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Removal of COD and TDS from Industrial Waste Water

B. Mishra and A. Mohapatra

Physico-chemical analyses of Rice Mill Waste Water (RMWW) indicate these to have high COD (Chemical Oxygen Demand) and TDS (Total Dissolved Solids) values. Six chemical treatments were employed for COD and TDS removal using two representative RMWW samples (viz., treatment T- 1 with added bleaching powder, T-2 with added ferric alum, T-3 with added lime, T-4 with bleaching powder, ferric alum and lime added together, T-5 with activated charcoal followed by bleaching powder, ferric alum and lime added together, and T-6 with rice husk charcoal followed by bleaching powder, ferric alum and lime added together). The observed results indicate that the treatment T-5 and to a slightly lesser extent treatment T-6 were found to be very effective in reduction of COD and TDS (as also removal of colour and odour) from RMWW. The kinetics of COD or TDS decrease by single reagent additives (e.g., T-1, T-2 & T-3) were smooth, mono-phasic and first order and the kinetics in the case of multiple additives (e.g. T-4, T-5 & T-6) exhibited bi-phasic first-order patterns. While the single phase kinetics may most probably correspond to a slow process of growth/precipitation, the bi-phasic kinetics most likely involve an initial step of nucleation/ sol formation, followed by a relatively slower step of growth/precipitation.