Zeolite is a natural rock with high cation exchange capacity. The cation exchange sites adsorb the positively charged ammonium ions. Zeolite has very small interconnected pores: 3 to 10 Angstrom units (3 x 10-10m). "Massive” deposits in can be found in the Western USA – California, Nevada, New Mexico. Zeolite was used to remove ammonium at Tahoe-Truckee for 30 years. Recharging of zeolite in wastewater treatment using brine requires additional treatment for the high salt content of the effluent. Using anammox to recharge zeolites avoids this additional step.