Characterization of nutrient and organic contents of water in the peripheral rivers of Dhaka city

Abstract

Dhaka city is surrounded by rivers. Ever increasing pollution level in peripheral rivers is causing huge problems for the environment of Dhaka city and jeopardizes the use of the river water for drinking and other useful purposes. Increasing trends of pollution level demands the study of water quality of peripheral rivers around Dhaka city. This study covers analysis and characterization of organic and nutrient contents of water in peripheral rivers around Dhaka city. Under this study water sample was collected from 7 (seven) locations of 6(six) peripheral rivers of Dhaka city, DND canal and several locations of different rivers. The parameters that have been examined in BUET laboratory are pH, DO, NH3-N, NO3-N, NO2- N, PO4, TDS, TSS, BOD5 and COD. All the data have been analyzed and monthly variation have been observed. The results of water quality analysis under this study have been compared with the previous data and trend of variation has been shown. A geospatial assessment has been made with spatial features using GIS tools. pH in peripheral river water was found in normal range and seasonal variation of pH was not significant except in Balu river, where pH was found high in the month of January, 2010 but below the permissible limit of 8.5. In all the peripheral rivers pH measured was within the allowable limit of 6.5-8.5 (Standard for Drinking Water, ECR,1997). Dissolved Oxygen measured in three locations of peripheral rivers namely Chandighat, Intake point of Sayedabad Water Treatment Plant at Sarulia and DND canal was below the standard value for inland surface water (ECR,1997). NH3-N content in these three points were found within limit in consideration of standard for inland surface water (<15 mg/l, agriculture, DoE,1991). But in consideration of standard for inland surface water for recreation (<2.0 mg/l, DoE,1993) some value is higher. In Tongi, Balu, Shitalakhya river the measured NO3--N contents were within the permissible limit of 10 mg/l (Standard for inland surface water for pisciculture, agriculture, DoE,1993) but in the Buriganga and Turag river NO3-N content exceeded this allowable limit. In DND canal the measured value of NO3-N was found within allowable limit. Except Turag, Shitalakhya river and DND canal, NO2-N contents in all the peripheral rivers were found high and increased as dry season progressed. Except the river Tongi PO4 contents in all other peripheral rivers and in DND canal were found within the normal range of 10.0 mg/l (Standard for inland surface water for pisciculture and agriculture, DoE,1993) and in the Tongi river the excess PO4 content was found only in the month of January, 2010. TDS contents in all peripheral rivers were found within the maximum allowable limit of 1000 mg/l (Standard for Drinking Water, ECR,1997). Almost all TSS content in the peripheral rivers and DND canal were found to exceed the allowable range of 25 mg/l (Standard for inland surface water for fishing, DoE, 1991). Except in Rupgonj Ferry ghat location of Shiatalakhya river, high BOD and COD values were measured in all the peripheral rivers including DND canal. All the nutrient and organic contents in the water of peripheral rivers around Dhaka city are increasing day by day and pollution level in river water is also increasing. The water of peripheral rivers around Dhaka city is not only unsuitable for drinking but appears to be not usable for any other purposes.