Ethoxylated Nonionic Surfactants Research Articles

Hydroformylation of branched olefins catalyzed by Co2(CO)8 for synthesis of branched alcohol ethoxylates and their surfactant properties

Abstract Branched-chain surfactants have lower equilibrium surface tension, superior wettability and emulsifying performance, making them suitable for exclusive applications. Linear α-olefins are rich in coal-based Fischer–Tropsch synthesized liquid products and are promising building blocks for the synthesis of branched-chain surfactants via dimerization and subsequent C=C bond functionalization. Herein, a new series of branched ethoxylate non-ionic surfactants (MDC6E n ) were prepared using 2-butyl-1-octene (1-hexene dimer, DC6), obtained by the dimerization of coal-based Fischer-Tropsch synthesized 1-hexene, as the hydrophobe via hydroxylation and ethoxylation. In particular, the hydroxylation of DC6 was carried out in a one-pot tandem hydroformylation and hydrogenation over unmodified Co2(CO)8 under mild conditions (140 °C and 4–8 MPa, CO:H2 = 1:1). A thorough investigation of their surfactant properties was carried out, including equilibrium surface tension, dynamic surface tension, foaming properties, wetting power, and emulsifying power. The results indicate that MDC6E9 performs comparably to a commercially available branched-chain surfactants, the iso-tridecyl alcohol ethoxylates (MULTISO 1390). This research provides a new direction for the synthesis of branched nonionic surfactants using Fischer–Tropsch synthesized products, further promoting the development of coal-based fine chemicals.

Reverse Micellar Dyeing of Cotton Fabric with Reactive Dye Using Biodegradable Non-Ionic Surfactant as Nanoscale Carrier: An Optimisation Study by One-Factor-at-One-Time Approach.

This study investigates the feasibility of using biodegradable secondary alcohol ethoxylate (SAE) non-ionic surfactant as a building block for the formation of reverse micelles, functioning as reactive dye carriers for the dyeing of cotton fabric in non-aqueous octane medium. Ten dyeing parameters were optimised, by a one-factor-at-a-time approach, namely: (i) effect of colour fixation agent; (ii) surfactant-to-water mole ratio; (iii) surfactant-to-co-surfactant mole ratio; (iv) volume of soda ash; (v) volume of dye; (vi) solvent-to-cotton ratio; (vii) dyeing temperature; (viii) dyeing time; (ix) fixation time; (x) soda-ash-to-cotton ratio. The colour properties, fastness properties and physical properties of SAE-dyed samples were experimentally compared with the conventional water-dyed samples. The optimised condition was found when SAE samples were dyed as follows: (a) 1:20 surfactant-to-water ratio; (b) 1:8 surfactant-to-co-surfactant ratio; (c) 10:1 solvent ratio; (d) 40 min dyeing time; (e) 60 min fixation time; and (f) 70 °C dyeing and fixation temperature. The results showed that SAE-dyed samples have better colour strength, lower reflectance percentage and comparable levelness, fastness and physical properties than that of water-dyed samples. SEM images revealed that the dyed cotton fibres had no severe surface damage caused by an SAE-based reverse micellar dyeing system. The TEM image depicts that the reverse micelle was of nanoscale, spherical-shaped and had a core-shell structure, validating the presence of reverse micelle as a reactive dye carrier and the potential of an SAE-based reverse micellar system for dyeing of cotton fabrics.

Corrosion Inhibition of Carbon Steel in Hydrochloric Acid Solution Using Ethoxylated Nonionic Surfactants Based on Schiff Base: Electrochemical and Computational Investigations.

Two ethoxylated nonionic surfactants (L400 and L600) based on Schiff base are prepared from polyoxyethylene, glyoxalic acid, and phenylenediamine. They are evaluated electrochemically as carbon steel corrosion inhibitors in 1 M HCl by electrochemical impedance spectroscopy (EIS) and Tafel techniques and complemented with microscopic analysis methods. The obtained Tafel data indicate the mixed-type behavior of the inhibitor used. The inhibition efficiency touches the peak at 1 × 10–4 M, exhibiting 92 and 94% for L400 and L600, respectively. The presence of the tested inhibitors decreases corrosion current density (icorr) and double-layer capacitance (Cdl) due to the formation of a protective adsorption layer in place of the already adsorbed water and aggressive Cl– ions. Both L400 and L600 adsorption modes follow Langmuir adsorption isotherm. The density functional theory (DFT) calculated indices (ΔEgap and EHOMO) indicate the superiority of L600 over the L400 counterpart as a reactive compound. Adsorption of L600 and L400 over the Fe(1 1 0) in simulated acidic medium is investigated by Monte Carlo (MC) simulation to verify their inhibition performance and are matched with adsorption free energy ΔGads calculated values. Both experimental and theoretical data are in agreement.

