Journal of Environmental Engineering

This paper deals with the potential of coal fly ash as a heterogeneous catalyst in peroxidative decolorization of aqueous solution of several reactive drimarene dyes using hydrogen peroxide (H₂O₂). The effects of various parameters (source of fly ash, fly ash loading, temperature, pH, initial concentration of dye and hydrogen peroxide, and deactivation of catalytic effect of fly ash) were studied. The rate of decolorization is zero order with respect to concentration of dye in the range of 50–200 mg/L and first order with respect to concentration of H₂O₂ in the range of 375–2,500 mg/L. It was found that at 333 K and pH 2.0, only 2% (weight/volume) fly ash loading can completely decolorize 100 mg/L dye solution within 180–1,770 s for an initial H₂O₂ concentration of 1,500 mg/L, depending on the source of fly ash and dye used. But maximum 25% decolorization was noticed after 3 h duration of reaction without fly ash. The negligible homogeneous catalytic action of trace amount of metals like Fe, Mn, and Cu leached from the fly matrix confirmed the sole heterogeneous catalytic nature of fly ash particles in decolorization reactions. The deactivation of fly ash was found to be <30% in nine repeated uses. Adsorption dynamics and mechanism of dyes onto fly ash also were studied in the absence of H₂O₂.

A ground-water treatment process is described in which contaminants are adsorbed onto granulated activated carbon (GAC) containing fixed iron oxide. Hydrogen peroxide (H₂O₂) is amended to the GAC suspension and reacts with the iron, forming hydroxyl radicals (˙OH). The radicals react with and oxidize sorbed and soluble contaminants regenerating the carbon surface. Laboratory results are presented in which 2-chlorophenol (2CP) was first adsorbed to GAC and subsequently oxidized via the Fenton-driven mechanism. Transformation of 2CP was indicated by the formation of carboxylic acids and Cl⁻release. The treatment efficiency of 2CP, defined as the molar ratio of Cl⁻released to H₂O₂ consumed, increased with increasing amounts of iron oxide and 2CP on the GAC. The extent of 2CP oxidation increased with H₂O₂ concentration. Lower treatment efficiency was evident at the highest H₂O₂ concentration utilized (2.1 M) and was attributed to increased ˙OH scavenging by H₂O₂. Aggressive oxidation procedures used in sequential adsorption/oxidation cycles did not alter the GAC surface to a degree that significantly interfered with subsequent 2CP adsorption reactions. Although process feasibility has not yet been established beyond bench-scale, experimental results illustrate the potential utility of the adsorption/oxidation process in aboveground systems or permeable reactive barriers for the treatment of contaminated ground water.

A feasibility study of a new technology for remediating sites contaminated with dense non-aqueous-phase liquids (DNAPLs) is presented. The technology combines two conventional remediation approaches, thermal treatment and in situ bioremediation, in an effort to improve bioavailability through increased dissolution and biodegradation rates at elevated temperatures. To evaluate this new approach, a simulation model has been developed that combines expressions for first-order dissolution of immobile DNAPL spheres, dual-Monod biodegradation kinetics, and diffusion-limited desorption from soil micropores. The model is used to simulate remediation of a possible future contained release at a test cell at the Groundwater Remediation Field Laboratory at Dover Air Force Base in Dover, Del. Model simulations were conducted for temperatures ranging from 15 to 40°C using parameter values obtained from the literature. Simulation results show that, by increasing the temperature from 15 to 35°C, the amount of mass removed in the effluent (i.e., the amount of mass not degraded in situ) is predicted to be reduced by 94%, and the time required to reach the cleanup objective is predicted to be reduced by 70%. Parameter value sensitivity was also examined. Only those parameters that substantially reduced the biodegradation rates were found to have a strong influence on the predicted benefits associated with elevated temperatures. Based on the results of these modeling experiments, coupling of these two remediation techniques appears to hold considerable promise for sites contaminated with DNAPLs.

