Anaerobic biodegradation of phenol in wastewater treatment: achievements and limits

A novel paraffin-based N/P controlled-release material for biostimulation of phenol biodegradation in groundwater

To address the problem of the weak natural restoration ability of oligotrophic groundwater environments, a novel N/P controlled-release material (CRM) for biostimulation, prepared by an improved method, was developed. CRMs can encapsulate N and P (N/P) salts for sustained release in aquifers. Paraffin-based CRMs can be used to control N/P release rates by adjusting the particle size of CRMs and the mass ratio of the paraffin. The developed CRMs had a more remarkable adaptability to groundwater than other materials. Specifically, 0.4-cm CRMs released N/P stably and efficiently over a wide temperature range (7-25 ℃), and the release properties of various CRMs were not affected by pH. The release of N/P followed Fickian diffusion, and a dissolution-diffusion model was established to elucidate the mechanism of the controlled release. In contrast to bare N/P, CRMs obviously enhanced the biodegradation rate of phenol and prolonged the effectiveness of supplying N/P. The degradation rate of phenol in the CRM system increased by 20.8 %. The different supply modes of N/P, CRMs and bare N/P, resulted in differences in salinity. Metagenomic analysis showed that this difference changed the proportion of various phenol-degrading genera and thus changed the abundance of genes associated with the phenol degradation pathway.

Two-stage conversion of syngas and pyrolysis aqueous condensate into L-malate

Hybrid thermochemical-biological processes have the potential to enhance the carbon and energy recovery from organic waste. This work aimed to assess the carbon and energy recovery potential of multifunctional processes to simultaneously sequestrate syngas and detoxify pyrolysis aqueous condensate (PAC) for short-chain carboxylates production. To evaluate relevant process parameters for mixed culture co-fermentation of syngas and PAC, two identical reactors were run under mesophilic (37 °C) and thermophilic (55 °C) conditions at increasing PAC loading rates. Both the mesophilic and the thermophilic process recovered at least 50% of the energy in syngas and PAC into short-chain carboxylates. During the mesophilic syngas and PAC co-fermentation, methanogenesis was completely inhibited while acetate, ethanol and butyrate were the primary metabolites. Over 90% of the amplicon sequencing variants based on 16S rRNA were assigned to Clostridium sensu stricto 12. During the thermophilic process, on the other hand, Symbiobacteriales, Syntrophaceticus, Thermoanaerobacterium, Methanothermobacter and Methanosarcina likely played crucial roles in aromatics degradation and methanogenesis, respectively, while Moorella thermoacetica and Methanothermobacter marburgensis were the predominant carboxydotrophs in the thermophilic process. High biomass concentrations were necessary to maintain stable process operations at high PAC loads. In a second-stage reactor, Aspergillus oryzae converted acetate, propionate and butyrate from the first stage into L-malate, confirming the successful detoxification of PAC below inhibitory levels. The highest L-malate yield was 0.26 ± 2.2 molL-malate/molcarboxylates recorded for effluent from the mesophilic process at a PAC load of 4% v/v. The results highlight the potential of multifunctional reactors where anaerobic mixed cultures perform simultaneously diverse process roles, such as carbon fixation, wastewater detoxification and carboxylates intermediate production. The recovered energy in the form of intermediate carboxylates allows for their use as substrates in subsequent fermentative stages.

Biodegradation of phenolic pollutants and bioaugmentation strategies: A review of current knowledge and future perspectives

The widespread use of phenolic compounds renders their occurrence in various environmental matrices, posing ecological risks especially the endocrine disruption effects. Biodegradation-based techniques are efficient and cost-effective in degrading phenolic pollutants with less production of secondary pollution. This review focuses on phenol, 4-nonylphenol, 4-nitrophenol, bisphenol A and tetrabromobisphenol A as the representatives, and summarizes the current knowledge and future perspectives of their biodegradation and the enhancement strategy of bioaugmentation. Biodegradation and isolation of degrading microorganisms were mainly investigated under oxic conditions, where phenolic pollutants are typically hydroxylated to 4-hydroxybenzoate or hydroquinone prior to ring opening. Bioaugmentation efficiencies of phenolic pollutants significantly vary under different application conditions (e.g., increased degradation by 10-95% in soil and sediment). To optimize degradation of phenolic pollutants in different matrices, the factors that influence biodegradation capacity of microorganisms and performance of bioaugmentation are discussed. The use of immobilization strategy, indigenous degrading bacteria, and highly competent exogenous bacteria are proposed to facilitate the bioaugmentation process. Further studies are suggested to illustrate 1) biodegradation of phenolic pollutants under anoxic conditions, 2) application of microbial consortia with synergistic effects for phenolic pollutant degradation, and 3) assessment on the uncertain ecological risks associated with bioaugmentation, resulting from changes in degradation pathway of phenolic pollutants and alterations in structure and function of indigenous microbial community.

