Activated Carbon is Ideal for PCB Removal

TIGG’s GAC adsorption equipment is used to remove PCBs from groundwater.

For more than 50 years, polychlorinated biphenyls (PCBs) were commonly used in industrial materials including, caulking, cutting oils, inks, paints and as dielectric fluids in electrical equipment such as transformers and capacitors. Concerns over health effects led to a North American ban of manufacturing PCBs in 1977. By the mid-1980s, an initiative was started to clean up contaminated areas and to phase out PCB-containing equipment and products that were still in use. This cleanup effort continues today.

Careless disposal practices and accidental discharges in the past contribute to the present amount of PCBs in groundwater and in sediments of rivers and lakes. Growing public and government concern over health hazards has led to new practices to safely remove and dispose of PCBs. Residual contamination has been effectively treated by systems using activated carbon adsorption media.

Activated carbon is widely used for the adsorption of many contaminants from liquid and air streams. The activated carbon is produced from carbonaceous organic substances including bituminous coal, coconut shell, lignite, bone, wood and other materials. It is used in many applications such as food production and liquid decolorization.

Adsorption results from a physical process in which layers of atoms or molecules of one substance are attracted onto the surface structure of another substance. Activated carbon’s extremely high surface area within its extensive pore structure makes it an ideal adsorbent. One pound of activated carbon has the surface area equivalent to six football fields.

Activated carbon exhibits a graphitic plate structure, and one may liken the formation of adsorption surfaces to a box of peanut brittle, with the highest energy adsorption sites formed at the intersections of the plates (see image below). The iodine number is used as a general measurement of the surface area of the activated carbon. These numbers generally range from 900-1100 for higher quality carbons.

Activated carbons tend to adsorb organic compounds with increasing affinity as adsorbate (the material being adsorbed) molecular weight, boiling point, and refractive index increase and as solubility decreases. Thus, activated carbon has a high affinity for PCBs due to their high molecular weight, high indices of refraction, and very low solubilities. PCBs have a very large molecular structure and for effective adsorption will require an activated carbon with a compatible pore size. Different base materials will yield different pore structures. For example, the pore structure of coal-based carbon will better accommodate these types of molecules as compared to coconut-based carbon. The latter are more suited to smaller molecular weight compounds with low boiling points and, therefore, are not as effective in this application.

The surface loading of adsorbate on activated carbon varies with the concentration and conditions in the fluid stream. In order to evaluate the economic potential of an application, the activated carbon isotherms can be developed for the particular compound at a given set of conditions. Many isotherms are already available for various compounds, including PCBs. They can be obtained from carbon manufacturers, purifications companies, and EPA literature. They also can be developed in the lab using simple procedures.

The figure below illustrates an isotherm for a PCB molecule with one chlorine atom on TIGG 5D 1240 coal-based activated carbon. As with any testing, these isotherms are performed under controlled laboratory conditions. Actual performance in the field can be affected by factors associated with the treatment system.

When dealing with PCB contaminated groundwater, the solubility of the PCB isomers molecules in the water can typically range between 20 parts per billion (ppb) and 60 ppb with solubilities generally below 1 part per million. Above these levels, the PCBs will be found as free product. As illustrated by the isotherm, PCBs are readily adsorbed by activated carbon, with the example of the PCB isomer with only one chlorine atom (the lowest affinity for all PCB isomers) showing excellent loading on the carbon, even at 1 ppb levels. The result is that effluent levels below 1 ppb are achievable.

Treatment of this water depends not only on keeping the carbon “clean” for proper kinetic transference of the molecules but also the contact time allowed for the adsorption to take place. Field experience has shown that often under turbid conditions, the PCB levels in the effluent following the carbon adsorbers in the treatment train can be as high as 5 ppb. The reason for the higher than expected levels in the effluent is that the PCBs will attach to colloidal material in the water or any carbon fines and pass through the bed without being adsorbed.

In order to decrease these residual levels, the treatment requires upstream and downstream filtration. Typically a 5-10 micron bagfilter is installed prior to the carbon bed and a 0.5 micron bagfilter is installed after the carbon bed, prior to discharge. These processes remove most suspended solids that may be entering the carbon and essentially “plugging” the bed of the carbon thus limiting adsorption; and, capturing any solids that may be making their way through to the effluent.

In addition to the pre- and post-filtration of the carbon bed, the carbon bed needs to be properly sized. Both the bed surface area and the carbon bed depth affect removal efficiency. About seven to eight minutes empty-bed contact time (EBCT, or time to pass fluid through a give actual volume of carbon present as a theoretically open volume) is optimal for proper adsorption.

Typically, a minimum of three feet carbon bed depth is required. The surface area is typically designed to promote a superficial velocity of four to six gallons per minute per square foot. Slower velocities can be used, but very low velocities should be avoided as this may promote the occurrence of channeling, or the liquid seeking a path of least resistance through the carbon bed, resulting in poor distribution.

Overall, activated carbon adsorption is an effective way of reducing PCB’s contamination in groundwater. Successful results can be achieved with a properly designed system that addresses both pre-filtration and post-filtration, along with proper carbon selection and bed design parameters including bed surface area, depth, and contact time.

For additional information on Activated Carbon’s role in Environmental remediation Applications, visit TIGG’s Activated Carbon Information Library at http://www.tigg.com/library

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Safety Main Goal As Expert Recertifies TIGG in HAZWOPPER Procedures

ImageTIGG technical sales representatives, engineers and other employees attended an eight-hour Hazardous Waste Operations and Emergency Response (HAZWOPER) refresher course on July 11 at the company’s Oakdale, Pa. headquarters.

