Ultimate Aerobic Biodegradability Research Articles

Japanese washi-paper-based green composites: Fabrication, mechanical characterization, and evaluation of biodegradability

In this study, sheets of Japanese washi-paper were layered and hot pressed with films of poly(butylene succinate) (PBS) in order to produce a fiber-reinforced composite material that can be biodegraded. Using traditional Japanese washi-paper, a thin yet remarkably strong green composite with excellent biodegradability was produced, proving the potential of washi-paper as an attractive reinforcer in green composites. The composite was biodegraded in compost, and the ultimate aerobic biodegradability as well as weight loss and loss of mechanical properties during biodegradation was evaluated. Specimens fabricated from three layers of washi-paper and two layers of PBS film had remarkable mechanical properties, including an ultimate tensile strength of 59.85 MPa. Scanning electron microscopy was used to study the cross-sectional structure of the material, which showed that the hollow washi-paper provides a structure for the polymer to settle into and surround the cellulose fibers. The large contact area between the cellulose fibers and the PBS caused a large internal friction which prevented failure by fiber pull-out, dramatically increasing the strength compared to neat washi-paper and neat PBS. Concerning biodegradability, the material reached 82 % biodegradation after 35 days. During biodegradation, the composite lost its mechanical properties fast, and was extremely fragile after 2 weeks inside the compost. After 6 weeks, the biodegradation had progressed so far that it was difficult to distinguish the material inside the compost. Due to its fast biodegradation and good mechanical strength, the washi-based composite material is potentially used in packaging, furniture, and agricultural applications such as mulch film.

Biodegradation of various forms of cellulose and chitin in natural waters with different salinity

This study evaluated the ultimate aerobic biodegradability of cellulose and chitin samples in natural water. The as-prepared cellulose powder, microcrystals, and gel, together with the chitin microcrystals, were observed under an electron microscope and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and nitrogen-adsorption measurement techniques. The samples were then subjected to biochemical oxygen demand testing at 20 °C, in the dark, for 30 d, in fresh water, brackish water, and seawater collected from the Kamogawa River and Osaka Bay, Japan. The biodegradability of the cellulose and chitin samples was greater than that of the poly(ε-caprolactone) film used as a positive control sample and was in the order of chitin microcrystals > cellulose hydrogel ≈ cellulose microcrystals > cellulose powder. These results indicate that the higher the specific surface area, the higher the degree of degradation of the cellulose samples. Chitin microcrystals displayed a higher degree of degradation than cellulose microcrystals although both had near-identical specific surface areas, indicating that chitin is more easily degraded than cellulose in natural waters. The degree of degradation in natural water was in the order of fresh water > brackish water > seawater. This trend implies that the higher the salinity, the more the degradation was suppressed.

Biochemical characterization, microbial diversity and biodegradability of coastal sediments in the Gulf of Gabès, Southern Mediterranean Sea

Coastal sediments are considered to be final receptacles for organic and inorganic contaminants. Characterizing those sediments and assessing their biodegradation potential have become a great challenge in recent years. In this study, the chemical composition, including the content in polycyclic aromatic hydrocarbons, the microbial community abundance and diversity (using culture-independent approaches targeting 16S rRNA genes), and the aerobic/anaerobic biodegradation potential of coastal sediments collected in the Sfax coastal area (Gulf of Gabès, Southern Mediterranean Sea) were investigated. The highest concentration of total polycyclic aromatic hydrocarbons (981 µg kg−1 dw) was recorded in Sidi Mansour harbor sediment, emphasized pyrogenic and petrogenic hydrocarbon sources. Organic matter, including total organic carbon, and the ultimate aerobic biodegradability, with 30% as the highest value in Sidi Salem channel sediment, were in a positive accordance with bacterial communities assigned within Actinobacteria, Clostridia and Flavobacteria classes. The correlation noticed between Thermocladium and Thermogladius genera and sulfate content explained that Sidi Mansour and PK4 sediments are located in terrestrial acid–sulfate areas. The highest cumulative methane produced with Marseille inoculum and Tunisian inoculum was recorded in Sidi Salem sediment and strongly correlated with methanogens among Methanobacteria, Methanococci and Methanomicobia classes showing the presence of industrial and municipal sources. The bioavailability of low and moderate polycyclic aromatic hydrocarbons in the current study may explain the occurrence of Methanobacterium which positively correlated with the anaerobic biodegradability using Tunisian inoculum with 50% as the highest value in Sidi Mansour sediment.

