Facile preparation of rice husk-derived green coagulant via water-based heatless and salt-free technique for the effective treatment of urban and agricultural runoffs

Abstract

The facile preparation of rice husk-derived green coagulant (RHC) via water-based heatless and salt-free technique has been attempted. The coagulating activity for the practical treatment of urban and agricultural runoffs has been examined with respect to the indicator parameters, specifically turbidity, total suspended solids (TSS) and chemical oxygen demand (COD), and optimized according to the effects of coagulant dosage, solution pH, temperature, settling time and stirring speed. The morphological characteristics, elemental composition and surface functionalities of RHC were detected by scanning electron microscopy, energy dispersive X-ray analysis and Fourier transform infrared spectroscopy, respectively, while the fundamental governing mechanism was postulated. The polymeric chains of polysaccharides and proteins within RHC, notably the pendant O- and N-bearing moieties, were accounted for the coagulative effect with the colloidal particulates, predominantly via sorption, charge neutralization and interparticle bridging interactions. The treatment performance compared favorably against the reported biomass-derived coagulants, in terms of both coagulating potential and environmental sustainability. The viable role of rice husk as a renewable resource for the preparation of an effective, green coagulant has been successfully presented.