Carbonair’s STAT Low Profile Air Strippers are certified to meet the requirements of NSF/ANSI 61G – Drinking Water System Components.

NSF and STAT

Carbonair’s line of highly efficient STAT Low Profile Air Strippers are now certified to meet the requirements of NSF/ANSI 61G.  Carbonair’s STAT air strippers are ideally suited for treatment of drinking water that is contaminated with volatile organic compounds including disinfection by-products like Chloroform, bromoform and other trihalomethanes.

Carbonair Environmental Systems Inc.  has been providing  innovative and effective water treatment systems to our customers in the environmental, municipal, petroleum and construction industries for over 30 years.  First introduced in 1992, our STAT low profile air strippers are a proven design that has been tested in thousands of applications in the US, Canada and Europe.  STAT air strippers are ideally suited for economically removing volatile organic compounds including disinfection by-products, from drinking water.  We currently have several STATs installed and operating in municipal drinking water plants in the US.

For more information about Carbonair’s NSF 61 certified STAT air strippers please visit  https://carbonair.com/stat-low-profile-air-stripper-for-sale/.

 

 

How to Deal with Oils When Treating Contaminated Construction Dewatering Water

Treating Contaminated Construction Dewatering Water can be very expensive and frusterated. Carbonair has created a guide to help you remove oils from water. Oils are defined as organic materials that are not completely dissolved in water and present in the forms of sheens, globules, droplets. If present at a construction dewatering site, oil will most likely need to be removed from water before discharge in order to meet the discharge limits for oil & grease (O&G) and/or specific contaminants of concern (COC) that oil may carry along through treatment systems. Based on the dispersion and stability in water, oils can be classified into four different forms: 1) free oil, 2) mechanically emulsified oil, 3) chemically emulsified oil, and 4) solids-bound oil.

Free oil is defined as oil that is larger than 20 microns in droplet size and not bound to any surface active chemicals. Free oil rises quickly to the water surface within a short period of time, and can be removed from water by buoyancy means using an oil/water separator. The droplet rising velocity is mainly dependent of droplet size and specific gravity. The larger the droplets and the smaller the specific gravity, the faster the droplets rise to the water surface. An oil/water separator can be used to remove oil droplets of larger than approximately 150 microns without the need for coalescing media. The removal of free oil droplets smaller than 150 microns requires an oil/water separator with coalescing media. Coalescing media are packing materials which are typically made of oleophilic (oil-loving) materials. In a coalescing oil/water separator, oil droplets will rise and hit the coalescing media before reaching the water surface and collide into each other to form larger droplets that rise faster to the water surface. Under the same operating condition, the size of an oil/ water separator with coalescing media will be much smaller than that without coalescing media.

Recommend Treatment for Oils

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Mechanically emulsified oil is defined as oil that is smaller than 20 microns in droplet size, and not bound to any surface active chemicals. Mechanically emulsified oil is typically formed by being sheared in centrifugal pumps. The oil droplets of smaller than 20 microns will rise at excessively slow velocities and cannot reach the water surface or the coalescing media in oil/water separators within a reasonable period of time. An excessively large oil/water separator, even with coalescing media, will be required to remove mechanically emulsified oil. Filtration through fabric (bag) or granular media is a more effective treatment method for the removal of mechanically emulsified oil than is the buoyancy method using an oil/water separator.

For the removal of mechanically emulsified oil, filtration with oleophilic fabric bags relies on the interception of oil droplets onto thin fabric layers (typically < 0.25 inches) whereas granular media filtration relies on the adsorption of oil droplets through deep beds of the media (typically 3-4 ft). The oleophilic bags have much smaller oil-holding capacities than do the granular media, and are recommended only where the oil concentration levels are relatively low. The granular media are typically made of either clay or zeolite, the particle surface of which are altered to be oleophilic by being impregnated and electrically charged with chemicals such as quaternary amine. These oleophilic granular media are different from granular activated carbons (GACs) which are commonly used for the removal of organic contaminants in the dissolved phase.

The surfaces of GAC particles are electrically neutral and not oleophilic. Even though the GACs are much more porous than the oleophilic clay or zeolite, most of the pores on the GACs will be too small for the oil droplets to enter. The oil-holding capacities of GACs are considerably smaller than those of the oleophilic granular media. GACs should be used for removing organic hydrocarbons only in the dissolved phase. When oil is present at a construction site and GAC is being used to remove organic hydrocarbons, it is always advisable to remove the oil prior to the GAC units so that the GAC life can be prolonged.

