Lactic acid as a substrate for fermentative hydrogen production

Soil was used as seed without pretreatment for the fermentation of lactate in order to produce H ₂. When the pH was kept at a constant level, H ₂ production occurred in three steps. The first was the production of small amounts of H ₂ during the initial growth of the microflora. Then, after a reasonably long period of inactivity during the cultivation stage, a large amount of H ₂ was produced in additional two steps. It was found that the reduction of the pH after the initial growth phase had a positive effect on the H ₂ yield. After cell growth at pH 6 and cultivation at pH 5, a total H ₂ yield of 154 mmol l ^-1 was achieved. It was found that acetate was essential for the rapid H ₂ formation. On the other hand, even small initial concentrations of butyrate impeded the H ₂ formation.