Investigating the effect of electrosprayed alginate/PVA beads size on the microbial growth kinetics: Phenol biodegradation through immobilized activated sludge

The presence of cyclic organic compounds, including phenol, in the wastewater of many industries has made phenol removal an important issue. Meanwhile, the biological methods of removing phenol have attracted the attention of researchers in recent years. Recently, the use of immobilized microbial cells is proposed as a new approach in industrial wastewater treatment. In this research, the aim is to study the effect of immobilized beads size on the phenol biodegradation efficiency and specific microbial growth rate. For this purpose, electrospray technique was used to immobilize activated sludge in hybrid matrix of alginate and polyvinyl alcohol (PVA). The fabricated alginate/PVA beads were characterized using Fourier transform infrared spectroscopy (FTIR). Evaluation of the results related to the free and immobilized cell systems in the shake flask experiments showed that at low phenol concentrations the immobilized cell system had the same performance as the free cell system, while the immobilized cell system at higher concentrations had a better performance in removing phenol so that at a concentration of 2000 mg/L, removal percentage has increased from 15% to 25-34%. On the other hand, in this survey, the kinetic behavior of activated sludge was in good agreement with Haldane's equation. Moreover, the maximum specific growth rate was measured 0.033 and 0.041 (h^-1) beside 544 and 636 mg/L substrate inhibition constant, for free and immobilized cell systems, respectively. This result shows that the phenol biodegradation has been improved by using the cell immobilization technique especially with applying the smaller beads, which is due to improved mass transfer and microbial cell protection from harsh environments.

Kinetic characterization of a new phenol degrading Acinetobacter towneri strain isolated from landfill leachate treating bioreactor

The objective of this study was to establish and to mathematically describe the phenol degrading properties of a new Acinetobacter towneri CFII-87 strain, isolated from a bioreactor treating landfill leachate. For this purpose, the biokinetic parameters of phenol biodegradation at various initial phenol concentrations of the A. towneri CFII-87 strain have been experimentally measured, and four different mathematical inhibition models (Haldane, Yano, Aiba and Edwards models) have been used to simulate the substrate-inhibited phenol degradation process. The results of the batch biodegradation experiments show that the new A. towneri CFII-87 strain grows on and metabolizes phenol up to 1000 mg/L concentration, manifests significant substrate inhibition and lag time only at concentrations above 800 mg/L phenol, and has a maximum growth rate at 300 mg/L initial phenol concentration. The comparison of the model predictions with the experimental phenol and biomass data revealed that the Haldane, Aiba and Edwards models can be used with success to describe the phenol biodegradation process by A. towneri CFII-87, while the Yano model, especially at higher initial phenol concentrations, fails to describe the process. The best performing inhibition model was the Edwards model, presenting correlation coefficients of R² > 0.98 and modelling efficiency of ME > 0.94 for the prediction of biomass and phenol concentrations on the validation datasets. The calculated biokinetic model parameters place this new strain among the bacteria with the highest tolerance towards phenol. The results suggest that the A. towneri CFII-87 strain can potentially be used in the treatment of phenolic wastewaters.

Valorization of phenol contaminated wastewater for lipid production by Rhodosporidium toruloides 9564T

Phenol is one of the most common hazardous organic compound presents in several industrial effluents which directly affects the aquatic environment. The present study envisaged the phenol biodegradation and simultaneous lipid production along with its underlying mechanism by oleaginous yeast Rhodosporidium toruloides 9564^T. Experiments were designed using simulated wastewater by varying phenol concentration in the range of 0.25-1.5 g/L and inoculum size of 1, 5, and 10% with and without glucose. The oleaginous yeast was found to completely degrade up to 0.75 g/L phenol with lipid accumulation of 26.3%. Phenol at > 0.5 g/L severely inhibited the growth of R. toruloides 9564^T at 1% and 5% inoculum size. Phenol toxicity up to 0.75 g/L can be overcome by increasing inoculum size to 10%. The maximum specific growth rate (μ_max) and phenol degradation rate (q_max) were found to be 0.0717 h^-1 and 0.01523 h^-1, respectively. The enzymatic pathway study suggested that R. toruloides 9564^T follows an ortho cleavage pathway for phenol degradation and lipid accumulation. Phytotoxicty and cytotoxicity tests for treated and untreated samples clearly demonstrated a decline in toxicity of the treated wastewater. R. toruloides brought about an important paradigm shift toward a circular economy in which industrial wastewater is considered a valuable resource for bioenergy production.

