Microbial community structure during oxygen-stimulated bioremediation in phenol-contaminated groundwater

Insights into the degradation process of phenol during in-situ thermal desorption: The overlooked oxidation of hydroxyl radicals from oxygenation of reduced Fe-bearing clay minerals

In-situ thermal desorption (ISTD) has attracted increasing attention owing to the efficient removal of organic contaminants from contaminated sites. However, it is poorly understood that whether and to what extent contamination degradation occurs upon oxygenation of reduced Fe-bearing clay minerals (RFC) in the subsurface during ISTD. In this study, we evaluated the mechanism of contaminant degradation upon oxygenation of reduced clay minerals during the ISTD. Reduced nontronite (rNAu-2) and montmorillonite (rSWy-3) were selected as RFC models. Results showed that thermal treatment during ISTD could significantly enhance phenol degradation, which increased from 25.8 % at 10 °C to 74.4 % at 70 °C in rNAu-2 and from 17.7 % at 10 °C to 49.8 % at 70 °C in rSWy-3. Correspondingly, the cumulative •OH at steady-state ([•OH]_ss) increased by 3.7 and 1.5 times, respectively. The acceleration of Fe(II) oxidation with increasing temperature could be mainly responsible for [•OH]_ss generation, which degrades phenol. Moreover, thermal treatment improved the fast oxidation of trioctahedral entities Fe(II)Fe(II)Fe(II) (TOF) and the slow oxidation of dioctahedral entities Fe(II)Fe(II) (DTF₁), AlFe(II) (DAF₁), and Fe(II)Fe(III) (DTF₂). Our study suggests that the overlooked degradation progress of phenol by oxygenation of RFC during ISTD, and it could be favorable for contaminant degradation during remediation.

Ecological role of Acinetobacter calcoaceticus GSN3 in natural biofilm formation and its advantages in bioremediation

This study assessed the role of a new Acinetobacter calcoaceticus strain, GSN3, with biofilm-forming and phenol-degrading abilities. Three biofilm reactors were spiked with activated sludge (R1), green fluorescent plasmid (GFP) tagged GSN3 (R2), and their combination (R3). More than 99% phenol removal was achieved during four weeks in R3 while this efficiency was reached after two and four further operational weeks in R2 and R1, respectively. Confocal scanning electron microscopy revealed that GSN3-gfp strains appeared mostly in the deeper layers of the biofilm in R3. After four weeks, almost 7.07 × 10⁷ more attached sludge cells were counted per carrier in R3 in comparison to R1. Additionally, the higher numbers of GSN3-gfp in R2 were unable to increase the efficiency as much as measured in R3. The presence of GSN3-gfp in R3 conveyed advantages, including enhancement of cell immobilization, population diversity, metabolic cooperation and ultimately treatment efficiency.

Highly efficient phenol degradation in a batch moving bed biofilm reactor: benefiting from biofilm-enhancing bacteria

In this study, the efficiency improvement of three moving bed biofilm reactors (MBBRs) was investigated by inoculation of activated sludge cells (R1), mixed culture of eight strong phenol-degrading bacteria consisted of Pseudomonas spp. and Acinetobacter spp. (R2) and the combination of both (R3). Biofilm formation ability of eight bacteria was assessed initially using different methods and media. Maximum degradation of phenol, COD, biomass growth and also changes in organic loading shock were used as parameters to measure the performance of reactors. According to the results, all eight strains were determined as enhanced biofilm forming bacteria (EBFB). Under optimum operating conditions, more than 90% of initial COD load of 2795 mg L^-1 was reduced at 24 HRT in R3 while this reduction efficiency was observed in concentrations of 1290 mg L^-1 and 1935 mg L^-1, in R1 and R2, respectively. When encountering phenol loading shock-twice greater than optimum amount-R1, R2 and R3 managed to return to the steady-state condition within 32, 24 and 18 days, respectively. SEM microscopy and biomass growth measurements confirmed the contribution of more cells to biofilm formation in R3 followed by R2. Additionally, established biofilm in R3 was more resistant to phenol loading shock which can be attributed to the enhancer role of EBFB strains in this reactor. It has been demonstrated that the bacteria with both biofilm-forming and contaminant-degrading abilities are not only able to promote the immobilization of other favorable activated sludge cells in biofilm structure, but also cooperate in contaminant degradation which all consequently lead to improvement of treatment efficiency.

