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Many newer treatment systems are having to deal with an altered wastestream containing backwashed levels of a well-known toxin.
One of the hottest and often controversial topics in worldwide water regulations is that of arsenic in drinking water. But arsenic can also be a problem when dealing with industrial wastewater streams, as the two are closely related. Arsenic is a naturally occurring chemical found in the earth’s crust. It can be dangerous to humans when it is released into drinking water supplies through the erosion of rocks and soils or when it finds its way back into the environment when released into a wastewater stream. Studies have linked long-term exposure to arsenic contamination with cancer and cardiovascular, pulmonary, immunological, neurological, and endocrine effects.
Arsenic from rocks and soils can be released into the environment through geological events, such as volcanic activity and erosion. Some industrial processes, such as mining, smelting, and the production of paints, metals, soaps, dyes, drugs, semi-conductors, and wood preservatives, may also release arsenic into the environment.
There are two different forms of arsenic: arsenite (arsenic III) and arsenate (arsenic V). Arsenic V is the most common form and is easier to remove from drinking water. Arsenic III is more difficult to remove and is more hazardous to human health.
Crossover In Challenges With Arsenic
In the United States, a big issue with arsenic is that since the EPA revised the drinking water standard, a lot of the treatment facilities and companies are installing new treatment systems—systems that now have to deal with an altered wastestream containing backwashed arsenic. As a result, new aquifer protection programs become important, according to Jason Jones, supervisor of the water quality-monitoring unit of the Arizona Department of Environmental Quality.
“They now have to figure out where to place that new wastewater,” says Jones. “They may decide to place it in an impoundment, which may be tough to do because of permitting issues. A lot of these different treatment systems using reverse osmosis have a wastestream; if they do and they go to an impoundment, we’d need to permit that. We protect the environment from anything that could discharge to the aquifer.”
In order to protect the aquifer, Jones makes sure that any companies involved receive a permit through his office. Various industries or municipalities must meet some main demonstrations using best available demonstrated control technology (BADCT). Also, they must show that they meet aquifer water control standards at a point of compliance or show that they are not going to further degrade them. Some other basic demonstrations for dischargers include such factors as being financially and technically capable and having the proper zoning in place.
“Once the business or agency has their operations permit in place, our compliance section then goes and makes sure all the standards are met,” says Jones. “We deal with any wastestream that is out there, and arsenic is simply one more that we deal with. We’re in the area of preventing pollution rather than dealing with it after the fact. If they have a permit from us, one of the things they must have demonstrated is that they have the financial wherewithal to eventually shut their operations down properly. Otherwise we wouldn’t issue the permit.”
One Industrial Wastestream
The focus on arsenic in drinking water has also shed light on the issue of arsenic in industrial wastewater. One Michigan wastewater remediation company, Kalkaska-based Great Lakes Carbon Treatment Inc. (GLCT), found arsenic to be a challenge in treating the wastewater generated from the cleaning of barges used for transporting petroleum. This wastewater comes from a Kentucky refining company that has hired GLCT to assist them with cleanup efforts.
To solve this problem, Bill Pierce, owner of GLCT was glad to find a Severn Trent Services’ product to meet the need. “The facility has a very advanced biological reduction system to break down the organics, but the problems with arsenic were another story,” says Pierce.
Pierce had previously worked with activated carbon filtration media. “Activated carbon works effectively with any dissolved hydrocarbons or chlorinated solvents, but it’s not cost-effective for arsenic,” he says.
According to Pierce, it’s uncertain where the arsenic at the refining process comes from, but it end up in the transport barges used for moving the fuel and ultimately in the rinse water involved with cleanup. The wastewater coming off the treatment at the facility had to be brought down below the acceptable discharge limit of 20 ppb set for arsenic, despite previous biological treatment of the wastewater from oil processing.
Pierce was searching for an absorptive media for arsenic removal. He’d worked with the Fort Washington, PA-based Severn Trent Services before and was familiar with the company and its work. “Severn Trent’s materials focus has mainly been on the drinking water applications; in those cases they’re dealing with a pretty clean water source or feedstock. But we are working with arsenic in wastewater.” GLCT has worked on this project for over two years, treating the wastewater with Severn Trent’s Bayoxide E IN-20 iron oxide adsorptive media. Bayoxide E IN-20 media is similar in chemistry to the Bayoxide E33 media developed for arsenic removal from drinking water applications. “We just applied a technology with success in drinking water into an industrial application,” says Pierce. “We found that even though it’s relatively expensive, we ended up getting four times the life expectancy out of the media.”
