Degradation Of Polynuclear Aromatic Hydrocarbons Research Articles

Advances in Polymer Nanocomposite Materials for Photocatalytic Degradation of Polynuclear Aromatic Hydrocarbons in Environmental Matrices: A Review

The immobilization of metal oxide nanoparticles into different anchoring media has recently gained great interest owing to their applications in water treatment. The choice of the polymers for the incorporation of the active catalyst particle is highly motivated by several advantages displayed by them. These include mechanical stability, chemical inertness and resistance to ultraviolet radiations, environmental stability, ease availability, and low prices. Additionally, the use of polymer nanocomposite materials (PNMs) as photocatalysts offers the possibility of a facile separation and reuse of the materials, eliminating thus the post-treatment separation processes and implicitly reducing the costs of the procedure. However, this review paper focused on recent advances made in PNMs for the photocatalytic decontamination of polynuclear aromatic hydrocarbons (PAHs) in environmental matrices. It further explores some trends in research and the markets. The review also shows the current advances made on the understanding of detoxification mechanisms and toxicological effects of PAHs in photocatalytic processes as a green alternative method for environmental pollution control and remediation. It further critically explores different ways to improve workflows for PNMs characterization and testing and the emerging need for the analysis of PAHs. It finally provides insights into the understanding of how to set up and optimize manufacturing methods of PNMs while avoiding costly time traps that prevent getting the correct answer in addressing PAH-related environmental pollution problems. 

Modeling growth kinetics and carbazole degradation kinetics of a Pseudomonas aeruginosa strain isolated from refinery sludge and uptake considerations during growth on carbazole

Although bacterial degradation of polynuclear aromatic hydrocarbons (PAH) have been studied using various pure cultures, only a few studies have explored the degradation kinetics and uptake mechanism of nitrogen heterocyclic PAHs (PANH) with three or more rings. This work explored growth kinetics of a PAH degrading bacterial strain, Pseudomonas aeruginosa RS1 on carbazole (CBZ) and concomitant degradation kinetics of CBZ over the concentration range 25 to 500 mg/L. For CBZ acclimatized strain, the specific growth rate (μ) and specific CBZ uptake rate (q) varied from 0.96 ± 0.05 to 2 ± 0.15 day−1 and from 0.002 ± 0.001 to 0.02 ± 0.01 mg CBZ mg VSS−1 day−1, respectively. The Moser and Monod model provided best fits to the μ vs CBZ concentration and q vs CBZ concentration profiles, respectively. Biosurfactant activity did not play a role in CBZ uptake. However, elevation in cell surface hydrophobicity as revealed through the water contact angle values on bacterial cell mat indicated the possible role of direct interfacial uptake in facilitating CBZ uptake over and above uptake after dissolution. Elevated catechol 1,2-dioxygenase enzyme activity was observed during CBZ degradation. Interestingly, the specific activity of this enzyme was higher in the culture supernatant than in the cell extract. However, during CBZ degradation, accumulation of some toxic metabolites in the aqueous phase was revealed through increase in TOC of the aqueous phase and Kirby-Bauer disc diffusion study performed using a E. coli strain. Both aqueous phase TOC and toxicity decreased beyond the log growth phase indicating further utilization of the degradation intermediates.

Degradation of polynuclear aromatic hydrocarbons by two strains of Pseudomonas.