Chemically emulsified oil is defined as oil that is bound to surface active chemicals such as soaps, detergents, and surfactants. The molecules of these surface active chemicals consist of two distinct ends – hydrophilic (water-loving) and hydrophobic (water-hating). When surface active chemicals are added into water containing oil, their molecules will tend to surround the oil droplets by orienting the hydrophobic ends towards the oil droplets and the hydrophilic ends towards the water, forming a structure called “micelles.” These micelles become repulsive to each other, and remain stable and suspended in water. The presence of chemically emulsified oil in water can be indicated by a milky or creamy appearance that does not turn clear even left undisturbed in a jar overnight. Before chemically emulsified oils can be removed from water by either buoyancy or filtration methods, the micellar structure must be broken to separate oils and surfactants from each other. Several organic and inorganic chemicals can be used as demulsifiers or emulsion breakers; however, inorganic chemicals such as aluminum and ferric chloride are commonly used. Fortunately, chemically emulsified oils are uncommonly encountered at construction dewatering sites.

Solids-bound oil is defined as oil that is attached to suspended solids. Solids-bound oil with large particle sizes can be simply removed from water by fabric bag filtration. Solids-bound oil can be troublesome when the suspended solids are very fine (so-called “colloids”) and cannot be captured with the smallest micron-rated fabric bags available (approximately 1 micron). The presence of colloids in water is indicated by a cloudy or hazy appearance that does not turn clear even left undisturbed in a jar overnight. If not removed from water before discharge, the colloidal solids-bound oil may result in the exceedance of the discharge limits for oil & grease or compounds of concern such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). In that case, chemical flocculation followed by sedimentation and filtration will be required to remove the colloidal solids-bound oil. There are a great number of both organic and inorganic chemical flocculants available on the market. Examples of commonly used inorganic flocculants are alum (aluminum sulfate), ferric chloride, and polyaluminum chloride (PAC). Examples of commonly used organic flocculants are polyacrylamide (PAM), diallyldimethyl ammonium chloride (DADMAC), and chitosan (made from crab and shrimp shells). The choices of the flocculants will depend upon the required dosages determined from bench-scale jar tests and upon the toxicity levels that must be approved by regulatory agencies.

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Temporary Water Treatment Systems Used to Treat Construction Dewatering Activities

Construction Dewatering Water Treatment Tips

In many cases when you have to dewater an area of a construction or remediation site to do an excavation or other subsurface work, the water is clean and can be easily discharged without treatment. However, in some cases, the soil and groundwater are contaminated, and if dewatering is required, it is highly likely that the discharge water will be contaminated and will require some type of treatment prior to discharge. If you think this may be required on your next job, it is important to do some planning for a temporary water treatment systems and the associated costs.

To accurately design and estimate the cost of a reliable temporary groundwater treatment system, you need to gather the right data. This can save you lots of money and headaches when you actually go to the field.

Ideally, the following questions should be answered:

  1. What is the actual flow rate that will need to be treated?
  2. Will the flow be continuous or intermittent?
  3. What is the estimated duration of the project?
  4. What are the estimated actual influent concentrations of the contaminants in the water?
  5. What are the discharge requirements in your discharge permit?
  6. What are the water quality data for the site’s groundwater including pH, alkalinity, turbidity, total suspended solids (TSS), hardness, iron & manganese concentrations, chloride, sulfate, conductivity, total dissolved solids (TDS), total organic carbon (TOC) and oil and grease.
  7. If metals are present in the groundwater, what are the total and dissolved concentrations? Methods of treating water for dissolved vs solids borne metals vary significantly.

Require that the company you consider for providing the water treatment equipment provides you with a basis for their design in the form of calculations or modeling. This establishes a solid basis for their design and can be very helpful in securing a discharge permit.

Allow for a pilot test, if recommended by the water treatment equipment supplier. It will require additional work up front but can save a great deal of money by getting the water treatment design right for your site. In many cases, this is the only way to get an accurate estimate of influent concentrations and to prove that a process will work with the specific water at your site, particularly if inorganic contaminants (metals) are involved.

Ensure that your project plan allows for enough space on the job site to house the water treatment system in a location that makes sense.
Leave the solids in the hole. Suspended solids are the enemy! Always use a screened well point or some other filtered recovery source for the dewatering system. Heavy solids loading can add significant costs to the water treatment process and it is always best to leave the solids in the ground whenever possible.

Questions? Contact us here.

Still need help, please contact Carbonair here, or call us at 1-800-526-4999. Important things to consider when you have to treat dewatering discharge water at your site. www.carbonair.com | sales@carbonair.com

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Environmental Remediation Technologies

Carbonair Environmental Systems provides a wide selection of products services for the remediation of contaminated water, air, and soil. These environmental remediation technologies include carbon adsorption, packed tower air stripping, and low-profile air stripping. The following handout is to describe the fundamentals and applications of each remediation technology.

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Carbon Adsorption

Adsorption is a process in which molecules of a liquid or gas are attached to and then held at the surface of a solid by electromagnetic forces or chemical bonding.

