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ENGINEERING SCIENCES • An. Acad. Bras. Ciênc. 93 (1) • 2021 • https://doi.org/10.1590/0001-3765202120190137 copy

Photocatalytic Ozonation Performance In Landfill Leachate Treatment

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

This work aims to identify the best treatment condition for removal of chemical oxigen demand (COD) and increase of biodegradability in an advanced oxidative process of photocatalytic ozonation with titanium dioxide (TiO₂), applied to the remediation of the leachate produced at the municipal landfill of Campo Mourão, Paraná. The experiment was carried out using a photocatalytic chamber and an ozonation system based on the corona effect. A statistical model of the central composite rotatable design (CCRD) was elaborated and three variables (pH, TiO₂ dose and airflow) were analyzed, to define the optimum condition that allows the highest perfomance of the treatment. The statistical model was valid for the data. The best condition identified was: pH = 3.3 TiO₂ dose = 0.012 g and flow = 9.0 L.min^-1 (8.79 g, O₃.min^-1). The removal of filtrate COD was approximately 30% and increase in biodegradability (BOD/COD) = 0.59 in the optimum condition. Factors such as the complex composition of the leachate and treatment time were considered as possible limitants for better results. The treatment did not allow to reach the permissible limits for disposal of the effluent at the environment, in Brazil.

Key words
Advanced oxidative processes; heterogeneous photocatalysis; Landfill Sanitary; leachate; ozonation; photocatalytic ozonation

Parameter	Method - equipment and materials
Hydrogen potential (pH)	Direct measure - pH meter pH-221 Lutron;
Temperature	Direct measure - digital thermometer WT-1;
Turbidity	Direct measure - turbidimeter HI 93414 Hanna;
Crude and filtrate COD	Spectrophotometric COD < 800 mg O₂.L^-1 – vacuum filter Micron; micro membrane of glass fibre GF-3 MN with 47 mm diameter; micro tubes Hach; digester block Policontrol; spectrophotometer DR 500 Hach;
BOD₅ ²⁰	Five days test – flasks and BOD sensors Velp Científica; incubator stove Nova Técnica;

Flowmeter flow (L.min^-1)	O₃ (g.min^-1)
12	7.18
11	7.26
9.0	8.79
7.0	5.98
6.0	6.68
3.0	4.00

Factors	Levels
Factors	-1.68 (-α)	-1	0	1	+1.68(+α)
pH	1.6	2.0	2.5	3.0	3.3
TiO₂ dose (g)	0.003	0.005	0.0075	0.010	0.012
Air flow (L.min^-1)	3.0	4.0	6.0	8.0	9.0

Tests	pH	TiO₂ dose (g)	Air flow (L.min^-1)
1	-1	-1	-1
2	+1	-1	-1
3	-1	+1	-1
4	+1	+1	-1
5	-1	-1	+1
6	+1	-1	+1
7	-1	+1	+1
8	+1	+1	+1
9	-1.68	0	0
10	+1.68	0	0
11	0	-1.68	0
12	0	+1.68	0
13	0	0	-1.68
14	0	0	+1.68
15	0	0	0
16	0	0	0
17	0	0	0

Physicochemical parameters	Min – Max
pH	8.89 – 8.98
Temperature (ºC)	24.5 – 24.83
Turbidity (NTU)	144 – 354
Crude COD (mg O₂.L^-1)	995.05 – 1019.80
COD-F (mg O₂.L^-1)	987.10 – 1003.90
BOD₅ ²⁰ (mg O₂.L^-1)	216 – 254
BOD/COD	0.22 – 0.25