In laboratory column studies we evaluated chlorinated solvent removal using food grade surfactant-based solubilization and mobilization systems. We used nonionic sorbitan polyethoxylate monostearate for solubilization experiments, and both bis-2-ethylhexyl sodium sulfosuccinate and sodium mono- and dimethyl naphthalene sulfonate in mobilization studies. Surfactant enhanced mobilization was shown to be more efficient than solubilization for removing tetrachloroethylene. Excellent removal efficiency was maintained even when the mobilization system was varied, demonstrating the robustness of this system for subsurface remediation. The selected food grade surfactants, however, suffered mass losses in the column, probably due to the occurrence of phase separations (e.g., formation of precipitates or liquid crystals). Thus, surfactant losses need to be minimized before using these systems in full-scale applications. This study also demonstrated that surfactant performance was influenced by a variety of factors, such as the type of microemulsion, temperature, and contaminant compositions, that must also be considered in design of field implementations.

A laboratory study using the upflow anaerobic sludge blanket reactor for treating high-strength wastewater containing tetrachloroethene (PCE) was carried out to study the effect of carbon source, recycle, and shock loading on dehalogenation of PCE and process performance. The PCE was dehalogenated to trichloroethylene, cis-1,2-dichloroethylene, vinyl chloride, and ethylene. During the study on the effect of carbon source, the PCE and COD removal up to 97% and biogas production of 0.518–0.47 m³/kg COD_rem with methane content up to 66% were achieved under steady-state operating conditions. An increase in the influent COD from 2,000 to 4,000 mg/L did not show any improvement in the PCE removal. Recycling of effluent at 50% showed the decrease in COD removal and increase in the effluent concentration of dichloroethylene and vinyl chlorides. Around 1–3.5% of influent PCE stripping to biogas was observed. It was observed that methanol has the stimulatory effect on the dehalogenation of PCE. A shock loading study showed that the upflow anaerobic sludge blanket reactor could assimilate 1.5–2 times the original PCE concentration (50 mg/L) without much effect on the process performance.

Biosurfactant was produced by fermenting kerosene and used vegetable oil using a Pseudomonas sp. under nonsterile conditions. The biosurfactant at a concentration of 0.5 g/L and pH of 10.5 lowered the surface tension of water to 25 mN/m. The biosurfactant was used to enhance the solubility of naphthalene, and the results are compared to an anionic (sodium dedecyl sulfate) and a nonionic (Triton X-100) surfactant. The biosurfactant (5 g/L at pH of 7) enhanced the solubility of naphthalene to more than 30 times its aqueous solubility. Solubilized naphthalene in Triton X-100 and biosurfactant solutions was biodegraded by the same microorganism that produced the biosurfactant. Naphthalene solubilized in biosurfactant and Triton X-100 (400–600 mg/L) was biodegraded in 40 days and 100 h, respectively. Naphthalene in the amount of 30 mg/L was degraded by the Pseudomonas sp. in 2 days. The biosurfactant was also biodegraded during the biodegradation of naphthalene, but this was not the case with Triton X-100. The biodegradation of the biosurfactant appeared to compete with the biodegradation of naphthalene. Sodium dedecyl sulfate inhibited the biodegradation of naphthalene at the conditions studied.

The effects of temperature and surfactant concentration on the degradation of pentachlorophenol (PCP) by a pure culture of Sphingomonas chlorophenolicum sp. Strain RA2 were studied. An anionic, a cationic, and two nonionic surfactants were tested at concentrations above and below their critical micellar concentrations (CMC). Each surfactant was tested at four temperatures between 10 and 25°C. PCP degradation curves were modeled based on Monod growth kinetics. Degradation curves were also fit using inhibition models accounting for the effects of temperature and surfactant concentration. No PCP degradation activity was observed in the presence of the cationic surfactant. The anionic surfactant had a more inhibitory effect at lower concentrations than the nonionic surfactants, which occurred at surfactant concentrations well below the CMC at all temperatures. Nonionic surfactants showed no inhibition at sub-CMC concentrations and higher temperatures. In general, the surfactants caused more inhibition at lower temperatures. The exception was a slight enhancement of PCP degradation at 10°C for low concentrations of the nonionic surfactants.

In this study the toluene removal efficiency of a composted pine bark biofilter was determined at loading rates ranging from 9.04 to 54.21 g m⁻³ h⁻¹, retention times of 0.25–3.0 min, and at various bed heights. Toluene removal efficiencies exceeding 90% were obtained when the biofilter was subjected to a gas retention time in excess of 0.32 min (19.2 s) and loading rates below 42 g m⁻³ h⁻¹. The data obtained were used to develop an empirical model. The empirical model successfully described the overall removal efficiency with an R² value of 0.98. The influence of oxygen concentration on the removal efficiency was also evaluated. Reduced biofilter performance was observed at oxygen concentrations below 5%. A wide range of microorganisms were isolated from the biofilter, which included Corynebacterium jeikeium A, Corynebacterium nitrilophilus, Micrococcus luteus, Pseudomonas mendocina, Sphingobacterium thalphophilum, and Turicella otitidis.

