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Selenium and oxygen isotope systematics can be useful tools for tracing sources and fate of Se oxyanions in water. In order to measure δ18O values of selenate, SeO42– must first be sequestered from water by precipitation as BaSeO4(s). However, other dissolved oxyanions insoluble with Ba2+ require removal. Dissolved selenate was separated from dissolved selenite, carbonate, phosphate, and arsenate by addition of Ce3+ cations that quantitatively removed these oxyanions by precipitation as insoluble Ce2(SeO3)3(s), Ce2(CO3)3(s), CePO4(s), and CeAsO4(s), respectively. δ18O-selenate (−8.19 ± 0.17 ‰) did not change after four replicates of selenite removal by Ce2(SeO3)3(s) precipitation and Ce3+ removal by cation exchange (−8.20 ± 0.14, −8.32 ± 0.09, −8.17 ± 0.13, and −8.29 ± 0.13 ‰). δ18O-selenate values (−10.86 ± 0.45 ‰) were preserved also when selenate was pre-concentrated on anion exchange resin, quantitatively retrieved by elution, and processed with Ce3+ to remove interfering oxyanions (−10.77 ± 0.07 ‰). The extraction and purification steps developed here successfully isolated dissolved selenate from interfering oxyanions while preserving δ18O-selenate values. This method should be useful for characterizing δ18O-selenate when present with the co-occurring oxyanions above in laboratory experiments and field sites with high Se concentrations, although further research is required for methods to eliminate any co-occurring sulphate. [ABSTRACT FROM AUTHOR]

The regulation of microbial subpopulations in wastewater treatment plants (WWTPs) with desired functions can guarantee nutrient removal. In nature, "good fences make good neighbors," which can be applied to engineering microbial consortia. Herein, a membrane-based segregator (MBSR) was proposed, where porous membranes not only promote the diffusion of metabolic products but also isolate incompatible microbes. The MBSR was integrated with an anoxic/aerobic membrane bioreactor (i.e., an experimental MBR). The long-term operation showed that the experimental MBR exhibited higher nitrogen removal (10.45 ± 2.73 mg/L total nitrogen) than the control MBR (21.68 ± 4.23 mg/L) in the effluent. The MBSR resulted in much lower oxygen reduction potential in the anoxic tank of the experimental MBR (-82.00 mV) compared to that of the control MBR (83.25 mV). The lower oxygen reduction potential can inevitably aid in the occurrence of denitrification. The 16S rRNA sequencing showed that the MBSR significantly enriched acidogenic consortia, which yielded considerable volatile fatty acids by fermenting the added carbon sources and allowed efficient transfer of these small molecules to the denitrifying community. Moreover, the sludge communities of the experimental MBR harbored a higher abundance of denitrifying bacteria than those of the control MBR. Metagenomic analysis further corroborated these sequencing results. The spatially structured microbial communities in the experimental MBR system demonstrate the practicability of the MBSR, achieving nitrogen removal efficiency superior to that of mixed populations. Our study provides an engineering method for modulating the assembly and metabolic division of labor of subpopulations in WWTPs. IMPORTANCE This study provides an innovative and applicable method for regulating subpopulations (activated sludge and acidogenic consortia), which contributes to the precise control of the metabolic division of labor in biological wastewater treatment processes., Competing Interests: The authors declare no conflict of interest.

Selenium and oxygen isotope systematics can be useful tools for tracing sources and fate of Se oxyanions in water. In order to measure δ 18 O values of selenate, SeO 4 2- must first be sequestered from water by precipitation as BaSeO 4(s) . However, other dissolved oxyanions insoluble with Ba 2+ require removal. Dissolved selenate was separated from dissolved selenite, carbonate, phosphate, and arsenate by addition of Ce 3+ cations that quantitatively removed these oxyanions by precipitation as insoluble Ce 2 (SeO 3 ) 3(s) , Ce 2 (CO 3 ) 3(s) , CePO 4(s) , and CeAsO 4(s) , respectively. δ 18 O-selenate (-8.19 ± 0.17 ‰) did not change after four replicates of selenite removal by Ce 2 (SeO 3 ) 3(s) precipitation and Ce 3+ removal by cation exchange (-8.20 ± 0.14, -8.32 ± 0.09, -8.17 ± 0.13, and -8.29 ± 0.13 ‰). δ 18 O-selenate values (-10.86 ± 0.45 ‰) were preserved also when selenate was pre-concentrated on anion exchange resin, quantitatively retrieved by elution, and processed with Ce 3+ to remove interfering oxyanions (-10.77 ± 0.07 ‰). The extraction and purification steps developed here successfully isolated dissolved selenate from interfering oxyanions while preserving δ 18 O-selenate values. This method should be useful for characterizing δ 18 O-selenate when present with the co-occurring oxyanions above in laboratory experiments and field sites with high Se concentrations, although further research is required for methods to eliminate any co-occurring sulphate.