day (with 37% reduction). However, the T-P increased
above the initial T-N of 2.058 mg/l starting on the 7th day
of measurement. The reversion may be due to the fact that
(1) the capacity of removing microorganisms attached to the
porous concrete reached the limit within a short period of
time because the water was circulated within a confined
water purification channel or (2) the microorganisms could
not be activated any more due to the lack of dissolved
oxygen depleted by fast growing bio-film facilitated by
abundant nitrogen, a nutrient for the aquatic microbes.
The relationships among the P/G, aggregate size and the
T-N are displayed in Fig. 12.