Equilibrium Aqueous Phase Concentration Research Articles

Equilibrium study on the reactive liquid–liquid extraction of 4-cyanopyridine with 4-nonylphenol

A liquid–liquid extraction equilibrium model was developed describing the extraction of aqueous 4-cyanopyridine with the reactive solvent 4-nonylphenol. The model describes the capacity of the solvent up to an equilibrium aqueous phase concentration of 20g/L within a temperature interval of 25 to 80°C. This model describes the transfer of 4-cyanopyridine from the aqueous to the 4-nonylphenol phase and takes into consideration the complexation in the solvent phase through hydrogen bonding of 4-nonylphenol with both functional groups of 4-cyanopyridine, as well as the oligomerization of 4-nonylphenol. The thermodynamic equilibrium parameters were regressed to the experimental data with good accuracy, the largest error at the confidence limit of the estimated parameters being 4%. The obtained results were in good agreement with the literature on the complexation of pyridines with phenols. The mean relative error between the model and the experimental data obtained in this work was 3.8%.

Sorption capacity of a new generation granular activated carbon—Bio‐Sep® bead—and its use in a suspended growth bioreactor

AbstractBACKGROUND: A new generation granular activated carbon—Bio‐Sep® beads—consist of 25% polymer (Nomex) and 75% powdered activated carbon. The porous structure and high surface area of these beads make them suitable for sorbent in adsorption columns, and for immobilization media in bioreactors. The aim of this study was to study the sorption characteristics of Bio‐Sep® beads for methyl t‐butyl ether (MTBE) and t‐butyl alcohol (TBA), and to demonstrate the advantage of their usage in a suspended growth bioreactor.RESULTS: The maximum uptake capacity of Bio‐Sep® beads for MTBE and TBA, in the studied concentration range (10–100 mg L−1), was observed to be 9.73 and 6.23 mg g−1, respectively. A 52 h desorption experiment resulted in 13.6–42.2% MTBE and 33–53% TBA desorption corresponding to the initial solid phase concentrations of 1.68–9.73 mg g−1 and 1.41–6.23 mg g−1, respectively. The sorption of TBA on the Bio‐Sep® beads was significantly hindered by the presence of MTBE. The addition of 10 g Bio‐Sep® beads (dry weight) in a suspended growth bioreactor was able to eliminate the inhibitory effect of 150 mg L−1 MTBE.CONCLUSIONS: At an equilibrium aqueous phase concentration (Ce) of 1 mg L−1, the solid phase concentration (qe) on Bio‐Sep® beads were observed as 1.44 and 0.47 mg g−1 for MTBE and TBA, respectively. The results obtained in this study indicate that Bio‐Sep® beads have reasonable sorption and desorption characteristics, which can be successfully exploited for the removal/degradation of toxic organic pollutants in high rate bioreactors. Copyright © 2007 Society of Chemical Industry

Modeling the transport of dissolved contaminants originating from a nonaqueous phase liquid source containing polycyclic aromatic hydrocarbon compounds in groundwater

A three-dimensional mathematical model is developed for simulating the transport of dissolved contaminants originating from a well-defined, multicomponent nonaqueous phase liquid (NAPL) source containing polycyclic aromatic hydrocarbon (PAH) compounds in groundwater. The dissolution process for each NAPL component is envisioned to occur in a successive series of small dissolution intervals (or pulses). The equilibrium aqueous phase concentration of each component and the source dimensions are assumed to remain constant for the duration of each dissolution interval. The model accounts for possible solidification of PAH components as the NAPL source dissolves. Aqueous phase contaminant concentrations resulting from each dissolution interval are calculated using an existing analytical solution. A synthetic PAH-rich NAPL mixture consisting of benzene and eight PAH components is used for model simulations. The model is useful for evaluation and prediction of downstream aqueous phase contaminant concentrations resulting from dissolution of a PAH-rich NAPL source. Key words: contaminant transport, groundwater, nonaqueous phase liquid (NAPL), mathematical modeling, polycyclic aromatic hydrocarbons.

Benzene degradation in a two-phase partitioning bioreactor by Alcaligenes xylosoxidans Y234

An aqueous-organic, two-phase bioreactor system was used for the biodegradation of benzene. Through a systematic solvent selection procedure considering biological, physical, operational, environmental and economic factors, hexadecane was chosen as the most promising solvent. The solvent has infinite solubility for benzene and shows very high phase stability with aqueous media. A lcaligenes xylosoxidans Y234 capable of degrading benzene without any other co-substrate was inoculated into the aqueous phase of the two-phase partitioning bioreactor, which consisted of a 1 l aqueous phase and 500 ml hexadecane. A feed of 7000 mg of benzene was loaded into the organic phase, which gave an initial equilibrium aqueous phase concentration of 100 mg/l. Over the course of 24 h, 63.8% of the benzene was degraded by the microorganism, and 36.2% was stripped by aeration. By installing a condenser and using a lower gas flow of pure oxygen to reduce stripping, more than 99% of a subsequent 7000 mg benzene addition was degraded by the organisms within 24 h.

Mass Transfer of Polynuclear Aromatic Hydrocarbons from Complex DNAPL Mixtures

Parameters governing the rates of mass transfer of the individual components of four synthetic dense non-aqueous phase liquid (DNAPL) mixtures into the aqueous phase were evaluated. The DNAPL mixtures, composed of toluene and eight polynuclear aromatic hydrocarbons (PAHs), were designed to serve as models for coal tars and creosotes. The reactor employed provided a relatively stable interface between internally mixed but segregated aqueous and DNAPL phases. Two parameters, the aqueous phase concentration at equilibrium and the overall film mass transfer coefficient, were quantified by simulating aqueous concentration profiles with a mass-transfer-limited rate model using a statistical parameter search and data fitting routine. DNAPL phase activity coefficient values for the various compounds derived from equilibrium aqueous phase concentrations were typically within a factor of 2 of Raoult's law prediction of unity; refinement of fugacity ratio estimates for the solid PAHs brought the values even closer to unity. Film transfer coefficients for all components of the mixtures studied were similar in magnitude, in the range 0.8−3 × 10-3 cm/s. No significant variations of the film transfer coefficient for naphthalene were noted across the DNAPL mixtures, over which the mole fraction of this compound was varied from 0.05 to 0.25.

Desorption and Unavailability of Aged Simazine Residues in Soil from a Continuous Corn Field

AbstractThe sorption/desorption behavior of field weathered (aged) simazine (2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine) residues from a 20‐year continuous corn (Zea mays L.) field was compared to that of 14C‐simazine recently added to the same soil. The apparent sorption coefficients of the aged residues determined from 24‐h and 48‐h desorption experiments were approximately 15 times higher than the sorption coefficients of added simazine. Aged simazine residues were also shown to be biologically unavailable to sugarbeet (Beta vulgaris L.) and to microbial degraders, whereas recently added simazine showed herbicidal damage to sugarbeet and was substantially (ca. 48%) degraded during a 34‐d incubation in soil. Apparently, the process of pesticide aging results in simazine residues that are less bioavailable, as shown by their resistance to plant uptake and microbial degradation, and that desorb slowly into soil solution. The concentration of simazine in water from field soil‐samples (C) was monitored throughout a growing season, and compared to the equilibrium aqueous phase concentration (Cc) predicted from the laboratory determined sorption coefficient (Koc of added 14C‐simazine. The fractional equilibrium values (C/Ce.) were approximately 1 at the time of simazine application in May but fell to 0.05 during July and August. These results show that the concentration of simazine in water contacting field soil is likely to be substantially lower than that predicted from laboratory determined sorption coefficients, except immediately following application.