Slurry-phase System Research Articles

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) by novel bacterial consortia tolerant to diverse physical settings – Assessments in liquid- and slurry-phase systems

Field-scale bioremediation of PAHs contaminated soils have proved to be difficult and challenging due to inhibited growth of PAH degrading microbes. In this study, for the first time mixed bacterial cultures designated as consortia-A and N were developed using elite metal or acid tolerant, N-fixing, P-solubilizing and biosurfactant producing PAH degraders enriched from manufactured gas plant sites. The two consortia could degrade both LMW and HMW PAHs. Kinetic studies of PAH degradation by the consortia showed the highest biodegradation rate constants (k = 0.027–0.61 day−1) and lowest half-life time (t1/2 = 1–26 days) values reported to date in liquid cultures and highlighted the use of consortium-A for the remediation of acidic soils due to its tolerance up to pH 5. Furthermore, bioaugmentation of these consortia has proven to be effective in degradation of LMW (>95%) and HMW (90%) PAHs from spiked soil slurries. Amendment of consortia-A and N exhibited 10.7 and 44.3% more total PAHs degradation, respectively than natural attenuation in 60 days even from the real long-term mixed contaminated soils. Thus the results of this study demonstrate the great potential of these novel bacterial consortia, particularly consortium-N for use in field-scale bioremediation of PAHs in long-term mixed contaminated neutral soils.

Fast bioremediation of petroleum-contaminated soils by a consortium of biosurfactant/bioemulsifier producing bacteria

Biodegradation of petroleum hydrocarbons as a decontamination mechanism is a relatively slow process. This study aimed to investigate the impact of a tailored consortium of bacteria with higher capacities in biosurfactant production and biodegradation on the acceleration of the biodecontamination process. To this end, 18 biosurfactant producing bacteria were isolated from the crude oil-contaminated soil samples of Isfahan refinery, and the activity of the produced biosurfactants was measured in terms of surface tension reduction and emulsification E24 test. Then, the isolates screened for the biodegradation of kerosene hydrocarbons and chemical structure of the purified biosurfactants produced by the most efficient isolates were partially characterized. Next, the isolates were sorted based on their surfactant activity and biodegradation efficiency, and the higher ranked bacteria thus selected were utilized to form an efficient consortium removing hydrocarbons from the oil-contaminated soil samples in a slurry phase system. The consortium consisted of Bacillus subtilis tb1 and Pseudomonas aeruginosa species having the highest biodegradation capabilities and surface activities. The results revealed that the hydrocarbon removal efficiency of the consortium was at least 25 % higher than single species, and the final removal efficiency for the consortium could be reached in a considerably shorter time.

Risk Reduction of Adverse Effects Due to Di-(2-Ethylhexyl) Phthalate (DEHP) by Utilizing Microbial Degradation

Di-(2-ethylhexyl) phthalate (DEHP), one of the major phthalates, was reported to be a suspected endocrine-disrupting chemical (EDC) that might produce developmental or reproductive toxicities. Therefore, much effort was undertaken to reduce the potential risk of adverse effects of DEHP on humans by diminishing environmental exposure to this chemical. A bacterium was isolated from soil contaminated with DEHP at a poly(vinyl chloride) (PVC) manufacturing site. Biodegradation kinetic experiments on DEHP-contaminated soil samples were performed in a slurry phase system. The DEHP concentration was decreased to a concentration of 0.5 g/kg by the addition of 1% culture medium to the soil. The microorganism degraded DEHP through the formation of a mono-2-ethylhexyl phthalate (MEHP), which was subsequently metabolized to phthalic acid (PA), as detected by GC-MS analysis. Micrococcus luteus was able to degrade almost 90% of the initial DEHP within 12 d. In addition, the microbial toxicity study of DEHP and its degradation products MEHP or PA, using recombinant bioluminescent bacteria, showed that PA or the mixture produced protein or DNA damage. Data thus suggest that a new strain of Micrococcus luteus with a strong ability to degrade DEHP into nontoxic metabolites may contribute to decontamination of environmental phthalates and consequently risk reduction of human exposure to DEHP.

