demonstr ated betwee n k and the influe nt loa d or the experiment du ration. The k variation may have bee n du e to the sewage com position.

The C0 values obtained after the modelization of the system pu rification capacity are identical to those obtained

HLR ) 30 L/ 48 h × m / 10 L × 24 h / day chann el area () 4 m × 0.15  m)

HLR ) 0.025 m / day or 2.5 cm / d

If the hydraulic loa ding rate (HLR) calculated is 2.5 cm / day,

TABLE2. Modelizationof Wastewater Quality Evolution in the Planted Channel  for Weeks 5, 10, and 20a

5 weeks (March) 10 weeks (April) 20 weeks (June)

parameters C1 C0 k r2  

C1 C0 k r2 C1 C0 k r2

SS 103 ( 2 5.4 ( 0.7 0.35 ( 0.02 0.988 153 ( 2 4.2 ( 1.1 0.24 ( 0.01 0.995 119 ( 3 11 ( 2 0.14 ( 0.01 0.983

BOD5 61 ( 2 4.6 ( 0.8 0.21 ( 0.02 0.974 89 ( 2 5.3 ( 1.1 0.18 ( 0.01 0.984 73 ( 1 3.6 ( 0.7 0.10 ( 0.01 0.994

COD 163 ( 3 36 ( 2 0.17 ( 0.01 0.989 473 ( 5 56 ( 3 0.11 ( 0.01 0.996 150 ( 2 37 ( 1 0.21 ( 0.01 0.995

TN 9.3 ( 0.1 5.9 ( 0.2 0.08 ( 0.01 0.975 29 ( 1 18 ( 2 0.19 ( 0.06 0.778 10 ( 1 5.7 ( 0.7 0.08 ( 0.02 0.850

TP 3.2 ( 0.1 1.5 ( 0.1 0.32 ( 0.06 0.868 5.9 ( 0.3 3.9 ( 0.2 0.07 ( 0.01 0.951 2.4 ( 0.1 1.8 ( 0.1 0.19 ( 0.02 0.956

a C1  (mg L-1), C0  (mg L-1), k, and r2  values in the planted channel; coefficient ( standard error  (n ) 30).

and, assu ming this, the wastewater flow is 150 L per person per day, the surface area necessary to treat a comm un e of 100  peo ple is

area ) daily flow rat e of wastewat er, m / day hydraulic loa ding rate, m / day

100  peo ple × 150 L/ person-day × m3 / 1000 L

was also observed in the plant-free system, with an incre ase from  0 to 8  mg L-1 in  72 h.

The conversion of amm oniu m to nitrite and subsequ ent oxidation of nitrite to nitrate was more marked with the plant system. The re moval of nitrogen is based on the nitrification / denitrification activity of root-a ssociated bacter ia (29). The plant root s provide a large surface area for microbial growth and allow for biofilm formation (30). The system of   waste-area )

water recirculation led to water oxygenation. The dissolved oxygen deter mined in the inflow was generally 0.8 ( 0.2 mg) 600 m2,  or 6 m2 of produ ction area per person

TP. The kinetics (Figure 2D) show that TP decrea sed, bu t it was not com pletely eliminated by the system; it decrea sed by 70% with the plants and by 50% in the plant-free system. The pu rification outpu ts were lower than SS, BOD5, and COD. C0 was not negligible versus C1 (Table 2), contrar y to what was observed for  SS,  BOD5,  and COD; C0  was  higher for str onger initial loa ds. The kTP varied bu t could be conn ecte d to neither the influe nt loa d nor the du ration of the experi- ment. The kTP variations observed can be explained by the fact  that P  could be prese nt in various forms that are  not re moved  or  assimilated  in  the  same  way  by  plants andbacter ia.

The average TP re moval after 48 h was 50 ( 18%. The maxim u m values of TP re moval rates (86%) were obtained after the fourth month of system installation and reached the standards necessary to allow for the discharge of water in eutro phically sensitive areas (Figure 4D). This period plant corres ponds to the initiation of flower formation and thu s to  the time when nu trition  needs were  maximal (26).

Phosph orus com pound s are comm only classified into orthoph osph ates (PO43-), acid-hydrolyzable ph osph ates, and organic ph osph ates. Acid-hydrolyzable ph osph ates are neg- ligible in sewage (27). Organic ph osph orus is converte d by the bacter ial activity into mineral ph osph orus that can be assimilated by the plants. Removal of ph osph orus occurs by sorption, com plexation, precipitation, and assimilation by microbial and plant biomass  (28).