2.1. Experimental setup overview
The experimental setup included 6 consecutive treatments
with inflow of secondary effluent (Fig. 1a): Secondary effluent
(inflow)
→
Primary SSVFW (1)
→
First-stage SMOPs (2)
→
Secondstage
SMOPs (3)
→
Third-stage SMOPs (4)
→
Fourth-stage SMOPs
(5)
→
SSVFW (6)
→
Final effluent.
Each water treatment was undertaken in a high-density
polypropylene cylindrical tank (1.3 m basal diameter; 1.38 m
height, 1.4 m top diameter,
∼2 m3) which was buried halfway into
the ground (Fig. 2a).The water moved downstream from tank 1 to
6 induced by gravity since the difference in elevation between two
consecutive tanks was 0.1 m, giving a total difference in elevation
of 0.5 m from tank 1 to 6. The inlet to each tank was through a PVC
tube (diameter 32 mm) running parallel to the upstream wall of the
tank and over the entire tank bed. The section of the tube running
on the tank bed was perforated to allow delivery of water to the
tank filtrating media. The water then moved upward in the tank
and flowed towards the consecutive tank. The outlet consisted of a
horizontal perforated PVC tube (32 mm diameter) placed radially
and 0.05 m below the surface of the tank, which collected the water
and transported it to the next downstream tank. Triangle-shaped
weirs were cut in the upward side of the outlet pipe.
Tanks 1 and 6 were filled with limestone gravel (particle size
30 mm - 50 mm, porosity 37%) to a height of 1.2 m. During normal
operation, there was 0.1 m free water above the gravel bed.
The emergent plant Acorus calamus L. was grown in the gravel