Enhancement of biodegradability of disposable polyethylene in controlled biological soil

Plastics as polyethylene are widely used in packaging and other agricultural applications. They accumulate in the environment at a rate of 25 million tons per year. Thus, the development and use of degradable plastics was proposed as a solution for plastic waste problem. Because of the ever-increasing use of plastic films, nowadays, biodegradability has become a useful characteristic for plastics. Conversely, the introduction of biodegradable plastics has generated a need for methods to evaluate the biodegradation of these polymers in landfills and solid waste treatment systems such as composting or anaerobic digestion treatment plants. The purpose of this study was to investigate the biodegradation of disposable low-density polyethylene bags containing starch (12%), autoxidizable fatty acid ester and catalytic agents in soil. Structurally this work intended to evaluate the capacity of Phanerochaete chrysosporium (ATCC 34541) to enhance polyethylene film biodegradation in soil microcosms. Soil samples inoculated with P. chrysosporium were mixed with LDPE/starch blend films and biological changes of the films and soil were monitored for 6 months. The biodegradation of polyethylene starch blend film has been determined by the physical, chemical and biological properties of the samples such as pH, biomass, CO₂ formation, percentage elongation, relative viscosity and FTIR spectrum.     

Biofouling and stability of synthetic polymers in sea water

Commercial synthetic polymers namely Polycarbonate (PC), Low density polyethylene (LDPE), High density polyethylene (HDPE), and Polypropylene (PP) coupons were immersed for a period of 12 months (Feb 2006 – Feb 2007) in Bay of Bengal, East coast, India. Samples were retrieved every month and the extent of biofouling and biodegradation were monitored. Biofouling was found to depend not only on the season but also on the chemical nature of the polymer. Surface energy of all the four polymers is positively correlated with fouling only at the initial stages (three months) while surface roughness had a negative correlation. The later increased during the study period. Total suspended solids and organic matter were more abundant on HDPE, followed by PP and LDPE, indicating that among polyolefins hydrophobic surfaces (lower surface energy) favor biofouling over one year. Maximum fouling was observed on polycarbonate during initial three months. Chlorophyll a showed a decreasing trend during the study, as secondary foulers such as Balanus amphitrite, were dominant after the monsoon (6th month in the present study). Maximum weight loss was seen in LDPE (1.9%), followed by that in HDPE (1.6%), PC (0.69%) and finally in PP (0.65%) samples in the 12 months time period. FTIR spectra of PC displayed a decrease in carbonate carbonyl index, while an initial increase and a decrease in carbonyl index of polyolefins as a function of time indicated biodegradation.     

Biodegradation of natural and synthetic rubbers: A review

Since polymeric materials do not decompose easily, disposal of waste polymers is a serious environmental concern. Widespread studies on the biodegradation of rubbers have been carried out in order to overcome the environmental problems associated with rubber waste. This report provides an overview on the microbial degradation of natural and synthetic rubbers. Rubber degrading microbes, bacteria and fungi, are ubiquitous in the environment especially soil. The qualitative data like plate assay, scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and Sturm test indicated that both natural and synthetic rubbers can be degraded by microorganisms. It has confirmed that the enzymes latex clearing protein (Lcp) and rubber oxygenase A (RoxA) are responsible for the degradation of natural and synthetic rubbers. Lcp was obtained from Gram-positive bacterium Streptomyces sp. strain K30 and RoxA from Gram-negative bacterium Xanthomonas sp. strain 35Y. Analysis of degradation products of natural and synthetic rubbers indicated the oxidative cleavage of double bonds in polymer backbone. Aldehydes, ketones and other carbonyl groups were detected as degradation products from cultures of various rubber degrading strains. This review emphasizes the importance of biodegradation in environmental biotechnology for waste rubber disposal.     

Biological degradation of plastics: a comprehensive review

Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. With the excessive use of plastics and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. Awareness of the waste problem and its impact on the environment has awakened new interest in the area of degradable polymers. The interest in environmental issues is growing and there are increasing demands to develop material which do not burden the environment significantly. Biodegradation is necessary for water-soluble or water-immiscible polymers because they eventually enter streams which can neither be recycled nor incinerated. It is important to consider the microbial degradation of natural and synthetic polymers in order to understand what is necessary for biodegradation and the mechanisms involved. This requires understanding of the interactions between materials and microorganisms and the biochemical changes involved. Widespread studies on the biodegradation of plastics have been carried out in order to overcome the environmental problems associated with synthetic plastic waste. This paper reviews the current research on the biodegradation of biodegradable and also the conventional synthetic plastics and also use of various techniques for the analysis of degradation in vitro.     

