Desorption Rate Constants Research Articles

Using the reversible inhibition of gastric lipase by Orlistat for investigating simultaneously lipase adsorption and substrate hydrolysis at the lipid–water interface

The lipolysis reaction carried out by lipases at the water-lipid interface is a complex process including enzyme conformational changes, adsorption/desorption equilibrium and substrate hydrolysis. Mixed monomolecular films of the lipase inhibitor Orlistat and 1,2-dicaprin were used here to investigate the adsorption of dog gastric lipase (DGL) followed by the hydrolysis of 1,2-dicaprin. The combined study of these two essential catalysis steps was made possible thanks to the highest affinity of DGL for Orlistat than 1,2-dicaprin and the fact that the inhibition of DGL by Orlistat is reversible. Upon DGL binding to mixed 1,2-dicaprin/Orlistat monolayers, an increase in surface pressure reflecting lipase adsorption was first recorded. Limited amounts of Orlistat allowed to maintain DGL inactive on 1,2-dicaprin during a period of time that was sufficient to determine DGL adsorption and desorption rate constants. A decrease in surface pressure reflecting 1,2-dicaprin hydrolysis and product desorption was observed after the slow hydrolysis of the covalent DGL-Orlistat complex was complete. The rate of 1,2-dicaprin hydrolysis was recorded using the surface barostat technique. Based on a kinetic model describing the inhibition by Orlistat and the activity of DGL on a mixed 1,2-dicaprin/Orlistat monolayer spread at the air-water interface combined with surface pressure measurements, it was possible to monitor DGL adsorption at the lipid-water interface and substrate hydrolysis in the course of a single experiment. This allowed to assess the kcat/KM* ratio for DGL acting on 1,2-dicaprin monolayer, after showing that mixed monolayers containing a low fraction of Orlistat were similar to pure 1,2-dicaprin monolayers.

Transport of nanoparticles and kinetics in packed beds: A numerical approach with lattice Boltzmann simulations and particle tracking

The lattice Boltzmann method is employed in conjunction with a Lagrangian particle tracking algorithm to investigate the fate and transport of nanoparticles as they propagate in porous columns that are packed with spherical particles. In this approach, physical phenomena that result in particle retention and remobilization are represented by a probability for adsorption and desorption, respectively. The method is validated with experiments where polymer-stabilized purified multi-walled carbon nanotubes propagate in a column packed with inert glass beads. Comparison of simulation results to the conventional filtration equation leads to the correlation of the simulation input parameters to macroscopically observed parameters, such as adsorption and desorption rate constants. It is found that adsorption and desorption nominal rates do not affect the diffusivity of the nanoparticles significantly (the change in particle diffusivity is less than 4%) and that particles with smaller size, where the Brownian motion is dominant, are retained more than larger particles. The difference in particle recovery for small versus large particles is of up to 36% when the probability for adsorption is as high as 0.01.

Pyridine‐N‐Oxide 2‐Carboxylic Acid: An Acceptor Group for Organic Sensitizers with Enhanced Anchoring Stability in Dye‐Sensitized Solar Cells

AbstractA D‐π‐A organic dye carrying a pyridine‐N‐oxide 2‐carboxylic acid anchoring group (BC1) was synthesized together with two analogs lacking the N‐oxide (BC2) or the carboxylic acid moiety (BC3). The distribution and energy of their molecular orbitals was determined, and modelling of their spectroscopic properties was performed through a TD‐DFT computational study. The photo‐ and electrochemical properties of the dyes were assessed together with their desorption kinetics from nanocrystalline TiO2. In solution, the absorption spectra of dyes BC1 and BC3 were red‐shifted compared with BC2, with the maximum absorption wavelength influenced by the dye protonation level. The 2‐substituted carbonitrile dye BC3 was not adsorbed on the titania surface. On the other hand, the pseudo‐first order desorption rate constants of BC1 and BC2 suggest that BC1 was removed from TiO2 more slowly than BC2 a reference cyanoacrylate dye, demonstrating that simultaneous use of the N‐oxide and the carboxylic acid anchoring functions enhanced the stability of the dye/semiconductor assembly. When used as a photosensitizer for dye‐sensitized solar cells, the photovoltaic performance of BC1 was better than BC2, which corresponds to approx. 66 % of that recorded with the reference dye.

