Investigating the effects of operational parameters on photofermentation in batch and semi-batch reactors and the applications of photofermentation in multi-stage energy systems


Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Faculty of Engineering, Department of Environmental Engineering, Turkey

Approval Date: 2018

Thesis Language: English

Student: MELİH CAN AKMAN

Principal Consultant (For Co-Consultant Theses): Tuba Hande Bayramoğlu

Co-Consultant: Ufuk Gündüz

Abstract:

The aim of this thesis study was to investigate the effects of operational parameters on photofermentation in batch and semi-batch reactors, and the application of photofermentation in multi-stage energy systems. Firstly, three operational conditions of the substrate concentration, Volatile Suspended Solids (VSS) concentration and the light intensity leading to the maximization of hydrogen production in a single stage were optimized. The highest hydrogen production rate (HPR) of 1.04 mmol H2/L.h was achieved at the optimum values of 35.35 mM HAc initial substrate concentration, 0.27 g VSS/L initial biomass (Rhodobacter capsulatus) concentration and 3955 lux (263.6 W/m2) light intensity. The highest HPR obtained in batch reactors, as second-stages of a two-stage dark fermentation and photofermentation system, was 0.48±0.08 mmol H2/L.h and hydrogen yield was 1.61±0.24 mol H2/mol acetate. The highest HPR and hydrogen yield were observed as 0.10±0.005 mmol H2/L.h and 0.95±0.03 mol H2/mol acetate in batch photofermentation reactors, as third-stages of a three-stage system composed of dark fermentation, methanogenesis and photofermentation processes in sequence. Finally, the HRT value leading to the highest hydrogen production was observed as 4 days in semi-batch photofermentation reactors in a three-stage system. The results of this thesis study are believed to be beneficial in photobioreactor designs and operational conditions for photofermentative hydrogen production with greater rates. Both the photofermentative hydrogen production yields and total energy yields obtained in three-stage system, which is not studied so far in literature, provide a preliminary knowledge for future three-stage systems and comparison for two-stage systems frequently encountered in literature.