Improved biodegradation of Congored by using Bacillus sp

The biodegradation of Congored, a toxic azo dye, was studied by using a hybrid technique involving sonolysis as pretreatment followed by biological treatment. The experiments were carried out with and without pretreatment using dye solution as a sole source of nutrition with an isolated and acclimatized strain of Bacillus sp. obtained from tannery industry effluent. The pretreatment time was varied as 30, 60, 90, 120, 150 and 180 min and then the pretreated dye solution was subjected to biological treatment. The effectiveness of pretreatment was compared with the results of biological degradation of non pretreated Congored and the results showed that the pretreatment improved the efficiency of the biodegradation of Congored. During the biological degradation, the increase in initial dye concentration decreased the decolorization rate and at high concentrations (1500 and 2000 mg/l), the inhibition was observed. The optimum pH and temperature were determined to be 7.0 and 37 degrees C, respectively. The data obtained through biodegradation experiments were fitted with five different kinetic models and the results were analyzed.     

生物降解聚烯烃类塑料研究进展

聚烯烃类塑料是一类以C–C键为骨架的高分子材料,被广泛应用于日常生活的各个领域。由于具有稳定的化学性质并且难以被环境中的微生物快速降解,聚烯烃塑料废弃物在全球范围内持续积累,造成了严重的环境污染及生态危机。近年来,利用生物方法降解聚烯烃类塑料引起了研究人员的广泛关注。自然界丰富的微生物资源为生物降解聚烯烃类塑料废弃物提供了可能,已经有一些对聚烯烃塑料具有降解能力的微生物被陆续报道。本文总结了聚烯烃类塑料生物降解资源及生物降解机制的研究进展,提出了目前聚烯烃类塑料生物降解过程存在的问题,并对未来的研究方向进行了展望。     

Call for biotechnological approach to degrade plastic in the era of COVID-19 pandemic

Plastic pollution is a global issue and has become a major concern since Coronavirus disease (COVID)-19. In developing nations, landfilling and illegal waste disposal are typical ways to dispose of COVID-19-infected material. These technologies worsen plastic pollution and other human and animal health problems. Plastic degrades in light and heat, generating hazardous primary and secondary micro-plastic. Certain bacteria can degrade artificial polymers using genes, enzymes, and metabolic pathways. Microorganisms including bacteria degrade petrochemical plastics slowly. High molecular weight, strong chemical bonds, and excessive hydrophobicity reduce plastic biodegradation. There is not enough study on genes, enzymes, and bacteria-plastic interactions. Synthetic biology, metabolic engineering, and bioinformatics methods have been created to biodegrade synthetic polymers. This review will focus on how microorganisms' degrading capacity can be increased using recent biotechnological techniques.     

Enhanced anaerobic gas production of waste activated sludge pretreated by pulse power technique

An electric pulse-power reactor consisting of one coaxial electrode and multiple ring electrodes was developed to solubilize waste activated sludge (WAS) prior to anaerobic digestion. By pretreatment of WAS, the soluble chemical oxygen demand (SCOD)/total chemical oxygen demand (TCOD) ratio and exocelluar polymers (ECP) content of WAS increased 4.5 times and 6.5 times, respectively. SEM images clearly showed that pulse-power pretreatment of WAS was found to result in destruction of sludge cells. Batch-anaerobic digestion of pulse-power treated sludge showed 2.5 times higher gas production than that of untreated sludge. Solubilized sludge cells by pulse-power pretreatment would be readily utilized for anaerobic microorganisms to produce anaerobically-digested gas. Slow or lagged gas production in the initial anaerobic digestion stage of pulse-power pretreated sludge implied that the methane-forming stage of anaerobic digestion would be the rate-limiting step for anaerobic digestion of pulse-power pretreated sludge.     

