Biodegradation of Naphthalene Using Glass Beads Roller Bioreactor: Application of Artificial Neural Network Modeling

A roller bioreactor containing inert glass beads was employed to enhance naphthalene biodegradation in an aqueous solution. Mixed culture of microorganisms was isolated from sewage waste sludge and adopted for naphthalene biodegradation. The biodegradation of 300mg/L naphthalene in the bioreactor with no glass beads proceeded slowly until depletion after seven days. In the presence of glass beads, the biodegradation rate was faster; it depleted after four days. The biodegradation rate of naphthalene was equal to 1.99 mgL-1 hr-1 for bioreactor with no beads, while it is equal to 5.42, and 5.54 mgL-1 hr-1 for bioreactor with 40%load, 6mm size and 50% load, 5mm size of glass beads, respectively. For 500mg/L naphthalene, nine days on the bioreactor with no glass beads and five days on glass beads bioreactors were required to complete depletion. The biodegradation rate is equal to 2.33, 7.29, and 7.85 mg/L-1hr-1 for bioreactors with no glass beads, 40% load with 6mm, and 50% load with 5mm glass beads, respectively. The specific growth rate was increased in the bioreactor with glass beads; it represents 0.031, 0.050, and 0.054 hr−1 for 300mg/L and 0.043, 0.061, and 0.065 hr−1 for 500mg/L respectively for the previously mentioned conditions. An artificial neural network was used to model naphthalene dissolution and biodegradation. A correlation coefficient of 99.2% and 98.3% were obtained between the experimental and predicted output values for dissolution and biodegradation, respectively, indicating that the ANN model could efficiently predict the experimental results. Time represents the most influential parameter on the dissolution and biodegradation treatment.

Aerobic and oxygen-limited naphthalene-amended enrichments induced the dominance of Pseudomonas spp. from a groundwater bacterial biofilm

In this study, we aimed at determining the impact of naphthalene and different oxygen levels on a biofilm bacterial community originated from a petroleum hydrocarbon–contaminated groundwater. By using cultivation-dependent and cultivation-independent approaches, the enrichment, identification, and isolation of aerobic and oxygen-limited naphthalene degraders was possible. Results indicated that, regardless of the oxygenation conditions, Pseudomonas spp. became the most dominant in the naphthalene-amended selective enrichment cultures. Under low-oxygen conditions, P. veronii/P. extremaustralis lineage affiliating bacteria, and under full aerobic conditions P. laurentiana–related isolates were most probably capable of naphthalene biodegradation. A molecular biological tool has been developed for the detection of naphthalene 1,2-dioxygenase-related 2Fe-2S reductase genes of Gram-negative bacteria. The newly developed COnsensus DEgenerate Hybrid Oligonucleotide Primers (CODEHOP-PCR) technique may be used in the monitoring of the natural attenuation capacity of PAH-contaminated sites. A bacterial strain collection with prolific biofilm-producing and effective naphthalene-degrading organisms was established. The obtained strain collection may be applicable in the future for the development of biofilm-based bioremediation systems for the elimination of PAHs from groundwater (e.g., biofilm-based biobarriers).

Enhanced biodegradation of naphthalene byPseudomonassp. consortium immobilized in calcium alginate beads

Polycyclic aromatic hydrocarbons (PAHs) belong to a large group of organic pollutant which considers as a potential health hazard to living beings. Herein, naphthalene biodegradation potential by free and immobilizedPseudomonas putidastrain KD10 andPseudomonassp. consortium were studied. Additionally, naphthalene 1, 2-dioxygenase (nahAc) was sequenced and analyzed, which reveals two altered amino acid residues. However, the altered amino acid residues are not present in the vicinity of the active site. The gas-phase binding free energy (ΔGLondon) of the mutant variant of naphthalene 1, 2-dioxygenase was -7.10 kcal mol-1which closely resembles the wild type variant. Naphthalene biodegradation rate byPseudomonas putidastrain KD10 was 79.12 mg L-1day-1and it was significantly elevated up to 123 mg L-1day-1by the immobilizedPseudomonassp. consortium. The half-life (t1/2) for naphthalene biodegradation was 3.1 days with the inhibition constant (ki), substrate saturation constant (ks) and maximum specific degradation rate constant (qmax) of 1268 mg L-1, 395.5 mg L-1and 0.65 h-1, respectively, for thePseudomonas putidastrain KD10. However, the t1/2value was significantly reduced to 2 days along withki,ksandqmaxvalues of 1475 mg L-1, 298.8 mg L-1and 0.71 h-1, respectively, by the immobilizedPseudomonassp. consortium. The GC-MS data suggest that KD10 might follow D-gluconic acid mediated meta-cleavage pathway of catechol biodegradation. It is concluded that naphthalene biodegradation performance by immobilizedPseudomonassp. consortium was superior to free or immobilizedPseudomonas putidaKD10. Microbial consortium immobilization could be a useful tool for water quality management and environmental remediation.HighlightsSuperior naphthalene biodegradation byPseudomonassp. consortium immobilized in calcium alginate beads.A common mutation prone amino acid stretch inside chain A of naphthalene 1, 2-dioxygenase has been identified.A new naphthalene biodegradation pathway byPseudomonas putidastrain KD10 has been proposed.