Microfluidic Dynamic Interfacial Tensiometry (μDIT)

We designed, developed and characterized a microfluidic method for the measurement of surfactant adsorption kinetics via interfacial tensiometry on a microfluidic chip. The principle of the measurement is based on the deformability of droplets as a response to hydrodynamic forcing through a series of microfluidic expansions. We focus our analysis on one perfluoro surfactant molecule of practical interest for droplet-based microfluidic applications. We show that although the adsorption kinetics is much faster than the kinetics of the corresponding pendant drop experiment, our droplet-based microfluidic system has a sufficient time resolution to obtain quantitative measurement at the sub-second time-scale on nanoliter droplet volumes, leading to both a gain by a factor of ∼10 in time resolution and a downscaling of the measurement volumes by a factor of ∼1000 compared to standard techniques. Our approach provides new insight into the adsorption of surfactant molecules at liquid-liquid interfaces in a confined environment, relevant to emulsification, encapsulation and foaming, and the ability to measure adsorption and desorption rate constants.

Impact of sewage sludge application on zinc desorption kinetics in some calcareous soils

Sewage sludge usually contains significant amount of Zinc (Zn) and is widely used in agricultural lands. A laboratory experiment was performed to determine Zn desorption characteristics in unamended and amended soils with sewage sludge. Ten calcareous soils were amended with 1 % (w/w) sewage sludge. Amended and unamended soils were incubated at field capacity at 25 ± 1 °C for 1 month. After incubation, the kinetics of Zn desorption in amended and unamended soils were determined by successive extraction with DTPA-TEA (diethylenetriaminepentaacetic acid-triethanolamine) in a period of 1–504 h at 25 ± 1 °C. The results of kinetics study showed that extracted Zn and desorption rate constants in the amended soils were significantly (p < 0.01) higher than in the unamended soils. The results showed that Zn desorption increased from 201 to 343 % in amended soil with respect to unamended soils. The amounts of desorbed Zn in the unamended soils ranged from 3.73 to 8.79 mg kg−1, while the amounts of desorbed Zn in amended soils ranged from 11.47 to 17.66 mg kg−1. Desorption kinetics of Zn in two soils conformed fairly well to first-order, parabolic diffusion and power function equations. The results of stepwise regression analysis indicated that calcium carbonate equivalent and clay could be used to estimate Zn desorption characteristics in DTPA-TEA solution in the amended and unamended calcareous soils. It can be concluded that sewage sludge applied to calcareous soils may enhance the source of Zn for the plants.

Comparative Adsorption of CO2 by Mono-, Di-, and Triamino-Organofunctionalized Magnesium Phyllosilicates

Carbon dioxide adsorbents, constituted by organofunctionalized magnesium phyllosilicates, were produced using 3-aminopropyltriethoxysilane (AMPTS), N-[3-(trimethoxysilyl)propyl]-ethylenediamine (TMSPEDA), N-[3-(trimethoxysilyl)propyl]-diethylenetriamine (TMSPETA), and tetraethoxyorthosilane (TEOS) as silicon sources with N/Si ratios of 1, 0.75, 0.5, and 0.25, by conventional and microwave heating. Adsorption studies were performed using TGA and temperature programmed desorption (TPD) methods. The results showed that the best temperatures for adsorption were 41, 45, and 90 °C, when magnesium phyllosilicate functionalized with TMSPETA, TMSPEDA, and AMPTS, respectively, were used as adsorbents. Using TPD technique, the maximum efficiency was found to be between 0.285 and 0.899 for 100% AMPTS and 33.33% TMSPETA, obtained by conventional heating. Adsorption efficiency of the materials prepared by conventional method is higher than those obtained using microwave as heating source, except for 100% AMPTS. Desorption kinetics of CO2, described using Avrami's model, show that the CO2 desorption rate constant is in the range from 0.130 to 0.178 min(-1), similar to the values for CO2 desorption from monoetamolamine-functionalized TiO2 and Li4SiO4 but in a narrower range of values.

Depletion kinetics of perfluoropolyether films with functional end groups using molecular dynamics simulation

Molecular dynamics simulation coupled with a coarse-grained model is employed to investigate the surface depletion kinetics of functional polyether film under heat treatment. The real-time evolutions of lubricant film desorption and decomposition are examined during rapid heating and isothermal stages. The reaction order of lubricant depletion is evaluated during the rapid heating using a constant heating rate and various coverages. It reveals that a peak in the desorption (decomposition) rate is formed and is independent of the mass (bond) coverage, which gives rise to a first-order, coverage independent depletion kinetics. The rate constants for lubricant desorption and decomposition are thus calculated based on a first-order kinetics-controlled reaction during the isothermal stage. The kinetics of functional lubricant depletion shows that desorption is the main mechanism of lubricant depletion under rapid and isothermal heat treatment and is the major cause of lubricant thermal instability on the surface.