A review of plastic waste biodegradation

With more and more plastics being employed in human lives and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. This review looks at the technological advancement made in the development of more easily biodegradable plastics and the biodegradation of conventional plastics by microorganisms. Additives, such as pro-oxidants and starch, are applied in synthetic materials to modify and make plastics biodegradable. Recent research has shown that thermoplastics derived from polyolefins, traditionally considered resistant to biodegradation in ambient environment, are biodegraded following photo-degradation and chemical degradation. Thermoset plastics, such as aliphatic polyester and polyester polyurethane, are easily attacked by microorganisms directly because of the potential hydrolytic cleavage of ester or urethane bonds in their structures. Some microorganisms have been isolated to utilize polyurethane as a sole source of carbon and nitrogen source. Aliphatic-aromatic copolyesters have active commercial applications because of their good mechanical properties and biodegradability. Reviewing published and ongoing studies on plastic biodegradation, this paper attempts to make conclusions on potentially viable methods to reduce impacts of plastic waste on the environment.     

Impacts of sterilization, microwave and ultrasonication pretreatment on hydrogen producing using waste sludge

Hydrogen production by sterilization, microwave and ultrasonication pretreated waste sludge was investigated in this study. A new strain of Pseudomonas sp. GZ1 (EF551040) was inoculated in pretreated waste sludge to produce hydrogen. The experimental results showed that different pretreated sludge had evident differences in the yield of hydrogen production and lag time. Sterilized sludge had the largest yield of hydrogen production, and the maximum yield was 15.02 ml/gTCOD. The lag time of using sterilized sludge was 15 h, longer than other two pretreated sludge. Using the ultrasonicated sludge, the hydrogen production yield was smallest and lag time was shortest in the three pretreated sludge. Protein and carbohydrate could be released from waste sludge by pretreatment. Protein was the main nutrient used for hydrogen production. The concentration of protein, carbohydrate and SCOD increased after pretreatment and fermentation. The impacts of different pretreatments on hydrogen production were also discussed in detail.     

Plant compounds that induce polychlorinated biphenyl biodegradation by Arthrobacter sp. strain B1B.

Plant compounds that induced Arthrobacter sp. strain B1B to cometabolize polychlorinated biphenyls (PCBs) were identified by a screening assay based on the formation of a 4,4'-dichlorobiphenyl ring fission product. A chemical component of spearmint (Mentha spicata), l-carvone, induced Arthrobacter sp. strain B1B to cometabolize Aroclor 1242, resulting in significant degradation of 26 peaks in the mixture, including selected tetra- and pentachlorobiphenyls. Evidence for PCB biodegradation included peak disappearance, formation of a phenylhexdienoate ring fission product, and chlorobenzoate accumulation in the culture supernatant. Carvone was not utilized as a growth substrate and was toxic at concentrations of greater than 500 mg liter-1. Several compounds structurally related to l-carvone, including limonene, p-cymene, and isoprene, also induced cometabolism of PCBs by Arthrobacter sp. strain B1B. A structure-activity analysis showed that chemicals with an unsaturated p-menthane structural motif promoted the strongest cometabolism activity. These data suggest that certain plant-derived terpenoids may be useful for promoting enhanced rates of PCB biodegradation by soil bacteria.     

A Review of Plastic Waste Biodegradation

ABSTRACT

With more and more plastics being employed in human lives and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. This review looks at the technological advancement made in the development of more easily biodegradable plastics and the biodegradation of conventional plastics by microorganisms. Additives, such as pro-oxidants and starch, are applied in synthetic materials to modify and make plastics biodegradable. Recent research has shown that thermoplastics derived from polyolefins, traditionally considered resistant to biodegradation in ambient environment, are biodegraded following photo-degradation and chemical degradation. Thermoset plastics, such as aliphatic polyester and polyester polyurethane, are easily attacked by microorganisms directly because of the potential hydrolytic cleavage of ester or urethane bonds in their structures. Some microorganisms have been isolated to utilize polyurethane as a sole source of carbon and nitrogen source. Aliphatic-aromatic copolyesters have active commercial applications because of their good mechanical properties and biodegradability. Reviewing published and ongoing studies on plastic biodegradation, this paper attempts to make conclusions on potentially viable methods to reduce impacts of plastic waste on the environment.     

New perspectives in plastic biodegradation

During the past 50 years new plastic materials, in various applications, have gradually replaced the traditional metal, wood, leather materials. Ironically, the most preferred property of plastics--durability--exerts also the major environmental threat. Recycling has practically failed to provide a safe solution for disposal of plastic waste (only 5% out of 1 trillion plastic bags, annually produced in the US alone, are being recycled). Since the most utilized plastic is polyethylene (PE; ca. 140 million tons/year), any reduction in the accumulation of PE waste alone would have a major impact on the overall reduction of the plastic waste in the environment. Since PE is considered to be practically inert, efforts were made to isolate unique microorganisms capable of utilizing synthetic polymers. Recent data showed that biodegradation of plastic waste with selected microbial strains became a viable solution.     

