Table 1 Design characteristics and operating parameters of the gravel bed hydroponic treatment units

Number of treatment units

4

Length (L)

2 m

Width (W)

0.75 m

Unit area

1.50 m²

Gravel depth

0.40 m

Gross capacity

0.60 m³

Macrophyte type

Typha latifolia

 Hydraulic loading rate

2.33 cm d^− 1

 TKN

0.44–1 g m⁻²d⁻¹

 NH4+ − N

0.42–0.72 g m^− 2d^− 1

 NO₃⁻ - N

0.2–0.4 g m^− 2d^− 1

 PO₄³⁻-P

0.19–0.54 g m⁻²d^− 1

 Hydraulic retention time

5 days