Evaluation of bacterial biodegradation and accumulation of phenanthrene in the presence of humic acid

Effect of ultra-high-density polyethylene microplastic on the sorption and biodegradation of organic micropollutants

Microplastics and organic micropollutants are two emerging contaminants that interact with each other in environmental and engineered systems. Sorption of organic micropollutants, such as pharmaceuticals, pesticides and industrial compounds, to microplastics can modify their bioavailability and biodegradation. The present study investigated the capacity of ultra-high density polyethylene particles (125 µm in diameter), before and after aging, to sorb 21 organic micropollutants at different environmentally relevant concentration. Furthermore, the biodegradation of these organic micropollutants by a biofilm microbial community growing on the microplastic surface was compared with the biodegradation by a microbial community originating from activated sludge. Among all tested organic micropollutants, propranolol (70%), trimethoprim (25%) and sotalol (15%) were sorbed in the presence of polyethylene particles. Growth of a biofilm on the polyethylene particles had a beneficial effect on the sorption of bromoxynil, caffeine and chloridazon and on the biodegradation of irbesartan, atenolol and benzotriazole. On the other hand, the biofilm limited the sorption of trimethoprim, propranolol, sotalol and benzotriazole and the biodegradation of 2,4-D. These results showed that ultra-high density polyethylene particles can affect both in a positive and negative way for the abiotic and biotic removal of organic micropollutants in wastewater. This project highlights the need for further investigation regarding the interaction between microplastics and organic micropollutants in the aquatic environment.

Dissolved organic matter influences the indigenous bacterial community and polycyclic aromatic hydrocarbons biodegradation in soils

In polycyclic aromatic hydrocarbon (PAH) contaminated soils, bioremediation is superior to other strategies owing to its low cost and environmental friendliness. However, dissolved organic matter (DOM) and indigenous bacterial communities can affect the efficiency of PAH-degrading bacteria (PDB). This study found that exogenous PDB (C1) including the genera Acinetobacter, Stenotrophomonas, and Comamonas, decreased the bacterial diversity of Alfisol, Ultisol, Inceptisol, and Mollisol, and DOM enhanced the diffusion of PDB and the bioavailability of PAH. In addition, bacteria preferred to ingest low molecular weight DOM fractions, and the abundances of lipid-like and protein-like substances decreased by 0.12-3.03 % and 1.73-4.60 %. The DOM fractions had a more marked influence on the indigenous bacteria than the exogenous PDB, and PDB dominated the PAH biodegradation process in the soils. More COO functional groups promoted the utilization of higher molecular weight-related homologue fractions by bacteria, and lower molecular weight fractions carrying more CH2 functional groups declined during biodegradation. This study investigated the variations in bacterial communities during biodegradation and revealed the effects of DOM fractions on biodegradation in PAH-contaminated soils at the molecular level. These results will promote the development of bioremediation strategies for organics-contaminated soil and provide guidance for prediction models of soil biodegradation kinetics.

Microbial Consortium HJ-SH with Very High Degradation Efficiency of Phenanthrene

Phenanthrene (PHE) is one of the model compounds of polycyclic aromatic hydrocarbons (PAHs). In this study, a natural PHE-degrading microbial consortium, named HJ-SH, with very high degradation efficiency was isolated from soil exposed to long-term PHE contamination. The results of GC analysis showed that the consortium HJ-SH degraded 98% of 100 mg/L PHE in 3 days and 93% of 1000 mg/L PHE in 5 days, an efficiency higher than that of any other natural consortia, and even most of the engineered strains and consortia reported so far. Seven dominating strains were isolated from the microbial consortium HJ-SH, named SH-1 to SH-7, which were identified according to morphological observation and 16S rDNA sequencing as Pseudomonas sp., Stenotrophomonas sp., Delftia sp., Pseudomonas sp., Brevundimonas sp., Curtobacterium sp., and Microbacterium sp., respectively. Among all the seven single strains, SH-4 showed the strongest PHE degradation ability, and had the biggest degradation contribution. However, it is very interesting that the microbial consortium can hold its high degradation ability only with the co-existence of all these seven single strains. Moreover, HJ-SH exhibited a very high tolerance for PHE, up to 4.5 g/L, and it can degrade some other typical organic pollutants such as biphenyl, anthracene, and n-hexadecane with the degradation ratios of 93%, 92% and 70%, respectively, under 100 mg/L initial concentration in 5 days. Then, we constructed an artificial consortium HJ-7 consisting of the seven single strains, SH-1 to SH-7. After comparing the degradation ratios, cell growth, and relative degradation rates, it was concluded that the artificial consortium HJ-7 with easier reproducibility, better application stability, and larger room for modification can largely replace the natural consortium HJ-SH. In conclusion, this research provided novel tools and new insights for the bioremediation of PHE and other typical organic pollutants using microbial consortia.

