Degradation of dissolved sulfide in water using multi-hole dielectric barrier discharge

Biogas obtained from livestock manure is used as fuel for solid oxide fuel cells. Although H2S is a typical biogas, it is a fatal disadvantage for fuel-cell power generation and, thus, must be removed. In this study, we proposed an effective method for sulfide removal from water using a multi-hole dielectric barrier discharge (DBD) system. In this system, active species, such as ozone, ultraviolet rays, hydroxyl radicals, and hydrogen peroxide, were simultaneously generated. Under optimal conditions, dissolved sulfide (initial concentration: 120 mg/L) was completely degraded within 10 min in air plasma and 6 min in oxygen plasma. Changes in the physical properties of the sulfide-treated water were confirmed by measuring the pH, oxidation-reduction potential, and dissolved oxygen. Results of the by-product analysis showed that sulfide was converted into sulfate by reacting with a large amount of ozone, and the active species were emitted from the multi-hole DBD system. In summary, multi-hole DBD technology has demonstrated merit as a water-contaminant purification technology and for the removal of dissolved sulfide.

Chitosan-assisted self-assembly of flower-shaped ε-Fe2O3 nanoparticles on screen-printed carbon electrode for Impedimetric detection of Cd2+, Pb2+, and Hg2+ heavy metal ions in various water samples

This study focuses on the fabrication of a novel sensing platform on a screen-printed carbon electrode, modified by a combination of hydrothermally synthesized iron dioxide (ε-Fe2O3) nanoparticles and Chitosan (CS) biopolymer. This unique organic-inorganic hybrid material was developed for Electrochemical Impedance Spectroscopy (EIS) sensing, specifically targeting heavy metal ions that include Hg2+, Cd2+, as well as Pb2+. The investigation encompassed a comprehensive analysis of various aspects of the prepared Fe2O3 and CS/ε-Fe2O3 nanocomposites, including phase identification, determination of crystallite size, assessment of surface morphology, etc. CS/ε-Fe2O3 was drop-casted and deposited on the Screen-Printed Electrode (SPE). The resulting sensor exhibited excellent performance in the precise and selective quantification of Hg2+, Cd2+, and Pb2+ ions, with minimal interference from other substances. The fabricated sensor exhibits excellent performance as the detection range for Hg2+, Cd2+, and Pb2+ ions linearity is 2-20 μM, sensitivity, and LOD are 243 Ω/ μM cm2 and 0.191 μM, 191 Ω/μM cm2, and 0.167 μM, 879 Ω/ μM cm2, and 0.177 μM respectively. The stability of the CS/ε-Fe2O3/SPE electrode is demonstrated by checking its conductivity for up to 60 days for Hg2+, Cd2+, and Pb2+ ions. The reusability of the fabricated electrode is 14 scans, 13 scans, and 12 scans for Hg2+, Cd2+, and Pb2+ ions respectively. The findings indicate the successful development of an innovative CS/ε-Fe2O3 electrode for the EIS sensing platform. This platform demonstrates notable potential for addressing the critical need for efficient and sensitive EIS sensors capable of detecting a range of hazardous heavy metal ions, including Hg2+, Cd2+, and Pb2+.

Impact of Gd3+ doping on structural, electronic, magnetic, and photocatalytic properties of MnFe2O4 nanoferrites and application in dye-polluted wastewater remediation