Activated carbon is the most common adsorbent which has been used for water and air treatment. It can be made from coal, nutshells or wood, which undergoes a process so that a highly porous structure is formed. Carbon adsorption can be used to remove a wide variety of contaminants from water and air. Common applications of carbon adsorption include groundwater treatment, chemical-spill response, industrial wastewater treatment, air-pollution control, and soil-venting and air-stripping off-gas treatment. Examples of organic contaminants which can be treated by carbon adsorption are: benzene, toluene, ethylbenzene, xylenes, trichlorolhene, tetrachloroethene, 1,1,1-trichloroethane, 1,2-dichloroethane, methyltert-butylether (MTBE), polynuclear aromatic hydrocarbons (PAH), pesticides, herbicides, and polychlorobiphenyls (PCB).

Most carbon-adsorption systems utilize granular activated carbon (GAC) with particle diameters of 1-4 mm in flow through fixed-bed column reactors. To design a GAC treatment system, the adsorption process in a fixed-bed column should be understood. When the bed is first brought on line, only the very top layer of the bed is exposed to the influent concentration since the adsorption depletes the contamination reaching the layers below. This depletion process establishes a finite depth in the bed, over which the concentration changes from the influent value [0 essentially zero. The column depth over which this occurs is called the “adsorption zone” or “mass transfer zone.” As the top layer continues to adsorb, it eventually reached saturation, where the concentration in the carbon is in equilibrium with the influent, and the adsorption zone moves downward. The concentration of the effluent exiting the column will remain essentially zero until the adsorption zone reaches the bottom of the column. When the effluent reaches some pre-determined concentration, term the breakthrough, the adsorber is generally removed from service. A plot of effluent concentration versus elapsed time is a called breakthrough profile.

For a specific flow rate, there is a minimum depth of a carbon adsorber, which is required to accommodate the adsorption zone. If the bed depth is shorter than the adsorption zone, the carbon bed will immediately breakthrough and the effluent concentration will exceed the treatment Objective. As the bed is larger, the carbon will be utilized more efficiently. The main purpose of a GAC treatment system design, therefore, is to determine the optimum size and configuration of the adsorbers. In some cases, a multiple-adsorber operation, such as two beds in series, can reduce the carbon usage rate. With a single-bed operation, the carbon bed must be replaced when the effluent concentration reaches the treatment.

Objective even though the bed is not fully exhausted. With a bed-in-series operation, the first stage adsorber can still be maintained in line until it is saturated with the influent concentration. When the carbon in the first stage is fully utilized, it can be exchanged with fresh carbon and returned to service as the second-stage adsorber. After the bed is exhausted, the adsorbed contaminants can be removed from the spent by a process so-called regeneration or reactivation, which usually employs thermal incineration. For more information about Activated Carbon Vessels click here

 

Packed-Tower Air Stripping

Air stripping is a process in which dissolved molecules are transferred from water into a flowing air stream. Air stripping is applicable for the removal of volatile organic compounds (VOCs) from contaminated water. Examples of common VOCS which can be treated by air stripping are benzene toluene, ethylbenzene, xylenes, trichloroethene, tetrachloroethene, 1,1,1-trichloroethane, 1,1 dichloroethene, 1,2-dichloroethene, 1,1-dichloroethane, 1,2-dichloroethane, vinyl chloride, methylene chloride, and methyl-tert-butylether (MTBE). Air stripping has found its widest application in the remediation of groundwater contaminated from leaking underground storage tanks and past solvent disposal practices.

Air stripping is most widely accomplished in a packed tower with counter current flow of air and water. Contaminated water is pumped to the top of the tower and sprayed uniformly across the packing through a distributor. It flows downward by gravity in a film layer along the packing surfaces. Air is blown into the base of the tower and flows upward, contacting
the water. The packing provides a very large surface area for mass transfer. Packings are normally made of polypropylene because of many benefits: inexpensive, chemically inert, lightweight and strong. VOCs are transferred from the water to the air and carried out the top of the column.

The design parameters for packed-tower air stripping are: 1) air-to-water ratio, 2) gas pressure drop, and 3) type of packing media. Knowing flow rates of water to be treated, types and concentrations of contaminants, and treatment objectives, the design parameters can be selected to optimize the tower size and air-to-water ratio so that the lowest capital and operating costs will be obtained.

