1.3.2. First stage

First and second phase: The quantity and percentage of wastes generated at the Central Wholesaler of Antioquia during the year 2011 are show at the Table 3 and Figure 6. The highest production of wastes was associated to cabbage and lettuce leaves then wastes of citrics (orange and lemon) and finally wastes of mango, guava and others tropical fruits. The Figure 7 shows some pictures of wastes in the storage containers at the Central Wholesaler of Antioquia. With the information of production were selected wastes of cabbage and lettuce leaves, orange, mango, papaya and guava to be employed at the bioprocess.

Third phase: The elemental analysis of wastes selected is show at the Table 4. To orange wastes, the relation C/N obtained was less than values reported in others research. In the others cases the results were close to values reported for wastes with similar characteristics. A relation C/N close to 30 is considered appropriate to growth of anaerobic bacteria [22].

Organics waste

■ Lettuce and cabbage leaves

■ Orange and lemon Pimento, cucumber

■ Mango

■ Tomato

Wastes	C	H	N	C/N	C/N (Literature)
Mango	37.6	6.0	1.5	25.9	34.8
Orange	40.6	5.5	1.3	31.5	75.6
Guava	40.9	5.7	1.4	29.2	34.8
Papaya	36.7	5.7	1.3	27.6	34.8
Lettuce and cabbage leaves	37.6	5.3	1.5	25.1	18.0

Table 4. Result of elemental analysis on dry basis (%), (Coil laboratory, National University of Colombia)

Figure 7. Pictures of wastes in the storage containers at the Central Wholesaler of Antioquia

The chemical composition analysis of wastes showed that the highest values of volatile solids were found in the tropical fruits (mango, orange, guava and papaya). The volatile solids are the proportion of the raw material that bacteria using to generate biogas and have an out­standing role during the anaerobic fermentation process.

Waste	ST (%)	SV (%ST)	SV (%)
Mango	97,4	15,1	14,71
Orange	96,6	14,3	13,81
Guava	96,7	15,3	14,79
Papaya	97,1	12,7	12,33
Lettuce and cabbage leaves	86,5	8	6,92

Table 5. Chemical composition analysis, (Chemical composition analysis laboratory, National University of Colombia)

In order to determinate the quantity of wastes to be used was obtained the density of each wastes, to this were taken samples and then were triturated, weighed and finally was calcu­lated the volume to employ. The bioreactor was loaded with 422 kilograms of wastes and 1110 kilograms of water, this provided an average relation (wastes: water) of 1:2,5.

Wastes	Density (kg/l)	So (g SV)/l	Organic load (g SV)/day [19]	Wastes to Wastes to use (l) use (kg)	Concentration of volatile solid (% SV)/day [20]	Relation (wastes: water)	Water to use (l)
Mango	0,8820	129,7	6,0	22	19	5	1 : 2.94	64
Orange	0,9639	133,1	6,0	22	21	5	1 : 2.76	61
Guava	1,1655	172,4	6,0	29	33	5	1 : 2.96	85
Papaya	1,1907	146,8	6,0	24	29	5	1 : 2.47	60
Lettuce and
cabbage	0,4579	31,7	6,0	5	2	5	1 : 1.38	7
leaves
Total				102	105			278
Total to 4 days				409	422			1110

Table 6. Quantity of wastes and water to the fermentation process Fourth phase:

Each waste was triturated and mixed with water during three minutes until to reach an average size of 2 centimeters. In order to reduce the quantity of methanogenic bacteria, the wastes were submitted to acidic conditions during three months with a value of pH close to 3,5. Afterwards was added during three days agricultural lime until to reach a pH of 6,2; in that moment the production of biohydrogen started. The quantity of agricultural lime added was 7 kilograms (Figure 9).

Figure 8. Bioreactor used by the first stage and wastes triturated Fifth phase:

The organics load showed an important reduction during the process, the total suspend solids were reduced in 83%, the chemical oxygen demand was reduced in 65% and the biochemical

oxygen demand was reduced in 63,6%. The environment temperature was between 21,8 у 31 °C, this meanthat the biohydrogen productionwas developed under mesophilic conditions. The averagereiativehumiditywas between 38y 73%.

Table 7. Organic load of wastes at the first stage (Laboratory of Sanitary Engineering, National University of Colombia)

80 70 60 E 50

40

30

І 20 10

6 11 16 21 26 31 36 41 46 51 56 61 66 71 16 80 8l 00 9h day

Humedad relativa

Figure 10. Behavioroftemperatureandrelativehumidityaverage

The gas production started three days after application of agricultural lime and continued for 22 days more. The hydrogen (biohydrogen) percentage found in gas ranged between 6,37 y 17,26; with a percentage of hydrogen less than 13,3; there was carbon dioxide and nitrogen in the biogas, however when the percentage of hydrogen was greater than 13,3; the gas compo­sition was only hydrogen and carbon dioxide. The greater value of methane was 1,25% and less was 0%, this mean that the pretreatment to reduce the methanogenic bacteria was satisfactory.

Sample	CO2 (%)	H2 (%)	N2 (%)	O2 (%)	CH4 (%)
1	31,79	6,72	48,19	13,06	0
2	70,99	13,31	2,63	0,42	1,25
3	75,67	17,26	0,65	0,096	0,73
4	80,98	13,51	ND	ND	0,6
5	32,80	6,37	48,13	13,16	0,24
ND: not detected

Table 8. Composition of gas generated (Coil laboratory, National University of Colombia)

The total production of hydrogen was 177 liters in 22 days, with a maximum value of 14,5 liters, an average of 7,4 liters of H2/day and maximum yield of 83 liters of H^/m3 of bioreactor. The maximum value of generation of hydrogen was registered 7 days after from started the gas production and the maximum rate of hydrogen generation was obtained between first and seventh days. The Figure 12 shows a several pictures of biohydrogen generated, the color blue is from silica gel used to remove the wet of the gas. The quantity of organic load removed was 26.400 mg/liter of O2 (COD).

Source: Information personal from research Figure 11. Pictures of biohydrogen generated

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180

150

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Figure 13. Productionaccumulatedofhydrogen