Biodegradation of Poly(Lactic Acid) Biocomposites under Controlled Composting Conditions and Freshwater Biotope.

The influence of additives such as natural-based plasticiser acetyl tributyl citrate (ATBC), CaCO3 and lignin-coated cellulose nanocrystals (L-CNC) on the biodegradation of polylactic acid (PLA) biocomposites was studied by monitoring microbial metabolic activity through respirometry. Ternary biocomposites and control samples were processed by a twin-screw extruder equipped with a flat film die. Commonly available compost was used for the determination of the ultimate aerobic biodegradability of PLA biocomposites under controlled composting conditions (ISO 14855-1). In addition, the hydro-degradability of prepared films in a freshwater biotope was analysed. To determine the efficiency of hydro-degradation, qualitative analyses (SEM, DSC, TGA and FTIR) were conducted. The results showed obvious differences in the degradation rate of PLA biocomposites. The application of ATBC at 10 wt.% loading increased the biodegradation rate of PLA. The addition of 10 wt.% of CaCO3 into the plasticised PLA matrix ensured an even higher degradation rate at aerobic thermophilic composting conditions. In such samples (PLA/ATBC/CaCO3), 94% biodegradation in 60 days was observed. In contrast, neat PLA exposed to the same conditions achieved only 16% biodegradation. Slightly inhibited microorganism activity was also observed for ternary PLA biocomposites containing L-CNC (1 wt.% loading). The results of qualitative analyses of degradation in a freshwater biotope confirmed increased biodegradation potential of ternary biocomposites containing both CaCO3 and ATBC. Significant differences in the chemical and structural compositions of PLA biocomposites were found in the evaluated period of three months.

Biodegradation of Cellulose in Laboratory-Scale Bioreactors: Experimental and Numerical Studies

Standard tests such as ISO 17556 (Plastics - determination of the ultimate aerobic biodegradability in soil by measuring the oxygen demand in a respirometer or the amount of carbon dioxide evolved. International Organization for Standardization, Geneva, Switzerland, 2019) or ASTM D5988 (Standard test method for determining aerobic biodegradation of plastic materials in soil. ASTM International, West Conshohocken, 2018) have been developed for measuring the biodegradation of polymers and assessing their biodegradability in soil. In several experiments performed according to these standard tests, the measured biodegradation of cellulose was reported unexpectedly between 80 and 85%. These results are difficult to justify since cellulose is a well-known biodegradable material. In the present study, this phenomenon is explained as the consequence of starvation occurring in a confined bioreactor. It is proposed that the favourable conditions applied to the small-size bioreactors accelerate the proliferation of the microorganisms which are responsible for the biodegradation. Such a dense microbial population may face starvation when cellulose is consumed. It is assumed that starvation causes the secretion of an inhibitory chemical signal, which can diffuse to neighbouring sites still containing food, and suppresses biodegradation. This hypothesis was supported by two experiments. First, it was shown that the final measured biodegradation increased when the microbial growth rate decreased by reducing temperature. In the second experiment, it was shown that the biodegradation proceeded slower when a new cellulose quantity was inserted into a previously used soil substrate. To confirm the hypothesis regarding the presence of an inhibitory starvation factor, which can suppress biodegradation, a Kinetic Monte Carlo (KMC) model was also developed. The KMC simulations reproduced qualitatively the experimental findings.

A method for the rapid evaluation of leather biodegradability during the production phase

Advances in technological–industrial processes have led to the development of new materials that generate different impacts on the environment when presented as waste. The application of sustainable manufacturing practices in order to improve the environmental behaviour of materials, including in the waste stage, is now an important industry responsibility. This study developed a new method for the rapid evaluation of leather biodegradability that can easily be operated by the tannery industry during the production phase. The method uses the OxiTop® system within which a solid sample is suspended in a liquid medium with no nutritional limitations at a constant temperature and stirring conditions. Ten leather samples were tested based on the existing methodology for determining aerobic biological activity (EN 16087-1: 2011), ultimate aerobic biodegradability of plastic materials in an aqueous medium (ISO 14851: 2004), and OECD 301F guidelines for testing of chemicals. The developed method has been shown to reliably distinguish (over 7 days) between samples produced using different manufacturing processes/treatments. Starch proved to be a better standard reference material for checking inoculum activity and the proper functioning of the measurement system than cellulose. Skin without treatment was shown to be a suitable reference material for defining the maximum biodegradation of leather materials. Double exponential and Gompertz mathematical models closely described the biodegradation of the tested samples. This method offers a way for industry to test and produce leather materials with higher levels of biodegradability, thus reducing the adverse environmental impacts of the final products when presented as solid waste.

