Abstract
Expansion of pH condition for thermophilic L-lactate fermentation of unsterilized artificial garbage was examined in batch mode culture with using L-lactate fermented broth as inoculum. The conditions were set at pH 6.0 and 55°C in order to bring pH condition close to optimal growth condition of Bacillus coagulans. The results showed that the fermentation with using L-lactate fermented broth of 400 mL/1L-Reactor as inoculum led to L-lactate fermentation instead of butyrate fermentation. Lactate concentration of 34 g/L, lactate yield based on initial carbohydrate concentration of 0.5 and optical purity of lactate of 99% were obtained in this fermentation. Then, possibility of semi-continuous fermentation was examined, because inoculation was conducted by the residual broth in fill-and-draw operation. The conditions set for the semi-continuous fermentation were pH 6.0, 55°C and COD loading of 44.8 g-COD/L-Reactor/day (HRT of 2 days and once a day operation). The fermentation resulted in lactate concentration of 26 g/L, the yield of around 0.5 and optical purity of produced lactate of 99% without any butyrate detection during 10 days operation.
A device for recording consumption of neutralization reagent by which pH condition was kept at given value was set up to the reactor for the sake of monitoring the fermentation process of lactate. Comparison between its records and analyzed lactate concentration through operation time revealed that the records described the lactate fermentation process well. Volumetric production rate of lactate could be calculated as 1.26 g/L/hr with the data monitored by this device.
