosan removal and reclaimed water disinfection

Water reclamation is a known solution to the water scarcity problem; however, concern over water contamination by emerging contaminants and pathogens is growing. This study investigates the simultaneous removal of emerging contaminants and pathogens by applying the continuous-flow electro-peroxone process. Triclocarban (TCC) and triclosan (TCS) were selected as model contaminants of emerging concern, while Escherichia coli strain DH5α was chosen as a representative pathogen. The effects of the initial concentration, water flow rate, and water matrices (direct reclaimed water (treated wastewater), indirect reclaimed water (groundwater), and natural surface water) on TCC, TCS, and E. coli removal were examined. The removal efficiency of TCC (2 mg/L) was up to 92.54 % in 120 min. TCS (non-ozone-resistant compound) was effectively removed in 15 min, while E. coli was instantly inactivated in 3 min. The increase in flow rate decreased the electrical energy per order (EEO) of TCC removal, with the lowest EEO of 19 kWh/m3 at 45 mL/min. The dissolved organic carbon content in water matrices (consuming O3 and H2O2) markedly inhibited the TCC removal, and the kinetic rate as well as reduced 3,4-dichloroaniline (intermediate product) formation. Overall, these findings show the use of the electro-peroxone process is effective in mitigating ozone- and non-ozone-resistant emerging contaminants (TCC and TCS) and pathogens with consideration of water matrices for reclaimed water application.

Uniformly dispersed FeOOH nanoparticles supported on alumina-carbon nanosheets for Cr(VI) removal

The mesoporous alumina-carbon nanosheets supported FeOOH nanoparticles were prepared by a facile and cost-effective hydrothermal synthesis for Cr(VI) removal in the wastewater, based on the affinity and selectivity of FeOOH and the accelerated mass transfer of nanosheet structure. The prepared nanoparticles with a small size of 2–5 nm were uniformly dispersed over the alumina-carbon nanosheets, attributed to the metal interaction and mesoporous confinement. The acid property after the introduction of alumina induced a positive charge on the surface of the adsorbent, which could enhance the adsorption of negatively charged metal ions. The Cr(VI) removal efficiency with the Al/Fe ratios showed a similar volcano curve. When Al/Fe ratio was around 3.3 and pHpzc was about 7.1, the adsorbent exhibited the best Cr(VI) removal efficiency of 99.4 %, owing to a large specific surface area, and small nanoparticle size, combined with abundant moderate-strong acid content of 294.5 μmol NH3 g−1.The Langmuir model could describe the adsorption process well, and the kinetic data was consistent with Pseudo-second-order. The thermodynamics revealed that the reaction process was spontaneous and endothermic. The adsorbent maintained a high removal efficiency of more than 80 % after running for five cycles and kept over 95 % under ionic co-existence and natural water conditions. Therefore, this study provides a new insight into the rational construction of efficient adsorbents with low-cost Cr(VI) removal.

Adsorption of Se(IV) on kaolinite and montmorillonite in the presence of fulvic acid

This study investigates the influence of fulvic acid, a representative of aquatic natural organic matter (NOM), on the pH-dependent adsorption of Se(IV) on kaolinite and montmorillonite. Given their negative charges in aqueous solutions, Se(IV) and fulvic acid compete for the limited and identical adsorptive sites of clay minerals, particularly in neutral to alkaline environments. This competition was most pronounced under acidic conditions, where both Se(IV) and fulvic acid adsorption are favored. At pH 3, the presence of 20–80 mg·L−1 fulvic acid reduced the Se(IV) adsorption by up to half on both clay adsorbents. However, in near-neutral to alkaline pH regions (pH 6 to 10), the competitive interaction between Se(IV) and fulvic acid was less pronounced, since the adsorption of both fulvic acid and Se(IV) decreased. In particular for kaolinite, a rise in Se(IV) adsorption was evident at lower fulvic acid concentrations (20 mg·L−1). This phenomenon arises from the absence of aqueous complexes between Se(IV) and fulvic acid under acidic conditions, contrasting with their strong interaction under alkaline conditions as observed in the ATR-FTIR spectra. This study sheds light on the influence of NOM on the mobility of Se(IV) in natural waters, an aspect yet to be thoroughly explored.

