Biodegradability of polylactide bottles in real and simulated composting conditions

As new biodegradable polymers and their packaging applications are emerging, there is a need to address their environmental performance. In particular, there is a need to understand the time required for their complete disintegration, before these materials are deployed in commercial composting processes. Standards developed by ASTM and ISO evaluate the biodegradation of biodegradable plastic materials in simulated controlled composting conditions. However, a more detailed understanding of the biodegradation of complete packages is needed in order to have a successful composting operation. This paper investigates the biodegradation performance of polylactide (PLA) bottles under simulated composting conditions according to ASTM and ISO standards, and these results are compared with a novel method of evaluating package biodegradation in real composting conditions. Two simulated composting methods were used in this study to assess biodegradability of PLA bottles: (a) a cumulative measurement respirometric (CMR) system and (b) a gravimetric measurement respirometric (GMR) system. Both CMR and GMR systems showed similar trends of biodegradation for PLA bottles and at the end of the 58th day the mineralization was 84.2±0.9% and 77.8±10.4%, respectively. PLA bottle biodegradation in real composting conditions was correlated to their breakdown and variation in molecular weight. Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day. The biodegradation observed for PLA bottles in both conditions explored in this study matches well with theoretical degradation and biodegradation mechanisms; however, biodegradation variability exists in both conditions and is discussed in this paper.     

Oxygen permeability of biodegradable copolycaprolactones

Polycaprolactone is one of the biodegradable polymers with good drug permeability. In the present paper, polycaprolactone and three kinds of copolycaprolactone–polycaprolactone–poly(ethylene oxide)– polycaprolactone triblock copolymer (PCE), polycaprolactone/polycaprolactone‐poly(ethylene oxide)/polylactide tricomponents random block copolymer (PCEL) and polycaprolactone/poly(ethylene terephthalate) random block copolymer (PETCL)– were synthesized. The biodegradation behavior of these polymers were shown by degradation tests in vitro, ex vivo and in vivo. The oxygen permeabilities of these polymers were in the range of 10⁻¹⁰ ∼ 10⁻⁹ cm³ (STP) cm/cm² sec cm Hg. Copolymers PCE and PCEL displayed O₂ and N₂ permeability coefficients (PO₂/PN₂) ratios of about 9. The effects of composition and crystallinity of the copolymers on biodegradability and the oxygen permeability of the polymer were discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Biodegradation of Pyridine and Pyridine Derivatives by Soil and Subsurface Microorganisms

Abstract

Large amounts of aromatic compounds are produced by various industries and two thirds of these are heterocyclic chemicals. Compared with the extensive information available on microbial degradation of homocyclic aromatic compounds, relatively little is known on the transformation and biodegradation of heterocyclic chemicals in soil. Recent concerns about the persistence of hazardous pollutants have led to a renewed interest in the biodegradation of heterocyclic compounds. Hence, we investigated the microbial degradation of pyridine and some of its alkylated derivatives under aerobic and anaerobic conditions in groundwater, subsurface sediment, and soil. Results of the investigation revealed that these compounds were degraded predominantly under aerobic conditions and, to a lesser extent, under anaerobic conditions, with nitrate or sulfate serving as electron acceptors. In groundwater polluted with various pyridine derivatives, biodegradation was limited by the absence of oxygen. Therefore, we conclude that, under appropriate conditions, bioremediation is a potentially feasible method for the clean-up of environments contaminated with heterocyclic chemicals and, in particular, pyridine derivatives.     

Novel evaluation method of biodegradabilities for oil-based polycaprolactone by naturally occurring radiocarbon-14 concentration using accelerator mass spectrometry based on ISO 14855-2 in controlled compost

The biodegradabilities of poly(?-caprolactone) (PCL) powders (av. size = 180.7 μm) in controlled compost at 58 °C have been studied using the microbial oxidative degradation analyzer (MODA) based on ISO 14855-2 entitled “Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions - Method by analysis of evolved carbon dioxide - Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test”. The biodegradability of the PCL powders was 101.4% in a 56-day test period by the ISO method. The biodegradabilities of PCL powders have been studied using percent modern carbon (pMC) measured by accelerated mass spectrometry (AMS). Trapped CO₂ was analyzed by AMS to determine the pMC (sample) using ¹⁴C radiocarbon concentration. By using the theory that the pMC (sample) was the sum of pMC (compost) (104.88%) and pMC (PCL) (0%) as the respective ratios in the determined period, CO₂ (respiration) was calculated only from one reaction vessel. The biodegradability of PCL powders was 79.9% in a 56-day test period by the AMS method. It was found that respiration activities in the sample vessel including PCL, compost and sea sand were the same as that in the blank vessel including compost and sea sand without PCL during the active biodegradation period (0-33 day) at 58 °C. It was confirmed that respiration activities in the sample vessel were slightly higher than that in the blank vessel after active biodegradation due to the propagation of microorganisms using energy and metabolites by PCL biodegradation during those periods.     

