Equilibrium Sorption Kinetics Research Articles

Removal of Oil from Contaminated Wastewater Using Thermo-Chemically Modified Lignocellulosic Biomass

The volume of oil-contaminated wastewater generated from petrochemical industries and various oil fields is significant. The discharge of such oily wastewater endangers terrestrial and aquatic ecosystems due to the high organic load and toxicity of the oily components. Currently, there are several technologies available for the treatment of oily wastewater among which adsorption was observed to be a promising technique for the removal of oil emulsions from wastewater. In this study, acid modified and base modified pyrolyzed date seed was investigated for the removal of oil and oil emulsions from contaminated water. The effect of pH in the range of (2-12), temperature (30°C-70°C), date seed dose of (0.1-1 g) and contact time of (1-240 mins) was investigated for both the acid modified and base modified activated date seeds samples. Equilibrium sorption was attained after a contact time of 120 minutes. It was observed that base modified activated date seed resulted in 83% removal of oil. Both acid and base modified activated date seed showed a high percentage removal of 92.9 % and 94.3 % respectively at a lower acidic pH of 2. Concerning the equilibrium sorption kinetics, Pseudo-Second-order kinetic Model showed better fit as compared to pseudo first order kinetic model. Therefore, the adsorption of oily wastewater onto both acid and base modified activated date seeds are consistent with the second-order kinetic model. The Langmuir isotherm was found to be linear with high correlation coefficient values over the entire concentration range, which confirms that the Langmuir isotherm is more accurate to represent sorption by acid modified date seed unlike the case of base modified activated date seed where Freundlich isotherms were found to better fit the adsorption equilibrium data for base modified date seed. Keywords: Pyrolyzed date seeds; chemically modified activated date seeds; thermo-chemically modified lignocellulosic biomass; kinetics; equilibrium isotherms.

Identifiability of sorption parameters in stirred flow-through reactor experiments and their identification with a Bayesian approach

This paper addresses the methodological conditions –particularly experimental design and statistical inference– ensuring the identifiability of sorption parameters from breakthrough curves measured during stirred flow-through reactor experiments also known as continuous flow stirred-tank reactor (CSTR) experiments. The equilibrium-kinetic (EK) sorption model was selected as nonequilibrium parameterization embedding the Kd approach. Parameter identifiability was studied formally on the equations governing outlet concentrations. It was also studied numerically on 6 simulated CSTR experiments on a soil with known equilibrium-kinetic sorption parameters. EK sorption parameters can not be identified from a single breakthrough curve of a CSTR experiment, because Kd,1 and k− were diagnosed collinear. For pairs of CSTR experiments, Bayesian inference allowed to select the correct models of sorption and error among sorption alternatives. Bayesian inference was conducted with SAMCAT software (Sensitivity Analysis and Markov Chain simulations Applied to Transfer models) which launched the simulations through the embedded simulation engine GNU-MCSim, and automated their configuration and post-processing. Experimental designs consisting in varying flow rates between experiments reaching equilibrium at contamination stage were found optimal, because they simultaneously gave accurate sorption parameters and predictions. Bayesian results were comparable to maximum likehood method but they avoided convergence problems, the marginal likelihood allowed to compare all models, and credible interval gave directly the uncertainty of sorption parameters θ. Although these findings are limited to the specific conditions studied here, in particular the considered sorption model, the chosen parameter values and error structure, they help in the conception and analysis of future CSTR experiments with radionuclides whose kinetic behaviour is suspected.

Kinetic Model for the Sorption of Ni(II), Cu(II) and Zn(II) onto Cocos Mucifera Fibre Waste Biomass from Aqueous Solution