Structure and Dynamics of Spherical and Rodlike Alkyl Ethoxylate Surfactant Micelles Investigated Using NMR Relaxation and Atomistic Molecular Dynamics Simulations.

Predicting and controlling the properties of amphiphile aggregate mixtures require understanding the arrangements and dynamics of the constituent molecules. To explore these topics, we study molecular arrangements and dynamics in alkyl ethoxylate nonionic surfactant micelles by combining NMR relaxation measurements with large-scale atomistic molecular dynamics simulations. We calculate parameters that determine relaxation rates directly from simulated trajectories, without introducing specific functional forms to describe the dynamics. NMR relaxation rates, which depend on relative motions of interacting atom pairs, are influenced by wide distributions of dynamic time scales. We find that relative motions of neighboring atom pairs are rapid and liquidlike but are subject to structural constraints imposed by micelle morphology. Relative motions of distant atom pairs are slower than nearby atom pairs because changes in distances and angles are smaller when the moving atoms are further apart. Large numbers of atom pairs undergoing these slow relative motions contribute to predominantly negative cross-relaxation rates. For spherical micelles, but not for cylindrical micelles, cross-relaxation rates are positive only for surfactant tail atoms connected to the hydrophilic headgroup. This effect is related to the lower packing density of these atoms at the hydrophilic-hydrophobic boundary in spherical vs cylindrical arrangements, with correspondingly rapid and less constrained motion of atoms at the boundary.

The effect of ethoxylate nonionic surfactants on phase inversion temperature and salinity: an alternative approach for vegetable oil recovery from spent bleaching earth

An accurate determination of the hydrophilic-lipophilic nature of surfactants plays an important role in guiding microemulsion formation. The objective of this study is to determine the effect of ethoxylate numbers (EONs) (3, 5, and 7 moles) of nonionic surfactants on a phase inversion temperature (PIT) and optimum salinity based on the equivalent alkane carbon numbers (ACNs) of vegetable oils. Three vegetable oils, soybean oil, crude rice bran oil and crude palm oil, were selected for use as a surrogate oil to represent the residual oils found in spent bleaching earth. In this study, the hydrophilic-lipophilic deviation (HLD) was used to predict the optimum salinity (0-20 %wt.) at various temperatures (25-55°C). The results showed that the ACNs of crude rice bran oil, crude palm oil, and soybean oil were 15.41±0.35, 13.71±0.41, and 17.60±0.28, respectively. In comparison, these predictions with the experimental results, the data showed slight deviations in the optimum salinity with the specific temperature. Finally, the ACN and the surfactant characteristics obtained in this study were combined with the HLD equation and used to validate its practically and utility for guiding the optimum microemulsion formulation.

Design of nonionic micelle-laden polysaccharide hydrogels for controlled delivery of hydrophobic drugs

The incorporation of micelle self-assembly in hydrogels has been used to produce self-healing materials, materials with tunable mechanical properties, and hydrophilic or hydrophobic drug delivery systems. However, little is known about the connection among formulation – structure – properties (particularly transport) in these systems. This connection is explored in alkyl ethoxylate micelle-laden gellan gum hydrogels used as delivery system for the hydrophobic drug dexamethasone. Phase behavior maps and rheological characterization of the micelle-laden hydrogels indicate that their properties are largely dominated by the concentration and cloud point (CP) of the alkyl ethoxylate nonionic surfactant. The sol-gel temperature of the hybrid hydrogels was found to be close to the CP of the surfactant, and their storage modulus (G’) was found to increase with increasing surfactant concentration. A detailed analysis of the phase behavior maps, and evaluations of the mesh size of the hybrid hydrogels suggest a novel mechanism whereby micelles associate with gellan gum strands during high temperature hydration, hindering the double-helix assembly of the strands upon cooling. This increases the number of single strands and the density of physical cross-links, reducing the mesh size of the hydrogel. This mesh size reduction led to a decrease in the effective diffusion coefficient of micelles in the gel, and extended the release time of dexamethasone from 2h in surfactant-free hydrogel to more than 2days in the micelle-laden hydrogel.