The yearly refresher course, which follows a one-time, 40-hour OSHA class, is mandatory for individuals whose duties may take them to a job site that could contain hazardous materials.

“I believe it is important for workers to identify and predict potential hazards for their own safety,” said David Thomson, an instructor for TMC LTD., an environmental, health and safety consulting firm. “My goal is to give participants the ability to make informed decisions when it comes to being safe.”

During his lecture, Thompson covered topics such as confined space entry, hazardous material placard identification, emergency response procedures and the proper use of protective equipment.

At one point in the lesson, participants donned protective gloves and the instructor filled the palms of their hands with shaving cream. They were then tasked with carefully removing the gloves by turning them inside out while trying not to let the shaving cream escape.

This exercise demonstrated the necessity to proceed with caution after coming into contact with hazardous materials.

TIGG Senior Vice President Anthony Mazzoni explained that the HAZWOPER recertification is essential because it means that credentialed company representatives can visit client sites to provide technical advice and expertise during system set-up and operations. It allows TIGG employees to be onsite while assessing various treatment technologies and helping clients troubleshoot complex adsorption and filtration systems.

“I think everything we talked about today was important,” said Mike Bickel, a participant in the HAZWOPER recertification class and TIGG business development manager.

“This refresher course helped put safety back at the top of my mind where it belongs.”

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HAZWOPER refresher course instructor David Thompson shows TIGG employees the proper way to remove protective gear during an eight-hour curse at TIGG’s Oakdale, Pa. headquarters on July 11.

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TIGG has article published in Pollution Engineering Magazine

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TIGG Integrates Ideas and Technologies to Provide Remediation Rental Success

When an environmental remediation company secured a contract to clean up the site of a former manufactured gas plant in a New York community, it realized the process would require a host of different technologies to address contaminated soil as well as ground and surface water.

TIGG Corporation was called upon to provide a solution for treating the contact water because of its ability to meet the company’s requirements of reasonable pricing, immediate rental equipment availability and technical expertise.

TIGG helped rescue the project, which initially employed one of its competitors, who provided inadequate engineering and a solution that was not meeting treatment objectives.

“With the goal of removing contaminants from groundwater in an area near a shopping center, we worked with the remediation contractor to help ensure the safety of the public,” said TIGG Director of Project Engineering Jeff Iman. “We delivered an idea and the apparatus to implement it in a little over three weeks.”

Initially, TIGG developed a water treatment system that combined various technologies to separate oil and coal-tar residuals from the contact water. This process included gravity separators, centrifugal pumps, bag filter units and vessels containing oil-absorbent media and activated carbon.

However, it was soon discovered that cyanide was prevalent in the water. The remediation contractor suggested that iron coprecipitation be used to treat the water and remove the substance. Prior to implementing this plan, the contractor asked TIGG to confirm the treatment process in the laboratory.

After meticulously bench-testing different treatment methods, TIGG identified an anion exchange resin as the best method for removing cyanide from the contact water.

Once the environmental remediation company saw the test results, TIGG incorporated a secondary bag filter skid into the plan and added two anion water filtration vessels. This additional equipment safely removed the cyanide from the water.

As part of its overall service agreement with the environmental remediation contractor, TIGG exchanged spent media with fresh media in the filtration vessels, while offering continuous technical support on the overall process.

“Thanks to our bench testing and ability to integrate various technologies to meet changing needs, the project was executed in a timely and effective manner,” said Iman. “The end result was clean water ready to be introduced back into the local ecosystem.”

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TIGG Engineers Add Durability to Municipal Project

A New Jersey water treatment plant needed to meet increasing demands on its services by initiating a new water filtration project. TIGG Corp.’s engineers looked at the municipality’s specifications and suggested improvements to extend the life of the filtration tanks, increasing the overall value of the project.

TIGG Corp. engineers came up with an enhanced under-drain design and recommended lining the filtration tank with a more durable epoxy. The improved epoxy provides tighter cross-linking, thereby decreasing the tank’s permeability.

“Making design recommendations to existing specifications is something our engineers do all the time,” said TIGG Corp. Vice President Anthony Mazzoni. “In this case, their expertise provided a more durable and robust system for the municipality.”

The tank, which will remove iron from the communities’ drinking water by using sand, anthracite, garnet and gravel as filtration media, is separated into three internal compartments by internal walls. The three compartments allow water flow to continue in two compartments, while the off-stream compartment is backwashing. The system lets the water treatment plant backwash one compartment using the water generated by the other two.

TIGG Corp. delivered the custom-built, 10 foot diameter, three-compartment pressure filter in July and the municipality is currently constructing a new building around it. The water treatment facility’s schedule calls for the pressure filter to come on line later this year.

“Not only does TIGG Corp. have a standard product line of equipment for treating potable water, we have the ability to customize and enhance existing designs to meet our customers’ unique requirements,” said Mazzoni.

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TIGG is Presenting at the Montreal Protocol

Today, Anthony Mazzoni of TIGG Corporaiton is presenting at the Montreal Protocol on Substances that deplete the Ozone Layer.

TIGG Corporation is presenting the TIGG Methyl Bromide Recapture System, an activated carbon filtration system that treats methyl bromide emissions to the USDA-APHIS standards.

Read more about TIGG’s Methyl Bromide Recapture System and what this means for industrial fumigators: http://www.tigg.com/newsarchives.html#MethylBromideRecaptureUsingActivatedCarbon

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