Efficiency of natural and engineered bacterial strains in the degradation of 4-chlorobenzoic acid in soil slurry

Two bacterial strains, the natural isolate Arthrobacter sp. FG1 and the engineered strain Pseudomonas putida PaW340/pDH5, were compared for their efficiency in the degradation of 4-chlorobenzoic acid in a slurry phase system. The recombinant strain was obtained by cloning the Arthrobacter sp. FG1 dehalogenase encoding genes in P. putida PaW340. In the slurry inoculated with pre-adapted cultures of Arthrobacter sp. FG1, the 4-chlorobenzoic acid degradation was found to be slower than that observed in the slurry inoculated with the recombinant strain P. putida PaW340/pDH5, regardless of the presence or absence of soil indigenous bacteria. Slurry inoculated with mixed cultures of Arthrobacter sp. FG1 and the 4-hyroxybenzoic acid degrader P. putida PaW340 did not show any improvement in 4-chlorobenzoic acid degradation.

Influence of the operating conditions on highly oxidative radicals generation in Fenton's systems

In this work, an indirect method for estimating the total amount and concentration of oxidative radicals in aqueous and slurry-phase Fenton's systems was developed. This method, based on the use of benzoic acid as probe compound, was applied for evaluating the effect of the operating conditions on the radicals amount produced, their production efficiency (i.e. moles of radicals generated per mole H 2O 2) and their concentration. A Rotatable Central Composite design (RCC) was used to select the operating conditions in order to get a statistically meaningful data set. Hydrogen peroxide and ferrous ion concentrations ranged between 0.2–1 mM and 0.2–0.5 mM, respectively; humic acid concentration between 0 and 15 mg/L, whereas the soil/water weight ratio in slurry-phase systems between 1:10 and 9:10. The probe compound concentration was 9 or 0.1 mM in experiments aimed to evaluate the total amount or concentration of oxidative radicals, respectively. The obtained results indicated that the amount of radicals generated in both aqueous and soil slurry Fenton's system increased with higher H 2O 2 concentration and, more specifically, that their production efficiency increased with increasing Fe(II):H 2O 2 molar ratio. Addition of dissolved organic compounds as humic acid did not notably affect the oxidative radicals amount and concentration. On the contrary, a one order of magnitude reduction in both radicals amount generated and concentration was observed when soil was added to the reaction environment.

Slurry-phase biodegradation of weathered oily sludge waste

We assessed the biodegradation of a typical oily sludge waste (PB401) in Mexico using several regimes of indigenous microbial consortium and relevant bioremediation strategies in slurry-phase system. Abiotic loss of total petroleum hydrocarbons (TPH) in the PB401 was insignificant, and degradation rates under the various treatment conditions ranged between 666.9 and 2168.7 mg kg −1 day −1 over a 15 days reaction period, while viable cell count peaked at between log 10 5.7 and log 10 7.4 cfu g −1. Biostimulation with a commercial fertilizer resulted in 24% biodegradation of the TPH in the oily waste and a corresponding peak cell density of log 10 7.4 cfu g −1. Addition of non-indigenous adapted consortium did not appear to enhance the removal of TPH from the oily waste. It would appear that the complexities of the components of the alkylaromatic fraction of the waste limited biodegradation rate even in a slurry system.

Bioremediation of Diesel Fuel Contaminated Soil: Effect of Non Ionic Surfactants and Selected Bacteria Addition

Aim of this work was to evaluate influence of two commercial surfactants and inoculum of selected bacteria on biodegradation of diesel fuel in different systems. Among alkyl polyethossilates (Brij family) and sorbitan derivates (Tween family) a first selection of surfactants was performed by estimation of Koc and Dafnia magna EC50 with molecular descriptor and QSAR model. Further experiments were conducted to evaluate soil sorption, biodegradability and toxicity. In the second part of the research, the effect of Brij 56, Tween 80 and selected bacteria addition on biodegradation of diesel fuel was studied in liquid cultures and in slurry and solid phase systems. The latter experiments were performed with diesel contaminated soil in bench scale slurry phase bioreactor and solid phase columns. Tween 80 addition increased the biodegradation rate of hydrocarbons both in liquid and in slurry phase systems. Regarding the effect of inoculum, no enhancement of biodegradation rate was observed neither in surfactant added nor in experiments without addition. On the contrary, in solid phase experiments, inoculum addition resulted in enhanced biodegradation compared to surfactant addition.

