IMPACT OF LEATHER PROCESSING INDUSTRIES ON CHROMIUM CONCENTRATION IN GROUNDWATER SOUTH OF CHENNAI CITY, INDIA

The groundwater quality is under threat due to disposal of effluents from a number of industries. Poor practice of treatment of wastes from tanning industries or leather processing industries lead to pollution of groundwater. This study was carried out with the objective of assessing the impact of tanneries on groundwater quality in Chromepet area which is a part of the metropolitan area of Chennai, Tamil Nadu, India. This area serves as the home town for a number of small and large scale tanning industries. People in certain parts of this area depend on the groundwater for their domestic needs as there is no piped drinking water supply system. Topographically this region is generally flat with gentle slope towards east and north east. The charnockite rocks occur as basement at the depth of about 15m from the surface of this area. Weathered charnockite rock occurs at the depth from 7m to 15m from the ground surface. The upper layer consists of loamy soil. Groundwater occurs in the unconfined condition at a depth from 0.5m to 5m. Thirty six groundwater samples were collected during March 2008 and the groundwater samples were analysed for their heavy metal (chromium) content using atomic absorption spectrophotometer. Bureau of Indian Standards (BIS) recommended the maximum permissible limit of chromium in drinking water as 0.05 mg/l. Considering this, it was found that 86% of the groundwater samples possessed concentration of chromium above the maximum permissible limit recommended by BIS. The tanneries use chrome sulphate to strengthen the leather and make it water repellent. The excess of chromium gets washed off and remains in the wastewater. This wastewater is disposed into open uncovered drains either untreated or after partial treatment. Thus the chromium leaches through the soil and reaches the groundwater table. Apart from this, there is also huge quantity of solid waste resulting from the hides and skins which are dumped off without suitable treatment. The percolation of the leachate rich in chromium will also add to chromium concentration in groundwater. The effluents from the tanning processes are sent to the common effluent treatment plant (CETP) by large scale industries. But small scale industries are not able to use such CETP for treating the wastewater generated by them. It is prominent from this study that the effluent from the tanning industries should be treated properly before disposing off into drains in order to prevent the pollution of groundwater. Reverse osmosis treatment of tanning effluent can be adopted for separation and recovery of chromium from the wastewater. For improving the already contaminated groundwater of this region, insitu bioremediation by the use of microorganisms isolated from the contaminated site will prove effective.