Maximum Biodegradation Rate Research Articles

Biodegradation behavior of poly (lactic acid) samples obtained by three‐dimensional printing: Influence of temperature and pigment presence

AbstractIn this study, the biodegradation behavior in the soil of natural and pigmented poly (lactic acid) (PLA) plates obtained by three‐dimensional (3D) printing or by compression molding was evaluated by the respirometry method at three different temperatures: 21, 28, and 35°C. PLA samples before and after aerobic biodegradation tests were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TG), and size exclusion chromatography analysis. The increase in test temperature enhanced the biodegradation process. At a test temperature of 35°C, the maximum biodegradation rates of natural PLA and pigmented PLA were 65% and 68% higher, respectively, compared to the maximum biodegradation rate observed at 21°C. DSC and TG analysis indicate that pigmented PLA samples were more susceptible to degradation by hydrolysis. However, the rate of biodegradation efficiency was lower in pigmented PLA samples, with a decrease of 16%, 24%, and 14% at 21, 28, and 35°C, respectively, compared to natural PLA. This behavior indicated that pigment hindered the hydrolysis by‐products absorption by microorganisms. Additionally, the presence of micro voids in PLA samples obtained through 3D printing accelerated the rate of biodegradation efficiency by 32% at 28°C compared to pressed samples.Highlights Poly (lactic acid) (PLA) plate biodegradation in soil was analyzed using respirometry method. Temperature, pigment presence, and sample preparation method were considered. Higher temperatures enhanced both natural and pigmented PLA biodegradation. Pigments appeared to act as antimicrobial agents, slowing down the process. Water presence in the micro voids accelerated hydrolysis and biodegradation.

Enhanced remediation of polyaromatic hydrocarbon using agro-industrial waste for biofuel production and environmental pollution mitigation.

In the present study, attention has been paid to the development of economically feasible strategies for enhanced remediation of anthracene and its conversion into biofuels. The strategies developed (B1, B2, B3, and B4) include bagasse and lipid-producing strain Rhodotorula mucilagenosa IIPL32 synthesizing surface active metabolites. The results indicate the highest production of surface-active metabolites in strategies B2, B3, and B4 along with a maximum biodegradation rate. GC-MS analysis affirmed the conversion of anthracene into phthalic acid in all the strategies. Biofuel quality of the lipid produced by the strain showed higher cetane number and improved cold flow property indicating the efficiency of the developed strategies for the production of commercial grade biodiesel. Furthermore, the phytotoxicity study of the spent wash revealed that 50% and 75% diluted spent wash were non-toxic and can be employed for ferti-irrigation. Thus, the study signifies the development of an economically feasible process that can be commercially employed in biofuel industries.

Biodegradation of Petroleum Sludge by Methylobacterium sp. Strain ZASH.

A bacterium was isolated from sludge-contaminated soil in a petroleum refinery and tested for its ability to degrade aliphatic hydrocarbon compounds present in petroleum sludge. The isolate was grown on minimal salt media agar supplemented with 1% (w/v) petroleum sludge. The isolate was tentatively identified as Methylobacterium s p. s t rain ZASH based on the partial 16s rDNA molecular phylogeny. The bacterium grew optimally between the temperatures of 30°C and 35°C, pH 7 and 7.5, 0.5% and 1.5% (v/v) Tween 80 as the surfactant, and between 1% and 2% (w/v) peptone as the nitrogen source. The constants derived from the Haldane equation were μmax = 0.039 hr-1, Ks = 0.385% (w/v) total petroleum hydrocarbons (TPH) or 3,850 mg/L TPH, and Ki =1.12% (w/v) TPH or 11,200 mg/L. The maximum biodegradation rate exhibited by this strain was 19 mg/L/hr at an initial TPH concentration of 10,000 mg/L. Gas chromatography analysis revealed that after 15 days the strain was able to degrade all aliphatic n-alkanes investigated with different efficiencies. Shorter n-alkanes were generally degraded more rapidly than longer n-alkanes with 90% removal for C-12 compared to only 30% removal for C-36. The addition of sawdust did not improve bacterial degradation of petroleum hydrocarbons, but it assisted in the removal of remaining undegraded hydrocarbons through adsorption.