Thermal behavior of aqueous iron oxide nano-fluid as a coolant on a flat disc heater under the pool boiling condition

This paper experimentally focuses on the pool boiling heat transfer characteristics of gamma Fe3O4 aqueous nano-fluids on a flat disc heater. The nano-fluid used in this research was prepared using two-step method and was stabilized using nonylphenol ethoxylate nonionic surfactant, pH setting, and sonication process as well. Influence of different operating parameters such as heat flux (0–1546 kW/m2), mass concentration of nano-fluids (weight concentration 0.1–0.3 %), bubble formation, critical heat flux (1170 kW/m2 for water, 1230 kW/m2 (wt% = 0.1), 1320 kW/m2 (wt% = 0.2), 1450 kW/m2 (wt% = 0.3) and fouling on pool boiling heat transfer coefficient of nano-fluid as a thermal performance index were experimentally investigated and briefly discussed. Results demonstrated that the pool boiling heat transfer coefficient increases with increasing the mass concentration and the applied heat flux. In addition, the rate of bubble formation is significantly intensified at higher heat fluxes and subsequently, larger bubbles detach the surface due to the intensification of bubble coalescence. In terms of fouling formation, it can be stated that fouling of nano-fluids is a strong function of time and rate of deposition is increased over the extended time while the pool boiling heat transfer coefficient was not decreased over the time, as porous deposited layer on the surface are detached from the surface by bubble interactions. In terms of critical heat flux, capillary action of the deposited layer was found to be the main reason responsible for increasing the critical heat flux as liquid is stored inside the porous deposited layer, which enhances the surface toleration against the critical heat flux crisis.

A Simplified Methodology to Measure the Characteristic Curvature (Cc) of Alkyl Ethoxylate Nonionic Surfactants

AbstractThis work introduces a simplified methodology for measuring the characteristic curvature (Cc) of commercial alkyl ethoxylate nonionic surfactants using carefully selected reference surfactants and oils that produce rapid and well defined separations in salinity scans. The Cc of the commercial reference surfactants was calculated using optimal salinities (S*) obtained from solubilization parameter curves, from interfacial tensions (for a selected system), and from emulsion stability tests. The latter provided a fast detection of S*, in a matter of minutes. The calibrated Cc of the reference surfactants was subsequently used to measure the Cc of various commercial alkyl ethoxylate surfactants. The combination of mixtures of test and reference surfactants and emulsion stability tests produced reproducible Cc values that could be obtained with simple bottle tests and in a timely manner. The values obtained using this methodology were cross‐checked, and proved to be consistent, when using different combinations of reference surfactants and oils, and when conducted by different individuals. The standard deviation of Cc from these measurements was typically ±0.2 Cc units, but it could be as large as 25 % of the Cc value for highly hydrophilic surfactants. After comparing the values of Cc obtained experimentally with values calculated from nominal structures (via a group contribution model) it became clear that there are differences between these values, likely because of the polydispersity of alkyl ethoxylate surfactants.

Recovery of Saponins from Jua (Ziziphus joazeiro) by Micellar Extraction and Cloud Point Preconcentration

AbstractJuá (Ziziphus joazeiro) is a Brazilian plant and its bark has been used as a detergent and phytotherapic due to its high saponin content (2–10 %). Saponins are triterpenic glycosides with some properties that aid their use in food, cosmetic and pharmaceutical industries. The object of the present work was to develop an extraction and concentration process of saponins from jua bark, using green solvents such as water and ethanol. Firstly, the extraction conditions optimization was carried out using a central composite design, and compared with other methods such as Soxhlet, ultrasound‐assisted extraction and micellar extraction. Then, cloud point preconcentration was tested to select the salt type and its concentration which promotes a higher concentration factor and partition coefficient at room temperature. Finally, the removal of a t‐octyl phenol ethoxylate (9–10 EO) nonionic surfactant by adsorption was evaluated by optimizing the adsorbent type and its concentration, temperature and time of adsorption, in addition to the adsorbent recycling. Orbital shaker extraction leads to a recovery of 45.6 % saponins under the following conditions: temperature, 38.8 °C; jua/solvent ratio, 0.272; stirring speed, 300 rpm; extraction time, 2 h. Under these conditions, saponins recovery reached 90.8 % when using 15 % v/v of the nonionic surfactant, and a preconcentration factor of 14.2 was obtained by adding sodium carbonate 20 % w/v. The preconcentration factor decreased to a value of 10.1, after nonionic surfactant removal by a hydrophobic crosslinked polystyrene copolymer resin.