Transcriptome analysis reveals phenanthrene degradation strategy of Pseudomonas stutzeri LH-42

Toxic polycyclic aromatic hydrocarbons (PAHs) are often released into the environment during the combustion and processing of fossil fuels and are capable of causing significant pollution to people and the environment. One of the representative substances of PAHs is phenanthrene, which is often studied as a model compound for PAHs treatment. In this study, we compared the results of transcriptome analysis of Pseudomonas stutzeri LH-42 in two different culture conditions under phenanthrene-induced culture (test group) and glucose-induced culture (control group), and analysed the key enzymatic mechanisms of Pseudomonas stutzeri LH-42 in the biodegradation of phenanthrene. In our experiments, the transcriptome results showed that a total of 380 genes were more than twofold differentially expressed in the test group, of which 187 genes were significantly up-regulated in expression under Phenanthrene induction. Among the 380 differentially expressed genes, 90 genes were involved in Phenanthrene biodegradation, mainly including genes involved in biometabolism, cellular chemotaxis, substrate transport, signal induction and other related processes. Based on the transcriptome sequence analysis of Pseudomonas stutzeri LH-42 at the time of phenanthrene induction, a total of 25 dioxygenase genes were identified, and the related genes were mainly concentrated in two relatively concentrated clusters of PAHs biodegradation genes. The transcriptome analysis resulted in a complete set of enzyme genes related to the phenanthrene biodegradation pathway. The analysis of key enzymes led to the inference of a possible phenanthrene biodegradation pathway: the salicylic acid degradation pathway. The results of this study provide a theoretical basis for in situ remediation of PAHs-contaminated environments using Pseudomonas stutzeri LH-42.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03473-7.

Growth, biofilm formation and atrazine degrading gene (trzN) expression of Arthrobacter sp. DNS10 cultured with montmorillonite, kaolinite and goethite

The viable and degradation potential of the strains which adhered to soil minerals are essential for eliminating organic pollutants from soil. Herein, the interaction (growth, biofilm formation and survive) of Arthrobacter sp. DNS10, an atrazine degrading strain, with three kinds of typical soil minerals, such as montmorillonite, kaolinite and goethite, as well as the atrazine degradation gene (trzN) expression of the strain in the minerals system were studied. The results showed that montmorillonite had significant promotion effect on the growth of strain DNS10, followed by kaolinite, but goethite significantly inhibited the growth of strain DNS10. In contrast, goethite notably promoted the biofilm formation and there was less biofilm detected in montmorillonite containing system. The percentage of the survival bacteria in the biofilm that formed on montmorillonite, kaolinite and goethite was 53.8%, 40.8% and 28.2%. In addition, there were more reactive oxygen species (ROS) were detected in the cells that exposed to goethite than those of the cells exposed to kaolinite and montmorillonite. These results suggest that the electrostatic repulsion between kaolinite/montmorillonite and strain DNS10 prevents them from contacting each other and facilitates bacterial growth by allowing the strain to obtain more nutrients. Oppositely, the needle-like morphology of goethite might damage the strain DNS10 cell when they were combined by electrostatic attraction, and the goethite induced ROS also aggravate the cytotoxicity of goethite on strain DNS10. In addition, the relative transcription of trzN in the cells contacted with montmorillonite, kaolinite and goethite was 0.94-, 0.27- and 0.20- fold of the no mineral exposure treatment. Briefly, this research suggests that the minerals with different structure and/or physicochemical characteristics might cause various trend for the biofilm formation and degradation potential of the bacteria.