Evaluation of scale-up effect on cold-active enzyme production and biodegradation tests using pilot-scale bioreactors and a 3D soil tank

Despite recent attention being paid to the biodegradation of petroleum hydrocarbons in cold environments, scale-up studies of biodegradation are lacking. Herein, the effect of scale-up on the enzymatic biodegradation of highly contaminated soil at low temperatures was studied. A novel cold-adapted bacteria (Arthrobacter sp. S2TR-06) was isolated that could produce cold-active degradative enzymes (xylene monooxygenase (XMO) and catechol 2,3-dioxygenase (C2,3D)). Enzyme production was investigated on 4 different scales (lab to pilot scale). The results showed a shorter fermentation time, and the highest production of enzymes and biomass (107 g/L for biomass, 109 U/mL, and 203 U/mL for XMO and C2,3D after 24 h) was achieved in the 150-L bioreactor due to enhanced oxygenation. Multi-pulse injection of p-xylene into the production medium was needed every 6 h. The stability of membrane-bound enzymes can be increased up to 3-fold by adding FeSO4 at 0.1% (w/v) before extraction. Soil tests also showed that biodegradation is scale-dependent. The maximum biodegradation rate decreased from 100% at lab-scale to 36% in the 300-L sand tank tests due to limited access of enzymes to trapped p-xylene in soil pores, low dissolved oxygen in the water-saturated zone, soil heterogeneity, and the presence of the free phase of p-xylene. The result demonstrated that formulation of enzyme mixture with FeSO4 and direct injection of enzyme mixture (third scenario) can increase the efficiency of bioremediation in heterogeneous soil. In this study, it was demonstrated that cold-active degradative enzyme production can be scaled up to an industrial scale and enzymatic treatment can be used to effectively bioremediate p-xylene contaminated sites. This study could provide key scale-up guidance for the enzymatic bioremediation of mono-aromatic pollutants in water-saturated soil under cold conditions.

Enhancements of mixed surfactants on Wucaiwan coal biodegradation by Nocardia mangyaensis

The use of surfactant to enhance the efficiency of coal biodegradation is a promising technology. In this paper, the effects of nonionic-anionic mixed surfactants TR-LAS and TW-LAS on Wucaiwan coal degradation by Nocardia mangyaensis (N. mangyaensis) were investigated, in which TR (octyl phenoxy poly ethoxy) and TW (polysorbate) were nonionic surfactants, and LAS (sodium dodecyl benzene sulfonate) was anionic surfactant. The results demonstrated the enhancement order of surfactant was TR-LAS > TW-LAS > TR > TW > LAS, and when the total mass of TR-LAS was 1000 mg/L and its ratio was 1200:800 (m/m), and the maximum biodegradation rate of Wucaiwan coal was 74.8% which increased by 23.6% than the control group (without surfactant). It was also found that nonionic surfactant TR was more effective than TW and LAS in promoting the growth of N. mangyaensis, meanwhile anionic surfactant LAS was more effective than TR and TW in increase the zeta potential of oxidized coal. The increase of bacterial growth will secrete more coal-degrading alkaline protease, and the increase of coal zata potential will make bacteria and coal contact easier, both of the above actions are conducive to biodegradation of coal. Thus, the mixed surfactants TR-LAS (1000 mg/L) achieved the strongest synergistic effect of nonionic and anionic surfactants, greatly promoting the biodegradation of coal. This study provides valuable information in designing the mixed surfactant to improve the efficiency of coal biodegradation process.

