Efficiency of electrocoagulation in the treatment of laundromat greywater

Caetano, Marcelo Oliveira; Silva, Isabela da; Carvalho, Éverton Cardoso de; Gomes, Luciana Paulo

doi:10.1590/S1413-4152201900025

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Engenharia Sanitaria e Ambiental

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Technical Article • Eng. Sanit. Ambient. 27 (1) • Jan-Feb 2022 • https://doi.org/10.1590/S1413-4152201900025 copy

Efficiency of electrocoagulation in the treatment of laundromat greywater

Tratamento por eletrofloculação de efluentes oriundos de lavandeiras domésticas

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The high consumption of water and the generation of greywater in laundromats underscore the need to investigate advanced treatment techniques to reuse this effluent. Based on the estimated growth figures of the laundromat sector in Brazil, this study looked into the efficiency of electrocoagulation to treat laundromat greywater. Electrodes were connected to an EC reactor on a monopolar parallel connection mode, with electric current of 6 A and current density of 400 A.m². The highest efficiency to treat laundromat greywater was observed at a distance of 15 mm between electrodes, voltage of 17.14 V, and operation time of 30 min, when the removal values of apparent color, true color, turbidity, biochemical oxygen demand, chemical oxygen demand, and surfactants were 92, 97, 88, 91, 98, and 96%, respectively. Electrode consumption was measured at 1.82 g.h, while energy consumption was 20.54 kWh.m³ and the total cost was US$ 4.10 per cubic meter of treated effluent. However, despite the high efficiency of the treatment, reuse of treated laundromat effluent requires polishing in order to meet the standards defined by Brazilian regulations.

Keywords:
laundromat; electrocoagulation; electrolytic treatment; greywater; effluent

Test	Distance between electrodes (mm)	Addition of NaCl (g.L)	Time (min)	Sample	Parameters analyzed
E_1-1 E_1-2 E_1-3	5 (d₅)	No NaCl (S₀)	60 (T₆₀)	Raw, 60 min	Apparent color, true color, turbidity, pH, BOD, COD, surfactants, residual chlorine
E_1-1 E_1-2 E_1-3	5 (d₅)	No NaCl (S₀)	60 (T₆₀)	15, 30, 45 min	Apparent color, true color, turbidity, pH
E_1-4 E_1-5	5 (d₅)	No NaCl (S₀)	180 (T₁₈₀)	Raw, 180 min	Apparent color, true color, turbidity, pH, BOD, COD, surfactants
E_1-4 E_1-5	5 (d₅)	No NaCl (S₀)	180 (T₁₈₀)	15, 30, 45, 60 min	Apparent color, true color, turbidity, pH
E_1-6	5 (d₅)	No NaCl (S₀)	180 (T₁₈₀)	Raw, 180 min	Apparent color, true color, turbidity, BOD, COD, surfactants, total and thermotolerant coliforms
E_1-6	5 (d₅)	No NaCl (S₀)	180 (T₁₈₀)	15, 30, 45, 60 min	Apparent color, true color, turbidity, pH
E_2-1	20 (d₂₀)	No NaCl (S₀); addition of 0.25 g.L (S₂₅)	60 (T₆₀)	Raw, 60 min	Apparent color, true color, turbidity, pH, conductivity, chlorides, BOD, COD, surfactants
E_2-1	20 (d₂₀)	No NaCl (S₀); addition of 0.25 g.L (S₂₅)	60 (T₆₀)	15, 30, 45 min	Apparent color, true color, turbidity, pH, conductivity
E_2-2 E_2-3 E_2-4	20 (d₂₀)	No NaCl (S₀); addition of 0.25 g.L (S₂₅) and 0.50 g.L (S₅₀)	60 (T₆₀)	Raw, 60 min	Apparent color, true color, turbidity, pH, conductivity, chlorides, BOD, COD, surfactants
E_2-2 E_2-3 E_2-4	20 (d₂₀)	No NaCl (S₀); addition of 0.25 g.L (S₂₅) and 0.50 g.L (S₅₀)	60 (T₆₀)	15, 30, 45 min	Apparent color, true color, turbidity, pH, conductivity
E_2-5 E_2-6	15 (d₁₅)	No NaCl (S₀); addition of 0.25 g.L (S₂₅) and 0.50 g.L (S₅₀)	60 (T₆₀)	Raw, 60 min	Apparent color, true color, turbidity, pH, conductivity, chlorides, BOD, COD, surfactants
E_2-5 E_2-6	15 (d₁₅)	No NaCl (S₀); addition of 0.25 g.L (S₂₅) and 0.50 g.L (S₅₀)	60 (T₆₀)	15, 30, 45 min	Apparent color, true color, turbidity, pH, conductivity
E_2-7	5 (d₅)	No NaCl (S₀)	60 (T₆₀)	Raw, 60 min	Apparent color, true color, turbidity, pH, conductivity.
E_2-7	5 (d₅)	No NaCl (S₀)	60 (T₆₀)	15, 30, 45 min	Apparent color, true color, turbidity, pH, conductivity

