Naphthalene biodegradation kinetics in an aerobic slurry-phase bioreactor

Research progress of bio-slurry remediation technology for organic contaminated soil

Bio-slurry remediation technology, as a controllable bioremediation method, has the significant advantage of high remediation efficiency and can effectively solve the problems of high energy consumption and secondary pollution of traditional organic pollution site remediation technology. To further promote the application of this technology in the remediation of organically polluted soil, this paper summarizes the importance and advantages of bio-slurry remediation technology compared with traditional soil remediation technologies (physical, chemical, and biological). It introduces the technical infrastructure and its technological processes. Then, various factors that may affect its remediation performance are discussed. By analyzing the applications of this technology to the remediation of typical organic pollutant-(polycyclic aromatic hydrocarbons(PAHs), polychlorinated biphenyls(PCBs), total petroleum hydrocarbons(TPH), and pesticide) contaminated sites, the following key features of this remediation technology are summarised: (1) the technology has a wide range of applications and can be used in a versatile way in the remediation projects of various types of organic-contaminated soil sites such as in clay, sand, and high organic matter content soil; (2) the technology is highly controllable. Adjusting environmental parameters and operational conditions, such as nutrients, organic carbon sources (bio-stimulation), inoculants (bio-augmentation), water-to-soil ratio, etc., can control the remediation process, thus improving the restoration performance. To sum up, this bio-slurry remediation technology is an efficient, controllable and green soil remediation technology that has broad application prospects.

Microbial degradation and transformation of benzo[a]pyrene by using a white-rot fungus Pleurotus eryngii F032

Polycyclic aromatic hydrocarbons (PAHs) are environmentally recalcitrant contaminants formed from naturally or incomplete combustion of organic materials and some of them are difficult to degrade due to their hydrophobicity and persistency. Benzo [a]pyrene (BaP), is one of PAHs that having five fused benzene and reported as mutagenic, carcinogenic and teratogenic compounds. Biodegradation is one of promising techniques due to its relatively low economic cost and microorganism is a natural capacity to consume hydrocarbons. In this investigation, Pleurotus eryngii F032 was grown in 20 mL of modified mineral salt broth (MSB) supplemented with BaP under static and agitated culture. Within 20 days, static culture removed 59% of BaP, whereas agitated culture removed the highest amount (73%). To expedite BaP elimination, the mechanism and behavior of BaP biosorption and biotransformation by Pleurotus eryngii F032 were additionally examined by gas chromatography-mass spectrometer (GC-MS). The optimal conditions for P. eryngii F032 to eliminate BaP were 25 °C, a C/N ratio of 8, pH 3 and 0.2% inoculum concentration. At an initial BaP content of 10 mg/L, more than 50% was effectively eliminated within 20 days under these conditions. Salinity, glucose, and rhamnolipids were the most important factors impacting BaP biodegradation. GC-MS found degradation products such as BaP-3,6-quinone, indicating plausible metabolic routes. Finally, it may be assumed that the primary mechanism by which white-rot fungi eliminate BaP is by the utilization of biotransformation enzymes such as laccase to mineralize the PAHs. Hence, Pleurotus eryngii F032 could be an ideal candidate to treat PAHs contaminated soils.

Salicylate or Phthalate: The Main Intermediates in the Bacterial Degradation of Naphthalene

