We investigate whether blending liquid hazardous wastes with hydrocarbons such as alkanes can improve the destruction efficiency and reduce the combustion byproduct levels in the post-flame region of a laboratory scale combustor. Outlet species concentrations are measured with an FTIR spectrometer for mixtures of 1,1,1-trichloroethane and 25% (by volume) dodecane or heptane injected as a spray of droplets. We also inject sprays of liquid pure 1,1,1-trichloroethane, gaseous pure 1,1,1-trichloroethane, and gaseous 1,1,1-trichloroethane with 25% (by volume) heptane. Once vaporized, the 1,1,1-trichloroethane decomposes to form CO2 and HCl through the intermediates 1,1-dichloroethylene, phosgene, acetylene, and carbon monoxide. The 1,1,1-trichloroethane/alkane mixtures also form the intermediate ethylene. No significant differences are observed between injecting the compounds as a droplet spray or as a gaseous jet, not an unexpected result as the mixing time of the gas jet is longer than the vaporization time of the droplets. The addition of heptane or dodecane to 1,1,1-trichloroethane produces two principal effects: an increase in ethylene, acetylene and carbon monoxide levels for injection temperatures between 950 to 1040 K, and a decrease in 1,1-dichloroethylene, phosgene, acetylene, and carbon monoxide levels for injection temperatures greater than 1050 K. Reaction of the injected alkane causes the former effect, while the additional heat of combustion of the alkane additives causes the latter.
ABSTRACT The rapid high temperature (580-680°C) formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the heterogeneous bed region of a spouted bed combustor occurred within fraction of seconds (0.1-0.2 seconds) using two different precursors; 1,2-dichlorobenzene and 2,4-dichlorophenol. Levels of PCDD/Fs produced from 2,4-dichlorophenol oxidation were two orders of magnitude higher than those produced from 1,2-dichlorobenzene, indicating that the high temperature PCDD/Fs formation rate is much faster from chlorophenol precursors. In agreement with typical incinerator observations, the PCDDs to PCDFs ratios were less than one under all conditions. Modeling calculations were performed using gas phase mechanisms for the formation of PCDDs with chlorophenols as precursors, under the conditions existing in the high temperature bed region. A semi-empirical surface-mediated model is suggested for estimating the formation of PCDDs from chlorophenols.
The volatilization characteristics of lead and cadmium were investigated by a series of experiments and theoretical analysis. The experimental part of the research included heating small amounts (approximately 3 gms) of pure metal samples to volatilization temperatures in a laboratory scale furnace and capturing the vapors by condensation and absorption. Temperatures as high as 900 degrees C were attained during experiments. Experiments were conducted with a carrier gas flow rate between 2 lpm and 6 lpm, corresponding to mean velocities of 1.7 to 5 cm/sec. The study showed that temperature, speciation, gas flow velocity over the waste matrix, and the amount of oxygen in the gas flow were the crucial factors affecting the metal volatilization in an incinerator-like environment.Equilibrium calculations were performed to predict the lead vaporization using the chemical equilibrium code, CET89 (1). The theoretical analysis also included modeling the metal vaporization using a transport phenomena approach. The theoretical analyses were compared with experimental results.Based on the experimental analysis it was found that the volatility of cadmium depended strongly on its oxidizing environment; it volatilized more quickly when it was heated in an inert environment than in an oxidizing environment. Further, the volatility of cadmium increased when the rate of flow of the carrier gas was increased. The amounts of lead volatilized with either air or nitrogen carrier gas were below the analytical detection limits of 20 mg/l in the sample solution even with minimum dilution of the collected sample. This corresponds to a maximum of 4 mg lead vaporization during the 15 minute experimental duration.
We have examined the suitability of laser spark spectroscopy as a real-time, in situ continuous monitor for toxic metals. A crucial issue for in situ monitors is the effects of ambient conditions on accuracy. Detailed measurements of the plasma parameters show that the laser-produced spark is remarkably insensitive to ambient conditions such as variations in the background gas, the presence of particles, humidity, and laser power. This is a very positive result for the field use of laser spark spectroscopy to measure toxic metals.