Influence of soil–water ratio on the performance of slurry phase bioreactor treating herbicide contaminated soil

The influence of soil–water ratio was studied on the performance of the slurry phase bioreactor operated in sequencing batch mode (anoxic–aerobic–anoxic microenvironments) during the bioremediation of soil contaminated with pendimethalin. The performance of the reactors was evaluated at different soil–water ratios (1:5–1:25; at soil loading rate (60 kg of soil/cum-day to 12 kg of soil/cum-day)) keeping the loading rate of pendimethalin constant (133.2 g/kg of soil-day) in six reactors and variable (66.6 g/kg of soil-day to 166.6 g/kg of soil-day) in other four reactors. At 1:20 soil–water ratio, the slurry phase system showed enhanced degradation of substrate (629 μg pendimethalin/g soil). The removal efficiency of pendimethalin in the reactors was dependent on the mass-transfer rates of the substrate from the soil to the aqueous phase. Soil–water ratio and substrate loading rates showed significant influence on the substrate portioning, substrate degradation efficiency and substrate desorption rate.

Bio-remediation of pendimethalin contaminated soil by bio-slurry phase reactor: bio-augmenting with ETP micro-flora

Bio-remediation of pendimethalin contaminated soil (500 µg/g) was studied in a bio-slurry phase reactor operated in the sequencing batch mode under anoxic–aerobic–anoxic micro-environment. The effect of augmentation with ETP micro-flora on the process performance of the reactor was also evaluated. The reactor was operated with a total cycle period of 120 hours comprising 3 hours of fill, 114 hours of react and 3 hours of decant phases. The Control reactor (without ETP micro-flora) showed 23% of substrate removal efficiency, which may be attributed to the volatile nature of the substrate. The Reactor operated with native soil micro-flora showed more or less equal degradation compared to the control reactor indicating the toxic and inhibitory nature of the substrate over the slurry micro-flora. The reactor augmented with mixed ETP micro-flora showed enhanced performance with more than 90% of substrate removal efficiency within 72 hours of the cycle period. Due to augmentation, the CFU values in the slurry phase system showed a two-fold increase. Process performance during reactor operation was assessed by monitoring pendimethalin concentration and bio-chemical process parameters viz. pH, dissolved oxygen (DO), colony forming units (CFU) and oxygen consumption rate (OCR), during sequence phase operation.

Biological removal of polychlorinated dibenzo-p-dioxins from incinerator fly ash by Sphingomonas wittichii RW1

The ability of Sphingomonas wittichii strain RW1 to remove polychlorinated dibenzo-p-dioxins (PCDDs) from fly ash was investigated. All experiments were carried out in a slurry-phase system. Preliminary studies with resting cells of strain RW1 in a model fly ash system showed the complete removal of dibenzofuran (DF) and 81% of dibenzo-p-dioxin (DD). Incubation of real fly ash collected from municipal waste incinerators with strain RW1 for 15 days resulted in a 75.5% reduction in toxic PCDDs. When the same experiment was carried out using dead strain RW1 cells a 20.2% reduction in toxic PCDDs was observed, indicating that adsorption onto biomass was an important factor in dioxin elimination. Further analyses revealed that live strain RW1 cells removed 83.8% of the 2,3,7,8-substituted congeners from the fly ash, while dead cells removed 32.1% of the same congeners. To enhance the removal efficiency of toxic PCDDs, the effects of adding surfactant, repeated inoculation, and pre-adaptation of cultures were also studied. The removal of toxic PCDDs was enhanced by up to 10.3% upon repeated inoculation of the strain RW1, but was not much affected by the addition of surfactant. The present results suggest that S. wittichii strain RW1 is a potential candidate for the industrial removal of PCDDs from incinerator fly ash.