Degradation of vinyl acetate by soil, sewage, sludge, and the newly isolated aerobic bacterium V2

Removal kinetics of vinyl acetate under aerobic and anoxic conditions in a batch bioreactor

Vinyl acetate is a volatile organic compound widely used in the chemical industry, and there is a need for effective and economic removal of this volatile organic compound from wastewater and waste gases in chemical industries. This study aims to determine the biological treatability of vinyl acetate both under aerobic and anoxic conditions using mixed cultures obtained from a wastewater treatment plant. Considering the previous studies in the literature, testing the biodegradability of vinyl acetate under both aerobic and anoxic conditions, together with evaluating the effect of other mechanisms, such as adsorption and volatilization, on the removal of vinyl acetate, can be regarded as the prominent part of this study. Wastewater containing artificially prepared vinyl acetate was treated in a batch bioreactor, and performance and kinetic constants were investigated. Aerobic treatment under batch conditions conformed to the Haldane biokinetic equation, and the biokinetic constants of μmax, Ks, and Ki were calculated as 0.66 h-1, 19.67 mg L-1 and 50.56 mg L-1, respectively. Anoxic treatment under batch conditions conformed to the Monod biokinetic equation, and the biokinetic constants of μmax and Ks were calculated as 0.31 h-1 and 33.88 mg L-1, respectively. Experiments revealed that vinyl acetate was not volatile, and its adsorption and biological treatment performances were 28% and 72%, respectively. The mixed culture had a very high performance for removing vinyl acetate under batch operating conditions. The primary mechanism of vinyl acetate removal was found to be biological treatment.

Influence of oxygen on the vinyl acetate elimination pathway and microbial community structure of methanogenic sludge

Methanogenic-aerobic coupled processes were used to biological degradation of vinyl acetate (VA) to provide evidence of oxygen role for their complete elimination from different angles. First, physiological characterization of a continuous methanogenic-aerobic reactor fed by VA and glucose (G) showed that by adding G, the VA got 100% hydrolyzed to acetate, and then, by adding 1 mg·L^-1 ·d^-1 of dissolved oxygen (DO), this acetate got methanized by 40% and aerobically mineralized by 60%. Second, batch assays in the presence and absence of sodium azide suggest that VA at different concentrations was eliminated by both anaerobic and aerobic metabolic pathways, because without azide and in the presence of 1 mg DO·L^-1 increased methane and carbon dioxide formation rates at 80% and 75%, respectively. Finally, microbial population dynamics analysis of the reactor by DGGE-sequencing highlighted that Brevibacillus agri (aerobic) and Methanosarcina barkeri (anaerobic) were identified as responsible for VA elimination by up to 98.6%. PRACTITIONER POINTS: Vinyl acetate is removed by simultaneous methanation and aerobic respiration. Methanosarcina barkeri and Brevibacillus agri removed up to 99% of vinyl acetate. DO and VA have a selective effect on the metabolism and population dynamics.

Can shielded brackets reduce mucosa alteration and increase comfort perception in orthodontic patients in the first 3 days of treatment? A single-blind randomized controlled trial

INTRODUCTION

Orthodontic patients can experience pain and discomfort on the oral mucosa from trauma caused by friction with the brackets and the wires. In this split-mouth design, single-blind randomized controlled trial, we aimed to investigate whether brackets with a self-snapping customized plastic shield would induce less mucosa alteration and discomfort than those without the shield.

METHODS

The overall sample comprised 42 patients (22 female, 20 male) from a government-funded orthodontic practice, with a mean age of 16.7 years. Eligibility criteria included, among others, no history of mouth ulcers or systemic diseases. Customized shields for the maxillary and mandibular brackets were fabricated and inserted on one side of the mouth. The null hypothesis was that bracket shielding would have no advantage. The primary outcomes were mucosal and discomfort assessments. As the secondary outcome, the numbers of spontaneous detachments of the shields were reported. Treatment allocation was mainly implemented using a random number table for selection of the intervention side. Only the raters in charge of assessing the oral mucosa were blinded to the side of the mouth where the shields had been placed. The mucosa was assessed by 3 calibrated raters at the following time points: immediately before bracket placement (baseline assessment, T0), 3 days after delivering the shields (direct assessment of intervention, T1), and 4 days after removal of the shields (indirect assessment of intervention, T2). The raters used a newly devised yardstick in which the higher the score, the more severe the alteration. Discomfort was assessed at T1 and T2 using a visual analog scale. The Mann-Whitney U test was performed at the 5% level of significance.