Degradation of Triclosan under Aerobic, Anoxic, and Anaerobic Conditions

Triclosan (2, 4, 4??-trichloro-2??-hydroxyl diphenyl ether) is a broad-spectrum antimicrobial agent present in a number of house hold consumables. Aerobic and anaerobic enrichment cultures tolerating triclosan were developed and 77 bacterial strains tolerating triclosan at different levels were isolated from different inoculum sources. Biodegradation of triclosan under aerobic, anoxic (denitrifying and sulphate reducing conditions), and anaerobic conditions was studied in batch cultures with isolated pure strains and enrichment consortium developed. Under aerobic conditions, the isolated strains tolerated triclosan up to 1?g/L and degraded the compound in inorganic-mineral-broth and agar media. At 10?mg/L level triclosan, 95?±?1.2% was degraded in 5?days, producing phenol, catechol and 2, 4-dichlorophenol as the degradation products. The strains were able to metabolize triclosan and its degradation products in the presence of monooxygenase inhibitor 1-pentyne. Under anoxic/anaerobic conditions highest degradation (87%) was observed in methanogenic system with acetate as co-substrate and phenol, catechol, and 2, 4-dichlorophenol were among the products. Three of the isolated strains tolerating 1?g/L triclosan were identified as Pseudomonas sp. (BDC 1, 2, and 3).     

Degradation of the Herbicide Bromoxynil in Batch Cultures Under Groundwater Conditions

Abstract

The biological degradation of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) under simulated groundwater conditions was investigated. The influence of aerobic and anaerobic conditions on the degradation rate was examined in batch cultures at 8[ddot]C during 32 days. The cultures consisted of 400 ml groundwater plus 2000 ml salt basal medium. Final bromoxynil concentration was I mg/1. Incubation was carried out with and without 100 mg/1 acetate added as carbon source. Dissolved organic carbon (DOC), oxygen, nitrate and sulphate, bacterial number (CFU), enzymatic hydrolysis of fluorescein-di-acetate (FDA), and bromoxynil concentration was estimated along the test. Only anaerobic, nitrate reducing conditions caused biodegradation of bromoxynil after 17-21 days. The addition of acetate delayed this process, although the complete degradation after 32 days in both tests amounted to 99%. In spite of a high bioactivity, no degradation of bromoxynil could be found under aerobic conditions within 32 days.     

Blue dye degradation in an aqueous medium by a combined photocatalytic and bacterial biodegradation process

This paper aimed at implementing a treatment system for polluted water with textile dyes, starting with a photocatalytic decomposition process using sunlight as a source of energy and continuing with a bacterial biodegradation process, in order to reach degradation percentages higher than those obtained using only one of the processes mentioned above. When water treatment with the dye in the combined system was over, an acute ecotoxicity test was performed to make sure that toxic metabolites were not produced due to biodegradation. Solophenyl Blue azoic dye, and Erionyl Blue and Terasil Blue anthraquinone dye-colored solutions were treated with the Pd/Al ₈₀ Ce ₁₀ Zr ₁₀ catalyst in a solar collector for the photocatalytic process. On the other hand, the waste dye, which was obtained from photocatalysis with a bacterial consortium from polluted areas by metals and hydrocarbons in aerobic conditions, was inoculated for biodegradation. Biodegradation was obtained for the dyes after both processes as 90.91% for the Solophenyl Blue azoic dye, and 87.80% and 87.94%, respectively, for the Erionyl Blue and Terasil Blue anthraquinone dyes. After the degradation processes, it was proven, via an ecotoxicity test with Daphnia magna , that toxic metabolites had not been produced.     

