Biodegradable materials — Present situation and future perspectives

Biodegradable polymers constitute a loosely defined family of polymers that are designed to degrade through the action of living organisms. They offer a possible alternative to traditional nonbiodegradable polymers if recycling is impractical or not economical. The main driving force behind this technology is the solid waste problem, particularly with regard to the decreasing availability of landfills, the litter problem and the pollution of marine environment by non-biodegradable plastics. Technologies like composting used for the disposal of food and yard waste are the most suitable for the disposal of biodegradable materials. European Standardisation Committee (CEN), Organic Reclamation and Composting Association (ORCA) and German Institute for Standardisation (DIN) have already defined, at a draft level, the basic requirements for a product to be declared compostable. They are based on: complete biodegradability of the product in a time period compatible with composting, measured through respirometric tests (ASTM D5338-9, ISO/CD14855, etc); disintegration of the material during the fermentation phase; no negative effects on compost quality; checking of laboratory-scale results on pilot/full-scale composting plants. These requirements set forth a common base for a universal marking system to readily identify products to be composted. Thermoplastic starch-based polymers and aliphatic polyesters are the two classes of biodegradable materials with the greatest near-term potential. This paper reviews a great variety of properties, structures and biodegradation behaviour of thermoplastic starch in combination with poly(vinyl alcohol) or some aliphatic polyesters like poly(hydroxybutyrate-co-hydroxyvalerate), poly(lactic acid), poly(ϵ-caprolactone) and poly(butanediyl succinate).     

Biodegradability of conventional and bio-based plastics and natural fiber composites during composting,anaerobic digestion and long-term soil incubation

Plastics are a major constituent of municipal solid waste that pose a growing disposal and environmental pollution problem due to their recalcitrant nature. To reduce their environmental impacts and allow them to be transformed during organic waste recycling processes, various materials have recently been introduced to improve the biodegradability of plastics. These include conventional plastics amended with additives that are meant to enhance their biodegradability, bio-based plastics and natural fiber composites. In this study, the rate and extent of mineralization of a wide range of commercially available plastic alternative materials were determined during composting, anaerobic digestion and soil incubation. The biodegradability was assessed by measuring the amount of carbon mineralized from these materials during incubation under conditions that simulate these three environments and by examination of the materials by scanning electron micrography (SEM). The results showed that during a 660 day soil incubation, substantial mineralization was observed for polyhydroxyalkanoate plastics, starch-based plastics and for materials made from compost. However, only a polyhydroxyalkanoate-based plastic biodegraded at a rate similar to the positive control (cellulose). No significant degradation was observed for polyethylene or polypropylene plastics or the same plastics amended with commercial additives meant to confer biodegradability. During anaerobic digestion for 50 days, 20–25% of the bio-based materials but less than 2% of the additive containing plastics were converted to biogas (CH₄ + CO₂). After 115 days of composting, 0.6% of an additive amended polypropylene, 50% of a plastarch material and 12% of a soy wax permeated paper pulp was converted to carbon dioxide. SEM analysis showed substantial disintegration of polyhydroxyalkanoate-based plastic, some surface changes for other bio-based plastics and coconut coir materials but no evidence of degradation of polypropylene or polypropylene containing additives. Although certain bio-based plastics and natural fibers biodegraded to an appreciable extent in the three environments, only a polyhydroxyalkanoate-based resin biodegraded to significant extents during the time scale of composting and anaerobic digestion processes used for solid waste management.     

To compost or not to compost: Carbon and energy footprints of biodegradable materials’ waste treatment

Many life cycle assessments of bio-based and biodegradable materials neglect the post-consumer waste treatment phase because of a lack of consistent data, even though this stage of the life cycle may strongly influence the conclusions. The aim of this paper is to approximate carbon and energy footprints of the waste treatment phase and to find out what the best waste treatment option for biodegradable materials is by modelling home and industrial composting, anaerobic digestion and incineration. We have compiled data-sets for the following biodegradable materials: paper, cellulose, starch, polylactic acid (PLA), starch/polycaprolactone (MaterBi), polybutyrate-adipate-terephthalate (PBAT, Ecoflex) and polyhydroxyalkanoates (PHA) on the basis of an extensive literature search, experiments and analogies with materials for which significant experience has been made. During biological waste treatment, the materials are metabolised so a part of their embodied carbon is emitted into air and the remainder is stored as compost or digestate. The compost or digestate can replace soil conditioners supporting humus formation, which is a benefit that cannot be achieved artificially. Experimental data on biodegradable materials shows a range across the amount of carbon stored of these materials, and more trials will be required in the future to reduce these uncertainties. Experimental data has also shown that home and industrial composting differ in their emissions of nitrous oxide and methane, but it should be noted that data availability on home composting is limited. The results show that anaerobic digestion has the lowest footprint for the current level of technology, but incineration may become better in the future if energy efficiency in waste incineration plants improves significantly. Home composting is roughly equal to incineration with energy recovery in terms of carbon and energy footprint when carbon credits are considered. The same applies to industrial composting if carbon credits are assigned for compost to replace straw. Carbon credits can therefore considerably affect the results, but there are significant uncertainties in how they are calculated. Incineration may become better than home composting in the future if the average energy efficiency in waste incineration plants improves significantly. However, biological waste treatment options should be chosen when soil carbon is a limiting factor.     