RESULTS

Of 60 patients, 42 were eligible, and 35 were randomly selected to have one side of the mouth receive the intervention. Two patients discontinued the intervention at T1, and 5 stopped at T2. Seven additional patients were recruited and completed all time points. Thus, 42 patients participated at T0, 40 at T1, and 35 at T2. Thirty-five patients participated at all time points. At T1, no statistically significant difference in terms of mucosa alteration was observed between the 2 sides (median of all differences [MD], 0.0; 95% CI, 0.0-1.0; P = 0.11). The same occurred at T2 (MD, 0.0; 95% CI, 0.0-0.0; P = 1.00). The comfort level was statistically higher at T1 on the shielded side (MD, 14.0; 95% CI, 1.0-36.0; P = 0.04), whereas no difference was observed at T2 (MD, 0.0; 95% CI, 0.0-1.0, P = 0.81). No serious harm was observed.

CONCLUSIONS

The customized bracket shields were effective in reducing discomfort during the first 3 days of orthodontic treatment despite no significant difference in terms of visible mucosa alteration.

REGISTRATION

This trial was not registered.

PROTOCOL

The protocol was not published before trial commencement.

FUNDING

Expenses for the fabrication of the shields were covered by the main author (L.P.B.P.). Orthodontic materials were from the Center for Dental Specialties in Cajazeiras, Brazil.

Enzymes involved in vinyl acetate decomposition by Pseudomonas fluorescens PCM 2123 strain

Esterases are widely used in food processing industry, but there is little information concerning enzymes involved in decompositions of esters contributing to pollution of environment. Vinyl acetate (an ester of vinyl alcohol and acetic acid) is a representative of volatile organic compounds (VOCs) in decomposition, of which hydrolyses and oxidoreductases are mainly involved. Their activities under periodically changing conditions of environment are essential for the removal of dangerous VOCs. Esterase and alcohol/aldehyde dehydrogenase activities were determined in crude cell extract from Pseudomonas fluorescens PMC 2123 after vinyl acetate induction. All examined enzymes exhibit their highest activity at 30–35 °C and pH 7.0–7.5. Esterase preferably hydrolyzed ester bonds with short fatty chains without plain differences for C₂ or C₄. Comparison of Km values for alcohol and aldehyde dehydrogenases for acetaldehyde suggested that this metabolite was preferentially oxidized than reduced. Activity of alcohol dehydrogenase reducing acetaldehyde to ethanol suggested that one mechanism of defense against the elevated concentration of toxic acetaldehyde could be its temporary reduction to ethanol. Esterase activity was inhibited by phenylmethanesulfonyl fluoride, while β-mercaptoethanol, dithiothreitol, and ethylenediaminetetraacetic acid had no inhibitor effect. From among metal ions, only Mg²⁺ and Fe²⁺ stimulated the cleavage of ester bond.

A comparative study of biodegradation of vinyl acetate by environmental strains

Four Gram-negative strains, E3_2001, EC1_2004, EC3_3502 and EC2_3502, previously isolated from soil samples, were subjected to comparative studies in order to select the best vinyl acetate degrader for waste gas treatment. Comparison of biochemical and physiological tests as well as the results of fatty acids analyses were comparable with the results of 16S rRNA gene sequence analyses. The isolated strains were identified as Pseudomonas putida EC3_2001, Pseudomonas putida EC1_2004, Achromobacter xylosoxidans EC3_3502 and Agrobacterium sp. EC2_3502 strains. Two additional strains, Pseudomonas fluorescens PCM 2123 and Stenotrophomonas malthophilia KB2, were used as controls. All described strains were able to use vinyl acetate as the only source of carbon and energy under aerobic as well as oxygen deficiency conditions. Esterase, alcohol dehydrogenase and aldehyde dehydrogenase were involved in vinyl acetate decomposition under aerobic conditions. Shorter degradation times of vinyl acetate were associated with accumulation of acetic acid, acetaldehyde and ethanol as intermediates in the culture fluids of EC3_2001 and KB2 strains. Complete aerobic degradation of vinyl acetate combined with a low increase in biomass was observed for EC3_2001 and EC1_2004 strains. In conclusion, P. putida EC1_2004 is proposed as the best vinyl acetate degrader for future waste gas treatment in trickle-bed bioreactors.

The effect of vinyl acetate in acetoclastic methanogenesis

The influence of vinyl acetate (VA) in the methanogenesis was evaluated, by using an upflow anaerobic sludge blanket reactor of 1.5L. The reactor was operated at 33.5 g/L volatile suspended solids to 30±2 °C, a hydraulic residence time of 1 day, an organic loading rate of 1 kgCOD/m3/d of two different mixtures of VA and glucose. The VA was methanized to 81% when its proportion was of 10% into reactor loading rate, when VA proportion increased to 25%, the methane production rate decreased to 62% and the acetate production rate increased almost 8 times. These results indicated that VA was only hydrolyzed and glucose was not used as a co-substrate. The effect of glucose on VA methanogenic degradation was evaluated through batch reactors of 60 mL, concluding that the glucose supported the methanogenesis without favoring the VA elimination. On the other hand, the results of the sludge from the reactor in the presence of VA demonstrated that VA caused an irreversibly inhibition of acetoclastic methanogenesis when the anaerobic sludge was exposed to this compound.