Promotion of the biodegradation of phenanthrene adsorbed on microplastics by the functional bacterial consortium QY1 in the presence of humic acid: Bioavailability and toxicity evaluation

The adsorption of hydrophobic organic compounds (HOCs) by microplastics (MPs) has attracted great attention in recent years. However, the ultimate environmental fate of the HOCs sorbed on MPs (HOCs-MPs) is poorly understood. In this work, we investigated the potential influence of the biotransformation process on the environmental fate of phenanthrene (PHE, a model HOC) sorbed on MPs (PHE-MPs) under the existence of humic acid (HA, the main ingredient of dissolved organic matter (DOM)) in the aquatic environment. The results indicated that the adsorption behavior of PHE on MPs decreased its bioavailability and thus inhibited its biotransformation efficiency. However, HA significantly promoted the biodegradation rate and percentage of PHE-MPs. This was probably because HA improved the desorption of PHE from MPs, which promoted the acquisition of PHE by bacteria from the aqueous phase. Further, HA dramatically increased the bacterial community diversity and richness and altered the community composition. The richness of some PHE-degrading bacteria, such as Methylobacillus and Sphingomonas, significantly increased, which may also be an important factor for promoting PHE biodegradation. Molecular ecological network analysis implied that HA enhanced the modularity and complexity of bacterial interaction networks, which was beneficial to maintaining the functional stability of the consortium QY1. Besides, HA decreased the cytotoxicity of functional microbes induced by HOCs-MPs. This work broadens our knowledge of the environmental fate of HOCs-MPs and interactions of MPs, HOCs, DOMs and functional microbial consortiums in aqueous environments.

Effects of Humic Substances on the Growth of Pseudomonas plecoglossicida 2,4-D and Wheat Plants Inoculated with This Strain

Both rhizosphere bacteria and humic substances (HSs) can promote plant growth when applied individually and even greater effects of their combination have been demonstrated. We aimed to elucidate the relative importance of the stimulating effects of HSs on bacterial growth and the effects of the combination of bacteria and HSs on plants themselves. The effects of humic (HA) and fulvic acids (FA) (components of humic substances) on the growth of Pseudomonas plecoglossicida 2,4-D in vitro were studied. We also studied the effects of this bacterial strain and HSs applied individually or in combination on the growth of wheat plants. Although the 2,4-D strain showed low ability to use HSs as the sole source of nutrition, the bacterial growth rate was increased by FA and HA, when other nutrients were available. HSs increased root colonization with bacteria, the effect being greater in the case of HA. The effects on roots and shoots increased when bacteria were associated with HSs. FA+ 2,4-D was more effective in stimulating shoot growth, while HA + 2,4-D was in the case of root growth. The latter effect is likely to be beneficial under edaphic stresses.

Effect of humic acid on phenanthrene removal by constructed wetlands using birnessite as a substrate

The binding of polycyclic aromatic hydrocarbons (PAHs) to humic acid (HA) can boost the complexation–flocculation process and promote pollutant oxidation through the role of HA as an electron shuttle. HA-coated biochar (BA) was added to study the effects of HA on phenanthrene (PHE) removal by constructed wetlands (CWs) using birnessite as a substrate. HA reduced the average PHE concentration of effluent by 26.58% due to its role as a complexing agent, based on Fourier-transform infrared spectroscopy analysis. For CWs with birnessite, the PHE removal performance was further enhanced due to the role of electron shuttles. X-ray photoelectron spectroscopy and illumina high-throughput analysis revealed an enhanced Mn–Fe cycle. The total relative proportions of Mn-oxidizing bacteria and iron-oxidizing bacteria in VFBCW-HA/BA were 2.33 and 5.50 times as high as those in VFBCW-BA and VFCW-HA/BA. Humic acid also accelerated the biodegradation of PAHs and the quantity of PAH degradative bacteria in VFBCW-HA/BA was 6.29 times greater than in VFBCW-BA.