GLCT now treats an average of 70,000 gallons of water per day. The water contains residual petroleum before it’s treated. A sequencing batch reactor is used to treat the residual petroleum, but the effluent going into the arsenic treatment system averages about 50 ppb of arsenic. This is above the contamination level—the effluent limit level is 20 ppb.
The life span of the media is approximately one year, and 20–21 million gallons of water are processed through the media over the course of that time.
Pierce explains that the problems of working with other arsenic removal technologies like ion-exchange resins include very low capacity, a lot of backwashing with acid solutions, and the fact that a great deal of highly-acidic and hazardous waste is generated from the required backwash process.
In ion-exchange resin applications, acids are generally used to recharge the ions. But the problem with such an operation is that backwashing must be done with four times the volume of the resins, which produces acid containing high arsenic levels.
Bayoxide works by binding with the ferrous compounds and making a colloid insoluble to water, so the harmful components are stabilized. “We are physically removing it,” says Pierce. “And then when we do a TCLP on it, the substance passes the test and can be simply landfilled as it has now become a solid granular material.”
“It’s like activated carbon or any other absorbent media: Once a contaminant adsorbs into its matrix, it has a very hard time giving it up. That’s the whole purpose of using adsorbent media.
“What we were trying to come up with was a solution where things had a very low labor-intensity and relatively low operational costs,” says Pierce. “Capital costs are always expensive; but how could we justify our costs to do a complete change-out of the media? Ours ended up being approximately two-tenths of a cent per gallon of water for processing; that’s not bad at all, especially for something as toxic as arsenic.”
Because GLCT builds a lot of temporary and rapid-response type systems, getting the system up and running wasn’t a big challenge. The building from the bio plant was already in place, and GLCT built the filters, the tanks, and the piping and installed them onsite. “What we had to do was to pick up the water from this source, run it through the filters, and put it out at another source,” says Pierce. “It took us about six months to get set up. By the time they came up with a solution, we’d developed some programs for them. We gave them the pricing and got the go-ahead, and within six months we were pumping water.”
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Two Types of Treatment
When it comes to arsenic, the main difference between treatments for drinking water and wastewater is the level of the contaminants and the matrix of the chemistry involved, according to Tom Carmody, business development consultant for Severn Trent Services. “With drinking water, there is a certain range of chemistries that we know from experience is going to be occurring,” he says.
“Ninety-nine percent of drinking water that has an arsenic problem is coming from groundwater sources. When you pull from the ground, there are going to be different ranges of iron, silica and other interferants in different parts of the world; however, even with the variability, our experience enables us to bracket those differences, resulting in a fairly homogeneous set of applications.
“With wastewater treatment applications, on the other hand, things are very eclectic or different. One plant may have high levels of phosphate contamination; the next may have high levels of metal contamination. It’s much more of a case-by-case scenario with wastewater applications.”
Wastewater applications also tend to involve multiple treatment steps prior to achieving cleanup, whereas with drinking water treatment, it is a relatively straightforward, one-step process. “In wastewater applications, there are typically several treatment steps before introduction of our Bayoxide media,” says Carmody. “To treat the wastewater generated by cleaning up an oil-transporting barge, biological treatment such as a sequencing batch reactor (SBR) or a number of other possible alternative biological methods can be used. Any time water is to be discharged to the environment, it must be treated to meet the local standards. Severn Trent, in the case of arsenic treatment, will be the last step to assure compliance.”
“Arsenic wastewater treatment is a much more difficult application,” Carmody continues. “But from a big-picture standpoint, what we’ve typically seen is that once the drinking water regulations come in, eventually states and local authorities start to adopt drinking water standards for wastewater; then you enter discussions about how much dilution is in the river or body of water. Slowly, state by state, county by county and even by [publicly owned treatment works] the regulators are starting to develop tighter arsenic limits similar to drinking water.”
