VOC removal

A wide range of organic pollutants can be adsorbed by MFl, Y and mixtures of the two structure types. In the VOC application fixed beds are comparatively few with most VOC adsorption being done by rotary adsorbers such as are built and sold by Seibu Giken. A few words about rotary adsorption applications follow in Section 9.7. 

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Eliminate use of open ponds - Open ponds used to cool, settle out solids and store process water can be a significant source of VOC emissions. Wastewater from coke cooling and coke VOC removal is occasionally cooled in open ponds where VOCs easily escape to the atmosphere. In many cases, open ponds can be replaced with closed storage tanks. 

VOC Removal efficiencies for gas absorbers vary for each pollutant-solvent system and with the type of absorber used. Most absorbers have removal efficiencies in excess of 90 percent, and packed-tower absorbers may achieve efficiencies greater than 99 percent for some pollutant-solvent systems. The typical collection efficiency range is from 70 to greater than 99%. 

Modification techniques for activated carhon were used to increase the removal capacity by surface adsorption and to improve the selectivity to volatile organic compounds (VOCs). Modified activated carbons (MACs) were prepared by modifying the purified activated carbon with various acids or bases. The effects of adsorption capacity and modified contents on the textural properties of the MACs were investigated. Furthermore, VOC adsorption and desorption experiments were carried out to determine the relationship between the adsorption capacity and the chemical properties of the adsorbents. High adsorption capacity for the selected VOCs was obtained over lwt%-H3P04/AC (lwt%-PA/AC). As a result, MAC was found to be very effective for VOC removal by adsorption with the potential for repeated use through desorption by simple heat treatment. 

Several techniques for VOC removal have been investigated such as thermal incineration, catalytic oxidation, condensation, absorption, bio-filtration, adsorption, and membrane separation. VOCs are present in many types of waste gases and are often removed by adsorption [1]. Activated carbon (AC) is commonly used as an adsorbent of gases and vapors because of its developed surface area and large pore volumes [2]. Modification techniques for AC have been used to increase surface adsorption and hence removal capacity, as well as to improve selectivity to organic compounds [3]. 

These results have confirmed that the VOC removal is more useful in a fluidized photoreactor than that in a steady photoreactor, and in particular when Al-Ti02 photocatalyst is used. 

Aeration can be applied to well water contaminated by VOCs. It has been reported that 95-99% reduction in high-level (>100 pg/L) VOCs can be obtained by aeration. However, it should be noted that aeration is less effective for VOCs removal at lower concentrations (<10 pg/L). Boiling can further enhance the reduction of VOCs.60101102... 

The results of the air quality surveys and interviews with the residents indicated that dust, particulates and bioaerosols are major problems in Hong Kong residential homes. The high level of carbon monoxide produced during cooking must be addressed. Odors are the most common complaints from the residents despite the recorded low level of VOCs. This is understandable since the threshold odor for most of these compounds is very low. The team therefore recommends that the product should feature aerosols (i.e., dust and particulates), bioaerosols (i.e., airborne bacteria and fungi), carbon monoxide and odor (i.e., VOCs) removal technologies. 

Table 12.9-3 summarizes the results of the VOC removal and remediation tests conducted on the Prototype Unit. The results indicate that better than 75 % per pass reduction can be obtained for VOC level less than 50 ppm. At least 50 % reduction is obtained for concentrated VOC (> 50 ppm) airstream. The conversion rate depends on the VOC and its concentration. The Prototype Unit is very effective in removing odorous compounds such as Chinese incense and air freshener used in most Hong Kong household. 

Figure 12.9-6. A small prototype unit (a) consists of a fan and coated monolith was placed in a test chamber shown in (b) and tested for VOC removal at ambient conditions, (c) The results show that the VOC level was decreased by half in less than an hour.

Biweekly laboratory VOC removal and remediation tests were conducted using 10-15 ppm of ethanol. The VOC removal remained unchanged at around 80 % per pass or 40 mmole/h. 