An enhanced birnessite constructed wetland for phenanthrene removal is proposed based on HA coated biochar and the strengthening mechanism is reported.

Humic acid enhanced pyrene degradation by Mycobacterium sp. NJS-1

The search for nature-based tools to enhance bioremediation is essential for the sustainable restoration of contaminated ecosystems. Humic acid (HA) is an important component of organic matter in soil and water, but its effect on the microbial degradation of organic pollutants remains unclear. In this study, the biodegradation of pyrene by Mycobacterium sp. NJS-1 with and without HA was investigated. Only around 10.5% of pyrene was biodegraded in the pyrene treatment alone, whereas the addition of HA significantly enhanced biodegradation to the point where over 90% of pyrene was biodegraded. The production of 4,5-dihydropyrene-4,5-diol and phenanthrene-3,4-diol indicated the metabolic pathway via attacking of 4,5-positions of pyrene. Interestingly, 1,2-dimethoxypyrene was detected with the addition of HA, suggesting that HA induced a new ring-opening pathway involving the attack on the 1,2-positions of pyrene. The addition of HA first induced protein self-cleavage behavior with a significant increase in phenylalanine, tyrosine, and tryptophan containing large numbers of COO^- groups. Furthermore, it altered the intracellular and extracellular ultrastructure of bacterial cells, promoting their growth in size and number as well as reducing the space between them. Overall, HA increased the ring-opening positions of pyrene and facilitated its interaction with bacterial cells, thus improving its biodegradability. Building upon the findings of this study to further research is conducive to the sustainable solution of environmental pollution.

Up-regulation of ribosomal and carbon metabolism proteins enhanced pyrene biodegradation in fulvic acid-induced biofilm system

The polycyclic aromatic hydrocarbons (PAHs) that enter the aqueous phase usually coexist with fulvic acid (FA). Therefore, we initiated this investigation to explore the influences of FA on bacterial biofilm formation and its potential to biodegrade pyrene (PYR), using electron microscopic techniques and isobaric tags for relative and absolute quantification (iTRAQ). Our results revealed that FA stimulated biofilm formation and enhanced the biodegradation of PYR. First, FA favored the three-dimensional proliferation of bacteria, with an OD590/OD600 value of up to 14.78, and the extracellular surfaces covered by a layer of biomaterials. Distinctive intracellular morphologies of texture and organization were accompanied by reduced inter-bacterial distances of less than 0.31 μm. The biofilms formed displayed interactions between FA and surficial proteins, as noted by band shifts for the C-O and CO groups. Strikingly, FA triggered the upregulation of 130 proteins that were either operational in biofilm formation or in metabolic adjustments; with the changes supported by the increasing intensity of free amino acids and the newly generated N-O bonds. The results above revealed that the enhanced biodegradation was related to the up-regulation of the proteins functioned for ribosomal and carbon metabolism, and the ultra-structural changes in FA-induced biofilm system.

How humic acid and Tween80 improve the phenanthrene biodegradation efficiency: Insight from cellular characteristics and quantitative proteomics

Polycyclic aromatic hydrocarbons (PAHs) are toxic and recalcitrant pollutants, with an urgent need for bioremediation. Systematic biodegradation studies show that surfactant-mediated bioremediation is still poorly understood. Here, we investigated a comprehensive cellular response pattern of the PAH degrading strain B. subtilis ZL09-26 to (non-)green surfactants at the cellular and proteomic levels. Eight characteristic cellular factor investigations and detailed quantitative proteomics analyses were performed to understand the highly enhanced phenanthrene (PHE) degradation efficiency (2.8- to 3-fold improvement) of ZL09-26 by humic acid (HA) or Tween80. The commonly upregulated pathway and proteins (Arginine generation, LacI-family transcriptional regulator, and Lactate dehydrogenase) and various metabolic pathways (such as phenanthrene degradation upstream pathway and central carbon metabolism) jointly govern the change of cellular behaviors and improvement of PHE transport, emulsification, and degradation in a network manner. The obtained molecular knowledge empowers engineers to expand the application of surfactants in the biodegradation of PAHs and other pollutants.

