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Hardness, iron, and manganese are common groundwater pollutants, that frequently surpass the established discharge standard concentrations. They can be effectively removed, however, through induced crystallization. This study has investigated the effectiveness of the simultaneous removal of hardness-iron-manganese and the crystallization kinetics of calcium carbonate during co-crystallization using an automatic potentiometric titrator. The impacts pH, dissolved oxygen (DO), and ion concentration on the removal efficiency of iron and manganese and their influence on calcium carbonate induced crystallization were assessed. The results suggest that pH exerts the most significant influence during the removal of hardness, iron, and manganese, followed by DO, and then the concentration of iron and manganese ions. The rate of calcium carbonate crystallization increased with pH, stabilizing at a maximum of 10 -10  m/s. Iron and manganese can be reduced from an initial level of 4 mg/L to <0.3 mg/L and 0.1 mg/L, respectively. The removal rate of iron, however, was notably higher than that of manganese. The DO concentration correlates positively with the removal of iron and manganese but has minimal impact on the calcium carbonate crystallization process. During the removal of iron and manganese, competitive interactions occur with the substrate, as increases in the concentration of one ion will inhibit the removal rate of the other. Characterization of post-reaction particles and mechanistic analysis reveals that calcium is removed through the crystallization of CaCO 3 , while most iron is removed through precipitation as Fe 2 O 3 and FeOOH. Manganese is removed via two mechanisms, crystallization of manganese oxide (MnO 2 /Mn 2 O 3 ) and precipitation. Overall, this research studies the removal efficiency of coexisting ions, the crystallization rate of calcium carbonate, and the mechanism of simultaneous removal, and provides valuable data to aid in the development of new removal techniques for coexisting ions., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Ruizhu Hu reports financial support was provided by National Natural Science Foundation of China., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Filamentous fungi can enter drinking water supply systems in various ways, and exist in suspended or sessile states which threatens the health of individuals by posing a high risk of invasive infections. In this study, the biofilms formation kinetics of the three genera of fungal spores, Aspergillus niger (A. niger), Penicillium polonicum (P. polonicum) and Trichoderma harzianum (T. harzianum) isolated from the groundwater were reported, as well as the effects of water quality parameters were evaluated. In addition, the efficiency of low- concentrations of chlorine-based disinfectants (chlorine, chlorine dioxide and chloramine) on controlling the formation of fungal biofilms was assessed. The results showed that the biofilms formation of the three genera of fungi could be divided into the following four phases: induction, exponential, stationary and sloughing off. The optimum conditions for fungal biofilms formation were found to be neutral or weakly acidic at 28 °C with rich nutrition. In fact, A. niger, P. polonicum, and T. harzianum were not observed to form mature biofilms in actual groundwater within 120 hr. Carbon was found to have the maximum effect on the fungal biofilms formation in actual groundwater, followed by nitrogen and phosphorus. The resistance of fungal species to disinfectants during the formation of biofilms decreased in the order: A. niger > T. harzianum > P. polonicum. Chlorine dioxide was observed to control the biofilms formation with maximum efficiency, followed by chlorine and chloramine. Consequently, the results of this study will provide a beneficial understanding for the formation and control of fungal biofilms., (Copyright © 2021. Published by Elsevier B.V.)

The co-contamination of groundwater with nitrate (NO 3 - -N) and manganese (Mn(II)) is a global issue that needs to be efficiently remediated. In this research, a novel denitrifying and manganese-oxidizing strain HY129 was isolated from the sediments sample of a drinking water and identified as Cupriavidus sp. HY129. The remediation ability of strain HY129 regarding the nitrate and Mn(II) pollution were investigated. The removal efficiency of nitrate and Mn(II) were 99.81% (0.229 mgL -1 h -1 ) and 87.24% (0.233 mgL -1 h -1 ) in bacterial culture after 72 h, respectively. Moreover, the addition of Mn(II) significantly enhanced the denitrification process, while excessive concentration of Mn(II) caused more NO 2 - -N accumulation. The impacts of adsorption and oxidation activity on Mn(II) removal were investigated. Protein in extracellular polymeric substance (EPS) which produced in the Mn-oxidizing process was speculated to be the main cause of extracellular adsorption of Mn(II). Characterization of biogenic manganese oxides (BMO) confirmed the formation of high-valent manganese and the trapping experiment with sodium pyrophosphate (NaPP) demonstrated the existence of Mn(III)-intermediates. Furthermore, multicopper oxidase gene amplification provided evidence for the molecular biology of Mn(II) oxidation by strain HY129., (Copyright © 2020 Elsevier B.V. All rights reserved.)