Electrochemistry of TEMPO: an assessment of the water diffusion constant in the aqueous liquid/vapor interfacial region

TEMPO, 2,2,6,6-tetramethylpiperidnyl-1-oxy, is a weak surfactant exhibiting a reversible redox activity: a one-electron oxidation to its oxonium cation. In the course of our earlier work (ref. Wu et al. in J Am Chem Soc 127:4490–4496, 2005; Glandut et al. in J Phys Chem B 110:6101–6109, 2006; Glandut et al. in Langmuir 22:10697–10704, 2006), we developed a full understanding of TEMPO’s electrochemistry at line microband electrodes. In these experiments TEMPO diffuses to the line electrode residing in the plane of the air/water interface in two coupled media, bulk aqueous phase with D = 7.7 × 10−6 cm2/s and along the 2D air/water interface with at least an order of magnitude greater surface diffusion constant, Dsurf. The magnitude of the TEMPO oxidation current depends jointly on Dsurf and on the rate of surface partitioning expressed by the desorption rate constant, kdes. The population of TEMPO partitioned to the air/water interface is largely unsolvated and couples to the aqueous solution by hydrogen bonding to predominately one water molecule. Our experimental methodology allows us to simultaneously determine Dsurf and kdes by recording TEMPO voltammetric curves with line microband and barrier microband electrodes. In this report, we present a new methodology of producing and characterizing barrier microband electrodes using vapor-deposited SiO and introduce additional measures such as aspiration of the air/water interface designed to substantially reduce if not eliminate negative error due to surface impurities. These investigations generated a more accurate value of Dsurf of 1.0 ± 0.3 × 10−4 cm2/s which we discuss in terms of the dynamic properties of water in the air/water interfacial region.

Mesoporous Thin Films of TiO2 on Attenuated Total Reflection Crystals. An In Situ Fourier-Transform Infrared Study of the Kinetics and Equilibrium of Adsorption and Photocatalysis of Carboxylic Acids

Highly organized titanium dioxide (TiO2) mesoporous thin films were deposited directly on silicon attenuated total reflection (ATR) crystals by dip-coating, submitted to two different thermal treatments, and characterized by ellipsometric porosimetry analysis (EPA), X-ray diffraction, and electron microscopy. The kinetics and equilibrium of the adsorption of oxalic acid as well as their photocatalytic efficiency were studied in situ by Fourier transformed infrared spectroscopy (FTIR-ATR). The spectral properties and the Langmuir constants of the detected surface complexes resemble those previously found in TiO2 Degussa P25 and anatase particulate films. The photocatalytic activity for the oxidation of oxalic acid was found to be similar to the corresponding one for Degussa P25. The kinetics of adsorption of oxalic acid follows a pseudo-first-order behavior. The pseudo-first-order rate constants show a linear relationship with the oxalic acid concentration. Adsorption (ka) and desorption rate constants (kd) were obtained. The ka values were analyzed in relation to the pore and neck sizes, accessible volume, thickness, and film area. The film area affects strongly the kinetic parameters, while no clear dependence on the thickness value was observed. When the film area is taken into account, adsorption rates on mesoporous films are appreciably larger than on particulate films. Thus, enhanced adsorption rates make mesoporous films better candidates as photocatalysts. The difference is interpreted in terms of a reduced tortousity in the ordered mesoporous films, probably due to their regular spatial order. It is also concluded that sensors and catalysts based on mesoporous films should respond faster than those based on conventional films.

Kinetics of the adsorption of hemoglobin on silica adsorbents with a bimodal distribution of pores

A comparative study of the adsorption kinetics of hemoglobin on silochrome and synthetic silicas with a bimodal distribution of pores is performed. The mechanism of adsorption is established and the presence of a reversible stage is demonstrated. The rate constants of adsorption, desorption, and irreversible binding are determined from the experimental data. The effect of synthesis conditions on the kinetic patterns of the adsorption process is shown.

