Volatilization ponds

Mathematical models have also predicted a low volatility for methyl parathion (Jury et al. 1983 McLean et al. 1988). One study using a laboratory model designed to mimic conditions at soil pit and evaporation pond disposal sites (Sanders and Seiber 1983) did find a high volatility from the soil pit model (75% of the deposited material), but a low volatility for the evaporation pond model (3. 7% of the deposited material). A study of methyl parathion and the structurally similar compound ethyl parathion, which have similar vapor pressures, foimd that methyl parathion underwent less volatilization than ethyl parathion in a review of the data, the reduced level of volatilization for methyl parathion was determined to be due to its adsorption to the soil phase (Alvarez-Benedi et al. 1999). 

Monkiedje et al. [10] investigated the fate of niclosamide in aquatic system both under laboratory and field conditions. The octanol/watcr partition coefficient (Kaw) of niclosamide was 5.880 x 10 4. Adsorption isotherm studies indicated that the Freundlich parameters (K, n) for niclosamide were 0.02 and 4.93, respectively, for powder activated carbon (PAC), and 9.85 x 10 5 and 2.81, respectively, for silt loam soil. The adsorption coefficient (Aoc) for the drug was 0.02 for PAC, and 4.34 x 10-3 for the same soil. Hydrolysis of niclosamide occurred in distilled water buffer at pH above 7. No photolysis of the drug was observed in water after exposure to long-wave UV light for 4 h. Similarly, neither chemically volatilized from water following 5 h of sample aeration. Under field conditions, niclosamide persisted in ponds for over 14 days. The half-life of niclosamide was 3.40 days. 

The dominant transport process from water is volatilization. Based on mathematical models developed by the EPA, the half-life for M-hexane in bodies of water with any degree of turbulent mixing (e.g., rivers) would be less than 3 hours. For standing bodies of water (e.g., small ponds), a half-life no longer than one week (6.8 days) is estimated (ASTER 1995 EPA 1987a). Based on the log octanol/water partition coefficient (i.e., log[Kow]) and the estimated log sorption coefficient (i.e., log[Koc]) (see Table 3-2), ii-hexane is not expected to become concentrated in biota (Swann et al. 1983). A calculated bioconcentration factor (BCF) of 453 for a fathead minnow (ASTER 1995) further suggests a low potential for -hcxanc to bioconcentrate or bioaccumulate in trophic food chains. 

Based on its very small calculated Henry s law constant of 4.0xl07-5.4xl0"7 atm-m3/mol (see Table 3-2) and its strong adsorption to sediment particles, endrin would be expected to partition very little from water into air (Thomas 1990). The half-life for volatilization of endrin from a model river 1 meter deep, flowing 1 meter per second, with a wind speed of 3 meters per second, was estimated to be 9.6 days whereas, a half-life of greater than 4 years has been estimated for volatilization of endrin from a model pond (Howard 1991). Adsorption of endrin to sediment may reduce the rate of volatilization from water. 

All passive systems rely on the natural hydraulic gradient to transport LNAPL to the recovery location. Under most circumstances, the flow of LNAPL into this type of system is very slow. At open surface recovery sites (trenches and ponds) constructed in low-permeability soils, the LNAPL migrates in so slowly that free volatile product often evaporates before it accumulates sufficiently to be collected. High-permeability soils typically are subject to a low hydraulic gradient, which limits the rate of flow into the system. Conditions that are more favorable to passive recovery, shown schematically in Figure 7.1, include ... 

Finally, open ponds used to cool, settle out solids, and store process water can be a significant source of volatile organic carbon emissions. Wastewater from coke cooling and coke volatile organic carbon removal is occasionally cooled in open ponds where volatile organic carbon easily escapes to the atmosphere. In many cases, open ponds can be replaced by closed storage tanks. 

The dominant fate process for chloroform in surface waters is volatilization. Chloroform present in surface water is expected to volatilize rapidly to the atmosphere. An experimental half-disappearance range of 18-25 minutes has been measured for volatilization of chloroform from a 1 ppm solution with a depth of 6.5 cm that was stirred with a shallow pitch propeller at 200 rpm at 25 °C under still air ( 0.2 mph air currents) (Dilling 1977 Dilling et al. 1975). Using the Henry s law constant, a half-life of 3.5 hours was calculated for volatilization from a model river 1 meter deep flowing at 1 meter/second, with a wind velocity of 3 m/second, and neglecting adsorption to sediment (Lyman et al. 1982). A half-life of 44 hours was estimated for volatilization from a model pond using EXAMS (1988). 

