Critical Review of Norms and Standards for Biodegradable Agricultural Plastics Part Ι. Biodegradation in Soil

A critical review of norms and standards and corresponding tests to determine the biodegradability in soil for biodegradable plastics, possibly applicable also to biodegradable agricultural plastics, is presented. There are only a few norms available at the international level about biodegradable plastics in soil. The criteria, parameters and testing methodologies for the characterization, labelling and validation of the agricultural plastic waste streams with respect to possible biodegradation in soil according to existing international standards are analysed while the relevant controversies are identified. To derive the best suited for agricultural plastics specs and testing methods, the possible developments or adaptation of available specs, is investigated. Considering the existing types of biodegradable plastic products in agriculture and their effective life management at the agricultural field, only a few norms appear to provide suitable tests that could be adapted, following appropriate research work, for testing biodegradability in soil under real field conditions. It is shown that some major revisions are needed, with the support of systematic research work, before a new universal norm and standard testing methods become available for testing agricultural plastics for biodegradation under real, and highly variable, soil conditions. Based on the analysis of the different norms and their content it appears necessary to incorporate provisions for transferability of results to different soils and climates, validation of tests through a positive reference and also, set prerequisites for soil media. Long term biodegradation in soil prediction is another open issue.     

Comparison of the weight-loss degradability of various biodegradable plastics under laboratory composting conditions

Eight kinds of biodegradable plastics were compared for their degradability in controlled laboratory composting conditions. A thin film of each plastic was mixed into the composting material, and weight-loss degradability was calculated from the weight changes of the film during composting. It was found that weight-loss degradability strongly depended on the specific kind of biodegradable plastic; two were very high, four moderate, and the remaining two very slight. The most easily degradable plastic degraded by as much as 81.4% over 8 days of composting. By comparing the weight-loss degradability with ultimate degradability, which is defined as a molar ratio of carbon loss as CO₂ to the carbon contained in the biodegradable plastic, the order of the ease of degradation of the biodegradable plastics differed. Received: February 7, 2000 / Accepted April 14, 2000     

Determining biodegradability of plastic materials under controlled and natural composting environments

With the advent of recently promulgated Government regulations on plastics in Mauritius, a study was initiated to examine the biodegradability of two different types of plastic, namely Willow Ridge Plastics - PDQ-H additive (Plastic A) and Ecosafe Plastic - TDPA additive (Plastic B) under controlled and natural composting environments. The results obtained from the controlled composting environment showed that the cumulative carbon dioxide evolution for Plastic A was much higher than that for Plastic B. Plastic A therefore showed a higher level of biodegradation in terms of CO2 evolution than Plastic B. However, from the regression analysis, it was found that the level of CO2 varying with time fitted the sigmoid type curves with very high correlation coefficients (R2 values: 0.9928, 0.9921 and 0.9816, for reference material, inoculum and Plastic A, respectively). The corresponding F-values obtained from the ANOVA analysis together with significance levels of p<0.05 indicated that the three treatments analysed in the biodegradability experiment were significant. The other experiment was undertaken to observe any physical change of Plastics A and B as compared to a reference plastic, namely, compostable plastic bag (Mater-Bi product-Plastic C), when exposed to a natural composting environment. Thermophilic temperatures were obtained for about 3-5 days of composting and the moisture content was in the range of 60-80% throughout the degradation process. It was observed that after 55 days of composting, Plastic C degraded completely while Plastic A and Plastic B did not undergo any significant degradation. It can be concluded that naturally based plastic made of starch would degrade completely in a time frame of 60 days, whereas plastics with biodegradable additive would require a longer time.     

Behaviour of biodegradable plastics in composting facilities

Composting is a preferred treatment strategy for biodegradable plastics (BDPs). In this sense, the collection of BDPs together with organic household wastes is a highly discussed possibility. Under the aspect of the behaviour of BDPs in composting facilities, a telephone survey was carried out with selected composting facility operators. They were interviewed with respect to treated wastes, content of impurities, processes for impurity separation, experiences with biodegradable plastics and assumptions to the behaviour of biodegradable plastics in their facility. Forty percent of the facilities had some experiences with BDPs due to test runs, and also since the occurrence of BDPs in their waste was known. The majority of the operators expressed apprehension regarding an increase of impurities resulting from a combined collection of biowaste and BDPs. In the facilities, measures for the impurity separation from the biowaste were used in common practice - in 33% of the cases, separation of disturbing plastics was done before composting, in 33% after composting, and in 13% before and after composting. The most important separation processes for conventional plastics were sieving and manual sorting. In two cases air classification was also used. When asked about the separation possibility of the conventional but not of the biodegradable plastics in their facilities, the majority of operators were not in a position to comment or they replied that it was not an option. No problems were seen in most cases if the impurity separation follows composting. If impurity separation takes place before composting it was often assumed that the BDPs are mainly separated by sieving. In conclusion, in more than half of the cases, BDPs would not be composted if delivered to a composting facility. Under the actual conditions regarding the collection and the treatment/disposal possibilities, an application of BDPs seems to only be reasonable for clean (i.e., source separated on their own) fractions of BDPs.     