Simultaneous removal of carbon, nitrogen, and phosphorus from landfill leachate using an aerobic granular reactor

In this study, aerobic granular reactor (AGR) was used to treat landfill leachate by changing the concentrations of chemical oxygen demand (COD) (668 ± 110-1149 ± 93 mg/L), ammonia (NH 3 –N) (30 ± 3.3-48 ± 1.3 mg/L), and phosphorus (PO 4 –P) (147 ± 18-221 ± 17 mg/L). The average COD removal was gradually reduced from 81 to 75%, increasing COD concentrations from 668 ± 110 to 1149 ± 93 mg/L. In phase I, the maximum removal of COD (94%) and NH 3 –N (85%) were observed at influent concentrations of 668 ± 110 mg/L and 30 ± 3.3 mg/L, respectively. Significant removal of PO 4 –P was observed, resulting in a maximum of up to 87%, further reducing up to 34% due to an increase in influent PO 4 –P concentration. The SVI 30 reduced from 77 mL/g to 24.15 mL/g towards the end of phase III indicates the formation of granular biomass. The stability of AGR was also investigated in extreme conditions like shut-down and shock-loading phases. The treatment of real leachate diluted with wastewater ( ∼ 20:80% v/v) in AGR showed a significant COD, NH 3 –N, and PO 4 –P removal of 62%–65%, 61%–93%, and 56%–64%, respectively. Mass balance analysis indicated that the AGR requires a lower nitrogen percentage for microbial assimilation than the COD and phosphorus. Proteobacteria and Planctomycetes were identified as the predominant (80%) bacterial community in aerobic granules responsible for removing COD, NH 3 –N, and PO 4 –P from leachate using AGR. The maximum biodegradation rate ( r max ) and half-saturation constant ( K s ) of COD in AGR were determined as 123.5 mg/L h and 309 mg/L, respectively. • Aerobic Granular Reactor (AGR) successfully treated landfill leachate. • Carbon, nitrogen, and phosphorus simultaneously removed using AGR. • A decrease in sludge volume index (SVI 30 ) indicates granule formation. • AGR showed better performance at higher shock loading of leachate. • Proteobacteria and Planctomycetes are predominant species in AGR.

Superior dimethyl disulfide degradation in a microbial fuel cell: Extracellular electron transfer and hybrid metabolism pathways

To enhance the biological degradation of volatile organic sulfur compounds, a microbial fuel cell (MFC) system with superior activity is developed for dimethyl disulfide (DMDS) degradation. The MFC achieves a removal efficiency near 100% within 6 h (initial concentration: 90 mg L−1) and a maximum biodegradation rate constant of 0.743 mM h−1. The DMDS removal load attains 2.684 mmol h−1 L−1, which is 6.18–2440 times the loads of conventional biodegradation processes reported. Meanwhile, the maximum power density output and corresponding current density output are 5.40 W m−3 and 40.6 A m−3, respectively. The main mechanism of extracellular electron transfer is classified as mediated electron transfer, supplemented by direct transfer. Furthermore, the mass balance analysis indicates that methanethiol, S0, S2−, SO42−, HCHO, and CO2 are the main intermediate and end products involved in the hybrid metabolism pathway of DMDS. Overall, these findings may offer basic information for bioelectrochemical degradation of DMDS and facilitate the application of MFC in waste gas treatment. Environmental implicationDimethyl disulfide (DMDS), which features poor solubility, odorous smell, and refractory property, is a typical pollutant emitted from the petrochemical industry. For the first time, we develop an MFC system for DMDS degradation. The superior DMDS removal load per unit reactor volume is 6.18–2440 times those of conventional biodegradation processes in literature. Both the electron transfer route and the hybrid metabolism pathway of DMDS are cleared in this work. Overall, these findings give an in-depth understanding of the bioelectrochemical DMDS degradation mechanism and provide an efficient alternative for DMDS removal.