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.

B9

The aim of this work is to study the synergistic effect of Stenotrophomonas sp. N5 and Advenella sp. B9 co-culture (COC) on enhancement of phenol biodegradation. These two strains utilizing phenol as sole carbon and energy source were isolated from phenol-containing coking wastewater. The results of biodegradation experiment showed the COC of N5 and B9 has stronger capability to degrade phenol than either of mono-culture (MOC). Growth kinetics studies indicated inhibitory effect of phenol on COC was reduced by the interaction of N5 and B9 in COC. The RNA-Seq results demonstrated that phenol biodegradation was enhanced by metabolic division of labor (DOL) in COC based on the expression of key genes for phenol degradation. GO enrichment analysis of differentially expressed genes (DEGs) indicated DEGs between COC and MOC degradation systems are mainly concentrated in the synthesis of cell components, microbial growth and metabolism, and catalytic activity. The expression of 3 transcriptional factors (LysR, Two-component system response regulator, and TetR families) which can regulate degradation of aromatic compounds, was identified beneficial to phenol degradation.

Biodegradation of phenol and dyes with horseradish peroxidase covalently immobilized on functionalized RGO-SiO2 nanocomposite

Horseradish peroxidase (HRP) was immobilized onto a functionalized reduced graphene oxide-SiO₂ through the covalent bonding process. By using scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR), the formed nanocomposites were characterized. The kinetic parameters including the catalytic constant, k_cat, and the catalytic efficiency, k_cat/K_m, increased 5.5 and 6 times, respectively, after immobilization. The circular dichroism analysis demonstrated that the α-helical content increased from 39% to 46% after immobilization. The immobilization improved the reusability of HRP as 70% of initial activity retained after 10 cycles. Due to the buffering effect, the immobilized HRP was less sensitive to pH changes as compared to the free HRP. At temperature 40 °C and during 90 min, the immobilized HRP retained 90% of the initial activity while 70% of initial activity remained for the free HRP. After 35-day storage, no reduction in the activity was observed for the immobilized HRP. The removal efficiency for phenol concentration (2500 mg/L) obtained 100% and 50% for the immobilized and free HRP, respectively. The results showed that the immobilized HRP promoted the dyes decolorization from 2-fold until 26-fold as compared to the free HRP. The decolorization efficiencies reached 100% for most dyes in the case of immobilized HRP.

Biochar as simultaneous shelter, adsorbent, pH buffer, and substrate of Pseudomonas citronellolis to promote biodegradation of high concentrations of phenol in wastewater

Microbial degradation is an elimination method for removal of organic contaminants from soil and water. However, the main factor limiting its practical application is high bacterial sensitivity to environmental factors such as pH, toxicity, and mass transfer. In this study, biochar was produced pyrolytically from peanut shells at 350 °C, 550 °C, and 750 °C (referred to as BC350, BC550, and BC750, respectively) and their promotion on phenol biodegradation in wastewater by the bacterium Pseudomonas citronellolis was investigated. Higher initial phenol concentration (>400 mg L^-1) showed obvious inhibition on biodegradation with the removal efficiencies being less than 46%, and even the bacterium failed to survive at the phenol concentrations of higher than 1000 mg L^-1. With biochar incorporated, the removal efficiencies of phenol increased from below 46% to up to 99% at the initial concentrations of 400-1200 mg L^-1. Immobilization of strains in biochar by calcium alginate further increased the microbial tolerance to high concentrations of phenol (i.e., 63% removal at 1200 mg L^-1). Scanning electron microscopy demonstrated that biochar acted as shelter to support the bacterium to struggle with extreme conditions. The initial adsorption of phenol by biochar alleviated the initial toxicity of phenol to bacterium and the subsequent gradual desorption controlled the bioavailability of phenol. In this regard, BC350 showed a comparable sorption capacity with BC550 and BC750, while a higher desorption potential than them, thus balanced better the toxicity and bioavailability of phenol to microbes. Alkalinity of BC550 and BC750 played important roles in rescuing the microbes from being damaged by pH shock via neutralizing the fast generation of acidic intermediates. The extractable organic substances in BC350 could be consumed by bacterium as substrates, which was confirmed by incubating the strains in water-extractable solution. Results of this study indicate that incorporation of microbes with biochar could promote the biodegradation of high concentration organic wastewater.

