STUDY OF IMPACT OF DOMESTIC SEWAGE AND INDUSTRIAL EFFLUENT ON WATER QUALITY OF RIVER BHARALU

Abstract

The river Bharalu is a left bank tributary of river Brahmaputra in Assam, which passes through Guwahati city. It adds an aesthetic value for the beautification of Guwahati city. The river water is used for washing clothes, bathing and other uses. It also acts as a natural drain for carrying industrial and domestic waste water generated from Guwahati city. The discharge of untreated municipal waste water causes degradation of water quality of river Bharalu in lower stretches of the river. The DO in lower stretches of the river becomes zero during winter, producing foul smell and rendering the water body unsuitable for uses. However during summer, the effect of dilution due to the rainfall is remarkable. In this present study, the pollution load of river Bharalu in post monsoon and premonsoon season has been studied Eight sampling stations were selected for collection of water sample from river Bharalu. ' The collected— water samples were analyzed in Environmental Laboratory of Assam Engineering College, Jalukbari, Guwahati- 13, Assam for various water quality parameters. Some of the samples were brought to Institute Instrumentation Centre, IIT Roorkee for testing of heavy metals. The observed values of various water quality parameters were discussed and compared with the prevailing standards, corresponding to use of the water body. For the development of BOD and DO model, the water samples from 53 drains were collected near outfall of each drain. The BOD and DO of the drains water and flow of drains have been determined. Further, the velocity, depth, width of flow and temperature of the river near outfall of each drain has been measured. These hydrodynamic parameters of the river were used to determine the reaeration rate and deoxygenation rate. The saturation concentration of oxygen in river water was determined from temperature values. The study covers about 13.93 km stretch of river starting from Natun Bazar Sluice gate at Basistha to Bharalumukh, from where the river enters the city. For convenience of study, a reference point is assumed near Natun Bazar Sluice Gate. The distances of each drain outfall from reference point were measured. The travel time in respective reaches were calculated on the basis of reach length and velocity. These data were used in BOD and DO model to predict the BOD and DO values throughout the stretch of the river. The predicted values of BOD and DO are then compared with the observed value of BOD and DO in eight sampling stations of the river. The comparison showed the variation iv of predicted and observed values of BOD is about 8.8% in station 2 - 4. The predicted and observed values of BOD and DO match well throughout the stretch. After validation of the model, the various options, such as flow augmentation, zero discharge from industries and combined effect of flow augmentation coupled with waste water treatment were evaluated to improve the water quality of the water body for usable purposes.