2023 Volume 79 Issue 25 Article ID: 23-25008
Bench-scale experiments were seasonally carried out to understand the effect of sunlight on schutzdecke for the slow sand filtration, with the special focus on its clogging. In spring and winter, the filtration under sunlight was clogged due to the rapid growth of algae in the schutzdecke, while the good performance of filtration was observed in the other seasons. The schmutzdecke in both summer and autumn had Melosira, which is known to help the stable sand filtration, as the dominant species of algae. The diversities of algae and bacteria found in the schmutzdecke were not associated with the performance of sand filtration. In the spring experiment, the irradiation of blue light emitting diode (LED), instead of sunlight, was also examined and it enabled to avoid the clogging of filtration found under sunlight. The additional experiment revealed that intermittent irradiation of blue LED at the interval of 12 hours achieved more stable filtration than its continuous irradication. The schutzdecke, in which Melosira was dominant, under the intermittent irradiation captured a smaller amount of suspended solids than that under sunlight and dark condition, indicating that it was well controlled by blue LED to balance the algal growth and its removal with captured solids.
