Influence of the apparent molecular size of humic substances on the efficiency of coagulation using Fenton's reagent

DE JULIO, MARCELO; DE JULIO, TATIANE S.; DI BERNARDO, LUIZ

doi:10.1590/S0001-37652013005000030

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Engineering Sciences • An. Acad. Bras. Ciênc. 85 (2) • June 2013 • https://doi.org/10.1590/S0001-37652013005000030 copy

Influence of the apparent molecular size of humic substances on the efficiency of coagulation using Fenton's reagent

Authorship SCIMAGO INSTITUTIONS RANKINGS

This work used Fenton's reagent as a coagulating agent in the treatment of water samples with high true colour caused by humic substances (HS) extracted from peat. In addition, the effects of the apparent molecular size of HS on coagulation, flocculation and flotation were studied. To that end, four distinct water samples having the same true colour were prepared using HS with different molecular sizes, which were obtained by ultrafiltration fractioning. Through optimisation of coagulant dosage and coagulation pH, as well as posterior construction of coagulation diagrams for each water sample, it was verified that the sample prepared with the smallest apparent molecular size of HS was the most difficult to treat, requiring higher coagulant (Fenton's reagent) dosages than samples prepared with larger HS molecular sizes. Furthermore, filtration experiments after dissolved air flotation (DAF) were carried out in an attempt to simulate conventional treatment. The most representative results in filtered water were: apparent colour ≤ 3 HU; turbidity < 0.5 NTU; and residual iron concentration < 0.005 mg/L. The absorbance and total organic carbon values of filtered water samples were also very low, suggesting that the formation of disinfection by-products with chlorine would likely be insignificant.

coagulation; DAF; drinking water; Fenton's reagent; humic substances; molecular size

Sand Type	pH_oxid	pH_coag	H_flot	pH_filtr	^* * Rem. ap. col. - Remaining apparent colour; Rem. ap. col. after flotation (HU)		253.7 nm rem. Abs after flotation (cm⁻¹)		^ % rem. Abs - Percentage remaining of Absorbance at 253.7 nm (cm−1); (A/A0)100 – A is the remaining absorbance (cm−1) and A0 is the absorbance (cm−1) of the water sample; % rem. Abs after flotation - (A/A₀)100		Rem. ap. col. after filtration (HU)	253.7 nm rem. Abs after filtration (cm⁻¹)	% rem. Abs after filtration - (A/A₀)*100	Turbidity after filtration (NTU)	^* ***** TOC – Total Organic Carbon. TOC after filtration (mg/L)	residual total Fe after filtration (mg/L)
Sand Type	pH_oxid	pH_coag	H_flot	pH_filtr	15 cm/min	5 cm/min	15 cm/min	5 cm/min	15 cm/min	5 cm/min	Rem. ap. col. after filtration (HU)	253.7 nm rem. Abs after filtration (cm⁻¹)	% rem. Abs after filtration - (A/A₀)*100	Turbidity after filtration (NTU)		residual total Fe after filtration (mg/L)
Test 1 – Water sample with the HS fraction filtered through a 0.45 µm membrane with 15 mg/L of FeSO₄ x 7H₂O; 5.5 mg/L of H₂O₂; and 4.5 mg/L of NaOH
1	4.29	5.88	6.39	6.50	69	36	0.106	0.064	70	42	< 1	0.007	5	0.28	0.770	< 0.005
2	4.32	5.86	6.40	6.54	51	28	0.083	0.053	55	35	< 1	0.009	6	0.28	0.667	< 0.005
3	4.34	5.81	6.35	6.52	61	37	0.098	0.065	64	43	1	0.011	7	0.29	0.398	< 0.005
Test 2 – Water sample with the HS fraction filtered through a 0.45 µm membrane with 15 mg/L of FeSO₄ x 7H₂O; 5.5 mg/L of H₂O₂; and 4.5 mg/L of NaOH
1	4.28	5.89	6.40	6.48	56	32	0.085	0.058	56	38	< 1	0.006	4	0.36	0.689	< 0.005
2	4.30	5.90	6.41	6.50	63	32	0.089	0.057	59	38	< 1	0.006	4	0.38	0.592	< 0.005
3	4.31	5.87	6.41	6.50	51	34	0.084	0.060	55	39	1	0.007	5	0.40	0.376	< 0.005
Test 3 – Water sample with the HS fraction filtered through a 0.45 µm membrane and > 100 kDa with 7.5 mg/L of FeSO₄ x 7H₂O; 2.75 mg/L of H₂O₂; and 3.0 mg/L of NaOH
1	4.75	5.87	6.28	6.51	67	37	0.077	0.042	56	31	< 1	0.003	2	0.38	0.517	<0.005
2	4.68	6.06	6.30	6.57	64	34	0.065	0.046	47	33	< 1	0.006	4	0.32	0.362	<0.005
3	4.67	5.98	6.27	6.55	74	41	0.089	0.049	65	36	< 1	0.008	6	0.33	0.393	<0.005
Test 4 – Water sample with the HS fraction filtered through a 0.45 µm membrane and > 100 kDa with 7.5 mg/L of FeSO₄ x 7H2O; 2.75 mg/L of H₂O₂; and 3.0 mg/L of NaOH
1	4.75	5.88	6.22	6.51	47	32	0.059	0.048	43	35	< 1	0.004	3	0.28	0.696	<0.005
2	4.71	5.97	6.34	6.50	54	35	0.065	0.049	47	36	< 1	0.007	5	0.31	0.403	<0.005
3	4.72	6.02	6.34	6.55	73	37	0.082	0.046	60	33	< 1	0.007	5	0.30	0.329	<0.005

