Activated carbon fiber loaded nano zero-valent iron for Microcystis aeruginosa removal: Performance and mechanisms.

Cyanobacterial blooms caused by Microcystis aeruginosa threaten environmental safety and daily life. In this study, an activated carbon fiber-supported nano zero-valent iron composite (ACF-nZVI) was developed to remove Microcystis aeruginosa. The results showed that nZVI was evenly distributed on the activated carbon fibers, preventing aggregation and oxidation. ACF-nZVI achieved a removal efficiency of more than 90 % within a pH range of 3-7. During the reaction, H2O2, which was generated by Fe0, was activated to form ·OH and ·O-2, which dismantled antioxidant enzymes and induced lipid peroxidation. Additionally, ACF-nZVI destroyed the cell wall and membrane, resulting in protein and humus leakage and causing 92.34 % cell damage and death. In this study, an environmentally friendly and stable nanomaterial was developed, offering a novel approach for the safe, cost-effective, and efficient removal of cyanobacteria.

Porous-carbon/manganese composite catalyst transformed from waste biomass as peroxymonosulfate activator for carbamazepine degradation.

Activation of peroxymonosulfate (PMS) with solid catalysts for organic pharmaceutical degradation still faces challenge due to the demand of inexpensive catalysts. In this study, manganese-oxidizing microalgae (MOM) and its associated biogenic manganese oxides (BMO) were employed to prepare biomass-transformed porous-carbon/manganese (B-PC/Mn) catalyst through high-temperature calcination (850 °C). Remarkably, 100 % of carbamazepine (CBZ) was degraded within 30 min in the B-PC/Mn/PMS system. The degradation kinetic constant was 0.1718 min-1, which was 44.0 times higher than that of the biomass-transformed porous carbon mixed with MnOx activated PMS system. 1O2 was generated in the B-PC/Mn/PMS system, which is responsible for CBZ degradation. The MOM-BMO-associated structure greatly increased the specific surface areas and the contents of the C = O and pyrrolic-N groups, which facilitated PMS activation. The structure also induced the generation of Mn5C2, which exhibited a strong adsorption towards PMS. This study provides a novel strategy for preparing catalysts by using waste biomass.

Ecological Impacts Associated with the Qinghai-Tibet Railway and Its Influencing Factors: A Comparison Study on Diversified Research Units.

The ecological impacts of the construction and operation of the main transport infrastructure on the Qinghai-Tibet Plateau cannot be disregarded. Based on different sections, buffers, bilateral sides, and periods, the authors of this study explored the ecological changes along the Qinghai-Tibet Railway through an integrated analysis of the landscape fragmentation index and ecological service value calculation from 2000 to 2020, as well as the influencing factors of differentiated trends, using multinomial logistic regression. It was discovered that there was heterogeneity among the sections, buffers, and bilateral sides in both the landscape fragmentation index and the ecological service value. It was also found that there was recoverability in the operation period, compared to the construction period. The negative correlation between the landscape fragmentation index and the ecological service value was only significant in 2020, which was not enough to fully explain the negative effect between them. Distinct human and natural circumstances have resulted in different consequences. However, regions far away from the main settlement areas, and with lower population densities, could aid in the simultaneous recovery of the ecological service value and landscape fragmentation index. According to these findings, prior studies may have exaggerated the ecological impact of the Qinghai-Tibet Railway. However, it should be highlighted that, in a location with a delicate ecological environment, it is still crucial to consider regional development, infrastructure construction, and ecological protection synchronously.

Carbamazepine removal by the synergistic effect of manganese-oxidizing microalgae and biogenic manganese oxides.

Forty strains of Mn-oxidizing microalgae (MnOMs) with different Mn2+ oxidation mechanisms were identified from two aquatic environments. Among them, three strains of isolates (Chlamydomonas sp. WH1-1, Chlamydomonas sp. WH1-4, and Chlorella sp. WH2-5) oxidize Mn2+ by increasing the ambient pH and by secreting Mn oxidation factors (e.g., superoxide-production enzymes and/or other Mn oxidases) into the extracellular environment at the same time. In carbamazepine (CBZ) removal by MnOMs and/or Bio-MnOx, the combination of MnOMs and Bio-MnOx significantly increased the CBZ (1 mg/L) removal efficiency from 36.05% (by MnOMs alone) and 20.11% (by Bio-MnOx alone) to 80.13% by two synergistic mechanisms. One of the synergistic mechanisms was confirmed as that the Mn2+ was re-oxidized by MnOMs to Bio-MnOx, which can promote the CBZ removal, and another was the mutual exchange of degradation products of CBZ as shared reactants between MnOMs and Bio-MnOx. The degradation intermediates of CBZ were analyzed using high-performance liquid chromatography-tandem mass spectrometry, based on which the CBZ degradation pathway by MnOMs and Bio-MnOx was proposed. These findings expand existing knowledge on the Mn2+ oxidation mechanisms of MnOMs, and indicate that MnOMs and their generated Bio-MnOx are promising for the removal of CBZ or other pharmaceutical contaminants from wastewater.

Effect of ammonium nitrogen on microalgal growth, biochemical composition and photosynthetic performance in mixotrophic cultivation.

To enhance microalgal growth and optimize ammonium utilization, the effect of ammonium on microalgal growth, biochemical composition and photosynthetic performance were investigated by mixotrophic cultivation of microalga Spirulina platensis comparing with autotrophic cultivation. The results indicated that elevated ammonium significantly affected the microalgal growth, but the microalga in mixotrophic cultivation showed better growth and stronger tolerance to higher ammonium. The microalgal proteins were increased by increasing nitrogen concentration. The synthesis of microalgal carbohydrates was inhibited by higher ammonium, especially in mixotrophic cultivation. The addition of ammonium decreased the microalgal lipids in autotrophic cultivation but increased microalgal lipids in mixotrophic cultivation. Ammonium negatively affected the microalgal photosynthetic performance. The inhibition was intensified by elevated ammonium, inducing stronger photosystem protection mechanism, particularly in mixotrophic cultivation. The rate of ammonium inhibition to the microalgal photosystem was quick in the early stage by decreasing electron transport rate of PS II.

Effect of nitrogen limitation on biochemical composition and photosynthetic performance for fed-batch mixotrophic cultivation of microalga Spirulina platensis.

In this study, the effect of nitrogen limitation on microalgal growth, biochemical composition and photosynthetic performance was investigated in fed-batch mixotrophic cultivation of microalga Spirulina platensis, compared with that in autotrophic cultivation. The microalgal biomass productivity was greatly enhanced by mixotrophic cultivation. With nitrogen limitation, the mixotrophic culture accelerated the degradation of microalgal pigments and proteins to supply intracellular nitrogen for maintaining higher biomass productivity, simultaneously accumulating more carbohydrates. The mixotrophic cultivation amplified the adverse effect of nitrogen limitation on the microalgal photosynthetic performance in comparison with autotrophic cultivation. This fed-batch mixotrophic cultivation is an effective strategy for enhancing biomass productivity and total carbohydrates yield under nitrogen limited conditions.