A lab-scale frugal solar bioreactor design for cleaner production of bioproducts from thermophilic bacteria in outdoor conditions

Our study introduces an economical solar-powered bioreactor design for producing a model bioproduct, elucidated as a variant of poly-gamma-glutamic acid, using a thermophilic Bacillus licheniformis in a sterile-compromised growth environment. This frugal solar bioreactor (SB) setup repurposes an out-of-service jacketed stirred tank reactor with a working volume of 5 L and incorporates solar photovoltaic (PV) modules and a solar thermal unit to supply the necessary electrical load (1680 Wh) and heat for carrying out 24-hour batch fermentation at 50 °C. By repurposing the condemned equipments, the cost of SB fabrication was brought down by 59 %. In a batch mode of operation, the solar bioreactor yielded a maximum biopolymer concentration of 19.8 ± 0.9 g/L, which was 14.5 % less than the biopolymer titre obtained from a commercial bioreactor under similar production conditions. The molecular weight (MW) of the biopolymer was found to be dependent on the temperature of fermentation, with a maximum MW of 865.7 kDa achieved at 50 °C. It is envisaged that the proposed solar bioreactor design can be used for the effective production of thermophilic bacterial products suited for various low-cost applications.