Calcium effect on fermentative hydrogen production in an anaerobic up-flow sludge blanket system

The effects of calcium ions on a granular fermentative hydrogen production system were investigated in four lab-scale UASB reactors that fed on sucrose (20 g COD/L). The reactors were seeded with anaerobic sewage sludge microflora and operated at a temperature of 35±1°, pH of 6.7 with hydraulic retention times (HRTs) of 24–6 h. The experimental results indicated that calcium ion addition (75∼150 mg/L) could enhance the granulation and elevate hydrogen production efficiency. However, an overly-high calcium concentration (300 mg-Ca⁺²/L) deteriorated the hydrogen productivity. A calcium concentration of 150 mg-Ca⁺²/L resulted in a peak HP of 3.6 mol H₂/mol-sucrose and HPR of 807 mmol-H₂/L-d at HRTs of 8 and 6 h, respectively. The EPS concentration of biohydrogenic biomass was higher than that of the aerobic or methanogenic biomass. The protein/carbon-ratio ranged from 0.17 to 0.26%. The multinomial regression analysis shows that the 75∼150 mg-Ca⁺²/L calcium concentrations and HRT of 6 h were the optimal operating conditions to efficiently produce hydrogen.