OPTIMIZATION OF ANAEROBIC TREATMENT OF CASSAVA PROCESSING WASTEWATER

Fleck, Leandro; Tavares, Maria H. F.; Eyng, Eduardo; Andrade, Minéia A. de M. de; Frare, Laercio M.

doi:10.1590/1809-4430-Eng.Agric.v37n3p574-590/2017

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Scientific Papers, Sanitation and Ambient Control • Eng. agríc. 37 (03) • May-Jun 2017 • https://doi.org/10.1590/1809-4430-Eng.Agric.v37n3p574-590/2017 copy

OPTIMIZATION OF ANAEROBIC TREATMENT OF CASSAVA PROCESSING WASTEWATER

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The main contribution of this research is to optimize the operating conditions of an anaerobic reactor applied to the treatment of wastewater from cassava starch production. A 20-L anaerobic reactor was used, operating in a batch system, with temperature control. Temperature and inoculum total volatile solids (TVS_i) were controlled for evaluation of effects on the removals of chemical oxygen demand (COD) and reactor total volatile solids (TVS_r) by means of a Central Composite Rotational Design (CCRD). Twelve trials were analyzed simultaneously by the desirable function approach. The higher COD removal (96.82%) was obtained at 42 °C and 12.0% TVS_i. The largest TVS_r removal (69.31%) was registered at 45 °C and 10.0% TVS_i. Equations representative of the process were obtained from the responses of variables, being statistically significant at a 90% confidence level. Based on the desirability function approach, we can conclude that an optimal operational condition for the anaerobic reactor is at 39.7 °C and 10.8% TVS_i. The estimated COD and TVS_r removal efficiencies under these operating conditions were 90.45% and 63.12%, respectively.

KEYWORDS:
anaerobic reactor; biogas; desirability function; mathematical modeling

Variables	Methodology
BOD	Method 5210B (APHA, 2012APHA. Standard methods for the examination of water and wastewater. 22th ed. Washinton, DC: Ed. American Public Health Association, American Water Works Association, Water Environment Federation, 2012.)
COD	Method 5220B (APHA, 2012APHA. Standard methods for the examination of water and wastewater. 22th ed. Washinton, DC: Ed. American Public Health Association, American Water Works Association, Water Environment Federation, 2012.)
TKN	Method 4500-Norg-C (APHA, 2012APHA. Standard methods for the examination of water and wastewater. 22th ed. Washinton, DC: Ed. American Public Health Association, American Water Works Association, Water Environment Federation, 2012.)
P	Method 4500E (APHA, 2012APHA. Standard methods for the examination of water and wastewater. 22th ed. Washinton, DC: Ed. American Public Health Association, American Water Works Association, Water Environment Federation, 2012.)
Total Alkalinity	Method 2320B (APHA, 2012APHA. Standard methods for the examination of water and wastewater. 22th ed. Washinton, DC: Ed. American Public Health Association, American Water Works Association, Water Environment Federation, 2012.)
Total Solids, Fixed and Volatile	Method 2540G (APHA, 2012APHA. Standard methods for the examination of water and wastewater. 22th ed. Washinton, DC: Ed. American Public Health Association, American Water Works Association, Water Environment Federation, 2012.)
pH	Method 4500 B (APHA, 2012APHA. Standard methods for the examination of water and wastewater. 22th ed. Washinton, DC: Ed. American Public Health Association, American Water Works Association, Water Environment Federation, 2012.)
Starch	Acid digestion in microwaves (CEREDA et al., 2004CEREDA, M. P.; DAIUTO, E. R.; VILPOUX, O. Metodologia de determinação de amido por digestão ácida em microondas. Revista da Associação Brasileira dos Produtores de Amido de Mandioca, Paranavaí, v.2, p.29, 2004.)

Trial	Temperature		TVS_i
Trial	Encoded Values	Real Values (°C)	Encoded Values	Real Values (%)
1	-1	28	-1	8.0
2	-1	28	1	12.0
3	1	42	-1	8.0
4	1	42	1	12.0
5	-1.41	25	0	10.0
6	1.41	45	0	10.0
7	0	35	-1.41	7.2
8	0	35	1.41	12.8
9	0	35	0	10.0
10	0	35	0	10.0
11	0	35	0	10.0
12	0	35	0	10.0

Variable	Value	Unity
DQO	6014	mg L⁻¹
DBO	1400	mg L⁻¹
Starch concentration	3.20	%
Total nitrogen	247	mg L⁻¹
Phosphor	83	mg L⁻¹
Total alkalinity	2021	mg L⁻¹
pH	4.02	-
Total solids	6581	mg L⁻¹
Total fixed solids	1431	mg L⁻¹
Total Volatile Solids	5151	mg L⁻¹

