Results andDiscussion

The res ults shown in Figures 2 and 3 represe nt data collecte d for 72 h du ring the 10th week of treat ment (April 2000), and

FIGURE2. Concentrationof (A) SS, (B) COD, (C) BOD5, (D) andtotal phosphorus in wastewater during 72 h of treatment in the planted channel (b) and in the unplanted channel (O) in April 2000;(- -) indicates the legal discharge level and (‚‚‚) indicates the legal discharge level ineutrophically sensitive areas. Values aremeans per channel ( standard deviation; n ) 5.

FIGURE 3.  Concentration of (A) total nitrogen, (B) NH +-N, (C)--N, and (D) NO --N in wastewater during 72 h of treatment

FIGURE4. Removal efficiencyby(A) SS, (B) BOD5, (C)COD, (D) total phosphorus, (E) andtotal nitrogen after48h intheplanted channel (02/2000-07/2000). Values are means per channel ( standard deviation; n ) 5.

TABLE1. General  DesignParametersawastewater

mean min max objectives

NO2 3

intheplantedchannel (b) intheunplantedchannel (O);(‚‚‚) indicates the legal discharge level in eutrophically sensitive areas. Values are means per channel ( standard deviation; n ) 5.

Figure 4 represe nts the re moval rate after 48 h of data collecte d for 6  months.

SS, BOD5, and COD Removals. From February to July, the sewage com position varied widely (Table 1; SS (37-400 mg L-1), BOD5  (64-1100 mg L-1), and COD (187-1650 mg

L-1)); the raw efflue nt conce ntrat ion was dependent on rainfall. As com pared to the plant-free chann el, the process with plants was very effective in redu cing SS, BOD5, and COD parameter s by 99%, 93%, and 90%, res pectively (Figure 2A-C). The legal discharge levels were reached in the planted chann el after 24 h of treat ment. The organic loa d reached constant values between 12 and 48 h. In the plant-free system, SS and BOD5 re mained constant, wherea s COD decrea sed by 45%.

The re moval of biodegradab le constituents in the system can be described using a first- order kinetic model. SS, BOD5, and COD decrea sed exponentially, and the C1, C0, k, and r2 values are represe nted in Table 2. The values of r2 indicate that the kinetic modeling was correct and that the model fits reality. The qua ntity of re moved pollution (C1) varied with the sewage loa d, bu t the minimal value of pollution after one infinite treat ment time(C0) re mained constant. The system pu rified  the  wastewater  correct ly,  whatever  the influe nt

aCharacteristics of the inlet (n ) 20) and treatment goals (mg L-1); discharge nor ms (Europ ean directive 91/271); (*) indicates the legal discharge level in eutrophi cally sensitive areas.

experimentally after 48 h of plant treat ment (Table 2). Thu s, we can assu me that, after 48 h, the system has reached maximal efficie ncy. The re moval efficie ncies observed after 48 h show that the system is stable for 6 months with re moval mea ns of 91%, 87%, and 83% for SS, BOD5, and COD, res pectively (Figure 4A-C). The organic matte r and the suspended solids did not block up the root systems, res ulting in a constant wastewater level in the chann el throughout experiment.

SS and thu s indirect ly BOD5 and COD were re moved by filtrat ion and adsorption; the solids tra pp ed in the root systems were then deco mposed and minera lized by bacter ia. The NFT system with Chrysanthem u m cinerariaefoliu m can str ongly redu ce the tota l organic loa d without root system saturation and without sedimentation of the hydroponic chann els.

Mathematically, it is possible to design an NFT system treat ment that could treat wastewater from comm unities. The sewage loa ding rate, in ter ms of the depth of raw sewage loa ding onto the hydroponic chann els in a 48 h of treat ment is 2.5  cm / day which is calculated  as follows:

organic loa d.  The  k  values vary,  bu t  no  correlation  was 3 3