Polycyclic aromatic hydrocarbons (PAHs) are widely presented in the environment and pose a serious environmental threat due to their toxicity. Among PAHs, naphthalene is the simplest compound. Nevertheless, due to its high toxicity and presence in the waste of chemical and oil processing industries, naphthalene is one of the most critical pollutants. Similar to other PAHs, naphthalene is released into the environment via the incomplete combustion of organic compounds, pyrolysis, oil spills, oil processing, household waste disposal, and use of fumigants and deodorants. One of the main ways to detoxify such compounds in the natural environment is through their microbial degradation. For the first time, the pathway of naphthalene degradation was investigated in pseudomonades. The salicylate was found to be a key intermediate. For some time, this pathway was considered the main, if not the only one, in the bacterial destruction of naphthalene. However, later, data emerged which indicated that gram-positive bacteria in the overwhelming majority of cases are not capable of the formation/destruction of salicylate. The obtained data made it possible to reveal that protocatechoate, phthalate, and cinnamic acids are predominant intermediates in the destruction of naphthalene by rhodococci. Pathways of naphthalene degradation, the key enzymes, and genetic regulation are the main subjects of the present review, representing an attempt to summarize the current knowledge about the mechanism of the microbial degradation of PAHs. Modern molecular methods are also discussed in the context of the development of “omics” approaches, namely genomic, metabolomic, and proteomic, used as tools for studying the mechanisms of microbial biodegradation. Lastly, a comprehensive understanding of the mechanisms of the formation of specific ecosystems is also provided.

Synergistic adsorption and biodegradation of heavy crude oil by a novel hybrid matrix containing immobilized Bacillus licheniformis: Aqueous phase and soil bioremediation

Recently, slurry phase bioremediation as a simple and economical method is shown to be a successful technique for remediation of clayey soils. Besides, the use of microbial cell immobilization as a promising technique has drawn the attention of some researchers. The primary objective of this survey is to examine the synergistic adsorption and biodegradation performance of heavy crude oil by an isolated Bacillus licheniformis immobilized in a novel hybrid matrix (PUF/alginate/microbial cell) in aqueous phase. Isotherm studies and adsorption kinetics of crude oil on PUF matrix were carried out and their results revealed a good correlation between experimental data and Langmuir's isotherm and maximum monolayer coverage was found out to be 1.25 g/g PUF. The other objective of this research is examination of hybrid matrix in slurry phase bioremediation of heavy crude oil polluted clayey soil as a reluctant model soil. In order to model, optimize, and investigate the factors affecting the total organic carbon (TOC) reduction, response surface methodology (RSM) was applied. For this purpose, the effect of three variables including crude oil concentration (5000-25,000 mg/kg dry soil), soil salinity (0-10%), and water to soil ratio (WSR: 2-10) have been studied. In this study, TOC reduction was achieved in ranging from 39% to 80% in crude oil polluted soil after 21 days. Additionally, experiments by polyurethane foam (PUF)-immobilized cell, alginate-immobilized cell, and freely cell suspended systems were conducted to compare the performance of hybrid-immobilized cell with other systems. Our results showed the superiority of immobilized cells in hybrid matrix of PUF/alginate compared to other immobilized cell (IC) and free cell (FC) systems. Overall, the results indicated that the hybrid matrix with simultaneous adsorption-biodegradation capacity is potentially suitable for further development for oil spill treatment and it can be used as an efficient cleaning method in TOC removal from actual polluted soils.

Degradation of phenanthrene and fluoranthene in a slurry bioreactor using free and Ca-alginate-immobilized Sphingomonas pseudosanguinis and Pseudomonas stutzeri bacteria

Biodegradation studies of three- and four-ring polycyclic aromatic hydrocarbons (PAHs) (phenanthrene [PHE] and fluoranthene [FLU]) were conducted using free and Ca-alginate-immobilized Sphingomonas pseudosanguinis strain J1-q (S1) and Pseudomonas stutzeri strain (S2) in bench-scale sediment slurry reactors. In this study, the effects of sodium alginate (SA) dosage on the characteristics of immobilized bacterial beads were investigated. The results indicated a 3% alginate concentration was optimal for immobilizing bacteria for PHE and FLU degradation. Scanning electron microscopy (SEM) images of the immobilized beads showed the presence of honeycomb structures and abundant interstices in the beads, which provided adequate space for microorganism adhesion and proliferation. The biodegradation of PHE and FLU using both free and immobilized bacteria fit a first-order reaction model well. The degradation efficiencies of PHE and FLU using immobilized bacteria were higher than those of free bacteria in sediment slurry reactors. The removal percentages of PHE and FLU using immobilized indigenous bacteria strain S1 after 42 d were 63.16% and 56.94%, respectively, which were higher than the removal percentages of exogenous strain S2.

