Abstract
In the present study, the performance of a 70 L photobioreactor, operating outdoors, was investigated using a purple bacterial strain as Rhodopseudomonas sp. S16-VOGS3 for producing poly-3-hydroxybutyrate (PHB). The novel photobioreactor was equipped with 5 rows L-shaped; the bottom of every row was placed in a stainless-steel tank containing water with controlled temperature. The photofermentation trials were carried out under fed-batch mode and under a semi-continuous regimen using lactic acid as the carbon source. The effect of the irradiance and the carbon/nitrogen ratio on the PHB accumulation was investigated, in order to evaluate the optimal bacterial growth. The results showed the feasibility of the prototype photobioreactor for the production of PHB by Rhodopseudomonas sp. S16-VOGS3 under the natural light/dark cycle. During the fed-batch growth (144 h long), the cumulative PHB increased quickly reaching a maximum value of 377 mg/L and decreased to 255 mg/L during the semi-continuous regimen (336 h long).
Highlights
Global petroleum-based plastic production passed 320 million tons (Mt) worldwide in 2016 and it is expected to double in the 20 years [1]
The results showed the feasibility of the prototype photobioreactor for the production of PHB by Rhodopseudomonas sp
The improved geometry configuration of the novel L-shaped row photobioreactor (L-SRP) tested in the present study is evident and significant respect to some typical horizontal tubular photobioreactors
Summary
Global petroleum-based plastic production passed 320 million tons (Mt) worldwide in 2016 and it is expected to double in the 20 years [1]. Better recycling and the replacement of the petrol plastics with bioplastics (BPs), compostable and biodegradable in different natural environments, could be a concrete answer to this serious environmental problem. The biodegradability of BPs in different natural environments, such as soil and marine/fresh water, is a key property that makes their life cycle more eco-sustainable compared to the conventional plastics. Despite the environmental benefits of BPs, their actual worldwide production is only about 1 Mt/y [1] but their demand is continuously growing and, in accordance with the last market data collected by European Bioplastics, the global BP production capacity is expected to increase from around 2 Mt/y in 2017 to around 2.4 Mt/y in 2022, in absence of government support measures, and to higher values with specific government incentives [4]. PHAs, with poly-3-hydroxybutyrate (PHB) as the simplest and most abundant PHA, are synthesized under stressful conditions by higher plants, bacteria (e.g., Halobacteriaceae and Archea) and many photosynthetic microorganisms such as purple non-sulfur bacteria (PNSB) or genetically enhanced species of microorganisms [5,6,7]
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