Comparison of compostable bags and aerated bins with conventional storage systems to collect the organic fraction of municipal solid waste from homes. A Catalonia case study

The separation of biowaste at home is key to improving, facilitating and reducing the operational costs of the treatment of organic municipal waste. The conventional method of collecting such waste and separating it at home is usually done by using a sealed bin with a plastic bag. The use of modern compostable bags is starting to be implemented in some European countries. These compostable bags are made of biodegradable polymers, often from renewable sources. In addition to compostable bags, a new model of bin is also promoted that has a perforated surface that, together with the compostable bag, makes the so-called “aerated system”. In this study, different combinations of home collection systems have been systematically studied in the laboratory and at home. The results obtained quantitatively demonstrate that the aerated bin and compostable bag system combination is effective at improving the collection of biowaste without significant gaseous emissions and preparing the organic waste for further composting as concluded from the respiration indices. In terms of weight loss, temperature, gas emissions, respiration index and organic matter reduction, the best results were achieved with the aerated system. At the same time, a qualitative study of bin and bag combinations was carried in 100 homes in which more than 80% of the families participating preferred the aerated system.     

Compostable cutlery and waste management: an LCA approach

The use of disposable cutlery in fast food restaurants and canteens in the current management scenario generates mixed heterogeneous waste (containing food waste and non-compostable plastic cutlery). The waste is not recyclable and is disposed of in landfills or incinerated with or without energy recovery. Using biodegradable and compostable (B&C) plastic cutlery, an alternative management scenario is possible. The resulting mixed homogeneous waste (containing food waste and compostable plastic cutlery) can be recycled through organic recovery, i.e., composting. This LCA study, whose functional unit is "serving 1000 meals", shows that remarkable improvements can be obtained by shifting from the current scenario to the alternative scenario (based on B&C cutlery and final organic recovery of the total waste). The non-renewable energy consumption changes from 1490 to 128MJ (an overall 10-fold energy savings) and the CO(2) equivalents emission changes from 64 to 22 CO(2) eq. (an overall 3-fold GHG savings).     

Validation of an Automated Multiunit Composting System

Biodegradable packaging has high potential to help solve the crisis of non-biodegradable plastic waste causing an increase in the footprint of landfills. However, more research needs to be executed to develop a larger assortment of biodegradable plastics for numerous applications and to make them more economical to manufacture. This paper discusses the design and validation of an automated composting system (AMUCS) that fits the requirements of the American Society for Testing and Materials (ASTM) 5338-11 standard. The results of the experiments show that the AMUCS was able to create and maintain the conditions for biodegradation of biodegradable polymers in compost using microcrystalline cellulose. The biodegradation caused by the composting environment was observed visually with the naked eye and on the micro scale with an environmental scanning electron microscope. The magnitude of biodegradation was measured by calculating the carbon metabolized from the samples. The carbon metabolized from the three compost replicates was consistent and linear, and there was only an 8 % difference between the non-biodegradable low density polyethylene and the compost. For the biodegradation study according to ASTM D 5338-11, the experiment was validated with the use of cellulose as a reference material. Under controlled composting conditions, the mineralization of microcrystalline cellulose yielded 72.05 %, which is slightly higher than the 70 % mineralization requirement.     