Comparison of treatment performance and microbial community evolution of typical dye wastewater by different combined processes

The degradation of typical dye wastewater is a focus of research in the printing and dyeing industry. In this study, a combined micro-electrolysis and microbial treatment method was established to treat refractory dye wastewater, and the pivotal factors in the microbial treatment were optimized. In the series and coupled modes, the removal rates of chroma reached 98.75% and 92.50%, and the removal rates of chemical oxygen demand (COD) reached 96.17% and 82.29%, respectively. The high-throughput sequencing results showed that the microbial communities in the microbial system varied at different treatment stages. From the culture stage to the domestication stage, the dominant phylum was Proteobacteria; however, the community abundance of microorganisms decreased. A combination of micro-electrolysis and biological methods can alter the characteristics of the microbial community, increase the number of dominant phyla, and increase the abundance of microorganisms. The degradation effect of the series mode and the overall strengthening effect of micro-electrolysis on the microorganisms were better than those of the coupled mode. In actual wastewater, the maximum removal rates of chroma, COD, total nitrogen (TN), ammonia nitrogen (NH3-N), and total phosphorus (TP) are 97.50%, 98.90%, 94.35%, 93.95%, and 91.17%, respectively. Three-dimensional fluorescence spectrum analysis showed that microbial processes could significantly degrade fluorescent components in wastewater, and methanogenic active enzymes in anaerobic processes could continue to react. The combined process can realize the efficient treatment of toxic dye wastewater by reducing the toxicity of wastewater and efficiently degrading organic matter, which has important guiding significance for the treatment of refractory dye wastewater.

Microbiological insights into anaerobic phenol degradation mechanisms and bulking phenomenon in a mesophilic upflow anaerobic sludge blanket reactor in long-term operation

In this study, a long-term operation of 2,747 days was conducted to evaluate the performance of the upflow anaerobic sludge blanket (UASB) reactor and investigated the degradation mechanisms of high-organic loading phenol wastewater. During the reactor operation, the maximum chemical oxygen demand (COD) removal rate of 6.1 ± 0.6 kg/m3/day under 1,680 mg/L phenol concentration was achieved in the mesophilic UASB reactor. After a significant change in the operating temperature from 24.0 ± 4.1 °C to 35.9 ± 0.6 °C, frequent observations of floating and washout of the bloated granular sludge (novel types of the bulking phenomenon) were made in the UASB reactor, suggesting that the change in operating temperature could be a trigger for the bulking phenomenon. Through the metagenomic analysis, phenol degradation mechanisms were predicted that phenol was converted to 4-hydroxybenzoate via two possible routes by Syntrophorhabdaceae and Pelotomaculaceae bacteria. Furthermore, the degradation of 4-hydroxybenzoate to benzoyl-CoA was carried out by members of Syntrophorhabdaceae and Smithellaceae. In the bulking sludge, a predominant presence of Nanobdellota, belonging to DPANN archaea, was detected. The metagenome-assembled genome of the Nanobdellota lacks many biosynthetic pathways and has several genes for the symbiotic lifestyle such as trimeric autotransporter adhesin-related protein. Furthermore, the Nanobdellota have significant correlations with several methanogenic archaea that are predominantly present in the UASB reactor. Considering the results of this study, the predominant Nanobdellota may negatively affect the growth of the methanogens through the parasitic lifestyle and change the balance of microbial interactions in the granular sludge ecosystem.

Thermodynamic and kinetic analysis of the response surface method for phenol removal from aqueous solution using graphene oxide-polyacrylonitrile nanofiber mats

Phenolic compound even at low concentrations, are considered to be priority pollutants due to their significant toxicity. Electrospinning was used to create a polyacrylonitril (PAN) nanofiber, which was then impregnated with graphene oxide (GO). After a preliminary investigation into the electrospinning parameters (e.g., using various voltages and polymer concentrations), the electrospun nanofibres were tuned, this study evaluated the effectiveness of these materials in removing phenolic compounds from wastewater through adsorption. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the synthesized nanofiber mats. The scanning electron microscopy (SEM) analysis revealed that the structure of nanofiber mats was altered by the addition of graphene oxide (GO) in different ratios. Specifically, the surface of the fibres exhibited increased roughness, and the diameter of the fibres also experienced an increase. The average diameter of the fibres was measured to be (134.9 ± 21.43 nm) for the PAN/2.5% GO composite and (198 ± 33.94 nm) for the PAN/5% GO composite. FTIR spectra of the PAN/GO nanocomposites nanofiber displayed distinct peaks associated with graphene oxide (GO). These included a wide peak at 3400 cm-1, related to the presence of hydroxyl (O-H) groups, as well as peaks on 1600 as well as 1000 cm-1, which indicated the existence of epoxy groups. In this study response surface methodology (RSM) was implemented. To enhance the efficiency of removing substances, it is necessary to optimise parameters such as pH, contact time, and dosage of the adsorbent. The optimum pH for removing phenol via all nanofiber mats was determined to be 7, while at a dose of 2 mg dose adsorbents maximum removals for pure PAN, PAN/2.5 GO, and PAN/5 GO were 61.3941, 77.2118, and 92.76139%, respectively. All the adsorbents obey Langmuir isotherm model, and the empirical adsorption findings were fitted with the second-order model kinetically, also non-linear Elovich model. The maximal monolayer adsorption capacities for PAN, PAN/2.5 GO, and PAN/5 GO were found to be 57.4, 66.18, and 69.7 mg/g, respectively. Thermodynamic studies discovered that the adsorption of phenol on all adsorbents nanofiber mats was exothermic, the adsorption of phenol on nanofiber mats decreases as the temperature increases. All the adsorbents exhibit negative enthalpy and entropy. The PAN/GO composite's superior phenol removal suggested that it could be used as a latent adsorbent for efficient phenol removal from water and wastewater streams.