Contamination of water, soil and air can sometimes be traced to improper disposal of residential household hazardous wastes. Almost every home produces some wastes that pose hazards if improperly disposed. One thousand Nebraskans were surveyed using a random sample selection to profile the attitudes and reported behavior regarding household hazardous waste management practices. The response rate was 49.8 percent with 494 questionnaires returned and a final sample of 474 householders. Most respondents (93.6 percent) reported that they had no community household hazardous waste collection programs. The majority (64.6 percent) agreed that their community should start a household hazardous waste program. However, there was a vast discrepancy in the amount the respondents said they were willing to pay for collection and the actual costs of collection programs. Only one-third reported that they were greatly reducing the type of products purchased that contribute to household hazardous waste. Respondents reported they were disposing of household hazardous waste in ways that may be harmful to the environment such as pouring on the ground, down the drain, or burning the wastes. They primarily placed the potentially hazardous waste in the trash for landfilling.
This paper describes the results of a computer simulation that models the transport and fate of methanol introduced into surface water and ground water environments. Several different scenarios involving substantial (5,000 gallon) releases of methanol were modeled using GEOTOX, a multimedia environmental compartment model for examining the transport and transformation of chemical substances in various environmental release situations. These results provide an improved theoretical basis to help explain the fate of methanol spilled or leaked into fresh surface or ground waters and better determine the extent of related public health risk. For comparative purposes, one fuel spill scenario was also modeled for the common gasoline constituents, benzene, toluene, ethylbenzene and xylenes (BTEX). The results presented in this paper show that approximately all of the methanol introduced into the environment from any of the three release scenarios will be removed fairly quickly due to either volatilization, advection or degradation. Thus the possibility of contaminating groundwater supplies to the extent of endangering human health is very small. In comparing the results of the first scenario to a similar gasoline release, the hazard posed by the BTEX compounds of the gasoline release will be greater than that of the methanol release. The BTEX compounds will persist much longer in the environment than methanol.
Thermal decomposition of CCl4 was investigated at a high temperature under oxygen-rich, isothermal conditions. The temperature ranges from 400 to 1000 degrees C under the conditions of reaction time 2 seconds and an equivalence ratio 0.5. According to those results, CCl4 can destruct 99.99 percent at a temperature of 900 degrees C. Products obtained from thermal oxidation are carbon dioxide, chlorine and carbon monoxide. Tetrachloroethylene is observed as an intermediate in the oxidation process, being formed to an insignificant extent only between 600 degrees C and 850 degrees C. No carbon-chlorine bonds are left at 900 degrees C. A detailed mechanism describing oxidation of CCl4 is obtained and comparisons with experimental results are made. Moreover, sensitivity analysis is performed to identify major reaction equations by combining with a rate of production analysis for key species observed experimentally.
The permeability of monolithic specimens of Selma chalk to six pure organic liquids - acetone, ethylene glycol, heptane, acetic acid, xylene, and aniline - representing some of the classes of organic compounds stored in hazardous waste repositories and to water. was measured in the laboratory. Specimens were core-drilled from large blocks of chalk obtained from the formation in western Alabama and in central Alabama, 150 km to the cast. Specimens of both ''virgin chalk'' and of chalk taken from naturally re-cemented crack zones were studied. In order to prevent viscosity effects from masking the changes in chalk structure brought on by contact with the permeant, intrinsic permeabilities rather than hydraulic conductivities are reported. Compared to data for water (intrinsic permeability of 1.5 x 10(-13) cm(2)) the mean values of the experimentally measured permeabilities to the organic liquids were found to be higher, but not by more than a factor often. The only exception was the permeability to ethylene glycol, which had a mean value about thirty times that to water. Higher mean values were significant at the 90% level of confidence only for ethylene glycol and aniline. There was not much difference found in permeability between specimens from the western and central Alabama locations or between ''virgin chalk'' and chalk taken from re-cemented crack zones.
