Lab #3 Gas Transfer

Lab #3 Gas Transfer - Laboratory 3 Gas Transfer Team 1 Ben...

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Laboratory 3 Gas Transfer Team 1 Ben Lamac, Nick Vaspoli, Jake Taylor, Miken Shah Environmental Engineering I, Fall 2011 CEE 08311 Section 2 Dr. Jahan 19 October 2011
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Laboratory 3: Gas Transfer, Jahan, 2 Abstract The purpose of this experiment was to find the gas transfer coefficient ( K L a ) in Glassboro tap water when using two different air diffusers. The temperatures and initial dissolved oxygen concentrations ( C* ) of two tap water samples were recorded. The initial concentrations for each sample were 8.68 mg/L and the temperature was 23 o C. In order to lower these initial concentrations of dissolved oxygen (O 2 ) to approximately 2.00 mg/L, cobalt chloride (CoCl 2 ) and sodium sulfite (Na 2 SO 2 ) were added to the water. The reaction between the dissolved oxygen and Na 2 SO 2 was sped up by the catalyst CoCl 2 and reduced the oxygen concentration within the sample of water until the reaction ended. Once around 2 mg/L of dissolved oxygen was present, the air diffuser and dissolved oxygen probe were inserted into the water and air was pumped into the water. As time increased, the dissolved oxygen concentration ( C t ) increased and raw data can be seen in Appendix A. The data was made linear by plotting the natural log of the difference between C* and C t versus time as seen in Figure 1 and Figure 2. When using the black air diffuser, the rate of gas transfer ( K L a ) into the water was 0.0054 sec -1 (19.44 hr -1 ) and rate of gas transfer with the white air diffuser was 0.009 sec -1 (32.4 hr -1 ). The white air diffuser increased the dissolve oxygen concentration in the tap water faster than the black air diffuser. Introduction In environmental processes, gas transfer is a vital unit operation that involves either the desorption or adsorption of gas. Wastewater treatment plants require enhanced transfer of oxygen into activated sludge tanks to maintain aerobic degradation. Water treatment plants require gas transfer to dissolve chlorine gas. Technologies that have been developed to enhance gas transfer include: aeration diffusers, packed-tower air stripping, and membrane stripping. Each of these technologies creates a high interface surface area to enhance gas transfer. Gas transfer simply put is the process of allowing any gas to dissolve in a fluid opposite of that, promoting the release of a dissolved gas from a fluid. The rate at which the gas is transferred is affected by the initial concentration of dissolved oxygen, the alkalinity of the water, how turbulent the mixing is, and the amount of air being pumped into the water. For this lab the team was required to determine the overall gas transfer coefficient. Using two different air diffusers, black and white, the team tested for the difference between the two air diffusers. In order to understand the data, the following equation for aeration kinetics was used;
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Laboratory 3: Gas Transfer, Jahan, 3 (1) where C* is the saturation concentration of oxygen in water (mg/L), K L a
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Lab #3 Gas Transfer - Laboratory 3 Gas Transfer Team 1 Ben...

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