Organic and inorganic model soil fractions instigate the formation of distinct microbial biofilms for enhanced biodegradation of benzo[a]pyrene

This study conducted the sorption and biodegradation of benzo[a]pyrene (BaP) by microbial biofilm communities developed on proxies for materials typically found in soils. The half-life of BaP was 4.7 and 2.3 weeks for biofilms on the inorganic carrier (BC_INOR, montmorillonite) and on the organic carrier (BC_OR, humic acid), respectively. In contrast, the half-life was 7.0 weeks for specialized planktonic cultures (PK). The exposure to BaP caused the development of lipid inclusion bodies inside the bacteria of the PK systems and biofilms of the BC_INOR, but not on the biofilms of the BC_OR system. Interestingly, the BC_OR displayed not only the greatest BaP sorption capacity but also the greatest bacterial density and membrane integrity and the shortest bacteria-to-bacteria distances, which were consistent with the increased production of cell surface extracellular polymeric substances on the BC_OR. Both carriers caused a noticeable shift in the bacterial genera during the biodegradation of the BaP. The BC_INOR selected for Rhodococcus, Brucella, Chitinophaga, and Labrys, whereas the BC_OR favored Rhodococcus and Dokdonella. It indicated that ultra-structure and BaP degradation within the organic carrier-attached biofilms differed from the inorganic ones, and suggested that the microstructural heterogeneity and microbial biodiversity from biofilms on the organic carrier promoted biodegradation.

Effect of humic acid on the composition of osmolytes and lipids in a melanin-containing phytopathogenic fungus Alternaria alternata

Humic substances (HS) have a direct impact on living cells, causing a wide range of various biological effects, and stimulating or inhibiting fungal growth. Therefore, it is important to reveal cellular indicators that could indicate the nature and level of HS' effects on living organisms. Paying attention to the important role of lipid and osmolytes in adaptation to stress, the aim of this work was to study the composition of osmolytes and lipids in the growth dynamics of the phytopathogenic melanin-containing fungus Alternaria alternata under the influence of humic acid (HA). HA was isolated from a commercial peat humic product. For cultivation, liquid Czapek medium with the addition of 200 mg/l HA (HA variant) was used, and with no HA for the control variant. The main osmolytes of the fungal mycelium were glucose, mannitol, and trehalose. Both in the control and in HA variants, a general pattern was observed during the growth process; the amount of glucose increased against the background of a decrease of mannitol. In the control, the amount of trehalose increased significantly by the stage of active melanin formation (day 4), while under the influence of HA, such an increase was not observed. Membrane lipids were represented by phospholipids, sphingolipids, and sterols. A characteristic feature of A. alternata was a high proportion of phosphatidic acids (PA) in the composition of membrane lipids. The amount and proportion of PA decreased during growth in the control, while under the influence of HA such decline was not observed. The influence of HA induced the increase in the amount of sterols (St) and phosphatidylcholines (PC) that were able to stabilise the membrane lipid bilayer. We can assume that general cellular response of A. alternata to HA influence, being expressed as a higher amount of PA, PC, St and a lower level of trehalose in comparison with the control, indicates the an absence of inhibition of growth processes of this phytopathogenic melanin-producing fungus. The effect of HA on the qualitative and quantitative composition of the osmolytes and membrane lipids of A. alternata may cause changes of virulence and stress resistance of this phytopathogen.

