Synergistic effects of biogenic manganese oxide and Mn(II)-oxidizing bacterium Pseudomonas putida strain MnB1 on the degradation of 17 α-ethinylestradiol

Removal of Manganese(II) from Acid Mine Wastewater: A Review of the Challenges and Opportunities with Special Emphasis on Mn-Oxidizing Bacteria and Microalgae

Many global mining activities release large amounts of acidic mine drainage with high levels of manganese (Mn) having potentially detrimental effects on the environment. This review provides a comprehensive assessment of the main implications and challenges of Mn(II) removal from mine drainage. We first present the sources of contamination from mineral processing, as well as the adverse effects of Mn on mining ecosystems. Then the comparison of several techniques to remove Mn(II) from wastewater, as well as an assessment of the challenges associated with precipitation, adsorption, and oxidation/filtration are provided. We also critically analyze remediation options with special emphasis on Mn-oxidizing bacteria (MnOB) and microalgae. Recent literature demonstrates that MnOB can efficiently oxidize dissolved Mn(II) to Mn(III, IV) through enzymatic catalysis. Microalgae can also accelerate Mn(II) oxidation through indirect oxidation by increasing solution pH and dissolved oxygen production during its growth. Microbial oxidation and the removal of Mn(II) have been effective in treating artificial wastewater and groundwater under neutral conditions with adequate oxygen. Compared to physicochemical techniques, the bioremediation of manganese mine drainage without the addition of chemical reagents is relatively inexpensive. However, wastewater from manganese mines is acidic and has low-levels of dissolved oxygen, which inhibit the oxidizing ability of MnOB. We propose an alternative treatment for manganese mine drainage that focuses on the synergistic interactions of Mn in wastewater with co-immobilized MnOB/microalgae.

Cultivation of a versatile manganese-oxidizing aerobic granular sludge for removal of organic micropollutants from wastewater

Organic micropollutants (OMPs) are frequently detected in water and wastewater, and have attracted wide attention due to potential adverse effects on ecosystems and human health. In this work, manganese-oxidizing aerobic granular sludge (Mn-AGS) was successfully cultivated and applied to remove OMPs from wastewater. Biogenic manganese (III,IV) oxides (bio-MnO_x) were generated and accumulated to 22.0-28.3 mg Mn/g SS in the final sludge. Neither the addition of allochthonous manganese-oxidizing bacteria (MnOB; Pseudomonas putida MnB1) nor the reduction in hydraulic retention time (HRT) facilitated the cultivation of Mn-AGS. Batch experiments of OMPs degradation indicated that Mn-AGS significantly improved (1.3-3.9 times) degradation rates of most OMPs. Removal rates of bisphenol A (BPA), 17α‑ethinylestradiol (EE2), tetracycline (TC), and chloramphenicol (CAP) were 3.0-12.6 μg/h/g SS by the traditional AGS and 8.0-16.3 μg/h/g SS by Mn-AGS; those of imazethapyr (IM) were relatively high, 64.7 ± 0.1 and 127.8 ± 2.5 μg/h/g SS by AGS and Mn-AGS, respectively. However, degradation of dichlorophenyl phosphine (DCPP) was slower by Mn-AGS than AGS, 9.0 ± 0.4 vs. 21.2 ± 0.9 μg/h/g SS, possibly due to inhibition of microbial activity by bio-MnO_x. This work provides a promising method for treating OMPs in organic wastewater, but the possible inhibition of microbes by bio-MnO_x should be noted.

Dissolved organic matter mediates in the anaerobic degradation of 17α-ethinylestradiol in a coupled electrochemical and biological system

Dissolved organic matter (DOM) can act as an electron shuttle in biogeochemical redox reactions to affect the fate of contaminants. Herein DOMs were tested for their ability to mediate in the degradation of 17α-ethinylestradiol (EE2) in a coupled electrochemical and biological system. Fulvic acid (FA) and Sigma humic acid (SHA) were found to promote degradation by the electro-domesticated micro-organisms in the coupled system. Analyses of superoxide dismutase levels, microbial community and clusters of orthologous groups of proteins showed that electrical stimulation promoted their growth and metabolism. It was confirmed that electron transfer in the coupled system was promoted in the presence of DOM as their protein-like components were converted into aromatic substances. The electrical stimulation improved the microorganisms' effectiveness in subsequent biodegradation under anaerobic condition. Stimulated micro-organisms seemed to increase their environmental tolerance and degrade EE2 effectively. These findings provide evidence about the fate of estrogens in bioelectrochemical water treatment.