The present work focuses on developing Gd-doped Mn spinel nanoferrites and their potential application in the photodegradation of water pollutants. The impact of Gd³⁺ ion substitution on structural, electronic, and magnetic characteristics of manganese ferrites has been studied. Nanocrystalline samples of MnGd_xFe_2-xO₄ (x = 0.0 to 0.10, in step size of 0.02) ferrites were prepared via sol-gel self-ignition route. The Rietveld, XPS, HRTEM, and SAED characterization methods confirmed the formation of phase pure ferrite nanoparticles (~ 8-22 nm) in the cubic spinel structure. The Gd³⁺ content in these nanoferrites responded to a systematic reduction in the size of nanocrystallites and an upsurge in the density of nanoferrites. The XPS study revealed fine assimilation of constituent elements in the fcc lattice and ruled out impurities in the nanoferrites. The Fe and the Gd ions were found to be in Fe³⁺ and Gd³⁺ states, respectively. While a major fraction of the Mn ions were found to be in the Mn²⁺ state, a small fraction of Mn⁴⁺ ions was observed on the surface of nanoparticles. The nanoferrites were found to exhibit a soft ferromagnetic state from 300 to 20 K limits. The highest saturation magnetization was observed for x = 0.02 (M_S = 66.6 emu/g at 20 K). The observed magnetic properties can be understood with the competing (Fe³⁺ and Mn²⁺)_A-O^2--[Fe³⁺, Mn²⁺, and Gd³⁺]_B superexchange interactions and magnetocrystalline anisotropy. Due to the small band gap energy of Gd-doped Mn ferrites than that of the pure Mn ferrite, they have demonstrated excellent photocatalytic activity for the degradation of methylene blue (MB) dye under visible light illumination. As much as 96.35% of the MB dye was found to get degraded in 70 min of light illumination over synthesized nanoparticles and the photodegradation reaction followed pseudo-first-order kinetics. The increased optical absorbance due to lower band gap, suppressed recombination rate of charge carriers, and enhanced charge mobility make them effective visible light active photocatalysts. This study revealed that the electronic, optical, and magnetic properties of MnFe₂O₄ nanoferrites could be easily tuned by varying the Gd³⁺ content and the prepared Gd-doped MnFe₂O₄ nanomaterials have boundless potential to be utilized in the future making promising active photocatalysts and degradation of harmful industrial dyes for enhanced protection in the fields of environment and health care.

Recent progress on adsorption of cadmium ions from water systems using metal-organic frameworks (MOFs) as an efficient class of porous materials

Various articles have been written about MOFs, which are organic-inorganic polymer structures that are unique in three-dimensional porosity, crystalline structure, and their ability to adsorb cadmium ion pollutants from aqueous solutions. These materials possess active metal sites, highly porous structures, high specific surfaces, high chemical functionality, and porous topologies. It is necessary to study adsorption kinetics, isotherms, and mechanisms in order to better understand the adsorption process. Adsorption kinetics can provide information about the adsorption rate and reaction pathway of adsorbents. Adsorption isotherms analyze the possibility of absorbances based on the Gibbs equation and thermodynamic theories. Moreover, in practical applications, knowledge of the adsorption mechanism is essential for predicting adsorption reactions and designing MOFs structures. In this review, the latest suggested adsorption mechanisms, kinetics, and isotherms of MOFs-based materials for removing cadmium ions are presented. A comparison is then conducted between different MOFs and the mechanisms of cadmium ion removal. We also discuss the future role of MOFs in removing environmental contaminants. Lastly, we discuss the gap in research and limitations of MOFs as adsorbents in actual applications, and probable technology development for the development of cost-efficient and sustainable MOFs for metal ion removal.

[Identification of factors affecting Oncomelania hupensis density in Eastern Dongting Lake regions]

OBJECTIVE

To evaluate the impact of water pollutants, water levels and meteorological factors on the Oncomelania hupensis density in Eastern Dongting Lake regions, so as to provide insights into schistosomiasis control.

METHODS

O. hupensis snails were surveyed using a systematic sampling method in snail-infested marshlands in Eastern Dongting Lake regions from 2007 to 2014, and data pertaining to water pollutants, water levels and meteorological factors were collected. The duration of submergence and the date of the start of submergence were calculated. The snail density and its influencing factors were descriptively analyzed, and a linear mixed model was generated to examine the impacts of variables on the snail density. In addition, smooth curves were fitted to investigate the relationship between snail density and variables.

RESULTS

The snail density appeared a fluctuation in Eastern Dongting Lake regions during the period from 2007 to 2014, with the highest density on October, 2010 (52.79 snails/0.1 m²) and the lowest density on January 2009 (2.15 snails/0.1 m²). Linear mixed-model analysis showed that permanganate index, total phosphorus and the date of the start of submergence affected the snail density (t = 6.386, -2.920 and -3.892, all P values < 0.01). Smooth curve analysis revealed that the associations of the snail density with the permanganate index and total phosphorus appeared an approximately quadratic curve. After the end of April, the earlier date of the start of submergence resulted in a higher snail density.

