Calcite Remineralization as a Low Maintenance Alternative for Stabilization of RO Permeate

A full-scale case study presents performance data and lessons learned from a multi-stage NF/RO system treating challenging groundwater for potable reuse. The system employs calcite remineralization as a low-maintenance, chemical-free approach to stabilize permeate for distribution. RO permeate with pH 5.0–6.0, low calcium (<1–2 mg/L), and minimal alkalinity (2–8 mg/L as CaCO₃) is treated in upflow calcite contactors to target pH 7.5–8.5, calcium 20–50 mg/L, and alkalinity 40–100 mg/L as CaCO₃. Key design parameters including hydraulic loading rate (9.5 gpm/ft²), empty bed contact time (1.5–2 minutes), and media particle size (1.0–1.2 mm) control dissolution kinetics. The approach eliminates chemical dosing and solids handling equipment, substantially reducing operational complexity and maintenance requirements.