Efficient biodegradation of phenol at high concentrations by Acinetobacter biofilm at extremely short hydraulic retention times

Efficient biofilm-forming bacteria are crucial for biofilm wastewater treatment reactors. Nevertheless, finding a suitable bacterial culture with high biodegradation capabilities and ability to grow a stable and effective biofilm that can survive the reactor environment poses a challenge. Here, we present a newly isolated bacterium Acinetobacter EMY that exhibits excellent growth rate, biofilm formation capability, and ability to biodegrade phenol at high concentrations. The phenol degradation rate of Acinetobacter EMY immobilized on polyethylene biocarriers in batch and continuous moving bed bioreactors (MBBRs) treated with phenol as the sole carbon source was significantly higher than that of a bacterial suspension. The continuous MBBR demonstrated impressive phenol removal rates (8.11 and 10.95 kg/m3/d at extremely short hydraulic retention times of 0.5 and 0.25 h, respectively). The phenol removal efficacy was 100% for hydraulic retention times of ≥0.5 h and 67.25% at 0.25 h. The Acinetobacter EMY biofilm batch bioreactor loaded with 165, 330, 665, 1150, and 2100 mg/L phenol achieved the maximum biodegradation rates of 7.65, 7.03, 9.15, 4.48, and 4.16 kg/m3/d, respectively. The new Acinetobacter EMY isolate showed enhanced phenol biodegradation capabilities compared with other isolates in similar studies. Chemical oxygen demand measurements proved that Acinetobacter EMY also consumed the intermediates of phenol degradation. In summary, Acinetobacter EMY is a promising bacterium for use in MBBR systems that treat water containing phenols.

Development of Biodegradable Cigarette Filter Material from Micro-fibers (Part 2) : Fabrication of Cigarette Filter and its Characteristics

Cellulose acetate, a raw material for cigarette filters, causes significant environmental pollution because it is not easily decomposed in nature. Thus, various efforts have been made to develop eco-friendly filter materials from biomass that can replace cellulose acetate. A cross-linking approach between polymeric chains in a polymer creates a three-dimensional mesh network and the resulting material could be used as a filter material. In this study, to create such a mesh structure, non-toxic glycerol diglycidyl ether was used as a cross-linking agent with five different microfibers having different particle sizes and lignin contents. The morphological, mechanical and physical properties of the cross-linked filters produced were characterized to identify the most suitable raw materials for cigarette filter production. The mesh structure of E-CNF (enzyme-cellulose nanofibrils) revealed the maximum strength properties whereas KOP (kneaded organosolv pulp) produced a better structure in water-holding and recovery abilities with different pore formations. In the 72 h enzymatic biodegradation test, a commercial cigarette filter revealed a 6.5% weight loss but L-MFC (lignin rich-microfibrillated cellulose) showed the maximum biodegradation rate of 74.7%. In addition, filter structures with E-CNF, KOP and L-MFC revealed remarkable cadmium adsorption properties. These results indicated that the pore structure from cross-linked microfibers can be used as filter material.

Impacts of bioreactor operating parameters on removal efficiency, biodegradation rate, molecular distribution, and toxicity of commercial naphthenic acids.

Effects of naphthenic acids (NAs) concentration (50-200mg NA L-1; 35-140mg TOC L-1) and loading rate (1.4-1249mg NA L-1h-1; 1-874mg TOC L-1h-1) on removal efficiency, removal rate, and molecular distribution of NAs, and effluent toxicity were evaluated for biodegradation of commercial NAs mixture in circulating packed bed bioreactors (CPBBs). Increase of NAs concentration and loading rate (shorter residence times) increased the removal rate, while removal efficiency initially declined and then stabilized. The maximum biodegradation rates for 50, 100, 150, and 200mg NA L-1 were 128.0, 321.7, 430.2, and 630.0mg TOC L-1h-1 at loading rates of 218.5, 455.6, 673.5 and 874.0mg TOC L-1h-1, respectively, with removal efficiencies of 58.6, 70.6, 63.9 and 72.1%. Analysis of influent and treated effluents with gas chromatography-mass spectrometry showed that molecular weight and cyclicity (C and Z numbers) affected the biodegradation, with low molecular weight acyclic NAs (C = 6-12) were the most amenable to biodegradation and those with intermediate and high molecular weights (C = 13-22) and moderate cyclicity (Z = -4, -6) were the most recalcitrant. In the biofilm, Proteobacteria and Actinobacteria were the most abundant phyla, and Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria were the dominant classes. Toxicity analyses with Artemia salina and Vibrio fischeri (Microtox) showed that high influent concentrations and loading rates (short residence times) led to higher NAs residual concentration and effluent toxicity. To design and operate large-scale CPBBs, intermediate loading rates and residence times that result in high removal efficiency, reasonable removal rates, and low toxicity are recommended.