Tests	Apparent color (mg Pt Co.L)	True color (mg Pt Co.L)	Turbidity (NTU)	Electrical conductivity (μS.cm)	pH	Chlorides (mg.L)	BOD (mg.L)	COD (mg.L)	Surfactants (mg.L MBAS)	Residual chlorine (mg.L)	Total coliforms (MPN.100 mL)
E_1-1	5840.0	5150.0	512.0	–	10.2	–	710.0	3238.0	191.4	<1.0	–
E_1-2	5650.0	3530.0	830.0	–	10.2	–	630.0	2580.6	164.2	<1.0	–
E_1-3	3070.0	2310.0	590.0	–	10.2	–	590.0	2631.2	144.9	<1.0	–
E_1-4	–			–	9.9	–		3845.5	223.9	–	–
E_1-5	4100.0	3180.0	363.0	–	10.3	–	360.0	2934.8	165.3	–	–
E_1-6	–			–	10.2	–	270.0	2833.6	169.5	–	<1.0
Mean	4665.0	3542.5	573.8	–	10.1	–	512.0	3010.6	176.5	–	–
Standard deviation	1141.7	1028.9	168.9	–	0.1	–	167.9	431.0	25.1	–	–
Coefficient of variation (%)	24	29	29	–	1	–	33	14	14	–	–
E_2-1	1220.1	1220.1	335.0	4.2	11.3	–	–	658.2	–	–	–
E_2-2	528.9	369.0	117.0	2.9	10.1	5.0	50.0	402.7	2.0	–	–
E_2-3	143.4	649.4	156.0	4.5	9.9	5.5	160.5	589.7	2.6	–	–
E_2-4	907.0	724.5	237.0	3.6	11.1	6.5	94.0	607.7	1.7	–	–
E_2-5	820.2	593.2	229.0	3.5	8.7	6.1	148.5	528.6	1.3	–	–
E_2-6	1151.8	700.4	325.0	2.6	10.8	4.3	132.5	684.8	1.8	–	–
E_2-7	1406.0	1100.0	103.0	3.1	10.2	–	–	–	–	–	–
Mean	882.5	765.2	214.6	3.5	10.3	5.5	117.1	578.6	1.9	–	–
Standard deviation	402.9	273.8	86.9	0.6	0.8	0.8	40.4	93.1	0.4	–	–
Coefficient of variation (%)	46	36	40	18	8	14	34	16	23	–	–

Parameter	Raw effluent: T₀	Treatment times (min)					Efficiency (%)
Parameter	Raw effluent: T₀	T₁₅	T₃₀	T₄₅	T₆₀	T₁₈₀	T₆₀	T₁₈₀
Apparent color (mg Pt Co.L)	4665.0 ± 1318.3	4557.5 ± 1323.3	3555.0 ± 1417.9	3562.5 ± 1253.8	3247.5 ± 1067.3	533.7 ± 288.0	30	89
True color (mg Pt Co.L)	3452.5 ± 1188.1	3030.0 ± 580.7	2542.5 ± 1205,8	2745.0 ± 1058.6	2400.0 ± 943.1	390.3 ± 343.5	32	89
Turbidity (NTU)	573.8 ± 195.1	478.8 ± 160.7	386.3 ± 111.5	305.8 ± 124.7	273.6 ± 127.4	64.0 ± 36.8	52	89
pH	10.1 ± 0.1	10.4 ± 0.1	10.4 ± 0.1	10.5 ± 0.2	10.5 ± 0.2	10.2 ± 0.2	–	–
BOD (mg.L)	512.0 ± 187.7	–	–	–	346.7 ± 47.3	155.0 ± 49.5	32	70
COD (mg.L)	3010.6 ± 472.2	–	–	–	1830.0 ± 129.8	573.3 ± 255.8	39	81
Surfactants (mg.L MBAS)	176.5 ± 27.5	–	–	–	112.9 ± 14.3	10.3 ± 0.5	36	94
Total coliforms (MPN.100 mL)	<1.0	–	–	–	–	< 1.0	–	–
Total coliforms (MPN.100 mL)	<1.0	–	–	–	–	< 1.0	–	–
Residual chlorine (mg.L)	<1.0	–	–	–	< 1.0	–	–	–

Parameter	Treatment time (min): d₅					Efficiency (%) T₆₀
Parameter	T₀	T₁₅	T₃₀	T₄₅	T₆₀	Efficiency (%) T₆₀
Apparent color (mg Pt Co.L)	1406.0	721.0	203.0	196.0	267.0	81
True color (mg Pt Co.L)	1100.0	203.0	69.0	71.0	72.0	93
Turbidity (NTU)	103.0	80.0	6.1	13.2	23.0	78
Conductivity (μS.cm)	3.1	3.2	2.8	2.9	3.2	–
pH	10.2	9.7	9.7	9.9	10.0	–