Flexible catabolism of monoaromatic hydrocarbons by anaerobic microbiota adapting to oxygen exposure

Microbe-mediated anaerobic degradation is a practical method for remediation of the hazardous monoaromatic hydrocarbons (BTEX, including benzene, toluene, ethylbenzene and xylenes) under electron-deficient contaminated sites. However, how do the anaerobic functional microbes adapt to oxygen exposure and flexibly catabolize BTEX remain poorly understood. We investigated the switches of substrate spectrum and bacterial community upon oxygen perturbation in a nitrate-amended anaerobic toluene-degrading microbiota which was dominated by Aromatoleum species. DNA-stable isotope probing demonstrated that Aromatoleum species was involved in anaerobic mineralization of toluene. Metagenome-assembled genome of Aromatoleum species harbored both the nirBD-type genes for nitrate reduction to ammonium coupled with toluene oxidation and the additional meta-cleavage pathway for aerobic benzene catabolism. Once the anaerobic microbiota was fully exposed to oxygen and benzene, 1.05 ± 0.06% of Diaphorobacter species rapidly replaced Aromatoleum species and flourished to 96.72 ± 0.01%. Diaphorobacter sp. ZM was isolated, which was not only able to utilize benzene as the sole carbon source for aerobic growth and but also innovatively reduce nitrate to ammonium with citrate/lactate/glucose as the carbon source under anaerobic conditions. This study expands our understanding of the adaptive mechanism of microbiota for environmental redox disturbance and provides theoretical guidance for the bioremediation of BTEX-contaminated sites.

Deterioration of sludge characteristics and promotion of antibiotic resistance genes spread with the co-existing of polyvinylchloride microplastics and tetracycline in the sequencing batch reactor

With the continuous increase in microplastics (MPs) and tetracycline (TC) entering wastewater treatment plants (WWTPs) along with sewage, the co-existence of MPs and TC in the biological treatment of wastewater has attracted extensive attention. This study investigated the effect of 1 mg/L polyvinyl chloride (PVC) MPs and 100 ng/L TC co-existing on sequencing batch reactors (SBRs) (S2) treating phenol wastewater in contrast to the control with TC alone (S1). The phenol removal efficiency was significantly inhibited by the co-existence of PVC MPs and TC. Sludge characteristics were also distinctively influenced. The decreased zone sludge velocity (ZSV) and increased sludge volume index (SVI) indicated that the combined effect of PVC MPs and TC deteriorated sludge settleability, which had positive and negative linear correlations with extracellular polymeric substances (EPS) content and the protein (PN)/polysaccharide (PS) ratio, respectively. Moreover, the decreased and increased relative abundances of potential phenol-degraders and antibiotic resistance gene (ARG) carriers may elucidate the inhibition of phenol removal and promotion of ARGs propagation with the co-occurrence of PVC MPs and TC. In addition, the enhanced potential ARGs hosts, loss of the EPS protective effect, and increased membrane permeability induced by reactive oxygen species (ROS) jointly promoted ARGs dissemination in the co-existence of PVC MPs and TC. Notably, the co-occurrence of ARGs and mobile genetic element (MGEs) indicated that the co-existence of PVC MPs and TC promoted the spread of some transposase-associated ARGs mediated by horizontal gene transfer (HGT).

Microbial electricity-driven anaerobic phenol degradation in bioelectrochemical systems

Microbial electrochemical technologies have been extensively employed for phenol removal. Yet, previous research has yielded inconsistent results, leaving uncertainties regarding the feasibility of phenol degradation under strictly anaerobic conditions using anodes as sole terminal electron acceptors. In this study, we employed high-performance liquid chromatography and gas chromatography-mass spectrometry to investigate the anaerobic phenol degradation pathway. Our findings provide robust evidence for the purely anaerobic degradation of phenol, as we identified benzoic acid, 4-hydroxybenzoic acid, glutaric acid, and other metabolites of this pathway. Notably, no typical intermediates of the aerobic phenol degradation pathway were detected. One-chamber reactors (+0.4 V vs. SHE) exhibited a phenol removal rate of 3.5 ± 0.2 mg L-1 d-1, while two-chamber reactors showed 3.6 ± 0.1 and 2.6 ± 0.9 mg L-1 d-1 at anode potentials of +0.4 and + 0.2 V, respectively. Our results also suggest that the reactor configuration certainly influenced the microbial community, presumably leading to different ratios of phenol consumers and microorganisms feeding on degradation products.

