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Table 3

Heavy metal concentrations (mean ± standard error) of raw wastewater (INLET) and of constructed wetlands throughout the experiment period (mg L⁻¹)

Filters	Cr	Cu	Pb
INLET	0.8 ± 0.06	3.0 ± 0.7	2.2 ± 0.7
HCW	0.6 ± 0.06	1.2 ± 0.2*	1.2 ± 0.6*
MHCW-1	0.5 ± 0.04	0.7 ± 0.2**	0.6 ± 0.2**
MHCW-2	0.5 ± 0.04	0.6 ± 0.1**	0.6 ± 0.2**
Vietnam's standard^a	1.1^b	2.0	0.5

Filters	Cr	Cu	Pb
INLET	0.8 ± 0.06	3.0 ± 0.7	2.2 ± 0.7
HCW	0.6 ± 0.06	1.2 ± 0.2*	1.2 ± 0.6*
MHCW-1	0.5 ± 0.04	0.7 ± 0.2**	0.6 ± 0.2**
MHCW-2	0.5 ± 0.04	0.6 ± 0.1**	0.6 ± 0.2**
Vietnam's standard^a	1.1^b	2.0	0.5

Asterisks indicate statistically significant differences between INLET and OUTLETs (HCW and MHCWs) (*for p < 0.05; **for p < 0.01).

^aVietnam's technical regulation on industry wastewater discharge quality (QCVN 40:2011/BTNMT).

^bTotal concentration of Cr (III) and Cr (VI).