Phosphate Removal from Digested Sludge Supernatant Using Modified Fly Ash
The removal of phosphate in digested sludge supernatant by modified coal fly ash was investigated in this study. Modification of the fly ash by the addition of sulfuric acid could significantly enhance its immobilization ability. The experimental results also showed that adsorption of phosphate by the modified fly ash was rapid with the removal percentage of phosphate reaching an equilibrium of 98.62% in less than 5 minutes. The optimum pH for phosphate removal was 9 and the removal percentage increased with increasing adsorbent dosage. The effect of temperature on phosphate removal efficiency was not significant from 20 to 40 °C. X‐ray diffraction and scanning electron microscope analyses showed that phosphate formed an amorphous precipitate with water‐soluble calcium, aluminum, and iron ions in the modified fly ash.
Fly ash characterization by SEM–EDS
A study conducted at the National Energy Technology Laboratory characterized twelve Class F fly ash samples from nine PC power plants in PA, WV, MD and TN, using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Both the surface and internal structure of fly ash particles were analyzed. All of the fly ash samples were comprised mainly of amorphous alumino-silicate spheres and a smaller amount of iron-rich spheres. The majority of the iron-rich spheres had two components: iron oxide and amorphous alumino-silicate. Both materials were apparent on the particle surface, and cross-sections clearly showed that the iron oxide and alumino-silicate were mixed throughout the fly ash particles. Calcium, the fourth most abundant element in the fly ash, was associated with oxygen, sulfur or phosphorous, not with silicon or aluminum. The calcium-rich material was distinct in both elemental composition and texture from the amorphous alumino-silicate spheres. The elemental concentrations, as determined by EDS, were consistent with ICP-OES and X-ray diffraction data.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.