Use of Agricultural Residues to Remove Iron from Groundwater in Modified Airlift Aerator

This work investigated groundwater iron adsorption capacity from rice husk, rice straw, water hyacinth and coconut shell, agricultural residues commonly found in Thailand. This study also investigated the adsorption behavior using an appropriate isotherm model in the batch process. The process was conducted using a modified airlift tray aerator. The use of a single adsorbent plate in a modified aerator obtained a removal capacity in the range of 0.3 to 0.9 mg/L, but the final iron concentration in the sample was above the regulatory standard. To increase the efficiency using the equivalent condition, the multiple adsorbent plate system was tested. The application of four rice husk plates achieved the allowance value and resulted in a final iron concentration of 0.28 mg/L. Based on the results, iron was reduced by increasing the number of adsorbent plates. Hence, rice husk can be sustainably used to adsorb iron in groundwater. At equilibrium, the adsorption isotherm was fitted to the Freundlich equation with an R2 value of 0.9805. This implied that the adsorption sites on the rice husk surface are heterogeneous in nature and presented a strong interaction between iron and rice husk. They revealed a maximum adsorption capacity of 0.73 mg/g. Moreover, this practice also decreased the amount of total hardness which could help alleviate nuisance and public health problems