Journal of Environmental Engineering

Adsorption on activated carbon of organic compounds from a particle-free and low temperature gas stream has been investigated previously. However, the adsorption processes in a fluidized bed adsorber of particles interfacing with high temperature flue gas has rarely been studied. The major objective of the work was to demonstrate the performance of a fluidized activated carbon adsorber for removal of organic compounds [polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX)] and particulate from flue gas of an incinerator at selected fluidized velocities, fixed bed heights, and bed temperatures. The particle-size distribution of particulate prior to and after flowing through the fluidized adsorption bed were also analyzed. The results indicate that the fluidized bed activated carbon adsorber has a high removal efficiency of PAHs and BTEX. Three evaluated parameters show different effects on PAHs, BTEX, and particles. That the fluidized bed activated carbon adsorber has the ability to filter coarse particles due to the inertia collision is also identified.

The sorption of phosphorus, in the form of dissolved phosphate, on aquatic sediments collected from the tropical Kranji reservoir in Singapore was investigated under oxic and anoxic conditions. Kinetic experiments on sediment samples, collected from three monitoring stations, show that the sorption process consists of fast and slow adsorption stages followed by an equilibrium stage in which further adsorption or desorption may take place. The periods for each stage are in the scale of minutes, hours, and days, respectively. About 67.3–96.6% of the sorption is completed in the first stage under oxic and anoxic conditions. First-order kinetic constants are estimated to be from 4.60 to 12.26 h⁻¹ for the fast adsorption stage, from 0.15 to 0.71 h⁻¹ for the slow adsorption stage, and from 0.005 to 0.028 h⁻¹ for the equilibrium stage. There were no significant differences observed between the sorption kinetic rates under oxic and anoxic conditions. The sorption isotherms of dissolved phosphate are found to be approximately described by the Langmuir equation, taking into consideration the native adsorbed phosphorus. The sorption capacities in different stations are 4.77–10.34 mg/g of dry sediment for oxic conditions and 2.28–6.01 mg/g of dry sediment for anoxic conditions. System redox potential has an apparent effect on the sorption capacity. Estimations of the natively sorbed phosphorus show that the sediments of the Kranji reservoir have initial amounts of phosphorus, ranging from 6.29 to 33.46% of the maximum sorption quantity. The sorption constants obtained are comparable to those obtained in temperate regions but have higher adsorption capacities.

Industrial sites frequently have arsenic-contaminated soils as a result of repeated applications of arsenic herbicides. Four such sites were investigated to determine the suitability of cement-based solidification/stabilization (S/S) for in situ soil treatment. Arsenic concentrations ranged up to about 2,000 ppm in the soil, although leachability was relatively low. No toxicity characteristic leaching procedure leachates showed As concentrations as high as 5 mg/L. The low leachability appears to be due, at least in part, to iron present in the soil. Although soils with higher As concentrations generally showed greater leachability, a somewhat stronger relationship existed between the percentage of As in the soil that was leached and the iron concentration in the soil. Another factor working in favor of the success of S/S in the present cases is the sandy character of the soils with little clay or organic content. Thus, the quartz sand will serve as an aggregate and should not offer any interferences to cement hydration. A third favorable circumstance is afforded by the oxidizing character of the soils. The weathered arsenic present in the soils should be in the form of As(V), and arsenate salts present a wider range of possibilities for precipitation of insoluble arsenic species than arsenite salts. A significant variable with the potential to affect S/S is the soil moisture content, which varied greatly among the four sites due to differing water table depth.

