Ban biên tập gửi đến bạn đọc bài tóm tắt luận văn tiến sỹ của TS. Trần Nguyễn Quỳnh Anh, giảng viên Đại học Khoa học thuộc Đại học Huế. Luận án tiến sĩ vê chuyên ngành Nguyên cứu môi trường toàn cầu:
Under the pressure of rapid urbanization and economic growth, the protection of water environment has become more difficult and urgent than ever. Poor management of material flows in urban areas has led to a great amount of pollutant flows going to the environment and caused the serious pollution. It is considered that surface and ground water pollution is one of the biggest environmental concerns in urban areas in developing countries. Since domestic wastewater discharge potentially has impact on material flows, well understanding of its characteristics and impact can help in identifying solutions for better management of material flows. However, wastewater discharge has been not well characterized in most of developing countries. This research aims to study the characteristics of domestic wastewater discharge and its impact on the material flows in urban areas in developing countries, with a case study in urban Hue city, Vietnam.
The research found that average discharge at the sewer outlet on dry days in dry season was 2.72±0.32 m3/h (44.9±5.4 L/cap/day) in 2015 and 2.27±0.44 m3/h (37.5±7.3 L/cap/day) in 2016, which was about half of that on dry days in rainy season (4.99±0.55 m3/h (82.5±9.1 L/cap/day) in 2015, and 5.38±2.15 m3/h (88.9±35.5 L/cap/day) in 2014). Hourly discharge flow rates on dry day fluctuated corresponding to the water consumption trends. Two peaks of discharge rates were observed on dry days from 6:00 – 16:00 and from 16:00 – 0:00, and the lowest rates were in the early morning (1:00 – 6:00). Meanwhile, discharge flow rates in rain events were affected by rainfall intensities. The study also supplied information on quality of sewer discharge and pollutant loads from the sewer system. Domestic wastewater discharge in urban Hue was characterized by low concentrations of SS, nutrients, and organic matter with small proportion of particulate matter, and not strongly fluctuation among hours in a day. Pollutant loads in study area were rather small compared to other areas and have a resemble pattern with discharge flow rate. Relationships between flow rates and pollutants loads were also investigated.
Water balances showed the same pattern for all dry days in both of dry and rainy seasons. Meanwhile, on rainy days in rainy season, the pattern was different at different rainfall intensity. It was noticeable that on dry days in dry season, discharge flow rate at the sewer outlet and went to the water body only accounted for 28.5% (in 2016) of total wastewater entered the sewer system. It means that a large amount of wastewater (71.5%) might be exfiltrated into the ground though sewer leakage.
The impact of domestic sewage discharge on phosphorus (P) and nitrogen (N) flow in an urban area in Hue was quantified. Sewage discharge was identified as the main source of P and N loads to the water body, which contributed 91.0% – 99.2% of total P and 96.1% – 99.6% of total N inputted the water body. Contribution of sewage discharge to P and N inputted to water body varied at different weather conditions. On dry days in dry season, 14.7% of P (20.7 g/ha/day) and 42.5% of N (267.1 g/ha/day) produced in the area were discharged to the water body. On rainy days in rainy season, these amounts increased greatly under the impact of heavy rain, which were 3 – 13 times higher than those on dry days in dry season. It is demonstrated that there were some other sources such as accumulated sludge inside sewer pipes and/or water infiltration from the ground added more P and N into the total P and N budget of the sewer system on these days.