Testing the performance and the disintegration of biodegradable bags for the collection of organic wastes

The biodegradability of five different biodegradable garbage bags were analyzed according to the DIN‐Standard draft 54'900 “Measurement of the compostability of polymers”. The tests have to prove that a “biodegradable polymer” can be degraded under controlled composting conditions. Five different types of bags were tested. The bags were made from cornstarch, polycaprolactone and Kraft paper. To claim compostability the material has to biodegrade and to disintegrate in a composting system, to mineralize completely to carbon dioxide and water, and to fulfill several quality criteria such as a limited amount of heavy metals, no toxic organic compounds and no organic non‐biodegradable additives. The analysis of the heavy metal content showed that the polymers themself contained very low amounts of heavy metals. However, the printing with green and blue colors with copper pigments was increasing the copper content in all products. The mineralization experiments showed that all five materials disintegrated during the rotting process in standardized compost and all five tested products also fulfilled the mineralization rate of 60% within six months.     

Thermo-valorisation in integrated waste management

In 2002, approximately 25 million tons of Municipal Solid Waste (MSW) were produced in Italy, but no more than 5.5 million were collected separately. Data analysis shows that despite the progress in differentiated waste collection and in the process of quality recovery, dumps are still the most common means of disposal.With reference to thermo-valorisation, although the number of active thermal plants and the amount of thermo-valorised waste has increased (by over 10% from 1999 to 2000), total processed waste appears to be excessively low compared to the amount of waste produced. Moreover, it is below the EU average.Our objective was to analyse three different scenarios for the quantity of thermally valorisable waste through to 2005.We have also evaluated the incineration of MSW taking into account the technological, environmental and economic factors in different plant types (with and without energy and heat recovery) considering emission quantity and quality with possible CO₂ recovery.The most economical and environmental solution might be the transformation of waste to synthetic gas for use as an energy and heat source in a conventional power plant in the future.From current information we understand that today thermo-destruction with energy recovery and a combined energy–heat cycle could be an option with great benefits for the environment, and could even be competitive compared to other solutions for replacing some energy sources.     

Biodegradation of packaging materials: composting of polyolefins

The compostability of LDPE, PP and heterophasic E-P Copolymers was studied for 5 months under normal and accelerated composting environments. Bio-susceptibility of pre-UV (290 nm) treated films (∼ 100μm, 5 X 5 cm) was measured by monitoring the weight loss, intrinsic viscosity [η], chain scission, functional group evolution (FT-IR) and surface morphology (SEM). It was found that with the increasing time of UV treatment, weight loss was increased in compost. Almost linear decrease in [η] was observed for irradiated and composted samples. The temperature of compost and extra addition of thermophilic microbes significantly influenced the biodegradation. In general, it was concluded that the composition of copolymer markedly affected the compostability and increased ethylene content, slowed down the microbial activity.     

A novel process for anaerobic composting of municipal solid waste

A novel process has been developed and evaluated in a pilotscale program for conversion of the biodegradable fraction of municipal solid waste (MSW) to methane via anaerobic composting. The sequential batch anaerobic composting (SEBAC) process employs leachate management to provide organisms, moisture, and nutrients required for rapid conversion of MSW and removal of inhibitory fermentation products during start-up. The biodegradable organic materials are converted to methane and carbon dioxide in 21–42 d, rather than the years required in landfills.     