Treatment of sandy soils contaminated with arsenic was investigated at a bench scale and carried through to remediation in the field. The initial treatability study looked at many combinations of cement binders and reagents. Salts of iron, barium, manganese, and magnesium were generally effective at reducing arsenic leachability. The most consistently low potential for leaching [toxicity characteristic leaching procedure (TCLP) and a modified version of the American Nuclear Society's ANS16.1] was observed when the soils were treated with a mixture of Type I portland cement and ferrous sulfate. For instance, the average of arsenic concentrations in TCLP leachates in many treated soil samples from four sites was 0.26 mg/L. Better protection against leaching was observed when the soil was pretreated with FeSO₄⋅7H₂O, then with portland cement. In addition to chemical containment, the mixture should prevent ground-water leaching by physical entrapment, because the permeabilities of the treated soils were in the range of 10⁻⁹–10⁻¹⁰ m/s. Scanning electron microscope micrographs showed a dense mass with minimal void space, and a combination of X-ray diffraction, thermal analysis, and solid-state nuclear magnetic resonance (NMR) spectroscopy indicated the formation of a normal hydrated cement matrix, with some excess ettringite being present due to the extra sulfate being added to the formulation. Results from the bench-scale treatability study were reproduced very faithfully in the field, with permeabilities and compressive strengths being similar to those observed in the laboratory and TCLP leachability being even lower than predicted by the laboratory study.

White phosphorus, a manufactured form of elemental phosphorus, is both toxic and persistent in saturated environments. This form of phosphorus (P₄) is used by militaries worldwide as a component for obscurants, tracer rounds, and incendiary munitions. At Eagle River Flats, an estuarine salt marsh located on Fort Richardson, Alaska, white phosphorus has been directly linked through carcass analysis to the deaths of thousands of dabbling waterfowl. Particulate residue from ordnance contaminates the permanently ponded areas of Eagle River Flats, where the waterfowl sieve the soft bottom sediments for food items, picking up P₄ particles in the process. Death follows within hours. Large-scale investigations into the nature, extent, and persistence of the contaminant were initiated in 1989, followed 4 years later by work on the testing and analysis of remediation methods. In 1997, a method for in situ remediation of the contaminant through low-impact pumping and draining of ponded areas to enhance natural attenuation of white phosphorus was tested. Results indicate that pond pumping is a very effective remediation technique.

Laboratory-scale temperature-controlled reactors were used to generate experimental data of thermophilic composting of vegetable waste. By fitting in experimental data of thermophilic composting, the obtained empirical model (also verified by F-test) appeared to be a quadratic form. The empirical model can be used to predict operating conditions (ratio of predried vegetable waste to rice husks, aeration rate, and reaction temperature and time) for thermophilic composting of vegetable waste in the subtropical region. Moreover, an innovative method for investigating kinetic behavior of thermophilic composting (an exoenzyme-catalyzed reaction followed by a multienzyme-catalyzed reaction) is proposed. The two biochemical reactions of thermophilic composting of vegetable waste followed Monod-type kinetics with the specific substrate utilization rate constants k₁ and k₂ of 0.026 and 4.5 mg COD/mg VSS/day, respectively. Accordingly, the exoenzyme-catalyzed reaction kinetically controls the overall process of thermophilic composting of vegetable waste.

Synthetic organic colorants, the majority of which are recalcitrant in nature, are used universally in many different manufacturing processes. The dyes are released into the environment in industrial effluents and are highly visible even at low concentrations (<1 mg/L). Added to this, certain dyes, dye precursors, and aromatic amines have been shown to be carcinogenic. Thus, appropriate treatment of dye wastewaters to remove color and the dye compounds is clearly an important issue. Methanogenic toxicity tests on several food dyes provided a range of toxicity results, from noninhibitory (IC₅₀ >20 g/L) to inhibitory (IC₅₀ 0.2 mg/L). Batch biodegradability assays indicated that the dyes were not readily utilized by the anaerobic microorganisms as a sole substrate. Decolorization of the dye tartrazine was investigated in a laboratory-scale anaerobic baffled reactor at a concentration of 250 mg/L. Reduction in COD of 50–60% and color reduction of about 95% was achieved. Initially the tartrazine was not readily decolorized; however, decolorization improved with acclimation of the biomass. An industrial wastewater from a food dye manufacturer was fed to a second laboratory-scale anaerobic baffled reactor at a concentration of 5% (volume-to-volume ratio) and then increased to 10% (volume-to-volume ratio). Anaerobic degradation of the wastewater was efficient. Methanogenic activity was high; the organic content of the influent was reduced by about 70%, and color was reduced by almost 90%