Biodegradation of poly(lactic acid) powders proposed as the reference test materials for the international standard of biodegradation evaluation methods

The methods for producing reference test materials for biodegradation evaluation tests have been studied. Mechanical crushing at low temperature of polymer pellets using dry ice was selected for the method of producing polymer powder of poly(lactic acid) (PLA). The powders were fractionated using 60 mesh (250 μm) and 120 mesh (125 μm) sieves. The size distributions were then measured. The average diameter of the PLA particles obtained by this method was 214.2 μm. The biodegradation speeds of these PLA polymer powders were evaluated by two methods based on the international standard and one in vitro method based on the enzymatic degradation. First, the degree of biodegradation for this PLA powder was 91% for 35 days in a controlled compost determined by a method based on ISO 14855-1 (JIS K6953) at 58 °C managed by the Mitsui Chemical Analysis and Consulting Service, Inc. (Japan). Second, these polymer powders were measured for biodegradation by the Microbial Oxidative Degradation Analyzer (MODA) in a controlled compost at 58 °C and 70 °C based on ISO/DIS 14855-2 under many conditions. The degree of biodegradation for this PLA powder was approximately 80% for 50 days. In addition, the polymer powders were biodegraded by Proteinase K which is a PLA degradation enzyme. This polymer powder was suitable as a reference material for the evaluation methods of biodegradation.     

Cellulose acetate butyrate as multifunctional additive for poly(butylene succinate) by melt blending: Mechanical properties, biomass carbon ratio, and control of biodegradability

We have evaluated the plasticizing effect of poly(butylene succinate) (PBS) and cellulose acetate butyrate (CAB). PBS and CAB were mixed with a melt-kneading machine. The tensile strength and strain at break in the case of the blend with 10% CAB in the PBS matrix were 547% and 35 MPa. It showed that CAB acted as a plasticizer for PBS. The biomass carbon ratio of the blends measured by accelerator mass spectrometry based on ASTM D6866 showed that the biomass carbon derived from a part of the CAB corresponded to the theoretical value of the polymer blend. The biodegradation of PBS with the CAB melt blend powders was evaluated by a microbial oxidative degradation analyzer under controlled compost conditions based on ISO 14855-2. PBS with 10% CAB was not degraded within 60 days due to the addition of CAB that could control the biodegradability of the PBS.     

A biostimulation-based accelerated method for evaluating the biodegradability of polymers

The high cost and long duration of the existing standard tests, such as ASTM D5338 and ISO 14855, represents an important drawback in evaluating the biodegradability of polymers. This works presents a new accelerated method for this purpose, based on the use of a Bartha respirometer and biostimulation with yeast extract. The new method was applied to microcrystalline cellulose (MCC), low density polyethylene (LDPE), poly(3-hidroxybutyrate) (PHB), poly(lactic acid) (PLA), poly(vinyl alcohol) (PVOH), polypropylene (PP) and poly(ethylene terephthalate) (PET). The results obtained with these polymers were consistent with those of the standard methods in terms of differentiating biodegradable and non-biodegradable polymers and relative order of biodegradation extent. Besides, a significant reduction of test duration was achieved (from 45 to 110 days with ASTM D5338 or ISO 14855 to 28 days). These results corroborate the potential of the proposed method as a fast test for assessment of biodegradation of polymeric materials.     

UV/TiO2 Photocatalytic Degradation of Xanthene Dyes

UV/titanium dioxide (TiO₂) degradation of two xanthene dyes, erythrosine B (Ery) and eosin Y (Eos), was studied in a photocatalytic reactor. Photocatalysis was able to degrade 98% of Ery and 73% of Eos and led to 65% of chemical oxygen demand removal. Experiments in buffered solutions at different initial pH values reveal the pH dependence of the process, with better results obtained under acidic conditions due to the electrostatic attraction caused by the opposite charges of TiO₂ (positive) and of anionic dyes (negative). Batch activity tests under methanogenic conditions showed the high toxicity exerted by the dyes even at low concentrations (~85% with initial concentration of 0.3 mmol L^?1), but the end products of photocatalytic treatment were much less toxic toward methanogenic bacteria, as detoxification of 85 ± 5% for Eos and 64 ± 7% for Ery were obtained. In contrast, the dyes had no inhibitory effect on the biogenic‐carbon biodegradation activity of aerobic biomass, obtained by respirometry. The results demonstrate that photocatalysis combining UV/TiO₂ as a pretreatment followed by an anaerobic biological process may be promising for the treatment of wastewaters produced by many industries.     

