Process and reactor design for biophotolytic hydrogen production

Abstract

The green alga Chlamydomonas reinhardtii has the ability to produce molecular hydrogen (H₂), a clean and renewable fuel, through the biophotolysis of water under sulphur-deprived anaerobic conditions. The aim of this study was to advance the development of a practical and scalable biophotolytic H₂ production process. Experiments were carried out using a purpose-built flat-plate photobioreactor, designed to facilitate green algal H₂ production at the laboratory scale and equipped with a membrane-inlet mass spectrometry system to accurately measure H₂ production rates in real time. The nutrient control method of sulphur deprivation was used to achieve spontaneous H₂ production following algal growth. Sulphur dilution and sulphur feed techniques were used to extend algal lifetime in order to increase the duration of H₂ production. The sulphur dilution technique proved effective at encouraging cyclic H₂ production, resulting in alternating Chlamydomonas reinhardtii recovery and H₂ production stages. The sulphur feed technique enabled photobioreactor operation in chemostat mode, resulting in a small improvement in H₂ production duration. A conceptual design for a large-scale photobioreactor was proposed based on these experimental results. This photobioreactor has the capacity to enable continuous and economical H₂ and biomass production using green algae. The success of these complementary approaches demonstrate that engineering advances can lead to improvements in the scalability and affordability of biophotolytic H₂ production, giving increased confidence that H₂ can fulfil its potential as a sustainable fuel of the future.