The goal of this investigation was to isolate competent polynuclear aromatic hydrocarbons degraders that can utilize polynuclear aromatic hydrocarbons of former industrial sites at McDoel Switchyard in Bloomington, Indiana. Using conventional enrichment method based on soil slurry, we isolated, screened and purified two bacterial species strains PB1 and PB2. Applying the ribotyping technique using the 16S rRNA gene analysis, the strains were assigned to the genus Pseudomonas (Pseudomonas plecoglossicida strain PB1 and Pseudomonas sp. PB2). Both isolates showed promising metabolic capacity on pyrene sprayed MS agar plates during the preliminary investigations. Using time course studies in the liquid cultures at calculated concentrations 123, 64, 97 and 94 ppm for naphthalene, chrysene, fluroanthene and pyrene, P. plecoglossicida strain PB1 and Pseudomonas sp. PB2 showed partial utilization of the polynuclear aromatic hydrocarbons. Naphthalene was degraded between 26% and 40%, chrysene 14% and 16%, fluroanthene 5% and 7%; pyrene 8% and 13% by P. plecoglossicida strain PB1 and Pseudomonas sp. PB2 respectively. Based on their growth profile, we developed a model R2 = 1 to predict the degradation rate of slow polynuclear aromatic hydrocarbon-degraders where all the necessary parameters are constant. From this investigation, we confirm that the former industrial site soil microbial communities may be explored for the biorestoration of the industrial site.

Extending the photoelectrocatalytic detection range of KHP by eliminating self-inhibition at TiO2 nanoparticle electrodes

The photoelectrocatalytic oxidation of potassium hydrogen phthalate (KHP) at a titanium dioxide (TiO2) nanoparticle electrode was investigated in the presence of phosphate, which is usually considered an inhibitor of the photocatalytic process. Self-inhibition was observed during the photoelectrocatalytic degradation of KHP in the electrolyte solution with a little and without phosphate. This self-inhibition phenomenon cannot be eliminated by improving the light intensity but can be improved in the presence of a specified amount of phosphate, which extends the detection range of KHP. The adsorption of KHP indicated that the effective separation of KHP molecules adsorbed on the surface of the TiO2 electrode is a key prerequisite for eliminating the self-inhibition phenomenon. It is well-known that phthalic acid is one of the principal intermediates in the photocatalytic degradation of polynuclear aromatic hydrocarbons. Therefore, this study can provide a solution to the self-inhibition that occurs during the photocatalytic/photoelectrocatalytic degradation of polynuclear aromatic hydrocarbons. More importantly, this study can also provide an approach to extending the detection range of chemical oxygen demand using the photoelectrocatalytic process in the presence of polynuclear aromatic hydrocarbons.

Biodegradation of pyrene by a Pseudomonas aeruginosa strain RS1 isolated from refinery sludge.

High molecular weight (HMW) polynuclear aromatic hydrocarbons (PAHs) with more than three rings are inherently difficult to degrade. Degradation of HMW PAHs is primarily reported for actinomycetes, such as, Rhodococcus and Mycobacterium. This study reports pyrene degradation by a Pseudomonas aeruginosa strain isolated from tank bottom sludge in a refinery. High cell surface hydrophobicity induced during growth on pyrene facilitated its utilization as sole carbon source. Specific growth rate (μ) in the range of 0.03-0.085 h(-1) could be achieved over the concentration range 25-500 mg/L. The specific growth rate and specific pyrene utilization rate increased linearly with increase in total pyrene concentration. Although various degradation intermediates were identified in the aqueous phase, accumulation of total organic carbon (TOC) in the aqueous phase was only a small fraction of TOC equivalents of pyrene lost from the cultures. The degradation pathway appears to be similar to that reported for Mycobacterium sp. PYR-I.

Electrolytic Oxidation of Polynuclear Aromatic Hydrocarbons from Creosote Solution Using TI/IRO2 and TI/SNO2 Circular Mesh Electrodes

The electrooxidation of polynuclear aromatic hydrocarbons (PAHs) in solution was investigated. Most of the PAHs compounds are toxic and hardly biodegradable, so that a chemical or physicochemical treatment is required. In this paper, we reported treatment of synthetic creosote oily effluent (COE) containing several PAHs by using Ti/ IrO2 and Ti/ SnO2 circular or cylindrical mesh anode electrodes. COE was prepared with distilled water and a commercial creosote solution in the presence of an amphoteric surfactant (CAS). In addition to anode material, different operating parameters were investigated such as current density, reaction time, recycling flow rate, and oxygen injection flow rate. The first series of experiments carried out in the recirculating batch reactor showed that circular Ti/ SnO2 electrode was found to be more effective in removing PAHs than circular or cylindrical Ti/ IrO2 electrodes. Current density and retention time played important roles for PAHs degradation efficiency, whereas circula...

