Adsorption Lab Method and Report

Objective - To better understand adsorption by observing the breakthrough of an organic dye through three columns, in series, packed with granular activated carbon (GAC). This may help teams understand the operation of water filters that incorporate activated carbon.

Equipment / Supplies - three columns, 75 cm long with a diameter of 2.5 cm, each filled with approximately 250 g activated carbon; ~200 L of ~ 20 mg/L Brilliant Blue G solution (a dye) and one large container to hold it all; one peristaltic pump capable of pumping between 20 ml/min; tubing and valves sufficient to connect the pump and the three GAC columns in series and to allow sampling before and after each GAC column; one spectrophotometer capable of reading the absorbence of 580 NM light; a large number of 1 cm spectrophotometer tubes; three 1 L beakers; and one 250 ml graduated cylinder; one stopwatch.

Method

1. Create a calibration curve for Brilliant Blue G. Measure the absorbence of light for solutions of 1.2, 6, and 30 mg/L Brilliant Blue G. Use 580 NM light. Plot Concentration (Y-axis) versus Absorbence (X-axis). Determine the equation of the best-fit line through the data using Excel (Make a plot, right-click on the data, use the trendline function). Your R-squared (R-squared can be determined using the trendline function "Options") value should be very close to 1 (at least 0.99). This equation is your calibration curve. You will use it to estimate the concentration of water sampled during the experiment.

2. Use your calibration curve to measure the concentration of the solution of Brilliant Blue G you'll be pumping through the columns (the influent). It should be ~20 mg/L. Record the absorbence and estimated concentration in your lab book. This experiment will run for at least three weeks, so we'll have to refill our 200L container more than three times.

3. Determine UMac, the unit mass of the activated carbon (g/cm3), using information given in the equipment list. UMac is the mass of activated carbon per unit volume of activated carbon. Determine the cross sectional area, A, of a column, using information given in the equipment list.

4. Create a data sheet in your Notebook. You will need 6 columns. Label the columns as shown below.

5. Fill one of the 1 L glass beakers with ~ 1 L tap water. Set the pump to the "line" and turn on. Make sure water is flowing the correct direction. Adjust the flow rate to 20 ml/min (+/- 1 ml/min) or another flow rate , as directed in class. Use the graduated cylinder and a stop watch to measure the flow rate. Record the flow rate periodically throughout the experiment, recording the time of measurement, using the clock on the column between 302 and 302.

6. Adjust the valves such that water will flow through the entire series of columns. Connect the pump to the first column. Place the inlet tube into the ~ 200 L solution of ~ 20 mg/L Brilliant Blue G. As soon as blue water reaches the bottom of the first column, record the time using the clock on the column between 302 and 302. Sample (and analyze) the effluent (outflow) of the first column as soon as water reaches its outlet valve. Record the time. Sample (and analyze) the effluent (outflow) of the first two columns as soon as water reaches the second column's outlet valve. Record the time. Once water exits the final column, sample the three columns at roughly the same time. Always record the time when you sample a column. You won't be able to sample columns simultaneously.

IMPORTANT - to collect a sample: open the sample valve, collect the sample, and close sample valve. You may also need to open and close the final valve to get water to come out the sample valve. Repeat this for each sample. Try to divert as little water as possible. Make sure that the water always has somewhere to go or you may wreck the columns! Imediately measure the absorbence of the solution in the spectrophotometer tube, then rinse it with DI water.If you reuse a 1 cm spectrophotometer tube and it has some water in it, rinse it with the water to be collected just before collecting the actual sample; however, don't use spectrophotometer tubes that are stained!

7. Sign up for sampling times. We will sample every hour for the first day, then twice daily for the remainder of the experiment.

8. Enter data into an Excel spreadsheet. Use nine columns, as shown below. Use the calibration equation to calculate concentration from absorbence.

9. Using Excel, plot concentration (Y-axis) versus time (X-axis) for each column, on one graph. Use the graph to determine the time to breakthrough for each GAC column (the time for the effluent concentration to reach 10 % of Co, where Co is the influent concentration to the first gAC column (i.e., 20 mg/L). Determine the time for the effluent concentration to reach 90 % of Co for each GAC column, if possible. Depending on how long we run the experiment, we may or may not be able to reach 90 % of Co for GAC columns 2 and 3.

10. Plot the time to reach 10 % of Co (Y-axis) versus bed depth (X-axis), where bed depth is the cumulative length of column up to a given sampling point (i.e., 75 , 150, and 225 cm). If possible, plot the time to reach 90 % of Co versus bed depth, on the same graph. For our system, the sampling points are at 75 , 150, and 225 cm bed depth. Fit a straight line to the line(s) using Excel (Make a plot, right-click on the data, use the trendline function). Record the line equation(s) and R-squareds. The inverse of the slope of the line(s) is the velocity with which the adsorption zone moves through the GAC Columns.

11. Estimate the amount of carbon needed per day to treat your flow rate using the equation given below.

Mac = A (1/a) UMac

Where Mac = mass of activated carbon needed per day, g/d; A = cross-sectional area of column, cm2; a = slope of time versus bed depth curve, d/cm; and UMac = unit mass of activated carbon, g/cm3.

NOTE: This kind of study is conducted at a specific loading rate (also called a flux). The loading rate is the flow rate divided by the cross-sectional area of the column. The data obtained at the loading rate are applicable only to designs that will use the same loading rate.

Format of Written Project

This is a "stand alone" report. The results of this experiment will not be included in the midsemester or final reports and presentations. However, completing this experiment (and report) should help students understand the operation of water filters that incorporate activated carbon, and this understanding should be incorporated into the final report and presentation.

Submit one report per team. Reports must be printed and stapled in the upper left-hand corner and have 2.5 cm margins on all sides. The type font must be 12 points. The line spacing should be double-spaced. Each page should be numbered (in Word, use Insert, Page Numbers). For help on report writing refer to the chapters "Representations of Technical Information" and "The logical structure of Technical Reports, Section by section" in the course text. The written project must contain the following:

1) A letter of transmittal addressed to your section professor stating the report title, what is in the report and why you are submitting it.

2) Cover Sheet - Use a descriptive title (give the brand and model) include team names, submittal date, and course and instructor name.

3) The body of the report, containing the following sections (see "The logical structure of Technical Reports, Section by section" in the course text for detailed descriptions):

Abstract

Introduction

Methods and Materials - this is called "the procedural section" in your course text.

Results - Include appropriate tables (e.g., results) and figures (e.g., drawings of the experimental apparatus, graphs of results) after their first mention in the text.

Discussion - The discussion section is based on information presented in previous sections. End the discussion by applying what you've learned to water filters incorporating activated carbon.

Appendix - include the raw results of testing in the appendix.