The use of refuse derived fuel (RDF) as additional fuel in multifuel fluidized bed boilers (FBC) is a promising way for rational waste management. Several combustion experiments using RDF as additional fuel have been carried out in the research program of combustion and gasification technologies in Finland under the title Liekki 2.The size of fluidized bed combustors used in these experiments ranged from 15 kW(th) up to 117 MW(th). The chlorine content of fuel rose up to 0.35% as a measured dry base (db). The emissions of the toxic PCDD/F compounds were found to follow fuel-Cl content trendwise, as expected. However, quantitatively the relative emission levels varied with the factor of 10(3) at the same Cl- content in fuel. Using statistical analysis correlations between PCDD/F emissions and combustion conditions (T-g, CO etc.) as well as fuel and ash properties were found.Most of the earlier measurements in commercial plants have been conducted usually after an electrostatic precipitator (ESP), which has made it difficult to relate emission results to corresponding combustion conditions. According to the laboratory scale fluidized bed reactor (15 kW(th)) using normal (primary and secondary) and staged (primary + secondary + tertiary) combustion air feeding it was found that in the staged condition (higher vertical temperature profile) the total amount of PCDD/F compounds (gas and particles) decreased, but the amount of PCDD/F in solid phase increased.Although the required European emission level of PCDD/F (0.1 ng/m(n)(3) I-TEQ, in 11% O-2) can be achieved, the detailed formation and destruction mechanisms of PCDD/F in combustion conditions are not known well enough for quantitative determination of the emissions.
The Department of Energy is currently evaluating SAIC's Plasma Hearth Process (PHP) for use as a new method of treating mixtures of radioactive and hazardous wastes. The PHP has been specifically designed for the treatment of both low-level and transuranic mixed waste. These mixed wastes range in composition from non-combustible inorganic sludge wastes to highly combustible plastic and organic sludge wastes. The unique aspect of the PHP technology is its ability to treat this wide range of materials even when combined as a poorly characterized heterogeneous mixture. The PHP uses a plasma-are torch to volatilize the organic components of the waste and vitrify residual inert materials. Hazardous organic constituents are destroyed in a secondary combustion chamber. Offgas from the process is thoroughly cleaned by state-of-the-art air pollution control equipment. This paper describes the results of the ''proof-of-principle'' testing of this technology and focuses on the results of the analysis of the offgas emissions. The results demonstrate that the PHP completely destroys organic material; that the PHP offgas emissions are readily controlled by state-of-the-art air pollution control equipment; and that the vitrified residual's leach characteristics are comparable to glass formulated for stabilization of high-level radioactive waste.
The parameters affecting complete thermal decomposition of methane, and 1,1-dichloroethane in a de argon plasma were investigated. The 1,1-dichloroethane was chosen as a representative reactant from chlorinated-compounds and chemical warfare agents. Theoretical studies were conducted using STANJAN thermochemical equilibrium solver-code on stoichiometric mixtures of methane-air and dichloroethane-air systems. In addition, the effect of 10% excess oxygen in the stoichiometric methane-air system was studied in order to understand the role of oxygen at a plasma condition. The results from these studies give valuable information in predicting the species concentrations and evaluating the quenching process. To conduct experimental investigations, a 10 kW laboratory scale de plasma generator was built and operated to produce a stable argon plasma. The representative organic species: methane, and dichloroethane were included in the argon stream for decomposition in the plasma. The decomposition of the species in the plasma was monitored by optical emission spectroscopy. The extent of thermal decomposition was measured by the emission spectrum obtained from the data acquisition system. The gas-now rate of the reactants and the power dissipated in the plasma were found to be important parameters for achieving complete decomposition of a particular chemical species. The argon-methane plasma was used as a reference, because methane is the simplest saturated hydrocarbon and we could use it to simulate the effluent from an incinerator. The plasma destruction of hazardous wastes was thus found to be very promising.
In this work the attention was focused on the adsorption of mercuric chloride on activated carbon and on Na2S impregnated activated carbon. The study was performed in an apparatus at laboratory scale in which simulated flue gas at a given temperature and HgCl2 concentration flowed through a fixed bed of adsorbent material. The experiments showed that the impregnation process definitely enhances the adsorption capacity of the carbon, and that the higher the temperature the lower the adsorption capacity, with an effect almost independent of the presence of Na2S. A possible interpretation of the experimental results is that impregnation with Na2S facilitates HgCl2 capture by activated carbon, possibly by increasing the concentration of sites available for adsorption. However the heat of adsorption, which was found to be about 25 kJ/mol both for raw and impregnated activated carbon, indicates that the process taking place can be defined as a physical adsorption. The gas-solid equilibrium data were used to evaluate the Langmuir's parameters for the three different materials under investigation, The differential equations modeling the adsorption phenomenon were integrated, leading to the evaluation of a kinetic parameter describing the experimentally determined breakthrough curves.
