COMPARATIVE EVALUATION OF THE POLYHYDROXYLALKANOATES (PHAs) FERMENTABILITY FROM DIFFERENT SOURCES FOR BIOREMEDIATION APPLICATIONS

Nowadays bioremediation technologies are receiving growing attention as cost-effective and in-situ applicable strategies for contaminated site. Moreover, in soil and groundwater naturally occurring microorganisms can effectively reduce chlorinated compounds, by the so-called Biological Reductive Dechlorination (BRD). They consist of several stages to convert a toxic organic contaminant (high chlorinated ethane/ethene) to less toxic components (until ethene). Nevertheless, the lack of electron donors is usually recognized as a limiting factor in BRD. To overcome the problem, the in-situ bioremediation of chlorinated solvents has been used based on the injection of electron donors to speed up the reductive dechlorination natural processes. In this context, the use of biopolymers known as polyhydroxybutyrates (PHBs), which are completely biodegradable polyesters, have been advantageously used as electron donors source for sustaining in-situ BRD (Matturro et al., 2018). These biopolymers are produced in very strictly conditions which cause high-cost of production. In recent years, more interest has been dedicated to polyhydroxylalkanates (PHAs) obtained by selected mixed microbial cultures (MMC) which reduce the total costs by combing the wastewater treatment with bioplastic production (Valentino et al., 2017). This work is aimed to investigate, by monitoring of Volatile Fatty Acids (VFAs) production in microcosms, the anaerobic fermentability of three laboratory-made PHA / PHB (as obtained by MMC), in comparison with three commercial PHB. The laboratory-made materials were: (i) raw biomass after PHA accumulation step, (ii) purified PHA extracted from the (i) ( (i) and (ii) were from Treviso-Italy wastewater full-scale plant) and (iii) PHB blending with zero-valent iron particles to combine consolidated chemically reactive media with a slow-releasing carbon source (prepared at the University of Rome “La Sapienza”) (Chronopoulou et al., 2016). The tests were set up by adding the different materials in serum bottles with anaerobic mineral medium and inoculated with an anaerobic activated sludge. After some latency period, the VFAs production increased for both commercial and lab-made products, although the differences are the way that they arrive at the maximum quantity of production. These differences can be attributed to the granulometry of the materials since they have been studied in powder and pellets formats which determines various surface areas and, therefore, different kinetics, and as expected the VFAs increase more rapidly for the powder ones. Moreover, the behavior observed for the raw PHA is very interesting due to its immediate fermentation with quantity of VFAs comparable to commercial ones; in addition, due to its possible environmental application, the cost of production is much lower as it has not been subjected of extraction and purification phase. Also, the PHB-ZVI composite material showed a rapid fermentation with high quantity of VFAs production; the advantage that this material could offer in the field of remediation resides in the synergistic effect is coupling of biotic and abiotic reductive dechlorination processes.