Installation of bioreactors and wastes to use

At the second stage were used the same wastes of first stage, but additionally were employed wastes of tomato, onion, garlic and husk of cape gooseberry (Table 10). The wastes were triturated and mixed with water during three minutes, the relation of wastes: water was 1:2,5 like at first stage. The quantity of wastes employed in each treatment was similar to quantity
used at first stage. The volume of work in each bioreactor was 70% and 30% was dedicated to storage the gas generated.

Figure 14. Set of bioreactors employed at the second stage

Repetition	Wastes	Quantity of wastes (kg)
		T1	T2	T3
	Lettuce and cabbage leaves, tomato, onion, garlic, pimento,	506	514	453
	orange, lemon, mango, guava and papaya
2	Lettuce and cabbage leaves, tomato, onion, garlic and husk of cape gooseberry	450	450	450
3	Lettuce and cabbage leaves, orange, mango, guava and papaya	500	500	400
Average		485,3	488	434,3

Table 9. Wastes used in each repetition

The highest values of chemical oxygen demand (COD) were obtained in the treatment 2 during the repetition 1 and the treatments 1 and 3 of the repetition 3 respectively, namely in these cases there were more quantity of food available to the microorganisms.

Analysis		Repetition 1		Repetition 2		Repetition 3
T1	T2	T3	T1, T2 y T3	T1	T2	T3
ST (mg/l)	5322	8198	4700	11280	16290	9830	10500
COD (mg/ lO2)	8667	18000	8000	12000	27140	17940	23340
BOD (mg/lO2)	7617	10983	6200	5840	24415	3775	14455

Table 10. Organic composition of wastes employed

Behavior of pH during the pretreatment and operation of bioreactors

Due to type of wastes employed in the repetition 2, was necessary to add muriatic acid into all bioreactors to achieve the pH of acidification, but there were not response (pH be­tween 3,5 and 4,5). However, during the repetitions 1 and 3, in all treatments was used wastes of orange and lemon, this allowed to apply the pretreatment of acidification, after­wards was added agricultural lime and was reached a pH between 5 and 6, values ade­quate to generate biohydrogen.

Figure 15. Behavior of pH in each treatment and repetition Production of biohydrogen

The gas generated in all treatments was compound of hydrogen, carbon dioxide, nitrogen and oxygen. The greater value of methane was 3,7% and the less was 0%, in many times the methane was not detected (ND), this mean that the pretreatment to reduce the methanogenic bacteria was satisfactory. The percentage of hydrogen in gas was between 5 and 18,08; this was the highest value in the research and was obtained in the treatment 3 during the repetition 3 when the wastes used were Lettuce and cabbage leaves, orange, lemon and papaya. In the repetition 2 in all treatments, there were not generation of hydrogen (NG). The oxygen content in some repetitions show maybe that some air entered to bioreactor when the samples were taken.

Treatment	Sample	CO2 (%)	H2 (%)	N2 (%)	O2 (%)	CH4 (%)
	1	35,1	6,7	53,9	3,0	1,4
1	2	16,2	6,4	64,8	13,6	ND
	3	18,2	0,02	67,2	13,9	0,8
	1	40,0	10,5	45,7	0,9	0,8
2	2	46,5	7,5	43,7	1,8	ND
	3	34,1	0,02	54,3	7,0	3,7
	1	40,2	7,7	45,0	2,5	0,4
3	2	43,9	7,0	47,0	2,1	ND
	3	4,0	0,02	77,3	18,1	ND
Table 11. Composition of gas generated, first repetition
Treatment	Sample	CO2 (%)	H2 (%)	N2 (%)	O2 (%)	CH4 (%)
	1	NG	NG	NG	NG	NG
1	2	NG	NG	NG	NG	NG
	3	NG	NG	NG	NG	NG
	1	11,4	5,5	41	13,4	0,2
2	2	37,8	5,5	36,2	5,4	0,5
	3	20,1	5,7	43,5	12	3,3
	1	NG	NG	NG	NG	NG
3	2	NG	NG	NG	NG	NG
	3	NG	NG	NG	NG	NG
Table 12. Composition of gas generated,	second repetition
Treatment	Sample	CO2 (%)	H2 (%)	N2 (%)	O2 (%)	CH4 (%)
	1	29,08	7,5	50,3	3,0	0,2
1	2	23,88	6,5	41,7	10,3	2,6
	3	42,14	8,2	36,1	7,1	1,4
	1	28	7,0	52,2	4,4	0,1
2	2	45,29	5,8	38,1	3,0	0,1
	3	40,69	5,3	40,8	3,2	0,1
	1	8,96	18,0	51,3	12,1	0,2
3	2	43,32	6,3	36,5	7,1	0,7
	3	52,85	5,0	30,5	5,1	0,3
ND: not detected NG: not generated

The maximum production of biohydrogen per day obtained at the first; stage was 15 liters, however at the second stage the maximum production was 38 liters, this mean that the production was duplicated during the second stage. In the repetition 3, in the treatment 3 were generated 32 liters of biohydrogen, meanwhile in the treatment 1 were generated 15 liters. The wastes employed sn both treatments were Lettuce and cabbage leaves, orange, lemon and tropical fruits as mango, guava and papaya, the initial pH was lesser to 4,5 during 7 and 8 days, and Che cHof bioreactorsoperation was between5and5,5.

Figure 16. Production of hydrogen

The greater accumulated production was reached in the treatment 2 and the repetition 1, followed by the treatment 3 in the repetition 3. In both cases were used vegetal wastes and tropical fruits in same proportions in addition, initially the wastes were subjected to acid conditions with a pH less to 4,0 during 8 days and a pH for operation of bioreactor between 5 and 5,5. Under those conditions the hydrogen content into gas ranged between 7,5 and 10,5%. The total production of hydrogen in the treatment 2 and the repetition 1 was 317,8 liters in 22 days, with 14,44 liters of H2/day (twice the result from the first stage), and maximum yield of 159 liters of H2/m3 of bioreactor. Other outstanding result was reached when were employed the same wastes, at beginning were applied acid conditions during 7 days under a pH less to 4,5; and then was used a pH for the operation of bioreactor between 5 and 5,5. In this case the percentage of hydrogen into gas ranged between 5 and 18,08% (the last value was the maxi­mum content reached in the research). The production of hydrogen was 231,1 liters of H2 in 22 days with 10,5 liters of H2/day (duplicated the value reached from the first stage) and a maximum yield of 115,6 liters of H2/m3 of bioreactor.

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Figure 17. Productionaccumulatedofhydrogen