Dual metabolic pathways co-determine the efficient aerobic biodegradation of phenol in Cupriavidus nantongensis X1

Phenol, as an important chemical raw material, often exists in wastewater from chemical plants and pollutes soil and groundwater. Aerobic biodegradation is a promising method for remediation of phenolic wastewater. In this study, degradation characteristics and mechanisms of phenol in Cupriavidus nantongensis X1 were explored. Strain X1 could completely degrade 1.5 mM phenol within 32 h and use it as the sole carbon source for growth. The optimal degradation temperature and pH for phenol by strain X1 were 30 °C and 7.0. The detection of 3-oxoadipate and 4-hydroxy-2-oxopentanoate indicated that dual metabolic pathways coexist in strain X1 for phenol degradation, ortho- and meta-pathway. Genome and transcriptome sequencing revealed the whole gene clusters for phenol biomineralization, in which C12O and C23O were key enzymes in two metabolic pathways. The ribosome proteins were also involved in the regulation of phenol degradation. Meanwhile, the degradation activities of enzyme C23O was 188-fold higher than that of C12O in vitro, which indicated that the meta-pathway was more efficient than ortho-pathway for catechol degradation in strain X1. This study provides an efficient strain resource for phenol degradation, and the discovery of dual metabolic pathways provides new insight into the aerobic biological metabolism and bioremediation of phenol.

Hydrodynamic performance assessment of photocatalytic reactor with baffles and roughness in the flow path: A modelling approach with experimental validation

Purification of wastewater is essential for human being as well as for the flora and fauna, and sustainable environment. Photocatalytic reactor with TiO2 coated layer can be used to degrade the pollutants but without proper pollutant mass transfer in the reactive surface, photocatalytic reactor decreases its effectiveness. The baffles and rough surface in the flow path can improve the fluid mixing to enhance pollutant mass transfer to improve the reactor's performance. In this study, a computational fluid dynamics (CFD) model has been developed to investigate the effect of four top baffles and three rough surfaces (semi-circular, triangle, and rectangle) on pressure drops, mass transfer and the hydrodynamic performance of the reactor. The experimental investigation was carried out using Formic Acid (FA) as pollutant in feed water for model validation. The simulated result varies only within 5% with the experimental data of FA concentration versus feed flow rate and fluid velocity. The model was run at fluid velocity of 0.15 m/s and 0.5 m/s (Reynolds number of 2150 (laminar flow) and 7500 (turbulent flow), respectively. The simulation result shows that the addition of baffles and roughness on the reactive surfaces increases the turbulent kinetic energy (minimum increase 8%) and consequently increases the mass transfer (maximum increase 37%) of the pollutant. The highest wall shear was observed to be 40 Pa when both square and triangular elements were used as roughness elements at turbulent flow condition. The results also shows that the highest pressure-drop of 8 kPa was found when the square roughness element was used at turbulent flow condition. Overall, the photocatalytic reactor performance is significantly enhanced by the application of combined baffles and roughness elements in the reactive surface.

The Effects of Preservatives on Antibiotic- and Preservative-Resistant Microbes and Nitrogen/Sulfur Cycle Associated Microbial Communities in Freshwater River Sediments

The intensive use of benzoic acid (BA), 4-hydroxybenzoic acid (HB), and dehydroacetate (DHA) as additives and preservatives in cosmetics and foods causes emerging environmental pollutions. Anthropogenic releases of BA, HB and DHA are primarily emissions into water and soil. However, few studies investigate the effects of BA, HB and DHA on microbial communities in freshwater river sediments. The aim of this study is to reveal the effects of BA, HB and DHA on microbial communities in freshwater river sediments. Tetracycline-, sulfamethoxazole- and preservative-resistant microbes were increased in the river sediments treated with BA, HB and DHA. The relative abundances of methanogen- and xenobiotic-degradation-associated microbial communities were also increased in the BA-, HB- and DHA-treated sediments. The relative abundance of four nitrogen cycle associated microbial groups (anammox, nitrogen fixation, denitrification, and dissimilatory nitrate reduction) were increased after the eighth week in the BA-, HB- and DHA-treated sediments. For the sulfur cycle, the relative abundance of thiosulfate oxidation associated microbial communities were increased after the eighth week in the BA-, HB- and DHA-treated sediments. Results of this study provide insight into the effects of BA, HB and DHA on antibiotic resistance, nitrogen cycle, sulfur cycle, drug resistance and methane production in freshwater aquatic environments.

