Performance and mechanism of microsand-ballasted flocculation for treating high-turbidity construction wastewater.

Abstract

The treatment of construction wastewater from pumped storage power stations remains a major challenge, due to its characteristically extreme and fluctuating suspended solid (SS) loads, which can reach concentrations on the order of 10,000 mg/L. This study systematically evaluates the performance of microsand-ballasted flocculation for such wastewater through integrated laboratory experiments and pilot-scale field validation. Laboratory jar tests optimized hydraulic conditions, chemical dosages, and microsand parameters, revealing that microsand addition significantly enhanced floc settleability and reduced chemical demand. A pilot-scale unit designed on the basis of these findings was deployed at a construction site for three months. The unit consistently produced effluent with SS below 10 mg/L and turbidity under 0.3 NTU, achieving over 99.99% removal efficiency. The unit also demonstrated a 28% reduction in dewatered sludge volume and a 98% water recovery rate. Key operational advantages included a 75% reduction in polyaluminum chloride dosage and a 67% reduction in polyacrylamide consumption compared to conventional treatment. The unit featured a compact containerized design that eliminated the need for large civil structures, which also incorporated a microsand recirculation system to ensure efficient reuse of the ballasting medium. Collectively, these findings demonstrate microsand-ballasted flocculation to be a robust, economical, and environmentally sound solution for the treatment of high-turbidity wastewater in large-scale construction projects.