Evaluating performance characteristics of recycled aggregate concrete: A study through experimentation

This study surveys the display characteristics of Recycled Aggregate Concrete (RAC) through experimentation, focusing on key material properties and mix degrees. The RAC blends, signified as R-0 and R-45 addressing various rates of Recycled Concrete Aggregate (RCA) substitution, were examined for new properties, compressive strength, and solidness. The blend extents included concrete (C), fine aggregate (FA), natural coarse aggregate (NCA), RCA, silica fume, water, and superplasticizer (SP). New properties, for example, compaction factor, alongside 28 days compressive strength, were determined for all RAC blends. Sturdiness tests included corrosive opposition, scraped area obstruction, and water penetrability tests. Results showed that RAC displayed decreased compressive strength and expanded weight reduction contrasted with traditional concrete (R-0) when exposed to corrosive assault. Be that as it may, the compressive strength decrease was less articulated in RAC exposed to sulfate assault, credited to the arrangement of ettringite. Scraped area obstruction tests uncovered that R-45 had higher normal misfortune in thickness contrasted with R-0 however remained inside adequate cutoff points. Water porousness tests showed higher profundity of entrance in RAC contrasted with R-0, conceivably because of stuck mortar. Nonetheless, both RAC and R-0 showed satisfactory water assimilation values. The study suggests that RAC could offer viable alternatives in construction applications while addressing sustainability concerns. Further research is recommended to explore RAC's performance under elevated temperatures and correlate split tensile strength with corresponding results.

Green Syngas Production from Natural Lignin, Sunlight, and Water over Pt-Decorated InGaN Nanowires.

Transformation of lignin to syngas can turn waste into treasure yet remains a tremendous challenge because of its naturally evolved stubborn structure. In this work, light-driven reforming of natural lignin in water for green syngas production is explored using Pt-decorated InGaN nanowires. The spectroscopic characterizations, isotope, and model compound experiments, as well as density function theory calculation, disclose that among a variety of groups including aromatic ring, -OH, -OCH3, -C3H7 with complex chemical bonds of O-H, C-H, C-C, C-O, etc., InGaN nanowires are cooperative with Pt for preferably breaking the C-O bond of the rich O-CH3 group in lignin to liberating ⋅CH3 by photogenerated holes with a minimum dissociation energy of 2.33 eV. Syngas are subsequently yielded from the continuous evolution of ⋅CH3 and ⋅OH from photocatalytic reforming of lignin in water. Together with the superior optoelectronic attributes of Pt-decorated InGaN nanowires, the evolution rate of syngas approaches 43.4 mol ⋅ g-1 ⋅ h-1 with tunable H2/CO ratios and a remarkable turnover number (TON) of 150, 543 mol syngas per mol Pt. Notably, the architecture demonstrates a high light efficiency of 12.1 % for syngas generation under focused light without any extra thermal input. Outdoor test ascertains the viability of producing syngas with the only inputs of natural lignin, water, and sunlight, thus presenting a low-carbon route for synthesizing transportation fuels and value-added chemicals.

High-Current Water-Enabled Electricity Generation in Mushrooms via Synergistic Ion Sieving and Adsorption.

Water-enabled electricity generation (WEG), which harvests energy from the natural water cycle, is a novel strategy for producing green electricity. Taking advantage of the ion sieving effect based on evaporation-induced water flows in charged nanopores, various WEG devices have been developed. Here, we report that a carbonized mushroom produces a record-high current output of up to 96.7 μA, which is attributed to a unique ion adsorption effect combined with an ion sieving effect. Specifically, the natural gradient potential from root to cap in a mushroom caused by tissue differentiation adsorbs different ions, enhancing the traditional ion sieving current. In synergy with the two effects, the mushroom can operate under a broad range of concentrations (0 to 0.6 mol L-1) and represents significant improvements in current, duration, and total charge transfer. These findings reveal the hidden talent of mushrooms as natural materials for WEG, providing inspiration for the development of high-performance WEG devices.

Destruction of perfluorooctane sulfonic acid (PFOS) in gas sparging incorporated UV-indole reductive treatment system – Benefits and challenges

Ultraviolet (UV) reductive treatment systems that generate hydrated electrons (eaq-) have emerged as a promising technology for the destruction of chemically inert per- and polyfluoroalkyl substances (PFAS). Here, we report on the evaluation of an indole derivative-based UV reductive treatment system that utilizes the amphipathic properties of PFAS at the gas-water interface (via nitrogen (N2) sparging) for more energy-efficient destruction of perfluorooctane sulfonic acid (PFOS). Results from this work illustrated that N2 sparging within UV systems can enhance the degradation and defluorination of PFOS compared to non-sparged conditions, but their overall treatment efficiency is low to industry standard. The inadequate system performance is likely originated from the insufficient accumulation of electron sources at the gas-water interface and their low water solubility level. In addition, carbonate species, which are ubiquitous in natural water and commonly applied as buffers in UV reductive treatment systems, negatively impact PFOS defluorination when indole is the electron source. The species-specific quenching imposed by carbonate species (e.g., HCO3- > H2CO3*) indicates that naturally occurring constituents and varying reactor conditions can substantially influence the remediation of PFOS. Other notable findings in this work include: 1) gramine, a cationic indole derivative, was able to remove > 99 % PFOS mass via electrostatic interaction within 0.5 h of reaction, signifying the electron source's structural property importance in UV reductive treatment systems, and 2) energy consumption calculations showed indole species are less energy-efficient as electron sources for PFOS destruction comparing to sulfite-iodide, but performance tradeoffs exist in both systems. The results of this work revealed both the benefits and challenges of utilizing N2 sparging and indole derivatives in UV-PFAS reductive treatment processes and provided critical information needed to improve the prediction and design of similar PFAS destruction technologies.

