Effect of pH, temperature and agitation on thermophilic biohydrogen production using immobilized cells on carbon composites (GAC-NiFe₃O₄)

Carbon composites-immobilized cell was utilized to enhance biohydrogen production. The initial pH, temperature and agitation effect was studied using the one-factor-at-a-time (OFAT) method. The optimal initial pH obtained was at pH 6.0 with hydrogen yield (HY) of 2.66 +/- 0.09 mol H-2/mol sugar, correlating with Gompertz constant of H-m = 974.99 mL, R-m = 17.90 mL/h and lambda = 1.70 h. At 60 degrees C, the highest HY was obtained at 2.75 +/- 0.11 mol H-2/mol sugar. These corresponded to the Gompertz constant of H-m = 934.58 mL, R-m = 18.78 mL/h and lambda = 1.89 h. The optimal agitation obtained was at 120 rpm, attaining the highest HY of 3.44 +/- 0.54 mol H-2/mol sugar, corresponding to the Gompertz constant of H-m = 1054.86 mL, R-m = 24.37 mL/h and lambda = 3.90 h. The rRNA sequencing result revealed that the predominant species in the study was Thermoanaerobacterium. This study provides critical insight into process control conditions on biohydrogen production.