Biodegradation of Agricultural Plastic Films: A Critical Review

The growing use of plastics in agriculture has enabled farmers to increase their crop production. One major drawback of most polymers used in agriculture is the problem with their disposal, following their useful life-time. Non-degradable polymers, being resistive to degradation (depending on the polymer, additives, conditions etc) tend to accumulate as plastic waste, creating a serious problem of plastic waste management. In cases such plastic waste ends-up in landfills or it is buried in soil, questions are raised about their possible effects on the environment, whether they biodegrade at all, and if they do, what is the rate of (bio?)degradation and what effect the products of (bio?)degradation have on the environment, including the effects of the additives used. Possible degradation of agricultural plastic waste should not result in contamination of the soil and pollution of the environment (including aesthetic pollution or problems with the agricultural products safety). Ideally, a degradable polymer should be fully biodegradable leaving no harmful substances in the environment. Most experts and acceptable standards define a fully biodegradable polymer as a polymer that is completely converted by microorganisms to carbon dioxide, water, mineral and biomass, with no negative environmental impact or ecotoxicity. However, part of the ongoing debate concerns the question of what is an acceptable period of time for the biodegradation to occur and how this is measured. Many polymers that are claimed to be ‘biodegradable’ are in fact ‘bioerodable’, ‘hydrobiodegradable’, ‘photodegradable’, controlled degradable or just partially biodegradable. This review paper attempts to delineate the definition of degradability of polymers used in agriculture. Emphasis is placed on the controversial issues regarding biodegradability of some of these polymers.     

Biodegradation of Compostable Plastics in Green Yard-Waste Compost Environment

Compostable plastic materials, produced from polylactic acid (PLA), corn starch, or sugarcane, degraded in a green yard-waste compost environment. The compostable plastics claim to meet ASTM D6400 standards for biodegradation, sustainable plant growth, and eco-toxicity. Biodegradation was measured by disintegration studies over 20 weeks. The commercially available compostable products, made from PLA, sugarcane, or corn starch, biodegraded while in a commercial compost facility with other common yard waste compostable items. The PLA container, cup, and knife completely degraded in 7 weeks at a rate similar to the Avicell micro-cellulose control. The corn starch-based trash bag and sugarcane plate degraded at a similar rate as the Kraft paper control. The three materials degraded between 80% and 90% after 20 weeks.     

Biodegradation and Ecotoxicity of Polyethylene Films Containing Pro-Oxidant Additive

The worldwide accumulation of non-degradable plastic materials, such as plastic bags, is one of the most important environmental concerns nowadays. The use of degradable materials is an option to mitigate the environmental impact generated by the consumption of plastics. One of the technologies used for the manufacture and use of degradable plastics is the use of pro-degradant additives that are incorporated in conventional plastics to promote their degradation under certain conditions. The aim of this study is to evaluate the process of oxidation, biodegradation and potential ecotoxicity of polyethylene films containing an oxo-degradable additive, according to the standard ASTM D-6954. This method establishes a procedure in which the samples are subjected to consecutive steps of accelerated oxidation, biodegradation by composting and ecotoxicity assessment. Furthermore, the effect of the presence of printing ink in the polyethylene samples with oxo-degradable additive was evaluated, and the results were compared with those obtained for samples of conventional polyethylene and polylactic acid. After 180 days of laboratory controlled composting, the samples reached the following percentages of biodegradation: polylactic acid, 41 %; printed oxo-degradable polyethylene, 32.24 %; oxo-degradable polyethylene, 25.84 %; printed polyethylene, 18.23 % and polyethylene, 13.48 %. The cellulose sample used as a control was mineralized in 58.45 %. Ecotoxicity assessment showed that the products of biodegradation of the samples tested, did not generate a negative effect on germination or development of the vegetal species studied. Under proper waste management conditions, these plastics can be used as an option to decrease the environmental impact of plastic films.     

Performance of compostable baby used diapers in the composting process with the organic fraction of municipal solid waste

In modern societies, disposable diapers constitute a significant percentage of municipal solid wastes. They have been traditionally landfilled or incinerated as only limited recycling processes are being implemented in some parts of Europe. With the implementation of separated collection systems for the organic fraction of municipal solid wastes (OFMSWs) and the need to preserve the environment, compostable diapers have appeared in the market to avoid the main environmental impacts associated to non-biodegradable disposable diapers. In this study, a full-scale composting of door-to-door collected OFMSW with a 3% (w/w) of compostable diapers has also been carried out. Previously, lab-scale experiments confirmed that almost 50% of carbon of compostable diapers is emitted as CO₂ under aerobic controlled conditions. The results obtained at full-scale demonstrate that both the composting process and the final end product (compost) are not altered by the presence of compostable diapers in crucial aspects such as pathogenic content, stability and elemental composition (including nutrients and heavy metals). The main conclusion of this study is that the collection of the OFMSW with compostable diapers can be a new way to transform this waste into high-quality compost.     