A new Rhodococcus aetherivorans strain isolated from lubricant-contaminated soil as a prospective phenol-biodegrading agent

Microbe-based decontamination of phenol-polluted environments has significant advantages over physical and chemical approaches by being relatively cheaper and ensuring complete phenol degradation. There is a need to search for commercially prospective bacterial strains that are resistant to phenol and other co-pollutants, e.g. oil hydrocarbons, in contaminated environments, and able to carry out efficient phenol biodegradation at a variable range of concentrations. This research characterizes the phenol-biodegrading ability of a new actinobacteria strain isolated from a lubricant-contaminated soil environment. Phenotypic and phylogenetic analyses showed that the novel strain UCM Ac-603 belonged to the species Rhodococcus aetherivorans, and phenol degrading ability was quantitatively characterized for the first time. R. aetherivorans UCM Ac-603 tolerated and assimilated phenol (100% of supplied concentration) and various hydrocarbons (56.2–94.4%) as sole carbon sources. Additional nutrient supplementation was not required for degradation and this organism could grow at a phenol concentration of 500 mg L⁻¹ without inhibition. Complete phenol assimilation occurred after 4 days at an initial concentration of 1750 mg L⁻¹ for freely-suspended cells and at 2000 mg L⁻¹ for vermiculite-immobilized cells: 99.9% assimilation of phenol was possible from a total concentration of 3000 mg L⁻¹ supplied at daily fractional phenol additions of 750 mg L⁻¹ over 4 days. In terms of phenol degradation rates, R. aetherivorans UCM Ac-602 showed efficient phenol degradation over a wide range of initial concentrations with the rates (e.g. 35.7 mg L⁻¹ h⁻¹ at 500 mg L⁻¹ phenol, and 18.2 mg L⁻¹ h⁻¹ at 1750 mg L⁻¹ phenol) significantly exceeding (1.2–5 times) reported data for almost all other phenol-assimilating bacteria. Such efficient phenol degradation ability compared to currently known strains and other beneficial characteristics of R. aetherivorans UCM Ac-602 suggest it is a promising candidate for bioremediation of phenol-contaminated environments.

High phenol degradation capacity of a newly characterized Acinetobacter sp. SA01: Bacterial cell viability and membrane impairment in respect to the phenol toxicity

An efficient phenol-degrading bacterial strain, belonging to Acinetobacter genus, was isolated and selected to study the impact of different environmentally relevant phenol concentrations on the degradation process. The bacterial isolate, labeled as Acinetobacter sp. SA01 was able to degrade the maximum phenol concentration of 1 g/l during 60 h at optimum condition of pH 7, 30 °C and 180 rpm. Aeration and initial cell density, the two important factors, were carefully examined in the optimal growth conditions. The results showed that these two variables related proportionally with phenol degradation rate. Further investigations showed no effect of inoculum size on the enhancement of degradation of phenol at over 1 g/l. Flow cytometry (FCM) study was performed to find out the relationship between phenol-induced damages and phenol degradation process. Single staining using propidium iodide (PI) showed increased cell membrane permeability with an increase of phenol concentration, while single staining with carboxyfluorescein diacetate (cFDA) demonstrated a considerable reduction in esterase activity of the cells treated with phenol at more than 1 g/l. A detailed investigation of cellular viability using concurrent double staining of cFDA/PI revealed that the cell death increases in cells exposed to phenol at more than 1 g/l. The rate of cell death was low but noticeable in the presence of phenol concentration of 2 g/l, over time. Phenol at concentrations of 3 and 4 g/l caused strong toxicity in living cells of Acinetobacter sp. SA01. The plate count method and microscopy analysis of the cells treated with phenol at 1.5 and 2 g/l confirmed an apparent reduction in cell number over time. It was assumed that the phenol concentrations higher than 1 g/l have destructive effects on membrane integrity of Acinetobacter sp. SA01. Our results also revealed that the toxicity did not reduce by increasing initial cell density. Scanning electron microscopy (SEM) examination of bacterial cells revealed the surface morphological changes following exposure to phenol. The bacterial cells, with wizened appearance and wrinkled surface, were observed by exposing to phenol (1 g/l) at lag phase. A morphological change occurred in the mid-logarithmic phase as the bacterial cells demonstrated coccobacilli form as well as elongated filamentous shape. The wrinkled cell surface were totally disappeared in mid-stationary phase, suggesting that the complete degradation of phenol relieve the stress and direct bacterial cells toward possessing smoother cell membrane.

