Anaerobic Biodegradability of Commercial Bioplastic Products: Systematic Bibliographic Analysis and Critical Assessment of the Latest Advances

Bioplastics have entered everyday life as a potential sustainable substitute for commodity plastics. However, still further progress should be made to clarify their degradation behavior under controlled and uncontrolled conditions. The wide array of biopolymers and commercial blends available make predicting the biodegradation degree and kinetics quite a complex issue that requires specific knowledge of the multiple factors affecting the degradation process. This paper summarizes the main scientific literature on anaerobic digestion of biodegradable plastics through a general bibliographic analysis and a more detailed discussion of specific results from relevant experimental studies. The critical analysis of literature data initially included 275 scientific references, which were then screened for duplication/pertinence/relevance. The screened references were analyzed to derive some general features of the research profile, trends, and evolution in the field of anaerobic biodegradation of bioplastics. The second stage of the analysis involved extracting detailed results about bioplastic degradability under anaerobic conditions by screening analytical and performance data on biodegradation performance for different types of bioplastic products and different anaerobic biodegradation conditions, with a particular emphasis on the most recent data. A critical overview of existing biopolymers is presented, along with their properties and degradation mechanisms and the operating parameters influencing/enhancing the degradation process under anaerobic conditions

Two-Stage Process for Energy Valorization of Cheese Whey through Bio-Electrochemical Hydrogen Production Coupled with Microbial Fuel Cell

The present work investigates a two-stage process scheme for cheese whey valorization through energy recovery in different forms by means of bio-electrochemical systems. The first stage consisted of an integrated bio-electrochemical process for H2 and electricity production. This combined dark fermentation with an electrochemical system with the aim of overcoming the typical thermodynamic/biochemical limitations of fermentation and enhancing H2 recovery. The second treatment stage involved a single-chamber microbial fuel cell, featuring an innovative configuration consisting of four air cathodes with fly ash as the oxygen reduction catalyst. The bio-electrochemical process performed in the first stage achieved promising results, displaying a three-times higher H2 production yield compared to conventional dark fermentation. In addition, the experiments using the MFC in the second stage were found to successfully exploit the effluent from the first stage, with COD removal yields of 86% +/- 8% and energy recovery with a maximum current output of 1.6 mA and a maximum power density of 1.2 W/m3

Disposable Mater-Bi® bioplastic tableware: Characterization and assessment of anaerobic biodegradability

In this study commercial starch-based (Mater-Bi®) disposable bioplastic tableware items, which are among the most widely used commercial products available on the market, were selected for lab-scale anaerobic degradability tests. Since the knowledge of the biodegradation profile of bioplastic products is still incomplete, the study was aimed at investigating the maximum biodegradation potential of the materials under ideal anaerobic conditions, as well as the biodegradability degree as a function of treatment time. The experiments were carried out under mesophilic and thermophilic conditions at different food to microorganism ratios and test material sizes, and the specific biogas production and associated kinetics were evaluated. Biogas production was observed only under thermophilic conditions, with conversion yields in the range 602–898 mL/gTOC for the tested cups and 1207 ± 52.8 mL/gTOC for the knives. The degrees of biodegradation and disintegration were found to be strongly dependent on the product composition. Physical, chemical and morphological analyses were used to characterize the tested materials before and after the degradation and potential correlations among process parameters and bioplastic characteristics were derived

Coupling bio- and electro-chemical processes for hydrogen production from organic residues

Hydrogen is a carbon-free energy carrier and the research on alternative production methods, low energy-demanding and not based on fossil sources, plays a key role in the energy transition target. In that context, dark fermentation is considered a promising strategy for bio-hydrogen generation since it allows energy recovery from residual materials such as biodegradable waste. The present work addresses from different perspectives those which are currently believed to be the major challenges of the process. Firstly, a research study on the production yields and the assessment of long-term stability in continuous systems was performed; the results from the experimental campaign involving a number of combinations of operating conditions were reported. Secondly, the feasibility of combining the dark fermentation with electrochemical method was investigated with the aim to overcome the biochemical constraints associated with reduced hydrogen yields. To this purpose, an innovative integrated bio-electrochemical process was designed and tested under different configurations at lab-scale. Lastly, the concept of a multi-stage layout was investigated by means of two different bio-electrochemical systems serving as post processes for the dark fermentation effluent, with the overall aim of achieving a fully energy recovery from the starting substrate through bio-methane and electric current generation as well as providing an adequate level of stabilization of the residual organic matter

Bio‑electrochemical production of hydrogen and electricity from organic waste: preliminary assessment

This study investigated the performance of a novel integrated bio-electrochemical system for synergistic hydrogen production from a process combining a dark fermentation reactor and a galvanic cell. The operating principle of the system is based on the electrochemical conversion of protons released upon dissociation of the acid metabolites of the biological process and is mediated by the electron flow from the galvanic cell, coupling biochemical and electrochemical hydrogen production. Accordingly, the galvanic compartment also generates electricity. Four different experimental setups were designed to provide a preliminary assessment of the integrated bio-electrochemical process and identify the optimal configuration for further tests. Subsequently, dark fermentation of cheese whey was implemented both in a stand-alone biochemical reactor and in the integrated bio-electrochemical process. The integrated system achieved a hydrogen yield in the range 75.5–78.8 N LH2/kg TOC, showing a 3 times improvement over the biochemical process

Anaerobic biodegradation of disposable PLA-based products: Assessing the correlation with physical, chemical and microstructural properties

In the present study commercial Polylactic Acid-based disposable cups and plates were selected for lab scale anaerobic degradability tests. The experiments were carried out under thermophilic conditions at different inoculum to substrate ratios and test material sizes, and the specific biogas production and associated kinetics were evaluated. Maximum biogas production was comparable for almost all the experimental runs (1620 and 1830 NmL/gTOCPLA) and a biodegradation degree in the range 86-100% was attained. Moreover, physical, chemical and microscopical analyses were used to characterize the tested materials before and after the degradation. The products composition was assessed and the presence of some additives (mainly Ca-based) was detected. Potential correlations among the process parameters and product composition were derived and a delay in process kinetics with increasing amount of additives embedded in the polymeric matrix was observed, confirming the relevant influence of the chemical blend on the biodegradation process