MTBE & TBA in Water
MTBE and TBA Removal with Ozone
For this test, 12 g/hr ozone concentration was bubbled into a 1.25 liter water column at 7% concentration by weight at a 2 LPM flow rate. Considering a 10% mass transfer rate, 1.2 g/hr ozone was dissolved into the water.
|Time (Minutes)||MTBA (PPM)||TBA (PPM)||Acetone (PPM)||Methyl (PPM)||Ozone Dosage (mg/l)|
* ND = not detectable (below 1 PPM) ** After 90 minutes the MTBE fell below the not detectable (ND) threshold of 1 PPM. The spike in TBA at 45 minutes is likely the result of ozone breaking MTBE down into TBA. However, with time, the ozone also removed most of the TBA. It was informative to obtain data on both levels to observe this relationship. Acetone and methyl acetate were both byproducts of the ozone reactions in this test. Over time, these compounds were also broke down. This test was carried out to verify that ozone would be effective in removing MTBE from water. The resulting data indicates that ozone was very effective in the laboratory testing.
MTBE: C5H12O Methyl tert-butyl ether is a chemical compound that is volatile, flammable, and colorless. Its presence in water at certain levels leads to an unpleasant taste and health concerns. TBA: C4H9OH tert-Butanol is a clear liquid that is very soluble in water and occurs naturally as a product of fermentation. It has a camphor-like odor and also poses health concerns to humans and animals at high levels.
Sulfate and Hydrogen Sulfide in Water
Sulfates and Hydrogen Sulfide
Sulfates are a combination of sulfur and oxygen (SO4, SO3) and are a part of naturally occurring minerals in some soil and rock formations that contain groundwater. The mineral dissolves over time and is released into groundwater.
Sulfur-reducing bacteria, which use sulfur as a food source, are the primary producers of large quantities of hydrogen sulfide (H2S). These bacteria chemically change natural sulfates (SO4) in water to hydrogen sulfide. Sulfur-reducing bacteria live in oxygen-deficient environments such as deep wells, plumbing systems, water softeners and water heaters. These bacteria strip the O2 molecule from the sulfate ion to leave (S) which combines with Hydrogen in water to form H2S. These bacteria usually flourish in large recirculating water tanks and ponds.
Hydrogen sulfide gas also occurs naturally in some groundwater. It is formed from decomposing underground deposits of organic matter such as decaying plant material. It is found in deep or shallow wells and also can enter surface water through springs, although it quickly escapes to the atmosphere. Hydrogen sulfide often is present in wells drilled in shale or sandstone, or near coal or peat deposits or oil fields.
Ozone is a powerful oxidizer that can destroy the sulfur reducing bacteria, this will reduce odors emanating from your water and improve water quality. Air Stripping is another common method used to remove H2S odors from water. See our air-stripping injection systems.
Indications of Sulfate and Hydrogen Sulfide
Sulfate minerals can cause scale buildup in water pipes similar to other minerals and may be associated with a bitter taste in water that can have a laxative effect on humans and young livestock. Sulfur-oxidizing bacteria produce effects similar to those of iron bacteria. They convert sulfide into sulfate, producing a dark slime that can clog plumbing and/or stain clothing. Blackening of water or dark slime coating the inside of toilet tanks may indicate a sulfur-oxidizing bacteria problem. Sulfur-oxidizing bacteria are less common than sulfur-reducing bacteria.
A nuisance associated with hydrogen sulfide includes its corrosiveness to metals such as iron, steel, copper and brass. It can tarnish silverware and discolor copper and brass utensils. Hydrogen sulfide also can cause yellow or black stains on kitchen and bathroom fixtures. Coffee, tea and other beverages made with water containing hydrogen sulfide may be discolored and the appearance and taste of cooked foods can be affected.