Sorption of divalent metals ions Ni(II), Cu(II) and Zn(II) unto coconut cocos mucifiera fibre waste biomass over a wide range of operation conditions and equilibrium-sorption kinetics were studied. The batch experiment showed that pH 2-3, was the best range for the sorption of the metal ions onto the biomass. The time-dependent experiments showed that the binding of the metal ions onto the adsorbent, was quite rapid and occurred within 25 minutes and completed within 50 minutes. The sorption process was examined by means of the Langmuir and the Freundlich isotherm models. The monolayer sorption capacity obtained using the Langmuir equation was 0.09 mg/g Ni (II), 0.08 mg/g Cu(II) and 0.09 mg/g Zn(II). The Freundlich isotherm model was not too appropriate for the sorption process, since R2 for all the three metals are less than 0.90. However the KF value of Zn(II) (0.880), is greater than that of Ni(II) (0.077) and Cu(II) (0.075), suggesting that Zn(II) has greater adsorption tendency towards the biomass. The kinetics of the sorption mechanism was evaluated using the pseudo-first order rate model and pseudo-second rate model. The results indicated that the pseudo-second order model provides a more appropriate description of the single and mixed metal-ion sorption process of Ni(II) Cu(II) and Zn(II) onto coconut fibre biomass.

Modeling Pesticide Fate and Nonideal Transport From Seeds Treated with a Slow-Release Pesticide in a Laboratory Soil Column

This research evaluated the predictive ability of a pesticide fate and transport model to simulate the potential for pesticide leaching from slow-release insecticide-treated corn seeds. No studies in the literature report model evaluation for pesticide-treated seeds. The column studies consisted of ten 60 cm soil columns of silt loam soil, each planted with one corn seed treated with the active ingredient of an experimental pesticide. The columns were modeled using the Root Zone Water Quality Model (RZWQM), which is capable of simulating slow-release, instantaneous equilibrium (IE) and equilibrium kinetic (EK) sorption, and irreversible binding. The model was calibrated for hydrology (i.e., leachate from the bottom of the soil columns), crop growth, and total pesticide in the soil profile. Measured concentrations were compared to model predictions for IE and EK sorption scenarios across a range of sorption parameters derived from batch and time-dependent sorption studies. Modeling scenarios failed to predict the observed pesticide confinement (70% of applied pesticide) to primarily the upper 15 cm of the soil profile, with 1% to 20% of applied in the upper 15 cm for IE sorption and 3% to 18% of applied for EK sorption at the end of the simulation period. Both IE and EK sorption scenarios failed to predict pesticide in leachate (observed cumulative of 0.12% of applied) unless using minimum IE and EK sorption parameters. Model deviations from observations were hypothesized to be due to the model representing a theoretical two-dimensional process in one-dimension and the potential for preferential flow paths formed by root formation. Long-term (i.e., 20-year) simulations suggested that significant differences (i.e., average of 8% compared to less than 1% cumulative leaching) arise between IE and EK sorption after several plantings of the pesticide-treated seed. The error in assuming IE sorption for an EK sorption process is negligible over the short term but increases with subsequent chemical applications over the long term.

GLEAMS-TC: A TWO-COMPARTMENT MODEL FOR SIMULATING TEMPERATURE AND SOIL WATER CONTENT EFFECTS ON PESTICIDE LOSSES

Many pesticide fate and transport models, including the GLEAMS model, overestimate pesticide degradation during its later stages of residence in soil. Except for runoff events shortly after pesticide application, models using equilibrium sorption kinetics often underestimate sediment-transported pesticides. To address concerns about transport of low levels of pesticides by runoff to sensitive ecosystems over annual or longer time cycles, GLEAMS was modified using a two-compartment pesticide-state model and algorithms for adjustment of degradation rates for temperature and soil water contents. Two pesticide pools, labile and nonlabile, were linked using first-order kinetics, with the forward and reverse rate constants between these pools as the only two additional inputs required for the model, GLEAMS-TC. GLEAMS-TC was calibrated successfully using 3 years of field data. Long-term pesticide persistence in soil was represented. Comparing model predictions with observed data, GLEAMS-TC simulated observed pesticide sediment transport, whereas GLEAMS underestimated observed data by a factor of 4. Sensitivity to rates of pesticide exchange between the two pools and impact on runofflosses were demonstrated with 50-year simulations. GLEAMS-TC is a research tool for investigating changes in pesticide state in soils as a function of exposure time, environmental variables, and interrelationships between pesticide degradation, mobility, and fate and transport in the environment.