Browsing by Subject "stabilization"
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Item Characterization and stabilization of arsenic in water treatment residuals(Texas A&M University, 2004-11-15) Wee, Hun YoungThe characterization of water treatment residuals containing arsenic was investigated in the first study. Arsenic desorption and leachability from the residuals were the focus of this study. Arsenic leaching from water treatment residuals was found to be underestimated by the toxicity characteristic leaching test (TCLP) due to the pH of the leachates being favorable for As(V) adsorption. Competitive desorption of arsenic with phosphate was significant because phosphate tends to compete with As(V) on the surface of the metal hydroxide for adsorption sites. However, arsenic desorption by the competition of sulfate and chloride was found to be negligible. The pH in the leachate was a critical variable in controlling arsenic stability in the residuals. The release of arsenic from the residuals was elevated at low and high pH due to the increase dissolution of the adsorbents such as Fe and Al hydroxides. In the second phase of the study, the stabilization techniques for arsenic contained residuals and were examined to develop methods to suitably stabilize arsenic to eliminate and/or minimize leaching. A decrease of arsenic leaching was achieved by the addition of lime to the residuals and believed to be due to the formation of less soluble and stable calcium-arsenic compounds. However, it is suggested that the ordinary Portland cement (OPC) should be added with the lime for the long term stabilization because lime can be slowly consumed when directly exposed to atmospheric CO2. The solidification and stabilization (S/S) technique with lime and OPC was shown to be successfully applied by the immobilization of a wide variety of arsenic tainted water treatment residuals.Item Synthesis and design of PID controllers(Texas A&M University, 2005-02-17) Xu, Haocontrollers for discrete-time systems and time-delayed systems. By using bilinear transformation and orthogonal transformation, earlier research results obtained in the continuous-time case are extended to discrete-time situation. The complete set of stabilizing PID controllers for the discrete-time systems is thus obtained. Moreover, this set remains to be a union of convex sets when one particular parameter is fixed. Thus a method to design robust and non-fragile digital PID controllers is proposed by following a similar design procedure for the continuous-time systems. In order to find the stabilizing controller set for systems with time-delays, the relationship between the Nyquist Criterion and Pontryagin?s theory is investigated. The conditions under which one can correctly apply the Nyquist Criterion to time-delayed systems are derived. Then, the complete set of stabilizing PID controllers for arbitrary order LTI systems with time-delay up to a given value is obtained. Furthermore, the stability issue of a system with fixed-delay is also studied and a formula which provides complete knowledge of the distribution of the closed-loop poles is presented. Based on this formula, stabilizing P and PI controller sets for the system with fixed-delay can be computed.