The researchers tested using dolochar, a waste product from the sponge iron industry, in slow sand filters to clean wastewater. They compared filters with just sand to filters with sand and dolochar. The dual media filter with dolochar removed more pollutants like COD, turbidity, phosphate, and TSS compared to the sand-only filter. It also removed more microbes. However, the dual media filter had more head loss, which can affect how long the filter can run. Overall, using dolochar in filters was shown to be effective and cost-efficient for cleaning water.