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Microbial processes are crucial in the redox transformations of toxic selenium oxyanions. This study focused on isolating an efficient selenate-reducing strain, Azospira sp. A9D-23B, and evaluating its capability to recover extracellular selenium nanoparticles (SeNPs) from selenium-laden wastewater in different reactor setups. Analysis using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) revealed significantly higher extracellular SeNPs production (99%) on the biocathode of the bioelectrochemical (BEC) reactor compared to the conventional bioreactor (65%). Further investigations into the selenate reductase activity of strain A9D-23B revealed distinct mechanisms of selenate reduction in BEC and conventional bioreactor settings. Notably, selenate reductases associated with the outer membrane and periplasm displayed higher activity (18.31 ± 3.8 µmol/mg-min) on the BEC reactor's biocathode compared to the upflow anaerobic conventional bioreactor (3.24 ± 2.9 µmol/mg-min). Conversely, the selenate reductases associated with the inner membrane and cytoplasm exhibited lower activity (5.82 ± 2.2 µmol/mg-min) on the BEC reactor's biocathode compared to the conventional bioreactor (9.18 ± 1.6 µmol/mg-min). However, the comparable kinetic parameter (K_m) across cellular fractions in both reactors suggest that SeNPs localization was influenced by enzyme activity rather than selenate affinity. Overall, the mechanism involved in selenate reduction to SeNPs and the strain's efficiency in detoxifying selenate below levels regulated by U.S. Environmental Protection Agency have broad implications for sustainable environmental remediation strategies.
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Tellurite Reduction and Extracellular Recovery of Tellurium Nanorods Using Bioelectrochemical Reactors
Tellurium is a critical mineral for the foreseeable future due to its scarcity and importance in future energy technology. A biocathode of a bioelectrochemical reactor (BEC) was used for the first time to extracellularly reduce TeO32- in simulated wastewater to elemental Te0 nanorods, which could potentially be recovered. Scanning transmission electron microscopy revealed that only 2% of the cells on the biocathode contained intracellular Te0 nanorods. In contrast, in the conventional bioreactor (CBR), 40% of the cells contained intracellular Te0 nanorods. Raman spectroscopy determined that the Te0 nanorods were trigonal and amorphous Te0. Microbial community analysis showed the dominance of Pseudomonas, Stenotrophomonas, and Azospira phylotypes in the cathode chamber, despite being < 8% in the inoculum. They were all putative TeO32- reducers due to their known ability to reduce tellurite and transfer extracellular electrons. The TeO32- removal efficiency in the BEC reactor reached 97% when the influent TeO32- was 5 mg Te/L. The reactor operating conditions, including the flow rate, the external resistor, and the cation exchange membrane, were optimized. This work demonstrates the potential of BEC reactors for continuous and green synthesis of Te0 nanorods.
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- Award ID(s):
- 2029682
- PAR ID:
- 10549863
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- ACS ES&T Water
- Volume:
- 4
- Issue:
- 10
- ISSN:
- 2690-0637
- Page Range / eLocation ID:
- 4579-4590
- Subject(s) / Keyword(s):
- biocathode, extracellular tellurium nanorods, resource recovery, scanning transmission electron microscopy, tellurite
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsestwater.4c00588
