Biohydrogen production using suspended and immobilized mixed microflora

Suspended and immobilized anaerobic sludge were utilized to produce hydrogen gas in batch reactors using sucrose as the sole carbon substrate. A variety of immobilization matrices and methods were examined for their suitability to make immobilized H₂ producers. The results show that cells immobilized by calcium alginate matrix supplemented with chitosan and titanium oxide carriers (CA+CH+TiO₂) were the most effective in H₂ production, giving a H₂ production rate of 21.3 mmol·L^-1·h^-1 (at 35°C and 20 g COD-L^-1 of sucrose), which was over three-fold of that obtained from suspended cells (6.8 mmol·L^-1· h^-1). The sucrose conversion was essentially 85% or higher in all runs, and the biogas consisted of only H₂ and CO₂. The major soluble metabolites were butyric acid, acetic acid, and propionic acid, while a small amount of ethanol was also produced. Addition of trace metal salts (Ca²⁺ and Ni²⁺) appeared to enhance the H₂ producing performance for the suspended culture, elevating H₂ production rate from 6.8 to 9.3 and 8.7 mmol·L^-1 ·h^-1, respectively. Moreover, the immobilization matrix containing TiO₂ seemed to result in better H₂ production in general.