Hydroxyapatite Fabrication for Enhancing Biohydrogen Production from Glucose Dark Fermentation

Hydroxyapatite (HA) had the effect of maintaining the pH balance of the reaction system and promoting enzyme activity. In this work, hydroxyapatite was synthesized by coprecipitation and characterized for biohydrogen (bioH₂) production from glucose. The highest bioH₂ yield obtained was 182.33 ± 2.41 mL/g glucose, amended with an optimal dosage of 400 mg/L HA, which was a 55.80% higher bioH₂ yield compared with the control group without any addition. The results indicated that HA facilitated the deterioration of organic substances and increased the concentration of soluble microbial products (SMPs). Microbial community analysis revealed that HA significantly increased the abundance of Firmicutes from 35.27% (0 mg/L, HA) to 76.41% (400 mg/L, HA), which played an essential role in bioH₂ generation. In particular, the abundance of Clostridium sensu stricto 1 increased from 15.33% (0 mg/L HA) to 45.17% (400 mg/L HA) and became the dominant bacteria. The results also indicated that HA likely improves bioH₂ production from organic wastewater in practice.