Fatigue mechanical properties and Kaiser effect characteristics of the saturated weakly cemented sandstone under different loading rate conditions

Weakly cemented sandstone (WCS) is a unique rock type widely distributed on the surface. Environmental factors such as groundwater and stress variations easily influence its fatigue mechanical properties and fracture characteristics. To design and evaluate the long-term stability of surrounding rock support in tunnel excavation and underground resource mining projects, investigating the fatigue mechanical properties and acoustic emission (AE) response characteristics of saturated WCS under different loading rates is of great practical and theoretical significance. This study employed experimental techniques such as X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and natural water absorption tests to investigate the mineral composition, pore size, and connectivity characteristics of WCS. The multi-level cyclic loading-unloading tests (MCLU) combined with the AE system were conducted on dry and saturated WCS specimens at different loading rates. The results reveal that the deformation modulus of these specimens initially increases and then decreases under cyclic loading conditions. Water significantly influences the fatigue strength and deformation resistance of sandstone. As the loading rate increases, the range of RA values broadens, accompanied by a marked increase in the number of AE signals with high RA values. Saturated sandstone specimens are more prone to developing macroscopic shear fracture surfaces. Water has a more substantial effect on the stress distribution ranges corresponding to the response of the Kaiser effect in WCS than loading rates. The capacity of the Kaiser effect to indicate the extent of rock damage is intricately linked to the progression of internal micro-cracks. When internal damage surpasses the critical value of the Kaiser effect memory damage, the accelerated propagation of shear cracks becomes pivotal in the internal damage of the sandstone. It seems that the presence of water within the interior of the rock may facilitate the dissolution of K-feldspar in WCS, which could result in the formation of kaolinite, which will be further transformed into illite. The hydration expansion of illite may further exacerbate the deterioration effect of the mechanical properties of WCS.

Assessment of water quality variation: tool for effective water treatment system operations

Water quality and treatment systems are dynamic because they constantly undergo seasonal variations in water chemistry, varying plant operating conditions, and new environmental laws, among others. Because of this, proper monitoring is essential to ensure that the water supplied by the treatment system safeguards public health from waterborne diseases. Selected surface water quality parameters as inflow were obtained before treatment against the treated water for different hydrological periods (2009 – 2019) from a water treatment system to determine the trend in water quality variation, water quality index, and effectiveness of the treatment process. Each hydrologic year had varying concentrations of selected parameters for raw and treated water quality. The concentration values of pH, electrical conductivity, total hardness, calcium and magnesium hardness, chloride, and total dissolved solids of the natural source water were within the recommended limit. Turbidity concentrations were above the recommended value for each hydrologic year, values ranging from 14.65 – 57.98 NTU, and iron concentration was above the permissible for 2010 and 2012. Selected parameters were all within the threshold limit after treatment with a water quality index (WQI) ranging between 1.09 – 39.39, rated as good/excellent water quality. The treatment system operations were effective throughout the observation period. However, turbidity, iron and hardness should be tested more frequently during the operational and verification monitoring process.

Investigation of bioelectricity generation potential of pharmaceutical wastewater through microbial fuel cells operation

Pharmaceutical wastewater (PWW) as an industrial wastewater presents a potential hazard to natural water systems. This wastewater contains organic matter, which is toxic to the various life forms of the system. PWW is one of the major health problems nowadays, not only for aquatic life but also for human beings and the environment. There are several methods such as filtration, advanced oxidation, coagulation and biological membranes been used for the treatment of PWW, however, all of these methods are limited in their results and applications. In this present study, Microbial Fuel Cells (MFCs) represent a new method for treating wastewater, generating electricity, and reducing COD simultaneously. A novel H-type MFC connected with a graphite electrode has been designed for bioelectricity generation, COD reduction as well as PWW treatment. The treatment of PWW showed adequate bioelectricity generation such as Voltage, Current, and Power, of about 775 mV, 0.421 mA, and 583.70 mW at 100 Ω respectively. The percentage of the COD removed ranged from 95.2-96.7% and 12-34% at the different process variables. This study established bioelectricity generation and bio-treatment of PWW.