Removal mechanisms in aerobic slurry bioreactors for remediation of soils and sediments polluted with hydrophobic organic compounds: An overview

Hydrophobic organic compound (HOC)-contaminated soils are a great environmental and public health concern nowadays. Further research is necessary to develop environmental friendly biotechnologies that allows public and private sectors to implement efficient and adaptable treatment approaches. Aerobic soil-slurry bioreactor technology has emerged as an effective and feasible technique with a high remediation potential, especially for silt and clay soil fractions, which often contain the highest pollutant concentration levels and are usually difficult to remove by implementing conventional methods. However, the mechanisms involved in the HOC removal in bioslurry reactor are still not completely understood. Gas-liquid and solid-liquid mass transfer, mass transport and biodegradation phenomena are the main known processes taking place in slurry bioreactors. This review compiles the most up-to-date information available about these phenomena and tries to link them, enlightening the possible interactions between parameters. It gathers the basic information needed to understand the complex bioremediation technology and raises awareness of some considerations that should be made.

Characterization of Dietzia cercidiphylli C-1 isolated from extra-heavy oil contaminated soil

Dietzia cercidiphylliC-1 isolated from extra-heavy oil contaminated soil can efficiently degrade extra-heavy oil.

Use of a packed-bed airlift reactor with net draft tube to study kinetics of naphthalene degradation by Ralstonia eutropha

Biodegradation of naphthalene by Ralstonia eutropha (also known as Cupriavidus necator) in a packed-bed airlift reactor with net draft tube (PBALR-nd) was studied; the Kissiris pieces were the packing material. The reactor hydrodynamics has been characterized under abiotic conditions and the dependencies of the superficial gas velocity (U G) on the gas holdup (εG), liquid mixing time, and mass transfer coefficient were determined. The improving role of the net draft tube in this small column reactor (height 42 cm, ID 5 cm) was confirmed. The flow regime was described using the εG α U G (n) expression, and bubbly flow was observed in PBALR-nd at U G < 2.83 cm/s. In the second step of the present work, the kinetics of biodegradation was modeled using the Haldane and Aiba equations. The fitting of the experimental results to the models were done according to the nonlinear least square regression technique. The biokinetic constants (q m, K s, and K i) were estimated and q m as the specific biodegradation rate was equaled to 0.415 and 0.24 mgnaph./mgcell h for the Haldane and Aiba equations, respectively. The goodness of fit reported as R (2) and root-mean-square error (RMSE) showed the adequate fitness of the Haldane and Aiba models in predicting naphthalene biodegradation kinetics. On the basis of the HPLC results, a hypothetical pathway for the biodegradation was presented.

Carbon content reduction in a model reluctant clayey soil: slurry phase n-hexadecane bioremediation

Clayey soils contaminated with organic pollutants are nowadays one of the important environmental issues as they are highly reluctant to conventional bioremediation techniques. In this study, biodegradability of n-hexadecane as a model contaminant in oil polluted clayey soil by an indigenous bacterium was investigated. Maximal bacterial growth was achieved at 8% (v/v) n-hexadecane as sole carbon and energy sources in aqueous phase. The predominant n-hexadecane uptake mechanism was identified to be biosurfactant-mediated using bacterial adhesion to hydrocarbon (BATH) test and surface tension measurements. The effect of n-hexadecane concentration, soil to water ratio, inoculum concentration and pH on total organic carbon (TOC) reduction from kaolin soil in slurry phase was investigated at two levels in shake flasks using full factorial experimental design method where 10,000 (mg n-hexadecane)(kg soil)(-1), soil-water ratio of 1:3, 10% (v/w) inoculum and pH of 7 resulted in the highest TOC reduction of 70% within 20 days. Additionally, slurry bioreactor experiments were performed to study the effect of various aeration rates on n-hexadecane biodegradation during 9 days where 2.5 vvm was found as an appropriate aeration rate leading to 54% TOC reduction. Slurry phase bioremediation is shown to be a successful method for remediation of clayey reluctant soils.