Trace metal bioavailability and chromium(III) removal were investigated in an anaerobic baffled reactor (ABR) treating a synthetic waste [COD = 4,000 mg/L, $\mathrm{COD}:{\mathrm{SO}}_{\mathit{4}}^{\mathit{2}\mathit{-}}$ ratio 8:1 and 40:1, Cr(III) = 50 mg/L]. Sulfide precipitation reduced nutrient bioavailability as follows (most deficient first): Fe > Co > Ni. However, the metals had the following affinity for complexation: Ni > Co >> Fe; complexation potential was greatest at the front and rear of the reactor. At the front, it was hypothesized that high concentrations of soluble microbial products provided an excess of potential ligands, which may have sequestered the metals. However, in the last compartment, a higher pH would have altered the competition between protons and metal cations for complexing sites in favor of the metal cations. The complexing potential in the ABR increased with sulfide levels, and this coincided with higher residual COD production, probably to provide a diffusion barrier to the harsh environmental conditions. Although the addition of chromium (50 mg/L) had no observable effect on reactor performance/stability, its removal was controlled by the following factors (most influential first): solubility > complexation > absorption > physical adsorption.

To understand the effect of a non-aqueous-phase liquid (NAPL) on bacterial transport, column experiments in the presence and absence of a NAPL were conducted using two bacterial strains and two different porous media. The presence of a NAPL (tetrachloroethene) decreased the retention of Pseudomonas fluorescens P17 in quartz and soil columns (factor of 2 for quartz and 1.6 for the soil). In contrast, there was little change in the overall transport of P. putida KT2442 in soil columns in the presence of a NAPL. To understand how a NAPL phase might affect bacterial transport, several different mechanisms of particle removal by a NAPL were hypothesized, and a filtration model was modified to test each hypothesis. Only one of the five models was consistent with the increased transport of P17 in the presence of the NAPL suggesting that the NAPL produced large, immobile zones of water. The presence of immobile water zones would decrease overall porosity, reduce the number of packing grains available for particle filtration, and increase water velocity, resulting in increased bacterial transport in the presence of a NAPL.

The effect of applied pressure on the permeate flux in cross-flow ultrafiltration (UF) and microfiltration (MF) was investigated both theoretically and experimentally. In UF and MF processes, the permeate fluxes are controlled by concentration polarization and cake formation over the membrane surface. As a better understanding of concentration polarization and cake formation becomes available, the permeate flux under any pressure can be theoretically predicted. Experiments were conducted in a ceramic tubular cross-flow filter with silica colloids of a narrow size distribution (model colloids). The pressure-dependent flux of the model colloidal suspension in cross-flow filtration was investigated under various experimental conditions. The experimental measurements were compared with the theoretical predictions, and the results showed that the pressure-dependent permeate flux in cross-flow filtration can be adequately predicted. Furthermore, theory and experiments demonstrated that the performance and operating state of UF and MF could be well characterized by the so-called “characteristic pressure” of the process.

A method is developed to quantify total freshwater input and flushing time in estuaries using measured flow and salinity data at the estuary-ocean boundary. A formula is derived to calculate the volume of mixed estuarine water that leaves the estuary on the ebb tide. The calculated volume of mixed estuarine water, along with the volume of new ocean water that enters the estuary on the flood tide, is used to quantify the total volume of freshwater input. The calculated volume of mixed estuarine water is also used to quantify the flushing time. The developed method is applied to Barnegat Bay, N.J. The volume of freshwater input calculated from the new method compares well with that estimated using watershed, aquifer, and meteorological data. The flushing time calculated from the new method is between that calculated from the classical tidal prism method and that from the fraction of freshwater method. An assessment is made on the sensitivity of calculated values to the quality of measured data at the estuary-ocean boundary. The volume of freshwater input and the flushing time calculated from the developed method are highly reliable when there is a significant salinity difference between flood and ebb tides.