To remove high concentrations of ammonium from groundwater, pure oxygen and compressed air were fed into a chemical catalytic filter and the ammonium removal efficiency was investigated. The experimental results showed that the oxygen content is the critical limiting factor for ammonium removal. Aeration with 40 mL/min pure oxygen or 100 mL/min compressed air from the bottom of the filter supplied adequate oxygen and approximately 4.2 mg/L of ammonium was removed in this process. Moreover, when the aeration device was moved to 1/3 of the height of the filter bed, the required flow rates of pure oxygen and compressed air decreased further and the turbidity removal was improved. Pouring ozone gas into the filter system, which can inactivate bacteria effectively, can also obtain the remarkable ammonium removal, indicating that ammonium removal was mainly due to the chemical catalytic oxidation in this process rather than the biodegradation. This study provides a novel method for removing high concentrations of ammonium from groundwater., Competing Interests: The authors declare no conflict of interest.

Manganese oxide has been found to be an active catalyst for ammonium oxidation. This work presented an innovative electrochemical system to improve the removal efficiency of ammonium by strengthening the generation of Mn(III). In this system, the manganese oxide coating activated carbon (MnO x /AC) particles were used as the cathode of a fuel cell (MnO x /AC-Ca). Compared to the conventional method using MnO x in a nonelectrochemical system (MnO x /AC-Control), the ammonium removal efficiency was doubled in the MnO x /AC-Ca system. Conversely, when using MnO x as the anode of a fuel cell (MnO x /AC-An), the ammonium removal efficiency was lower than that in the MnO x /AC-Control system. XPS results showed that Mn(III) in the MnO x /AC-Ca system was obviously higher than that in the MnO x /AC-Control system. Conversely, more Mn(IV), which was less active than Mn(III) for NH 4 + - N removal, was detected in the MnO x /AC-An system. The possible pathway for the ammonium removal by MnO x was that Mn(III) reacted with NH 4 + - N and produced Mn 2+ . These Mn 2+ were then reoxidized into new active MnO x under the self-catalysis of MnO x , resulting in a continuous ammonium removal. Moreover, nitrite, the intermediate product of ammonium oxidation, can be oxidized by MnO x , thus helping the ammonium oxidation process. PRACTITIONER POINTS: Mn(III) was generated by using MnO x as the cathode of fuel cells. Ammonium removal efficiency went up with the content of Mn(III) in MnO x . Mechanism of the NH 4 + - N removal by MnO x was discussed., (© 2019 Water Environment Federation.)

Arsenic, a common contaminant in groundwater environments, usually coexists with other contaminants, for example, ammonium, iron, and manganese. In our previous studies, an iron-manganese (Fe-Mn) oxides filter media was developed for catalytic oxidation removal of ammonium, iron, and manganese. In this study, batch oxidation/adsorption kinetic experiments revealed that the filter media could easily oxidize arsenite (As(III)) to arsenate (As(V)). And the sorption kinetics was found to follow the pseudo-second-order kinetic model. X-ray powder diffraction (XRD) and Fourier transform infrared spectra (FTIR) along with X-ray photoelectron spectroscopy (XPS) were used to analyze the surface change in the Fe-Mn oxides. Based on sorption and spectroscopic measurements, the mechanism of As(III) removal by the Fe-Mn oxides filter media was found to be an oxidation coupled with sorption approach. As(III) in the aqueous solution was firstly oxidized to As(V) on the surfaces of the Fe-Mn oxides filter media. Then the converted As(V) was attracted to the Fe-Mn oxides filter media surfaces and bounded with the active sites (-OH groups), through weak intermolecular H-bondings. Our results indicated that the novel Fe-Mn oxides filter media could be applied for the simultaneous removal of ammonium, iron, manganese, and As(III) in drinking water treatment and environmental remediation. PRACTITIONER POINTS: A novel iron-manganese oxides filter for efficient As(III) removal was established. The exhausted filter media could be easily regenerated by NaHCO 3 solution. Mn(III) related to surface lattice oxygen species was responsible for As(III) oxidation. The oxidation and adsorption processes were involved in As(III) removal. The filter media could be successfully applied to simultaneous removal of ammonium, manganese, iron, and arsenic., (© 2019 Water Environment Federation.)

