Towards green thermal power plants with blowdown water reuse and simultaneous biogenic nanostructures recovery from waste

Abstract

In thermal power plants, the cooling tower blowdown (CTBD) water represents a substantial amount of wastewater generated, whose recyclability holds the potential of enormous water savings. However, silica in reactive and colloidal form is a major contaminant, with inefficient removals by existing treatment technologies that prevent CTBD water reuse. The present work illustrates a sustainable approach for simultaneous silica removal and biogenic silica production from CTBD water of a thermal power plant. The 3 L attached biofilm reactor, inoculated with enriched diatom consortium ‘D’ (Navicula vilaplanii and Denticula subtilis) was utilized for treatment. D consortium efficiently removed both reactive (66.76%) and colloidal silica (83.05%) below the make-up water desired limit, and gave high biomass productivity (2.21± 0.17 g m − 2d−1). Also, a reduction of 91.84% total dissolved phosphorous, 69.61% nitrate nitrogen, 48.4% chemical oxygen demand, and 15.38% total dissolved solids were achieved. On downstream processing of D consortium biomass, 52.4% frustules, 19.6% lipid, 11.9% protein, and 8.2% carbohydrates were recovered per diatom cell weight. The extracted frustules were found to be negatively charged, symmetrical pennate-shaped, robust, mesoporous structures composed of SiO2 with wide nanotechnological applications. Projection analysis of the proposed biofilm process for a 500 MW power plant illustrated 1485 million liters of water-saving along with 57 tonnes of frustules, 22 tonnes of lipid, and 13.2 tonnes of protein production annually. This diatom based biofilm technology can provide a paradigm shift in blowdown water management practices and help build a fresh ‘waste to wealth’ industrial perspective.