Polycaprolactone-collagen hydrolysate thermoplastic blends: Processability and biodegradability/compostability

Thermoplastic blends of polycaprolactone (PCL) and hydrolyzed collagen (HC) derived from the tannery industry were investigated to assess the feasibility of producing by conventional melting-based procedures biodegradable items for applications in agriculture and plant nurseries. The used HC was obtained by alkaline hydrolysis of the shavings of the tanning process. PCL/HC blends, with 10, 20 and 30 wt.% of HC, were processed by extrusion and compression molding, and characterized in terms of thermal, rheological, morphological and mechanical properties. In view of their possible applications in agriculture, phytotoxicity assays were carried out by using cress (Lepidium sativum L.) germination test and growth analyses of lettuce plants (Lactuca sativa L., cv Canasta), used as reference. Small pots were produced by fused deposition modeling (FDM) and their compostability was evaluated by the standard disintegration test UNI EN ISO 14045. The ultimate aerobic biodegradability of the blends was assessed by the standard UNI EN ISO 14855-1. PCL/HC blends were successfully processed by extrusion providing cohesive and flexible filaments suitable for the FMD 3D-printing. A decrease in the melt viscosity was observed with the addition of HC due to its plasticizing effect. The addition of HC led to a clear decrease of the tensile modulus and, with 30 wt.% HC, a break elongation higher than 600% as pure PCL. Despite the release in water of soluble salts, responsible of a moderate phytotoxicity assessed by L. sativum germination test, PCL/HC blends were not phytotoxic to the lettuce growth. Moreover, PCL/HC blends showed very high biodegradation rates in compost, even higher than cellulose. Composting trial performed under real conditions also confirmed the biodegradability of these blends, showing complete disintegration of the produced 3D printed pots in just 30 days.

Improvement of Biodegradation of Wood Plastic Composites using Rice-Bran Mixture

Wood-plastic composites (WPCs) are currently discarded using incineration treatment, which is very expensive. Hence, this study was performed to improve the biodegradation of WPCs, such that they could potentially be buried after use, and to estimate their bending strength. A biodegradation test (determining the ultimate aerobic biodegradability of plastic materials under controlled composting conditions) was performed according to ISO 14855-1. Two groups of specimens were prepared using rice-bran mixture as the bioresource. One group contained rice-bran mixtures of 5, 7.5, and 10 wt.% instead of wood flour contents, and another group contained rice-bran mixtures of 8, 16, and 24 wt.% instead of the talc component. During the 20 days of the biodegradation experiment, the WPC (control) showed 18% biodegradation, and 7.5%-rice-bran-mixture-added specimen showed the highest biodegradation of 32%. Furthermore, the bending strength (MOR) was increased by up to 140% by adding rice-bran mixture as a biodegradable component. Therefore, the rice-bran mixture improved the biodegradation and mechanical properties of WPCs.

Active biodegradable sodium caseinate films manufactured by blown-film extrusion: Effect of thermo-mechanical processing parameters and formulation on lysozyme stability

Sodium caseinate-based edible/biodegradable films containing lysozyme were prepared directly by extrusion processes to obtain antimicrobial films. Thermoplastic pellets containing 1% (w/w) lysozyme were blown by an industrial-like blown-film-extruder to obtain thermoplastic thin films. Lysozyme stability depended mainly on processing temperature and glycerol content. A correct choice of these parameters allowed obtaining pellets and films with 40.8±0.5% and 26.4±0.6% lysozyme residual activity, respectively. Whatever the storage temperature (−20°C or room temperature), lysozyme activity of pellets remained constant for at least 5 weeks of storage. Antimicrobial activity against Micrococcus luteus was assayed in Tryptone Soya Broth (TSB): no bacterial growth was observed for 25h at 37°C in the presence of 0.05g.L−1 pellets, while a 2.4 log increase of bacterial population was observed in the presence of control pellets without lysozyme. Traditional properties of films such as their water sorption and mechanical properties were also investigated and proved that addition of lysozyme at a 1% concentration did not affect these properties as well as their ultimate aerobic biodegradability. The application potential of such edible antimicrobial films is discussed in relation with these properties.