Two types of filter media in groundwater treatment were conducted for a comparative study of surface structure and catalytic performance. Natural filter media was adopted from a conventional aeration-filtration groundwater treatment plant, and active filter media as a novel and promising filter media was also adopted. The physicochemical properties of these two kinds of filter media were characterized using numerous analytical techniques, such as X-Ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and Zeta potential. The catalytic activities of these filter media were evaluated for ammonium and manganese oxidation. XRD data showed that both active filter media and natural filter media belonged to birnessite family. A new manganese dioxide (MnO 2 ) phase (PDF#72-1982) was found in the structure of natural filter media. The SEM micrograph of natural filter media showed honeycomb structures and the active filter media presented plate structures and consisted of stacked particle. These natural filter media presented lower level of some trace elements such as calcium and magnesium, lower degree of crystallinity, lower Mn(III) content and lattice oxygen content than that of active filter media, which were associated with its poor ammonium and manganese catalytic activities. In addition, some γ-Fe 2 O 3 and MnCO 3 were found in the coating which may hinder the ammonium and manganese catalytic oxidation. This study provides a thorough and comprehensive understanding about the most commonly used filter media in water treatment, which can provide a theoretical guide to practical applications., (Copyright © 2018. Published by Elsevier B.V.)

The high concentration of ammonium (NH₄⁺-N) and manganese (Mn 2+ ) in underground water poses a major problem for drinking water treatment plants. Effective catalytic oxidative removal of NH₄⁺-N and Mn 2+ by iron-manganese co-oxide film (MeO x ) filters was first developed by our group in a previous study. In this study, several identical pilot-scale filters were employed to optimize the start-up process for simultaneous removal of NH₄⁺-N and Mn 2+ from potable water supplies. Experiments were conducted to assess the influence of Mn 2+ concentration, Fe 2+ concentration, filtration rate and dosing time on the start-up period of the filter. Results demonstrated that the ability of the filter to remove completely 1.5 mg/L NH₄⁺-N could be achieved on the sixth day at the soonest and the removal of Mn 2+ could reach 1 mg/L by the 18th day. Filter R3 feeding with 1 mg/L Fe 2+ , 2 mg/L Mn 2+ and 3.5 mg/L MnO₄ - during the start-up period exhibited the optimum NH₄⁺-N and Mn 2+ removal effect. Short dosing time was not conducive to attaining full NH₄⁺-N removal in filters, especially the activity of NO₂ - -N conversion to NO₃ - -N. The compositional analysis and element distribution analysis results demonstrated that there was an abundance of C, O, Mn, Mg, Fe, Ca and Si across the entire area of the surface of the filter media and the elemental distribution was homogeneous, which was different from the biofilter media. Knowledge-guided performance optimization of the active iron-manganese co-oxide could pave the way for its future technological use.

Fungi in aquatic environments received more attention recently; therefore, the characteristics of inactivation of fungal spores by widely used disinfectants are quite important. Nonetheless, the inactivation efficacy of fungal spores by chlorine dioxide is poorly known. In this study, the effectiveness of chlorine dioxide at inactivation of three dominant genera of fungal spores isolated from drinking groundwater and the effects of pH, temperature, chlorine dioxide concentration, and humic acid were evaluated. The inactivation mechanisms were explored by analyzing the leakage of intracellular substances, the increase in extracellular adenosine triphosphate (ATP), deoxyribonucleic acid (DNA), and proteins as well as the changes in spore morphology. The kinetics of inactivation by chlorine dioxide fitted the Chick-Watson model, and different fungal species showed different resistance to chlorine dioxide inactivation, which was in the following order: Cladosporium sp.>Trichoderma sp. >Penicillium sp., which are much more resistant than Escherichia coli. Regarding the three genera of fungal spores used in this study, chlorine dioxide was more effective at inactivation of fungal spores than chlorine. The effect of disinfectant concentration and temperature was positive, and the impact of pH levels (6.0 and 7.0) was insignificant, whereas the influence of water matrices on the inactivation efficiency was negative. The increased concentration of characteristic extracellular substances and changes of spore morphology were observed after inactivation with chlorine dioxide and were due to cell wall and cell membrane damage in fungal spores, causing the leakage of intracellular substances and death of a fungal spore., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Fungi pollution in water can lead to serious problems, such as turbidity, odor, food pollution, mycotoxin production, and increased opportunistic infections among people with an immune deficiency. Few studies have reported the fungi community composition, quantity of fungi, and origin of fungi in groundwater. To study the change of quantity and community composition of fungi in groundwater at different times of year, this study evaluated the number of fungi and dominant fungi genera in groundwater and the factors affecting fungi quantity. The results showed that 18 genera of fungi were observed in the study area's groundwater, among which Penicillium (18–27%), Aspergillus (17–26%), Acremonium (12–28%) were the three most dominant. The numbers of dominant fungi genera were as follows: Penicillium (21–62 CFU/100 mL), Aspergillus (18–43 CFU/100 mL), and Acremonium (15–38 CFU/100 mL). The number of fungi in water closely correlates with environmental variables such as pH, dissolved oxygen (DO), turbidity, and total organic carbon (TOC). Various genera of fungi were affected differently by unique environmental variables. The fungi in the water were also affected by components of the external environment, such as rainfall, surface farming, surface water sources, and so on. This study aims to provide meaningful information for understanding fungi pollution in groundwater. [ABSTRACT FROM AUTHOR]