Kinetics of manganese adsorption, desorption, and oxidation in coastal marine sediments

Ejection of excavated manganese (Mn)‐laden particles from anoxic subsurface sediment onto an oxic sediment‐water interface by infauna and by other physical disturbances triggers desorption and oxidation of reduced manganese species. These competing reactions determine whether adsorbed Mn(II) will be desorbed and escape into the water column or be oxidized to Mn(IV) and retained as an insoluble component of the sediment. Consequently, the net flux of Mn(II) to the water column depends on the relative rates of the two reactions. We determined the rates of Mn(II) adsorption, desorption, and oxidation by incubating slurries of natural anoxic sediment at 25°C and monitoring the concentration of manganese in the aqueous phase of the slurry. The kinetics of adsorption, desorption, and oxidation were fitted to first‐order rate laws. The first‐order rate constants for adsorption ( = 7.0 ± 3.4 h−1) and desorption ( = 12.7 ± 3.3 h−1) are more than two orders of magnitude greater than the first‐order rate constant for oxidation ( = 0.020 ± 0.006 h−1). The combination of rapid desorption kinetics and slow oxidation kinetics allows dissolved manganese to be dispersed into the bottom water by turbulent diffusion and escape local reoxidation and retention at the sediment‐water interface. Thus, advection of anoxic sediment to the sediment‐water interface contributes to the overall flux of manganese from the sediment to the water column.

A Combined Radio- and Stable-Isotopic Study of a California Coastal Aquifer System

Stable and radioactive tracers were utilized in concert to characterize geochemical processes in a complex coastal groundwater system and to provide constraints on the kinetics of rock/water interactions. Groundwater samples from wells within the Dominguez Gap region of Los Angeles County, California were analyzed for a suite of major cations (Na+, K+, Mg2+, Ca2+) and anions (Cl−, SO42−), silica, alkalinity, select trace elements (Ba, B, Sr), dissolved oxygen, stable isotopes of hydrogen (δD), oxygen (δ18O), dissolved inorganic carbon (δ13CDIC), and radioactive isotopes (3H, 222Rn and 223,224,226,228Ra). In the study area, groundwater may consist of a complex mixture of native groundwater, intruded seawater, non-native injected water, and oil-field brine water. In some wells, Cl− concentrations attained seawater-like values and in conjunction with isotopically heavier δ18O values, these tracers provide information on the extent of seawater intrusion and/or mixing with oil-field brines. Groundwater 3H above 1 tritium unit (TU) was observed only in a few select wells close to the Dominguez Gap area and most other well groundwater was aged pre-1952. Based on an initial 14C value for the study site of 90 percent modern carbon (pmc), groundwater age estimates likely extend beyond 20 kyr before present and confirm deep circulation of some native groundwater through multiple aquifers. Enriched values of groundwater δ13CDIC in the absence of SO42− imply enhanced anaerobic microbial methanogenesis. While secular equilibrium was observed for 234U/238U (activity ratios ~1) in host matrices, strong isotopic fractionation in these groundwater samples can be used to obtain information of adsorption/desorption kinetics. Calculated Ra residence times are short, and the associated desorption rate constant is about three orders of magnitude slower than that of the adsorption rate constant. Combined stable- and radio-isotopic results provide unique insights into aquifer characteristics, such as geochemical cycling, rock/water interactions, and subsurface transport and mixing.

A new approach for the extraction of pollutants from wastewaters handled by the graphic industry

It is widely recognized that the Graphic Industry handles toxic products and produces, in its various operations, toxic wastes. These wastes can cause serious environmental damages and can lead to severe health problems.In this work we report an efficient, simple and cheap to run method for the removal of some of the most common pollutants involved in the various stages of the Graphic Industry production, using a Solid-Phase Extraction (SPE) methodology. We have determined equilibrium constants, Keq, and adsorption (kup) and desorption (koff) rate constants for the extraction of benzene, xylene, toluene and ethylbenzene (BXTE) from water, using C18 disks. The removal of these compounds was monitored by UV–vis spectroscopy, at room temperature. Average extraction efficiencies were of 60% in a mixture of BXTEs and close to 80% when pollutants were assessed separately.Since the retention mechanism in the C18 disk is essentially governed by hydrophobic interactions between the compounds and the alkyl chains of the disk, we have also shown that these pollutants' lipophilicity plays an important role in the rationalization of their behavior during the extraction process.