Treatment of domestic sewage and leachate using a moving bed hybrid bioreactor

The treatment of domestic sewage using a moving bed hybrid bioreactor (MBHBR) was investigated by varying the concentrations of chemical oxygen demand (COD) (156 ± 14-1141 ± 78 mg/L), ammonia (NH3-N) (2 ± 0.08-48.24 ± 0.93 mg/L), phosphorus (PO4-P) (97 ± 3.2-281 ± 2.65 mg/L), and hydraulic retention times (HRTs). Initially, the reactor was operated at start-up mode (COD: 156 ± 14 mg/L), and gradually the COD concentrations were increased from phase-I (257 ± 24 mg/L) to phase-V (1141 ± 78 mg/L) by reducing the HRTs from 48 to 3 h. A significant improvement in COD removal, maximum up to 96%, was observed at a concentration of 858 ± 51 mg/L (phase-IV), then a sudden drop up to 81% was observed at a higher concentration of 1141 ± 78 mg/L (phase-V). Due to the increase in COD concentrations, average NH3-N removal was dropped from 85 to 32% from phase-I to Phase-V, respectively. In addition, the stability of MBHBR was studied to understand its performance in shut-down and shock loading phases. The co-treatment of sewage and leachate was also performed in MBHBR (COD: 864-881 mg/L and HRT: 6 h), which showed a COD removal of 77%–80% and NH3-N removal of 60%–94%. Proteobacteria was identified as a predominant species in MBHBR, which played a significant role in the co-treatment of sewage and leachate. The maximum biodegradation rate (rmax) and half-saturation constant (Ks) were estimated as 13.3 mg/L h and 361.8 mg/L, respectively.

Characterization and biocompatibility evaluation of artificial blood vessels prepared from pristine poly (Ethylene-glycol-co-1,4-cyclohexane dimethylene-co-isosorbide terephthalate), poly (1, 4 cyclohexane di-methylene-co-isosorbide terephthalate) nanofibers and their blended composition

Herein, we prepared three-dimensional artificial blood vessels (ABV) from electrospun pristine Poly (Ethylene-glycol-co-1,4-Cyclohexane di-methylene-co-isosorbide terephthalate) (PEICT), Poly (1, 4 cyclohexane di-methylene-co-isosorbide terephthalate) (PICT) and their blend (BLEND) nanofibers for the first time with three different cross-sectional diameters (0.9, 1.5 and 2.0) mm. Biocompatibility was evaluated by culturing Human Breast Epithelial Cells (MCF-10A) on all samples. Interestingly, collective properties of PICT and PEICT were distinctively imparted onto the surface of BLEND ABVs without reliance upon any special surface treatment. BLEND showed an enhanced wettability and a smooth and compacted morphology making them suitable to hold more (MCF-10A) cells compared to pristine PICT and PEICT. Additionally, BLEND achieved a maximum biodegradation rate as well as the special feature of tensile strength tunability, which reveals its potential and suitability for vascular regeneration and cell culture applications.

Biodegradation of surrogate naphthenic acids and electricity generation in microbial fuel cells: bioelectrochemical and microbial characterizations.