An efficient immobilized denitrification bioreactor functioning under anaerobic conditions was developed by combining bacterial immobilization technology with iron-carbon (Fe–C) particles. The effects of key factors on nitrate (NO3−–N) removal efficiency were invested, such as the carbon-nitrogen ratio (C/N), pH and hydraulic retention time (HRT). Experimental results show that 100.00% NO3−–N removal efficiency and a low level of nitrite (NO2−–N) accumulation less than 0.05 mg L−1 were obtained under the condition of a C/N ratio of 3, pH 7.0 and HRT of 6 h. Meteorological chromatographic analysis showed that the final product of denitrification was mainly nitrogen (N2). The main component of precipitation formed in the bioreactor was characterized as Fe3O4 by X-ray diffraction. High-throughput sequencing analysis indicated that the dominant bacterial class in the Fe–C bioreactor was Gammaproteobacteria, while the dominant genera were Zoogloea and Azospira, the relative abundances of which were as high as 23.25 and 15.43%, respectively. [ABSTRACT FROM AUTHOR]

BACKGROUND: This work further investigates fluoride removal from groundwater by induced crystallization in batch experiments and in a fluidized bed reactor (FBR). Phosphate rock (PR), which is an abundant ore and represents the basic raw material for the phosphatic fertilizer industry, was used as seed crystal in the induced crystallization process. RESULTS: Induced crystallization in FBR reduced the concentration of F− in synthetic groundwater from 9.5 mg L‐1 to <1.0 mg L‐1. Phases with the potential for precipitation were calculated through thermodynamic equilibrium modeling. The formed precipitates were identified by powder x‐ray diffraction (XRD) and scanning electron microscopy, coupled with energy dispersive spectroscopy (SEM–EDS). Finally, fluorapatite crystallization mechanisms were confirmed by the induced crystallization of Ca5(PO4)3F on the surface of PR. CONCLUSION: The fluorapatite crystallization process in FBR removed F− from groundwater, and the used seed crystal PR was rich in phosphorus and that could be recovered as raw material for the phosphatic fertilizer industry. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

High concentration of ammonium (NH 4 + ) often occurs in groundwater. In this study, the behavior of NH 4 + catalytic oxidation by a manganese oxide (MnO x ) filter was investigated systematically and the formation and evolution of the MnO x films were characterized extensively. It was found that the MnO x based filter could be successfully started up within 6 days with the NH 4 + removal efficiency increasing from 1 to 96%. After start-up, the removal efficiency of NH 4 + could keep almost constant under different operating conditions, implying the MnO x filter has a good stability towards NH 4 + removal. Both X-ray diffraction (XRD) and Raman results suggested that MnO x was related to hexagonal birnessite which has low crystallinity and small crystallite sizes. The X-ray photoelectron spectroscopy (XPS) spectra of the Mn2p taken on the surface of MnO x revealed Mn(II), Mn(III) and Mn(IV) species existed in MnO x materials and their atomic concentrations were 20.2%, 57.8% and 22%, respectively. More importantly, the catalysis of films towards NH 4 + oxidation was expected to be closely related to its feature structure. Specifically, the ability of manganese to cycle between +2, +3 and +4 oxidation states during catalysis was considered to play important roles in the NH 4 + conversion on MnO x surface. Based on the above discussion, three major steps involve in NH 4 + catalytic oxidation by MnO x were proposed, which are NH 4 + adsorption, catalytic oxidation, and desorption of reaction products. [ABSTRACT FROM AUTHOR]

