3. Results and discussion
3.1. Estimating setup stage period and media porosity
Average values of the measured porosity along cell length for the three media cells are presented in Table 1 and graphically shown in Fig. 3. After 6 months from start of operation, it was noticed that reduction in porosity values was very small and may be considered as the end of setup stage and the beginning of steady stage of treatment media. The initial media porosity values were 0.866, 0.576 and 0.431 for plastic, rubber and gravel respectively. The plastic porosity was twice the gravel and 1.5 times the rubber porosity. Gradual and remarkable porosity reductions were observed during the first 90 days of wetlands operation due to sedimentation of degradable fine particles and suspended solids, development of reeds roots as well as growing of bacterial biofilm attachment to the media surface. Slight porosity reductions were observed during the next 30 days of wetlands operation (days 80–110) as media pores gradually filled with fine solids clear from degradable matter and both reeds rhizomes and attached biofilm layers were nearly in stable size. During the next period (days 110–218) porosity reduction was very small in all media and reduction trends were almost flat starting from day 180.