Best mode for photo-fermentation hydrogen production: The semi-continuous operation

In this study, a semi-continuous culture mode was used for photo-hydrogen production by Rhodopseudomonas sp. nov. strain A7 and 3 key operating parameters (the interval feeding time, initial feeding time and the feeding volume ratio) were optimized to improve hydrogen production performance. The rate and yield of hydrogen production decreased from 19.7 ml-H₂/l/h to 4.63 ml-H₂/l/h with the interval feeding time increased from 1 day to 3 days, and the yield of hydrogen decreased gradually and reached the maximum value of 2.11 mol-H₂/mol acetate when the interval feeding time is at 1 day. The initial feeding time was extended from 3 days to 4 days, the rate of hydrogen production decreased from 24.8 ml-H₂/l/h to 23 ml-H₂/l/h, and the rate of hydrogen production decreased to 22.2 ml-H₂/l/h when it was extended to 5 days. And specific yield of hydrogen production of 2.65, 2.48 and 2.38 mol-H₂/mol-acetate was obtained, respectively. The yield of hydrogen increased with the increase of feeding volume ratio from 10% to 40% and reached a maximum value of 3.22 mol-H₂/mol acetate at feeding volume ratio of 40%, the specific yield and rate of hydrogen production gradually decreased with the feeding volume ratio further increased to 60%. The optimal parameters of semi-continuous operation are as following: the initial feeding time of 3 days, interval feeding time of 1 day and feeding volume ratio of 40%. In these conditions, the maximum yield (3.22 mol-H₂/mol acetate) and rate (30 ml-H₂/l/h) of hydrogen production and light energy conversion efficiency of 1.9% were obtained. Compared to other hydrogen production mode (batch, continuous and fed-batch culture), the semi-continuous culture mode for photo-hydrogen production exhibited great potential due to following advantages: less loss of biomass, the well stability of system, easy operation and control. Therefore it is the best operation mode for photo-hydrogen production with high yield of hydrogen production and light energy conversion efficiency.