Although dissolved oxygen (DO) is a key factor for the removal of manganese (Mn) from aqueous solutions, this study presents an efficient method for Mn removal without any DO consumption. We demonstrate the feasibility of using an iron (Fe)–Mn co-oxide filter film to continuously remove Mn from groundwater under anaerobic conditions. A pilot-scale filter equipped with Fe–Mn co-oxide filter media (120 cm high) was adapted to explore the Mn removal performance under three DO levels (6–7 mg/L, 1–2 mg/L, and 0–0.2 mg/L). The Fe–Mn co-oxide filter exhibited a higher Mn removal performance under anaerobic conditions (no DO consumption) than under the other two DO conditions. The morphology, structure, and Mn valence changes of the Fe–Mn co-oxide filter film were studied using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer Emmett Teller (BET) theory, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The Fe–Mn co-oxide filter film under anaerobic conditions had a large contact surface area and large pore volume, and thus possessed more adsorption sites and reaction channels for Mn removal. By considering all of the characterization and reaction data reported in this study, we conclude that H 2 O ligands, hydrogen bonding (-OH), and vacant sites affect the transformation of Mn, thus play important roles in the continuous removal of Mn under anaerobic conditions. This discovery presents a new and effective approach for Mn removal during groundwater treatment. Unlabelled Image • Effects of three DO conditions (6–7, 1–2, and 0–0.2 mg/L) were evaluated. • Filter morphology, structure, and composition during operation were considered. • More H+ ion was released under anaerobic conditions. • The Fe–Mn co-oxides possess more adsorption sites and reaction channels. • Manganese could be removed without any DO consumption. [ABSTRACT FROM AUTHOR]

Outbreaks of fungi in groundwater sources of drinking water can produce taste and odor problems, and cause ill health in immunocompromised individuals. The groundwater treatment process is simple; generally, only disinfection is used in China. Efficient disinfection methods to control fungi are required. In the present study, we investigated the inactivation efficiency of 4 dominant genera of fungal spores (a Trichoderma sp., Acremonium sp. , Penicillium sp., and Cladosporium sp.) using ultraviolet irradiation (UV) and UV-based advanced oxidation processes, and explored the mechanisms of inactivation by monitoring the leakage of intracellular contents and changes in spore morphology. The inactivation of fungal spores is consistent with first-order Chick–Watson kinetics. The resistance of each of the fungi to UV ( Cladosporium sp. > Penicillium sp. > Acremonium sp. > Trichoderma sp.) was greater than that of E. coli , due to their larger sizes and more complex structures. UV/peroxymonosulfate (UV/PMS) treatment had a markedly better inactivation rate constant than UV alone. Furthermore, UV/PMS exhibited similar effects on fungal inactivation in phosphate buffer and in groundwater, whereas UV inactivation efficiency markedly decreased in groundwater. UV/PMS treatment resulted in cell wall and cell membrane damage, the leakage of intracellular contents, and the shriveling of fungal spores, due to the reactive radicals produced by the treatment. Thus, UV/PMS is a promising method to control fungi in drinking water sources. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solar disinfection of fungal spores fits well with GInaFiT. • The effects of humic acid, pH and temperature on disinfection were evaluated. • Solar inactivation of fungal spores was illustrated as an endogenous mechanism. • No regrowth was observed in the fungal spores in groundwater and surface water. Water contamination with fungi has gained attention increasingly, while solar disinfection (SODIS) is a potential method, especially for developing countries. In this work, inactivation kinetics, influencing factors, mechanisms and regrowth of fungal spores in the SODIS process were firstly investigated. The inactivation fitted well with the Geeraerd and Van Impe inactivation model-fitting tool and P. polonicum was more sensitive to simulated sunlight than A. niger. The pH value within the range of 5–9 and low concentration humic acid did not affect the solar inactivation of fungal spores, while HA at the concentration above 5.0 mg/L inhibited the solar inactivation efficiency. Over the tested range, the inactivation efficiency was obtained at the temperature near the optimal growth temperature (30-40 °C for A. niger , 20–30 °C for P. polonicum). According to the results of flow cytometry, ATP concentration and scanning electron microscopy, the solar inactivation of fungal spores was ascribed to endogenous actions. During the SODIS process, the DNA and respiratory chain of fungal spores were attacked. Subsequently, esterase activity was induced. As a result, the spores lost the culturability firstly, accompanied by the exhaustion of ATP, finally the membrane became permeable. Although no fungal spore regrowth was observed in ground water and surface water after SODIS, they remained a certain regrowth potential in nutrient-rich water like R2A. This work uncovered the control of waterborne fungi by SODIS. [ABSTRACT FROM AUTHOR]