STUDIES ON THE SORPTIVE PROPERTIES OF BED SEDIMENTS OF RIVER GANGES AND TRANSPORT OF SOME HEAVY METAL IONS

Abstract

The incidence and transport of eight heavy metals - Manganese, Iron, Cobalt, Nickel, Copper, Zinc, Cadmium and Lead in the water and sediments of river Ganges, from Badrinath 2+ 2 + to Narora, alongwith the study on adsorption of Cu , Zn and Pb 2+ by bed sediments of the river have been presented in this thesis. River Ganges, the most extensively used river of India, serves a major part of Indian population in various capacities The area of study chosen is the initial 480 km stretch of this river from Badrinath to Narora. The first 240 km stretch from Badrinath to Rishikesh is mountaneous and the rest half is plain. This stretch of the river is commonly believed to be least polluted, but systematic and extensive pollutional study on this region is lacking. The central board for control and prevention of water pollution (India) with a network of 41 sampling stations along this river has not cared to set up a single monitoring station in the 240 km mountaneous. stretch, (under investigation). In the pollutional study of riverine system heavy metal pollution should not be neglected, rather it should be given utmost priority. Unlike organic pollution, heavy metal pollu tion can not be removed by natural oxidation or microbial activity. However, it is buffered by the adsorption on sedi ments whereby the pollutants may be kept in dora nt state. (ii) Studies on heavy metal pollution and sorptive properties of the river sediment have not been reported for the region mentioned above). (The present study, therefore, is an attempt to find out the heavy metal status and the sorptive property of the bed -QCWkx&K^ Lg-^ lv>cm tc> £ <A<Nul* sediment of a hitherto unexplored region of the most important river of the country. Covering the 480 km stretch of the river through a network of 12 sampling stations viz. Badrinath, Nandprayag, Rudraprayag, Srinagar, Devprayag, Rishikesh, Satyanarayana, Balawali, Bijnor, Garhmukteswar, Anupsahar and Narora, the study has been carried out from October '85 to Jan. 1987. The sampling has been done at a frequency of once in two months. < The physicochemical parameters •of the river, viz. pH, ORP, COD, total and suspended residue, which control the concentration and transport of the heavy metals have been investigated. The data obtained are used in explaining the trends of the heavy metals in the river. The total and dissolved metal content of the water column and the extractable heavy metal content of the bed sediments have been determined. From these data the heavy metal status of Upper Ganges has been compared with other rivers of the world. Comparison of the water quality with the WHO (1984) guidelines for drinking water reveals that (iiil the dissolved metal, contents (Mn, Fe, Co, Ni, Cu, Zn, Cd & Pb) of the stretch of the river is well below the permissible limit. The major use of the river water is for irrigation, as such the heavy met air contents of the water has been compared with the permissible limit for irrigation water and it has been found that in no case this limit is exceeded. The data obtained for extractable heavy metals in sedi ments have been analysed to ascertain anomalous occurrence of the heavy metals. Comparison with 'Shale standard' has indicated Pb and Cd concentrations to be higher than the world average. The metal pair ratio analysis indicates an enrichment of Co, Ni, Cu and Pb at a number of sites. t No distinct source of man-made heavy metal pollution could be identified. The incidence of heavy metals may be attributed to the geochemical weathering of rocks and soils. The sorptive properties of the sediment collected from the river bed of Rudraprayag have been studied for the uptake of Cu 2+, Zn 2+ and Pb2+ ions. The parameters controlling the uptake viz. the solution pH, sediment dose, minimum contact time and effect of competing ions have been evaluated. It is observed that the extent of adsorption increases with the increase of pH of the solution but on the other hand, metal ion concentration decreases with pH increase. With the help of Langmuir and Frieundlich models, some parameters - viz., monolayer capacity and sorption intensity have been (iv) calculated for the systems. pore diffusion kinetics has been utilised to study the adsorption of Cu2+ and Pb2+ ions on silt + clay fraction (< 63 m) of the river sediments, and the effective diffusion coefficient (D.) has also been calculated. The rate of diffu sion of Cu2+ ion has been found to be higher than, that for Pb ion. In addition to the adsorption experiments, the desorption of metal ions, sorbed on sediments, by the river water has also been undertaken. It is observed that the river water in its natural state is capable of leaching out sufficient quantity of metal ions from sediments ,though the pH of the river water is about 8.0.