Abstract
Purpose of this study is to clarify the effects of sunlight, bottom sediment and biofilm support media on the capacity of natural purification in small channels fed with gray water. Model channels (depth=0.03m, width=0.08m, length=24m) made of PVC were used for the study. Hydraulic retention time (HRT) in the channels were 3. 2-13h. Specific conclusion of the study are as follows :
1) Removal of suspended solids (SS) in the channels was obvious. Percent removal of SS was more than 50% at HRT 3h. Percent removal of dissolved organic carbon (DOC), however, was less than 25% at HRT 3h.
2) Percent removal of dissolved nitrogen (D-N) and dissolved phosphorous (D-P) in open channels with sunlight tended to show larger value than that without sunlight. Removal of D-N and D-P was probably derived from the nutrient uptake by attached algae and prohibition of nutrients release from bottom sediment in aerobic condition made by photosynthesis of attached algae.
3) Accumulation of bottom sediment caused deterioration of water quality in channels in high temperature season, arising nutrient release from bottom sediment under depleted DO condition.
4 ) Support media settled on channel bed were not effective for purification of gray water. The media seemed to make low DO sites in channels and cause nutrients release from bottom sediment.