Remediation of source zones at sites contaminated with dense non-aqueous-phase liquids using aggressive in situ flushing technologies, such as the addition of chemical additives known as cosolvents, have been implemented and successfully demonstrated in recent field tests. However, treatment of the waste fluids generated from such cleanup technologies has not received much attention. The purpose of this laboratory research was to evaluate the feasibility of using sonication as a method for treating waste fluids produced during in situ alcohol flushing at a site contaminated with a dense non-aqueous-phase liquid. Experimental results showed that sonochemical destruction of perchloroethylene (PCE) followed pseudo first-order kinetics and that increasing ethanol cosolvent percentages in the aqueous effluent resulted in decreasing degradation rates of PCE in solution. The energy efficiency (G = degradation/energy input) of the sonication treatment also decreased as the ethanol volume fraction increased. Overall, sonication was seen to degrade PCE in aqueous solutions, becoming less effective as the cosolvent fraction increased.

Dissolved organic carbon has been typically used as a measure of organic content in source waters. However, dissolved organic carbon is an aggregate parameter and does not provide information on the organic character of natural organic matter in water. The spectral fluorescent signatures technique coupled with a multiple linear regression model was applied for the rapid identification of six dissolved organic matter (DOM) fractions (hydrophobic acid, hydrophobic neutral, hydrophobic base, hydrophilic acid, hydrophilic neutral, and hydrophilic base) along a major river in a New Jersey watershed. The technique/model enabled rapid spatial and temporal determination for the rapid qualitative and quantitative measurement of the DOM fraction(s) in the river. The analysis of DOM fractions also enables screening of the watershed for variations in humic and nonhumic substances input/output along the reaches.

ANSWERS-2000, a non-point-source planning model was modified to simulate long-term nitrogen (N) and phosphorus (P) transport from rural watersheds. The model simulates infiltration, evapotranspiration, percolation, and runoff and losses of nitrate, adsorbed and dissolved ammonium, adsorbed total Kjeldahl N, and adsorbed and dissolved P losses. Eight soil nutrient pools are modeled: stable organic N, active organic N, nitrate, ammonium, and stable mineral P, active mineral P, organic P, and exchangeable P. The model was validated on two small watersheds without calibration and on a large watershed with calibration of only the sediment detachment parameters. Predicted cumulative runoff, sediment, nitrate, dissolved ammonium, adsorbed total Kjeldahl N, and orthophosphorus P losses were within a factor of 2 of observed values (−40 to +44% of observed values). Predictions of individual runoff event losses were not as accurate (−98 to +250%). The model seriously underpredicted adsorbed ammonium losses by up to 97%, and additional work is recommended on this submodel. In a practical application, the use of the model in evaluating the cost-effectiveness of alternative management scenarios was demonstrated.

Although several methods are available for dispersion in natural streams, no method is accurate enough to satisfactorily predict the time variation of stream pollution concentration. Further, limited studies exist for dispersion of nonconservative pollutants. In this paper a six-parameter concentration equation for dispersion of conservative and nonconservative pollutants has been proposed. The parameters of the equation have been related to hydraulic variables and stream geometry. Using these predictors, the equation is fairly accurate for concentration predictions. It is hoped that the equation is useful in water quality management studies.

Biodegradation experiments using mixed bacterial cultures are difficult to compare because repeatable rates may not be produced in different experiments when cultures are normalized on a cell mass or number basis. A technique was therefore developed to quantify [¹⁴C]substrate-specific biodegradation activity of mixed cultures. The technique can be used to obtain a preliminary estimate of the substrate-degrading activity of a culture for more substantial experiments. The technique is applied to 1-naphthol-humic acid bioavailability experiments using both mixed and pure cultures to help isolate the impact of humic acid from differences between the cultures.