A Simple Material and Energy Input–Output Performance in Evaluating Silica Production from Conventional, Fume, and Biomass Thermochemical Conversion Routes

Rice husk valorization to produce silica is believed to involve an eco-friendly process rather than silica production from conventional and fume routes. Nevertheless, the quantitative point of view regarding this is still not widely disclosed. In this study, a simple material and energy input–output analysis (M&E I/O) is employed to compare the environmental impact of the production of 1 tonne of silica from conventional, fume, and biomass thermochemical conversion routes. The scope consideration includes raw material, transportation, utility systems, main production process, and output streams as environmental impact. Results show that conventional and fume routes need 3.86 tonnes of sandstone and biomass thermochemical conversion route needs 6.56 tonnes of rice husk. For conventional and fume routes, energy is supplied from 1194.08 and 1954.99 kg of coal combustion, whereas the biomass thermochemical conversion route uses rice husk as fuel and additional coal of only 238.38 kg. Further, the lowest CO2-equivalent emission of 0.85 tonnes is nominated to the biomass thermochemical conversion route, while conventional and fume routes are 10.09 and 18.62 tonnes, respectively. The produced wastewater from conventional, fume, and biomass thermochemical conversion routes is 27.27, 27.13, and 24.76 tonnes, successively. This study concludes and proves that silica production from rice husk is more eco-friendly and has low environmental impact, but wastewater treatment to meet the effluent standard should be applied.