Performance Evaluation of Blast Furnace Slag as Filter Media for Water Treatment

Abstract

Owing to the degree of contamination, treatment of water has been practised from ancient periods using various naturally available materials. It was initially carried out with a general idea of using a readily available resource material as the filter medium. The commonly used filter media worldwide for drinking water treatment is river sand. But it will not be a reliable resource because of its increased demand and multifarious application. There are several naturally existing materials similar to sand. As per the available literature, the by-products from various industries are promising source of materials that could be used as filter media. Since the discarding of these stuffs poses a threat to the environment, their wise usage in waste water treatment may be helpful to reduce the impact. Blast furnace slag is an industrial by-product of the iron and steel industry. The slags contain a significant portion of silica, calcium, aluminium and magnesium compounds with a little amount of iron. Besides their manifold use in construction practices, their use in environmental engineering is highly valuable. Ferrous slag has been used in the treatment of waste water enriched with nutrients, heavy metals and treatment of acidic mine drainage. In addition, the characteristics showed its usage as a landfill liner material. Very little literature is available on their effective use in drinking water treatment, even though some works dealt with certain specific biological parameters. In view of these, the utilisation of slag as a replacement for sand is considered both sustainable as well as economical. The present research aims at the application of ferrous slag in drinking water treatments. Bench-scale filter proved the ability of slag as a potential alternative material to sand. In the present work, the performance evaluation of slag filter with sand as a control, a filter with partial replacement of slag with charcoal and the variation of head loss in the slag filter and its comparison with the Carman-Cozeny model were studied. The performance of a slag filter with intermittent washing was evaluated for various filtration rates such as 0.32 m3hr-1m-2, 0.64 m3hr-1m-2, 0.96 m3hr-1m-2 and 1.28 m3hr-1m- 2 and different concentration ranges. Slag filter media of 40 cm height was found to be sufficient for removing 99.9 % of turbidity, total suspended solids and colour. The slag filter performed similarly to the sand filter in removing E.coli. The dual media filter of slag with charcoal was not as good in removing suspended impurities from the water. The maximum head loss observed in a slag filter was lesser than the sand filter. The scatter plots of measured and simulated heads based on the Carman-Kozeny equation show that the model fits the observed heads. Considering the effluent values of various water quality parameters such as hardness, sulphate, chloride and nitrate, both the flow type and concentrations are significant at 1% level of significance (p-value <.01). But for iron, only the concentration is significant at 5% level of significance (p-value <.05). The type of filter material is not significant for all the parameters except iron, where it is significant at a 1% level of significance (p-value <.01). Thus iron is the only parameter whose removal efficiency is dependent on the type of media. The treated water pH from the slag filter showed fairly consistent pH in the normal range of drinking water. These results showed that the slag would be useful in the locations where there is a scarcity of sand and no further alternative technique for drinking water treatment exists. It would be practically beneficial for the surface as well as groundwater treatment.