Development of a novel,two-step process for treating municipal biosolids for beneficial reuse

Modern municipal sewage waste treatment plants use conventional mechanical and biological processes to reclaim wastewaters. This process has an overall effect of converting a water pollution problem into a solid waste disposal problem (sludges or biosolids). An estimated 10 million tons of biosolids, which require final disposal, are produced annually in the United States. Although numerous disposal options for biosolids are available, including land application, landfilling, and incineration, disposal costs have risen, partly because of increased federal and local environmental restrictions(1). A novel, thermomechanical biosolids pre-treatment process, which allows for a variety of potential value-added uses, was developed. This two-step process first employs thermal explosive decompression to inactivate or kill the microbial cells and viruses. This primary step also results in the rupture of a small amount of the microbial biomass and increases the intrinsic fluidity of the biosolids. The second step uses shear to effect a near-complete rupturing of the microbial biomass, and shears the nondigested organics, which increases the overall surface area. Pretreated biosolids may be subjected to a secondary anaerobic digestion process to produce additional fuel gas, and to provide for a high-quality, easily dewatered compost product. This novel biosolids pretreatment process was recently allowed a United States patent.     

The influence of biotic and abiotic factors on the rate of degradation of poly(lactic) acid (PLA) coupons buried in compost and soil

Poly(lactic) acid (PLA) is a compostable biopolymer and has been commercialised for the for the manufacture of short-shelf life products. As a result, increasing amounts of PLA are entering waste management systems and the environment; however, the degradation mechanism is unclear. While hydrolysis of the polymer occurs abiotically at elevated temperature in the presence of water, potential catalytic role for microbes in this process is yet to be established. In this study, we examined the degradation of PLA coupons from commercial packaging at a range of temperatures (25°, 37°, 45°, 50° and 55 °C) in soil and compost and compared with the degradation rates in sterile aqueous conditions by measuring loss of tensile strength and molecular weight (Mw). In addition, in order to assess the possible influence of abiotic soluble factors in compost and soil on degradation of PLA, degradation rates in microorganism-rich compost and soil were compared with sterile compost and soil extract at 50 °C. Temperature was determined to be the key parameter in PLA degradation and degradation rates in microorganism-rich compost and soil were faster than in sterile water at temperatures 45° and 50 °C determined by tensile strength and Mw loss. Furthermore, all tensile strength was lost faster after 30 and 36 days in microorganism-rich compost and soil, respectively, than in sterile compost and soil extract, 57 and 54 days, respectively at 50 °C. Significantly more Mw, 68% and 64%, was lost in compost and soil, respectively than in compost extract, Mw, 53%; and in soil extract, 57%. Therefore, degradation rates were faster in microorganism-rich compost and soil than in sterile compost and soil extract, which contained the abiotic soluble factors of compost and soil at 50 °C. These comparative studies support a direct role for microorganisms in PLA degradation at elevated temperatures in humid environments. No change in tensile strength or Mw was observed either 25° or 37 °C after 1 year suggesting that accumulation of PLA in the environment may cause future pollution issues.     

Recycling of polyethylene terephthalate (PET Or PETE) plastics – An alternative to obtain value added products: A review

Waste management is become one of the world's most pressing issues. Plastic is one of the most widely utilised materials in the modern world. Plastic manufacturing and usage have risen globally in recent decades due to its low weight and outstanding mechanical properties. Plastic has a wide range of applications due to such good properties include lightweight, high strength, and extended durability. Because of plastics are non- or low-biodegradable, a vast quantity of plastic waste is generated every day, making waste disposal the most pressing matter globally. Furthermore, improper waste disposal pollutes the environment. An ecologically friendly approach is necessary to locket these issues. One of the solutions is to recycle this sort of garbage. There are many plastic recycling technologies available, however practically all of them have certain restrictions. Chemical recycling of plastic, on the other hand, has been shown to be more efficient than other recycling methods. This article provides a quick overview of chemical recycling of PET post-consumer waste and the synthesis of potentially value-added products such as dye or dyestuffs, bolaform surfactant, bio-degradable polyesters, drug carrier, Metal-organic framework (MOF), bio-degradable polymeric scaffolds, polyurethane foam and coating materials etc.     

Determination of trimethylsilanol in the environment by LT-GC/ICP-OES and GC-MS

The combination of element-specific investigation by low temperature gas chromatography coupled on-line with inductively coupled plasma optical emission spectroscopy (LT-GC/ICP-OES) and gas chromatography using mass spectrometry detection (GC-MS), as an additional analytical technique for molecular identification, was employed for the determination of volatile organosilicon species. Gaseous and liquid samples from waste deposit sites, waste composting tanks and sewage-disposal plants were investigated. It was frequently possible to identify the labile silanol compound trimethylsilanol as a dominant silicon species in waste disposal and waste composting gases. The results presented give rise to the assumption that trimethylsilanol is a volatile product of the degradation of organosilicon materials under special environmental conditions.     