Degradation and cis-to-trans isomerization of poly[(2,4-difluorophenyl)acetylene]s of various initial molecular weight: SEC,NMR, DLS and EPR study

Molecular weight (MW) and configurational stabilities of a series of high-cis poly[(2,4-difluorophenyl)acetylene]s (PdFPhA, M_w from 2.2 × 10⁴ to 9.7 × 10⁵) exposed to the atmosphere and diffuse daylight are reported. Polymers dissolved in THF-d₈ undergo simultaneous cis-to-trans isomerization and degradation under formation of a bimodal MW distribution. Degradation and isomerization rates are tightly connected and decrease with decreasing MW of the parent PdFPhAs. This finding may be interesting for the functional applications of substituted polyacetylenes. The partly aged PdFPhAs contain two separable fractions: higher-MW high-cis macromolecules containing a low amount of unpaired electrons and lower-MW deeply isomerized cis/trans macromolecules enriched in the unpaired electrons content. The difference in MW of these fractions reflects the various degradation rates of isomerized and high-cis macromolecules. Only a slow degradation without changes in the configurational structure proceeds if PdFPhA is allowed to age in the solid state. The suppression of the cis-to-trans isomerization reflects the suppression of motion of the polymer chains segments in the solid state.     

Behaviour of Phenoxyacetic Acids During Underground Passage with Different Redox Zones

Abstract

The behaviour of the three phenoxyacetic acid herbicides 2,4-D, 2,4,5-T and MCPA during underground passage and bankfiltration was tested in a model system consisting of laboratory filter columns filled with natural underground materials. Different redox environments were reproduced by operating the filters with natural aerobic and anaerobic groundwater. In the presence of oxygen, biodegradation of the three herbicides started after a lag phase. Under sulfate reducing conditions, no degradation could be observed. To assess the factors that may influence microbial degradation in the anaerobic environment, the concentration of herbicides, the time and the nutrient content were varied, but this did not increase degradation. The maximum retention of the herbicides in the filters was 30%, mainly due to adsorption to the filter material.     

Carbon and hydrogen isotope fractionation of benzene during biodegradation under sulfate‐reducing conditions: a laboratory to field site approach

The microbial carbon and hydrogen isotope fractionation of benzene under sulfate‐reducing conditions was investigated within systems of increasing complexity: (i) batch laboratory microcosms, (ii) a groundwater‐percolated column system, and (iii) an aquifer transect. Recent molecular biological studies indicate that, at least in the laboratory microcosms and the column system, benzene is degraded by similar bacterial communities. Carbon and hydrogen enrichment factors (ε_C, ε_H) obtained from laboratory microcosms and from the column study varied significantly although experiments were performed under similar redox and temperature conditions. Thus, enrichment factors for only a single element could not be used to distinguish benzene degradation under sulfate‐reducing conditions from other redox conditions. In contrast, using correlation of changes of hydrogen vs. carbon isotope ratios (Λ = Δδ²H/Δδ¹³C), similar Λ‐values were derived for the benzene biodegradation under sulfate‐reducing conditions in all three experimental systems (Λ_{laboratory microcosms} = 23 ± 5, Λ_column = 28 ± 3, Λ_aquifer = 24 ± 2), showing the robustness of the two‐dimensional compound‐specific stable isotope analysis (2D‐CSIA) for elucidating distinct biodegradation pathways. Comparing carbon and hydrogen isotope fractionation data from recent studies, an overlap in Λ‐values was observed for benzene biodegradation under sulfate‐reducing (Λ = 23 ± 5 to Λ = 29 ± 3) and methanogenic (Λ = 28 ± 1 to Λ = 39 ± 5) conditions, indicating a similar initial benzene reaction mechanism for both electron‐acceptor conditions. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparative study of the adsorption performance of an active multi-sorbent bed tube (Carbotrap, Carbopack X, Carboxen 569) and a Radiello(®) diffusive sampler for the analysis of VOCs

A simple comparison is made to evaluate the relative performance of active and passive sampling methods for the analysis of volatile organic compounds (VOCs) in ambient air. The active sampling is done through a multi-sorbent bed tube (Carbotrap, Carbopack X, Carboxen 569) created in our laboratory and the passive sampling through the Radiello^® diffusive sampler specified for thermal desorption (filled with Carbograph 4). Daily duplicate samples of multi-sorbent bed tubes were taken during a period of 14 days. During the same period of time, quadruplicate samples of Radiello^® tubes were taken during 3 days, 4 days, 7 days and 14 days. The sampling was carried out indoors during the months of February and March 2010 and outdoors during the month of July 2010 in La Canonja (Tarragona, Spain). The analysis was performed by automatic thermal desorption (ATD) coupled with capillary gas chromatography (GC)/mass spectrometry detector (MSD). The analytical performance of the two sampling approaches was evaluated by describing several quality assurance parameters. The results show that the analytical performances of the methodologies studied are quite similar. They display low limits of detection, good precision, accuracy and desorption efficiency, and low levels of breakthrough for multi-sorbent bed tubes. However, the two monitoring methods produced varying air-borne concentration data for most of the studied compounds, and the Radiello^® samplers generally gave higher results. Sampling rates (Q_k) were determined experimentally, and their values were higher than those supplied by the producer. As the experimental calculation of Q_k values is generally carried out by the suppliers in exposure chambers with only the target compounds present in the air samples, as well as in concentrations dissimilar to those found in ambient air, the use of constant settled Q_k can lead to inaccurate results in complex samples.     

