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Photofermentative hydrogen production from molasses in tubular photobioreactor with pH control

Oflaz, Fatma Betül
Biological hydrogen production has the potential to supply hydrogen from various wastes as feedstock and operation under ambient conditions. In order to obtain cost effective production, photobioreactors (PBRs) that can operate for long durations while utilizing waste are necessary. Two primary issues limiting the duration are decrease in pH and the non-optimal C/N ratio. The main aim of this study was to construct and operate a pH control system for a pilot scale photobioreactor (20 L) to achieve prolonged outdoor hydrogen production from molasses by R. capsulatus by stabilizing pH during operation. Optimum C/N ratio was also investigated for molasses utilization by R. capsulatus for indoor and simulated outdoor conditions in small scale photobioreactors in batch mode. Simulated outdoor conditions for day and night cycle were designed as indoor experiments with changing temperature and light/dark cycle. Effects of constant pH under indoor were investigated to increase molasses utilization in small scale. Long-term outdoor hydrogen production on diluted molasses in a pilot-scale PBR using photofermentative bacteria was demonstrated. The experiment lasted 48 days and carried out on August 16 and October 2, 2017. PID control system was chosen to control pH and it was successfully implemented. The highest productivity was 0.69 mol H2/(m3.h). For small-scale experiments, the C/N ratio was decided as 45 and the highest productivities were 0.38 and 0.69 mol H2/(m3.h), under indoor and simulated outdoor conditions, respectively. With constant pH conditions, molasses concentration could be increased to 15 from 5 mM with better productivity.