Monitoring Biohydrogen Production and Metabolic Heat in Biofilms by Fiber Bragg Grating Sensors.

A fiber Bragg grating (FBG) was created to accurately and simultaneously monitor the biohydrogen and metabolic heat production in biofilms containing Rhodopseudomonas palustris CQK-01 photosynthetic bacteria (PSB). The proposed hydrogen sensor was made from an FBG unit separated into two regions by a wet etching process; a thin region with a diameter of 15 μm was employed to monitor the temperature. A smaller region of the etched FBG with a diameter of 8.0 μm was coated with a 50 nm-thick Pd film by sputtering to determine the responses to the temperature and hydrogen concentration. To monitor the biohydrogen production and metabolic heat within the biofilms, three FBGs were evenly distributed in a polydimethylsiloxane channel (biofilm carrier) with vertical distances of 80 μm. In addition, the thickness, surface morphology, active biomass, and porosity of the biofilms were investigated. The FBG sensor can rapidly and accurately determine the difference in Bragg wavelength shifts caused by changes in the hydrogen concentration and temperature. The measured biohydrogen concentration is highly correlated with the real biohydrogen production with a correlation of 0.9765. The biohydrogen production capacity of PSB in the surface layer is much higher than that internally because of sharp decreases in the active biomass and porosity from the surface to within the biofilm. The highest biohydrogen concentration is obtained at 1.218 × 104 ppm for a biofilm thickness of 165 μm, and the temperature difference from metabolic heat production is ∼1.1 °C in the biofilm culture.