Characterization of phenanthrene degradation by strain polyporus sp. S133

Polyporus sp. S133, a fungus collected from contaminated soil, was used to degrade phenanthrene, a polycyclic aromatic hydrocarbon, in a mineral salt broth liquid culture. A maximal degradation rate (92%) was obtained when Polyporus sp. S133 was cultured for 30 days with agitation at 120 r/min, as compared to 44% degradation in non-agitated cultures. Furthermore, the degradation was affected by the addition of surfactants. Tween 80 was the most suitable surfactant for the degradation of phenanthrene by Polyporus sp. S133. The degradation rate increased as the amount of Tween 80 added increased. The rate in agitated cultures was about 2 times that in non-agitated cultures. The mechanism of degradation was determined through the identification of metabolites; 9,10-phenanthrenequinone, 2,2'-diphenic acid, phthalic acid, and protocatechuic acid. Several enzymes (manganese peroxidase, lignin peroxidase, laccase, 1,2-dioxygenase and 2,3-dioxygenase) produced by Polyporus sp. S133 were detected during the incubation. The highest level of activity was shown by 1,2-dioxygenase (187.4 U/L) after 20 days of culture.

Biodegradation of chrysene, an aromatic hydrocarbon by Polyporus sp. S133 in liquid medium

Polyporus sp. S133, a fungus collected from contaminated-soil was used to degrade chrysene, a polycyclic aromatic hydrocarbon (PAH) in a mineral salt broth (MSB) liquid culture. Maximal degradation rate of chrysene (65%) was obtained when Polyporus sp. S133 was incubated in the cultures supplemented with polypeptone (10%) for 30 days under agitation of 120 rpm, as compared to just 24% degradation rate in non-agitated culture. Furthermore, the degradation of chrysene was affected by the addition of carbon and nitrogen sources as well as kind of surfactants. The degradation rate was increased with increase in added amount of carbon and nitrogen sources, respectively. The degradation rate in agitated cultures was enhanced about 2 times higher than that in non-agitated cultures. The degradation mechanism of chrysene by Polyporus sp. S133 was determined through identification of several metabolites; chrysenequinone, 1-hydroxy-2-naphthoic acid, phthalic acid, salicylic acid, protocatechuic acid, gentisic acid, and catechol. Several enzymes (manganese peroxidase, lignin peroxidase, laccase, 1,2-dioxygenase and 2,3-dioxygenase) produced by Polyporus sp. S133 were detected during the incubation. The highest enzyme activity was shown by 1,2-dioxygenase (237.5 U l(-1)) after 20 days of incubation.

Biodegradation of phenanthrene by fungi screened from nature

Microbial degradation of Phenanthrene with several fungi screened from nature was conducted to select fungi for the bioremediation ofPhenanthrene. Thrichoderma sp. S019, a fungus collected from soil, had the highest rate of degradation on the agar medium containing Phenanthrene. Maximal degradation (72%) was obtained when Trichoderma sp. S019 was incubated for 30 days after the addition of 0.1 mM of Phenanthrene to the liquid medium. Furthermore, the degradation of Phenanthrene was affected by the addition of a carbon source, the addition of a nitrogen source and agitation. Also, 1,2-Dioxygenase and 2,3-Dioxygenase were produced by Trichoderma sp. S019 in a liquid medium. These enzymes play an important role in the metabolism of substrates, revealing a high stereoselectivity for initial dioxygenase and enzymatic hydration since the K-region of phenanthrene was the major site of metabolism. Phenanthrene was indeed degraded by Trichoderma sp. S019 because 1-Hydroxy-2-naphthoic acid, Salicyaldehyde, Salicylic acid and Catechol, considered to be the intermediates in the bioremediation of Phenanthrene, were detected among the reaction products.