High concentrations of dissolved hydrogen sulfide also can foul the resin bed of an ion exchange water softener. When a hydrogen sulfide odor occurs in treated water (softened or filtered) and no hydrogen sulfide is detected in the non-treated water, it usually indicates the presence of some form of sulfate-reducing bacteria in the system. Water softeners provide a convenient environment for these bacteria to grow. A “salt-loving” bacteria, that uses sulfates as an energy source, may produce a black slime inside water softeners.
Potential Health Effects
Sulfate may have a laxative effect that can lead to dehydration and is of special concern for infants. With time, people and young livestock will become acclimated to the sulfate and the symptoms disappear. Sulfur-oxidizing bacteria pose no known human health risk. The Maximum contaminate level is 250 mg/L.
Hydrogen sulfide is flammable and poisonous. Usually it is not a health risk at concentrations present in household water, except in very high concentrations. While such concentrations are rare, hydrogen sulfide’s presence in drinking water when released in confined areas has been known to cause nausea, illness and, in extreme cases, death.
Ozone and Color Removal
Wastewater & Dye Color Removal
Water is shown colored when visible radiation is absorbed from dissolved materials, or when light is reflected on suspended solids. These two sources of color are the base for the distinction between the pseudo and true color. The pseudo color is due to absorption as well as light reflection. The true color depends exclusively from the kind and quantity of the dissolved substances. Particles with a size of 400-800 nm, that means within the wavelength of visible light, are responsible for light reflection. It is possible with filtering (membrane 0.45 micron) the phenomenon of reflection to be eliminated. It must also be noted that the difference between the pseudo and true color is related to water’s turbidity.
True color is created by the presence of compounds that absorb visible light in wavelengths of 400-800 nm, or from compounds that fluoresce in the 200-400 nm spectrum. These are compounds of poly-aromatic structure, substituted aromatic structure, polyenia, concentrated hetero-circular molecules or perplex ions. It should be noted that p bonds absorb into the UV (~200nm ) spectrum and the existence of conjugate bonds (polyenia) is necessary for the absorption in visible light spectrum. Most compounds responsible for color creation contain one or more aromatic rings and start absorbing color at 250 nm.
The synthetic color carriers come mainly from industrial plants as dye-houses, clothing industries with washing-machines, food and beverage industries, slaughterhouses etc.
Wastewater is processed with ozone after its exit from the chemical or/and biological treatment plant and the usual dosage varies from 50-150 mg/l, according to the wastewater origin, its temperature, and the degree of its previous process.
Ozone-wastewater Contact System
The contact system consists of a three-chamber tank, height of 4.5-5 meters with inside splits that guide the wastewater to a vertical labyrinthine flow. Ozone is supplied to the tanks through diffusers made of a special porous material of high resistance. These diffusers have the ability to create multi-numbered and very thin ozone bubbles, with a diameter of 0.2 mm. With their appropriate geometric installation in the bottom of the contact tank, better distribution but also increase in the liquid-gas contact surface to its maximum, is achieved.
The diffuser is used due to the high rate of transport (70%) and its trivial energy consumption. In a tank of three-chambers, diffusers are installed in depth of 5 meters and succeed a transport rate more than 75%. The wastewater must have a hydraulic retention time greater than 45 minutes.
Color Removal Quality
The quality of the ozone treatment effluent in terms of color removal, depends on:
- The color values of the feed
- The ozone dosage
- The wastewater type (Typically color values do not decrease below 200 Pt-Co units even if an especially high ozone dosage is applied)
- The wastewater temperature (better results with effluent from the existing treatment whose temperature is much lower than the temperature of wastewater from the equalization tank)
- The values of the other wastewater characteristics that ozone also affects (better results if BOD, COD and SS have already been decreased in a previous treatment level)
The best results concerning color removal are achieved if the wastewater has been previously treated in order to lower the values of the other characteristics so that the ozone oxidizing effect is consumed only or at least at a maximum proportion in color removal. Additionally the temperature must be below 30-deg C in order to achieve the best physical conditions for its solubility.