Comparative Biodegradation in Soil Behaviour of two Biodegradable Polymers Based on Renewable Resources

This work presents the last phase of long-term experimental studies on the biodegradation in soil behaviour of polymers destined for agricultural applications. The paper focuses on comparative studies between the biodegradation in soil behaviour of two important biodegradable polymers based on renewable resources: poly(lactic acid) (PLA) versus polyhydroxyalkanoates (PHA). Full-scale experiments were carried out during the period June 2008–January 2009. Different methods of exposure were applied in the case of polyhydroxyalkanoates, simulating the agricultural biodegradable mulching films use and their fate in soil after the end of their useful lifetime. The field results were compared with the results of biodegradation under controlled laboratory conditions simulating biodegradation in soil, using soil from the experimental field. Further, the field results were compared against the results of biodegradation under farm composting conditions.     

Definition of compostability criteria for packaging: Initiatives in Italy

The management of solid waste is changing. The traditional approach based on landfilling of mixed refuses is shifting toward a system based on the at-source sorting of waste into specific fractions. The biological treatment of the organic fraction is considered to be an appropriate form of disposal not only for the “traditional≓ feedstock such as food scraps and vegetable and garden waste, but also for biodegradable packaging, when not recyclable in other ways. Any change from a complex system to another is difficult since many factors are to be organized and optimized. Industry must develop and manufacture compostable products, municipalities must build composting plants and organize source-separated collection, and regulatory bodies must define widely acceptable criteria of compostability. In Europe, the European Union has assigned the last task to the CEN, to provide common criteria and avoid hindrance to commercial exchanges. In Italy the UNI, the national standardization organization, has produced a working document to contribute to the discussion on the European level. In this paper the UNI scheme is described. A condensed version of this paper was presented by one of the authors (F.D.I.) at the 5th annual meeting of the BEDP Society, held in Nashville, September 22–26, 1996, during a session covering International Standards for Biodegradation Testing.     

An Overview on the Mechanical Behaviour of Biodegradable Agricultural Films

The mechanical behavior of various types of biodegradable materials depends, mainly, on their chemical composition and the application conditions. Various additives are added into the bioblends to improve their properties, which sometimes even reach the levels of the conventional plastics. It is well known that the environmental conditions during production, storage, and usage of these materials influence their mechanical properties. Ageing during the useful lifetime also causes great losses in the elongation. In the present paper, the overall mechanical behavior of biodegradable films, which may be considered suitable for agricultural applications, but also of partially biodegradable films, is reviewed and analyzed. Selected critical mechanical properties of films before their exposure to biodegradation are investigated and compared against those of conventional agricultural films.     

Cellulose Fiber/Bentonite Clay/Biodegradable Thermoplastic Composites

Adding cellulose fiber reinforcement can improve mechanical properties of biodegradable plastics, but fiber must be well dispersed to achieve any benefit. The approach to dispersing fiber in this study was to use aqueous gels of sodium bentonite clay. These clay-fiber gels were combined with powdered compostable thermoplastics and calcium carbonate filler. The composite was dried, twin-screw extruded, and injection molded to make thin parts for tensile testing. An experimental design was used to determine the effect of fiber concentration, fiber length, and clay concentration. Polybutylene adipate/terephthalate copolymer (PBAT) and 70/30 polylactic acid (PLA)/PBAT blend were the biodegradable plastics studied. The composite strength decreased compared to the thermoplastics (13 vs. 19 MPa for PBAT, 27 vs. 38 MPa for the PLA/PBAT blend). The composite elongation to break decreased compared to the thermoplastics (170% vs. 831% for PBAT, 4.9% vs. 8.7% for the PLA/PBAT blend). The modulus increased for the composites compared to the thermoplastic standards (149 vs. 61 MPa for PBAT, 1328 vs. 965 MPa for the PLA/PBAT blend). All composite samples had good water resistance.     

Investigating Malaysian stakeholders’ perceptions of the government’s aim to replace conventional plastic bags with biodegradable and compostable bioplastic bags

Journal of Material Cycles and Waste Management - A transition from petroleum-based plastic bags to biodegradable and compostable bioplastic bags will affect stakeholders across the value chain of...     