Effect of Additives on the Cloud Point of the Octylphenol Ethoxylate (30EO) Nonionic Surfactant

AbstractThe effect of different additives on the cloud point (CP) of an octylphenol ethoxylate (OPEO30) aqueous solution was investigated. The CP of OPEO30 is higher than 100 °C due to its approximately 30 oxyethylene units per molecule, which limits its use in cloud point extraction (CPE) procedures at room temperature. However, the presence of additives can promote a decrease in CP, allowing its use in CPE. Halide presence decreased the CP of OPEO30 in the following order F− > Cl− > Br−. It was also observed that the addition of divalent anions resulted in a more pronounced salting‐out effect than monovalent anions. Blends of OPEO30 and its counterpart with 7.5 units of ethylene oxide (OPEO7.5) were also investigated, and it was verified that the CP of OPEO30 decreased linearly with increasing OPEO7.5 concentration, showing that mixing surfactants is a strategy to be explored. In the presence of small amounts of alcohols that are partially soluble in aqueous solution, such as isobutanol and pentanol, cloudiness was observed at temperatures below the CP of pure OPEO30 solution.

Temperature-Dependent Phase Behavior, Particle Size, and Conductivity of Middle-Phase Microemulsions Stabilized by Ethoxylated Nonionic Surfactants

The present paper deals with the influence of salinity and temperature on the phase behavior and conductivity of middle-phase microemulsions stabilized by ethoxylated nonionic surfactants. Optimal salinity of microemulsion increases with increases in temperature. Middle phase microemulsion shows stability for temperatures up to 330 K, and then the relative phase volume of middle phase decreases slightly. Particle size distribution of the microemulsion formulations with different ethoxylated nonionic surfactants have been studied by dynamic light scattering. Percolation behavior of the middle-phase microemulsion systems have been studied as a function of mass fraction of water for different nonionic surfactants at 0.02 mass fractions of NaCl concentration by electrical conductivity measurement. The temperature effect on the electrical conductivity of middle-phase microemulsions is also studied. With an increase in temperature, the conductivity increases and the activation energy of the system also increase...

The Influence of Ethoxylated Nonionic Surfactants on the Potentiometric Determination of Anionic Surfactants

The Influence of Ethoxylated Nonionic Surfactants on the Potentiometric Determination of Anionic Surfactants

Simultaneous potentiometric determination of cationic and ethoxylated nonionic surfactants in liquid cleaners and disinfectants

A sensitive potentiometric surfactant sensor based on a highly lipophilic 1,3-didecyl-2-methyl-imidazolium cation and a tetraphenylborate (TPB) antagonist ion was used as the end-point detector in ion-pair potentiometric surfactant titrations using sodium TPB as a titrant. Several analytical and technical grade cationic and ethoxylated nonionic surfactants (EONS) and mixtures of both were potentiometrically titrated. The sensor showed satisfactory analytical performances within a pH range of 3–10 and exhibited satisfactory selectivity for all CS and EONS investigated. Ionic strength did not influence the titration except at 0.1 M NaCl, in which a slight distortion of the second inflexion corresponded with the nonionic surfactant. Two-component combinations of four CS and three EONS were potentiometrically titrated using the sensor previously mentioned as the end-point detector. The quantities of the surfactants varied between 2 and 6 μmol for CS and 2.50 and 7.50 μmol for EONS. The known addition methodology was used for determination of the surfactant with considerably lower concentration in the mixture. Three commercial products containing cationic surfactants as disinfectants and nonionic surfactants were potentiometrically titrated, and the results for both type of surfactants were compared with those obtained with standard conventional methods.