CONCLUSIONS

Permenganate index, total phosphorus and the date of the start of submergence affect the O. hupensis snail density in Eastern Dongting Lake regions.

Four decades of progress in cylindrospermopsin research: The ins and outs of a potent cyanotoxin

The cyanotoxin cylindrospermopsin (CYN), a toxic metabolite from cyanobacteria, is of particular concern due to its cosmopolitan occurrence, aquatic bioaccumulation, and multi-organ toxicity. CYN is the second most often recorded cyanotoxin worldwide, and cases of human morbidity and animal mortality are associated with ingestion of CYN contaminated water. The toxin poses a great challenge for drinking water treatment plants and public health authorities. CYN, with the major toxicity manifested in the liver, is cytotoxic, genotoxic, immunotoxic, neurotoxic and may be carcinogenic. Adverse effects are also reported for endocrine and developmental processes. We present a comprehensive review of CYN over the past four decades since its first reported poisoning event, highlighting its global occurrence, biosynthesis, toxicology, removal, and monitoring. In addition, current data gaps are identified, and future directions for CYN research are outlined. This review is beneficial for understanding the ins and outs of this environmental pollutant, and for robustly assessing health hazards posed by CYN exposure to humans and other organisms.

A low-cost graphitized sand filter to deliver MC-LR-free potable water: Water treatment plants and household perspective

Scale-up feasibility of the graphitized sand filter (GS1) for Microcystin-LR (MC-LR) removal and its impact on other water pollutants (WPs) was assessed through a mass-balance study, using a laboratory-based drinking water treatment plant (DWTP) micromodel named: SAP-1©. The treatment system comprised: raw water tank, pre-oxidation tank (oxidant: potassium permanganate), followed by a coagulation/flocculation tank (alum supplemented), sedimentation tank, filtration module and finally disinfection tank (dosed with hypochlorite solution). Two filter modules (FMs) were studied: a) FM1: graphitized-sand media + sand media = ½ GS1 + ½ sand and b) FM2: ½ sand + ½ sand. The MC-LR removal study (initial concentration: 50 μg/L) was performed for two varieties of MC-LR source: a) commercial MC-LR, and b) algal-biomass released MC-LR. Along with MC-LR, other WPs were also evaluated including metal ions (Fe²⁺ and Cu²⁺), total coliform, turbidity, ammonia-N and dissolved organic carbon. The removal efficiency of these WPs was determined for each treatment unit (as it passed). FM1 was able to reduce the inflow residual of MC-LR (coming from the preceding unit: sedimentation unit) from 12.1 μg/L and 25.4 μg/L (for commercial and algal-cell MC-LR source, respectively) to <0.61 μg/L and hence successfully complying the WHO guidelines (<1 μg/L). The protein phosphatase 1A (PP1A) toxicity assay confirmed a much safer and more toxic-free filtrate (by 40%-50%) for FM1 as compared to the filtrate obtained from FM2. The techno-economic evaluation showed that for an annual household filter application, 160 CAD needs to be spent on one GS1-based filter unit as compared to over 6000 CAD (equivalent price) for the conventional sand-based filter to provide MC-LR-free water. The present study demonstrates the feasibility of the utilization of these units in household filtration systems.

Dataset on specific UV absorbances (SUVA254) at stretch components of Perak River basin

Perak River basin is in Perak state of Peninsular Malaysia. In this research, the river stretch serves as water intake for domestic, agricultural and industrial purposes in Perak Tengah, Hilir Perak and Manjung regions. It is located in mixed use area whilst exposing the river to anthropogenic elements. The sampling locations were conducted at selected points of Perak River namely Tanjung Belanja Bridge (TBB), Water Treatment Plant Parit (WTPP), Parit Town discharge (PTD), Water Treatment Plant Senin (WTPS) and Water Treatment Plant Kepayang (WTPK). The existence of aromatic hydrocarbons in freshwater samples was pre-assessed via qualification analysis; specific ultraviolet absorbance (SUVA₂₅₄) method at 254 nm of wavelength. The SUVA dataset were 48.38 L/mg-m (TBB), 50.54 L/mg-m (WTPP), 8.05 L/mg-m (PTD), 85.75 L/mg-m (WTPS) and 217.39 L/mg-m (WTPK). The SUVA₂₅₄ values of fresh water at the river basin have exceeded the water quality standards value equivalent to 2.0 L/mg-m permitted by the Environmental Protection Agency of United States. The exceeding values were an indication of a large portion of aromatic compounds in the water. Qualification analyses evident the existence of water pollutants at treacherous concentrations for public health in freshwater samples of Perak River basin. Thus, this research has presented important findings towards further research and countermeasure for a better alternative of water treatment in Malaysia.