Parameter	Treatment time (min): d₁₅					Efficiency (%) T₆₀
Parameter	T₀	T₁₅	T₃₀	T₄₅	T₆₀	Efficiency (%) T₆₀
Apparent color (mg Pt Co.L)	986.0 ± 234.5	490.4 ± 281.4	58.8 ± 26.6	131.4 ± 66.9	75.7 ± 6.9	92
True color (mg Pt Co.L)	646.8 ± 75.8	108.0 ± 77.7	26.6 ± 8.8	27.2 ± 19.2	18.6 ± 0.0	97
Turbidity (NTU)	277.0 ± 67.9	105.5 ± 71.4	7.6 ± 0.0	47.3 ± 29.2	32.7 ± 3.5	88
Conductivity (μS.cm)	3.0 ± 0.6	2.9 ± 0.5	2.8 ± 0.3	3.0 ± 0.5	3.0 ± 0.5	–
pH	9.7 ± 1.5	9.6 ± 1.8	10.1 ± 1.1	10.4 ± 0.9	10.7 ± 1.1	–
Chlorides (mg.L)	5.2 ± 1.2	–	5.1 ± 1.1	–	5.0 ± 1.1	3
BOD (mg.L)	140.5 ± 11.3	–	–	–	12.0 ± 0.0	91
COD (mg.L)	606.7 ± 110.5	–	–	–	10.0 ± 0.0	98
Surfactants (mg.L MBAS)	1.6 ± 0.4	–	–	–	0.1 ± 0.0	96

Parameter	Treatment time (min): d₂₀					Efficiency (%) T₆₀
Parameter	T₀	T₁₅	T₃₀	T₄₅	T₆₀	Efficiency (%) T₆₀
Apparent color (mg Pt Co/L)	699.8 ± 466.3	606.1 ± 368.2	207.9 ± 174.1	86.3 ± 37.0	89.8 ± 38.0	87
True color (mg Pt Co/L)	740.7 ± 354.3	388.5 ± 414.9	141.8 ± 167.2	60.8 ± 43.4	48.0 ± 66.3	94
Turbidity (NTU)	211.3 ± 96.5	145.5 ± 92.8	47.0 ± 42.0	29.3 ± 6.0	27.1 ± 22.0	87
Conductivity (μS/cm)	3.8 ± 0.7	3.3 ± 0.4	3.4 ± 0.5	3.4 ± 0.7	3.6 ± 0.5	–
pH	10.6 ± 0.7	10.5 ± 0.9	10.4 ± 0.8	10.3 ± 0.6	10.6 ± 0.6	–
Chlorides (mg/L)	168.8 ± 326.3	–	5.8 ± 0.6	–	46.9 ± 82.5	72
BOD (mg/L)	101.5 ± 55.6	–	–	–	12.7 ± 17.0	88
COD (mg/L)	533.4 ± 113.5	–	–	–	163.3 ± 43.8	69
Surfactants (mg/L MBAS)	2.1 ± 0.5	–	–	–	0.5 ± 0.7	77

Addition of NaCl	Main elements	Secondary elements	Trace elements
S₀	Al	Cl, Si, S, Fe	Ca, Fe, Mg, Cu, Zn, K, Mn, Cr, Sr, Ga, Br, Si, S, Zr
S₂₅	Al	Cl, Si, S, Fe, Ca	Ca, Fe, Mg, Cu, Zn, K, Mn, Cr, Sr, Ga, Si, S, Zr
S₅₀	Al	Cl, Si, S, Ca, Na	Ca, Fe, Mg, Cu, Zn, K, Mn, Cr, Sr, Ga, Br, Si, S, Zr

Addition of NaCl (S)	Distance between electrodes (d) mm	Electrode consumption (g.h)	Aluminum consumption (g.h)^* * Considering the content of aluminum used equal to 98.56%.	M_calculated (g.h)	Efficiency of current (%)
S₀	5	3.31 ± 0.29	3.26 ± 0.29	2.01	162 ± 14
	15	1.86 ± 0.66	1.83 ± 0.65	2.01	91 ± 32
	20	3.67 ± 0.64	3.62 ± 0.63	2.01	180 ± 31
S₂₅	15	3.00 ± 0.87	2.95 ± 0.86	2.01	146 ± 43
S₂₅	20	3.99 ± 1.09	3.93 ± 1.07	2.01	195 ± 53
S₅₀	15	3.98 ± 0.76	3.92 ± 0.75	2.01	195 ± 37
S₅₀	20	4.47 ± 1.53	4.40 ± 1.50	2.01	218 ± 75

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[1] * Corresponding author: mocaetano@unisinos.br