The above remark certainly concerns the practical usage of ozone technology in wastewater treatment, as it indicates that the increase of the ozone dosage could give good results even in unprocessed wastewater as long as it has been efficiently cooled.
Wastewater color removal requires an ozone dosage which in most cases fluctuates from 50 to 100 mg/l, for color reduction of 85-92%. This dosage succeeds simultaneously a COD reduction about 40%, while small increases of BOD in the area of 3-7% have been noticed.
The ozone treatment installation represent a significant construction and purchase cost. On the other hand a conventional treatment scheme using chemical coagulants for color removal, has high operational costs (cost of the coagulants themselves and cost for the produced sludge management requirements). In general and for the same effluent quality, the investment of an ozone installation can be paid off in 3-5 years, depending on the size and other specific details of each case.
Konstantinos J. Delimpasis
Ozone and Algae
Ozone supports algae flocculation and removal.
Flocculation kinetic experiments were used to measure the effect of ozone on algal particle stability by determining alpha values. Singer and Chang (1989) used this approach in their studies of the effect of ozone as an aid to coagulation. Experiments were conducted in which algae were added at a known (measured) cell number concentration. Over time, the algal suspension was mixed at a known velocity gradient of 10 or 50s-1, and samples were withdrawn for particle size and number measurements.
Flocculation kinetic experiments were conducted for Chlorella for a calcium concentration of 30 mg/L as CaCO3. The water also contained 10-3 M NaHCO3 and the pH was 7. Three experiments were done for the following ozonation conditions: (1) no ozone, (2) ozone at an absorbed dose of 1mg/L, and (3) ozone at an absorbed dose of 3 mg/L. No coagulant was used so that the direct effect of ozone on algal particle stability could be compared against the no-ozone case. Flocculation kinetic experiments with Scenedesmus were first performed for the standard calcium concentration case of 30 mg/L as CaCo3. This yielded a total of nine experiments.
The kSmoluchowski for orthokinetic flocculation was used as a basis to calculate alpha, the stability factor, from the measurements. When waters are ozonated, the particle volume concentration f may not remain constant. It may increase following ozonation due to production of particles through precipitation (e.g., oxidation of Fe or Mn producing Fe(OH)3 or MnO2 particles) or it may decrease due to breakup or shrinkage of organic part such as algae. In the controlled experiments with synthetic waters, precipitation from Fe or Mn would not occur; however shrinkage or breakup of the algal cells can occur. Alpha values indicate the stability of the particles, low values, e.g., 0.01, indicate stable particles that flocculate very slowly, whereas higher alpha values approaching 1 indicate destabilized particles that flocculate rapidly.
Results and Discussion
The kinetic experiments for Chlorella were run in duplicate. The data show that no measurable flocculation for Chlorella occurred with or without preozonation (i.e., little, if any, change in the cell concentration N time). Alpha values in most cases approach zero, so any computation of alpha would be highly inaccurate. Nevertheless, it can be concluded from these results that Chlorella is stable and that ozone has no positive effect on the flocculation kinetics of Chlorella. Based on these results and the jar test data, no additional kinetic experiments were done with Chlorella.
Unlike Chlorella, Scenedesmus did undergo flocculation; consequently, alpha values were computed and then normalized or put on a relative basis with respect to an ozone effect as presented below.
Kinetic flocculation experiments with algae are difficult to perform because living organisms are used. The particle volume concentration (f) may change upon ozonation affecting rates of particle flocculation. Therefore, absolute alpha values cannot be determined accurately. What is more important is the relative effect of ozone on alpha. For these reasons, the relative effect of ozone on alpha, not absolute alpha values, are present. Relative alpha a rel is defined as follows.
a rel = a (test) / a (ref)
Where a (test) = the alpha value for any test case.
