Assessment of impact of pollutants in the river Buriganga using a water quality model

Abstract

The river Buriganga, which runs by the side of the Dhaka city, is at present one of the most polluted rivers in Bangladesh. The Dhaka city is one of the densely populated cities in the world, but only partly sewered. Consequently, an enormous amount of domestic and industrial wastes are being released in the Buriganga everyday. This disposal rate is increasing at an alarming rate. The objectives of this study were to investigate the status of the Buriganga river water quality in terms of some important water quality parameters, and to assess the impact of pollutants using an existing water quality model. To assess the water quality, extensive sampling of water and wastewater were carried out for subsequent laboratory investigations. In situ measurements were carried out for some water quality parameters. In addition, extensive literature survey was conducted to collect available data on water quality of the Buriganga river. The present status of pollution in the Buriganga as well as the trend of pollution was addressed through the analyses of the water quality data. The modelling study focuses on the impact of pollutant of biodegradable nature which causes depletion of Dissolved Oxygen (DO) in a river. Suitable DO concentration in river t. water is the most important criterion for the survival of aquatic life, and maintenance of the aquatic ecosystem. A one dimensional water quality model was developed for the assessment of impact of oxygen demanding wastes on the Dissolved Oxygen (DO) in the river. MIKE II river modelling system developed by the Danish Hydraulic Institute (DHI) and available with the Surface Water Modelling Centre (SWMC) was used for the development of the model. In this study, the December, 1994 hydrodynamic and water quality data were used for dry season calibration. Alternative scenarios with varying loading conditions of the biodegradable pollutant were considered and the most likely condition of the river water quality under each scenario was predicted. In lieu of the inherent shortcomings of a one-dimensional model, the observed DO levels of the Buriganga river were well replicated. Alternative scenario study gives possible response of the Buriganga river quality following different loading conditions. The model results indicate that the Buriganga river water quality may not improve appreciably with respect to DO, following reduction of a single major point source such as the Dholai Khal or the Hazaribagh tannery outfall. An integrated approach involving treatment of a number of major point sources followed by their disposal at a distant point near the confluence of the Dhaleswari-Lakhya river may prove effective in improving the DO of the Buriganga river. However, lack of data and time constraint have restricted the .model verification process in this study. In addition, other water quality parameters such as Ammonia, Nitrate, Phosphate, Coliforms could not be modelled due to lack of sufficient data. Thus, verification of the model using additional set of data may provide valuable assistance in making policy decisions using this model.