Quantitative determination of toluene,ethylbenzene, and xylene degradation products in contaminated groundwater by solid-phase extraction and in-vial derivatization

Benzylsuccinic acid (BSA) and methylbenzylsuccinic acids (mBSAs) are unambiguous indicators of anaerobic toluene and ethylbenzene/xylene degradation, and so the determination of these compounds in landfill leachates and contaminated groundwater is highly relevant. Samples were diluted to <0.8?mS?cm^?1 in order to reduce their ionic strength, and subsequently extracted through strong anion exchange disks, followed by simultaneous in-vial elution and methylation. A detection limit of 0.1?µg?L^?1 was obtained for 100?mL samples. Using this method, 19.3?µg?L^?1 of BSA was measured in a landfill leachate, and low µg?L^?1 levels of all of the mBSAs were measured in gasoline-contaminated groundwater. The results were compared with the findings of BSAs at 16 other contaminated sites, and BSAs as indicators of biodegradation were evaluated. The estimation of biodegradation rates based on parent hydrocarbons and BSA concentrations or ratios is questionable. However, the degradation products serve as good qualitative in situ indicators for anaerobic biodegradation in contaminated groundwater.     

Molecular weight and configurational stability of poly(phenylacetylene) prepared with Rh catalyst

High-cis poly(phenylacetylene) (PPhA) has been prepared by polymerization of phenylacetylene with [Rh(COD)acac] catalyst and its molecular weight (MW) and configurational stability studied by SEC, ¹H NMR, UV/vis and IR techniques. PPhA dissolved in THF and THF-d₈ and exposed to the atmosphere and daylight at room temperature was found to undergo simultaneous cis-trans isomerisation and oxidative degradation accompanied by formation of a small amount (∼2 wt. %) of 1,3,5-triphenylbenzene. The extent of 1,3,5-triphenylbenzene formation was at least one order of magnitude lower than the extent of formation of new (shorter) PPhA macromolecules via their scission from the longer ones. Preparative MW-based fractionation revealed that a partly aged PPhA contains both (i) deeply isomerised macromolecules (forming the lower-MW fraction) and (ii) microstructurally unperturbed high-cis macromolecules (forming the higher-MW fraction). A hypothesis is postulated explaining the non-uniform distribution of high-cis and deeply isomerised trans-rich macromolecules along the MW distribution of partly aged PPhA. The hypothesis particularly assumes the acceleration of degradation of PPhA chains by simultaneous cis-trans isomerisation due to which the unpaired electron content is enhanced on the isomerised chains.     

Use of [13C]/[12C] ratios as an indicator of the role of microorganisms in protection of plants from the phytotoxic action of naphthalene

Using molecular and isotopic mass spectrometry, we investigated the toxic effect of naphthalene as a representative of polycyclic aromatic hydrocarbons (PAHs) on plants growing under sterile conditions and plants inoculated with microorganisms capable and incapable of naphthalene degradation. Tobacco plants of the Samsun variety were grown in a closed gas-nutrient system on a mineral medium with sucrose as a carbon source. Naphthalene used as a toxicant at a concentration of 5.2 × 10^?4% contained ¹³C isotope whose amount was characterized by the value δ¹³C = +281.4 ± 0.6‰ relative to the PDB standard and differed from that of sucrose, the main source of carbon (δ¹³C = ?12.0 ± 0.1‰). Degradation of naphthalene was determined by the inclusion of its carbon in metabolic CO₂ and plant tissues (the root, stem, leaves). The effect of naphthalene on plants was indicated by the rates of O₂ production and CO₂ uptake during the light period as compared with the dark period of exposure. A decrease of the toxic effect of naphthalene on plants was observed only at the inoculation of plants with Pseudomonas aureofaciens BS1393 rhizosphere bacteria bearing plasmid pBS216, which controls the naphthalene biodegradation ability. The occurrence of other heterotrophic microorganisms incapable of naphthalene degradation had no similar protective effect.