Soil. The major soil metabolite is 2,6-dichlorobenzamide which degrades to 2,6-dichloro-benzoic acid. The estimated half-lives ranged from 1 to 12 months (Hartley and Kidd, 1987). Under field conditions, dichlobenil persists from 2 to 12 months (Ashton and Monaco, 1991). The disappearance of dichlobenil from a hydrosol and pond water was primarily due to volatilization and biodegradation. The times required for 50 and 90% dissipation of the herbicide from a hydrosol were approximately 20 and 50 d, respectively (Rice et al., 1974). Dichlobenil has a high vapor pressure and volatilization should be an important process. Williams and Eagle (1979) found... 

Once In an evaporation bed, a pesticide can adsorb to a soil colloid, undergo chemical or microbial degradation, or escape from the bed by volatilization. An evaporation bed has the potential advantage over an open pond of decreasing pesticide volatilization while allowing for Increased degradation through microbial and soil-catalyzed reactions. 

In this paper, the volatilization of five organophosphorus pesticides from model soil pits and evaporation ponds is measured and predicted. A simple environmental chamber is used to obtain volatilization measurements. The use of the two-film model for predicting volatilization rates of organics from water is illustrated, and agreement between experimental and predicted rate constants is evaluated. Comparative volatilization studies are described using model water, soil-water, and soil disposal systems, and the results are compared to predictions of EXAMS, a popular computer code for predicting the fate of organics in aquatic systems. Finally, the experimental effect of Triton X-100, an emulsifier, on pesticide volatilization from water is presented. 

It should be noted that hydrolysis of these pesticides is expected to occur simultaneously with volatilization for the pesticides studied (Table I). Over a 7 day experiment, however, only malathion and mevlnphos would be expected to hydrolyze to a significant extent. We determined the loss rate of mevlnphos to be 0.0016 0.0002 hr l (tjj = 18 days), and of malathion to be 0.011 0.001 hr-1 (t j = 2.6 days) at 22 2°C, at pH 8.2+0.2 for a model evaporation pond by daily sampling of duplicate pesticide solu-Xlons (covered to prevent volatilization) for 7 days and plotting log concentration versus time. For both of these pesticides, then, degradation was a much more important route of pesticide loss from water than volatilization. The relatively slow loss rate of the other pesticides could not be determined in our 7 day... 

The relative importance of the two processes in a model evaporation pond, along with the time lor 97% loss of the applied pesticide (system purification time), were calculated (Table V). This calculation confirmed that mevinphos and malathion dissipated primarily by hydrolysis, with malathion the more rapid of these two chemicals. For methyl and ethyl parathion, both processes were significant, although volatilization was the dominant dissipation route. However, since both processes were relatively slow for these pesticides, the purification time was fairly long. Diazinon was predicted to be lost primarily via volatilization, and the purification time was relatively short. 

In order to more closely represent the volatilization environment that would be encountered in an evaporation pond, Triton X-100, a non-ionic emulsifier similar to those used in some pesticide formulations, was added to prepared pesticide solutions at 1000 ppm. The presence of this emulsifier caused a decrease in the percent pesticide volatilized in one day in all cases except for mevinphos (Table VI). Three mechanisms are probably in operation here. First, Triton X-100 micelles will exist in solution because its concentration of 1000 ppm is well above its critical micelle concentration of 194 ppm (30). Pesticide may partition into these micelles, reducing the free concentration in water available for volatilization, which will in turn reduce the Henry s law constant for the chemical (31). Second, the pesticides may exhibit an affinity for the thin film of Triton that exists on the water surface. One can no longer assume that equilibrium exists across the air-water interface, and a Triton X-100 surface film resistance... 