Waters contaminated with naphthenic acids (NAs) and associated tailings are one of the major environmental challenges associated with the processing of oil sands and production of heavy oil. In the current work biodegradation of linear and cyclic naphthenic acids, namely octanoic acid and 4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), individually and in mixture were evaluated in microbial fuel cells (MFCs). In batch MFCs with single rod electrodes and freely suspended bacteria, biodegradation rate increased as NA initial concentration increased from 100 to 250mg L-1 with no further improvement when a concentration of 500mg L-1 was evaluated. During the co-biodegradation, diauxic microbial growth and preferential use of octanoic acid were observed. Moreover, the presence of octanoic acid enhanced the biodegradation of trans-4MCHCA. In the continuous flow MFCs with granular graphite electrodes and biofilm, increases in NA concentration and loading rate led to higher biodegradation rates and improvement of electrochemical output. Furthermore, MFC operated with octanoic acid outperformed its counterpart that was fed with trans-4MCHCA, with the maximum biodegradation rate, current and power densities for octanoic acid and trans-4MCHCA being 49.9 and 36.5mg L-1 h-1, 6000.0 and 4296.3mA m-3, and 963.0 and 481.5mW m-3, respectively. Co-biodegradation of NAs in continuous flow MFCs with biofilm acclimated to octanoic acid or trans-4MCHCA revealed development of distinctly different microbial communities, simultaneous biodegradation of NAs albeit at faster rates for octanoic acid, and superior performance of MFC with the biofilm developed with trans-4MCHCA.

Biodegradation of ethylthionocarbamates by a mixed culture of iron-reducing bacteria enriched from tailings dam sediments

Ethylthionocarbamates (ETC), which is the most widely used as collectors in the flotation of sulfide, is known to cause serious pollution to soil and groundwater. The potential biodegradation of ETC was evaluated by applying a mixed culture of iron-reducing bacteria (IRB) enriched from tailings dam sediments. The results showed that ETC can be degraded by IRB coupled to Fe(III) reduction, both of which can be increased in the presence of anthraquinone-2,6-disulfonate (AQDS). Moreover, Fe(III)-EDTA was found to be a more favorable terminal electron acceptor compared to α-Fe2O3, e.g., within 30 d, 72% of ETC was degraded when α-Fe2O3+AQDS was applied, while it is 82.67% when Fe(III)-EDTA+AQDS is added. The dynamic models indicated that the kETC degradation was decreased in the order of Fe(III)-EDTA+AQDS>α-Fe2O3+AQDS>Fe(III)-EDTA>α-Fe2O3, with the corresponding maximum biodegradation rates being 2.6, 2.45, 2.4 and 2.0 mg/(L.d), respectively, and positive parallel correlations could be observed between kFe(III) and kETC. These findings demonstrate that IRB has a good application prospect in flotation wastewater.

Biodegradation rate of biodegradable plastics at molecular level

Plastics are solid materials where biodegradation happens on the surface. Only the surface is affected by biodegradation while the inner part should not be readily available for biodegradation. Thus, at a laboratory level, the biodegradation rate is expected to be a function of the surface area of the tested sample. The higher the surface area, the higher the biodegradation rate, all other environmental conditions being equal. In order to further explore the role of particle size on biodegradability, plastic pellets of polybutylene sebacate were milled and sieved into different particle sizes, thus obtaining four samples, pellets included, with different specific surface areas (33, 89, 193, and 824 cm2g-1). The surface areas were assessed through direct measurement (pellets) or a theoretical estimation followed by an image analysis. The different samples were tested for biodegradation in soil for 138 days. The rates calculated with a linear regression in the first part of the biodegradation process were related to the respective total available surface area. The data are well described by a linear regression of the double reciprocal plot (the Lineweaver-Burk approach used in enzymatic kinetics) that enables the estimation of the theoretical maximum biodegradation rate (kmax = 97 mg Cpolymer day−1). The kmax can be considered as an estimation of the biodegradation rate at molecular level, when the available surface area is not limiting biodegradation. An additional hypothesis is that the same polymer tested in soils with different microbial loads would display different kmax. The Michaelis constant (Km), i.e. the surface area at which the reaction rate k is half the maximum rate, is 1122 cm2. It is remarkable to notice that if polybutylene sebacate could be tested in a nanopolymeric form, it could very likely satisfy the Organization for Economic Co-operation and Development (OECD) criteria of “ready biodegradability” for chemicals (e.g. 60% biodegradation in a 10-day window within a 28-day test). This is the first time that the biodegradation kinetics of a solid polymer have been estimated by using the Michaelis-Menten approach.

