The results of kinetic considerations based on modified Gompertz equation (Eq. 4) are shown in table 6. Independently from the kind of food waste (in the active of concentration) it was observed that the increase of the volume of generated hydrogen, small drops in reaction rate and prolongation of the lag phase.

2. Conclusions

The presented results shows that the waste studied in this paper represent a vary good substrate in photophermentation by Rhodobacter sphaeroides. Light intensity of 9 klx and inoculum concentration of 0.36 g dry wt/l (30% v/ v) were used as the most effective (high light conversion efficiency and short duration of the process). The studied wastes has to be treated with high temperature (20 min in 120oC). This pretreatment significantly increases H2 production. The optimum concentrations of wastes were estimated: 40% v/ v for dairy waste and 10% v/v for brewery waste with high COD. These wastes represent the effective (comparable with L-malic acid) nutrient for hydrogen production. Higher wastes concentrations inhibit the process as it initiate fermentation which starts to compete with hydrogen production and additionally increases NHp concentration, which also negatively affect the process. Brewery waste with low COD shows low efficiencies and needs to be concentrated to supply sufficient concentration of organic compounds. An application of untreated dairy wastewater containing suspensions in efficient hydrogen generation process can be performed only at controlled acidity (pH = 7.0). Kinetic measurements proved that the rate of hydrogen generation drops with concentration of the waste and prolongs the lag phase.

3. Acknowledgements

These studies were supported by Polish Ministry of Science and Higher Education (grant no: N N204 185440).