Sustainable biodegradation of phenol by immobilized Bacillus sp. SAS19 with porous carbonaceous gels as carriers

In this study, high-efficient phenol-degrading bacterium Bacillus sp. SAS19 which was isolated from activated sludge by resuscitation-promoting factor (Rpf) addition, were immobilized on porous carbonaceous gels (CGs) for phenol degradation. The phenol-degrading capabilities of free and immobilized Bacillus sp. SAS19 were evaluated under various initial phenol concentrations. The obtained results showed that phenol could be removed effectively by both free and immobilized Bacillus sp. SAS19. Furthermore, for degradation of phenol at high concentrations, long-term utilization and recycling were more readily achieved for immobilized bacteria as compared to free bacteria. Immobilized bacteria exhibited significant increase in phenol-degrading capabilities in the third cycle of recycling and reuse, which demonstrated 87.2% and 100% of phenol (1600 mg/L) degradation efficiency at 12 and 24 h, respectively. The present study revealed that immobilized Bacillus sp. SAS19 can be potentially used for enhanced treatment of synthetic phenol-laden wastewater.

Phenol degradation and genotypic analysis of dioxygenase genes in bacteria isolated from sediments

The aerobic degradation of aromatic compounds by bacteria is performed by dioxygenases. To show some characteristic patterns of the dioxygenase genotype and its degradation specificities, twenty-nine gram-negative bacterial cultures were obtained from sediment contaminated with phenolic compounds in Wuhan, China. The isolates were phylogenetically diverse and belonged to 10 genera. All 29 gram-negative bacteria were able to utilize phenol, m-dihydroxybenzene and 2-hydroxybenzoic acid as the sole carbon sources, and members of the three primary genera Pseudomonas, Acinetobacter and Alcaligenes were able to grow in the presence of multiple monoaromatic compounds. PCR and DNA sequence analysis were used to detect dioxygenase genes coding for catechol 1,2-dioxygenase, catechol 2,3-dioxygenase and protocatechuate 3,4-dioxygenase. The results showed that there are 4 genotypes; most strains are either PNP (catechol 1,2-dioxygenase gene is positive, catechol 2,3-dioxygenase gene is negative, protocatechuate 3,4-dioxygenase gene is positive) or PNN (catechol 1,2-dioxygenase gene is positive, catechol 2,3-dioxygenase gene is negative, protocatechuate 3,4-dioxygenase gene is negative). The strains with two dioxygenase genes can usually grow on many more aromatic compounds than strains with one dioxygenase gene. Degradation experiments using a mixed culture representing four bacterial genotypes resulted in the rapid degradation of phenol. Determinations of substrate utilization and phenol degradation revealed their affiliations through dioxygenase genotype data.

for phenol biodegradation by adaptive laboratory evolution

Microalgae are highly efficient photosynthesis cell factories for CO2 capture, biofuel productions and wastewater treatment. Phenol is a typical environmental contaminant. Microalgae normally have a low tolerance for, and a low degradation rate to, high concentration of phenol. Adaptive laboratory evolution was performed for phenolic wastewater treatment by Chlorella sp. The resulting strain was obtained after 31 cycles (about 95d) under 500mg/L phenol as environmental stress. It could grow under 500mg/L and 700mg/L phenol without significant inhibition. The maximal biomass concentrations of the resulting strain at day 8 were 3.40g/L under 500mg/L phenol and 2.70g/L under 700mg/L phenol, respectively. They were more than two times of those of the original strain. In addition, 500mg/L phenol was fully removed by the resulting strain in 7d when the initial cell density was 0.6g/L.