Biodegradable Soy-Based Plastics: Opportunities and Challenges

Today's plastics are designed with little consideration for their ultimate disposability or the effect of the resources (feedstocks) used in making them. This has resulted in mounting worldwide concerns over the environmental consequences of such materials when they enter the mainstream after their intended uses. This led to the concept of designing and engineering new biodegradable materials–materials that have the performance characteristics of today's materials but that undergo biodegradation along with other organic waste to soil humic materials. Hence, the production of biodegradable materials from annually renewable agricultural feedstocks has attracted attention in recent years. Agricultural materials such as starches and proteins are biodegradable and environmentally friendly. Soybean is a good candidate for manufacturing a large number of chemicals, including biodegradable plastics, as it is abundantly available and cheap. Soy protein concentrate, isolate, or flakes could be compounded with synthetic biodegradable plastics such as polycaprolactone or poly (lactic acid) to make molded products or edible films or shopping bags and make the environment cleaner and greener.     

Carbon dioxide and ammonia emissions during composting of mixed paper, yard waste and food waste

The objective of the work was to provide a method to predict CO2 and NH3 yields during composting of the biodegradable fraction of municipal solid wastes (MSW). The compostable portion of MSW was simulated using three principal biodegradable components, namely mixed paper wastes, yard wastes and food wastes. Twelve laboratory runs were carried out at thermophilic temperatures based on the principles of mixture experimental and full factorial designs. Seeded mixed paper (MXP), seeded yard waste (YW) and seeded food waste (FW), each composted individually, produced 150, 220 and 370 g CO2-C, and 2.0, 4.4 and 34 g NH3-N per dry kg of initial substrate, respectively. Several experimental runs were also carried out with different mixtures of these three substrates. The effect of seeding was insignificant during composting of food wastes and yard wastes, while seeding was necessary for composting of mixed paper. Polynomial equations were developed to predict CO2 and NH3 (in amounts of mass per dry kg of MSW) from mixtures of MSW. No interactions among components were found to be significant when predicting CO2 yields, while the interaction of food wastes and mixed paper was found to be significant when predicting NH3 yields.     

Experimental Processing of Biodegradable Drip Irrigation Systems—Possibilities and Limitations

The increased cost associated with the waste removal and disposal of conventional agricultural plastic in contact with the soil combined with the gradually decreasing cost of the biodegradable plastics allowed the commercialization of biodegradable mulching films. Since the conventional thin wall or tape drip irrigation system lies under the mulching film and is used for one season only, it would be desirable to replace it with a biodegradable one. This paper presents the results of a research work investigating the possibilities and limitations in developing biodegradable drip irrigation thin wall pipes and pipes. The first ever experimental biodegradable drip irrigation thin wall pipes were produced. Rigid pipes were also produced for experimental purposes. Manufacturing problems were encountered in the processing of the biodegradable drippers and irrigation thin wall pipes with the experimental materials due to the complex formulation of the raw materials and the fact that the machinery used was specifically designed for PE processing. Experimental biodegradable thin wall pipes made of Bioflex with embedded drippers made of Mater-Bi were produced. The processing problems encountered with the production of thin wall pipes were surpassed during the experimental production of rigid type irrigation pipes. A biodegradable rigid irrigation pipe made of a grade of Mater-Bi, with embedded cylindrical drippers made of another grade of Mater-Bi was produced successfully. A better understanding of the thermal profile of the biodegradable raw materials and the use of processing equipment adapted to this profile might allow in the future the manufacturing of thin wall drip irrigation pipes for agricultural applications, and the use of alternative biodegradable materials.     

Household, hotel and market waste audits for composting in Vietnam and Laos.

In Da Nang and Ha Long, Vietnam and in Vientiane, Laos, there was interest by local authorities in separating and composting waste in order to reduce environmental and health problems at the local landfills and to produce a soil conditioner for local agricultural use. To assist in the planning of composting projects, three studies were carried out to estimate waste quantities and composition. 1. A 9-day audit of waste from 45 vendors in a market in Vientiane, the capital of Laos. The total quantity of waste and the quantity in each of nine categories were estimated for each of six different types of vendors. 2. A 7-day audit of waste disposed by three hotels in the tourist area of Ha Long, Vietnam. Waste quantities were estimated in total, on a per guest basis, and in three main categories: compostables, recyclables and miscellaneous. 3. A 7-day audit of waste collected from 74 households in Da Nang, the fourth largest city in Vietnam. Waste from each household was separated into compostable and non-compostable waste. Over 60% of each waste source comprised compostable waste and this was considered significant enough to warrant further planning of composting operations.