Compostable Films of Mater-Bi Z Grades

Abstract

This paper focuses on the composting behavior of Mater-Bi Z grades for filming and on their in-use behavior, mainly as composting bags for the collection of organic waste. The compostability of Mater-Bi Z grades was demonstrated by means of a three-step test by following the approach of different international committees working on this matter comprising lab tests (biodegradability tests such as ASTM D 5338, ASTM 5901, and terrestrial toxicity tests) and full-scale composting tests. In addition to their compostability, the in-use behavior was estimated by tests of separate collection of organic wastes in different municipalities (Furstenfeldbruck/Bavaria, Korneuburg/Austria) comparing paper bags with Mater-Bi bags.     

Heavy metal contamination in compost. A possible solution

With the objective of improving qualitative characteristics of compost, an analytical survey was carried out in a composting plant in Lombardy (Italy) in all process of production, with particular reference to heavy metals (HM) Zn and Pb. The investigation was principally aimed to study the contents and the accumulation of HM during composting process and to identify a technological solution for reducing HM content in the final product. A merceological analysis of Municipal Solid Waste (MSW) input to the composting plant, a chemical analysis of the organic fraction of MSW after mechanical separation, and a comparison with values reported by some authors, showed that Zn and Pb are significant contaminants, even though concentrations have recently decreased in comparison to previous years. On the basis of Zn and Pb content in raw material input to the plant, an estimate of the theoretical value of Zn and Pb in produced compost was made. The comparison of theoretical values with the real ones, experimentally determined, confirmed that at the end of composting process the concentration is 2.6 times the initial value for Zn and 1.6 times the initial value for Pb, as suggested by some authors. Finally, the analytical investigation of Zn and Pb contents in the compost refining line, carried out by means of sieving tests, showed that by eliminating a fraction of compost < 1 mm, both Zn and Pb, which is the more critical one, can be largely removed, without a substantial yield loss (only 10% of the final product is eliminated).     

Recycling of waste from polymer materials: An overview of the recent works

Polymer recycling is a way to reduce environmental problems caused by polymeric waste accumulation generated from day-to-day applications of polymer materials such packaging and construction. The recycling of polymeric waste helps to conserve natural resource because the most of polymer materials are made from oil and gas. This paper reviews the recent progress on recycling of polymeric waste form some traditional polymers and their systems (blends and composites) such as polyethylene (PE), polypropylene (PP), and polystyrene (PS), and introduces the mechanical and chemical recycling concepts. In addition, the effect of mechanical recycling on properties including the mechanical, thermal, rheological and processing properties of the recycled materials is highlighted in the present paper.     

Recent advances and challenges in recycling and reusing biomedical materials

Medical waste has increased in the past 3 years as a result of the coronavirus disease 2019 (COVID-19) pandemic. This condition is expected to exacerbate due to the growing healthcare markets and aging population, posing health threats to the public via environmental footprints. To alleviate these impacts, there is an urgent need for medical waste management. This article highlights the drawbacks of current disposal methods and the potential of medical waste reuse and recycling, emphasizing the processes, materials, and chemistry involved in each practice. Further discussion is provided on the chemical and mechanical recycling of plastics as the dominating material in biomedical applications, and possible strategies and challenges in recycling and reusing biomedical materials are explored in this review.     

Lignocellulose degradation in mushroom composts

The edible mushroomAgaricus bisporus is grown commercially on composted manure/straw mixtures. However, this proven composting procedure is wasteful of raw materials. A nonmanure compost was developed (Smith, 1980) with two main aims:

1. To conserve raw materials, while still producing a compost favoringAgaricus bisporus colonization and giving an economic yield of mushrooms.
2. To speed up composting, hence making more efficient use of labor, farm equipment, and buildings.