Isolation and characterization of Indigenous Bacilli strains from an oil refinery wastewater with potential applications for phenol/cresol bioremediation

Phenolic compounds are frequently occurring in wastewaters from various industrial processes at high concentrations, imposing prominent risk to aquatic biosphere and human health. Bioremediation has been proven to be an effective approach to remove these compounds, and hunting for functional organisms is still of primary importance to develop efficient processes. In this study, we report several newly isolated bacillus strains with superior performances in metabolizing phenols, one of which showed paramount efficiencies to metabolize phenol at concentrations up to 1200 mg L^-1 and could simultaneously degrade a wide range of other phenolic compounds. The genes encoding for phenol hydroxylase (PH) and catechol-2,3-dioxygenase (C23O) have been detected and characterized, evidencing that phenol degradation occurs via the meta pathway. The GC level of the PH gene was found to be much higher than that of genes from other Bacilli but was quite close to that of the genes from Rhodococcus, and the induction of both enzymes by phenols was confirmed by RT-PCR experiments. We intend to believe this novel strain might be promising to serve as preferred organisms for developing more robust and efficient bioremediation processes of degrading phenolic compounds due to its validated performance.

Degradation and transformation of linear alkyl-benzene sulfonates (LAS) in integrated constructed wetland-microbial fuel cell systems

Linear alkylbenzene sulfonates (LAS) are the most commonly-used anionic surfactants in cleaning agents and detergents. Taking sodium dodecyl benzene sulfonate (SDBS) as the target LAS, this study investigated the degradation and transformation of LAS in integrated constructed wetland-microbial fuel cell (CW-MFC) systems. Results showed that, SDBS was able to improve the power output and reduce the internal resistance of CW-MFCs by reducing transmembrane transfer resistance of organics and electrons because of the amphiphilicity and solubilization, however, SDBS with relatively high concentration had a great potential to inhibit electricity generation and organics biodegradation of CW-MFCs because of the toxic effects on microorganisms. C atoms on alkyl group and O atoms on sulfonic acid group of SDBS had greater electronegativity and were prone to oxidation reaction. The biodegradation of SDBS in CW-MFCs was a process of alkyl chain degradation, desulfonation and benzene ring cleavage in sequence via ω, β and/or α-oxidations and radical attacks under the action of coenzymes and oxygen, in which 19 intermediates were produced, including four anaerobic degradation products (toluene, phenol, cyclohexanone and acetic acid). Especially, for the first time cyclohexanone was detected during the biodegradation of LAS. The bioaccumulation potential of SDBS was greatly reduced through the degradation by CW-MFCs, and thus the environmental risk of SDBS was effectively reduced.

Phenol Degradation by Pseudarthrobacter phenanthrenivorans Sphe3

Phenol poses a threat as one of the most important industrial environmental pollutants that must be removed before disposal. Biodegradation is a cost-effective and environmentally friendly approach for phenol removal. This work aimed at studying phenol degradation by Pseudarthrobacter phenanthrenivorans Sphe3 cells and also, investigating the pathway used by the bacterium for phenol catabolism. Moreover, alginate-immobilized Sphe3 cells were studied in terms of phenol degradation efficiency compared to free cells. Sphe3 was found to be capable of growing in the presence of phenol as the sole source of carbon and energy, at concentrations up to 1500 mg/L. According to qPCR findings, both pathways of ortho- and meta-cleavage of catechol are active, however, enzymatic assays and intermediate products identification support the predominance of the ortho-metabolic pathway for phenol degradation. Alginate-entrapped Sphe3 cells completely degraded 1000 mg/L phenol after 192 h, even though phenol catabolism proceeds slower in the first 24 h compared to free cells. Immobilized Sphe3 cells retain phenol-degrading capacity even after 30 days of storage and also can be reused for at least five cycles retaining more than 75% of the original phenol-catabolizing capacity.

Degradation of high-strength acrylic acid wastewater with anaerobic granulation technology: A mini-review

The anaerobic granulation technology has been successfully applied full-scale for treating high-strength recalcitrant acrylic acid wastewater. This mini-review highlighted the recalcitrance of acrylic acid and its biological degradation pathways. And then, the full-scale practices using anaerobic granulation technology for acrylic wastewater treatment were outlined. The granules are proposed to provide barriers for high-concentration acrylic acid to the embedded anaerobic microbes, maintaining its high degradation rate without apparent substrate inhibition. Based on this proposal, the prospects of applying anaerobic granulation technology to handle a wide range of high-strength recalcitrant wastewaters, to improve the current process performances, and to recover renewable resources were delineated. The anaerobic granulation for high-strength recalcitrant wastewater treatment is an emergent technology that can assist in fulfilling the appeals of the circular bioeconomy of modern society.