Biodegradation Behaviors of Poly(p-dioxanone) in Different Environment Media

This work was aimed at researching the aerobic biodegradation of poly(p-dioxanone) (PPDO), a novel kind of degradable polymer material, by simulating real-life conditions in a laboratory-scale test, specified by the standard methods based on two biodegradation environments, composting and aqueous media. To measure and describe the biodegradability of PPDO, not only had carbon dioxide produced by respiratory metabolism of microorganism been measured, which determines the ultimate aerobic biodegradability of chemical compounds, but also the detailed results of biodegradation were further characterized by monitoring physical, chemical and thermal properties changes of test materials at different incubation times in the two media, confirmed by using the appropriate analytical techniques. Scanning electron microscopy was used to observe the surface morphology, and the thermal performance of PPDO was characterized by differential scanning calorimetry. The changes of molecular weight were detected by intrinsic viscosity ([η]) and gel permeation chromatography, and the variations of the molecular structure were monitored by the nuclear magnetic resonance and FT-IR. The results show that PPDO has outstanding character of biodegradation and may be more adapted for biodegrading in liquid medium than in composting.

Environmental Impact of Ether Carboxylic Derivative Surfactants

AbstractThe ultimate aerobic biodegradability and toxicity of three ether carboxylic derivative surfactants having different alkyl chains and degrees of ethoxylation were investigated. Ultimate aerobic biodegradability was screened by means of dissolved organic carbon determinations at different initial surfactant concentrations. For comparison, the characteristic parameters of the biodegradation process, such as half‐life, mean biodegradation rate, and residual surfactant concentration, were determined. Increased surfactant concentrations decreased mineralization and lengthened the estimated half‐life. The results demonstrate that the ultimate aerobic biodegradability is higher for the surfactants with the shortest alkyl chain and highest degree of ethoxylation. Toxicity values of the surfactants, and their binary mixtures, were determined using three test organisms, the freshwater crustacea Daphnia magna, the luminescent bacterium Vibrio fischeri and the microalgae Selenastrum capricornutum. The toxicity is lower for the surfactants with the shortest alkyl chain and highest degree of ethoxylation. The toxicity of binary mixtures of the three ether carboxylate surfactants at a 1:1 weight ratio was also measured. The least toxic mixture is formed by the surfactants having lower individual toxicity.

Biodegradation of Poly(butylene succinate) Powder in a Controlled Compost at 58 °C Evaluated by Naturally-Occurring Carbon 14 Amounts in Evolved CO2 Based on the ISO 14855-2 Method

The biodegradabilities of poly(butylene succinate) (PBS) powders in a controlled compost at 58 °C have been studied using a Microbial Oxidative Degradation Analyzer (MODA) based on the ISO 14855-2 method, 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 evolved CO2 was trapped by an additional aqueous Ba(OH)2 solution. The trapped BaCO3 was transformed into graphite via a serial vaporization and reduction reaction using a gas-tight tube and vacuum manifold system. This graphite was analyzed by accelerated mass spectrometry (AMS) to determine the percent modern carbon [pMC (sample)] based on the 14C radiocarbon concentration. By using the theory that pMC (sample) was the sum of the pMC (compost) (109.87%) and pMC (PBS) (0%) as the respective ratio in the determined period, the CO2 (respiration) was calculated from only one reaction vessel. It was found that the biodegradabilities determined by the CO2 amount from PBS in the sample vessel were about 30% lower than those based on the ISO method. These differences between the ISO and AMS methods are caused by the fact that part of the carbons from PBS are changed into metabolites by the microorganisms in the compost, and not changed into CO2.

