Effect of Agitation on Anaerobic Co-Digestion of Swine Manure and Food Waste

The synergism of food waste associated with swine manure can provide an increase in biogas production, besides promoting greater stability in the anaerobic co-digestion process. To verify this effect, co-digestion tests were performed in two reactors, one with agitation, and the other without agitation. In both systems, gasometers were used to measure biogas production in an experiment lasting two hydraulic retention times (HRT). On each feeding day, the temperatures of the ambient and of the effluent taken from the reactors were measured, and samples of the food waste and effluent were collected to perform analysis of pH, total solids (TS), volatile solids (VS), fixed solids (FS), volatile acidity (AV), and total alkalinity (TA). In addition, the chemical oxygen demand (COD) was determined every five days, and gas composition was determined at the beginning of the second HRT. As important results, in both reactors a decrease in pH was verified due to the weakening of the buffer effect of the medium. This was due to the low alkalinity found in the food waste, causing an increase in acidity in the contents of the reactors. The volume of biogas produced was higher in the reactor with agitation, which meant an increased efficiency of the process. Finally, a low methane content was verified through chromatographic analyses, indicating a reduction in the activity of the microorganisms present in the medium. Thus, it is concluded that agitation linked to anaerobic co-digestion of swine manure with food waste exerted a positive effect on biogas production.

Keywords:
agitation in reactors; co-digestion; food waste

Accessories	Amount
Polyvinyl chloride (PVC) pipe (200 mm diameter)	47 cm
PVC pipe cap (200 mm diameter)	2
PVC hose barb½''	3
PVC Female adapter ½''	3
Polyurethane	---

Accessories	Amount
PVC pipe (100 mm diameter)	30 cm
PVC pipe cap (100 mm diameter)	1
PVC hose barb ½''.	1
PVC Female adapter ½''	1
Polyurethane	---
PVC pipe guide (150 mm diameter)	30 cm

Reactor/Flow	Mondays(L)	Wednesdays(L)	Fridays(L)
Reactor with agitation	1.5	1.5	2.3
Reactor without agitation	1	1	1.5

Variable	Unit	Principle	Methodology
pH	-	Potentiometric	--
T	⁰C	Thermometer	--
TS	g L^-1	Gravimetric	[²¹21 American Public Health Association (APHA). Standard Methods for Examining Water and Wastewater. American Public Health Association, American Water Works Association, Water Environmental Federation, 21.ed. Washington. 2005.]
FS	g L^-1	Gravimetric	[²¹21 American Public Health Association (APHA). Standard Methods for Examining Water and Wastewater. American Public Health Association, American Water Works Association, Water Environmental Federation, 21.ed. Washington. 2005.]
VS	g L^-1	Gravimetric	[²¹21 American Public Health Association (APHA). Standard Methods for Examining Water and Wastewater. American Public Health Association, American Water Works Association, Water Environmental Federation, 21.ed. Washington. 2005.]
VA	mg CH₃COOOH L^-1	Titulometric	[²¹21 American Public Health Association (APHA). Standard Methods for Examining Water and Wastewater. American Public Health Association, American Water Works Association, Water Environmental Federation, 21.ed. Washington. 2005.]
TA	mg CaCO₃ L ^-1	Titulometric	[²¹21 American Public Health Association (APHA). Standard Methods for Examining Water and Wastewater. American Public Health Association, American Water Works Association, Water Environmental Federation, 21.ed. Washington. 2005.]
COD_soluble	g O₂ L ^-1	Spectro	[²¹21 American Public Health Association (APHA). Standard Methods for Examining Water and Wastewater. American Public Health Association, American Water Works Association, Water Environmental Federation, 21.ed. Washington. 2005.]

First HRT				Second HRT
Days	TS (g/L)	VS (g/L)	FS (g/L)	Days	TS (g/L)	VS (g/L)	FS (g/L)
1	28.38	23.67	4.70	2	63.94	58.64	5.29
4	28.01	25.21	2.80	5	126.48	117.85	8.63
6	68.30	63.32	4.98	7	44.37	41.02	3.35
8	157.35	126.04	31.31	9	79.24	74.37	4.88
11	111.08	104.84	6.24	12	94.66	89.49	5.17
13	105.46	101.01	4.45	14	108.69	103.85	4.84
15	42.34	40.19	2.15	16	154.51	149.80	4.71
18	17.86	15.70	2.16	19	130.14	123.93	6.20
20	67.69	63.81	3.88

	First HRT		Second HRT
Parameter	No agitation	With agitation	No agitation	With agitation
TS Removal (%)	68.1	70.6	67.7	53.5
VS Removal (%)	76.3	77.8	71.9	58.7

First HRT
	Food waste		Effluent (no agitation)		Effluent (with agitation)
Day	Average (g O₂ L^-1)	±SD	Average (g O₂ L^-1)	±SD	Average (g O₂ L^-1)	± SD
1	86.0	4.3	31.8	2.8	29.5	4.2
6	91.5	1.7	46.4	6.9	22.9	0.4
11	32.4	0.9	57.3	5.2	28.5	0.9
15	53.8	5.2	38.6	1.4	63.6	8.0
20	112.8	25.0	49.2	8.6	48.9	0.7
Second HRT
	Food waste		Effluent (no agitation)		Effluent (with agitation)
Day	Average (g O₂ L^-1)	±SD	Average (g O₂ L^-1)	±SD	Average (g O₂ L^-1)	±SD
5	117.1	1.7	77.8	12.0	74.7	14.2
9	58.6	6.9	44.4	7.4	75.7	3.2
14	121.4	2.6	83.0	9.2	74.5	2.4
19	102.5	10.3	128.5	2.5	120.4	14.0

Period	No agitation Yield (Lbiogas gCOD_feed ^-1)	With agitation Yield (Lbiogas gCOD_feed ^-1)
First HRT	2.4	2.9
Second HRT	2.0	2.2

Instituto de Tecnologia do Paraná - Tecpar Rua Prof. Algacyr Munhoz Mader, 3775 - CIC, 81350-010 Curitiba PR Brazil, Tel.: +55 41 3316-3052/3054, Fax: +55 41 3346-2872 - Curitiba - PR - Brazil
E-mail: babt@tecpar.br

Acompanhe os números deste periódico no seu leitor de RSS

[1] *Correspondence: fabiana.marqui22@gmail.com; Tel.: +55-44-999625622 (F.M.M.)