Anaerobic co-digestion of swine manure with sweet potato or cassava in different C/N ratios

Villa, Lisandra Maraia; Orrico, Ana Carolina Amorim; Akamine, Luana Alves; Lucas Junior, Jorge de; Sunada, Natália da Silva

doi:10.1590/0103-8478cr20190734

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SOIL SCIENCE • Cienc. Rural 50 (10) • 2020 • https://doi.org/10.1590/0103-8478cr20190734 copy

Anaerobic co-digestion of swine manure with sweet potato or cassava in different C/N ratios

Co-digestão anaeróbia dos dejetos de suínos com batata doce ou mandioca em diferentes relações C/N

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT:

Anaerobic co-digestion (AcoD) of waste is a method of increasing methane (CH₄) yield and improving biofertilizer quality. This study aimed to evaluate the best AcoD conditions for swine manure (SM) with sweet potato (SP) or cassava (C) in different amounts in semi-continuous biodigesters. Initially, using batch biodigesters, an AcoD test of the SM with SP or C was performed, adopting carbon/nitrogen (C/N) ratios of 10/1, 13/1, 17/1, and 22/1. Based on the results, a C/N ratio of 10/1 was chosen, which was the proportion that resulted in the highest reduction of volatile solids (VS) and specific biogas production. From these results, the experiment was carried out in semi-continuous biodigesters, consisting of three treatments (control (SM), SP 10/1, and C 10/1) with five replicates and a hydraulic retention time (HRT) of 30 days. Total solid (TS) and volatile solid (VS) reductions, biogas and CH₄ yields, alkalinity, and volatile acidity were measured. The control treatment differed from the others and resulted in decreased biogas yield (752 L_N.kg_VSadded ^-1), CH₄ (449 L_N.kg_VSadded ^-1), and CH₄ content (59.7%). The AcoD treatments (SP and C) did not differ significantly for biogas yield (respectively, 901 and 883 L_N.kg_VSadded ^-1) and CH₄ (respectively, 590 and 547 L_N.kg_VSadded ^-1); however, they differed in CH₄ content (65.5% and 61.9% respectively). The treatments showed general reduction averages of 76.1% and 85.9% for TS and VS, respectively, with no statistical difference found between them. The AcoD of the SM with SP or C increased the production and quality of the biogas, increasing the concentration of CH₄ therein.

Key words:
acidification; anaerobic biodigestion; carbohydrates; methanogenesis; tuberous roots.

Universidade Federal de Santa Maria Universidade Federal de Santa Maria, Centro de Ciências Rurais , 97105-900 Santa Maria RS Brazil , Tel.: +55 55 3220-8698 , Fax: +55 55 3220-8695 - Santa Maria - RS - Brazil
E-mail: cienciarural@mail.ufsm.br

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[1] E-mail: luana.a.akamine@gmail.com. ^*Corresponding author

Parameters	---------------------------------------------------------Treatments-------------------------------------------------------									CV (%)
	Control	SP 10/1	SP 13/1	SP 17/1	SP 22/1	C 10/1	C 13/1	C 17/1	C 22/1
pH (afflu.)	6.9	7.0	7.1	7.3	7.4	7.0	7.1	7.2	7.3	0.57
pH (efflu.)	7.4^a	7.3^a	7.3^a	7.3^a	5.3^b	7.3^a	5.6^b	4.9^c	4.5^c	2.5
TS (g L^-1)	36.7	37.3	36.2	35.2	35.0	37.1	35.1	35.1	35.0	-
Reduction (%)	44.5^a	47.5^a	45.8^a	44.7^a	42.4^ab	45.0^a	35.4^bc	33.8^c	30.1^c	7.1
VS (g L^-1)	28.6	32.3	31.2	29.0	30.3	30.9	30.1	30.8	30.7	-
Reduction (%)	50.3^bc	57.3^a	55.5^abc	52.1^abc	49.7^c	56.3^ab	37.7^d	35.9^d	33.0^d	5.46
Biogas (L_N)	14.6^d	17.9^a	15.6^c	14.5^d	5.4^e	16.7^b	3.2^f	2.1^g	1.7^g	2.83
Biogas (L_N.kg_TSadded ^-1)	221.6^c	266.7^a	241.2^bc	229.5^bc	86.2^d	251.2^ab	50.7^e	32.9^e	27.2^e	6.73
Biogas (L_N.kg_VSadded ^-1)	283.6^ab	308.4^a	280.5^ab	278.3^b	99.5^c	300.8^ab	59.2^d	37.4^d	31.0^d	6.57

Parameters	Unit	------------------------------------Treatments-------------------------------			CV (%)
		Control	SP 10/1	C 10/1
TS (afflu.)	g L^-1	17.0	16.2	16.3	-
Reduction	%	76.8^a ± 1.1	75.7^a ± 0.8	76.0^a ± 0.6	1.16
VS (afflu.)	g L^-1	13.8	13.5	13.6	-
Reduction	%	86.2^a ± 0.8	85.7^a ± 0.3	85.7^a ± 0.2	0.66
C (afflu.)	%	28.70	38.56	38.13	-
Reduction	%	22.72	45.51	42.41	-
N (afflu.)	%	3.37	3.18	3.09	-
Reduction	%	10.39	7.55	0.97	-
Biogas	L_N.d^-1	20.7^c ± 0.1	24.3^a ± 0.1	24.0^b ± 0.1	0.29
Biogas	L_N.kg_TSadded ^-1.d^-1	607.8^b ± 27.2	752.0^a ± 15.7	734.4^a ± 15.2	2.84
Biogas	L_N.kg_VSadded ^-1.d^-1	752.5^b ± 33.6	901.5^a ± 18.7	883.1^a ± 18.3	2.85
CH₄	L_N.kg_VSadded ^-1.d^-1	449.5^c ± 23.0	590.5^a ± 23.9	546.8^b ± 14.9	3.68
CH₄	%	59.7^c ± 0.7	65.5^a ± 1.4	61.9^b ± 1.1	1.75