[Effect of Magnetic Chitosan Hydrogel Beads with Immobilized Feammox Bacteria on the Removal of Ammonium from Wastewater].

The bacterial reaction of ammonium oxidation coupling with iron reduction (Feammox) has been discovered recently. To improve the ammonium removal efficiency from wastewater of Feammox bacteria, magnetic chitosan hydrogel beads (MCHBs) were prepared via sodium hydroxide co-precipitating-sol-gel method, Feammox bacteria were immobilized to 1-5 mm MCHBs, and the ammonium removal efficiency by MCHBs-Feammox bacteria was compared to free-Feammox bacteria. In addition, the influences of initial ammonium concentration, pH and temperature were assessed. The results showed that the MCHBs were ferromagnetic and exhibited high crystallinity, with the magnetization of saturation of 29.46 emu·g-1. The average rates of ammonia oxidation and iron reduction increased by 42.96% and 20.75% after Feammox bacteria immobilization, respectively, and the most significant effect was observed on 1-2 mm MCHBs-Feammox bacteria (P<0.05). Furthermore, 1-2 mm MCHBs immobilized bacteria worked in less favorable matrix concentrations, temperatures, and pH. Particularly, it could maintain high ammonium removal efficiency with 60.00 mg·L-1 initial ammonium concentration, 25℃ temperature and 4.50 pH. In addition, nitrate and ferrous ions were detected in the system. The highest ammonium removal rate occurred on day 16, reaching 53.62%. These results indicated that MCHBs immobilization can improve the ammonium removal efficiency of Feammox.

Accelerated crystallization of magnetic 4A-zeolite synthesized from red mud for application in removal of mixed heavy metal ions.

To cope with the increasing environmental issues of red mud, an integrated technological route for its comprehensive utilization was developed through the extraction of valuable components and the synthesis of magnetic 4A-zeolite. To accelerate the crystallization process of the synthesized 4A-zeolite, sodium chloride (NaCl) was innovatively employed under hydrothermal treatment. The effects of various parameters, including mass ratio of red mud/NaOH, alkali fusion temperature, alkali fusion time and molar ratio of NaCl/Al2O3, were systematically investigated. The results showed that approximately 81.0% Al, 76.1% Si and 95.8% Fe were utilized from red mud using alkali fusion and acid leaching methods. The optimal conditions of the alkali fusion process were determined as: mass ratio of red mud/NaOH = 1/2, alkali fusion temperature of 800 °C, and time of 90 min. Furthermore, when the molar ratio of NaCl/Al2O3 was kept at 1.5, the crystallization time reduced from 240 min to 150 min, and particle size distributions narrowed from 20-100 µm to 1-10 µm. The practical applications in removal of mixed heavy metal ions (Zn2+, Cu2+, Cd2+, Ni2+, and Pb2+) from wastewater indicated that the as-synthesized magnetic 4A-zeolite is a promising candidate for heavy metals adsorption.

Effects of sulfur on lead partitioning during sludge incineration based on experiments and thermodynamic calculations.

Experiments in a tubular furnace reactor and thermodynamic equilibrium calculations were conducted to investigate the impact of sulfur compounds on the migration of lead (Pb) during sludge incineration. Representative samples of typical sludge with and without the addition of sulfur compounds were combusted at 850 °C, and the partitioning of Pb in the solid phase (bottom ash) and gas phase (fly ash and flue gas) was quantified. The results indicate that three types of sulfur compounds (S, Na2S and Na2SO4) added to the sludge could facilitate the volatilization of Pb in the gas phase (fly ash and flue gas) into metal sulfates displacing its sulfides and some of its oxides. The effect of promoting Pb volatilization by adding Na2SO4 and Na2S was superior to that of the addition of S. In bottom ash, different metallic sulfides were found in the forms of lead sulfide, aluminosilicate minerals, and polymetallic-sulfides, which were minimally volatilized. The chemical equilibrium calculations indicated that sulfur stabilizes Pb in the form of PbSO4(s) at low temperatures (<1000 K). The equilibrium calculation prediction also suggested that SiO2, CaO, TiO2, and Al2O3 containing materials function as condensed phase solids in the temperature range of 800-1100 K as sorbents to stabilize Pb. However, in the presence of sulfur or chlorine or the co-existence of sulfur and chlorine, these sorbents were inactive. The effect of sulfur on Pb partitioning in the sludge incineration process mainly depended on the gas phase reaction, the surface reaction, the volatilization of products, and the concentration of Si, Ca and Al-containing compounds in the sludge. These findings provide useful information for understanding the partitioning behavior of Pb, facilitating the development of strategies to control the volatilization of Pb during sludge incineration.

Effect of different sulfides on cadmium distribution during sludge combustion based on experimental and thermodynamic calculation approaches.

The effects of sulfur compounds on the migration of a semi-volatile heavy metal (cadmium) during sludge incineration were investigated with two methods, i.e., experiments in a tubular furnace reactor and thermodynamic equilibrium calculations. The representative typical sludge with and without the addition of sulfur compounds was incinerated at 850 °C. The partitioning of Cd among the solid phase (bottom ash) and gas phase (fly ash and flue gas) was quantified. The results indicate that sulfur compounds in the elemental form and a reduced state could stabilize Cd in the form of CdS, aluminosilicate minerals, and polymetallic sulfides, whereas sulfur in the oxidized forms slightly increases Cd volatilization during incineration. For Cd solidification points, the inhibition effect on the volatilization of Cd is as follows: S > Na2SO4 > Na2S. Chemical equilibrium calculations indicate that sulfur binds with Cd and alters Cd speciation at low temperatures (<950 K). Furthermore, SiO2- and Al2O3-containing minerals can function as sorbents stabilizing Cd as condensed phase solids (CdSiO4 and CdAl2O4) according to the results of equilibrium calculations. These findings provide useful information for understanding the partitioning of Cd and thus facilitate the development of strategies to control Cd volatilization during sludge incineration.

[Effects of chlorides on Cd transformation in a simulated grate incinerator during sludge incineration process ].

The effects of organic chloride-PVC and inorganic chloride-NaCl on Cd partitioning during sludge incineration with adding Cd(CH3COO)2 . 2H2O to the real sludge were investigated using a simulated tubular incineration furnace. And transformation and distribution of Cd were studied in different sludge incineration operation conditions. The results indicated that the partitioning of Cd tended to be enhanced in the fly ash and fule gas as the chloride content increasing. The migration and transformation of Cd-added sludge affected by different chloride were not obvious with the increasing of chloride content. With increasing temperature, organic chloride (PVC) and inorganic chloride (NaC1) can reduce the Cd distribution in the bottom ash. However, the effect of chlorides, the initial concentration and incineration time on Cd emissions had no significant differences. Using SEM-EDS and XRD technique, different Cd compounds including CdCl2, Na2CdCl4, K2CdCl6, K2CdSiO4 and NaCdO2 were formed in the bottom ash and fly ash after adding NaCl to the sludge. In contrast, after adding PVC to the sludge, the Na2CdCl4 and CdCl2 were the main forms of Cd compounds, at the same time, K4CdCI6 and K6CdO4 were also formed. The two different mechanisms of chlorides effects on Cd partitioning were affected by the products of Cd compound types and forms.