Sand Type	pH_oxid	pH_coag	pH_flot	pH_filtr	^* * Rem. ap. col. - Remaining apparent colour; Rem. ap. col. after flotation (HU)		253.7 nm rem. Abs after flotation (cm⁻¹)		^ % rem. Abs - Percentage remaining of Absorbance at 253.7 nm (cm−1); (A/A0)100 – A is the remaining absorbance (cm−1) and A0 is the absorbance (cm−1) of the water sample; % rem. Abs after flotation - (A/A₀)100		Rem. ap. col. after filtration (HU)	253.7 nm rem. Abs after filtration (cm⁻¹)	% rem. Abs after filtration - (A/A₀)*100	Turbidity after filtration (NTU)	^* ***** TOC – Total Organic Carbon. TOC after filtration (mg/L)	residual total Fe after filtration (mg/L)
Sand Type	pH_oxid	pH_coag	pH_flot	pH_filtr	15 cm/min	5 cm/min	15 cm/min	5 cm/min	15 cm/min	5 cm/min	Rem. ap. col. after filtration (HU)	253.7 nm rem. Abs after filtration (cm⁻¹)	% rem. Abs after filtration - (A/A₀)*100	Turbidity after filtration (NTU)		residual total Fe after filtration (mg/L)
Test 5 – Water sample with the HS fraction with apparent molecular size between 30 and 100 kDa with 20 mg/L of FeSO₄ x 7H₂O; 7.3 mg/L of H₂O₂; and 6.0 mg/L of NaOH
1	3.85	5.81	5.99	6.16	64	34	0.079	0.051	50	32	2	0.006	3	0.36	0.824	< 0.005
2	3.77	5.81	5.85	6.24	64	32	0.078	0.048	49	30	2	0.004	3	0.41	0.589	< 0.005
3	3.80	5.66	5.93	6.16	71	36	0.085	0.054	53	34	3	0.006	3	0.41	0.533	< 0.005
Test 6 – Water sample with the HS fraction with apparent molecular size between 30 and 100 kDa with 20 mg/L of FeSO₄ x 7H₂O; 7.3 mg/L of H₂O₂; and 6.0 mg/L of NaOH
1	3.75	5.75	6.05	6.10	60	32	0.070	0.049	44	31	2	0.002	1	0.49	0.600	< 0.005
2	3.81	5.75	6.12	6.18	64	31	0.086	0.048	54	30	2	0.002	1	0.45	0.599	< 0.005
3	3.80	5.60	5.85	5.94	60	32	0.078	0.046	49	29	3	0.004	3	0.44	0.586	< 0.005
Test 7 – Water sample with the HS fraction with apparent molecular size < 30 kDa with 40 mg/L of FeSO₄ x 7H₂O; 14.7 mg/L of H₂O₂; and 12.0 mg/L of NaOH
1	3.64	5.70	5.87	5.87	124	48	0.160	0.079	59	29	2	0.011	4	0.52	0.897	< 0.005
2	3.65	5.76	5.92	6.02	130	41	0.092	0.068	34	25	2	0.012	5	0.60	0.895	< 0.005
3	3.65	5.70	5.86	5.91	114	49	0.160	0.082	59	30	3	0.016	6	0.55	0.850	< 0.005
Test 8 – Water sample with the HS fraction with apparent molecular size < 30 kDa with 40 mg/L of FeSO₄ x 7H₂O; 14.7 mg/L of H₂O₂; and 12.0 mg/L of NaOH
1	3.74	5.83	5.90	6.03	140	46	0.132	0.083	49	31	2	0.010	4	0.44	0.895	< 0.005
2	3.67	5.89	6.00	6.02	142	41	0.202	0.067	75	25	2	0.015	5	0.42	0.967	< 0.005
3	3.70	5.89	6.08	6.08	135	49	0.187	0.078	69	29	3	0.016	6	0.48	0.915	< 0.005

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[1] Correspondence to: Marcelo De Julio E-mail: dejulio@ita.br