Originally, Bayoxide technology was developed for drinking water applications, says Carmody. “Now, as the drinking water regulations have started to be adopted into the wastewater ranks, it is also a tool that can be used by solutions providers for these same kinds of problems on the wastewater side. The ultimate solution provider, such as Great Lakes Carbon, needs to have other tools in their bag such as biological treatment to do the pretreatment; it’s not a magic bullet, but if applied correctly Bayoxide E33 can be very cost-effective and provide the user with an assurance that he will be meeting his discharge limit every day.”
Another technological method of removing arsenic is coagulation and filtration. This is an accepted technology but is more operator-dependent and expensive with some of the chemicals and labor used, particularly when it comes to use at low levels, according to Carmody. “It’s kind of a good technology when used to meet the a limit of 50 ppb, but as the limits move toward 10 and 20 on the effluent side, it’s a good idea to have a system like Severn Trent’s working in tandem with coagulation filtration. The coagulation and filtration works for a gross separation and Severn Trent’s technology follows for final polishing. By combining technologies you get the best features of each technology.”
The Severn Trent SORB 33 arsenic removal system consists of a pressurized vessel—constructed either of fiberglass or steel, depending on its size and the demands on it—full of the media, with a port at the top. The media compound is composed entirely of iron. Water is pumped into the top of the vessel through the media. Water collects at the bottom in an under-drain while the media is held back. The treated water then escapes out of the bottom.
Severn Trent’s adsorption vessels, depending upon the application, can range from one that fits under the kitchen sink all the way up to those with a 12-foot diameter for treating millions of gallons of water per day. “Often we use a dual-vessel setup, for two reasons,” says Carmody. “They can either be set up in parallel, so that one may be taken offline and maintained with the media replaced while the other’s still operating, or they can be run in lead-lag, which means the first unit will take the bulk and the second one acts as a polishing filter. Typically, you are able to get more net adsorbed onto the media if the system is run that way.”
Carmody considers Severn Trent Services leaders in this area of technology. “There are many other different media out there that incorporate different types of iron,” says Carmody. “But Severn Trent’s is unique. Being a dry crystalline form, it’s very easy to handle and easy to design around. With other designs the materials are not crystalline. When those materials get placed in a vessel, they get compressed and it’s hard to tell how much material is contained inside. As a result, your treatment may vary because it’s based on the contact time with the media. If compression has taken place, that contact time will be less; there are a lot of little subtleties about these media. Empty bed contact time [EBCT], which dictates the amount of water resident within the bed of media required to effect complete arsenic adsorption, is another key process parameter of our treatment technology. Our typical design value is a three-minute EBCT.” The Bayoxide is a patented media. Severn Trent does not hold the patent, but holds the exclusive worldwide distribution rights from LANXESS (formerly Bayer AG) on this product.
Arsenic Removal Media
The dry, crystalline granular Bayoxide E IN-20 media was designed with a high capacity for arsenic, providing long operating cycles and low operating costs. The media’s life expectancy is dependent on site-specific water quality and operating levels. Media is transferred into the vessels from sacks, by gravity or else hydraulically. The exhausted media is nonhazardous and can be sent to a landfill, passing TCLP or landfill leachate requirements. Spent media can be removed hydraulically or by vacuum.
Adsorption tests on Bayoxide have shown that it will adsorb antimony, cadmium, chromate, lead, molybdenum, selenium, and vanadium. Bayoxide will adsorb arsenic in preference to these other ions. Under high pH conditions, high levels of vanadium, phosphate (>1.0 ppm) and silica (>50 ppm) can present interference and reduce the media’s adsorption capacity for arsenic.
Dennis Bitter, North American sales manager for Severn Trent’s arsenic removal program, has worked extensively with oil refining processes and refining technologies, as well as with municipal waste projects. “Due to changes in regulations over the past few years, we’ve been looking a great deal at arsenic removal from drinking water,” says Bitter. “The Bayoxide product works extraordinarily well in drinking water applications; it’s simple, easy, it works and is very cost-effective. GLTC studied the situation and results and simply used the product for a different application.
“Drinking water is pretty clean to start with. Industrial applications are always more challenging. In years past the emphasis in refinery applications was on organics. Now inorganics have become more prominent in dealing with the industrial wastestream, driven largely by these changes in the regulations for drinking water.”
Pete Hildebrandt is a writer specializing in science and engineering topics.
OW - November/December 2006
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