Stability Analysis of a Chemostat Model for Phenol and Sodium Salicylate Mixture Biodegradation

In this paper we consider a mathematical continuous-time model for biodegradation of phenol in the presence of sodium salicylate in a chemostat. The model is described by a system of three nonlinear ordinary differential equations. Based on the dynamical systems theory we provide mathematical investigations of the model including local and global analysis of the solutions. The local analysis consist in computation of two equilibrium points—one interior and one boundary (washout) equilibrium—in dependance of the dilution rate as a key model parameter. The local asymptotic stability of the equilibria is also presented. The global analysis of the model solutions comprises proving existence, uniqueness and uniform boundedness of positive solutions, as well as global asymptotic stabilizability of the dynamics. The theoretical investigations are illustrated by some numerical examples. The results in this study can be used in practice as a tool to control and optimize the chemostat performance of simultaneous biodegradation of mixed substrates in wastewater.

Molecular Mechanisms and Applications of N-Acyl Homoserine Lactone-Mediated Quorum Sensing in Bacteria

Microbial biodiversity includes biotic and abiotic components that support all life forms by adapting to environmental conditions. Climate change, pollution, human activity, and natural calamities affect microbial biodiversity. Microbes have diverse growth conditions, physiology, and metabolism. Bacteria use signaling systems such as quorum sensing (QS) to regulate cellular interactions via small chemical signaling molecules which also help with adaptation under undesirable survival conditions. Proteobacteria use acyl-homoserine lactone (AHL) molecules as autoinducers to sense population density and modulate gene expression. The LuxI-type enzymes synthesize AHL molecules, while the LuxR-type proteins (AHL transcriptional regulators) bind to AHLs to regulate QS-dependent gene expression. Diverse AHLs have been identified, and the diversity extends to AHL synthases and AHL receptors. This review comprehensively explains the molecular diversity of AHL signaling components of Pseudomonas aeruginosa, Chromobacterium violaceum, Agrobacterium tumefaciens, and Escherichia coli. The regulatory mechanism of AHL signaling is also highlighted in this review, which adds to the current understanding of AHL signaling in Gram-negative bacteria. We summarize molecular diversity among well-studied QS systems and recent advances in the role of QS proteins in bacterial cellular signaling pathways. This review describes AHL-dependent QS details in bacteria that can be employed to understand their features, improve environmental adaptation, and develop broad biomolecule-based biotechnological applications.

Anaerobic recalcitrance in wastewater treatment: A review

Anaerobic treatment is applied as an alternative to traditional aerobic treatment for recalcitrant compound degradation. This review highlighted the recalcitrant compounds in wastewaters and their pathways under aerobic and anaerobic conditions. Forty-one recalcitrant compounds commonly found in wastewater along with associated anaerobic removal performance were summarized from current research. Anaerobic degradability of wastewater could not be appropriately evaluated by BOD/COD ratio, which should only be suitable for determining aerobic degradability. Recalcitrant wastewaters with a low BOD/COD ratio may be handled by anaerobic treatments after the adaption and provision of sufficient electron donors. Novel indicator characterizing the anaerobic recalcitrance of wastewater is called for, essential for emergent needs to resource recovery from high-strength recalcitrant wastewater for fulfilling appeals of circular bioeconomy of modern societies.

Increasing N,N-dimethylacetamide degradation and mineralization efficiency by co-culture of Rhodococcus ruber HJM-8 and Paracoccus communis YBH-X

In this work, Rhodococcus ruber HJM-8 and Paracoccus communis YBH-X were isolated and used to enhance N,N-dimethylacetamide (DMAC) degradation and mineralization efficiencies. The monoculture and co-culture of the two strains for DMAC degradation were compared; results indicated that, a degradation efficiency of 97.62% was obtained in co-culture, which was much higher than that of monocultures of HJM-8 (57.34%) and YBH-X (34.02%). The degradation mechanism showed that co-culture could efficiently improve extracellular polymeric substances production, electron transfer, and microbial activity. Meanwhile, the mineralization mechanism suggested that acetate was the dominant intermediate which had an inhibitory effect on HJM-8, and co-culture was conducive to mineralization due to the high performance of acetate conversion and Na⁺ K⁺-ATPase vitality. Besides, a pathway of DMAC biodegradation was proposed for co-culture: DMAC was degraded into acetate by HJM-8, then the accumulated acetate was mineralized by YBH-X. Additionally, the co-culture system was further optimized by Box-Behnken design.

Pseudomonas phenolilytica sp. nov., a novel phenol-degrading bacterium

This study describes a bacterium strain RBPA9 isolated from a municipality waste dumping area capable of degrading phenol, proposed as a novel species of Pseudomonas. Cells are Gram-negative, rod shaped, aerobic and motile. The genome is 3.92 Mb, and the G + C content is 64.64%. The overall genome relatedness indices such as in silico DNA-DNA hybridization (isDDH), average nucleotide identity (ANI), and average amino acid identity (AAI) values were below 70% and 95-96%, respectively. Phylogenetic analysis based on genome-wide core genes and 16S rRNA gene sequences revealed that strain RBPA9 clustered with Pseudomonas stutzeri ATCC 17588 ^T in both the phylogenetic trees. Maximum growth was recorded at 200 mg /L concentration of phenol which was consumed within 24 h. A gene cluster of phenol degradation pathway was detected. The quantitative real-time PCR (RT-PCR) demonstrated the expression of all the genes required in the meta-cleavage pathway of phenol in RBPA9. Our results reveal that strain RBPA9 represents a novel species for which Pseudomonas phenolilytica sp. nov. is proposed. The type strain is RBPA9^T (= TBRC 15231 ^T = NBRC 115284 ^T).