A “conservation compost” (wheat straw, bran, whey, urea, peat, and gypsum) is ready for inoculation with mushroom mycelium (spawning) after 7 d preparation, i.e., 2 d pre-wetting of straw, then 4–5 d composting under controlled conditions. Whereas a traditional manure/wheat straw compost is produced by composting in windrows (8–11 d) followed by a controlled pasteurization phase (5–7 d). In the preparation of a traditional mushroom compost, as much as 60% of the initial dry matter is lost by microbial degradation prior to spawning. By shortening the composting process to 7 d conservation of cellulose and hemicellulose is achieved with only some 30% loss in dry matter. Straw hemicelluloses are degraded much quicker than cellulose during composting. Hence, the measurable extracellular laminarinase and xylanase activities of the compost microflora appear much greater than their cellulase activities at this period in both composts. A peak in laminarinase and xylanase activity after 48 h in manure compost corresponds with the increase in microbial populations. A pronounced increase in thermophilic bacterial and actinomycete populations occurs in “conservation composts” as readily available soluble carbohydrates are assimilated. Initially, this results in higher uniform compost temperatures (60?C+) and leads to a reduced thermophilic fungal population (10³ viable propagules g^-1 dry wt compost), which may explain the lowered enzyme activities found in the “conservation composts” and thus the reduced degradation of lignocellulose. The compost microflora showed no laccase activity during composting, and little if any lignin was degraded. However,Agaricus bisporus does possess a moderately active lignolytic system and a strongly active cellulolytic system. Subsequent experiments have shown that increased mushroom yields may be obtained from these composts when urea is replaced by chicken manure as the nitrogen supplement (Smith, 1983); this has not affected compost “selectivity” for mushroom growth, dry matter loss, or the duration of the process. Although yield of mushrooms, based on compost weights at spawning tend to be lower than what would be expected from traditional composts, yield calculated on the basis of weight of starting materials is usually much higher.     

Determination of trimethylsilanol in the environment by LT-GC/ICP-OES and GC-MS

The combination of element-specific investigation by low temperature gas chromatography coupled on-line with inductively coupled plasma optical emission spectroscopy (LT-GC/ICP-OES) and gas chromatography using mass spectrometry detection (GC-MS), as an additional analytical technique for molecular identification, was employed for the determination of volatile organosilicon species. Gaseous and liquid samples from waste deposit sites, waste composting tanks and sewage-disposal plants were investigated. It was frequently possible to identify the labile silanol compound trimethylsilanol as a dominant silicon species in waste disposal and waste composting gases. The results presented give rise to the assumption that trimethylsilanol is a volatile product of the degradation of organosilicon materials under special environmental conditions. Received: 24 July 1997 / Revised: 8 October 1997 / Accepted: 21 October 1997     

Anaerobic digestion of municipal solid waste

Tuna processing wastes (sludges high in fat, oil, and grease [FOG]) and municipal solid waste (MSW) generated on Tutuila Island, American Samoa, represent an ongoing disposal challenge. The biological conversion of the organic fraction of these wastes to useful products, including methane and fertilizer-grade residue, through anaerobic high-solids digestion is currently in scale-up development. The suitability of the anaerobic digestion residues as a soil amendment was evaluated through extensive chemical analysis and greenhouse studies using corn as an indicator crop. Additionally, native Samoan soil was used to evaluate the specific application rates for the compost. Experiments established that anaerobic residues increase crop yields in direct proportion to increases in the application rate. Additionally, nutrient saturation was not demonstrated within the range of application rates evaluated for the Samoan soil. Beyond nutrient supplementation, organic residue amendment to Samoan soil imparts enhanced water- and nutrient-binding capacities.     

Conversion of food industrial wastes into bioplastics with municipal activated sludge

Plastics have become an integral part of our contemporary life because of many desirable properties including durability and resistance to degradation. However, these non-degradable, petrochemicals-derived plastics accumulate in the environment at a rate of 25 million tons per year. Recently there is an interest in the development of a class of microbially produced bioplastics, e.g., polyhydroxyalkanoates (PHAs) which retain the desired physical and chemical properties of conventional synthetic plastics. Broader usage of biodegradable plastics in packaging and disposable products as a solution to the environmental problem would heavily depend on further reduction of costs and the discovery of novel biodegradable plastics with improved properties. In this paper, the microbial production of PHAs by activated sludge utilizing food industrial wastes is reported. The melting points of the products as well as the co-polymer composition of the products investigated by GC and NMR were compared. By use of activated sludge to convert the carbon source into PHAs not only environment-friendly bioplastics are produce, but also part of the problem of the disposal of municipal activated sludge is solved. The selection of food industrial waste as carbon resource can also further reduce the cost of production of PHAs.     

Ash and Slag Waste as a Secondary Raw Material

In the process of industrial corporation activities a lot of waste, which pollutes the atmosphere, is generated, for example ash and slag. In Tomsk region, by estimates, ash stores occupy about 600 hectares, which contain about 25 million tons by weight. In Russian thermal power-stations ash disposal areas there are about 1.3 billion tons of ash, and only 10% of it is used. That is why this problem is topical enough. In this paper the scheme of producing ash ceramic bricks and complex ash and slag waste processing is shown. Besides, profitability of the project is presented.