Adsorption Mechanism of High-Concentration Ammonium by Chinese Natural Zeolite with Experimental Optimization and Theoretical Computation

Removal of Ammonium Ions from Aqueous Solutions Using Alkali-Activated Analcime as Sorbent

Five alkali-activated analcime (ANA) sorbents (ANA-MK 1, ANA 2, ANA 3, ANA-MK 4, and ANA-MK 5) were developed for ammonium (NH4+) ion removal. Acid treatment and calcination were used as pre-treatments for analcime, and metakaolin (MK) was used as a blending agent in three sorbents. Sorption experiments were performed to evaluate the effects of sorbent dosage (1–20 g L−1), initial NH4+ ion concentration (5–1000 g L−1), and contact time (1 min–24 h). ANA-MK 1, ANA 2, and ANA-MK 4 were the most efficient sorbents for NH4+ ion removal, with a maximum experimental sorption uptake of 29.79, 26.00, and 22.24 mg g−1, respectively. ANA 3 and ANA-MK 5 demonstrated lower sorption capacities at 7.18 and 12.65 mg g−1, respectively. The results for the sorption of NH4+ ions onto the alkali-activated analcime surfaces were modeled using several isotherms. The Langmuir, Freundlich, Sips, and Bi-Langmuir isotherms were the best isotherm models to represent the studied systems. The results of the kinetic studies showed the maximum NH4+ ion removal percentage of the sorbents was ~80%, except for ANA-MK 5, which had a ~70% removal. Moreover, the pseudo-first-order, pseudo-second-order, and Elovich models were applied to the experimental data. The results showed that the sorption process for ANA-MK 1, ANA 2, ANA 3, and ANA-MK 4 followed the Elovich model, whereas the pseudo-second-order model provided the best correlation for ANA-MK 5.

Metabolic fates and response strategies of microorganisms to aromatic compounds with different structures

In this study, the metabolic fates and response strategies of microorganisms to aromatic compounds with different structures (phenol, naphthalene, phenanthrene, and pyrene) were comparatively studied. The results indicated that the phenol (90.9%), naphthalene (68.4%), phenanthrene (69.5%), and pyrene (67.1%) could be mineralized, and the biotoxicity also has been drastically reduced. The degradation characteristics and toxic effects were closely related to their chemical structure. The microorganisms showed different response strategies to aromatic compounds with different structures. Phenol had a simple structure and low toxicity, the microbial community structure was simple, and the rapid expression of key enzymes enabled it to be rapidly degraded. For the hydrophobic and complex naphthalene, phenanthrene, and pyrene, the more complex the structure, the higher the microbial diversity, the EPS showed different response for the purpose of improving their bioavailability, and the activity of key enzymes was positively correlated with their structural complexity.