The VOCS emitted from the air stripping tower are diluted by the air stream and dispersed into the atmosphere. Many compounds, such as trichloroethene and tetrachloroethene will break down in the atmosphere under the effects of the solar radiation. However, due to the zero-discharge policy, several states in the U.S. have already required that all air discharges from stripping towers be treated before released to the atmosphere. The off-gases are usually treated by passing them through vapor phase carbon adsorbers. At first glance, this configuration appears superfluous since liquid-phase carbon could treat the water directly. However, this system may save on carbon usages and operating costs because vapor-phase carbon can often hold more contaminants before it becomes saturated. Organic chemicals can transport more easily through the air than the water. There are also fewer chemicals in the vapor stream competing for the available pore space since many harmless compounds will remain in the liquid phase. Other treatment techniques, such as thermal and catalytic incineration, may be more appropriate when the off-gas concentrations and carbon usage rates are very high. The operating cost for thermal and catalytic oxidation systems is dependent upon the amount of supplemental heat energy required to raise the process stream temperature to a critical point where near complete oxidation of the VOC contaminants occurs.

A common concern about stripping tower operation is plugging of the packing. Plugging may occur in some waters with very high iron and hardness contents. The dissolved iron can be oxidized to in the tower and precipitate out onto the packing. In an air stripping process, carbon dioxide can be stripped out of the water, resulting in an increase of pH. If the water contains an appreciate hardness content, calcium and magnesium will precipitate in the forms of hydroxides. For iron and hardness contents less than 2 ppm and 200 ppm as Cac03’ respectively, acids can be fed into the water stream to sequester the precipitation. For the higher iron and hardness contents, pretreatment of the water to remove iron and hardness is needed prior to the air stripping tower. Chemical oxidation using permanganate or preaeration with pH control, clarification and filtration can be used to remove iron. Lime softening can be used to remove the high content of hardness. For more information about air stripping click here

Low-Profile Air Stripping

Low-profile air strippers can be classified into two major groups: multiple sieve-tray style and multiple diffused-chamber style. Carbonair’s low-profile air strippers are in the former group in which water and air are contacted in step-wise
fashion on multiple trays. Contaminated water enters at the top and flows downward by gravity. On the way, it flows across each tray and through a downspout to the tray below. The air passes upward through openings in the trays, then bubbles through the water to form a surface of foam which provides extreme turbulence and excellent mass transfer for organic volatilization. Since the water in sieve-tray air strippers flows horizontally across each tray, the traveling path length of water and the required removal efficiency can be achieved by increasing the number and length of the trays. Therefore the sieve-tray units have much lower height than the conventional packed-tower units.

When comparing the air utilization in sieve-tray air strippers to that in the diffused-chamber air strippers, only one air stream passes through every tray before exiting the sieve tray units whereas multiple air streams are introduced into the bottom of each chamber through diffusers such as perforated tubes or orifice. Therefore, the air requirement is much less than that for the diffusedchamber units. As a result of a minimal air flow, the organic contaminants in the off-gas are concentrated and can effectively be treated. The sieve-tray units also reduces the potential for fouling of suspended solids, iron and calcium since it contains no packing media and possesses an extreme turbulent condition. Normally, the gas pressure drops encountered in sieve-tray units (10-30 inches W.C.) are higher than those in packed-tower air strippers (1-3 inches W.C.). This is due to the fact that the air must be bubbled through a thick layer of water in each tray. Therefore, the blowers for the sieve-tray air strippers usually are sized larger in horsepower. The Sieve-tray air strippers are recommenced for the application with the following requirements: height limitation, need for minimal visibility of equipment, high content of suspended solid, iron and hardness.

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For more information about renting or purchasing equipment from Carbonair, contact Carbonair directly at 1-800-526-4999. Or if you prefer, please fill out our contact-us form and a Carbonair representative will contact you to answer your questions.

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New Mobile Water Treatment Trailer for Rent

Carbonair’s mobile water treatment trailer is a perfect fit for a variety of temporary water treatment applications including,  construction dewatering, groundwater remediation, underground storage tank replacement and pipeline hydrostatic test water treatment.

The system consists of four custom designed Carbonair MPC 28 Filter Vessels with special internal piping, preceded by a dual multi-round bag filter skid.  The filter vessels are equipped with piping and valves to allow for running them in parallel or series, as well as isolation of any single vessel and for performing backwashing as required.  The trailer comes equipped with a 1000 gpm dual multi-round pre-filter that allows for exchange of bag filters in one filter housing, while continuing to run in forward flow at 1000 gpm through the second housing.  The filter vessels can be supplied with a variety of Granular Activated Carbon (GAC) as well as other specialty filtration media including ion exchange resin, oil adsorbing media, arsenic removal media,  amine impregnated zeolite and others.   The system is trailer mounted and self contained, making delivery and setup fast and safe.

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Additional Features of the Mobile Water Treatment Trailer

  • 112 sq ft Filtration Surface Area
  • Flow rates up to 1000 GPM nominal
  • 20,000 lb GAC capacity
  • Can be used with a variety of other filtration media
  • Piping for Series or Parallel Operation
  • Trailer mounted with internal piping
  • Dual Multi-round Bag Filter Included
  • Trailer mounted for easy transport and startup
  • Ideal for mobile water treatment applications

 

 

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