Immunochemical rapid determination of quinoxyfen, a priority hazardous pollutant

In 2013, quinoxyfen was included in the list of priority hazard pollutants of the European Water Framework Directive due to its toxicity to aquatic organisms. However, few analytical methods for the analysis of this fungicide have been reported and no rapid immunochemical methods have been published so far. In the present study, immunoreagents for quinoxyfen analysis were generated for the first time and an enzyme-linked immunosorbent assay was developed. Two carboxylated derivatives of quinoxyfen were designed on the basis of the minimum energy conformation of the target compound. Active esters of those novel compounds were prepared using N,N'-disuccinimidyl carbonate, and purified for covalent coupling to proteins. Matrix-assisted laser desorption mass spectrometry of the prepared bioconjugates showed optimum hapten-to-protein molar ratios. Moreover, high-affinity antibodies specific of quinoxyfen were raised. As proof of concept, an immunoassay was evaluated using a heterologous conjugate, which afforded sensitivity values in the low nanomolar range. Moreover, excellent recoveries and coefficients of variation were obtained from the analysis of environmental water samples fortified with quinoxyfen. A limit of quantification of 60 μg/L was determined. The prepared bioconjugates and antibodies could be valuable immunoreagents for the development of a variety of rapid immunosensors for quinoxyfen determination in environmental samples.

Development of yeast reporter assays for the enhanced detection of environmental ligands of thyroid hormone receptors α and β from Xenopus tropicalis

Thyroid hormones (THs) are involved in the regulation of metabolic homeostasis during the development and differentiation of vertebrates, particularly amphibian metamorphosis, which is entirely controlled by internal TH levels. Some artificial chemicals have been shown to exhibit TH-disrupting activities. In order to detect TH disruptors for amphibians, we herein developed a reporter assay using yeast strains expressing the thyroid hormone receptors (TRs) α and β together with the transcriptional coactivator SRC-1, all of which were derived from the frog Xenopus tropicalis (XT). These yeast strains responded to endogenous THs (T₂, T₃, and T₄) in a dose-dependent manner. They detected the TR ligand activities of some artificial chemicals suspected to exhibit TH-disrupting activities, as well as TR ligand activity in river water collected downstream of sewage plant discharges, which may have originated from human excrement. Moreover, the responses of XT TR strains to these endogenous and artificial ligands were stronger than those of yeast strains for human TRα and β assays, which had previously been established in our laboratory. These results indicate that the yeast reporter assay system for XT TRα and β is valuable for assessing TR ligand activities in environmental samples that may be particularly potent in amphibians.

Functional classification and biochemical characterization of a novel rho class glutathione S-transferase in Synechocystis PCC 6803

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A novel class of glutathione S-transferase (GST) is reported.

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This GST catalyzes dichloroacetate (DCA) degradation and hydroperoxide reactions.

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Functionally this GST is similar to zeta and theta/alpha classes but structurally very different.

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In contrast to other bacterial GSTs, this GST exists as a monomer in solution.

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First report of DCA degradation by any bacterial GST and has potential biotechnological applications.

We report a novel class of glutathione S-transferase (GST) from the model cyanobacterium Synechocystis PCC 6803 (sll1545) which catalyzes the detoxification of the water pollutant dichloroacetate and also shows strong glutathione-dependent peroxidase activity representing the classical activities of zeta and theta/alpha class respectively. Interestingly, sll1545 has very low sequence and structural similarity with these classes. This is the first report of dichloroacetate degradation activity by any bacterial GST. Based on these results we classify sll1545 to a novel GST class, rho. The present data also indicate potential biotechnological and industrial applications of cyanobacterial GST in dichloroacetate-polluted areas.