Assessment of Long-Term Fermentability of PHA-Based Materials from Pure and Mixed Microbial Cultures for Potential Environmental Applications

Neda Amanat,Francesco Valentino,Marta Rossi,Marianna Villano,Bruna Matturro,Marco Petrangeli Papini

doi:10.3390/w13070897

Neda Amanat, Francesco Valentino + Show 4 more

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https://doi.org/10.3390/w13070897

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Abstract

The use of polyhydroxyalkanoates (PHA) as slow-release electron donors for environmental remediation represents a novel and appealing application that is attracting considerable attention in the scientific community. In this context, here, the fermentation pattern of different types of PHA-based materials has been investigated in batch and continuous-flow experiments. Along with commercially available materials, produced from axenic microbial cultures, PHA produced at pilot scale by mixed microbial cultures (MMC) using waste feedstock have been also tested. As a main finding, a rapid onset of volatile fatty acids (VFA) production was observed with a low-purity MMC-deriving material, consisting of microbial cells containing 56% (on weight basis) of intracellular PHA. Indeed, with this material a sustained, long-term production of organic acids (i.e., acetic, propionic, and butyric acids) was observed. In addition, the obtained yield of conversion into acids (up to 70% gVFA/gPHA) was higher than that obtained with the other tested materials, made of extracted and purified PHA. These results clearly suggest the possibility to directly use the PHA-rich cells deriving from the MMC production process, with no need of extraction and purification procedures, as a sustainable and effective carbon source bringing remarkable advantages from an economic and environmental point of view.

Highlights

Polyhydroxyalkanoates (PHA) are biologically synthesized polyesters that are completely biodegradable in the environment and can be bio-based, i.e., derived from renewable resources
Two of them were produced through a multi-stage pilot plant process involving mixed microbial cultures (MMC) and wastes of urban origin as feedstock [6]
The PHA-rich biomass directly deriving from the accumulation stage of the process is hereafter referred to as “MMCRaw PHA,” while the polymer extracted from the microbial cells after the accumulation stage is referred to as “MMC-Extracted PHA1.”

Summary

Introduction

Polyhydroxyalkanoates (PHA) are biologically synthesized polyesters that are completely biodegradable in the environment (under both aerobic and anaerobic conditions) and can be bio-based, i.e., derived from renewable resources. They are considered three-time bio-polymers [1,2]. PHA are not a single polymer, but a family of copolymers featuring a wide array of physical and mechanical properties which depend on the length and composition of the side chains. The polyhydroxybutyrate (PHB) homopolymer is largely studied and well characterized and the copolymer poly(hydroxybutyrate-hydroxyvalerate) (PHBV) is interesting because it has properties similar to polypropylene. PHA can be used for a broad portfolio of applications in numerous fields, including the production of packaging materials, disposable utensils, cosmetic containers, as well as medical applications as drug delivery carriers and environmental applications as a source for long-term release of carbon to drive specific reductive reactions [4,5]

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