Alternated biodegradation of naphthalene (NAP), acenaphthylene (ACY) and acenaphthene (ACE) in an aerobic granular sludge reactor (GSBR)

The paper presents quantitative changes of selected 2- and 3-ring PAHs after process phases of GSBR reactor. The studies have been carried out for 264 cycles of GSBR reactor, during which concentration of naphthalene was increased in the range of 3.00-710.00 μg/L, acenaphthylene 1.00-160.00 μg/L, acenaphthene 3.00-440.00 μg/L. GSBR operating cycle consisted of filling (30 min), mixing (90 min), aeration (540 min), sedimentation (10 min), decanting (30 min) and downtime (20 min) phases. Activated sludge dry mass concentration was 4.00 kg/m³. Conducted studies showed that in GSBR reactor naphthalene was degraded with the highest intensity. Results of the statistical analysis confirmed that naphthalene concentrations were statistically significantly different (α = 0.05) after each individual GSBR process phase, while in case of acenaphthene and acenaphthylene, the differences were observed only between mixing and aeration phases. Additionally, equations estimating concentrations of PAHs in treated wastewater were developed. Selected activated sludge technological parameters (sludge volume index, sludge and hydraulic retention time) and concentration of PAHs were used for equations. The R² coefficients of equations were above 0.99, which indicates a good adjustment of estimation to observed values.

Highly efficient anaerobic co-degradation of complex persistent polycyclic aromatic hydrocarbons by a bioelectrochemical system

Polycyclic aromatic hydrocarbons (PAHs) that undergo long-distance migration and have strong biological toxicity are a great threat to the health of ecosystems. In this study, the biodegradation characteristics and combined effects of mixed PAHs in bioelectrochemical systems (BESs) were studied. The results showed that, compared with a mono-carbon source, low-molecular-weight PAHs (LMW PAHs)-naphthalene (NAP) served as the co-substrate to promote the degradation of phenanthrene (PHE) and pyrene (PYR). The maximum degradation rates of PHE and PYR were 89.20% and 51.40% at 0.2500 mg/L in NAP-PHE and NAP-PYR at the degradation time of 120 h, respectively. Intermediate products were also detected, which indicated that the appending of relatively LMW PAHs had different effects on the metabolism of high-molecular-weight PAHs (HMW PAHs). The microbe species under different substrates (NAP-B, PHE-B, PYR-B, NAP-PHE, NAP-PYR, PHE-PYR) are highly similar, although the structure of the microbial community changed on the anode in the BES. In this study, the degradation regularity of mixed PAHs in BES was studied and provided theoretical guidance for the effective co-degradation of PAHs in the environment.

Humic Acid Can Enhance the Mineralization of Phenanthrene Sorbed on Biochars

Biodegradation of hydrophobic organic contaminants by bacteria has been widely studied, but how dissolved organic matter (DOM) may affect their removal if accumulated on biochars is poorly understood. To address this knowledge gap, microbial mineralization of phenanthrene (PHE) spiked on various biochars by Mycobacterium vanbaalenii PYR-1 in the presence of humic acid (HA, a model DOM) at two concentrations was investigated. Our findings showed that HA greatly increased the rate and extent of PHE mineralization. This could be attributed to enhanced PHE desorption by HA, which facilitated access to it by bacteria in the aqueous phase. Furthermore, the high HA affinity for PHE facilitated PHE flow toward the bacterial cells with HA acting as a carrier in the aqueous phase. The mineralization enhancement of PHE by HA within 480 h was negatively influenced by the aromatic carbon contents and micropore volumes in biochars. This shows the importance of the physicochemical properties of biochars in altering the HA effect. Results of this study provide novel information on how to achieve complete removal of PHE accumulated on biochars with a strong sorption affinity for it, using a microbial technique and natural DOM.

