A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science. School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1999

West Lake is located within Hanoi City, the capital of Vietnam. However, water quality in the lake has been polluted. More precisely, pollution is P- Mezosaprobe type. The major cause for this has been identified as the direct discharge of wastewater into the Lake. The construction of a BOD model is needed to serve as a tool for water environmental management. The model should incorporate both exogenous and endogenous factors to reflect the effects of climate, waste load, and biological processes in the lake's water body over time, especially for a long-term perspective. A relevant BOD model has been developed based on mass balance equation of BOD, phytoplankton and phosphorus, and calibrated based on available data. The model's emphasis is placed on relationships between water quality in the Lake and BOD content in wastewater to assess the water quality change in terms of seasons and time scales. The model's simulation indicates that water quality of the Lake, with the city's master plan, will be rapidly degraded in the years to come and will reach a level much lower than the water quality standard. Extensive experiments with the model reveal different effects on water quality of different levels of BOD input reduction. If an acceptable long-term water quality is to be achieved, a substantial wastewater pre-treatment at sources (to reduce up to 40% BOD input) is required along with a central treatment plant afterward. The technical and administrative aspects of wastewater control framework as required have been discussed for implementing, by taking into account economic efficiency and suitability criteria as well as socio-economic conditions. Thus, the study aims to identify the close relationship between the water quality management and waste water control by subsuming the cause and effect factors that have been widely recognized, so that water quality can be maintained by controlling discharged wastewater.