Enhanced peroxymonosulfate activation for phenol degradation over MnO2 at pH 3.5-9.0 via Cu(II) substitution

Cu(II) doped mesoporous MnO₂ (Cu-MnO₂) was prepared to establish an intimate functional link between the structure substitution and catalytic peroxymonosulfate (PMS) activation. Based on the characterization of powder X-ray diffraction (XRD), N₂ adsorption-desorption measurement, scanning electron microscope (FE-SEM) and transmission electron microscope (TEM), Cu-MnO₂ had a typical long range ordered mesoporous structure and Cu was successfully introduced in octahedral framework. It exhibited excellent catalytic activity and stability for the phenol degradation by PMS. Phenol was always efficiently degraded over Cu-MnO₂ at a pH range of 3.5-9.0. For example, the reaction rate constant at pH 7.0 was 0.073 min^-1, which was two times higher than that of MnO₂ (0.039 min^-1). Importantly, ¹O₂ was identified as the primary reactive species in Cu-MnO₂/PMS system. X-ray photoelectron spectroscopy (XPS) confirmed that more exposed surface oxygen defects due to Cu doping were responsible to the enhancement of PMS activation for phenol degradation. The results of PMS decomposition and oxygen evolution indicated that surface oxygen defects lower the reaction energy barrier of PMS decomposition by generating ¹O₂ via the energy trapping by oxygen. Finally, the heterogeneous PMS activation mechanism over Cu-MnO₂ was proposed.

Community Analysis and Recovery of Phenol-degrading Bacteria from Drinking Water Biofilters

Phenol is a ubiquitous organic contaminant in drinking water. Biodegradation plays an important role in the elimination of phenol pollution in the environment, but the information about phenol removal by drinking water biofilters is still lacking. Herein, we study an acclimated bacterial community that can degrade over 80% of 300 mg/L phenol within 3 days. PCR detection of genotypes involved in bacterial phenol degradation revealed that the degradation pathways contained the initial oxidative attack by phenol hydroxylase, and subsequent ring fission by catechol 1,2-dioxygenase. Based on the PCR denatured gradient gel electrophoresis (PCR-DGGE) profiles of bacteria from biological activated carbon (BAC), the predominant bacteria in drinking water biofilters including Delftia sp., Achromobacter sp., and Agrobacterium sp., which together comprised up to 50% of the total microorganisms. In addition, a shift in bacterial community structure was observed during phenol biodegradation. Furthermore, the most effective phenol-degrading strain DW-1 that correspond to the main band in denaturing gradient gel electrophoresis (DGGE) profile was isolated and identified as Acinetobacter sp., according to phylogenetic analyses of the 16S ribosomal ribonucleic acid (rRNA) gene sequences. The strain DW-1 also produced the most important enzyme, phenol hydroxylase, and it also exhibited a good ability to degrade phenol when immobilized on granular active carbon (GAC). This study indicates that the enrichment culture has great potential application for treatment of phenol-polluted drinking water sources, and the indigenous phenol-degrading microorganism could recover from drinking water biofilters as an efficient resource for phenol removal. Therefore, the aim of this study is to draw attention to recover native phenol-degrading bacteria from drinking water biofilters, and use these native microorganisms as phenolic water remediation in drinking water sources.

Microbiological characteristics of multi-media PRB reactor in the bioremediation of groundwater contaminated by petroleum hydrocarbons

A multi-media bio-PRB reactor was designed to treat groundwater contaminated with petroleum hydrocarbons. After a 208-day bioremediation, combined with the total petroleum hydrocarbons content in the groundwater flowed through the reactor, microbiological characteristics of the PRB reactor including microbes immobilized and its dehydrogenase activity were investigated. TPH was significantly reduced by as much as 65% in the back of the second media layer, whereas in the third layer, the TPH content reached lower than 1 mg l⁻¹. For microbes immobilized on the media, the variations with depth in different media were significantly the same and the regularity was obvious in the forepart of the media, which increased with depth at first and then reduced gradually, while in the back-end, the microbes almost did not have any variations with depth but decreased with the distance. The dehydrogenase activity varied from 2.98 to 16.16 mg TF L⁻¹ h⁻¹ and its distribution illustrated a similar trend with numbers of microbial cell, therefore, the noticeable correlation was found between them.

Groundwater remediation using an enricher reactor-permeable reactive biobarrier for periodically absent contaminants

A combined enricher reactor (ER)-permeable reactive biobarrier (PRBB) system was developed to treat groundwater with contaminants that appear in batches. An enricher reactor is an offline reactor used to enrich contaminant degraders by supplying necessary growth materials, and the enriched degraders are used to augment PRBB to increase its performance after a period of contaminant absence. Bench-scale experiments on PRBBs with and without bacterial supply from the enricher reactor were conducted to evaluate PRBB removal performances for benzene, which was used as a model contaminant. Benzene absence periods of 10 and 25 days were tested in the presence and absence of ethanol. The PRBBs without the bioaugmentation from the enricher reactor experienced a decrease in performance from approximately 65% to 30% after benzene reappeared. The presence of ethanol accelerated the benzene removal performance recovery of PRBBs. The 25-day benzene absence period caused greater changes in the bacterial community structure, regardless of the ethanol availability.