Derivatization of fatty alcohol ethoxylate non‐ionic surfactants using 2‐sulfobenzoic anhydride for characterization by liquid chromatography/mass spectrometry

A derivatization procedure has been developed for the improved characterization of fatty alcohol ethoxylate non-ionic surfactants by liquid chromatography/mass spectrometry. The end hydroxyl group of each surfactant species was converted into an oxycarbonylbenzene-2-sulfonic acid group with 2-sulfobenzoic anhydride under mild conditions. The produced sulfonic acid group allows all species, including fatty alcohols and those with less than three ethoxylates, to be uniformly ionized by electrospray ionization (ESI) mass spectrometry. Both acid and base can be used as a mobile phase additive for liquid chromatography without affecting M(n) and average ethoxylate values, although ion intensities are suppressed during the ESI process. The method was used to analyze seven commercial fatty alcohol ethoxylate non-ionic surfactants, and the determined M(n) and EO values were comparable with the results obtained by NMR. The relative ratio of different fatty alcohol based ethoxylates in a sample can also be determined using the summed mass spectral data.

Potentiometric sensor for polyethoxylated nonionic surfactant determination

A new liquid membrane surfactant sensor based on a 1,3-didecyl-2-methylimidazolium–tetraphenylborate ion-exchange complex was tested in different ethoxylated nonionic surfactants (EONS) and polyethylene glycols. The sensor also responded to tetraphenylborate (slope = −56.1 ± 0.8 mV/decade of activity) in the 1 × 10 −6 to 2 × 10 −3 M concentration range. The selectivity performance of the sensor toward alkaline, alkaline earth, and heavy metal cations was investigated. The sensor exhibited a fast response (within a few seconds), when in solution with some metal cations, for a 10-fold concentration change of Triton X-100. Its main application is in indicating the end-point in a potentiometric titration of EONS using sodium tetraphenylborate as the titrant. Several pure and technical grade EONS and polyethylene glycols were successfully titrated. The sensor can be used for titrations within a pH range of 3–11. The resulting potentiometric titration curves revealed an analytically usable inflection for all investigations, enabling reliable equivalence point detection using the first derivative method. The sensor was also applied to the study of barium ion reaction stoichiometry and Triton X-100 pseudoionic complex formation, as well as its reaction with tetraphenylborate.

Salt effect on aqueous two-phase system composed of nonylphenyl ethoxylate non-ionic surfactant

Phase diagrams of detergent-based aqueous two-phase systems composed of nonylphenyl ethoxylate (4- C 9H 19C 6H 4(OCH 2CH 2) 9OH, NP-9) non-ionic surfactant and various salt solutions were studied experimentally at 298.15 K. The salts used were magnesium sulfate, sodium sulfate and sodium chloride. The salting-out power of salts in these systems were determined and this power can be arranged with respect to the cations as Mg 2+>Na + and anions as SO 4 2−>Cl −. The experimental results of the phase diagrams were correlated using DH-NRTL model. It was found that, this model represent the experimental liquid–liquid equilibrium data of the surfactant aqueous two-phase systems with good accuracy.

Biodegradability of highly ethoxylated nonionic surfactants: Determination of intermediates and pathways of biodegradation

Existing data regarding alcohol ethoxylate (AE) surfactants indicate that structures with greater than 20 ethoxylate (EO) units per molecule or with multibranched alkyl chains may not pass a ready biodegradability test. This could have important consequences for complying with regional regulatory requirements and for the potential risks these chemicals could present to the environment. We investigated the influence of chemical structure on the biodegradability of AEs with different alkyl chain branching and EO content. The AEs investigated were a multibranched AE (average, 18 EO), an oxo-AE (monobranched; average, 23 EO), and a linear AE of oleochemical origin (average, 40 EO). The aims of the present study were to assess the ready biodegradability of AEs with high EO content and to establish the mechanism or pathway by which biodegradation occurs for the oxo-AE. Biodegradation studies were conducted using standard test conditions (International Standards Organization 14593). Solid-phase extraction and liquid chromatography with electrospray mass spectrometry were used to detect profiles in both derivatized and underivatized extracts of samples. Derivatization with phthalic anhydride was used to improve ionization of the lower-ethoxylated AEs and free alcohol that were key indicators in the present study. All AEs were rapidly biodegraded, achieving more than 60% mineralization of parent material. Central fission was the predominant mechanism for the oxo-AE, as confirmed by identification of the oligomeric distribution and quantification of polyethylene glycol released during biodegradation.