a (ref) = the alpha value for the reference condition of no preozone
Ozone increases the flocculation kinetics of Scenedesmus for all calcium cases as indicated by the increase in a rel. When Ca is low (0 and 30 mg/L [CaCO3]), the effect of ozone on the algae particles is about the same as that indicated by the approximately equal a rel values. At the highest Ca concentration tested, ozone has a great effect at 1mg/L (a rel of 10), while increasing ozone to 3 mg/L decreases a rel to 5. This increase in a rel at 1 mg/L and then decrease at higher ozone may be due to interacting effects between ozone and calcium
J Chang and Singer (1991) have reported on a study in which they measured a values before and after ozone addition for waters collected form seven locations throughout the United Stated. They found that ozone reduction of particle stability (i.e., increased alpha) depended on both the ozone dose and the water hardness, which they expressed in terms of the raw-water hardness to total organic carbon (TOC) ratio. Specifically, they found increases in alpha for ozone doses of 0.4 to 0.8 mg O3/mg TOC and hardness-to-TOC ratios of at lease 25 mg CaCO3/mg TOC. While they did not address the role of algae, at least on a seasonal basis: Los Angeles (Owens River Aqueduct), Monroe, Mich. (Lake Erie), and Bay City, Mich. (Saginaw Bay of Lake Huron). Chang and Singer (1991) found for all three of these supplies that ozone at low doses increased alpha, while at higher ozone doses alpha decreased, in some cases approaching the alpha for no preozonation. For Monroe, alpha increased for ozone doses up to 1 mg/L and then decreased at a dose of 2 mg/L. For Bay City, for a water sample collected during the summer, alpha increased with ozone up to a dose of 2 mg/L and then decreased at an ozone dose of 3 mg/L. For Los Angeles, the results were similar but at lower ozone doses. In the work of Chang and Singer, all three supplies had higher hardness (70 to 144 mg/L CaCO3) values than the hardness used in the algae work of this project (0 to 50 mg/L CaCO3), but the hardness-to-TOC ratios are comparable — 35 to 60 mg CaCO3/mg TOC for the three supplies in the Chang and Singer work versus 15 to 30 mg CaCO3/mg TOC for the two calcium cases of this project. Independent DOC measurements for the algae experiments indicated values of about 2 mg/L with little particulate carbon. IN summary, the results for Scenedesmus and Chlorella show the effect of ozone on alpha depends on ozone dose, calcium and hardness and algae type.
Elimination of Algae with Ozone
People involved in water treatment speak generally of an “algae” problem. In fact, it is more accurate to use the term “plankton”. This term includes all the micro-algae that under favorable conditions (the presence of ideal amounts of nutrients, heat, and sunlight in the environment) can undergo periods of explosive growth. It also includes animal plankton (zooplankton), which belong to a higher level in the food chain, as well as actinomycetes. All these organisms are sized within a range of a few microns to a few millimeters.
List of Species Generally Predominant in Water and the Effects They Produce
The following table presents a list of plankton species generally predominant in water and the effects they produce: (Krauter 1974; Palmer 1980)
|List of Species Generally Predominant in Water and the Effects They Produce|
Ozone has been used for algae elimination for years with very good results. In the following table you can compare ozone with some other very strong oxidants and you will see that ozone obtains very good results in a short amounts of time.
|Oxidant Used||Oxidation Conditions||Oxidation Conditions||% Inactivation|
|Name||Dose (mg/l)||Reaction Time (min)||%|
With the following graph you can compare a system which has only filtration, with a system which has added ozone to do the algae control. For almost all kind of algae, ozone can reduce it more than 95%.
As you can see, the correct installation is crucial for getting the best results from your system. If the ozone system is not well designed and installed, you will not get the desired benefits.
“Ozone in Water Treatment” – Bruno Laglis, David A. Reckhow, Deborah R. Brink
“Ozone in Water Treatment” – International Ozone Association – San Francisco 1993
“Ozone as an Aid to Coagulation and Filtration” – American Water Works Association: Research Foundation
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