Heavy metal profile, mobility, and source characterization in size-fractionated bed-sediments of River Ganga, India.

Sediment quality assessment is vital while assessing the quality of rivers since sediments can alter the water quality depending on pH, redox conditions, and other physico-chemical characteristics. The present study aims to assess the heavy metal concentration in the size-fractionated sediments of River Ganga, and ascertain the sources of contamination in upper Himalayan stretch of around 300 km. The bed sediments of River Ganga were collected from Gomukh, Bhojwasa, Gangotri, Jhala Bridge, Chinyalisaur, Devaprayag, and Rishikesh; and these were size-fractionated in the range of 0-75, 75-150, 150-200, 200-250, 350-300, 300-450, 450-600 µm particle size to determine the concentration of heavy metals associated with each range of particle size using Atomic Absorption Spectrophotometer (AAS). The mean concentration of the metals in the sediments varied in the order Al (126 g/kg) > Fe (68 g/kg) > Cr (79 mg/kg) > Zn (67 mg/kg) > Pb (59 mg/kg) > Ni (38 mg/kg) > Cu (36 mg/kg) > Cd (2 mg/kg), and representing more affinity of metals with finer particle size of sediments. Contamination Factor and Metal Enrichment Factor indicated that sediments in the lower stretch were contaminated and enriched with many toxic metals. Geo-accumulation index, Sediment Pollution Index, and Pollution Load Index revealed that the sediments of Chinyalisaur, Devaprayag, and Rishikesh were moderately to strongly polluted and are progressively getting deteriorated by metals, thus, classifying these locations as hotspots of contamination. The major sources of Al and Fe were found to be natural; whereas Cr, Zn, Pb, Ni, Cu and Cd were mainly contributed by anthropogenic sources. The study stresses for immediate interventions to control further contamination by restricting addition of wastewater directly to River Ganga, or through other streams in Ganga basin.

Comparison of TiO2 catalysis and Fenton's treatment for rapid degradation of Remazol Red Dye in textile industry effluent.

The contamination of water bodies by toxic industrial effluents is a serious threat to environment and the exposed organisms. The treatment of carcinogenic azo dyes in wastewater of grossly polluting textile industry is a major challenge considering the persistent nature of chemical dyes against biological treatment. The present study explores efficacy of advanced oxidation processes-photocatalysis and photo-Fenton, towards degradation of Remazol Red dye in the textile industry effluent. It was observed that both processes can completely remove the colour and approximately 85% mineralization of the dye within reaction time of 60 min and 8 min, respectively. The economic analysis placed photo-Fenton as a cost-effective method with treatment cost of approx. 0.0090 US $/litre of wastewater containing Remazol Red dye. Although, Photocatalysis was relatively slow, it is substantially effective in removal/degradation of colour from textile effluent against the biological treatment. The study concludes that photo-Fenton and Photocatalysis are cost-effective and substantial treatment options for removal of toxicity arising from coloured textile effluents.