Lab Report
Lab Report
Introduction
Air stripping lacks an official academic definition, but a widely accepted definition within the field regards it as the transfer of contaminants from aqueous solutions to air [1]. This process is commonly performed to decontaminate waste water and groundwater for public health purposes, given its ample use in the removal of volatile organic compounds (VOCs) from water into air. Air strippers, the devices that carry out this process, are composed of a cylindrical tank which can contain different materials such as steel, ceramic or plastic. Contaminated water is pumped into the apparatus through its upper inlet, proceeds to flow through the tank and its composing materials which perform the decontamination, and subsequently exists through the outlet placed at the bottom of the device for collection [2]. These devices function under the principle of steady state mass balance.
The experiment consisted in the utilization of two columns with the same dimensions, which were four feet of height and three and a half inches of diameter, but different packing materials. The materials used were 5/8” plastic Pall rings and 1 cm ceramic intalox paddles. Each group varied in the air and water flow rates through the towers. Figures 1, 2 and 3 show the packed column or tower used for this experiment, plastic palls and ceramic saddles, respectively.
Figure 1 – The inlet of contaminated water into the tank is located on the bottom left, and the purified water exits through the outlet in the bottom right. The gas enters through the tube on the bottom left of the tower and is liberated into the atmosphere through the outlet at the top.
Figure 2 – Plastic pall ring
Figure 3 – Ceramic saddle
The first step taken by the groups was the measurement and annotation of the liquid temperatures and atmospheric pressure. Different water and air flow rates were selected and implemented for the operation of the towers, and water samples were collected from each one, after sufficient time had passed to allow for the columns to achieve a steady state. Subsequently, the lab manager used a GC to determine the concentration of toluene in each water sample, through the delta P/Z KLa computation. Afterwards, the overall liquid-capacity coefficients for each test were determined, using the measured outlet and inlet concentrations, as well as the air and water flow rates. These computations were performed in order to have a basis for result comparison, and effectively selecting the best packing material out of the alternatives tested (plastic pall rings or ceramic saddles) by determining the one with the largest KLa. KLa indicates the rate in which mass transfer occurs; therefore, the best packing materials are those with the highest KLa. The analysis of these results is shown in section 3.1.
The final part of this laboratory, the scale up section, consisted in the design of a full size column from the packing material selected as the best performing in toluene-removal from wastewater. The parameters established for this design were: (a) Wastewater flow rate: 800 gpm, (b) Inlet toluene concentration: 40 mg/L, (c) Permissible outlet toluene concentration: 0.5 mg/L. To achieve this outlet concentration given the inlet parameters, each group shall select the adequate air flow rate, air concentration, tower height and diameter, given 300 Pa/m for a specific temperature of operation and atmospheric temperature [3].
Conclusions
This laboratory experiment consisted in testing the process of air stripping, through the use of packed towers to purify toluene-contaminated water. Each team conducted small-scale trials, using towers composed of different packing materials. After analyzing the results, the scale up experiment consisted in the design of a full-sized tower, considering parameters such as liquid and gaseous flow rates, geometry of the packing material, rate of mass transfer and tower dimensions. The designed air stripper tower should be designed with the capacity of purifying industrial amounts of water. In consideration, the comprehension of the air stripping process is important given its wide applications in the industrial water management field.