Synergistic on engineering layered N-doped carbon/MXene heterostructure: A potential scaffold for simultaneous electrochemical detection of Cu2+ and Hg2+ ions

The presence of heavy metal ions (HMIs) like Cu2+ and Hg2+ in natural water and foods is a major health and environmental concern. Thus advanced electrochemical sensors are required to monitor these ions. Herein, we introduce a nitrogen-rich carbon-MXene composite (layered N-doped carbon/MXene) as an electrochemical sensor suitable for the simultaneous detection of Cu2+ and Hg2+. Synthesizing 2D/2D heterostructure interfaces using controlled thermal decomposition conditions with the incorporation of quaternary nitrogen from choline chloride and the formation of hydrogen bonds of urea within the MXene (Ti3C2Tx) provided active surfaces area that is suitable for the detection of Cu2+ and Hg2+. The intermediate structure of layered N-doped carbon/MXene, had a nitrogen content of ∼6 %, maximized sensitivity for Cu2+ and Hg2+. The layered N-doped carbon/MXene composite exhibited excellent electrochemical sensing for Cu2+ and Hg2+ in 0.1 M acetate buffer at low sensing potentials. The limits of detection (LODs) of layered N-doped carbon/MXene were 0.019 and 0.056 µM with a sensitivity of 114.54 and 64.317 µA µM−1 cm−2 for Cu2+ and Hg2+, respectively. Furthermore, the layered N-doped carbon/MXene heterostructure exhibited high selectivity for Cu2+ and Hg2+ in the presence of potentially interfering common metal ions. This study introduces a promising advanced material for rapid Cu2+ and Hg2+ detection in food and environmental applications.

Dissolved ammonia catalyzes proto-dolomite precipitation at Earth surface temperature

Marine carbonate rocks are the major reservoir of carbon through CaCO3 and CaMg(CO3)2 precipitation extracting CO2/HCO3- from the atmosphere/oceans; hence dolomite is one of the major sinks in the global carbon cycle. Most ancient dolomite has been considered as mainly precipitated under Earth surface conditions. Previous studies have demonstrated that microbes can mediate dolomite formation. However, the “microbial dolomite” model is not sufficient to explain the dolomite that shows no or little evidence of a microbial origin. Although attempted for decades, the synthesis of inorganically-produced dolomite at normal temperatures (<50 °C) has been relatively unsuccessful. Hence, this "dolomite enigma" has been one principal research focus this century. Here we demonstrate that NH3 catalyzes proto-dolomite precipitation inorganically with higher Mg/Ca molar ratios and CO32- activity at normal temperatures of 30 °C and 40 °C. NH3 dissolution increases the alkalinity of the solution and transformes into NH4+ ions, which prefer to bond with H2O on Mg[(H2O)6]2+ rather than free H2O, thus releasing Mg2+ to facilitate proto-dolomite nucleation. Furthermore, the low dielectric constant and low dipole moment allow NH4+ absorbed on crystal surfaces to lower the energy barrier of Mg[(H2O)6]2+ dehydration, promoting proto-dolomite nucleis growth. The system for proto-dolomite precipitation in our experiments closely simulates the natural aqueous environment. This study brings new insights to understanding the mechanisms of dolomite precipitation in natural waters.

Calcium self-release bioremediation system combined with microbially induced calcium precipitation for the removal of ammonium nitrogen, phosphorus and heavy metals

Natural landscape water and substrate were taken to simulate the release of substrate pollutants in micropolluted water bodies, and a calcium silicate- sodium alginate (CS-SA) bioremediation system was constructed. The removal of ammonium nitrogen (NH4+-N), total nitrogen (TN) and Phosphate (PO43--P) were 99.14 %, 98.90 % and 84.44 %, respectively. The Ca2+ continuously released by CS-SA provided good microbial-induced calcium precipitation (MICP) conditions for Acinetobacter calcoaceticus strain HM12, and the removal efficiency of both Zn2+ and Cd2+ was 100 %, and the pH after remediation was consistent with that of natural water bodies. NH4+-N was removed by heterotrophic nitrification- aerobic denitrification (HN-AD) of strain HM12, and heavy metals and phosphorus were removed by co-precipitation and adsorption by MICP. High-throughput sequencing results showed that strain HM12 was effective as a bioinoculant for the remediation of the aquatic environment. The construction and operation of this bioremediation system provided a method for micropolluted water treatment and recovery of phosphorus and heavy metals.