Considerable interest exists in the use of mineral-based sorbents for capturing and retaining hazardous constituent trace metals in the incineration process. The suitability of six minerals, silica, diatomaceous earth, kaolin, bauxite, alumina and attapulgite clay, as potential sorbents for the capture and immobilization of trace metals was evaluated. The behavior of five trace metals, arsenic, cadmium, chromium, lead and nickel was tested. The first five minerals constitute a spectrum of alumino-silicate compounds ranging from pure SiO2 (silica) to pure Al2O3 (alumina). The sixth mineral, attapulgite clay, is primarily a magnesium hydroxide-silicate compound with alumina as an impurity. II has frequently been used in trace metal related test programs at the Incineration Research Facility (IRF) as a carrier of metals and organics in blended synthetic waste streams.The objective of this test program was to evaluate the candidate sorbents with respect to:the degree to which they facilitate retention of the trace metals in the sorbentthe degree to which they retain trace metals in the sorbent when subjected to TCLP extractionBench-scale tests were conducted in the IRF's thermal treatability unit (TTU). The test matrix was defined by varying:mineral (sorbent) typetreatment temperature; treatment temperatures of 540 degrees, 700 degrees, and 870 degrees C were testedchlorine concentration in the feed; 0 and 4 percent by weight chlorine in the feed were tested.Given the preliminary nature of the tests the results must be viewed qualitatively. Nevertheless, overall trends indicate that under specific conditions, varying for each mineral, all of the mineral sorbents showed promise in limiting metal vaporization, and or TCLP leachability. Combining the dual criteria of limiting metal vaporization and reducing leachability, kaolin and attapulgite clay appear to have the greatest promise as potential sorbents.
Simultaneous plume control and subsurface treatment technologies are receiving increasing attention in site remediation. In this paper computer modeling and laboratory pilot scale results are presented to demonstrate the effectiveness of the Trench Bio-Sparge (TBS) system for in-situ treatment of groundwater contaminated with organic compounds. The TBS technology achieves simultaneous hydraulic control and treatment by directing the contaminated plume through a subsurface reactor where groundwater treatment is accomplished by physical or biological means or combinations thereof. Plume capture is achieved by a set of diversion wing walls. Specifically it is demonstrated that velocity equalization is necessary to attain uniform residence time distribution in the reactor. The modeling studies showed that the geometry of the plume diversion system is very important in the design of an efficient reactor. Results of laboratory studies are presented which demonstrate that very high treatment efficiency of organics can be achieved in relatively short reactors having short residence times. Experiments performed with phenol and BTEX contaminated groundwater demonstrated overall removal efficiencies exceeding 99.0%.
Selective removal of heavy metals from sludges or soil is a challenging problem because the heavy metals constitute a small fraction (usually <5%) of the solid phase, the rest being a background of innocuous non-toxic materials which are not important from a regulatory viewpoint. However, the non-toxic background materials may interact with the heavy metals through generation of high buffer capacity, ion-exchange, complexation, etc., thus compounding the problem. This study explores the feasibility of using composite ion-exchange membranes under such unfavorable conditions. This paper also reports on aspects of tailoring the chemistry within the sludge reactor to get optimum results.
The oxidation of 1,2-dichlorobenzene (DCB), 1,3,5-trichlorobenzene (TCB) and pentanoic acid (PA) by ozone, ozone/UV, ozone/H2O2 and ozone/UV/H2O2 was studied. The greatest removal of TCB using ozone/H2O2 treatment was achieved using a H2O2 concentration of 60 mu M. At pH values < 6, ozone/UV performed significantly better than the other processes. However, at circumneutral pH, the removal efficiencies of TCB and DCB by the three AOPs were nearly equal (similar to 97% for TCB; 98% for DCB). At high pH (> 9) the removal efficiencies for all processes studied were nearly equal.The DCB and TCB removal efficiencies for all the processes studied were usually lower when humic acid was present, however, at a concentration of 1.6 mg/L humic acid slightly enhanced the rate of TCB and PA degradation by ozone. For all the processes studied the rates of oxidation of TCB and DCB were significantly slower in the presence of added bicarbonate.In the systems studied, it appears that the reaction of DCB, TCB and PA with (OH)-O-. is primarily responsible for the degradation of these compounds. Estimates of the steady-state (OH)-O-. concentrations were made using the PA data. The concentration of (OH)-O-. ranged from 6 x 10(-14) to 6 x 10(-12) M.
