Title : Biotechnological approach to valorize emissions: Biological conversion of styrene to polyhydroxyalkanoates using two-phase partitioning bioreactors
Abstract:
Styrene is an important pollutant released from chemical industry. Manufacturing of reinforced plastic, synthetic rubber and resin is the main source of styrene to atmosphere. These industrial activities consume about 15 million tons per year of styrene. In the best of scenarios, styrene emissions are recycled in 60 % and released to atmosphere in 20 %. However, in Mexico, all styrene emissions are released to atmosphere due to lack in emissions legislation. In order to promote sustainable processes to treat emissions from industrial sources in Mexico, this research work is focused to valorize styrene emissions using biotechnological processes to produce high added value products. To achieve this, the use of two-phase partitioning bioreactors (TPPB) which combine aqueous medium with a hydrophobic non-aqueous phase liquid (NAPL) is proposed. Firstly, the NAPL will increase the solubility of styrene into liquid medium because styrene is hydrophobic. Secondly, the use of NAPL will avoid the inhibition of styrene to microorganisms which can be toxic at high concentrations. Thus, NAPL will work as a mass transfer vector of styrene from gaseous to liquid medium and as a reservoir which will reduce the risk of styrene inhibition to microorganisms. This strategy has been successful in the biodegradation of hydrophobic gaseous pollutants, but, TPPB has not been proved in the conversion of this type of pollutants to biopolymers. In order to test the assumptions detailed, two NAPL such as silicon oil and ionic liquids and the strain Pseudomonas putida S12 were chosen. P. putida S12 has been reported to consume styrene and produce polyhydroxyalkanoates (PHAs, a high added value biopolymer). After caring out affinity to target compound, biodegradability and toxicity tests to choose the best NAPL to consume styrene and produce PHAs, it was found that ionic liquid absorbed 7.5 times more styrene than silicon oil (Hsty/IL = 0.0030; Hsty/SO = 0.0226; 28 °C) and both silicon oil and ionic liquid were non-biodegradable by P. putida S12 . However, the ionic liquid caused inhibition to P. putida S12 in contrast to silicon oil which was not toxic for the strain. Then, it was concluded that silicon oil is the best NAPL for the TPPB experiments. Kinetic experiments were performed with and without NAPL to know if the addition of this increases the rate to produce the biopolymer. Results show that styrene removal rate and production rate of biopolymer in the presence of silicon oil were two times greater than control experiments in one phase (without silicon oil). Finally, the use of TPPB is a good alternative to valorize emissions of hydrophobic gaseous pollutants like styrene to produce high valuable products such as PHAs. However, investigations of this technology to show its viability in large scale are need.