Respiratory Adsorption of Organic Pollutants in Wastewater by Superhydrophobic Phenolic Xerogels

Organogel adsorbents are widely used for the adsorption of hard-to-degrade organic pollutants in wastewater due to their natural affinity to the organic phase in water. In this study, phenolic xerogels (PF) synthesised in the ethylene glycol inorganic acid system are used as a backbone and superhydrophobic phenolic xerogels (ASO-PF) are obtained by grafting aminosilanes onto the PF backbone via the Mannich reaction. The modified ASO-PF not only retains the pore structure of the original PF (up to 90% porosity), but also has excellent superhydrophobic properties (water contact angle up to 153°). Owing to the unique pore structure, ASO-PF has excellent compression properties, cycling 50% compression deformation more than 10 times without being damaged, with a maximum compression deformation of up to 80%. A squeeze-suction-squeeze approach is proposed for selective adsorption of organic pollutants in homogeneous solutions based on the recyclable compression properties of ASO-PF. The ASO-PF is put under negative pressure by squeezing, and when the pressure is released, the adsorbed liquid enters the ASO-PF, where the organic pollutants are retained by the adsorption sites in the skeleton, and then the remaining water is discharged by squeezing. This breathing ASO-PF holds great promise for organic pollutant adsorption and recovery applications.

Correlating bacterial and archaeal community with efficiency of a coking wastewater treatment plant employing anaerobic-anoxic-oxic process in coal industry

Coking wastewater (CWW) contains various complex pollutants, and biological treatment processes are frequently applied in the coking wastewater treatment plants (CWWTPs). The present work is to evaluate the contaminants removal of a full-scale CWWTP with an anaerobic-anoxic-oxic process (A/A/O), to reveal function of bacterial and archaeal community involved in different bioreactors, and to clarify the relationship between the performance and microbial community. Illumina Miseq sequencing of bacteria showed that β-proteobacteria dominated in three bioreactors with relative abundance of 60.2%~81.7%. 75.2% of sequences were assigned to Petrobacter in the bioreactor A1, while Thiobacillus dominated in A2 and O with relative abundance of 31.8% and 38.7%, respectively. Illumina Miseq sequencing of archaea revealed a high diversity of methanogens existed in A1 and A2 activated sludge. Moreover, Halostagnicola was the dominant archaea in A1 and A2 activated sludge with relative abundance of 41.8% and 66.5%, respectively. Function predicted analysis explored that function of bacteria was similar to that of archaea but the relative abundance differed from each other. A putative biodegradation model of CWW treatment in A/A/O process indicated that A1 and A2 activated sludge mainly reduced carbohydrate, protein, TN, phenol and cyanide, as well as methane production. Bacteria in the bioreactor O were responsible for aerobic biotransformation of residual carbohydrates, refractory organics and nitrification. The redundancy analysis (RDA) further revealed that removal of COD, TN, and NO₃^--N, phenol and cyanides were highly correlated with some anaerobic bacteria and archaea, whereas the transformation of NH₄⁺-N was positively correlated with some aerobic bacteria.

Biodegradation of a Complex Phenolic Industrial Stream by Bacterial Strains Isolated from Industrial Wastewaters

Molecular and metabolomic tools were used to design and understand the biodegradation of phenolic compounds in real industrial streams. Bacterial species were isolated from an industrial wastewater treatment plant of a phenol production factory and identified using molecular techniques. Next, the biodegradation potential of the most promising strains was analyzed in the presence of a phenolic industrial by-product containing phenol, alfa-methylstyrene, acetophenone, 2-cumylphenol, and 4-cumylphenol. A bacterial consortium comprising Pseudomonas and Alcaligenes species was assessed for its ability to degrade phenolic compounds from the phenolic industrial stream (PS). The consortium adapted itself to the increasing levels of phenolic compounds, roughly up to 1750 ppm of PS; thus, becoming resistant to them. In addition, the consortium exhibited the ability to grow in the presence of PS in repeated batch mode processes. Results from untargeted metabolomic analysis of the culture medium in the presence of PS suggested that bacteria transformed the toxic phenolic compounds into less harmful molecules as a survival mechanism. Overall, the study demonstrates the usefulness of massive sequencing and metabolomic tools in constructing bacterial consortia that can efficiently biodegrade complex PS. Furthermore, it improves our understanding of their biodegradation capabilities.

