Predictive model of limestone scaling in ammonia stripping towers and its experimental validation on a treatment plant fed by MSW leachate-polluted groundwater

Groundwater pollution by municipal solid waste (MSW) landfill leachate is a global concern. Stripping towers are one of the most implemented techniques for the removal of ammonia pollution. This study presents a predictive computational model to estimate calcium carbonate precipitation in ammonia stripping towers. The model considers the Ca2+ super-saturation condition due to the water pH, temperature and salinity. The results have been validated through experimental data obtained from a plant fed with MSW landfill leachate-polluted groundwater. The plant consisted of two parallel lines composed of a coagulation-flocculation stage at high pH followed by a stripping tower. Six combinations of water pH and temperature conditions were tested. Maximum precipitation was 1,400 kgCaCO3 after a period of 120 days, observed at inlet pH and temperatures of 10.5 and 38 C The maximum removal efficiency of ammonia was reported as 91%, 87% and 80% respectively. Finally, a good relationship between the loss of efficiency in ammonia removal and the increase of precipitating CaCO3 to the tower plain area ratio, valid for all water pH and temperatures, has been found.