Simultaneous recovery of silica and treatment of rice mill wastewater using rice husk ash: An economic approach

•Adsorptive treatment of rice mill wastewater with rice husk ash, another waste generated from rice mill.•Enhancement of contaminants removal was achieved by the use of MgCl2 and its reusability was explored.•Extraction of value added silica and its characterization using SEM, XRD and FTIR.

An economical, effective and eco-friendly route for utilizing agricultural byproduct rice husk ash (RHA) in the treatment of rice mill wastewater has been investigated in the present study. Precious silica was extracted as value added product from RHA and characterized by using SEM, FTIR and XRD. The basic carbonaceous RHA residual was then used for the abatement of rice mill wastewater as an adsorbent with increasing its pH. Adsorptive process exhibited the percentage reduction of color, lignin, phenol and COD were 69.38, 73.43, 66.07 and 67.85, respectively from rice mill effluent. The batch adsorption kinetic study of this basic adsorbent fitted well to pseudo second order model. Additional removal of pollution parameters was achieved by employing MgCl2 as coagulant. For this, MgCl2 was added in the wastewater at a dose of 12 g/L at pH 12. This enhanced the percentage removal of lignin, color, phenol and COD by 75.21, 75.38, 40.29 and 40.14, respectively. In further study, this coagulation process was augmented with the use of Ca(OH)2 along with MgCl2. The proposed study was made more economical by recovering MgCl2 from the coagulation sludge for repeated application. Reusability of MgCl2 was explored for up to four recycles with the objective of improving the entire work economically viable.

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