Biodegradation of aged polycyclic aromatic hydrocarbons in agricultural soil by Paracoccus sp. LXC combined with humic acid and spent mushroom substrate

Paracoccus sp. LXC combined with humic acid (HA) and spent mushroom substrate (SMS) obtained from Auricularia auricular and Sarcomyxa edulis was tested for the remediation of agricultural soil contaminated with aged polycyclic aromatic hydrocarbons (PAHs). The biomass and diversity of bacteria and fungi and the soil enzyme activity were analyzed. PAH removal and dissipation kinetics were examined. The highest degradation rate of PAHs was 56.5% when soil was amended with Paracoccus sp. LXC combined with HA and unsterilized SMS from A. auricular. The half-life of PAHs decreased from 2323.3 days in natural attenuation to 66.6-277.2 days in amended treatments. Soil treated with Paracoccus sp. LXC combined with HA and SMS from A. auricular acquired high contents of organic matter and nutrients. HA and SMS aided the growth of PAH-degrading bacteria and promoted the diversity of bacteria but not of fungi. The degradation rate of PAHs was mainly correlated positively with soil laccase activity. Low- and middle-molecular-weight PAHs were significantly removed by Paracoccus sp. LXC, HA and SMS. High-molecular-weight PAHs were removed by SMS but not by Paracoccus sp. LXC. Biodegradation by Paracoccus sp. LXC combined with HA and SMS is a promising choice for remediating aged PAH-contaminated agricultural soils.

Aerobic denitrifiers with petroleum metabolizing ability isolated from caprolactam sewage treatment pool

To improve the biological nitrogen removal efficiency of petrochemical wastewater, three aerobic denitrifiers were isolated from caprolactam sewage treatment pool. They were identified as Acinetobacter sp. YY1, Sphingomonas sp. YY2 and Pseudomonas sp. YY3, respectively. The nitrification and denitrification enzyme genes could be detected using polymerase chain reaction (PCR). Moreover, the strain YY2 was a novel aerobic denitrifier belongs to genus of Sphingomonas, which showed great ability for metabolizing aromatic hydrocarbons. In the nitrification and denitrification process, the total nitrogen (TN) removal efficiency after 48 h was 94.22% and 90.10%, respectively. In the process of simultaneous nitrification and denitrification in mixed N-source, ammonia nitrogen was preferentially utilized. Furthermore, the strain YY2 exhibited excellent extracellular polymer secretion properties and excellent aerobic denitrification capacity using petroleum refractory organic compounds, which are beneficial for the formation of bacterial micelles and the engineering applications for the treatment of petrochemical wastewater.

Soil Particles and Phenanthrene Interact in Defining the Metabolic Profile of Pseudomonas putida G7: A Vibrational Spectroscopy Approach

In soil, organic matter and mineral particles (soil particles; SPs) strongly influence the bio-available fraction of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), and the metabolic activity of bacteria. However, the effect of SPs as well as comparative approaches to discriminate the metabolic responses to PAHs from those to simple carbon sources are seldom considered in mineralization experiments, limiting our knowledge concerning the dynamics of contaminants in soil. In this study, the metabolic profile of a model PAH-degrading bacterium, Pseudomonas putida G7, grown in the absence and presence of different SPs (i.e., sand, clays and humic acids), using either phenanthrene or glucose as the sole carbon and energy source, was characterized using vibrational spectroscopy (i.e., FT-Raman and FT-IR spectroscopy) and multivariate classification analysis (i.e., PLS-DA). The different type of SPs specifically altered the metabolic profile of P. putida, especially in combination with phenanthrene. In comparison to the cells grown in the absence of SPs, sand induced no remarkable change in the metabolic profile of the cells, whereas clays and humic acids affected it the most, as revealed by the higher discriminative accuracy (R², RMSEP and sensitivity) of the PLS-DA for those conditions. With respect to the carbon-source (phenanthrene vs. glucose), no effect on the metabolic profile was evident in the absence of SPs or in the presence of sand. On the other hand, with clays and humic acids, more pronounced spectral clusters between cells grown on glucose or on phenanthrene were evident, suggesting that these SPs modify the way cells access and metabolize PAHs. The macromolecular changes regarded mainly protein secondary structures (a shift from α-helices to β-sheets), amino acid levels, nucleic acid conformation and cell wall carbohydrates. Our results provide new interesting evidences that SPs specifically interact with PAHs in defining bacteria metabolic profiles and further emphasize the importance of studying the interaction of bacteria with their surrounding matrix to deeply understand PAHs degradation in soils.

