Reduction of metronidazole in municipal wastewater and protection of activated sludge system using a novel immobilized Aspergillus tabacinus LZ-M

Impact of LED radiation intensity on gold nanoparticles photodeposition on TiO2 with physicochemical and photocatalytic characterization

This study investigates the influence of LED radiation intensity on the photodeposition of gold nanoparticles onto TiO2 substrates, examining their physicochemical properties and photocatalytic activities. Utilizing a range of radiation intensities and wavelengths, TiO2-Au composites were synthesized and characterized through techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The deposition process, markedly enhanced by shorter wavelengths and higher intensities, efficiently formed gold nanoparticles. This research distinctly highlights observable morphological changes in the nanoparticles; increased radiation intensity not only augmented the size but also altered their shape from spherical to hexagonal. These morphological transformations significantly improve the composites' light absorption and catalytic properties due to the surface plasmon resonance of the gold nanoparticles. Photocatalytic assessments, using metronidazole as a model pollutant, demonstrated that composites prepared with higher LED intensities showed significantly enhanced degradation capabilities compared to those synthesized with lower intensities. The findings underscore that manipulating photodeposition parameters can critically influence the structural and functional properties of TiO2-Au composites, potentially advancing their applications in environmental remediation and solar energy utilization.

Removal of metronidazole using a novel ZnO-CoFe2O4@Biochar heterostructure composite in an intimately coupled photocatalysis and biodegradation system under visible light

The intimate coupling of photocatalysis and biodegradation (ICPB) technology has received much attraction because of the advantages of both photocatalytic reaction and biological treatment. In this study, ZnO-CoFe2O4@BC (ZCFC) with p-n heterojunction was prepared and used in an ICPB system to degrade metronidazole (MNZ) wastewater. The microstructure, morphology, and optical behavior of heterojunctions in ZCFC were investigated using SEM, XRD, UV-vis, FTIR, and XPS techniques. The results showed that ZCFC inherited the advantages of bamboo biochar's large pore size, and its large pore structure could provide a habitat for bacterial colonization in ICPB, thus shortening the internal mass transfer distance. The degradation of MNZ and chemical oxygen demand (COD) by the ICPB system was 86.8% and 58.5%, respectively, which was superior to single photocatalysis (72.5% for MNZ and 43.8% for COD) and single biodegradation (23.5% for MNZ and 20.1% for COD). In ICPB, photocatalysis and biodegradation showed a synergistic effect in the removal of MNZ, and the order of the major reactive oxygen species (ROS) leading to reduced toxicity of MNZ to the biofilm was •OH > h+ > O2•-. High-throughput sequencing analysis showed continuous evolution of biofilm structures in ICPB enriched a variety of functional species, among which the electroactive bacteria Alcaligenes and Brevundimonas played an important role in the degradation of MNZ. In this study, we investigated the possible mechanism of photocatalytic and microbial synergistic degradation of MNZ in the ICPB system and proposed a new technology for degrading antibiotic wastewater that combines the advantages of photocatalysis and biodegradation.

Human health risk assessment associated with the reuse of treated wastewater in arid areas

Qatar produces more than 850,000 m3/day of highly treated wastewater. The present study aims at characterizing the effluents coming out of three central wastewater treatment plants (WWTPs) of chemical pollutants including metals, metalloids and antibiotics commonly used in the country. Additionally, the study is assessing human health risks associated with the exposure to the treated wastewater (TWW) via dermal and ingestion routes. Although the origin of domestic wastewater is desalinated water (the only source of fresh water), the results show that the targeted parameters in TWW were within the international standards. Concentrations of Cl, F, Br, NO3, NO2, SO4 and PO4, were 389, <0.1, 1.2, 25, <0.1, 346, and 2.8 mg/L, respectively. On the other hand, among all cations, metals and metalloids, only boron (B) was 2.1 mg/L which is higher than the Qatari guidelines for TWW reuse in irrigation of 1.5 mg/L. Additionally, strontium (Sr) and thallium (Tl) were detected with relatively high concentrations of 30 mg/L and 12.5 μg/L, respectively, due to their natural and anthropogenic sources. The study found that the low concentrations of all tested metals and metalloids do not pose any risk to human health. However, Tl presents exposure levels above the 10 % of oral reference dose (HQ = 0.4) for accidental oral ingestion of TWW. The results for antibiotics show that exposure for adults and children to TWW are far below the admissible daily intakes set using minimum therapeutic dose and considering uncertainty factors. Treated wastewater of Qatar can be used safely for irrigation. However, further investigations are still needed to assess microbiological quality.

Enhanced metronidazole removal in seawater using a single-chamber bioelectrochemical system

The aim of this study was to investigate the removal of metronidazole (MNZ) from seawater using a bioelectrochemical system (BES). Single-chamber BES (i.e., S-BES) and dual-chamber BES (i.e., D-BES) were constructed with carbon brush as the anode and cathode. With the inoculum of sea mud and 2 g/L of glucose as the substrate in seawater, S-BES and D-BES were acclimated to test the MNZ removal. Results showed that S-BES could remove almost 100 % of 200 mg/L MNZ within 120 h and remain stable within 10 cycles of operation (∼50 d) under the applied voltage of 0.8 V. The MNZ removal reached ∼100 % and 60.2 % in the cathodic and anodic chambers of D-BES fed by 100 mg/L MNZ under 0.8 V, respectively. The MNZ concentration of 200 mg/L significantly inhibited the sulfur metabolism, decreased the ratio of live to dead cells in the electrode biofilms, and thus reduced the SO42- removal in the S-BES. The MNZ degradation and S2- oxidation was mainly attributed to the cathodic and anodic biofilms of S-BES, respectively. Three degradation pathways of MNZ were proposed based on the identified intermediates and results of density functional theory calculations. The synergies among different genus species in the bacterial communities of biofilms, and between anodic and cathodic reactions could be responsible for the high performance of S-BES. Results from this study should be not only useful for the MNZ removal but also for effective MNZ inhibition of sulfate-reducing bacteria induced microbiologically influenced corrosion in seawater.

Transcriptome analysis reveals self-redox mineralization mechanism of azo dyes and novel decolorizing hydrolases in Aspergillus tabacinus LZ-M

Bio-degradation is the most affordable method of azo dye decontamination, while its drawbacks such as aromatic amines accumulation and low degradation efficiency must be overcome. In this study, a novel mechanism of azo dye degradation by a fungus was discovered. At a concentration of 400 mg/L, the decolorization efficiency of Acid Red 73 (AR73) by Aspergillus tabacinus LZ-M was 90.28%. Metabolite analysis and transcriptome sequencing analysis revealed a self-redox process of AR73 degradation, where the electrons generated in carbon oxidation were transferred to the reduction of -C-N = and -NN. The metabolites, 2-hydroxynaphthalene and N-phenylnitrous amide were mineralized into CO₂ through catechol pathway and a glycolytic process. Furthermore, the mineralization ratio of dye was computed to be 31.8% by the carbon balance and electron balance. By using comparative transcriptome, a novel decoloring enzyme Ord95 was discovered in unknown genes through gene cloning. It hydrolyzed AR73 into 2-hydroxynaphthalene and N-phenylnitrous amide, containing a glutathione S-transferase domain with three arginines as key active sites. Here the new mechanism of azo dye degradation was discovered with identification of a novel enzyme in Aspergillus tabacinus LZ-M.