Removal of ammonium from RO permeate of anaerobically digested wastewater by natural zeolite

The purpose of this paper was to study simultaneous removal of ammonia and potassium retained in wastewater by ion exchange with original and sodium conditioned zeolite after membrane treatment of anaerobically digested cattle manure effluents. Batch and column flow-through ion exchange tests were conducted to determine ion exchange capacity, pH effect, exchange kinetics, column runs and regeneration conditions. The exchange capacity of ammonium by original and sodium zeolite, according to the Langmuir equation, was 1.03 +/- 0.11 and 1.14 +/- 0.050 mmol/g, respectively. The kinetic experiments showed that the sorption of ammonium with coexisting K+ was rapid at the first 10 min, and approached equilibrium in 1 h. Ammonium removal was stable from lower pH to 9 and significantly decreased at pH. 10, while potassium removal was slightly increased at pH > 10. Column tests at a flow rate of 8.6-9.8 BV/h with a feed water containing 270 ppm of NH4+-N and 200 ppm of K+ showed that the total exchange capacity was approximately 8.8 mg/g for NH4+-N and 8.3 mg/g for K+. Both batch and column tests confirmed that zeolite had higher selectivity with potassium than with ammonium. On-column regeneration experiments showed that the exhausted zeolite could be efficiently regenerated by 5 BV brine solution containing 50 g/L NaCl and 0.2 M NaOH. The regenerated zeolite could be further reused for ammonium and potassium removal.