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Pollution Assimilation Capacity of Buriganga River

Mohammad Rezaur Rahman
Institute of Flood Control and Drainage Research, Bangladesh University of Engineering and Technology, Dhaka -1000, Bangladesh

Md. Yunus Rana
Institute of Flood Control and Drainage Research, Bangladesh University of Engineering and Technology, Dhaka -1000, Bangladesh

Abstract/ Executive Summary:

The Buriganga River receives partially treated sewage effluent, sewage polluted surface runoff and untreated industrial effluent of Dhaka city. Already the minimum dissolved oxygen, the prime indicator of water quality had been found to be less than the desirable level at certain sections of the Buriganga river. Early implementation of efficient management practices will save the Buriganga river from the fate of many rivers in different parts of the world. Before developing management program it is necessary to investigate the assimilative capacity of the rivers. The basic objectives of this study was to investigate the assimilative capacity of thc Buriganga river. It had been seen that Buriganga river has considerable pollution assimilation capacity. Current pollution load will therefore pose no problem if they are properly managed using existing facilities. If tannery units at Hazartbag are shifted to Savar as proposed by the Government then additional loads can be discharged through Pagla Sewage Treatment Plant without violating water quality standards.

Keywords: Burtganga, Pollution assimilation, Effluent management

Location: Bangladesh University of Engineering and Technology, Dhaka, Bangladesh

Start Date: 00-00-1984

End Date: 00-00-1992

Program Area: Risk Management in Agriculture

Commodity: Contamination

Objectives:

Objective of the study was to investigate the pollution assimilation capacity of the Buriganga river.

Methodology:

DOE (1992) analyzed cumulative data for three parameters namely total solid, DO and BOD from 1984 to 1992 for the Buriganga river. Although in general the parameters are within acceptable limits the water quality has been shown to follow a downward trend. BOD is approaching 3 mg/l for both dry and wet seasons. During the dry season. DO has fallen below 5 mg/l. In the wet season it has fallen below 6 mg/l. Both domestic and industrial wastes find its way into the river Buriganga, Hazaribag station being the most polluting station. DO at Hazaribag can be as low as 2 mg/l in May while the standard value for DO in surface water in Bangladesh is at least 4 mg/l (DOE. 1991). Hydraulically the Buriganga is not an isolated river. Many other rivers are hydraulically connected with the Buriganga and influence the flow of the Buriganga. It is hydraulically connected with the Balu, the Dhaleswari, the Kaliganga, the Karnatali, the Lakhya, the Tongi khal and the Turag. The network of the river system hydraulically connected with the Buriganga. Upstream end of the Buriganga is at 11 km down from the Mirpur bridge and downstream end is at Hariharpara. Total length of the Buriganga river is 17 km. Average width of the river around Dhaka city is nearly 500 m. Average flow during wet season (May to October) is about 700 cumec and average now during dry season (November to April) is about 140 cumec. In this research project. a widely used software called Mikell was used for river flow investigation. The details of model description. data used. model setup and model calibration and verification was shown In Rahman and Rana (19941. Model was calibrated for hydrological year 1989-90 and 1990-91. The main calibration parameter was Manning roughness coefficient of the rivers. A range of roughness coefficient from 0.03 to 0.04 was used to calibrate the model. Optimum roughness coefficient was obtained by best fitting of model estimated water level against observed one. This was done by trial and error basis. Model calibration and verification Indicate that performance of this model in reproducing water level was satisfactory. So, model computed discharges and velocities was representative. DO is the prime indicator of the water quality. In this study impact on DO due to pollutant load in terms of BOD was investigated. In any water quality management program for a river, the objective was to maximize the use to assimilative capacity of the river keeping the water quality acceptable. Such objective and constraint were used in this study. Gils (1991) suggests that management program should use such models which are easily interpretable to the decision makers. In this study, impact on DO due to BOD load was investigated using the widely used Streeter-Phelps equation as shown below: D= (K₁L_o)/(k₂-k₁) X {(e^-K1^t-e-^K2^t) + (D₀e^-k2^t)} Where, D = DO deficiency, k₁ = BOD reaction rate constant, k₂ = reaeration rate constant, L_o = BOD load, D_o = initial DO deficiency, t = time. The reach of Buriganga between Hazaribag and Dhaleswari confluence was considered. The distance between Hazaribag and Dhaleswari confluence is 15 km and this reach was subdivided into 15 segments each 1 km long. Since dry season is critical from water quality consideration, therefore, in this study only dry season flow was considered. The DO profiles under existing pollutant discharge pattern corresponding to 20% (80 cumec), 30% (110 cumec). 40% (130 cumec) and 50% (140 cumec) flow are shown respectively. An initial DO level of 6 mg/l was assumed from available literature and temperature of 20° Celsius was considered.

Source of Information: Journal of Civil Engineering, The Institution of Engineers. Bangladesh, VoL CE 24. No.1. 1996

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It has been seen that Buriganga river has considerable pollution assimilation capacity. Such assimilation capacity provides considerable opportunity for proper management of Buriganga river water quality. Either a treatment plant at Hazaribag or shifting of tannery units to Sayar will allow further utilization of the assimilation capacity of Buriganga river. A treatment plant at Hazaribag is necessary not only to manage the BOD load but also to treat the chromium contents of the discharges from Hazaribag tanneries.

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