Effects of cell entrapment on nucleic acid content and microbial diversity of mixed cultures in biological wastewater treatment

The effects of entrapment on nucleic acid content and microbial diversity of mixed cultures in biological municipal wastewater treatment were investigated. Deoxyribonucleic acid content increased 1.6-5.5 times more in alginate entrapped cells than in free and polyvinyl alcohol (PVA) entrapped cells. PVA entrapment resulted in 1.1- to 5.9-fold more increases in ribonucleic acid content compared to that experienced by free and alginate entrapped cells. Entrapment in carrageenan changed the bacterial community structure more than the alginate and PVA entrapments (35-80% versus 0-35%) as determined by single-strand conformation polymorphism analyses. The change in the bacterial community structure of alginate entrapped cells was less time dependent than that of PVA entrapped cells. This study enhances understandings on the physiology of entrapped cells and their community evolution in wastewater treatment environments.

A permeable reactive barrier for the bioremediation of BTEX-contaminated groundwater: Microbial community distribution and removal efficiencies

This study was conducted with column experiments, batch experiments, and bench-scale permeable reactive barrier (PRB) for monitoring the PRB in the relation between BTEX (benzene, toluene, ethylbenzene, and p-xylene) decomposition efficiency and the distribution of a microbial community. To obtain the greatest amount of dissolved oxygen from oxygen-releasing compounds (ORCs), 20-d column tests were conducted, the results of which showed that the highest average amount of dissolved oxygen (DO) of 5.08 mg l(-1) (0.25 mg-O(2)d(-1)g(-1)-ORC) was achieved at a 40% level of CaO(2). In the batch experiments, the highest concentrations of benzene and toluene in which these compounds could be completely degraded were assumed to be 80 mg l(-1). Long-term monitoring for a PRB indicated that ORCs made with the oxygen-releasing rate of 0.25 mg-O(2)d(-1)g(-1)-ORC were applicable for use in the PRB because these ORCs have a long-term effect and adequately meet the oxygen demand of bacteria. The results from the DGGE of 16S rDNAs and real-time PCR of catechol 2,3-dioxygenase gene revealed the harmful effects of shock-loading on the microbial community and reduction in the removal efficiencies of BTEX. However, the efficiencies in the BTEX decomposition were improved and the microbial activities could be recovered thereafter as evidenced by the DGGE results.

A feasibility study of immobilized and free mixed culture bioaugmentation for treating atrazine in infiltrate

A feasibility study of phosphorylated-polyvinyl alcohol immobilized and free mixed bacterial culture bioaugmentation for removing atrazine in agricultural infiltrate was conducted utilizing a sand column setup. The effects of bacterial cell loading and infiltration rate on atrazine degradation were investigated by short-term tests in which the amount of synthetic infiltrate fed through was five times of the void volume (five pore volumes) of the sand column. In addition, the loss of the inoculated atrazine-degrading cultures and the change of bacterial community were determined. Selected tests were continued for monitoring a long-term performance of the system (50 pore volumes of the sand column). The results indicated that the inoculated cells removed 42-80% of the atrazine. The infiltration rate and cell loading significantly affected the atrazine removal. In the short-term tests, the immobilized and free cells provided similar atrazine removal; however, leaching of the free cells was much greater than that of the immobilized cells. For the long-term performance, only the immobilized cells provided consistent atrazine removal efficiency throughout the test. Both immobilized and free cell systems exhibited a significant change in bacterial community structure during the atrazine degradation experiments. The infiltration rate was a significant factor for the change.

Identification and genetic characterization of phenol-degrading bacteria from leaf microbial communities

Microbial communities on aerial plant leaves may contribute to the degradation of organic air pollutants such as phenol. Epiphytic bacteria capable of phenol degradation were isolated from the leaves of green ash trees grown at a site rich in airborne pollutants. Bacteria from these communities were subjected, in parallel, to serial enrichments with increasing concentrations of phenol and to direct plating followed by a colony autoradiography screen in the presence of radiolabeled phenol. Ten isolates capable of phenol mineralization were identified. Based on 16S rDNA sequence analysis, these isolates included members of the genera Acinetobacter, Alcaligenes, and Rhodococcus. The sequences of the genes encoding the large subunit of a multicomponent phenol hydroxylase (mPH) in these isolates indicated that the mPHs of the gram-negative isolates belonged to a single kinetic class, and that is one with a moderate affinity for phenol; this affinity was consistent with the predicted phenol levels in the phyllosphere. PCR amplification of genes for catechol 1,2-dioxygenase (C12O) and catechol 2,3-dioxygenase (C23O) in combination with a functional assay for C23O activity provided evidence that the gram-negative strains had the C12O-, but not the C23O-, phenol catabolic pathway. Similarly, the Rhodococcus isolates lacked C23O activity, although consensus primers to the C12O and C23O genes of Rhodococcus could not be identified. Collectively, these results demonstrate that these leaf surface communities contained several taxonomically distinct phenol-degrading bacteria that exhibited diversity in their mPH genes but little diversity in the catabolic pathways they employ for phenol degradation.