Non-steady state partitioning of dry cleaning surfactants between tetrachloroethylene (PCE) and water in porous media

Trapped organic solvents, in both the vadose zone and below the water table, are frequent sources of environmental contamination. A common source of organic solvent contamination is spills, leaks, and improper solvent disposal associated with dry cleaning processes. Dry cleaning solvents, such as tetrachloroethylene (PCE), are typically enhanced with the addition of surfactants to improve cleaning performance. The objective of this work was to examine the partitioning behavior of surfactants from PCE in contact with water. The relative rates of surfactants partitioning and PCE dissolution are important for modeling the behavior of waste PCE in the subsurface, in that they influence the interfacial tension of the PCE, and how (or if) interfacial tension changes over time in the subsurface. The work described here uses a flow-through system to examine simultaneous partitioning and PCE dissolution in a porous medium. Results indicate that both nonylphenol ethoxylate nonionic surfactants and a sulfosuccinate anionic surfactant partition out of residual PCE much more rapidly than the PCE dissolves, suggesting that in many cases interfacial tension changes caused by partitioning may influence infiltration and distribution of PCE in the subsurface. Non-steady-state partitioning is found to be well-described by a linear driving force model incorporating measured surfactant partition coefficients.

Ethoxylated Nonionic Surfactants in Hydrophobic Solvent: Interaction with Aqueous and Membrane-Immobilized Poly(acrylic acid)

Interaction between ethoxylated nonionic surfactants and poly(acrylic acid) (PAA) in aqueous solutions is well-documented in the literature. In the present study, pure ethoxylated surfactant solution in a hydrophobic solvent was permeated through a partially cross-linked PAA composite membrane to quantify the surfactant-PAA interaction in the heterogeneous system. Partitioning of the mixture of the surfactants (15-S-5) between the hydrophobic solvent and aqueous solution of PAA was also studied. The role of ethylene oxide group variation in the surfactant-PAA interaction for the heterogeneous system was established by performing experiments with pure surfactants having the same alkyl chain length but varying ethoxylate chain lengths. It was observed that the surfactants with a higher number of ethylene oxide groups per molecule exhibit stronger interaction with PAA. The literature data for adsorption of pure ethoxylated surfactants (C12E(n)) on a hydrophobic solid-water interface was correlated and compared with the data obtained in our study. It was calculated that resistance in terms of transfer of surfactant molecules from a hydrophobic solvent domain to PAA domain lowers the extent of PAA-surfactant interaction by an order of magnitude. Only 40% of available carboxyl groups were accessible for interaction with the ethoxylated nonionic surfactants due to diffusion limitations. Finally the pH sensitivity of the PAA-surfactant complex was verified by successful regeneration of the membrane on permeation of slightly alkaline water. The regeneration and reuse of membrane is especially attractive in terms of process development for nonionic surfactant separation from hydrophobic solvents.

Effect of a commercial alcohol ethoxylate surfactant (C11-15E7) on

Biodegradation of poorly soluble polycyclic aromatic hydrocarbons (PAHs) has been a challenge in bioremediation. In recent years, surfactant-enhanced bioremediation of PAH contaminants has attracted great attention in research. In this study, biodegradation of phenanthrene as a model PAHs solubilized in saline micellar solutions of a biodegradable commercial alcohol ethoxylate nonionic surfactant was investigated. The critical micelle concentration (CMC) of the surfactant and its solubilization capacity for phenanthrene were examined in an artificial saline water medium, and a type of marine bacteria, Neptunomonas naphthovorans, was studied for the biodegradation of phenanthrene solubilized in the surfactant micellar solutions of the saline medium. It is found that the solubility of phenanthrene in the surfactant micellar solutions increased linearly with the surfactant concentrations, but, at a fixed phenanthrene concentration, the biodegradability of phenanthrene in the micellar solutions decreased with the increase of the surfactant concentrations. This was attributed to the reduced bioavailability of phenanthrene, due to its increased solubilization extent in the micellar phase and possibly lowered mass transfer rate from the micellar phase into the aqueous phase or into the bacterial cells. In addition, an inhibitory effect of the surfactant on the bacterial growth at high surfactant concentrations may also play a role. It is concluded that the surfactant largely enhanced the solubilization of phenanthrene in the saline water medium, but excess existence of the surfactant in the medium should be minimized or avoided for the biodegradation of phenanthrene by Neptunomonas naphthovorans.