Effect of root-derived substrates on the expression of nah-lux genes in Pseudomonas fluorescens HK44: implications for PAH biodegradation in the rhizosphere.

The bioluminescent reporter strain Pseudomonas fluorescens HK44 with a nah-lux fusion, was used to investigate the effect of root material (from hybrid poplars, willow, kou, milo, Osage orange, mulberry, and switch grass) and potential root-derived substrates (e.g., sugars, carboxylic acids, amino acids, and phenolics) on the expression of nahG, one of the genes responsible for naphthalene dioxygenase transcription. Whereas nahG was induced by some phenolic substrates that could be released by plants (i.e., salicylate, methyl salicylate, and acetyl salicylate), no induction by root extracts was observed. Rather, increasing root extract concentrations (50 to 275 mg L(-1) as total organic carbon) inhibited nahG expression in assays with cells concurrently exposed to naphthalene. Root extracts also decreased nahG expression at the individual cell level during naphthalene degradation assays. However, treatments with root extracts exhibited significantly higher microbial growth and overall bioluminescence, indicating a higher level of nahG expression by the resulting larger microbial population. This generally resulted in faster naphthalene degradation rates, suggesting that plant-promoted proliferation of competent genotypes could compensate for the interference that labile substrates exert on the expression of genes that code for the degradation of polynuclear aromatic hydrocarbons (PAHs). This could explain the faster PAH degradation commonly reported in planted than in unplanted soils.

Novel method for determining pyrene biodegradation using synchronous fluorimetry

To study the biodegradation rate of pyrene dissolved in liquid medium supplemented with mineral salts, a synchronous fluorimetry (SF) method was established. The limit of detection for pyrene dissolved in mineral salts medium (MSM) was determined as 0.19 ng/ml with a relative standard deviation of less than 1.3% ( n=9). The pyrene degrading rates of four bacterial strains were investigated using this method under the same experimental conditions. The degradation rates of the three active strains ranged from 76% to 87% after a 14-h incubation. The results were confirmed by the gas chromatography with a flame ionized detector (GC/FID) method. This implies that pyrene degradation can be directly monitored by the SF method without the solvent extraction of samples. The advantages of SF are that it is less laborious, faster, and less expensive than the GC/FID determination method with solvent extraction. The SF method provides a new tool for studying the degradation of polynuclear aromatic hydrocarbons (PAHs) in the natural environment and under experimental conditions.

Evaluating the relationship between the sorption of PAHs to bacterial biomass and biodegradation

Petroleum refinery wastewater containing polynuclear aromatic hydrocarbons (PAHs) are typically treated by biological processes in the United States. PAHs are recalcitrant, hydrophobic compounds and sorption to biological solids may be a significant mechanism for the removal of PAHs from refinery wastewater. The goal of this research was to investigate PAH sorption by bacterial biomass and examine the relationship between PAH biosorption and biodegradation. In this study, phenanthrene was used as a model PAH for biosorption studies and pyrene and fluoranthene were used as model compounds in biodegradation studies. It was found that phenanthrene biosorption varied with bacterial genus and species. Bacteria with the highest sorption capacity (Kp) belong to the Nocardioforms, organisms that often cause solids separation problems in activated sludge plants. Consequently, blooms of these difficult to settle organisms in refinery treatment plants could exasperate PAH releases to the environment. The measured sorption capacities were reproducible and appeared to represent surface sorption, based on the apparent competition between naphthalene and phenanthrene for sorption sites. Based on a comparison of Kp values, pure bacterial cultures can serve as valid models of biosorption by activated sludge MLSS. Finally it was found that PAH sequestration by high Kp, non-degraders has a significant impact on PAH biodegradation. The results of this study suggest that although biosorption can decrease the rate of PAH biodegradation in the short term, it can also result in the removal of PAHs from the wastewater and PAH retention in the treatment system where it may be ultimately biodegraded. This research improves our understanding of processes contributing to PAH degradation in petroleum refinery wastewater treatment plants.