The Prototype Unit was cleaned and tested for VOC removal and remediation using 10-15 ppm of ethanol. The VOC removal remained unchanged at around 80 % per pass or 40 mmole/h. This indicates that the formulated catalyst remained active after a total of one-month laboratory test and six months of field study at the clinic. The Prototype Unit was given as a gift to the doctor for permitting us to conduct the field test at the clinic. 

SPSH has several advantages. It is applicable to sites where contaminants are present as non-aqueous-phase liquids (NAPLs). The technology reduces volatile organic carbon (VOC) removal time to a few weeks for a typical site, whereas soil vapor extraction (SVE) alone requires years for remediation. This reduction in removal time can signrhcantly decrease costs over SVE (from 2 to 10 times). Excavation and ex situ soil treatment is typically much more expensive to implement than SPSH, especially at deep sites. 

The unit cost of the technology during a pilot-scale demonstration at the DOD s Shaw Air Force Base in Sumter, South Carolina, was 8700/lb of VOCs removed. Based on this test, the estimated cost for a full-scale demonstration of 400-by-300-ft area was 2.5 million over 3 years (D200964, p. 17). 

The duration of the remediation is dependent on the soil type, water content, and the nature of the contaminants. The HRUBOUT process cannot remove metals from soils. Polychlorinated biphenyls (PCBs) cannot be totally removed. The in situ HRUBOUT process is designed for removing contaminants from the vadose zone, (i.e., the zone between the surface aud the water table). Low permeability lowers system effectiveness and raises remediation costs. Soils with variable permeabilities may cause uneven delivery of air to contaminants. VOC removal rates may be reduced by high organic content in the soil because soil orgauics have a high VOC-sorption capacity. 

At the Sand Creek Superfund site, project costs were 2.14 million. This value does not include the cost for demobilization activities. It was determined that 81,231 of the total cost of the project was spent on mobilization and other pretreatment activities. Activities relating to treatment accounted for 2,058,564 of the total project cost. This corresponds to a treatment cost of 39 to 65/yd of soil treated and 11.70/lb of VOCs removed (D22777U, p. 23). 

E-Z Stacker and E-Z Tray are commercially available modular air strippers for the ex situ removal of volatile organic compounds (VOCs) from groundwater. E-Z Stacker consists of 4 or 6 stacking units E-Z Tray units are arranged in pull-out drawers. The multiple sieve tray design of the E-Z Stacker uses forced-draft air bubble generation to provide VOC removal. All information is from the vendor and has not been independently verified. 

Pounds of VOCs removed during vacuum extraction 12,096 (5485 kg)... 

The U.S. Department of Energy s (DOE s) Los Alamos National Laboratory (LANE) conducted a costs analysis of in situ air stripping technology based on data from a 1995 demonstration at the DOE s Savannah River Site (SRS) near Aiken, South Carolina. Capital costs were annualized over an estimated 10-year equipment life. Carbon adsorption was included for off-gas treatment. The total cost of the demonstration was 15.59/lb of VOC removed. Table 1 shows a more detailed breakdown of these costs (D15726Q D188083). 

In 1996, the Environmental Process Improvement Center (EPIC) estimated the remediation costs for a two-phase extraction process would range from 70 to 160/lb of VOCs removed. EPIC is an alliance between the U.S. Department of Defense s (DOD s) McClellan Air Force Base, the U.S. Environmental Protection Agency (EPA), and the Cahfomia Environmental Protection Agency (Cal-EPA) (D21566H, pp. 1, 3). 

For optimum efficiency, humidity levels, temperature, and pressure should be monitored and controlled during the adsorption. The adsorption process of VOCs removal is exothermic in the most cases, which should be considered as a significant design parameter, since there is a risk of fire in the removal of high loads of organic compounds that exhibit high heats of adsorption. 

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