Scale-up impacts on mass transfer and bioremediation of suspended naphthalene particles in bead mill bioreactors

Scale-up effects on mass transfer and bioremediation of suspended naphthalene particles have been studied in 20 and 58L bead mill bioreactors and compared to data generated earlier with a laboratory scaled bioreactor. The bead mill bioreactor performance with respect to naphthalene mass transfer rate was dependent on the size and loading of the inert particles, as well as the rotational speed of the roller apparatus. The optimum operating conditions were found to be 15mm glass beads at a loading of 50% (total volume of particles/working volume of bioreactor: v/v%) and a bioreactor rotational speed of 50rpm. The highest naphthalene mass transfer coefficients obtained in the large scale system under these optimum conditions (19.6 and 22.4h(-1) for 20 and 58L vessels, respectively) were higher than those determined previously in a 2.5L bead mill bioreactor (0.7h(-1)). The acute toxicity tests indicated that the bioreactor effluent was less toxic than the untreated naphthalene suspension. Biodegradation rates obtained in these large scale bead mill bioreactors under optimum conditions (36-37.4mgL(-1)h(-1)) were higher than those achieved in the control bioreactors of similar sizes (11.4 and 11.6mgL(-1)h(-1)) but were slower than those previously determined in a 2.5L bead mill bioreactor (59-61.5mgL(-1)h(-1)). The limitation of oxygen in the large scale systems and damage of the bacterial cells due to the crushing effects of the large beads are likely contributing factors in the lower observed biodegradation rates. The optimum conditions with respect to naphthalene mass transfer might not necessarily translate to optimum performance with regard to bioremediation.

Biodegradation of aged polycyclic aromatic hydrocarbons (PAHs) by microbial consortia in soil and slurry phases

Microbial consortia isolated from aged oil-contaminated soil were used to degrade 16 polycyclic aromatic hydrocarbons (15.72 mgkg(-1)) in soil and slurry phases. The three microbial consortia (bacteria, fungi and bacteria-fungi complex) could degrade polycyclic aromatic hydrocarbons (PAHs), and the highest PAH removals were found in soil and slurry inoculated with fungi (50.1% and 55.4%, respectively). PAHs biodegradation in slurry was lower than in soil for bacteria and bacteria-fungi complex inoculation treatments. Degradation of three- to five-ring PAHs treated by consortia was observed in soil and slurry, and the highest degradation of individual PAHs (anthracene, fluoranthene, and benz(a)anthracene) appeared in soil (45.9-75.5%, 62-83.7% and 64.5-84.5%, respectively) and slurry (46.0-75.8%, 50.2-86.1% and 54.3-85.7%, respectively). Therefore, inoculation of microbial consortia (bacteria, fungi and bacteria-fungi complex) isolated from in situ contaminated soil to degrade PAHs could be considered as a successful method.

Slurry phase bioremediation of PAHs in industrial landfill samples at laboratory scale

The effect of Tween 80 and selected bacteria additions on the bioremediation of PAH contaminated landfill soil (70.38mgkg(-1)) was evaluated in a slurry phase bioreactor. A phenanthrene-degrading consortium was selected by enrichment cultures and used as autochthonous inoculum. The Tween 80 addition increased the aqueous concentration of both high and low molecular weight PAHs. In the experiment with Tween 80 and inoculum addition, added microorganisms improved (>90%) the biodegradation of two- and three-ring PAHs as well as of the four-ring PAHs pyrene and fluoranthene. Biodegradation of the higher molecular weight PAHs was about 30% in experiments with Tween 80 addition, with and without inoculum addition.