Comparative biodegradation of HDPE and LDPE using an indigenously developed microbial consortium

A variety of bacterial strains were isolated from waste disposal sites of Uttaranchal, India, and some from artificially developed soil beds containing maleic anhydride, glucose, and small pieces of polyethylene. Primary screening of isolates was done based on their ability to utilize high- and low-density polyethylenes (HDPE/LDPE) as a primary carbon source. Thereafter, a consortium was developed using potential strains. Furthermore, a biodegradation assay was carried out in 500-ml flasks containing minimal broth (250 ml) and HDPE/ LDPE at 5 mg/ml concentration. After incubation for two weeks, degraded samples were recovered through filtration and subsequent evaporation. Fourier transform infrared spectroscopy (FTIR) and simultaneous thermogravimetric-differential thermogravimetry-differential thermal analysis TG-DTG-DTA) were used to analyze these samples. Results showed that consortium-treated HDPE (considered to be more inert relative to LDPE) was degraded to a greater extent 22.41% weight loss) in comparison with LDPE (21.70% weight loss), whereas, in the case of untreated samples, weight loss was more for LDPE than HDPE (4.5% and 2.5%, respectively) at 400 degrees . Therefore, this study suggests that polyethylene could be degraded by utilizing microbial consortia in an eco-friendly manner.     

Fungal bioremediation of polyethylene: Challenges and perspectives

Plastics have become ubiquitous in both their adoption as materials and as environmental contaminants. Widespread pollution of these versatile, man-made and largely petroleum-derived polymers has resulted from their long-term mass production, inappropriate disposal and inadequate end of life management. Polyethylene (PE) is at the forefront of this problem, accounting for one-third of plastic demand in Europe in part due to its extensive use in packaging. Current recycling and incineration processes do not represent sustainable solutions to tackle plastic waste, especially once it becomes littered, and the development of new waste-management and remediation technologies are needed. Mycoremediation (fungal-based biodegradation) of PE has been the topic of several studies over the last two decades. The utility of these studies is limited by an inconclusive definition of biodegradation and a lack of knowledge regarding the biological systems responsible. This review highlights relevant features of fungi as potential bioremediation agents, before discussing the evidence for fungal biodegradation of both high- and low-density PE. An up-to-date perspective on mycoremediation as a future solution to PE waste is provided.     

Thermophilic whole-cell degradation of polyethylene terephthalate using engineered Clostridium thermocellum

Polyethylene terephthalate (PET) is a mass-produced synthetic polyester contributing remarkably to the accumulation of solid plastics waste and plastics pollution in the natural environments. Recently, bioremediation of plastics waste using engineered enzymes has emerged as an eco-friendly alternative approach for the future plastic circular economy. Here we genetically engineered a thermophilic anaerobic bacterium, Clostridium thermocellum, to enable the secretory expression of a thermophilic cutinase (LCC), which was originally isolated from a plant compost metagenome and can degrade PET at up to 70°C. This engineered whole-cell biocatalyst allowed a simultaneous high-level expression of LCC and conspicuous degradation of commercial PET films at 60°C. After 14 days incubation of a batch culture, more than 60% of the initial mass of a PET film (approximately 50 mg) was converted into soluble monomer feedstocks, indicating a markedly higher degradation performance than previously reported whole-cell-based PET biodegradation systems using mesophilic bacteria or microalgae. Our findings provide clear evidence that, compared to mesophilic species, thermophilic microbes are a more promising synthetic microbial chassis for developing future biodegradation processes of PET waste.     

Methods for Assessment of Biodegradability of Plastic Films in Soil

Traditional and novel techniques were tested and compared for their usefulness in evaluating biodegrad-ability claims made for newly formulated “degradable” plastic film products. Photosensitized polyethylene (PE), starch-PE, extensively plasticized polyvinyl chloride (PVC), and polypropylene (PP) films were incorporated into aerobic soil. Biodegradation was measured for 3 months under generally favorable conditions. Carbon dioxide evolution, residual weight recovery, and loss of tensile strength measurements were supplemented, for some films, by gas chromatographic measurements of plasticizer loss and gel permeation chromatographic (GPC) measurement of polymer molecular size distribution. Six- and 12-week sunlight exposures of photosensitized PE films resulted in extensive photochemical damage that failed to promote subsequent mineralization in soil. An 8% starch-PE film and the plasticized PVC film evolved significant amounts of CO₂ in biodegradation tests and lost residual weight and tensile strength, but GPC measurements demonstrated that all these changes were confined to the additives and the PE and PVC polymers were not degraded. Carbon dioxide evolution was found to be a useful screening tool for plastic film biodegradation, but for films with additives, polymer biodegradation needs to be confirmed by GPC. Photochemical cross-linking of polymer strands reduces solubility and may interfere with GPC measurements of polymer degradation.     

