Performing Department
(N/A)
Non Technical Summary
Plastic pollution has become a global environmental problem, and most currently utilized plastics are virtually non-degradable and difficult to recycle. In recent years, a number of biodegradable and compostable plastics have been developed, but commercial composting facilities do not want to handle them because they are difficult to break down. As a result, many businesses around the country are buying biodegradable plastics in an effort to be sustainable, but they end up in landfills where they do not break down. Anaerobic digestion is a promising strategy for treating biodegradable plastics, especially as part of a larger organic waste collection system. However, prior research involving the anaerobic digestion of bioplastics suggests that their degradation rate is slower than other substrates and needs to be improved before they become a viable addition to these systems. An anaerobic digestion facility is being planned on the Oklahoma State University campus, which would include substrates such as food waste, animal production waste, and hopefully plastic waste. The proposed project involves the evaluation of various strategies to enhance the breakdown of bioplastics during anaerobic digestion. The main objectives are to evaluate potential pretreatment strategies to enhance the breakdown of bioplastics during anaerobic digestion and to evaluate the use of phenazine to enhance methane production during the anaerobic digestion of bioplastics.
Animal Health Component
70%
Research Effort Categories
Basic
30%
Applied
70%
Developmental
(N/A)
Goals / Objectives
Plastic pollution is a growing concern, and anaerobic digestion is a well-established method for transforming organic waste into biogas, which can be used for heat and power production. Ifall single-use plasticscould be made of bioplastics and sent to anaerobic digestion facilities for disposal, the environmental pollution caused by plastics could be virtually eliminated.The main goal of the proposed projectis to increase the rate of degradation of bioplastics during anaerobic digestion for the development of an optimized digester that can handle food waste, plastic waste, and animal waste.The specific objectives include:Evaluate potential pretreatment strategies for an enhanced breakdown of bioplastics during anaerobic digestion.Evaluate the use of conductive phenazines to enhance methane production during the anaerobic digestion of bioplastics.
Project Methods
In order to facilitate an improved rate of degradation for bioplastics, the two specific objectives will be evaluated in parallel during the first year, and then in combination during the second year. During year one, numerous pretreatments of bioplastics will be evaluated as well as the use of numerous different phenazines in the presence of bioplastics. All treatments will be applied to severaldifferent bioplastics. The best-performing treatments from each objective will then be combined during year two.Lab Scale Anaerobic Digestion Setup Small-scale mesophilic anaerobic digestate incubations will be performed in 250 ml serum bottles. An active methane-producing digestate has been established utilizing food waste from an OSU dining facility and animal waste from the OSU dairy farm. The digestate will be combined with a mineral medium (described previously) for seeding all the small incubators (Beckmann et al., 2016). Serum bottles will be purged with nitrogen gas, capped with butyl rubber stoppers, and crimped with aluminum seals. The incubations will be stored in the dark at a constant temperature of 20oC and will be monitored for methane production and bioplastic degradation at regular intervals. Biogas volume will be measured with gastight syringes at room temperature. Subsamples from the digesters will be analyzed for gas composition and fatty acid composition (methane, CO2, H2, and volatile fatty acids) once per week using a gas chromatograph (GC) with an FID, and PDD detector.Bioplastic Substrates While many different bioplastics exist, two of the most widely used by industry include polylactic acid (PLA) and polyhydroxybutyrate (PHB), both of which can be made from renewable resources such as starch and have been shown to be biodegradable in various environments (Haider et al, 2019; Al Hosni et al., 2019). They are both also heavily used in food service products, so PLA and PHB will be the initial focus of this study. Four different commercially available products will be selected, in the form of precast food containers or cups (which represent the type of products used in dining facilities). Bioplastic coupons will initially be cut to a uniform size (approx.1 x 1 cm) to fit into serum bottles.Evaluation of Different Bioplastic Pretreatments Previous studies have shown that temperature is a critical parameter for the degradation of some bioplastics. One of the goals is to screen a number of pretreatment options for each of the bioplastics being evaluated. Pretreatments will include heating in hot water at 70 oC for 20 min or 2 hours, steam treatment for 20 min, autoclave (121oC for 20 min), and infrared heat treatment (240 oC) for 2 min or 5 min (for a total of 7 different pretreatments for each of the 4 bioplastics). After pretreatment, bioplastic sample coupons will be inserted into serum bottles containing digestate and placed in controlled temperature conditions for degradation. Each flask will contain ten coupons of identical size (1 cm x 1 cm). Every 10 days, one bottle will be removed per treatment for evaluation of plastic degradation. Samples will be removed, washed, dried, and measured to observe the reduction in size. In addition, biogas production will be monitored weekly for all AD incubations.Use of Phenazines for Process Enhancement Digestate incubations with and without phenazine treatments and with and without bioplastic amendment will be established in the lab at OSU. A wide spectrum of phenazines with conductive and semi-conductive potential will be added to the digesters for the direct transfer of electrons to methanogenic archaea and bioplastic-degrading bacteria. The following phenazines will be utilized: Neutral red, Phenazine ethosulfate, Phenazine methosulfate, 2, 3-Diaminophenazine, Phenazinol, and Pycocyanin.All phenazines will be added at a final concentration of 50-250 mM to the ADs. In addition to gas composition, overall cell concentration in the AD incubations will be determined using fluorescence microscopy with SybrGreen I and live/dead cell staining. Redox potential and pH of all ADs will be measured weekly using a combined pH-redox probe.Genomic Analyses A digestion environment will include a complex mixture of enzymes and microorganisms. In addition, the microbial community will evolve over time. It is hypothesized that this evolution will include the growth and development of bioplastic-degrading organisms. Microbial community composition will be determined periodically for the most successful AD incubations. Genomic analyses will be carried out from active incubations. Bacterial and archaeal 16S rRNA gene sequencing will determine the composition while metagenomic sequencing will decipher the potential function of the microbial communities in the digesters. Therefore, DNA will be extracted and purified for a comprehensive 16S rRNA and metagenomic analysis.Particle Morphology Analysis Bioplastic particles recovered from the incubations will be visualized using a Scanning Electron Microscope (Joel JSM 6360, Peabody MA) to evaluate changes in the morphology of the particles. The beads will be attached to stubs using adhesive tape, coated with gold, and examined using an acceleration voltage of 10 kV at various levels of magnification.