Vinyl acetate degradation by Brevibacillus agri isolated from a slightly aerated methanogenic reactor

In a previous paper, the authors showed that a slight aeration of a methanogenic reactor treating wastewater from the manufacture of polymeric resins could improve its performance, by increasing or allowing the removal of some of its contaminants, including vinyl acetate (VA). This paper reports the isolation under aerobic conditions of a VA-biodegrading axenic culture (strain C1) retrieved from the sludge of a slightly aerated methanogenic reactor at 1 mg L(-1) d(-1) of dissolved oxygen (DO). The axenic culture obtained was phenotypically (morphology, biochemical properties, VA consumption kinetics) and phylogenetically characterized. It formed white colonies with a branched and flat morphology on solid medium. The cell morphology of the isolate was bacillus with round endings and flagellate. The cells could form chains and were stained Gram-negative. The isolate required simple nutritional elements and had a growth rate of 0.024 h(-1). The phylogenetical analysis showed that the aerobic bacterium was identified as Brevibacillus agri, with 99.3% similarity. The VA consumption kinetics in the methanogenic sludge were: volumetric consumption rate (rVA) of 1.74 +/- 0.2 mg L(-1) h(-1), maximum specific consumption rate (qVAmax) of 3.98 mg g(-1) volatile suspended solids (VSS) h(-1) and affinity constant (Ks) of 457.1 mg L(-1). The same parameters in the axenic culture were 1.69 +/- 0.04 mg L(-1) (h-1), 4.09 mg g(-1) dry weight h(-1) and 421.9 mg L(-1), respectively. These results show evidence that the aerobic isolated bacterium, identified as Brevibacillus agri, carried out the VA hydrolysis in the slightly aerated methanogenic sludge, which is the limiting step in the degradation of this compound.

Physical and chemical aspects of long-term biodeterioration of some polymers and composites

A biodeterioration study was performed on synthetic polymeric materials including homogenous film made from poly(tetrafluorine ethylene), copolymer film made from tetrafluorine ethylene and perfluoromethyl vinyl ether, vulcanized rubber containing natural caoutchouc, and vulcanized rubber, the main component of which was synthetic butadiene nitrile caoutchouc. The materials were exposed for 12 years to the open air, in mycological containers, and in a cellar in maritime climate conditions: air humidity 72%-90% and seasonal average temperature of 17 degrees C in summer and -2.5 degrees C in winter. The studies of optical and electron microscopy revealed that microorganisms were able to develop not only on the surface of the materials but also to penetrate inside into deeper layers. The fungi that produced the most intensive deterioration in the fluorine polymers and vulcanized rubbers belonged to the Alternaria, Aspergillus, Aureobasidium, Cladosporium, Penicillium, Oidiodendron and Trichoderma genera. The fungi Aspergillus fumigatus, A. niger, Aureobasidium pullulans, and Trichoderma viride produced the most intensive deterioration in the fluorine films, whereas Alternaria tenuissima, Cladosporium herbarum, C. sphaerospermum, and fungi of the Oidiodendron genus were widespread on vulcanized rubbers. Fungi of the Aspergillus and Penicillium genera prevailed on both fluorine films and rubbers exposed in a cellar. Infrared spectroscopy indicated that the structures of poly(tetrafluorine ethylene) and the copolymer of tetrafluorine ethylene and perfluoromethyl vinyl ether did not change after the 12-year exposure; only insignificant changes in surface morphology were observed by optical microscopy. Vulcanized rubber made both from natural and from synthetic caoutchouc exposed for the same length of time showed rather evident changes in appearance and structure. X-ray graphical analysis revealed that new crystallization of the caoutchouc and a possible change in chemical composition of the fillers had occurred.

Screening and characterization of aldehyde dehydrogenase gene from Halomonas salina strain AS11

A population survey was made of moderately halophilic bacteria in prawn pond sediment in the Songkla region of Thailand. Twenty-two isolated halophilic bacteria capable of growing on modified ATCC culture medium 1270 for halobacterium were then assayed for aldehyde dehydrogenase (ALDH) activity which might be involved in the metabolism of xenobiotic compounds. One isolate, designated AS11, was selected based on its high amount of ALDH activity. This organism can grow at sodium chloride concentrations ranging from 2.5 to 25%, although optimum growth occurs at 5% NaCl. Phenotypic and phylogenetic studies indicated that AS11 was an isolate of Halomonas salina. The aldh gene coding for this enzyme was then cloned. The open reading frame of the aldh gene was 1521-bp long and coded for a protein of 506 amino acid residues with a calculated molecular mass of 55 kDa. The aldh gene product proved to be 76% identical to the NAD-dependent acetaldehyde dehydrogenase gene from Pseudomonase aeruginosa.