Modeling hydrogen permeation through a thin titanium oxide film and palladium

Models that describe hydrogen permeation through a thin TiO2 film deposited on Pd have been developed based on a mass-balance equation consisting of diffusion, reversible hydrogen absorption/desorption, and irreversible hydrogen trapping. These models were numerically simulated by the finite element method. By comparing model simulations with experimental permeation curves, values of the parameters associated with permeation, such as diffusion coefficients, absorption and desorption rate constants, trapping rate constants, and saturation concentrations, can be evaluated. The TiO2 film noticeably impedes hydrogen permeation, essentially due to slow hydrogen transport in the oxide. The diffusion coefficient of hydrogen in TiO2 was found to be 10−13cm2/s, three orders of magnitude lower than that in Ti metal.

Structural attributes affecting peptide entrapment in PEO brush layers

A more quantitative understanding of peptide loading and release from polyethylene oxide (PEO) brush layers will provide direction for development of new strategies for drug storage and delivery. In this work we recorded selected effects of peptide structure and amphiphilicity on adsorption into PEO brush layers based on covalently stabilized Pluronic®F 108. Optical waveguide lightmode spectroscopy and circular dichroism measurements were used to characterize the adsorption of poly-l-glutamic acid, poly-l-lysine, and the cationic amphiphilic peptide WLBU2, to the brush layers. The structure of WLBU2 as well as that of the similarly-sized homopolymers was controlled between disordered and more ordered (helical) forms by varying solution conditions. Adsorption kinetic patterns were interpreted with reference to a simple model for protein adsorption, in order to evaluate rate constants for peptide adsorption and desorption from loosely and tightly bound states. While more ordered peptide structure apparently promoted faster adsorption and elution rates, resistance to elution while in the PEO layer was dependent on peptide amphiphilicity. The results presented here are compelling evidence of the potential to create anti-fouling surface coatings capable of storing and delivering therapeutics.

Quantifying nisin adsorption behavior at pendant PEO layers

The antimicrobial peptide nisin shows potent activity against Gram-positive bacteria including the most prevalent implant-associated pathogens. Its mechanism of action minimizes the opportunity for the rise of resistant bacteria and it does not appear to be toxic to humans, suggesting good potential for its use in antibacterial coatings for selected medical devices. A more quantitative understanding of nisin loading and release from polyethylene oxide (PEO) brush layers will inform new strategies for drug storage and delivery, and in this work optical waveguide lightmode spectroscopy was used to record changes in adsorbed mass during cyclic adsorption-elution experiments with nisin, at uncoated and PEO-coated surfaces. PEO layers were prepared by radiolytic grafting of Pluronic® surfactant F108 or F68 to silanized silica surfaces, producing long- or short-chain PEO layers, respectively. Kinetic patterns were interpreted with reference to a model accounting for history-dependent adsorption, in order to evaluate rate constants for nisin adsorption and desorption, as well as the effect of pendant PEO on the lateral clustering behavior of nisin. Nisin adsorption was observed at the uncoated and F108-coated surfaces, but not at the F68-coated surfaces. Nisin showed greater resistance to elution by peptide-free buffer at the uncoated surface, and lateral rearrangement and clustering of adsorbed nisin was apparent only at the uncoated surface. We conclude peptide entrapment at the F108-coated surface is governed by a hydrophobic inner region of the PEO brush layer that is not sufficient for nisin entrapment in the case of the shorter PEO chains of the F68-coated surface.

Kinetic Model of Fischer–Tropsch Synthesis in a Slurry Reactor on Co–Re/Al2O3 Catalyst

A kinetic model for Fischer–Tropsch synthesis is derived using a Langmuir–Hinshelwood–Hougen–Watson approach. Experiments were conducted over 25% Co/0.48% Re/Al2O3 catalyst in a 1 L slurry reactor over a range of operating conditions (T = 478, 493, 503 K; P = 1.5, 2.5 MPa; H2/CO = 1.4, 2.1; WHSV = 1.0–22.5 NL/(gcat·h)). Rate equations were based on the elementary reactions corresponding to a form of well-known carbide mechanism. The 1-olefin desorption rate constant was assumed to be a function of carbon number due to the effect of weak interaction of the hydrocarbon chain with the catalyst surface. Values of estimated activation energies are in good agreement with those reported previously in the literature. The kinetic model was able to correctly predict all of the major product distribution characteristics, including the increase in chain growth probability and decrease in olefin-to-paraffin ratio with carbon number, as well as formation rates of methane and ethylene.