Biodegradation of phenol in batch and continuous flow microbial fuel cells with rod and granular graphite electrodes

ABSTRACTPhenol biodegradation was evaluated in batch and continuous flow microbial fuel cells (MFCs). In batch-operated MFCs, biodegradation of 100–1000 mg L−1 phenol was four to six times faster when graphite granules were used instead of rods (3.5–4.8 mg L−1 h−1 vs 0.5–0.9 mg L−1 h−1). Similarly maximum phenol biodegradation rates in continuous MFCs with granular and single-rod electrodes were 11.5 and 0.8 mg L−1 h−1, respectively. This superior performance was also evident in terms of electrochemical outputs, whereby continuous flow MFCs with granular graphite electrodes achieved maximum current and power densities (3444.4 mA m−3 and 777.8 mW m−3) that were markedly higher than those with single-rod electrodes (37.3 mA m−3 and 0.8 mW m−3). Addition of neutral red enhanced the electrochemical outputs to 5714.3 mA m−3 and 1428.6 mW m−3. Using the data generated in the continuous flow MFC, biokinetic parameters including μm, KS, Y and Ke were determined as 0.03 h−1, 24.2 mg L−1, 0.25 mg cell (mg phenol)−1 and 3.7 × 10−4 h−1, respectively. Access to detailed kinetic information generated in MFC environmental conditions is critical in the design, operation and control of large-scale treatment systems utilizing MFC technology.

Efficient degradation of chlorimuron-ethyl by a bacterial consortium and shifts in the aboriginal microorganism community during the bioremediation of contaminated-soil

Excessive application of chlorimuron-ethyl has led to soil contamination and limited crop rotation; therefore, tactics to decrease and eliminate residual chlorimuron-ethyl in the environment have attracted increasing attention. In this study, two chlorimuron-ethyl-degrading bacterial strains (Rhodococcus sp. D310-1; Enterobacter sp. D310-5) were used to ferment and prepare a chlorimuron-ethyl-degrading bacterial consortium. To improve the degradation efficiency of the bacterial consortium, the cultivation conditions were optimized using response surface methodology (RSM). The maximum biodegradation rate (87.42%) was obtained under optimal conditions (carbon concentration, 9.21gL−1; temperature, 26.15°C; pH, 6.95). The rate of chlorimuron-ethyl degradation by the bacterial consortium in the chlorimuron-ethyl-contaminated soil was monitored and reached 80.02% at the end of a 60-d incubation period. Illumina MiSeq sequencing results showed that microbial diversity was high, and 33 phyla were identified in the analyzed samples. Proteobacteria, Acidobacteria, Acidobacteria, Firmicutes and Bacteroidetes were present in relatively high abundances in the samples. The bacterial consortium made a positive impact on the remediation of chlorimuron-ethyl-contaminated soil and somewhat altered the composition of the bacterial community in the chlorimuron-ethyl-contaminated soil. These findings provide highly valuable information on the production of bacterial consortium for the remediation of chlorimuron-ethyl and other sulfonylurea-herbicide-contaminated soil.

Biodegradation of the endocrine disrupter 4-tert-octylphenol by the yeast strain Candida rugopelliculosa RRKY5 via phenolic ring hydroxylation and alkyl chain oxidation pathways

4-(1,1,3,3-tetramethylbutane)-phenol (4-tert-OP) is one of the most prevalent endocrine disrupting pollutants. Information about bioremediation of 4-tert-OP remains limited, and no study has been reported on the mechanism of 4-tert-OP degradation by yeasts. The yeast Candida rugopelliculosa RRKY5 was proved to be able to utilize 4-methylphenol, bisphenol A, 4-ethylphenol, 4-tert-butylphenol, 4-tert-OP, 4-tert-nonylphenol, isooctane, and phenol under aerobic conditions. The optimum conditions for 4-tert-OP degradation were 30°C, pH 5.0, and an initial 4-tert-OP concentration of 30mgL−1; the maximum biodegradation rate constant was 0.107d−1, equivalent to a minimum half-life of 9.6d. Scanning electron microscopy revealed formation of arthroconidia when cells were grown in the presence of 4-tert-OP, whereas the cells remained in the budding form without 4-tert-OP. Identification of the 4-tert-OP degradation metabolites using liquid chromatography–hybrid mass spectrometry revealed three different mechanisms via both branched alkyl side chain and aromatic ring cleavage pathways.