Immobilization of Sphingomonas sp. GY2B in polyvinyl alcohol-alginate-kaolin beads for efficient degradation of phenol against unfavorable environmental factors

In this study, batch experiments were carried out to evaluate the biodegradation of phenol by Sphingomonas sp. GY2B, which were immobilized in polyvinyl alcohol (PVA)-sodium alginate-kaolin beads under different conditions. The optimal degradation performance was achieved by GY2B immobilized in beads containing 1.0% (w/v) of kaolin, 10% (w/v) of PVA, 0.3% (w/v) of sodium alginate, 10% (v/v) of biomass dosage, and exposed to an initial phenol concentration of 100 mg/L. The experimental results indicated that PVA-sodium alginate-kaolin beads can accelerate the degradation rate of phenol by reducing the degradation time and also improve degradation rate. The biodegradation rate of phenol by immobilized cells (16.79 ± 0.81 mg/(L·h)) was significantly higher than that of free cells (11.49 ± 1.29 mg/(L·h)) under the above optimal conditions. GY2B immobilized on beads was more competent than free GY2B in degradation under conditions with high phenol concentrations (up to 300 mg/L) and in strong acidic (pH = 1) and alkaline (pH = 12) environments. Higher phenol concentrations inhibit the biomass and reduce the biodegradation rate, while the lower biodegradation rate at low initial phenol concentrations is attributed to mass transfer limitations. The Haldane inhibitory model was in agreement with the experimental data well, revealing that phenol showed a considerable inhibitory effect on the biodegradation by Sphingomonas sp. GY2B, especially at concentrations higher than 90 mg/L. Intra-particle diffusion model analysis suggests that adsorption of phenol by immobilized beads was controlled by both rapid surface adsorption as well as pore diffusion mechanism. It's worth noting that the presence of 1 mg/L Cr(VI) enhanced the biodegradation of phenol by free cells, while Cr(VI) showed no obvious impact on the removal of phenol by immobilized cells. In addition, immobilized cells were reused 16 times and removed 99.5% phenol, and when stored at 4 °C for 90 days, more than 99% phenol was removed. These results showed that immobilized cells can significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. It is implied that PVA -sodium alginate-kaolin beads have great potential to be applied in a practical and economical phenolic wastewater treatment system.

Removal and fate of polycyclic aromatic hydrocarbons in a hybrid anaerobic-anoxic-oxic process for highly toxic coke wastewater treatment

Elimination of polycyclic aromatic hydrocarbons (PAHs) from coke wastewater is crucial to minimize the PAHs contamination levels to the environment. Knowledge about the characteristics of PAHs removal in biological treatment processes, especially hybrid systems, for real coke wastewater treatment has been very scarce. In this study, a lab-scale hybrid anaerobic-anoxic-oxic (A₁/A₂/O) process was used to treat highly toxic coke wastewater and operated more than 600 d at total hydraulic retention time (HRT) of 50 h, 40 h, 30 h, 20 h and internal mixed liquor recirculation ratio (R) of 3, 6, 9. Removal performance and behaviors of priority PAHs in the hybrid A₁/A₂/O system were investigated. The results showed that the appropriate total HRT and R from oxic reactor to anoxic reactor for organics and nitrogen removal was 40 h and 3, respectively. The concentrations of total PAHs were very high (254-488 μg/L) in the raw coke wastewater, and effectively reduced to 4.1-4.5 μg/L in the final effluent by the present system under the optimized operational conditions. Among the three treatment units, anoxic reactor made the largest contribution to the total PAHs removal. Large amounts of PAHs (415-1310 μg/g) were adsorbed to the activated sludge in the anoxic and oxic reactor, leading to a much higher load of PAHs (2535 μg/d) in the excess sludge than that in the treated coke wastewater (93 μg/d) at SRT 60 d. Therefore, the excess sludge was identified as the major emission source of PAHs in coke wastewater during the hybrid A₁/A₂/O process, and might pose an environmental risk if the excess sludge was not properly treated and disposed.