SEWER DISCHARGE CHARACTERISTICS AND WATER BALANCE IN DRY SEASON IN HUE, VIETNAM
Keywords:combined sewer system, dry season, flow rate, sewer discharge, water balance.
Vietnam has been developing sewerage recently. Although sewer discharge quantity and quality data is vital for proper sewage management, their fluctuation has not been well characterized in most of cities in developing countries. This study aimed to characterize a combined sewer discharge in a residential drainage area (11.2 ha) in Hue city, Vietnam on dry days in dry season (DdDs). A 24-hour survey on sewage quantity and quality was conducted at the sewer outlet on two weekdays and two weekends in July 2015. Household water consumption was hourly recorded from water meters for 23 households. Then results of discharge characteristics were compared with those on dry days in rainy season (DdRs) of our previous study. Results showed that hourly variations of flow rate corresponded to the water consumption trend. Average discharge flow rate was equivalent to 38.5 ± 4.4 L/cap/day, which was much lower than that on DdRs (64.2 ± 25.0 L/cap/day). In contrast, pollutant concentrations on DdDs were higher than those on DdRs and fluctuated slightly in a day and among days in a week. Low concentrations of discharge in both dry season and rainy season showed that domestic wastewater in urban Hue was not strongly polluted in terms of organic matter and nutrients. Sewer water balance showed that only 29 % of total water inputted to the sewer system was discharged through the outlet on DdDs, while the remaining 71 % was likely exfiltrated to the ground from the sewer system, which will be a potential pollution source to soil and groundwater.