Phenol promoted caproate production via two-stage batch anaerobic fermentation of organic substance with ethanol as electron donor for chain elongation

The conversion of organic wastes/wastewater into medium chain fatty acids (MCFAs) such as caproate has attracted much attention, while the effects of toxic compounds on the process have rarely been studied. The present study investigated the effects of phenol (0-1.5 g/L), which is a toxicant and present in various organic wastes, on the caproate production in the chain elongation (CE) process with ethanol as electron donor via two-stage batch anaerobic fermentation of glucose. The results showed phenol ≤ 1 g/L did not affect short chain fatty acids (SCFAs) production, while 1 g/L phenol increased caproate production by 59.9% in the following CE process. The higher selectivity of caproate and higher consumption of ethanol contributed to the higher caproate production at 1 g/L phenol. It was also shown 1 g/L phenol had more positive effect on CE of butyrate than acetate. 1.5 g/L phenol inhibited both SCFAs production and CE processes. 16S rRNA genes analysis showed phenol had slight effect on the microbial communities for SCFAs production, while it obviously changed the dominant microbes in CE process. For CE process, metagenomic analysis was further conducted and phenol mainly affected fatty acid biosynthesis (FAB) pathway, but not reverse β-oxidization (RBO) pathway. 1 g/L phenol increased the abundances of genes in FAB pathway, which could be related with the higher caproate production. Genome reconstruction identified the dominant microbial species in CE process, which were changed with different concentrations of phenol. Most of the dominant species were new microbial species potentially involved in CE. The syntrophic cooperation between Petrimonas mucosa FDU058 and Methanofollis sp. FDU007 might play important role in increased caproate production at 1 g/L phenol, and their adaption to phenol could be due to the presence of genes relating with active efflux system and refolding of proteins.

Analysis of Phenol Biodegradation in Antibiotic and Heavy Metal Resistant Acinetobacter lwoffii NL1

Phenol is a common environmental contaminant. The purpose of this study was to isolate phenol-degrading microorganisms from wastewater in the sections of the Chinese Medicine Manufactory. The phenol-degrading Acinetobacter lwoffii NL1 was identified based on a combination of biochemical characteristics and 16S rRNA genes. To analyze the molecular mechanism, the whole genome of A. lwoffii NL1 was sequenced, yielding 3499 genes on one circular chromosome and three plasmids. Enzyme activity analysis showed that A. lwoffii NL1 degraded phenol via the ortho-cleavage rather than the meta-cleavage pathway. Key genes encoding phenol hydroxylase and catechol 1,2-dioxygenase were located on a megaplasmid (pNL1) and were found to be separated by mobile genetic elements; their function was validated by heterologous expression in Escherichia coli and quantitative real-time PCR. A. lwoffii NL1 could degrade 0.5 g/L phenol within 12 h and tolerate a maximum of 1.1 g/L phenol, and showed resistance against multiple antibiotics and heavy metal ions. Overall, this study shows that A. lwoffii NL1 can be potentially used for efficient phenol degradation in heavy metal wastewater treatment.

Biodegradation of phenol by a halotolerant versatile yeast Candida tropicalis SDP-1 in wastewater and soil under high salinity conditions

In this study, a novel halotolerant phenol-degrading yeast strain, SDP-1, was isolated from a coastal soil in Jiangsu, China, and identified as Candida tropicalis by morphology and rRNA internal transcribed space region sequence analysis. Strain SDP-1 can efficiently remove phenol at wide ranges of pH (3.0-9.0), temperature (20-40 °C), and NaCl (0-5%, w/v), as well as the tolerance of Mn²⁺, Zn²⁺ and Cr³⁺ in aquatic phase. It also utilized multiple phenol derivatives and aromatic hydrocarbons as sole carbon source and energy for growth. Free cells of SDP-1 were able to degrade the maximum phenol concentration of 1800 mg/L within 56 h under the optimum culture conditions of 10% inoculum volume, pH 8.0, 35 °C and 200 rpm agitation speed. Meanwhile, SDP-1 was immobilized on sodium alginate, and the capability of efficiently phenol degradation of free cells and immobilized SDP-1 were evaluated. Shortened degradation time and long-term utilization and recycling for immobilized SDP-1 was achieved compared to free cells. The 1200 mg/L of phenol under 5% NaCl stress could be completely degraded within 40 h by immobilized cells. In actual industrial coking wastewater, immobilized cells were able to completely remove 383 mg/L phenol within 20 h, and the corresponding chemical oxygen demand (COD) value was decreased by 50.38%. Besides, in phenol-contained salinity soil (3% NaCl), 100% of phenol (500 and 1000 mg/kg) removal efficiency was achieved by immobilized SDP-1 within 12 and 26 days, respectively. Our study suggested that versatile yeast Candida tropicalis SDP-1 could be potentially used for enhanced treatment of phenol-contaminated wastewater and soil under hypersaline or no-salt environmental conditions.