A simple environmental chamber is quite useful for obtaining volatilization data for model soil and water disposal systems. It was found that volatilization of low solubility pesticides occurred to a greater extent from water than from soil, and could be a major route of loss of some pesticides from evaporation ponds. Henry s law constants in the range studied gave good estimations of relative volatilization rates from water. Absolute volatilization rates from water could be predicted from measured water loss rates or from simple wind speed measurements. The EXAMS computer code was able to estimate volatilization from water, water-soil, and wet soil systems. Because of its ability to calculate volatilization from wind speed measurements, it has the potential of being applied to full-scale evaporation ponds and soil pits. 

The toxic pollutants present in raw wastewaters from tire and inner tube manufacturing operations are volatile organic pollutants that are used as degreasing agents in tire production. These toxic pollutants (methylene chloride, toluene, trichloroethylene) were found to be reduced to insignihcant levels across sedimentation ponds. 

Freshwater mammals such as heaver may leave odors on the surface of their ponds and olfactorily sample the water or layer of air immediately above it. Lipids on water may form micelles, small blobs of molecules (from Latin mica, a grain, crumb, morsel) that enhance evaporation into the air layer by increased chemical potential. Some seahirds hunt hy odor (e.g. Hutchison and Wenzel, 1980 Nevitt, 1999). They may respond to prey volatiles (from krill, squid, or fish) that rise to the water surface and evaporate into the air. The air-water equilibrium for dilute solutions can be expressed by using partition coefficients, relative volatility, or Henry s law (Thibodeaux, 1979). 

Verschueren 1983). The magnitude of the estimated Henry s law constant (4.4-7.7x10 atm- m /mole) indicates that 2-hexanone will volatilize from water, with a half-life in river water of about 10-15 days (Mabey et al. 1982). Volatilization will be slower from lakes or ponds (Mabey et al. 1982). There is no information on whether 2-hexanone in water is expected to partition to soils and sediments. 

Aeration basins are wastewater ponds or lagoons that have air introduced by mechanical action. Aeration may be performed to assist aerobic bioremediation and/or to remove volatile organic compounds. In an aeration basin, oxygen is usually supplied by surface aerators or by diffused aeration units. The action of the aerators and that of the rising air bubbles from the diffuser is used to keep the contents of the basin in suspension. Aeration is widely used in wastewater treatment and can be adapted to treat groundwater. 

As regards organic contaminants, leachates from semi-coke contain compounds such as phenols, for example, cresols, resorcinols, and xylenols, which occur at mg/L concentrations. Indeed, Kahru et al. (2002) found total phenols at concentrations up to 380 mg/L in semi-coke dump leachates. Phenols also volatilize from such leachates, depending on temperature and pH (Kundel Liblik 2000). Atmospheric phenol concentrations of 4-50 xg/m3 have been observed in the proximity of leachate ponds (Koel 1999). Generally, aliphatic hydrocarbons, carboxylic acids, and organo-nitro and organo-sulpho compounds do not occur at elevated concentrations in leachates from Estonian semi-coke (Koel 1999). 

Kundel, H. Liblik, V. 2000. Emission of volatile phenols from stabilization ponds of oil shale ash dump leachate. Oil Shale, 17, 81-94. 

Diazinon released to water from both point and nonpoint sources may be emitted to the atmosphere by volatilization, sorbed to soils and sediments, or accumulated in aquatic organisms. While evaporation may not be expected to be significant based upon the Henry s law constant (see Table 3-2), volatilization of diazinon can be an important transport process. Sanders and Seiber (1983) reported that 17% of the diazinon added to a model pond volatilized in 24 hours. Diazinon released to water also may be adsorbed moderately by soils and sediments based on its organic carbon partition coefficient (K00) values measured in soil (Sharom et al. 1980a). Because this pesticide is only moderately adsorbed by some soils, leaching into groundwater can occur. 

Karlson, U. Frankenberger, W.T. Jr, (1990). Volatilization of selenium from agricultural evaporation pond sediments. The Science of the Total Environment, 92, 41-54. 

As in the case of the slag tank, there was no way to measure quantitatively the precipitator residue flow rate. These residues are slurried with water and flushed continuously into the ash pond. However, for all of the elements except selenium, the precipitator was extremely efficient (>95%) as calculated from the inlet and outlet fly ash concentrations using Equation 6. The reason that selenium fails to be scavenged effectively is not known and certainly warrants investigation. One possibility is that part of the selenium is in a volatile state but is readily adsorbed on particulates trapped by the alundum thimbles. 

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