Tests	Factors			Responses
	pH	TiO ₂ dose (g)	Air flow (L.min^-1)	COD-F (mg O₂.L^-1)		COD-F removal (%)	BOD₅²⁰(mg O₂.L^-1)		Biodegradability (DBO/DQO)
	pH	TiO ₂ dose (g)	Air flow (L.min^-1)	Raw	Treated	COD-F removal (%)	Raw	Treated	Raw	Treated
1	2.0	0.005	3.0	744.12	671.37	9.78	259	338	0.35	0.50
2	3.0	0.005	3.0	786.21	688.48	12.43	236	327	0.30	0.48
3	2.0	0.01	3.0	818.30	622.15	23.97	130	221	0.16	0.36
4	3.0	0.01	3.0	811.17	605.74	25.33	130	251	0.16	0.41
5	2.0	0.005	9.0	821.16	626.43	23.71	244	311	0.30	0.50
6	3.0	0.005	9.0	826.86	663.52	19.75	244	288	0.29	0.43
7	2.0	0.01	9.0	756.25	570.08	24.62	244	346	0.32	0.61
8	3.0	0.01	9.0	778.36	594.33	23.64	235	338	0.30	0.57
9	1.6	0.0075	6.0	766.95	573.64	25.20	235	348	0.31	0.61
10	3.3	0.0075	6.0	761.24	540.83	28.95	235	346	0.31	0.64
11	2.5	0.003	6.0	744.83	686.34	7.85	243	252	0.33	0.37
12	2.5	0.012	6.0	800.47	690.62	13.72	243	342	0.30	0.50
13	2.5	0.0075	4.0	809.03	654.25	19.13	243	326	0.30	0.50
14	2.5	0.0075	8.0	794.77	678.50	14.63	234	261	0.29	0.38
15	2.5	0.0075	6.0	744.83	661.38	11.20	259	308	0.35	0.47
16	2.5	0.0075	6.0	806.89	669.94	16.97	234	283	0.29	0.42
17	2.5	0.0075	6.0	746.26	628.57	15.77	259	281	0.35	0.45

COD-F removal (%)
Factors/Interactions	Effect	Mean	t(10)	p-value
Main Interactions	13.34	1.22	10.94	0.00
pH (L)	0.80	1.52	0.52	0.61
pH (Q)	10.22	1.61	6.36	0.00
Air flow (L.min^-1) (L)	4.07	1.52	2.67	0.02
Air flow (L.min^-1) (Q)	2.96	1.61	1.84	0.09
TiO₂ dose (g) (L)	6.09	1.52	3.99	0.00
Air flow x TiO₂ dose (L)	-5.60	1.99	-2.81	0.02
Biodegradability increase (BOD/COD)
Main Interactions	0.43	0.01	39.27	0.00
pH (L)	-0.003	0.02	-0.15	0.88
pH (Q)	0.12	0.02	6.70	0.00
Air flow (L.min^-1) (L)	0.08	0.02	4.48	0.00
TiO₂ dose (g) (L)	0.04	0.02	2.07	0.06
Air flow x TiO₂ dose (L)	0.11	0.02	4.78	0.00

Variation source	SQ	DF	MQ	Fcal	Ftab	p-value (Fcal/Ftab)
COD-F(%) removal
Regression	571.04	6	95.17	11.99	3.01	0.00
Waste	79.39	10	7.94
Lack of fit	60.64	8	7.58	0.81	6.09	0.66
Pure error	18.75	2	9.37
Total	650.43	16	40.65
R²	0.88
R-adjusted	0.80
Biodegradability increase (BOD/COD)
Regression	0.103	5	0.021	18.443	3.012	0.00
Waste	0.012	11	0.001
Lack of fit	0.011	9	0.001	2.595	6.094	0.31
Pure error	0.001	2	0.000
Total	0.115	16	0.007
R²	0.89
R-adjusted	0.84

Variable response	Experimental results	Predicted results
COd-F (%) removal	30.13%	29%
Biodegradability increase (BOD/COD)	0.59	0.64

Descriptive statistics
Parameter	Mean	Minimum	Maximum	Stardard Deviation
COD-F (raw)	783,40	744,12	826,86	29,96
COD-F (treated)	636,83	540,83	690,62	46,42
BOD₅ ²⁰ (raw)	230	130	259	38,53
BOD₅ ²⁰ (treated)	304	221	348	40,14

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