Sewerage supply in rural community is the important for water quality protection of water system such as river, lake
and wetland. And characteristic of small scale wastewater system that have wide range of inflow and concentration in
sewage should be considered for stable operation of small scale wastewater treatment plant. In this research,
characteristics of flow ratio (flow / designed flow), effect on treatment efficiency of small scale wastewater treatment
plant and assessment of optimal flow ratio were conducted through analysis on operation result of 18 small scale
wastewater treatment plant in Bong-hwa gun. As a result, flow ratio shows the higher value during summer.
However pollutants concentration in sewage was shown the higher concentration during autumn and winter.
Treatment of small scale wastewater treatment plant is increased when flow ratio increased, and nutrient treatment
efficiency is more sensitive to change of flow ratio than organic compound and suspended solids. According to this
research result, it need to be maintained flow ratio 0.8 over value for stable treatment efficiency of small scale
wastewater treatment plant.