Electrical stimulation on biodegradation of phenol and responses of microbial communities in conductive carriers supported biofilms of the bioelectrochemical reactor

Conductive carbon felts (Cf) were used as biofilm carriers in bioelectrochemical reactors to enhance the electrical stimulation on treatment of phenol-containing synthetic wastewater. In batch test, phenol biodegradation was accelerated under an optimum direct current (DC), which was 2mA for Cf biofilm carriers, lower than that for non-conductive white foam carriers. The stimulation effect was consistent with Adenosine Triphosphate contents in biofilms. The long-term operation further demonstrated that a high and stable phenol removal efficiency could be achieved with applied DC of 2mA, and intermittent DC application was better than continuous one, with phenol removal efficiency of over 97%. Although the quantities of whole microbial communities kept at a high level under all conditions, special microorganisms related with genera of Zoogloea and Desulfovibrio were distinctively enriched under intermittent applied DC pattern. This study shows that the electrical stimulation is potentially effective for biofilm reactors treating phenol-containing wastewater.

Characteristics of phenol degradation in saline conditions of a halophilic strain JS3 isolated from industrial activated sludge

Several halophilic bacteria have been reported to degrade phenol. However, there are a few works about salt-tolerant fungi which can utilize phenol as sole source of carbon. In this study, a halophilic strain JS3 which could degrade phenol with high efficiency was separated and identified. The effect of initial phenol concentration on phenol biodegradation was investigated and optimal pH, temperature, as well as salt-tolerance were evaluated. The isolate could degrade less than 800 mg/L phenol completely in 72 h. It grew well when pH, temperature, and salinity were at values of 4.0-9.0, 30-40°C, and 0-7%, respectively. The optimal pH, temperature and salinity were 6.0, 35°C and 0%. More than 99% of 500 mg/L phenol was degraded in the optimal condition within 24h. The tolerance of wide range of pH, temperature and salinity indicated that strain JS3 was effective for phenol removal in hypersaline wastewaters.

The potential of autochthonous microbial culture encapsulation in a confined environment for phenol biodegradation

Olive mill wastewater (OMWW) is claimed to be one of the most polluting effluents produced by agro-food industries, providing high contaminants load that encase cytotoxic agents such as phenolic and polyphenolic compounds. Therefore, a significant and continuous stress episode is induced once the mixed liquor of the wastewater treatment plants (WWTP's) is being exposed to OMWW. The use of bio-augmentation treatment procedures can be useful to eliminate or reduce such stress episodes. In this study, we have estimated the use of autochthonous biomass implementation within small bioreactor platform (SBP) particles as a bio-augmentation method to challenge against WWTPs stress episodes. Our results showed that SBP particles significantly reduced the presence of various phenolics: tannic, gallic and caffeic acid in a synthetic medium and in crude OMWW matrix. Moreover, the SBP particles succeeded to biodegrade a very high concentration of phenol blend (3000 mg L(-1)). Our findings indicated that the presence of the SBP microfiltration membrane has reduced the phenol biodegradation rate by 50 % compared to the same suspended culture. Despite the observed reduction in biodegradation rate, encapsulation in a confined environment can offer significant values such as overcoming the grazing forcers and dilution, thus achieving a long-term sufficient biomass. The potential for reducing stress episodes caused by cytotoxic agents through bio-augmentation treatment procedure using the SBP technology is discussed.

Effects of a static magnetic field on phenol degradation effectiveness and Rhodococcus erythropolis growth and respiration in a fed-batch reactor

The aim of this study was to evaluate the impact of short-term repeated exposure to a static magnetic field (induction 370 mT) on the Rhodococcus erythropolis cells. Specifically, it was ascertained the magnetic field's potential to influence degradation of a phenol substrate, cell growth and respiration activity (oxygen consumption) during substrate biodegradation. The experiment took place over 3 days, with R. erythropolis exposed to the magnetic field for the first day. During the experiment, different recirculation rates between the reactor and the magnetic contactor has been tested. Use of the magnetic field at higher recirculation rates (residence time in contactor was less than 7 min) stimulated substrate (phenol) oxidation by around 34%; which, in turn, promoted R. erythropolis growth by around 28% by shortening the lag- and exponential-phases and increasing bacterial respiration activity by around 10%.