EFFECTS OF BLUE LED INSTALLED IN SLOW SAND FILTRATION PROCESS ON QUALITY OF TREATED WATER AND BIOLOGICAL FILTRATION MEMBRANE

Abstract

 Slow sand filtration process is frequently used for water treatment using a variety of microorganisms including photosynthetic organisms which is dependent on sunlight. In this study, for proposing a technology to cover the filtration pond and equip it with blue LED as the light source, effects of the LED on quality of treated water and biological filtration membrane (BFM) were investigated in a lab-scale experiment of slow sand filtration, comparing with sunlight and dark conditions. The result of experiment demonstrated both blue LED and sunlight contributed to growth of BFM and maintained aerobic condition on the surface of the membrane. Microbial community analysis of BFM revealed these lights did not change the density of bacteria in the membrane but reduced the diversity of microbes probably due to increase of photosynthesis bacteria like Cyanobacteria. The analysis also found Cyanobacteria related to nitrate assimilation in the conditions of LED and sunlight, resulting in a lower concentration of nitrates in the treated water than in the dark condition. The findings obtained in this study lead to our expectation that blue LED can contribute to a stable performance of slow sand filtration process, even if the filtration pond is covered for a security reason, by increase of photosynthesis bacteria and slower growth of BFM than sunlight.