Concurrent microbial reduction of high concentrations of nitrate and perchlorate in an ion exchange membrane bioreactor.

We investigated effective simultaneous removal of high loads of nitrate and perchlorate from synthetic groundwater using an ion exchange membrane bioreactor (IEMB). The aim of this research was to characterize both transport aspects and biodegradation mechanisms involved in the treatment process of high loads of the two anions. Biodegradation process was proven to be efficient with over 99% efficiency of both perchlorate and nitrate, regardless of their load. The maximum biodegradation rates were 18.3 (mmol m(-2) h(-1) ) and 5.5 (mmol m(-2) h(-1) ) for nitrate and perchlorate, respectively. The presence of a biofilm on the bio-side of the membrane only slightly increased the nitrate and perchlorate transmembrane flux as compared to the measured flux during a Donnan dialysis experiment where there is no biodegradation of perchlorate and nitrate in the bio-compartment. The nitrate flux in presence of a biofilm was 18.3 (±1.9) (mmole m(-2) h(-1) ), while without the biofilm, the flux was 16.9 (±1.5) (mmole m(-2) h(-1) ) for the same feed inlet nitrate concentration of 4 mM. The perchlorate transmembrane flux increased similarly by an average of 5%. Samples of membrane biofilm and suspended bacteria from the bio-reactor were analyzed for diversity and abundance of the perchlorate and nitrate reducing bacteria. Klebsiella oxytoca, known as a glycerol fermenter, accounted for 70% of the suspended bacteria. In contrast, perchlorate and nitrate reducing bacteria predominated in the biofilm present on the membrane. These results are consistent with our proposed two stage biodegradation mechanism where glycerol is first fermented in the suspended phase of the bio-reactor and the fermentation products drive perchlorate and nitrate bio-reduction in the biofilm attached to the membrane. These results suggest that the niche exclusion of microbial populations in between the reactor and membrane is controlled by the fluxes of the electron donors and acceptors. Such a mechanism has important implications for controlling the bio-reduction reaction in the IEMB when using glycerol as a carbon source and allowing treating a complex contamination of high concentrations of perchlorate and nitrating in groundwater and successfully biodegrading them to non-hazardous components. Biotechnol. Bioeng. 2016;113: 1881-1891. © 2016 Wiley Periodicals, Inc.

Anoxic biodegradation of a surrogate naphthenic acid coupled to reduction of nitrite

Large volumes of waters contaminated with naphthenic acids (NAs) are produced during the processing of oil sands. Anoxic biodegradation of trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA) coupled to nitrate reduction was reported earlier. Given the generation of nitrite as an intermediate of nitrate reduction, its subsequent use as secondary electron acceptor and its potential inhibitory effect, biodegradation of trans-4MCHCA coupled to nitrite reduction was investigated in the current work.Batch experiments revealed the optimum temperature as 24±2°C and that the nitrite inhibitory effect was severe at 1150mg nitrite L−1. Maximum biodegradation rates in the stirred tank and biofilm reactors were 14.4 and 82.2mgL−1h−1, and the corresponding nitrite reduction rates were 44.2 and 361.6mgL−1h−1, respectively. Using the experimental data, maximum specific growth rate (μm), saturation constant (Ks), and yield (Y) were determined as 0.4h−1, 20.9mg trans-4MCHCA L−1, and 0.3mg biomass (mg trans-4MCHCA)−1, respectively. Comparison of anoxic biodegradation results with nitrate and nitrite demonstrated the superiority of nitrate as an electron acceptor for anoxic biodegradation of NAs.