Kinetics of lubricant desorption and decomposition under heat treatment: a molecular dynamics study

Understanding the kinetics of lubricant depletion under rapid and isothermal heat treatment is of fundamental importance in maintaining the stability and reliability of lubricated surfaces. In this paper, molecular dynamics simulation coupled with a coarse-grained bead-spring polymer model is employed to study lubricant depletion instability. During rapid heating, the lubricant decomposes at an increasing rate with temperature. However, a maximum rate is observed during desorption due to the influence of lubricant-to-substrate interaction. During the isothermal stage, the rates of desorption (rdes) and decomposition (rdec) decrease over time, showing an exponential depletion process. It is found that rdes or rdec increases with both the temperature and lubricant mass or bond coverage. Moreover, the rate constants for desorption (kdes) and decomposition (kdec) are calculated based on a first-order kinetics-controlled reaction. For a given lubricant mass coverage, ln(kdes) exhibits a non-linear relation with 1/T, indicating non-Arrhenius-like behavior of lubricant desorption. However, for a given lubricant bond coverage, ln(kdec) versus 1/T yields a straight line, signifying Arrhenius-like behavior of lubricant decomposition. The kinetics of lubricant depletion also shows that lubricant desorption is favored over decomposition under heat treatment to high temperatures and is the major cause of lubricant degradation and failure on the surface.

Influence of Activated Charcoal on Desorption Kinetics and Biodegradation of Phenanthrene in Soil

The observed strong sorption of polycyclic aromatic hydrocarbons (PAHs) to black carbon (BC) presents potential implications for PAH bioaccessibility in soils. The effects of BC on the desorption kinetics and mineralization of phenanthrene in four soils was investigated after 1, 25, 50, and 100 d soil-PAH contact time, using sequential hydroxypropyl-β-cyclodextrin (HPCD) extractions in soils amended with 0, 0.1, 1, and 5% (dry wt. soil) activated charcoal (AC, a form of BC). The rapidly (%F(rap)) and slowly (%F(slow)) desorbing phenanthrene fractions and their rate constants were determined using a first-order two-compartment (biphasic) desorption model. A minimum 7.8-fold decrease in %F(rap) occurred when AC was increased from 0 to 5%, with a corresponding increase in %F(slow). Desorption rate constants followed the progression k(rap) (% h(-1)) > k(slow) (% h(-1)) and were in the order of 10(-1) to 10(-2) and 10(-3) to 10(-4), respectively. Linear regressions between %F(rap) and the fractions degraded by a phenanthrene-degrading inoculum (%F(min)) indicated that slopes did not approximate 1 at concentrations greater than 0% AC; %F(min) often exceeded %F(rap), indicating a fraction of sorbed phenanthrene (%F(slow)) remained microbially accessible. Therefore, HPCD-desorption kinetics alone may not be an adequate basis for the prediction of the bioaccessibility of PAHs to microorganisms or bioremediation potential in AC-amended soils.

Effect of initial biomass concentration on bioregeneration of 4-chlorophenol-loaded granular activated carbon: kinetic and efficiency studies

Background Information on the effects of initial biomass concentration on bioregeneration rate and efficiency is lacking as many of the bioregeneration studies were conducted at constant initial biomass concentration. The objectives of this study are: (i) to develop kinetic models incorporating adsorption, desorption, biodegradation and the irreversibility of adsorption in describing the bioregeneration of granular activated carbon (GAC) loaded with 4-chlorophenol (4-CP); and (ii) to investigate the effect of initial biomass concentration on the rate and efficiency of bioregeneration of 4-CP-loaded GAC in simultaneous adsorption and biodegradation processes. Results The bioregeneration model with Haldane biodegradation kinetics gave a better fit (R2 > 0.956) than the model with first-order biodegradation kinetics (R2 > 0.805) to the experimental data. Values of the rate constant of desorption generated from the models showed that there was no observed effect of varying biomass concentration on the bioregeneration rate. The efficiency study revealed no observed effect of varying biomass concentration on the bioregeneration efficiency provided there was no inhibition effect due to 4-CP. Conclusions Change in the initial biomass concentration had no observed effect on the bioregeneration rate and efficiency, if there was no inhibitory effect due to the substrate in the latter case. © 2012 Society of Chemical Industry.