Red mud with enhanced dealkalization performance by supercritical water technology for efficient SO2 capture.

The total de-alkalization treatment of industrial solid waste red mud (RM) has been a worldwide challenge. Removing the insoluble structural alkali fraction from RM is the key to enhancing the sustainable utilization of RM resources. In this paper, supercritical water (SCW) and leaching agents were used for the first time to de-alkalize the Bayer RM and to remove sulfur dioxide (SO2) from flue gas with the de-alkalized RM slurry. The results showed that the optimum alkali removal and Fe leaching rates of RM-CaO-SW slurry were 97.90 ± 0.88% and 82.70 ± 0.95%, respectively. Results confirmed that the SCW technique accelerated the disruption of (Al-O) and (Si-O) bonds and the structural disintegration of aluminosilicate minerals, facilitating the conversion of insoluble structural alkalis to soluble chemical alkalis. The exchangeable Ca2+ displaced Na+ in the remaining insoluble base, producing soluble sodium salts or alkalis. CaO consumed SiO2, which was tightly bound to Fe2O3 in RM, and released Fe2O3, which promoted Fe leaching. RM-SCW showed the best desulfurization performance, which maintained 88.99 ± 0.0020% at 450 min, followed by RM-CaO-SW (450 min, 60.75 ± 6.00%) and RM (180 min, 88.52% ± 0.00068). The neutralization of alkaline components, the redox of metal oxides, and the liquid-phase catalytic oxidation of Fe contributed to the excellent desulfurization performance of the RM-SCW slurry. A promising approach shown in this study is beneficial to RM waste use, SO2 pollution control, and sustainable growth of the aluminum industry.

Investigation of catalytic methane oxidation over Ag/Co2MOx (M = Co, Ni, Cu) catalysts with varying interfacial electron transfer.

Atom-doped Co3O4 catalysts loaded with Ag were examined as cost-effective catalysts for methane oxidation. The synthesized Ag/Co2NiOx catalysts exhibited distinctive surface characteristics in contrast with Ag/Co3O4 and Ag/Co2CuOx catalysts prepared using a similar method. Characterization results unveiled that Ag/Co2NiOx featured a higher presence of active surface oxygen species, lattice defects, a larger surface area, and enhanced reducibility. A methane oxidation catalytic performance followed the sequence: Ag/Co2NiOx > Ag/Co3O4 > Ag/Co2CuOx. The investigation delved into methane degradation pathways on the surfaces of three catalysts, examining their behavior under both aerobic and anaerobic atmospheres through in-situ DRIFTS analysis. Furthermore, introducing Ag showed a marked positive effect on Co-Ni mixed oxide, inducing electron transfer and a more active electron system, whereas it exhibited an inverse impact within the surface of Co-Cu mixed oxide. This work provides innovative perspectives on the development of forthcoming environmental catalysts.

Efficient pyridine biodegradation by Stenotrophomonas maltophilia J2: Degradation performance, mechanism, and immobilized application for wastewater.

Stenotrophomonas maltophilia J2, a highly efficient pyridine-degrading bacterium, was isolated from the aerobic tank of a pesticide-contaminated wastewater treatment plant. The strain J2 demonstrated an impressive pyridine degradation rate of 98.34% ± 0.49% within 72 h, at a pyridine concentration of 1100 mg·L-1, a temperature of 30 °C, a pH of 8.0, and a NaCl concentration of 0.5%. Notably, two new pyridine metabolic intermediates, 1,3-dihydroxyacetone and butyric acid, were discovered, indicating that J2 may degrade pyridine through two distinct metabolic pathways. Furthermore, the immobilized strain J2 was obtained by immobilizing J2 with biochar derived from the stem of Solidago canadensis L. In the pyridine-contaminated wastewater bioremediation experiment, the immobilized strain J2 was able to remove 2000 mg·L-1 pyridine with a 98.66% ± 0.47% degradation rate in 24 h, which was significantly higher than that of the control group (3.17% ± 1.24%), and remained above 90% in subsequent cycles until the 27th cycle. High-throughput sequencing analysis indicated that the J2 +B group had an elevated relative abundance of bacteria and functional genes that could be associated with the degradation of pyridine. The results offer a foundation for the effective use of immobilized strain in the treatment of recalcitrant pyridine-contaminated wastewater.

Detoxification of typical nitrogenous heterocyclic compound from pharmaceutical wastewater by mixed microbial consortia.

Microbial consortia HY3 and JY3 with high degradation efficiency of 2-Diethylamino-4-hydroxy-6-methylpyrimidine (DHMP) were isolated from aerobic and parthenogenic ponds of DHMP-containing pharmaceutical wastewater, respectively. Both consortia were enriched and reached stable degradation performance with a DHMP concentration of 1500 mg L-1. The DHMP degradation efficiencies of HY3 and JY3 were 95.66% ± 0.24% and 92.16% ± 2.34% under the condition of shaking at 180 r·min-1 and the temperature of 30 °C for 72 h. And the removal efficiencies of chemical oxygen demand were 89.14% ± 4.78% and 80.30% ± 11.74%, respectively. High-throughput sequencing results indicated that three bacterial phyla of Proteobacteria, Bacteroidetes, and Actinobacteria were dominant in both HY3 and JY3, but their dominances varied. At the genus level, the richness of Unclassified Comamonadaceae (34.23%), Paracoccus (14.75%), and Brevundimonas (13.94%) ranked top three in HY3 whereas Unclassified Comamonadaceae (40.80%), Unclassified Burkholderiales (13.81%) and Delftia (13.11%) were dominant in JY3. The metabolites of DHMP degradation by HY3 and JY3 were analyzed in detail. Two pathways for cleavage of the nitrogenous heterocyclic ring were speculated, one of which was identified for the first time in this study.

Characterization of pyridine biodegradation by two Enterobacter sp. strains immobilized on Solidago canadensis L. stem derived biochar.

In this study, two pyridine-degrading strains namely Enterobacter cloacae complex sp. BD17 and Enterobacter sp.BD19 were isolated from the aerobic tank of a pesticide wastewater treatment plant. The mixed bacteria H4 composed of BD17 and BD19 at a ratio of 1:1 was immobilized by Solidago canadensis L. stem biochar with a dosage of 2 g·L-1. The highest pyridine removal rate of 91.70% was achieved by the immobilized H4 at an initial pyridine concentration of 200 mg·L-1, pH of 7.0, temperature of 28 °C and salinity of 3.0% within 36 h. The main intermediates of pyridine degradation by BD17 were pyridine-2-carboxamide, 2-aminopropanediamide, and 2-aminoacetamide, while 2-picolinic acid, isopropyl acetate, isopropyl alcohol, and acetaldehyde were identified with BD19 by adopting GC-MS technique. Interestingly, there was a possibility of totally mineralization of pyridine and the corresponding degradation pathways of BD17 and BD19 were revealed for the first time.