© 2020 Hydrogen Energy Publications LLCThe duration of photofermentative hydrogen production from sugar-based nutrients is limited by gradual acidification caused by the production of organic acids, leading to suboptimal pH. To address this issue, a custom pH control system was built and installed on a 20 L tubular photobioreactor, and operated under outdoor conditions. Long-term, single-stage hydrogen production from molasses was achieved using the purple non-sulfur bacterium, Rhodobacter capsulatus. The run lasted for 48 days, the longest duration achieved in a tubular photobioreactor on molasses as the only feed. pH was maintained close to its optimum value. High-purity hydrogen (above 90% by mole, on average) and near-complete conversion of sucrose was observed. The highest hydrogen productivity was 0.69 molH2/(m3.h). On the other hand, hydrogen production was observed to cease after periods of activity. Production resumed after dilution followed by artificial illumination, indicating that the production activity could be recovered during prolonged runs.