Two treatments showed the highest production of biohydrogen, the treatment 2 in the repetition 1 and the treatment 3 in the repetition 3, the maximum value was obtained with the treatment 2 in the repetition 1 in which were used wastes from lettuce and cabbage leaves, tomato, onion, garlic, pimento, orange, lemon, mango, guava and papaya. The acid conditions were implemented 8 days with value of pH near to 4, the operation of bioreactor was between 5 and 5,5. In the treatment 3 in the repetition 3 were used the same wastes, the acid condition was applied during 7 days with value of pH near to 4,5; the pH of bioreactor operation was between 5 and 5,5. Although was generated more quantity of hydrogen in the treatment 2 during the repetition 1, was in the treatment 3 in the repetition 3 where was obtained the greater hydrogen contentinthegas (18,04%) andgreaterrateofgeneration ofhydrogen.

The maximum production of hydrogen was obtained at the second stage when the pretreat­ment of acidification was applied during 8 days with a value for the pH of 4, a pH of reactor operation between 5 and 5,5; and a value of chemical oxygen demand (COD) near to 20.000 mg/liter of O2. At the first stage when was used a quantity of wastes from tropical fruits greater than wastes of lettuce and cabbage leaves, the chemical oxygen demand (COD) initial was 54.000 mg/liter of O2, however the hydrogen production was significantly less respect to second stage. This indicates that a high value of chemical oxygen demand could inhibit the hydrogen generation; this result is according to reports of different authors [13, 23—29]. When were used vegetal wastes (without wastes of tropical fruits) as lettuce and cabbage leaves, tomato, onion, garlic and husk of cape gooseberry, there were no acid conditions at beginning the process and was necessary to add acid, however there was no response in the biosystems and the pH always was upper than 4,5. Under these conditions there was no production of hydrogen. In addition the chemical oxygen demand was low (12.000 mg/liter of O2).

The results shows that is feasible to produce biohydrogen (hydrogen) when are employed organic wastes from the Central Wholesaler of Antioquia. The wastes should be submitted to a pretreatment acid with a pH between 3,5 y 4,0; during 7 days (or less), then the operation pH should be increased until a value between 5 and 5,5. The chemical oxygen demand (COD) should be between 20.000 and 54.000 mg/liter of O2 this is possible to reach when in the bioprocess is employed a proportion similar of tropical fruit waste and vegetal waste.

2. Conclusions

• It was possible to generate hydrogen from organic wastes of Central Wholesaler of Antio — quia and to improve the bioprocess.

• The chemical oxygen demand (COD) promoted the biohydrogen production, the best results were obtained to values between 20.000 and 54.000 mg/liter of O2. These values were achieved with a heterogeneous mix of fruits and vegetal wastes.

• There was not generation of biohydrogen when the bioprocess started with a pH upper than 4. This ratifies that to generate biohydrogen by anaerobic fermentation is necessary to apply a pretreatment, in this research, a pretreatment under acid conditions (pH between 3,5 and 4,0) was successful.

• Colombia has a high potential to generate hydrogen by anaerobic fermentation due to organic wastes available, these wastes could generate until 28’825.609 m3 of biohydrogen and supply an energetic potential of 144 GW, value upper than the installed potential (13,5 GW).

• The results show that is possible to produce biohydrogen by anaerobic fermentation of organic wastes and providing new sources energetic.

Acknowledgements

The authors acknowledge to National University of Colombia in Medellm and the Central Wholesaler of Antioquia by the financial support to research.

Author details

Edilson Leon Moreno Cardenas*, Deisy Juliana Cano Quintero and Cortes Marin Elkin Alonso

*Address all correspondence to: elmorenoc@unal. edu. co

Engineering Agricultural Department, National University of Colombia, Medellm, Colombia