Multiple-pathway arsenic oxidation and removal from wastewater by a novel manganese-oxidizing aerobic granular sludge

Aerobic granular sludge (AGS) is a powerful biotechnology to remove various heavy metal(loid)s from wastewater, but not including arsenic (As). In this study, a novel manganese-oxidizing aerobic granular sludge (Mn-AGS) was developed to remove As from organic wastewater. Eight sequencing batch reactors (SBRs) were operated in duplicate to investigate the feasibility of As removal by Mn-AGS. The immobilized As in the granular sludge was characterized by sequencing extraction, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and Raman spectroscopy. Oxidation pathways for As and their contributions in Mn-AGS were evaluated by seven batch experiments under different conditions. The results indicated that As removal efficiency was much higher by Mn-AGS than by AGS. In Mn-AGS, As(III) was efficiently oxidized into As(V) (74.6%-82.6%) and then mostly bound on amorphous ferrihydrite and biogenic Mn oxides (bio-MnO_x) (56.2%-65.0%), while metal arsenates, such as ferric arsenate, were not detected. Importantly, As removal was greatly improved by a small addition of Fe(II) in Mn-AGS. This might be primarily caused by Fenton reactions, because this improvement was removed when H₂O₂, self-generated in Mn-AGS, was scavenged by exogenous catalase (CAT). This study provided a novel extension of the traditional AGS technology to treat As in organic wastewater with an acceptable degree of efficiency.

Identification and characterization of plant growth-promoting endophyte RE02 from Trifolium repens L. in mining smelter

Endophyte-assisted phytoremediation is considered to be an effective approach for bioremediation of heavy metal-contaminated soil; however, few information is available on Trifolium repens L. and its endophytes to remediate heavy metal-polluted soils. In this study, heavy metal-resistant endophytes were isolated from T. repens growing in mining smelter and identified by BIOLOG system. The isolate was also evaluated for promoting plant growth in heavy metal-contaminated soils in pot experiments. A total of eight Cd²⁺-resistant endophytes were isolated and these isolates preferred to grow on L-aspartic acid and α-D-glucose. All the isolates had at least two plant growth-promoting properties including siderophore production, phosphate solubilization activity, indole acetic acid (IAA) production, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. Strain RE02, identified as Pseudomonas putida by Biolog system, showed the highest Cd tolerance and could reduce Cd concentration from 20 to 1.84 mg L^-1 in about 49 h in liquid medium, amounting to about 90.8%. Among the five endophytes which have positive effect on the growth of T. repens, RE02, whose IAA production ability was 7.06 mg L^-1 and phosphate solubilization was 134.76 mg L^-1, could improve T. repens root and shoot biomass by 25.9% and 37.7% in cadmium-contained soil, respectively. Our research may provide a new microbial-enhanced phytoremediation of heavy metal-polluted soils and improve the remediation efficiency.

A novel manganese oxidizing bacterium-Aeromonas hydrophila strain DS02: Mn(II) oxidization and biogenic Mn oxides generation

The extensive applications of biogenic manganese oxides (BioMnOx) generated by manganese oxidizing bacteria (MOB) have attracted considerable attentions. In this study, we report on a novel MOB that has been isolated from sediments and identified as Aeromonas hydrophila strain DS02. The Mn(II) oxidation activity of strain DS02 under Mn(II) stress and the application of the associated BioMnOx products were investigated. Nearly 90.0% (495 mg L^-1) of the soluble Mn(II) were removed and 45.6% (240 mg L^-1) was converted to Mn(III/IV). Fitting the XPS data showed that Mn(IV)-oxide is the major component (82.0%) of the flake-shaped BioMnOx, corresponding to an average Mn oxidation number of 3.71. When the BioMnOx were coupled with the PMS activation, a 99.5% catalytic degradation of 2,4-dimethylaniline was observed after 80 min, revealing a high degradation efficiency.