Study of the Determination of the Ultimate Aerobic Biodegradability of Plastic Materials Under Controlled Composting Conditions

Several ISO standards for determining the ultimate aerobic/anaerobic biodegradability of plastic materials have been published. In particular, ISO 14855-1 is a common test method that measures evolved carbon dioxide using such methods as continuous infrared analysis, gas chromatography or titration and others (ISO 14855-1(2005.9)). This method is a small-scale test for determining the ultimate aerobic biodegradability of plastic materials, where the amounts of compost inoculum and test sample in one tenth comparing with that of ISO 14855-1. This method is well versed in ISO/DIS 14855-2 which the carbon dioxide evolved from test vessel is determined by gravimetric analysis of carbon dioxide absorbent. The focus of this study is to elucidate statistically the results of round robin test by seven countries used MODA, which were various deviations among the experiments.

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(ɛ-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 CO 2 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, CO 2 (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.

Effect of the inoculation level in aerobic biodegradability tests of polymeric materials

The composition and the quantity of the microbial inoculum are well-known factors affecting the reproducibility of results of biodegradability tests. Experiments with polyhydroxy–butyrate/valerate (PHBV, a biopolymer), cellulose (natural polymer) and acetate (soluble substance) as substrates were carried out to evaluate the impact of non-controlled inocula on test response. The European Committee of Normalization (ECN) Standard for packaging materials was the method chosen to evaluate the ultimate aerobic biodegradability, in order to establish carbon balances. Inocula were obtained from activated sludges sampled in the aerated tank of a municipal wastewater treatment plant. Activated sludges were collected at different periods, so the inoculum concentration (X0) in the test was dependent on the seasonal variations of the source. As the initial carbon content (S0) was maintained to a well-defined value, various S0/X0 ratios were obtained. At high S0/X0 ratios, cellular growth and soluble residual carbon accumulation were favoured and low mineralization levels were obtained. An increase in the quantity of mineralized carbon due to a low S0/X0 ratio seems to support the notion of standardized biodegradability tests in relation to this parameter, which could enhance the reliability of test results of polymeric materials.

ISO standard activities in standardization of biodegradability of plastics—development of test methods and definitions

A new working group (WG22) of subcommittee (SC 5) on biodegradability was created by the International Organization for Standardization (ISO) Technical Committee on Plastics (TC61) in 1993. The following three aerobic test methods have recently advanced to the DIS (Draft of International Standard) stage: (1) evaluation of the ultimate aerobic biodegradability in an aqueous medium—method by determining the oxygen demand in a closed respirometer; (2) evaluation of the ultimate aerobic biodegradability in an aqueous medium—method by analysis of released carbon dioxide; and (3) evaluation of the ultimate aerobic biodegradability and disintegration of plastics under controlled composting conditions—method by analysis of released carbon dioxide. The definition of biodegradation should be as wide as possible and consistent with the meaning intended. The level of biodegradation should be established in standard test methods. In addition, WG22 plans to develop two test methods for anaerobic biodegradability as well as a test scheme for the final acceptance of the compostability.

Aerobic biodegradability of surfactants at low concentrations using an automated pressure transducer system

We have developed a simple and reliable automated pressure transducer system (APTS) to evaluate the ready and ultimate aerobic biodegradability of surfactants in 28 days at low concentrations (5 mg C/L) using modifications of existing CO 2 evolution assays (Sturm & Gledhill). Pressure transducers (PT) are fitted to Gledhill-type flasks containing Sturm minerals solution, dilute (50 mg/L) unacclimated activated sludge microbial seed and test compound. PT monitor microbial respiration through oxygen consumption from the headspace and CO 2 from metabolism is absorbed in a 1M KOH solution within the flask. Results with nonionic ethoxylate (AE-7) and anionic sulfate (AS) surfactants prepared from linear or 2-alkyl branched C 14−15 alcohol moieties show that sewage bacteria readily consumed 02 (70–140% ThO 2) and degraded these compounds to C02 (65–75% ThCO 2) in 12 days at 25C. However, when a more branched alcohol ethoxylate (NPE-9) was tested in the APTS, only 50% of both the ThO 2 was consumed and ThCO 2 was produced. Glucose and benzoic acid were biodegraded to CO 2 similarly to the AE-7 and AS surfactants. Comparison of alcohol ethoxylate degradation data in the APTS with those published from traditional Sturm test methods demonstrated that the C0 2 recovery results were the same for readily metabolized compounds. Our experience with the APTS indicate that the method is reliable, less cumbersome and requires less manipulation than the Sturm and Gledhill assays. Furthermore, the method can be adapted to screen the ready biodegradability of volatile, insoluble and other organic compounds for which radiolabelled material is not available to study microbial degradation.