Trial	Temperature (°C)	TVS_i(%)	COD Removal (%)	TVS_r Removal (%)	IA/PA final ratio
1	28	8.0	41.53	21.90	0.35
2	28	12.0	32.01	55.10	0.32
3	42	8.0	12.44	40.52	0.33
4	42	12.0	96.82	68.90	0.26
5	25	10.0	31.70	18.51	0.30
6	45	10.0	58.49	69.31	0.40
7	35	7.2	14.14	27.97	0.32
8	35	12.8	26.71	33.56	0.29
9	35	10.0	95.09	63.10	0.30
10	35	10.0	90.10	60.30	0.28
11	35	10.0	94.51	57.60	0.38
12	35	10.0	88.50	59.10	0.33

Trial	Experimental conditions		Biogas Production (L_N biogas g⁻¹ COD removed)	Characterization Biogas (%)
Trial	T(°C)	TVS_i(%)	Biogas Production (L_N biogas g⁻¹ COD removed)	CH₄	CO₂	H₂S	Others
1	28	8.0	0.154	63.25	32.81	-	3.94
2	28	12.0	0.066	61.00	20.00	-	19.00
3	42	8.0	0.291	55.23	22.30	0.02	22.45
4	42	12.0	0.002	57.20	33.51	0.01	9.28
5	25	10.0	0.070	58.25	20.12	-	21.63
6	45	10.0	0.158	57.23	21.26	-	21.51
7	35	7.2	0.194	71.00	29.00	-	-
8	35	12.8	0.158	65.00	35.00	-	-
9	35	10.0	0.317	63.21	20.32	-	16.47
10	35	10.0	0.000	-	-	-	-
11	35	10.0	0.163	65.11	14.09	0.01	20.79
12	35	10.0	0.071	62.52	30.67	0.24	3.57

	Factor	Sum of Squares	Degrees of freedom	Average Square	p_value
	Temperature (LT)	677.18	1	677.18	0.0637^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
	Temperature (QT)	1260.50	1	1260.50	0.0212^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
COD Removal	TVS_i (LT)	1074.66	1	1074.66	0.0289^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
	TVS_i (QT)	6741.78	1	6741.78	0.0003^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
	TxTVS_i	2204.30	1	2204.30	0.0064^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
	Residue	789.08	6	131.51
	Total	12747.50	11
TVS_r Removal	Temperature (LT)	1357.29	1	1357.29	0.0164^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
	Temperature (QT)	71.68	1	71.68	0.4766
	TVS_i (LT)	604.92	1	604.92	0.0696^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
	TVS_i (QT)	966.27	1	966.27	0.0317^* * Statistically significant with a 90% confidence interval, LT refers to the linear term, while QT refers quadratic term of the equations 3 and 4.
	TxTVS_i	5.81	1	5.81	0.8361
	Residue	746.58	6	124.43
	Total	3752.55	11

	Factor	Effect	p-value
COD Removal	Average	92.01	3.72E-06^* * Statistically significant with a 90% confidence interval
	Temperature (LT)	18.43	0.0637^* * Statistically significant with a 90% confidence interval
	Temperature (QT)	-40.51	0.0043^* * Statistically significant with a 90% confidence interval
	TVS_i (LT)	23.21	0.0289^* * Statistically significant with a 90% confidence interval
	TVS_i (QT)	-65.33	0.0003^* * Statistically significant with a 90% confidence interval
	TxTVS_i	46.95	0.0064^* * Statistically significant with a 90% confidence interval
TSV_r Removal	Average	59.99	0.0000^* * Statistically significant with a 90% confidence interval
	Temperature (LT)	26.09	0.0163^* * Statistically significant with a 90% confidence interval
	Temperature (QT)	-11.45	0.2434
	TVS_i (LT)	17.42	0.0696^* * Statistically significant with a 90% confidence interval
	TVS_i (QT)	-24.68	0.0317^* * Statistically significant with a 90% confidence interval
	TxTVS_i	-2.41	0.8361

	Change Source	Sum of Squares	Degrees of freedom	Average Square	p-value	R²
COD Removal	Regression	11958.42	5	2391.68	0.001^* * Statistically significant at a 90% confidence interval.	0.94
	Residues	789.08	6	131.51
	Total	12747.50	11
TVS_r Removal	Regression	3005.97	5	601.19	0.041^* * Statistically significant at a 90% confidence interval.	0.80
	Residues	746.58	6	124.43
	Total	3752.55	11

Variable	Expected efficiency (%)	Observed efficiency (%)	Error (%)
COD Removal	94.85	90.45	4.86
TVS_r Removal	67.32	63.12	6.65

Associação Brasileira de Engenharia Agrícola SBEA - Associação Brasileira de Engenharia Agrícola, Departamento de Engenharia e Ciências Exatas FCAV/UNESP, Prof. Paulo Donato Castellane, km 5, 14884.900 | Jaboticabal - SP, Tel./Fax: +55 16 3209 7619 - Jaboticabal - SP - Brazil
E-mail: revistasbea@sbea.org.br

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[1] *Corresponding author. Universidade Estadual do Oeste do Paraná - UNIOESTE/ Cascavel - PR, Brasil. E-mail: fleckmissal@gmail.com