Biodegradation and bioremediation of endosulfan contaminated soil

Among the three mixed bacterial culture AE, BE, and CE, developed by enrichment technique with endosulfan as sole carbon source, consortium CE was found to be the most efficient with 72% and 87% degradation of alpha-endosulfan and beta-endosulfan, respectively, in 20 days. In soil microcosm, consortium AE, BE and CE degraded alpha-endosulfan by 57%, 88% and 91%, respectively, whereas beta-endosulfan was degraded by 4%, 60% and 67% after 30 days. Ochrobacterum sp., Arthrobacter sp., and Burkholderia sp., isolated and identified on the basis of 16s rDNA gene sequence, individually showed in situ biodegradation of alpha-endosulfan in contaminated soil microcosm by 61, 73, and 74, respectively, whereas degradation of beta-endosulfan was 63, 75, and 62, respectively, after 6 weeks of incubation over the control which showed 26% and 23 % degradation of alpha-endosulfan and beta-endosulfan, respectively. Population survival of Ochrobacterum sp., Arthrobacter sp., and Burkholderia sp., by plate count on Luria Broth with carbenicillin showed 75-88% survival of these isolates as compared to 36-48% of survival obtained from PCR fingerprinting. Arthrobacter sp. oxidized endosulfan to endosulfan sulfate which was further metabolized but no known metabolite of endosulfan sulfate was detected.     

Degradation and metabolism of synthetic plastics and associated products by Pseudomonas sp.: capabilities and challenges

Synthetic plastics, which are widely present in materials of everyday use, are ubiquitous and slowly‐degrading polymers in environmental wastes. Of special interest are the capabilities of microorganisms to accelerate their degradation. Members of the metabolically diverse genus Pseudomonas are of particular interest due to their capabilities to degrade and metabolize synthetic plastics. Pseudomonas species isolated from environmental matrices have been identified to degrade polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, polyethylene terephthalate, polyethylene succinate, polyethylene glycol and polyvinyl alcohol at varying degrees of efficiency. Here, we present a review of the current knowledge on the factors that control the ability of Pseudomonas sp. to process these different plastic polymers and their by‐products. These factors include cell surface attachment within biofilms, catalytic enzymes involved in oxidation or hydrolysis of the plastic polymer, metabolic pathways responsible for uptake and assimilation of plastic fragments and chemical factors that are advantageous or inhibitory to the biodegradation process. We also highlight future research directions required in order to harness fully the capabilities of Pseudomonas sp. in bioremediation strategies towards eliminating plastic wastes.     

Design of a Papain Immobilized Antimicrobial Food Package with Curcumin as a Crosslinker

Contamination of food products by spoilage and pathogenic microorganisms during post process handling is one of the major causes for food spoilage and food borne illnesses. The present green sustainable approach describes the covalent immobilization of papain to LDPE (low density polyethylene), HDPE (high density polyethylene), LLDPE (linear low density polyethylene) and PCL (polycaprolactam) with curcumin as the photocrosslinker. About 50% of curcumin and 82-92% of papain were successfully immobilized on these polymers. After 30 days, the free enzyme retained 87% of its original activity, while the immobilized enzyme retained more than 90% of its activity on these polymers. Papain crosslinked to LLDPE exhibited the best antibiofilm properties against Acinetobacter sp. KC119137.1 and Staphylococcus aureus NCIM 5021 when compared to the other three polymers, because of the highest amount of enzyme immobilized on this surface. Papain acts by damaging the cell membrane. The enzyme is able to reduce the amount of carbohydrate and protein contents in the biofilms formed by these organisms. Meat wrapped with the modified LDPE and stored at 4°C showed 9 log reduction of these organisms at the end of the seventh day when compared to samples wrapped with the bare polymer. This method of crosslinking can be used on polymers with or without functional groups and can be adopted to bind any type of antimicrobial agent.