Defluoridation Priced at the Working Point: Activated Alumina Costed from Its Isotherm Against Nalgonda Precipitation Costed from Its Dose, and a 1,000 L/day Village Kiosk Sized on the Winner

Two defluoridation routes for fluoride-belt groundwater at 2, 5 and 10 mg/L to a 1.0 mg/L target are priced under one accounting rule. Activated alumina capacity is taken from a Langmuir isotherm evaluated at each feed (usable capacities 2.03, 2.58 and 2.84 mg/g at pH 6, all below a 3.5 mg/g datasheet value), with regeneration charged in full (5% capacity loss per cycle, 14 cycles per media life). Running unadjusted at pH 7.5 cuts capacity by 65.4%, 55.9% and 49.3%. Nalgonda-type precipitation is cheaper on chemicals at every feed (USD 0.057, 0.229 and 0.516 per m3 against USD 0.295, 0.864 and 1.735) but its computed residual aluminium of 0.389 and 0.875 mg/L exceeds the stated 0.2 mg/L limit at the 5 and 10 mg/L feeds, so precipitation wins only at 2 mg/L and adsorption wins at the higher feeds. A 1,000 L/day kiosk at the 5 mg/L design feed is sized on adsorption: two alternating 11 kg beds, weekly regeneration, 72.62 m3 per bed life, USD 0.864 per m3, 4.23 operator hours per week. SIMULATED, NOT MEASURED: a reproducible computation, nothing built or tested.