Controlled formation of magnetic yolk-shell structures with enhanced catalytic activity for removal of acetaminophen in a heterogeneous fenton-like system

Encapsulating magnetic nanoparticles in a silica shell is a promising approach in many research fields. We recently demonstrated that the magnetic yolk-shell structure of Fe₃O₄@SiO₂, which consists of an inner magnetite core and outer silica shell separated by a hollow void space, and its modified counterparts can be used as an effective catalyst for removal of acetaminophen in a heterogeneous Fenton-like reaction. The present study develops this approach further in an effort to design an effective procedure for preparing an optimum yolk-shell structure capable of greater catalytic performance. We investigated the use of a controlled synthesis strategy to fabricate an Fe₃O₄@SiO₂ yolk-shell structure under varying conditions. Our focus was a single-step process that examines the effects of Stöber solution temperature, tetraethyl orthosilicate (TEOS) and hexadecyltrimethylammonium bromide (CTAB) concentrations, ethanol and water volume ratio, incubation time, and temperature on Fe₃O₄@SiO₂ textural morphologies. The catalytic performance of the prepared materials was evaluated through oxidative degradation of acetaminophen in a heterogeneous Fenton-like reaction. Field emission transmission electron microscopy observation showed that magnetic yolk-shell structures with appropriate diameter, shell thickness, and hollow void space could be generated through tight control of synthesis conditions. Particle size and hollow void space increased when TEOS concentration increased from 22.10 to 88.50 mM. Hollow void space also increased as incubation time increased from 24 h to 72 h or incubation temperature increased from 50 to 90 °C. However, a yolk-shell structure did not form at a TEOS concentration of 11.10 mM, an incubation time of 3 h, or with an inappropriate ratio of ethyl alcohol and deionized water. Catalytic activity for degradation of acetaminophen increased with increasing hollow void space and thinning silica shell. In addition, the selected appropriate materials exhibited effective catalytic performance over five cycles of regeneration. This study demonstrates the significance of controlling the formation of yolk-shell structures, which enabled us to produce Fe₃O₄@SiO₂ yolk-shell structures of desired and predictable size, hollow void space volume, and shell thickness for higher catalytic performance in degradation of pharmaceuticals in heterogeneous Fenton-like systems.

Simultaneous remediation of As(III) and dibutyl phthalate (DBP) in soil by a manganese-oxidizing bacterium and its mechanisms

Soils are experiencing increasing pollution with arsenic (As) and phthalate esters (PAEs), which is threatening human health. In this study, the feasibility of simultaneous remediation of soil As(III) and a PAE, dibutyl phthalate (DBP), by a manganese-oxidizing bacterium (MnOB) was evaluated. As immobilization and DBP degradation were simultaneously enhanced by MnOB addition. The effects of initial concentrations of As(III), DBP, and Mn(II), and moisture content on the removal of As(III) and DBP were investigated. The results indicated that there was a competitive interaction between As(III) and DBP removal, and 40 mg/kg of Mn(II) dosage and 20%-30% soil moisture content were recommended for optimal and simultaneous removal of As(III) and DBP. Microbial community analysis revealed that community structure and diversity were not changed significantly by MnOB addition. Taken together, the findings from this study indicated that DBP was degraded primarily by microorganisms, whereas As(III) was removed largely by biogenic Mn oxides and immobilized by adsorption onto Mg/Fe oxides and/or formation of metal arsenate precipitates/co-precipitates. This study offers a novel and high-efficiency strategy to remediate the combined contamination of As and PAEs in soils.

Removal of precursors of typical nitrogenous disinfection byproducts in ozonation integrated with biological activated carbon (O3/BAC)

The O₃/BAC process has been widely used in drinking water treatment to improve the removal of dissolved organic matters (DOMs), including the precursors of nitrogenous disinfection byproducts (N-DBPs). In this study, the removal of N-DBP precursors by biological activated carbon (BAC) filters with different usage time of granular activated carbon (GAC) was investigated. Results showed that the BAC filter with 6 years of usage time of GAC (old BAC filter) had a poor performance in the removal of precursors of N-DBPs such as dichloroacetonitrile (DCAN; an average of only 4.7%), dichloroacetamide (DCAcAm), and trichloronitromethane (TCNM) when compared with the BAC filter with 1 year of usage time of GAC (new BAC filter). Particularly, the organic fraction >10 kDa and the percentage of autochthonous substances were increased in the effluent of the old BAC filter. The red shift of the fluorescence peaks was evident in the excitation-emission matrix spectrum of the effluent from the old BAC filter. The abiotic adsorption of precursors by the old BAC filter was less. In addition, less amino acids and polysaccharides were removed, but more amino sugars and proteins were produced because of microbial metabolism. The metabolism strength of the attached biofilm decreased with increased operation time of the BAC filter. The relative abundance of Sphingomonas significantly decreased in the biofilm of the old BAC filter. The diversity of microbial community in the old BAC filter was higher, but the equitability was lower than those of the new BAC filter. The less removal of N-DBP precursors by the old BAC filter was attributed to the changes in abiotic adsorption capacity and microbial metabolism properties, in which soluble microbial products played an important role.