Degradation of Polynuclear Aromatic Hydrocarbons under Bench-Scale Compost Conditions

The relationship between biomass growth and degradation of polynuclear aromatic hydrocarbons (PAHs) in soil, and subsequent toxicity reduction, was evaluated in 10 in-vessel, bench-scale compost un...

A unique biodegradation pattern of the oil spilled during the 1991 Gulf War

A laboratory degradation study of the oil spilled during the 1991 Gulf War has shown a unique degradation pattern. Very fast degradation rates of several polynuclear aromatic hydrocarbons (PAH) and sulphur-containing PAH compounds were observed compared with the saturated n-alkane fraction of the oil. The degradation pattern and rate of biodegradation were found to be dependent on the oil concentration and on the presence of nutrients. Faster rates were observed at lower oil concentrations, while the addition of nutrients greatly slowed the degradation of PAHs and enhanced the degradation of the saturates. The study suggested the presence of naturally occurring micro-organisms in the oil/water system which are very effective in rapidly biodegrading several PAH compounds. However, it appears that the activity of these micro-organisms is greatly affected by nutrients' addition. Minimal PAHs degradation was noticed during the experiment's time frame when nutrients were added to the system. The study has also shown that the use of C17/pristane and C18/phytane ratios may underestimate the magnitude of oil biodegradation in the presence of these micro-organisms. These results supported the need to monitor the changes in both saturates and aromatic hydrocarbons in order to assess the biodegradation of spilled oil. If changes in one fraction were monitored, prediction of the effect on the other fractions of the oil could not be made.

Bioremediation of soil contaminated with polynuclear aromatic hydrocarbons (PAHs): A review

Polynuclear aromatic hydrocarbons (PAHs) constitute a group of priority pollutants which are present at high concentrations in the soils of many industrially contaminated sites. Criteria established for the removal or treatment or both of soils contaminated with PAHs vary widely within and between nations. The bioremediation of contaminated soils with in-situ, on-site, and bioreactor techniques is reviewed, together with the factors affecting PAH degradation. Current in-situ remediation techniques are considered ineffective for the removal of most PAHs from contaminated soil. On-site ‘landforming’ methods have been used successfully (and within a reasonable period of time) to degrade only those PAHs with three or fewer aromatic rings. Bioreactors have proved most effective for soil remediation, since conditions for enhanced degradation can be achieved most readily. However, bioreactors are still at the development stage, and further research is required to optimise their efficiency and economy for routine use. Degradation of the more recalcitrant high-molecular-weight PAHs is contaminated soil has not been particularly successful to date. Further research needs are identified to help develop bioremediation into a most cost-effective technology. The importance of full site assessments and treatability studies for successful application in the field is emphasised.

The long-term persistence of polynuclear aromatic hydrocarbons (PAHs) in an agricultural soil amended with metal-contaminated sewage sludges

Polynuclear aromatic hydrocarbon (PAH) data are presented from a long-term field experiment in which soil plots were amended with single additions of sewage sludges over 20 years ago. Five sludges, each containing a different concentration of PAHs and enriched with different heavy metals (Cu, Cr, Ni or Zn), were applied to five soil plots in 1968. This increased soil PAH concentrations substantially, but by 1972 some plots had lost up to 60% of the PAHs applied. By 1989, losses had increased to about 90%. Individual PAHs have behaved differently with compound persistence a function of molecular weight. Half-lives for the compounds in soil increased from < 2 years for naphthalene to > 16 years for coronene. It is argued that biological degradation is the most important loss mechanism for PAHs in this soil. Overall, calculated half-lives are significantly longer than those previously reported under experimental conditions. The implications of this are discussed. Slower PAH degradation was observed in the plot amended with the Ni-rich sludge; by 1989, 35% of the applied PAHs was still detectable in the soil. This may be indicative of long-term heavy metal interference in microbial processes.